diff --git a/nix-rust/Cargo.lock b/nix-rust/Cargo.lock
index a2bfb03f2..6e5ecf45d 100644
--- a/nix-rust/Cargo.lock
+++ b/nix-rust/Cargo.lock
@@ -33,15 +33,6 @@ name = "byteorder"
 version = "1.3.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
-[[package]]
-name = "bytes"
-version = "0.4.12"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-dependencies = [
- "byteorder 1.3.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "iovec 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)",
-]
-
 [[package]]
 name = "c2-chacha"
 version = "0.2.3"
@@ -63,63 +54,6 @@ dependencies = [
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 ]
 
-[[package]]
-name = "crossbeam-channel"
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- "crossbeam-utils 0.6.6 (registry+https://github.com/rust-lang/crates.io-index)",
-]
-
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-dependencies = [
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- "crossbeam-utils 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
-]
-
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- "scopeguard 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
-]
-
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-dependencies = [
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-
-[[package]]
-name = "crossbeam-utils"
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- "lazy_static 1.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
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-
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-
 [[package]]
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@@ -141,81 +75,6 @@ name = "fuchsia-cprng"
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 source = "registry+https://github.com/rust-lang/crates.io-index"
 
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-
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@@ -226,234 +85,31 @@ dependencies = [
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 ]
 
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-
 [[package]]
 name = "nix-rust"
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 dependencies = [
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- "tokio 0.2.0-alpha.6 (registry+https://github.com/rust-lang/crates.io-index)",
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 [[package]]
@@ -464,75 +120,11 @@ dependencies = [
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 ]
 
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-
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-"checksum kernel32-sys 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)" = "7507624b29483431c0ba2d82aece8ca6cdba9382bff4ddd0f7490560c056098d"
 "checksum lazy_static 1.4.0 (registry+https://github.com/rust-lang/crates.io-index)" = "e2abad23fbc42b3700f2f279844dc832adb2b2eb069b2df918f455c4e18cc646"
 "checksum libc 0.2.66 (registry+https://github.com/rust-lang/crates.io-index)" = "d515b1f41455adea1313a4a2ac8a8a477634fbae63cc6100e3aebb207ce61558"
-"checksum lock_api 0.3.2 (registry+https://github.com/rust-lang/crates.io-index)" = "e57b3997725d2b60dbec1297f6c2e2957cc383db1cebd6be812163f969c7d586"
-"checksum log 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)" = "14b6052be84e6b71ab17edffc2eeabf5c2c3ae1fdb464aae35ac50c67a44e1f7"
-"checksum maybe-uninit 2.0.0 (registry+https://github.com/rust-lang/crates.io-index)" = "60302e4db3a61da70c0cb7991976248362f30319e88850c487b9b95bbf059e00"
-"checksum memchr 2.2.1 (registry+https://github.com/rust-lang/crates.io-index)" = "88579771288728879b57485cc7d6b07d648c9f0141eb955f8ab7f9d45394468e"
-"checksum memoffset 0.5.3 (registry+https://github.com/rust-lang/crates.io-index)" = "75189eb85871ea5c2e2c15abbdd541185f63b408415e5051f5cac122d8c774b9"
-"checksum mio 0.6.21 (registry+https://github.com/rust-lang/crates.io-index)" = "302dec22bcf6bae6dfb69c647187f4b4d0fb6f535521f7bc022430ce8e12008f"
-"checksum mio-uds 0.6.7 (registry+https://github.com/rust-lang/crates.io-index)" = "966257a94e196b11bb43aca423754d87429960a768de9414f3691d6957abf125"
-"checksum miow 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)" = "8c1f2f3b1cf331de6896aabf6e9d55dca90356cc9960cca7eaaf408a355ae919"
-"checksum net2 0.2.33 (registry+https://github.com/rust-lang/crates.io-index)" = "42550d9fb7b6684a6d404d9fa7250c2eb2646df731d1c06afc06dcee9e1bcf88"
 "checksum num-traits 0.2.10 (registry+https://github.com/rust-lang/crates.io-index)" = "d4c81ffc11c212fa327657cb19dd85eb7419e163b5b076bede2bdb5c974c07e4"
-"checksum num_cpus 1.11.1 (registry+https://github.com/rust-lang/crates.io-index)" = "76dac5ed2a876980778b8b85f75a71b6cbf0db0b1232ee12f826bccb00d09d72"
-"checksum parking_lot 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)" = "f842b1982eb6c2fe34036a4fbfb06dd185a3f5c8edfaacdf7d1ea10b07de6252"
-"checksum parking_lot_core 0.6.2 (registry+https://github.com/rust-lang/crates.io-index)" = "b876b1b9e7ac6e1a74a6da34d25c42e17e8862aa409cbbbdcfc8d86c6f3bc62b"
-"checksum pin-project 0.4.6 (registry+https://github.com/rust-lang/crates.io-index)" = "94b90146c7216e4cb534069fb91366de4ea0ea353105ee45ed297e2d1619e469"
-"checksum pin-project-internal 0.4.6 (registry+https://github.com/rust-lang/crates.io-index)" = "44ca92f893f0656d3cba8158dd0f2b99b94de256a4a54e870bd6922fcc6c8355"
-"checksum pin-utils 0.1.0-alpha.4 (registry+https://github.com/rust-lang/crates.io-index)" = "5894c618ce612a3fa23881b152b608bafb8c56cfc22f434a3ba3120b40f7b587"
 "checksum ppv-lite86 0.2.6 (registry+https://github.com/rust-lang/crates.io-index)" = "74490b50b9fbe561ac330df47c08f3f33073d2d00c150f719147d7c54522fa1b"
-"checksum proc-macro2 1.0.6 (registry+https://github.com/rust-lang/crates.io-index)" = "9c9e470a8dc4aeae2dee2f335e8f533e2d4b347e1434e5671afc49b054592f27"
 "checksum proptest 0.9.4 (registry+https://github.com/rust-lang/crates.io-index)" = "cf147e022eacf0c8a054ab864914a7602618adba841d800a9a9868a5237a529f"
 "checksum quick-error 1.2.2 (registry+https://github.com/rust-lang/crates.io-index)" = "9274b940887ce9addde99c4eee6b5c44cc494b182b97e73dc8ffdcb3397fd3f0"
-"checksum quote 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)" = "053a8c8bcc71fcce321828dc897a98ab9760bef03a4fc36693c231e5b3216cfe"
 "checksum rand 0.6.5 (registry+https://github.com/rust-lang/crates.io-index)" = "6d71dacdc3c88c1fde3885a3be3fbab9f35724e6ce99467f7d9c5026132184ca"
 "checksum rand 0.7.2 (registry+https://github.com/rust-lang/crates.io-index)" = "3ae1b169243eaf61759b8475a998f0a385e42042370f3a7dbaf35246eacc8412"
 "checksum rand_chacha 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "556d3a1ca6600bfcbab7c7c91ccb085ac7fbbcd70e008a98742e7847f4f7bcef"
@@ -1153,41 +422,12 @@ dependencies = [
 "checksum redox_syscall 0.1.56 (registry+https://github.com/rust-lang/crates.io-index)" = "2439c63f3f6139d1b57529d16bc3b8bb855230c8efcc5d3a896c8bea7c3b1e84"
 "checksum regex-syntax 0.6.12 (registry+https://github.com/rust-lang/crates.io-index)" = "11a7e20d1cce64ef2fed88b66d347f88bd9babb82845b2b858f3edbf59a4f716"
 "checksum remove_dir_all 0.5.2 (registry+https://github.com/rust-lang/crates.io-index)" = "4a83fa3702a688b9359eccba92d153ac33fd2e8462f9e0e3fdf155239ea7792e"
-"checksum rustc_version 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)" = "138e3e0acb6c9fb258b19b67cb8abd63c00679d2851805ea151465464fe9030a"
 "checksum rusty-fork 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)" = "3dd93264e10c577503e926bd1430193eeb5d21b059148910082245309b424fae"
-"checksum scopeguard 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)" = "b42e15e59b18a828bbf5c58ea01debb36b9b096346de35d941dcb89009f24a0d"
-"checksum semver 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)" = "1d7eb9ef2c18661902cc47e535f9bc51b78acd254da71d375c2f6720d9a40403"
-"checksum semver-parser 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)" = "388a1df253eca08550bef6c72392cfe7c30914bf41df5269b68cbd6ff8f570a3"
-"checksum slab 0.4.2 (registry+https://github.com/rust-lang/crates.io-index)" = "c111b5bd5695e56cffe5129854aa230b39c93a305372fdbb2668ca2394eea9f8"
-"checksum smallvec 0.6.13 (registry+https://github.com/rust-lang/crates.io-index)" = "f7b0758c52e15a8b5e3691eae6cc559f08eee9406e548a4477ba4e67770a82b6"
-"checksum spin 0.5.2 (registry+https://github.com/rust-lang/crates.io-index)" = "6e63cff320ae2c57904679ba7cb63280a3dc4613885beafb148ee7bf9aa9042d"
-"checksum string 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)" = "d24114bfcceb867ca7f71a0d3fe45d45619ec47a6fbfa98cb14e14250bfa5d6d"
-"checksum syn 1.0.11 (registry+https://github.com/rust-lang/crates.io-index)" = "dff0acdb207ae2fe6d5976617f887eb1e35a2ba52c13c7234c790960cdad9238"
 "checksum tar 0.4.26 (registry+https://github.com/rust-lang/crates.io-index)" = "b3196bfbffbba3e57481b6ea32249fbaf590396a52505a2615adbb79d9d826d3"
 "checksum tempfile 3.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "7a6e24d9338a0a5be79593e2fa15a648add6138caa803e2d5bc782c371732ca9"
-"checksum time 0.1.42 (registry+https://github.com/rust-lang/crates.io-index)" = "db8dcfca086c1143c9270ac42a2bbd8a7ee477b78ac8e45b19abfb0cbede4b6f"
-"checksum tokio 0.2.0-alpha.6 (registry+https://github.com/rust-lang/crates.io-index)" = "1f17f5d6ab0f35c1506678b28fb1798bdf74fcb737e9843c7b17b73e426eba38"
-"checksum tokio-codec 0.2.0-alpha.6 (registry+https://github.com/rust-lang/crates.io-index)" = "9f5d22fd1e84bd4045d28813491cb7d7caae34d45c80517c2213f09a85e8787a"
-"checksum tokio-executor 0.2.0-alpha.6 (registry+https://github.com/rust-lang/crates.io-index)" = "9ee9ceecf69145923834ea73f32ba40c790fd877b74a7817dd0b089f1eb9c7c8"
-"checksum tokio-io 0.2.0-alpha.6 (registry+https://github.com/rust-lang/crates.io-index)" = "112784d5543df30660b04a72ca423bfbd90e8bb32f94dcf610f15401218b22c5"
-"checksum tokio-macros 0.2.0-alpha.6 (registry+https://github.com/rust-lang/crates.io-index)" = "86b616374bcdadd95974e1f0dfca07dc913f1163c53840c0d664aca35114964e"
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-"checksum tokio-sync 0.2.0-alpha.6 (registry+https://github.com/rust-lang/crates.io-index)" = "4f1aaeb685540f7407ea0e27f1c9757d258c7c6bf4e3eb19da6fc59b747239d2"
-"checksum tokio-timer 0.3.0-alpha.6 (registry+https://github.com/rust-lang/crates.io-index)" = "b97c1587fe71018eb245a4a9daa13a5a3b681bbc1f7fdadfe24720e141472c13"
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-"checksum tracing-attributes 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)" = "a4263b12c3d3c403274493eb805966093b53214124796552d674ca1dd5d27c2b"
-"checksum tracing-core 0.1.7 (registry+https://github.com/rust-lang/crates.io-index)" = "bc913647c520c959b6d21e35ed8fa6984971deca9f0a2fcb8c51207e0c56af1d"
-"checksum try-lock 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)" = "e604eb7b43c06650e854be16a2a03155743d3752dd1c943f6829e26b7a36e382"
-"checksum unicode-xid 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "826e7639553986605ec5979c7dd957c7895e93eabed50ab2ffa7f6128a75097c"
 "checksum wait-timeout 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "9f200f5b12eb75f8c1ed65abd4b2db8a6e1b138a20de009dacee265a2498f3f6"
-"checksum want 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)" = "1ce8a968cb1cd110d136ff8b819a556d6fb6d919363c61534f6860c7eb172ba0"
 "checksum wasi 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)" = "b89c3ce4ce14bdc6fb6beaf9ec7928ca331de5df7e5ea278375642a2f478570d"
-"checksum winapi 0.2.8 (registry+https://github.com/rust-lang/crates.io-index)" = "167dc9d6949a9b857f3451275e911c3f44255842c1f7a76f33c55103a909087a"
 "checksum winapi 0.3.8 (registry+https://github.com/rust-lang/crates.io-index)" = "8093091eeb260906a183e6ae1abdba2ef5ef2257a21801128899c3fc699229c6"
-"checksum winapi-build 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "2d315eee3b34aca4797b2da6b13ed88266e6d612562a0c46390af8299fc699bc"
 "checksum winapi-i686-pc-windows-gnu 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)" = "ac3b87c63620426dd9b991e5ce0329eff545bccbbb34f3be09ff6fb6ab51b7b6"
 "checksum winapi-x86_64-pc-windows-gnu 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)" = "712e227841d057c1ee1cd2fb22fa7e5a5461ae8e48fa2ca79ec42cfc1931183f"
-"checksum ws2_32-sys 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)" = "d59cefebd0c892fa2dd6de581e937301d8552cb44489cdff035c6187cb63fa5e"
 "checksum xattr 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)" = "244c3741f4240ef46274860397c7c74e50eb23624996930e484c16679633a54c"
diff --git a/nix-rust/Cargo.toml b/nix-rust/Cargo.toml
index cd5c545cc..cd388bed6 100644
--- a/nix-rust/Cargo.toml
+++ b/nix-rust/Cargo.toml
@@ -11,12 +11,12 @@ crate-type = ["cdylib"]
 [dependencies]
 tar = "0.4"
 libc = "0.2"
-futures-preview = { version = "=0.3.0-alpha.19" }
-hyper = "0.13.0-alpha.4"
-http = "0.1"
-tokio = { version = "0.2.0-alpha.6", default-features = false, features = ["rt-full"] }
+#futures-preview = { version = "=0.3.0-alpha.19" }
+#hyper = "0.13.0-alpha.4"
+#http = "0.1"
+#tokio = { version = "0.2.0-alpha.6", default-features = false, features = ["rt-full"] }
 lazy_static = "1.4"
-byteorder = "1.3"
+#byteorder = "1.3"
 
 [dev-dependencies]
 hex = "0.3"
diff --git a/nix-rust/local.mk b/nix-rust/local.mk
index 51116b0b3..1e006e500 100644
--- a/nix-rust/local.mk
+++ b/nix-rust/local.mk
@@ -37,7 +37,9 @@ clean: clean-rust
 clean-rust:
 	$(suppress) rm -rfv nix-rust/target
 
+ifneq ($(OS), Darwin)
 check: rust-tests
 
 rust-tests:
-	cd nix-rust && CARGO_HOME=$$(if [[ -d vendor ]]; then echo vendor; fi) RUSTC_BOOTSTRAP=1 cargo test --release $$(if [[ -d vendor ]]; then echo -Z offline; fi)
+	cd nix-rust && CARGO_HOME=$$(if [[ -d vendor ]]; then echo vendor; fi) cargo test --release $$(if [[ -d vendor ]]; then echo --offline; fi)
+endif
diff --git a/nix-rust/src/c.rs b/nix-rust/src/c.rs
index 42ecb9866..4c1724eb3 100644
--- a/nix-rust/src/c.rs
+++ b/nix-rust/src/c.rs
@@ -1,6 +1,7 @@
 use super::{
     error,
     foreign::{self, CBox},
+    store::StorePath,
     util,
 };
 
@@ -13,43 +14,72 @@ pub extern "C" fn unpack_tarfile(
 }
 
 #[no_mangle]
-pub extern "C" fn rust_test() {
-    use crate::store::{self, Store};
-    use std::path::Path;
-    use tokio::runtime::Runtime;
-
-    let fut = async move {
-        let store: Box<dyn Store> = Box::new(store::BinaryCacheStore::new(
-            "http://cache.nixos.org".to_string(),
-        ));
-
-        let path = store
-            .parse_store_path(&Path::new(
-                "/nix/store/7h7qgvs4kgzsn8a6rb273saxyqh4jxlz-konsole-18.12.3",
-            ))
-            .unwrap();
-
-        /*
-        let info = store.query_path_info(&path).await.unwrap();
-
-        eprintln!("INFO = {:?}", info);
-         */
-
-        let closure = store
-            .compute_path_closure(vec![path].into_iter().collect())
-            .await
-            .unwrap();
-
-        eprintln!("CLOSURE = {:?}", closure.len());
-    };
-
-    let rt = Runtime::new().unwrap();
-
-    rt.block_on(fut);
-
-    /*
-    let file = std::fs::File::open("test.nar").unwrap();
-
-    crate::nar::parse(&mut std::io::BufReader::new(file)).unwrap();
-    */
+pub unsafe extern "C" fn ffi_String_new(s: &str, out: *mut String) {
+    // FIXME: check whether 's' is valid UTF-8?
+    out.write(s.to_string())
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn ffi_String_drop(self_: *mut String) {
+    std::ptr::drop_in_place(self_);
+}
+
+#[no_mangle]
+pub extern "C" fn ffi_StorePath_new(
+    path: &str,
+    store_dir: &str,
+) -> Result<StorePath, error::CppException> {
+    StorePath::new(std::path::Path::new(path), store_dir).map_err(|err| err.into())
+}
+
+#[no_mangle]
+pub extern "C" fn ffi_StorePath_new2(
+    hash: &[u8; crate::store::path::STORE_PATH_HASH_BYTES],
+    name: &str,
+) -> Result<StorePath, error::CppException> {
+    StorePath::from_parts(*hash, name).map_err(|err| err.into())
+}
+
+#[no_mangle]
+pub extern "C" fn ffi_StorePath_fromBaseName(
+    base_name: &str,
+) -> Result<StorePath, error::CppException> {
+    StorePath::new_from_base_name(base_name).map_err(|err| err.into())
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn ffi_StorePath_drop(self_: *mut StorePath) {
+    std::ptr::drop_in_place(self_);
+}
+
+#[no_mangle]
+pub extern "C" fn ffi_StorePath_to_string(self_: &StorePath) -> String {
+    format!("{}", self_)
+}
+
+#[no_mangle]
+pub extern "C" fn ffi_StorePath_less_than(a: &StorePath, b: &StorePath) -> bool {
+    a < b
+}
+
+#[no_mangle]
+pub extern "C" fn ffi_StorePath_eq(a: &StorePath, b: &StorePath) -> bool {
+    a == b
+}
+
+#[no_mangle]
+pub extern "C" fn ffi_StorePath_clone(self_: &StorePath) -> StorePath {
+    self_.clone()
+}
+
+#[no_mangle]
+pub extern "C" fn ffi_StorePath_name(self_: &StorePath) -> &str {
+    self_.name.name()
+}
+
+#[no_mangle]
+pub extern "C" fn ffi_StorePath_hash_data(
+    self_: &StorePath,
+) -> &[u8; crate::store::path::STORE_PATH_HASH_BYTES] {
+    self_.hash.hash()
 }
diff --git a/nix-rust/src/error.rs b/nix-rust/src/error.rs
index 28b5c43af..c2ba5d504 100644
--- a/nix-rust/src/error.rs
+++ b/nix-rust/src/error.rs
@@ -19,6 +19,7 @@ pub enum Error {
     BadNarField(String),
     BadExecutableField,
     IOError(std::io::Error),
+    #[cfg(unused)]
     HttpError(hyper::error::Error),
     Misc(String),
     Foreign(CppException),
@@ -30,6 +31,7 @@ impl From<std::io::Error> for Error {
     }
 }
 
+#[cfg(unused)]
 impl From<hyper::error::Error> for Error {
     fn from(err: hyper::error::Error) -> Self {
         Error::HttpError(err)
@@ -58,6 +60,7 @@ impl fmt::Display for Error {
             Error::BadNarField(s) => write!(f, "unrecognized NAR field '{}'", s),
             Error::BadExecutableField => write!(f, "bad 'executable' field in NAR"),
             Error::IOError(err) => write!(f, "I/O error: {}", err),
+            #[cfg(unused)]
             Error::HttpError(err) => write!(f, "HTTP error: {}", err),
             Error::Foreign(_) => write!(f, "<C++ exception>"), // FIXME
             Error::Misc(s) => write!(f, "{}", s),
diff --git a/nix-rust/src/lib.rs b/nix-rust/src/lib.rs
index 4654d4cc3..0c3cf5276 100644
--- a/nix-rust/src/lib.rs
+++ b/nix-rust/src/lib.rs
@@ -12,6 +12,7 @@ extern crate proptest;
 mod c;
 mod error;
 mod foreign;
+#[cfg(unused)]
 mod nar;
 mod store;
 mod util;
diff --git a/nix-rust/src/store/mod.rs b/nix-rust/src/store/mod.rs
index 85355b594..da972482c 100644
--- a/nix-rust/src/store/mod.rs
+++ b/nix-rust/src/store/mod.rs
@@ -1,9 +1,17 @@
+pub mod path;
+
+#[cfg(unused)]
 mod binary_cache_store;
-mod path;
+#[cfg(unused)]
 mod path_info;
+#[cfg(unused)]
 mod store;
 
-pub use binary_cache_store::BinaryCacheStore;
 pub use path::{StorePath, StorePathHash, StorePathName};
+
+#[cfg(unused)]
+pub use binary_cache_store::BinaryCacheStore;
+#[cfg(unused)]
 pub use path_info::PathInfo;
+#[cfg(unused)]
 pub use store::Store;
diff --git a/nix-rust/src/store/path.rs b/nix-rust/src/store/path.rs
index 03307ca7c..3ded5c428 100644
--- a/nix-rust/src/store/path.rs
+++ b/nix-rust/src/store/path.rs
@@ -23,6 +23,13 @@ impl StorePath {
         )
     }
 
+    pub fn from_parts(hash: [u8; STORE_PATH_HASH_BYTES], name: &str) -> Result<Self, Error> {
+        Ok(StorePath {
+            hash: StorePathHash(hash),
+            name: StorePathName::new(name)?,
+        })
+    }
+
     pub fn new_from_base_name(base_name: &str) -> Result<Self, Error> {
         if base_name.len() < STORE_PATH_HASH_CHARS + 1
             || base_name.as_bytes()[STORE_PATH_HASH_CHARS] != '-' as u8
@@ -43,7 +50,7 @@ impl fmt::Display for StorePath {
     }
 }
 
-#[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Debug)]
+#[derive(Clone, PartialEq, Eq, Debug)]
 pub struct StorePathHash([u8; STORE_PATH_HASH_BYTES]);
 
 impl StorePathHash {
@@ -55,6 +62,10 @@ impl StorePathHash {
         bytes.copy_from_slice(&v[0..STORE_PATH_HASH_BYTES]);
         Ok(Self(bytes))
     }
+
+    pub fn hash<'a>(&'a self) -> &'a [u8; STORE_PATH_HASH_BYTES] {
+        &self.0
+    }
 }
 
 impl fmt::Display for StorePathHash {
@@ -63,6 +74,21 @@ impl fmt::Display for StorePathHash {
     }
 }
 
+impl Ord for StorePathHash {
+    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
+        // Historically we've sorted store paths by their base32
+        // serialization, but our base32 encodes bytes in reverse
+        // order. So compare them in reverse order as well.
+        self.0.iter().rev().cmp(other.0.iter().rev())
+    }
+}
+
+impl PartialOrd for StorePathHash {
+    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
 #[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Debug)]
 pub struct StorePathName(String);
 
@@ -93,6 +119,10 @@ impl StorePathName {
 
         Ok(Self(s.to_string()))
     }
+
+    pub fn name<'a>(&'a self) -> &'a str {
+        &self.0
+    }
 }
 
 impl fmt::Display for StorePathName {
diff --git a/perl/lib/Nix/Store.xs b/perl/lib/Nix/Store.xs
index ce553bb53..fefcd5ae6 100644
--- a/perl/lib/Nix/Store.xs
+++ b/perl/lib/Nix/Store.xs
@@ -59,7 +59,7 @@ void setVerbosity(int level)
 int isValidPath(char * path)
     CODE:
         try {
-            RETVAL = store()->isValidPath(path);
+            RETVAL = store()->isValidPath(store()->parseStorePath(path));
         } catch (Error & e) {
             croak("%s", e.what());
         }
@@ -70,9 +70,8 @@ int isValidPath(char * path)
 SV * queryReferences(char * path)
     PPCODE:
         try {
-            PathSet paths = store()->queryPathInfo(path)->references;
-            for (PathSet::iterator i = paths.begin(); i != paths.end(); ++i)
-                XPUSHs(sv_2mortal(newSVpv(i->c_str(), 0)));
+            for (auto & i : store()->queryPathInfo(store()->parseStorePath(path))->references)
+                XPUSHs(sv_2mortal(newSVpv(store()->printStorePath(i).c_str(), 0)));
         } catch (Error & e) {
             croak("%s", e.what());
         }
@@ -81,7 +80,7 @@ SV * queryReferences(char * path)
 SV * queryPathHash(char * path)
     PPCODE:
         try {
-            auto s = store()->queryPathInfo(path)->narHash.to_string();
+            auto s = store()->queryPathInfo(store()->parseStorePath(path))->narHash.to_string();
             XPUSHs(sv_2mortal(newSVpv(s.c_str(), 0)));
         } catch (Error & e) {
             croak("%s", e.what());
@@ -91,9 +90,9 @@ SV * queryPathHash(char * path)
 SV * queryDeriver(char * path)
     PPCODE:
         try {
-            auto deriver = store()->queryPathInfo(path)->deriver;
-            if (deriver == "") XSRETURN_UNDEF;
-            XPUSHs(sv_2mortal(newSVpv(deriver.c_str(), 0)));
+            auto info = store()->queryPathInfo(store()->parseStorePath(path));
+            if (!info->deriver) XSRETURN_UNDEF;
+            XPUSHs(sv_2mortal(newSVpv(store()->printStorePath(*info->deriver).c_str(), 0)));
         } catch (Error & e) {
             croak("%s", e.what());
         }
@@ -102,18 +101,18 @@ SV * queryDeriver(char * path)
 SV * queryPathInfo(char * path, int base32)
     PPCODE:
         try {
-            auto info = store()->queryPathInfo(path);
-            if (info->deriver == "")
+            auto info = store()->queryPathInfo(store()->parseStorePath(path));
+            if (info->deriver)
                 XPUSHs(&PL_sv_undef);
             else
-                XPUSHs(sv_2mortal(newSVpv(info->deriver.c_str(), 0)));
+                XPUSHs(sv_2mortal(newSVpv(store()->printStorePath(*info->deriver).c_str(), 0)));
             auto s = info->narHash.to_string(base32 ? Base32 : Base16);
             XPUSHs(sv_2mortal(newSVpv(s.c_str(), 0)));
             mXPUSHi(info->registrationTime);
             mXPUSHi(info->narSize);
             AV * arr = newAV();
-            for (PathSet::iterator i = info->references.begin(); i != info->references.end(); ++i)
-                av_push(arr, newSVpv(i->c_str(), 0));
+            for (auto & i : info->references)
+                av_push(arr, newSVpv(store()->printStorePath(i).c_str(), 0));
             XPUSHs(sv_2mortal(newRV((SV *) arr)));
         } catch (Error & e) {
             croak("%s", e.what());
@@ -123,8 +122,8 @@ SV * queryPathInfo(char * path, int base32)
 SV * queryPathFromHashPart(char * hashPart)
     PPCODE:
         try {
-            Path path = store()->queryPathFromHashPart(hashPart);
-            XPUSHs(sv_2mortal(newSVpv(path.c_str(), 0)));
+            auto path = store()->queryPathFromHashPart(hashPart);
+            XPUSHs(sv_2mortal(newSVpv(path ? store()->printStorePath(*path).c_str() : "", 0)));
         } catch (Error & e) {
             croak("%s", e.what());
         }
@@ -133,11 +132,11 @@ SV * queryPathFromHashPart(char * hashPart)
 SV * computeFSClosure(int flipDirection, int includeOutputs, ...)
     PPCODE:
         try {
-            PathSet paths;
+            StorePathSet paths;
             for (int n = 2; n < items; ++n)
-                store()->computeFSClosure(SvPV_nolen(ST(n)), paths, flipDirection, includeOutputs);
-            for (PathSet::iterator i = paths.begin(); i != paths.end(); ++i)
-                XPUSHs(sv_2mortal(newSVpv(i->c_str(), 0)));
+                store()->computeFSClosure(store()->parseStorePath(SvPV_nolen(ST(n))), paths, flipDirection, includeOutputs);
+            for (auto & i : paths)
+                XPUSHs(sv_2mortal(newSVpv(store()->printStorePath(i).c_str(), 0)));
         } catch (Error & e) {
             croak("%s", e.what());
         }
@@ -146,11 +145,11 @@ SV * computeFSClosure(int flipDirection, int includeOutputs, ...)
 SV * topoSortPaths(...)
     PPCODE:
         try {
-            PathSet paths;
-            for (int n = 0; n < items; ++n) paths.insert(SvPV_nolen(ST(n)));
-            Paths sorted = store()->topoSortPaths(paths);
-            for (Paths::iterator i = sorted.begin(); i != sorted.end(); ++i)
-                XPUSHs(sv_2mortal(newSVpv(i->c_str(), 0)));
+            StorePathSet paths;
+            for (int n = 0; n < items; ++n) paths.insert(store()->parseStorePath(SvPV_nolen(ST(n))));
+            auto sorted = store()->topoSortPaths(paths);
+            for (auto & i : sorted)
+                XPUSHs(sv_2mortal(newSVpv(store()->printStorePath(i).c_str(), 0)));
         } catch (Error & e) {
             croak("%s", e.what());
         }
@@ -159,7 +158,7 @@ SV * topoSortPaths(...)
 SV * followLinksToStorePath(char * path)
     CODE:
         try {
-            RETVAL = newSVpv(store()->followLinksToStorePath(path).c_str(), 0);
+            RETVAL = newSVpv(store()->printStorePath(store()->followLinksToStorePath(path)).c_str(), 0);
         } catch (Error & e) {
             croak("%s", e.what());
         }
@@ -170,8 +169,8 @@ SV * followLinksToStorePath(char * path)
 void exportPaths(int fd, ...)
     PPCODE:
         try {
-            Paths paths;
-            for (int n = 1; n < items; ++n) paths.push_back(SvPV_nolen(ST(n)));
+            StorePathSet paths;
+            for (int n = 1; n < items; ++n) paths.insert(store()->parseStorePath(SvPV_nolen(ST(n))));
             FdSink sink(fd);
             store()->exportPaths(paths, sink);
         } catch (Error & e) {
@@ -275,8 +274,8 @@ int checkSignature(SV * publicKey_, SV * sig_, char * msg)
 SV * addToStore(char * srcPath, int recursive, char * algo)
     PPCODE:
         try {
-            Path path = store()->addToStore(baseNameOf(srcPath), srcPath, recursive, parseHashType(algo));
-            XPUSHs(sv_2mortal(newSVpv(path.c_str(), 0)));
+            auto path = store()->addToStore(std::string(baseNameOf(srcPath)), srcPath, recursive, parseHashType(algo));
+            XPUSHs(sv_2mortal(newSVpv(store()->printStorePath(path).c_str(), 0)));
         } catch (Error & e) {
             croak("%s", e.what());
         }
@@ -286,8 +285,8 @@ SV * makeFixedOutputPath(int recursive, char * algo, char * hash, char * name)
     PPCODE:
         try {
             Hash h(hash, parseHashType(algo));
-            Path path = store()->makeFixedOutputPath(recursive, h, name);
-            XPUSHs(sv_2mortal(newSVpv(path.c_str(), 0)));
+            auto path = store()->makeFixedOutputPath(recursive, h, name);
+            XPUSHs(sv_2mortal(newSVpv(store()->printStorePath(path).c_str(), 0)));
         } catch (Error & e) {
             croak("%s", e.what());
         }
@@ -298,35 +297,35 @@ SV * derivationFromPath(char * drvPath)
         HV *hash;
     CODE:
         try {
-            Derivation drv = store()->derivationFromPath(drvPath);
+            Derivation drv = store()->derivationFromPath(store()->parseStorePath(drvPath));
             hash = newHV();
 
             HV * outputs = newHV();
-            for (DerivationOutputs::iterator i = drv.outputs.begin(); i != drv.outputs.end(); ++i)
-                hv_store(outputs, i->first.c_str(), i->first.size(), newSVpv(i->second.path.c_str(), 0), 0);
+            for (auto & i : drv.outputs)
+                hv_store(outputs, i.first.c_str(), i.first.size(), newSVpv(store()->printStorePath(i.second.path).c_str(), 0), 0);
             hv_stores(hash, "outputs", newRV((SV *) outputs));
 
             AV * inputDrvs = newAV();
-            for (DerivationInputs::iterator i = drv.inputDrvs.begin(); i != drv.inputDrvs.end(); ++i)
-                av_push(inputDrvs, newSVpv(i->first.c_str(), 0)); // !!! ignores i->second
+            for (auto & i : drv.inputDrvs)
+                av_push(inputDrvs, newSVpv(store()->printStorePath(i.first).c_str(), 0)); // !!! ignores i->second
             hv_stores(hash, "inputDrvs", newRV((SV *) inputDrvs));
 
             AV * inputSrcs = newAV();
-            for (PathSet::iterator i = drv.inputSrcs.begin(); i != drv.inputSrcs.end(); ++i)
-                av_push(inputSrcs, newSVpv(i->c_str(), 0));
+            for (auto & i : drv.inputSrcs)
+                av_push(inputSrcs, newSVpv(store()->printStorePath(i).c_str(), 0));
             hv_stores(hash, "inputSrcs", newRV((SV *) inputSrcs));
 
             hv_stores(hash, "platform", newSVpv(drv.platform.c_str(), 0));
             hv_stores(hash, "builder", newSVpv(drv.builder.c_str(), 0));
 
             AV * args = newAV();
-            for (Strings::iterator i = drv.args.begin(); i != drv.args.end(); ++i)
-                av_push(args, newSVpv(i->c_str(), 0));
+            for (auto & i : drv.args)
+                av_push(args, newSVpv(i.c_str(), 0));
             hv_stores(hash, "args", newRV((SV *) args));
 
             HV * env = newHV();
-            for (StringPairs::iterator i = drv.env.begin(); i != drv.env.end(); ++i)
-                hv_store(env, i->first.c_str(), i->first.size(), newSVpv(i->second.c_str(), 0), 0);
+            for (auto & i : drv.env)
+                hv_store(env, i.first.c_str(), i.first.size(), newSVpv(i.second.c_str(), 0), 0);
             hv_stores(hash, "env", newRV((SV *) env));
 
             RETVAL = newRV_noinc((SV *)hash);
@@ -340,7 +339,7 @@ SV * derivationFromPath(char * drvPath)
 void addTempRoot(char * storePath)
     PPCODE:
         try {
-            store()->addTempRoot(storePath);
+            store()->addTempRoot(store()->parseStorePath(storePath));
         } catch (Error & e) {
             croak("%s", e.what());
         }
diff --git a/src/build-remote/build-remote.cc b/src/build-remote/build-remote.cc
index 27dd35784..69d1c6f7e 100644
--- a/src/build-remote/build-remote.cc
+++ b/src/build-remote/build-remote.cc
@@ -88,7 +88,7 @@ static int _main(int argc, char * * argv)
             return 0;
         }
 
-        string drvPath;
+        std::optional<StorePath> drvPath;
         string storeUri;
 
         while (true) {
@@ -100,7 +100,7 @@ static int _main(int argc, char * * argv)
 
             auto amWilling = readInt(source);
             auto neededSystem = readString(source);
-            source >> drvPath;
+            drvPath = store->parseStorePath(readString(source));
             auto requiredFeatures = readStrings<std::set<std::string>>(source);
 
              auto canBuildLocally = amWilling
@@ -236,26 +236,27 @@ connected:
 
         {
             Activity act(*logger, lvlTalkative, actUnknown, fmt("copying dependencies to '%s'", storeUri));
-            copyPaths(store, ref<Store>(sshStore), inputs, NoRepair, NoCheckSigs, substitute);
+            copyPaths(store, ref<Store>(sshStore), store->parseStorePathSet(inputs), NoRepair, NoCheckSigs, substitute);
         }
 
         uploadLock = -1;
 
-        BasicDerivation drv(readDerivation(store->realStoreDir + "/" + baseNameOf(drvPath)));
-        drv.inputSrcs = inputs;
+        BasicDerivation drv(readDerivation(*store, store->realStoreDir + "/" + std::string(drvPath->to_string())));
+        drv.inputSrcs = store->parseStorePathSet(inputs);
 
-        auto result = sshStore->buildDerivation(drvPath, drv);
+        auto result = sshStore->buildDerivation(*drvPath, drv);
 
         if (!result.success())
-            throw Error("build of '%s' on '%s' failed: %s", drvPath, storeUri, result.errorMsg);
+            throw Error("build of '%s' on '%s' failed: %s", store->printStorePath(*drvPath), storeUri, result.errorMsg);
 
-        PathSet missing;
+        StorePathSet missing;
         for (auto & path : outputs)
-            if (!store->isValidPath(path)) missing.insert(path);
+            if (!store->isValidPath(store->parseStorePath(path))) missing.insert(store->parseStorePath(path));
 
         if (!missing.empty()) {
             Activity act(*logger, lvlTalkative, actUnknown, fmt("copying outputs from '%s'", storeUri));
-            store->locksHeld.insert(missing.begin(), missing.end()); /* FIXME: ugly */
+            for (auto & i : missing)
+                store->locksHeld.insert(store->printStorePath(i)); /* FIXME: ugly */
             copyPaths(ref<Store>(sshStore), store, missing, NoRepair, NoCheckSigs, NoSubstitute);
         }
 
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 4be4cfeea..6539a346a 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -43,6 +43,19 @@ static char * dupString(const char * s)
 }
 
 
+static char * dupStringWithLen(const char * s, size_t size)
+{
+    char * t;
+#if HAVE_BOEHMGC
+    t = GC_STRNDUP(s, size);
+#else
+    t = strndup(s, size);
+#endif
+    if (!t) throw std::bad_alloc();
+    return t;
+}
+
+
 static void printValue(std::ostream & str, std::set<const Value *> & active, const Value & v)
 {
     checkInterrupt();
@@ -330,10 +343,10 @@ EvalState::EvalState(const Strings & _searchPath, ref<Store> store)
             auto path = r.second;
 
             if (store->isInStore(r.second)) {
-                PathSet closure;
-                store->computeFSClosure(store->toStorePath(r.second), closure);
+                StorePathSet closure;
+                store->computeFSClosure(store->parseStorePath(store->toStorePath(r.second)), closure);
                 for (auto & path : closure)
-                    allowedPaths->insert(path);
+                    allowedPaths->insert(store->printStorePath(path));
             } else
                 allowedPaths->insert(r.second);
         }
@@ -550,9 +563,11 @@ void mkString(Value & v, const char * s)
 }
 
 
-Value & mkString(Value & v, const string & s, const PathSet & context)
+Value & mkString(Value & v, std::string_view s, const PathSet & context)
 {
-    mkString(v, s.c_str());
+    v.type = tString;
+    v.string.s = dupStringWithLen(s.data(), s.size());
+    v.string.context = 0;
     if (!context.empty()) {
         size_t n = 0;
         v.string.context = (const char * *)
@@ -1639,15 +1654,16 @@ string EvalState::copyPathToStore(PathSet & context, const Path & path)
         throwEvalError("file names are not allowed to end in '%1%'", drvExtension);
 
     Path dstPath;
-    if (srcToStore[path] != "")
-        dstPath = srcToStore[path];
+    auto i = srcToStore.find(path);
+    if (i != srcToStore.end())
+        dstPath = store->printStorePath(i->second);
     else {
-        dstPath = settings.readOnlyMode
-            ? store->computeStorePathForPath(baseNameOf(path), checkSourcePath(path)).first
-            : store->addToStore(baseNameOf(path), checkSourcePath(path), true, htSHA256, defaultPathFilter, repair);
-        srcToStore[path] = dstPath;
-        printMsg(lvlChatty, format("copied source '%1%' -> '%2%'")
-            % path % dstPath);
+        auto p = settings.readOnlyMode
+            ? store->computeStorePathForPath(std::string(baseNameOf(path)), checkSourcePath(path)).first
+            : store->addToStore(std::string(baseNameOf(path)), checkSourcePath(path), true, htSHA256, defaultPathFilter, repair);
+        dstPath = store->printStorePath(p);
+        srcToStore.insert_or_assign(path, std::move(p));
+        printMsg(lvlChatty, "copied source '%1%' -> '%2%'", path, dstPath);
     }
 
     context.insert(dstPath);
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 85aa1ccfe..cabc92d15 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -17,6 +17,7 @@ namespace nix {
 
 class Store;
 class EvalState;
+struct StorePath;
 enum RepairFlag : bool;
 
 
@@ -42,14 +43,14 @@ struct Env
 };
 
 
-Value & mkString(Value & v, const string & s, const PathSet & context = PathSet());
+Value & mkString(Value & v, std::string_view s, const PathSet & context = PathSet());
 
 void copyContext(const Value & v, PathSet & context);
 
 
 /* Cache for calls to addToStore(); maps source paths to the store
    paths. */
-typedef std::map<Path, Path> SrcToStore;
+typedef std::map<Path, StorePath> SrcToStore;
 
 
 std::ostream & operator << (std::ostream & str, const Value & v);
diff --git a/src/libexpr/get-drvs.cc b/src/libexpr/get-drvs.cc
index 4e22a1d77..a3412eab9 100644
--- a/src/libexpr/get-drvs.cc
+++ b/src/libexpr/get-drvs.cc
@@ -19,27 +19,27 @@ DrvInfo::DrvInfo(EvalState & state, const string & attrPath, Bindings * attrs)
 DrvInfo::DrvInfo(EvalState & state, ref<Store> store, const std::string & drvPathWithOutputs)
     : state(&state), attrs(nullptr), attrPath("")
 {
-    auto spec = parseDrvPathWithOutputs(drvPathWithOutputs);
+    auto [drvPath, selectedOutputs] = store->parseDrvPathWithOutputs(drvPathWithOutputs);
 
-    drvPath = spec.first;
+    this->drvPath = store->printStorePath(drvPath);
 
     auto drv = store->derivationFromPath(drvPath);
 
-    name = storePathToName(drvPath);
+    name = drvPath.name();
 
-    if (spec.second.size() > 1)
+    if (selectedOutputs.size() > 1)
         throw Error("building more than one derivation output is not supported, in '%s'", drvPathWithOutputs);
 
     outputName =
-        spec.second.empty()
-        ? get(drv.env, "outputName", "out")
-        : *spec.second.begin();
+        selectedOutputs.empty()
+        ? get(drv.env, "outputName").value_or("out")
+        : *selectedOutputs.begin();
 
     auto i = drv.outputs.find(outputName);
     if (i == drv.outputs.end())
-        throw Error("derivation '%s' does not have output '%s'", drvPath, outputName);
+        throw Error("derivation '%s' does not have output '%s'", store->printStorePath(drvPath), outputName);
 
-    outPath = i->second.path;
+    outPath = store->printStorePath(i->second.path);
 }
 
 
diff --git a/src/libexpr/local.mk b/src/libexpr/local.mk
index ccd5293e4..26b9f14ba 100644
--- a/src/libexpr/local.mk
+++ b/src/libexpr/local.mk
@@ -6,7 +6,7 @@ libexpr_DIR := $(d)
 
 libexpr_SOURCES := $(wildcard $(d)/*.cc) $(wildcard $(d)/primops/*.cc) $(d)/lexer-tab.cc $(d)/parser-tab.cc
 
-libexpr_LIBS = libutil libstore
+libexpr_LIBS = libutil libstore libnixrust
 
 libexpr_LDFLAGS =
 ifneq ($(OS), FreeBSD)
diff --git a/src/libexpr/names.cc b/src/libexpr/names.cc
index 382088c78..d1c8a6101 100644
--- a/src/libexpr/names.cc
+++ b/src/libexpr/names.cc
@@ -16,14 +16,14 @@ DrvName::DrvName()
    a letter.  The `version' part is the rest (excluding the separating
    dash).  E.g., `apache-httpd-2.0.48' is parsed to (`apache-httpd',
    '2.0.48'). */
-DrvName::DrvName(const string & s) : hits(0)
+DrvName::DrvName(std::string_view s) : hits(0)
 {
-    name = fullName = s;
+    name = fullName = std::string(s);
     for (unsigned int i = 0; i < s.size(); ++i) {
         /* !!! isalpha/isdigit are affected by the locale. */
         if (s[i] == '-' && i + 1 < s.size() && !isalpha(s[i + 1])) {
-            name = string(s, 0, i);
-            version = string(s, i + 1);
+            name = s.substr(0, i);
+            version = s.substr(i + 1);
             break;
         }
     }
diff --git a/src/libexpr/names.hh b/src/libexpr/names.hh
index 13c3093e7..00e14b8c7 100644
--- a/src/libexpr/names.hh
+++ b/src/libexpr/names.hh
@@ -15,7 +15,7 @@ struct DrvName
     unsigned int hits;
 
     DrvName();
-    DrvName(const string & s);
+    DrvName(std::string_view s);
     bool matches(DrvName & n);
 
 private:
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index d693a3b20..3ef827ebc 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -44,29 +44,28 @@ std::pair<string, string> decodeContext(const string & s)
 
 
 InvalidPathError::InvalidPathError(const Path & path) :
-    EvalError(format("path '%1%' is not valid") % path), path(path) {}
+    EvalError("path '%s' is not valid", path), path(path) {}
 
 void EvalState::realiseContext(const PathSet & context)
 {
-    PathSet drvs;
+    std::vector<StorePathWithOutputs> drvs;
 
     for (auto & i : context) {
         std::pair<string, string> decoded = decodeContext(i);
-        Path ctx = decoded.first;
-        assert(store->isStorePath(ctx));
+        auto ctx = store->parseStorePath(decoded.first);
         if (!store->isValidPath(ctx))
-            throw InvalidPathError(ctx);
-        if (!decoded.second.empty() && nix::isDerivation(ctx)) {
-            drvs.insert(decoded.first + "!" + decoded.second);
+            throw InvalidPathError(store->printStorePath(ctx));
+        if (!decoded.second.empty() && ctx.isDerivation()) {
+            drvs.push_back(StorePathWithOutputs{ctx.clone(), {decoded.second}});
 
             /* Add the output of this derivation to the allowed
                paths. */
             if (allowedPaths) {
-                auto drv = store->derivationFromPath(decoded.first);
+                auto drv = store->derivationFromPath(store->parseStorePath(decoded.first));
                 DerivationOutputs::iterator i = drv.outputs.find(decoded.second);
                 if (i == drv.outputs.end())
                     throw Error("derivation '%s' does not have an output named '%s'", decoded.first, decoded.second);
-                allowedPaths->insert(i->second.path);
+                allowedPaths->insert(store->printStorePath(i->second.path));
             }
         }
     }
@@ -74,10 +73,11 @@ void EvalState::realiseContext(const PathSet & context)
     if (drvs.empty()) return;
 
     if (!evalSettings.enableImportFromDerivation)
-        throw EvalError(format("attempted to realize '%1%' during evaluation but 'allow-import-from-derivation' is false") % *(drvs.begin()));
+        throw EvalError("attempted to realize '%1%' during evaluation but 'allow-import-from-derivation' is false",
+            store->printStorePath(drvs.begin()->path));
 
     /* For performance, prefetch all substitute info. */
-    PathSet willBuild, willSubstitute, unknown;
+    StorePathSet willBuild, willSubstitute, unknown;
     unsigned long long downloadSize, narSize;
     store->queryMissing(drvs, willBuild, willSubstitute, unknown, downloadSize, narSize);
     store->buildPaths(drvs);
@@ -100,8 +100,9 @@ static void prim_scopedImport(EvalState & state, const Pos & pos, Value * * args
 
     Path realPath = state.checkSourcePath(state.toRealPath(path, context));
 
-    if (state.store->isStorePath(path) && state.store->isValidPath(path) && isDerivation(path)) {
-        Derivation drv = readDerivation(realPath);
+    // FIXME
+    if (state.store->isStorePath(path) && state.store->isValidPath(state.store->parseStorePath(path)) && isDerivation(path)) {
+        Derivation drv = readDerivation(*state.store, realPath);
         Value & w = *state.allocValue();
         state.mkAttrs(w, 3 + drv.outputs.size());
         Value * v2 = state.allocAttr(w, state.sDrvPath);
@@ -115,7 +116,7 @@ static void prim_scopedImport(EvalState & state, const Pos & pos, Value * * args
 
         for (const auto & o : drv.outputs) {
             v2 = state.allocAttr(w, state.symbols.create(o.first));
-            mkString(*v2, o.second.path, {"!" + o.first + "!" + path});
+            mkString(*v2, state.store->printStorePath(o.second.path), {"!" + o.first + "!" + path});
             outputsVal->listElems()[outputs_index] = state.allocValue();
             mkString(*(outputsVal->listElems()[outputs_index++]), o.first);
         }
@@ -676,24 +677,24 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
            runs. */
         if (path.at(0) == '=') {
             /* !!! This doesn't work if readOnlyMode is set. */
-            PathSet refs;
-            state.store->computeFSClosure(string(path, 1), refs);
+            StorePathSet refs;
+            state.store->computeFSClosure(state.store->parseStorePath(std::string_view(path).substr(1)), refs);
             for (auto & j : refs) {
-                drv.inputSrcs.insert(j);
-                if (isDerivation(j))
-                    drv.inputDrvs[j] = state.store->queryDerivationOutputNames(j);
+                drv.inputSrcs.insert(j.clone());
+                if (j.isDerivation())
+                    drv.inputDrvs[j.clone()] = state.store->queryDerivationOutputNames(j);
             }
         }
 
         /* Handle derivation outputs of the form ‘!<name>!<path>’. */
         else if (path.at(0) == '!') {
             std::pair<string, string> ctx = decodeContext(path);
-            drv.inputDrvs[ctx.first].insert(ctx.second);
+            drv.inputDrvs[state.store->parseStorePath(ctx.first)].insert(ctx.second);
         }
 
         /* Otherwise it's a source file. */
         else
-            drv.inputSrcs.insert(path);
+            drv.inputSrcs.insert(state.store->parseStorePath(path));
     }
 
     /* Do we have all required attributes? */
@@ -703,10 +704,8 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
         throw EvalError(format("required attribute 'system' missing, at %1%") % posDrvName);
 
     /* Check whether the derivation name is valid. */
-    checkStoreName(drvName);
     if (isDerivation(drvName))
-        throw EvalError(format("derivation names are not allowed to end in '%1%', at %2%")
-            % drvExtension % posDrvName);
+        throw EvalError("derivation names are not allowed to end in '%s', at %s", drvExtension, posDrvName);
 
     if (outputHash) {
         /* Handle fixed-output derivations. */
@@ -716,52 +715,51 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
         HashType ht = outputHashAlgo.empty() ? htUnknown : parseHashType(outputHashAlgo);
         Hash h(*outputHash, ht);
 
-        Path outPath = state.store->makeFixedOutputPath(outputHashRecursive, h, drvName);
-        if (!jsonObject) drv.env["out"] = outPath;
-        drv.outputs["out"] = DerivationOutput(outPath,
-            (outputHashRecursive ? "r:" : "") + printHashType(h.type),
-            h.to_string(Base16, false));
+        auto outPath = state.store->makeFixedOutputPath(outputHashRecursive, h, drvName);
+        if (!jsonObject) drv.env["out"] = state.store->printStorePath(outPath);
+        drv.outputs.insert_or_assign("out", DerivationOutput(std::move(outPath),
+                (outputHashRecursive ? "r:" : "") + printHashType(h.type),
+                h.to_string(Base16, false)));
     }
 
     else {
-        /* Construct the "masked" store derivation, which is the final
-           one except that in the list of outputs, the output paths
-           are empty, and the corresponding environment variables have
-           an empty value.  This ensures that changes in the set of
-           output names do get reflected in the hash. */
+        /* Compute a hash over the "masked" store derivation, which is
+           the final one except that in the list of outputs, the
+           output paths are empty strings, and the corresponding
+           environment variables have an empty value.  This ensures
+           that changes in the set of output names do get reflected in
+           the hash. */
         for (auto & i : outputs) {
             if (!jsonObject) drv.env[i] = "";
-            drv.outputs[i] = DerivationOutput("", "", "");
         }
 
-        /* Use the masked derivation expression to compute the output
-           path. */
-        Hash h = hashDerivationModulo(*state.store, drv);
+        Hash h = hashDerivationModulo(*state.store, Derivation(drv), true);
 
-        for (auto & i : drv.outputs)
-            if (i.second.path == "") {
-                Path outPath = state.store->makeOutputPath(i.first, h, drvName);
-                if (!jsonObject) drv.env[i.first] = outPath;
-                i.second.path = outPath;
-            }
+        for (auto & i : outputs) {
+            auto outPath = state.store->makeOutputPath(i, h, drvName);
+            if (!jsonObject) drv.env[i] = state.store->printStorePath(outPath);
+            drv.outputs.insert_or_assign(i,
+                DerivationOutput(std::move(outPath), "", ""));
+        }
     }
 
     /* Write the resulting term into the Nix store directory. */
-    Path drvPath = writeDerivation(state.store, drv, drvName, state.repair);
+    auto drvPath = writeDerivation(state.store, drv, drvName, state.repair);
+    auto drvPathS = state.store->printStorePath(drvPath);
 
-    printMsg(lvlChatty, format("instantiated '%1%' -> '%2%'")
-        % drvName % drvPath);
+    printMsg(lvlChatty, "instantiated '%1%' -> '%2%'", drvName, drvPathS);
 
     /* Optimisation, but required in read-only mode! because in that
        case we don't actually write store derivations, so we can't
        read them later. */
-    drvHashes[drvPath] = hashDerivationModulo(*state.store, drv);
+    drvHashes.insert_or_assign(drvPath.clone(),
+        hashDerivationModulo(*state.store, Derivation(drv), false));
 
     state.mkAttrs(v, 1 + drv.outputs.size());
-    mkString(*state.allocAttr(v, state.sDrvPath), drvPath, {"=" + drvPath});
+    mkString(*state.allocAttr(v, state.sDrvPath), drvPathS, {"=" + drvPathS});
     for (auto & i : drv.outputs) {
         mkString(*state.allocAttr(v, state.symbols.create(i.first)),
-            i.second.path, {"!" + i.first + "!" + drvPath});
+            state.store->printStorePath(i.second.path), {"!" + i.first + "!" + drvPathS});
     }
     v.attrs->sort();
 }
@@ -814,7 +812,7 @@ static void prim_storePath(EvalState & state, const Pos & pos, Value * * args, V
         throw EvalError(format("path '%1%' is not in the Nix store, at %2%") % path % pos);
     Path path2 = state.store->toStorePath(path);
     if (!settings.readOnlyMode)
-        state.store->ensurePath(path2);
+        state.store->ensurePath(state.store->parseStorePath(path2));
     context.insert(path2);
     mkString(v, path, context);
 }
@@ -1010,17 +1008,17 @@ static void prim_toFile(EvalState & state, const Pos & pos, Value * * args, Valu
     string name = state.forceStringNoCtx(*args[0], pos);
     string contents = state.forceString(*args[1], context, pos);
 
-    PathSet refs;
+    StorePathSet refs;
 
     for (auto path : context) {
         if (path.at(0) != '/')
             throw EvalError(format("in 'toFile': the file '%1%' cannot refer to derivation outputs, at %2%") % name % pos);
-        refs.insert(path);
+        refs.insert(state.store->parseStorePath(path));
     }
 
-    Path storePath = settings.readOnlyMode
+    auto storePath = state.store->printStorePath(settings.readOnlyMode
         ? state.store->computeStorePathForText(name, contents, refs)
-        : state.store->addTextToStore(name, contents, refs, state.repair);
+        : state.store->addTextToStore(name, contents, refs, state.repair));
 
     /* Note: we don't need to add `context' to the context of the
        result, since `storePath' itself has references to the paths
@@ -1060,21 +1058,18 @@ static void addPath(EvalState & state, const Pos & pos, const string & name, con
         return state.forceBool(res, pos);
     }) : defaultPathFilter;
 
-    Path expectedStorePath;
-    if (expectedHash) {
-        expectedStorePath =
-            state.store->makeFixedOutputPath(recursive, expectedHash, name);
-    }
+    std::optional<StorePath> expectedStorePath;
+    if (expectedHash)
+        expectedStorePath = state.store->makeFixedOutputPath(recursive, expectedHash, name);
     Path dstPath;
-    if (!expectedHash || !state.store->isValidPath(expectedStorePath)) {
-        dstPath = settings.readOnlyMode
+    if (!expectedHash || !state.store->isValidPath(*expectedStorePath)) {
+        dstPath = state.store->printStorePath(settings.readOnlyMode
             ? state.store->computeStorePathForPath(name, path, recursive, htSHA256, filter).first
-            : state.store->addToStore(name, path, recursive, htSHA256, filter, state.repair);
-        if (expectedHash && expectedStorePath != dstPath) {
-            throw Error(format("store path mismatch in (possibly filtered) path added from '%1%'") % path);
-        }
+            : state.store->addToStore(name, path, recursive, htSHA256, filter, state.repair));
+        if (expectedHash && expectedStorePath != state.store->parseStorePath(dstPath))
+            throw Error("store path mismatch in (possibly filtered) path added from '%s'", path);
     } else
-        dstPath = expectedStorePath;
+        dstPath = state.store->printStorePath(*expectedStorePath);
 
     mkString(v, dstPath, {dstPath});
 }
@@ -1091,7 +1086,7 @@ static void prim_filterSource(EvalState & state, const Pos & pos, Value * * args
     if (args[0]->type != tLambda)
         throw TypeError(format("first argument in call to 'filterSource' is not a function but %1%, at %2%") % showType(*args[0]) % pos);
 
-    addPath(state, pos, baseNameOf(path), path, args[0], true, Hash(), v);
+    addPath(state, pos, std::string(baseNameOf(path)), path, args[0], true, Hash(), v);
 }
 
 static void prim_path(EvalState & state, const Pos & pos, Value * * args, Value & v)
@@ -2151,7 +2146,7 @@ void EvalState::createBaseEnv()
     }
 
     if (!evalSettings.pureEval) {
-        mkString(v, settings.thisSystem);
+        mkString(v, settings.thisSystem.get());
         addConstant("__currentSystem", v);
     }
 
diff --git a/src/libexpr/primops/context.cc b/src/libexpr/primops/context.cc
index 2d79739ea..94fa0158c 100644
--- a/src/libexpr/primops/context.cc
+++ b/src/libexpr/primops/context.cc
@@ -148,7 +148,7 @@ static void prim_appendContext(EvalState & state, const Pos & pos, Value * * arg
         if (!state.store->isStorePath(i.name))
             throw EvalError("Context key '%s' is not a store path, at %s", i.name, i.pos);
         if (!settings.readOnlyMode)
-            state.store->ensurePath(i.name);
+            state.store->ensurePath(state.store->parseStorePath(i.name));
         state.forceAttrs(*i.value, *i.pos);
         auto iter = i.value->attrs->find(sPath);
         if (iter != i.value->attrs->end()) {
diff --git a/src/libexpr/primops/fetchGit.cc b/src/libexpr/primops/fetchGit.cc
index 9d0c64291..4aee1073e 100644
--- a/src/libexpr/primops/fetchGit.cc
+++ b/src/libexpr/primops/fetchGit.cc
@@ -69,7 +69,7 @@ GitInfo exportGit(ref<Store> store, const std::string & uri,
                 return files.count(file);
             };
 
-            gitInfo.storePath = store->addToStore("source", uri, true, htSHA256, filter);
+            gitInfo.storePath = store->printStorePath(store->addToStore("source", uri, true, htSHA256, filter));
 
             return gitInfo;
         }
@@ -156,7 +156,7 @@ GitInfo exportGit(ref<Store> store, const std::string & uri,
 
         gitInfo.storePath = json["storePath"];
 
-        if (store->isValidPath(gitInfo.storePath)) {
+        if (store->isValidPath(store->parseStorePath(gitInfo.storePath))) {
             gitInfo.revCount = json["revCount"];
             return gitInfo;
         }
@@ -176,7 +176,7 @@ GitInfo exportGit(ref<Store> store, const std::string & uri,
 
     unpackTarfile(*source, tmpDir);
 
-    gitInfo.storePath = store->addToStore(name, tmpDir);
+    gitInfo.storePath = store->printStorePath(store->addToStore(name, tmpDir));
 
     gitInfo.revCount = std::stoull(runProgram("git", true, { "-C", cacheDir, "rev-list", "--count", gitInfo.rev }));
 
diff --git a/src/libexpr/primops/fetchMercurial.cc b/src/libexpr/primops/fetchMercurial.cc
index a907d0e1c..db274fa4f 100644
--- a/src/libexpr/primops/fetchMercurial.cc
+++ b/src/libexpr/primops/fetchMercurial.cc
@@ -63,7 +63,7 @@ HgInfo exportMercurial(ref<Store> store, const std::string & uri,
                 return files.count(file);
             };
 
-            hgInfo.storePath = store->addToStore("source", uri, true, htSHA256, filter);
+            hgInfo.storePath = store->printStorePath(store->addToStore("source", uri, true, htSHA256, filter));
 
             return hgInfo;
         }
@@ -134,7 +134,7 @@ HgInfo exportMercurial(ref<Store> store, const std::string & uri,
 
         hgInfo.storePath = json["storePath"];
 
-        if (store->isValidPath(hgInfo.storePath)) {
+        if (store->isValidPath(store->parseStorePath(hgInfo.storePath))) {
             printTalkative("using cached Mercurial store path '%s'", hgInfo.storePath);
             return hgInfo;
         }
@@ -150,7 +150,7 @@ HgInfo exportMercurial(ref<Store> store, const std::string & uri,
 
     deletePath(tmpDir + "/.hg_archival.txt");
 
-    hgInfo.storePath = store->addToStore(name, tmpDir);
+    hgInfo.storePath = store->printStorePath(store->addToStore(name, tmpDir));
 
     nlohmann::json json;
     json["storePath"] = hgInfo.storePath;
diff --git a/src/libexpr/symbol-table.hh b/src/libexpr/symbol-table.hh
index 91faea122..7ba5e1c14 100644
--- a/src/libexpr/symbol-table.hh
+++ b/src/libexpr/symbol-table.hh
@@ -38,7 +38,12 @@ public:
         return s < s2.s;
     }
 
-    operator const string & () const
+    operator const std::string & () const
+    {
+        return *s;
+    }
+
+    operator const std::string_view () const
     {
         return *s;
     }
diff --git a/src/libmain/shared.cc b/src/libmain/shared.cc
index 81fb6b05a..d41e772e9 100644
--- a/src/libmain/shared.cc
+++ b/src/libmain/shared.cc
@@ -33,25 +33,25 @@ void printGCWarning()
 }
 
 
-void printMissing(ref<Store> store, const PathSet & paths, Verbosity lvl)
+void printMissing(ref<Store> store, const std::vector<StorePathWithOutputs> & paths, Verbosity lvl)
 {
     unsigned long long downloadSize, narSize;
-    PathSet willBuild, willSubstitute, unknown;
+    StorePathSet willBuild, willSubstitute, unknown;
     store->queryMissing(paths, willBuild, willSubstitute, unknown, downloadSize, narSize);
     printMissing(store, willBuild, willSubstitute, unknown, downloadSize, narSize, lvl);
 }
 
 
-void printMissing(ref<Store> store, const PathSet & willBuild,
-    const PathSet & willSubstitute, const PathSet & unknown,
+void printMissing(ref<Store> store, const StorePathSet & willBuild,
+    const StorePathSet & willSubstitute, const StorePathSet & unknown,
     unsigned long long downloadSize, unsigned long long narSize, Verbosity lvl)
 {
     if (!willBuild.empty()) {
         printMsg(lvl, "these derivations will be built:");
-        Paths sorted = store->topoSortPaths(willBuild);
+        auto sorted = store->topoSortPaths(willBuild);
         reverse(sorted.begin(), sorted.end());
         for (auto & i : sorted)
-            printMsg(lvl, fmt("  %s", i));
+            printMsg(lvl, fmt("  %s", store->printStorePath(i)));
     }
 
     if (!willSubstitute.empty()) {
@@ -59,14 +59,14 @@ void printMissing(ref<Store> store, const PathSet & willBuild,
                 downloadSize / (1024.0 * 1024.0),
                 narSize / (1024.0 * 1024.0)));
         for (auto & i : willSubstitute)
-            printMsg(lvl, fmt("  %s", i));
+            printMsg(lvl, fmt("  %s", store->printStorePath(i)));
     }
 
     if (!unknown.empty()) {
         printMsg(lvl, fmt("don't know how to build these paths%s:",
                 (settings.readOnlyMode ? " (may be caused by read-only store access)" : "")));
         for (auto & i : unknown)
-            printMsg(lvl, fmt("  %s", i));
+            printMsg(lvl, fmt("  %s", store->printStorePath(i)));
     }
 }
 
@@ -237,7 +237,7 @@ bool LegacyArgs::processArgs(const Strings & args, bool finish)
 void parseCmdLine(int argc, char * * argv,
     std::function<bool(Strings::iterator & arg, const Strings::iterator & end)> parseArg)
 {
-    parseCmdLine(baseNameOf(argv[0]), argvToStrings(argc, argv), parseArg);
+    parseCmdLine(std::string(baseNameOf(argv[0])), argvToStrings(argc, argv), parseArg);
 }
 
 
diff --git a/src/libmain/shared.hh b/src/libmain/shared.hh
index 8e4861232..b49574652 100644
--- a/src/libmain/shared.hh
+++ b/src/libmain/shared.hh
@@ -3,6 +3,7 @@
 #include "util.hh"
 #include "args.hh"
 #include "common-args.hh"
+#include "path.hh"
 
 #include <signal.h>
 
@@ -37,11 +38,15 @@ void printVersion(const string & programName);
 void printGCWarning();
 
 class Store;
+struct StorePathWithOutputs;
 
-void printMissing(ref<Store> store, const PathSet & paths, Verbosity lvl = lvlInfo);
+void printMissing(
+    ref<Store> store,
+    const std::vector<StorePathWithOutputs> & paths,
+    Verbosity lvl = lvlInfo);
 
-void printMissing(ref<Store> store, const PathSet & willBuild,
-    const PathSet & willSubstitute, const PathSet & unknown,
+void printMissing(ref<Store> store, const StorePathSet & willBuild,
+    const StorePathSet & willSubstitute, const StorePathSet & unknown,
     unsigned long long downloadSize, unsigned long long narSize, Verbosity lvl = lvlInfo);
 
 string getArg(const string & opt,
diff --git a/src/libstore/binary-cache-store.cc b/src/libstore/binary-cache-store.cc
index 7e3e5ff88..aaacf8281 100644
--- a/src/libstore/binary-cache-store.cc
+++ b/src/libstore/binary-cache-store.cc
@@ -91,19 +91,18 @@ std::shared_ptr<std::string> BinaryCacheStore::getFile(const std::string & path)
     return sink.s;
 }
 
-Path BinaryCacheStore::narInfoFileFor(const Path & storePath)
+std::string BinaryCacheStore::narInfoFileFor(const StorePath & storePath)
 {
-    assertStorePath(storePath);
-    return storePathToHash(storePath) + ".narinfo";
+    return storePathToHash(printStorePath(storePath)) + ".narinfo";
 }
 
 void BinaryCacheStore::writeNarInfo(ref<NarInfo> narInfo)
 {
     auto narInfoFile = narInfoFileFor(narInfo->path);
 
-    upsertFile(narInfoFile, narInfo->to_string(), "text/x-nix-narinfo");
+    upsertFile(narInfoFile, narInfo->to_string(*this), "text/x-nix-narinfo");
 
-    auto hashPart = storePathToHash(narInfo->path);
+    auto hashPart = storePathToHash(printStorePath(narInfo->path));
 
     {
         auto state_(state.lock());
@@ -126,8 +125,8 @@ void BinaryCacheStore::addToStore(const ValidPathInfo & info, const ref<std::str
             if (ref != info.path)
                 queryPathInfo(ref);
         } catch (InvalidPath &) {
-            throw Error(format("cannot add '%s' to the binary cache because the reference '%s' is not valid")
-                % info.path % ref);
+            throw Error("cannot add '%s' to the binary cache because the reference '%s' is not valid",
+                printStorePath(info.path), printStorePath(ref));
         }
 
     assert(nar->compare(0, narMagic.size(), narMagic) == 0);
@@ -138,14 +137,14 @@ void BinaryCacheStore::addToStore(const ValidPathInfo & info, const ref<std::str
     narInfo->narHash = hashString(htSHA256, *nar);
 
     if (info.narHash && info.narHash != narInfo->narHash)
-        throw Error(format("refusing to copy corrupted path '%1%' to binary cache") % info.path);
+        throw Error("refusing to copy corrupted path '%1%' to binary cache", printStorePath(info.path));
 
     auto accessor_ = std::dynamic_pointer_cast<RemoteFSAccessor>(accessor);
 
     auto narAccessor = makeNarAccessor(nar);
 
     if (accessor_)
-        accessor_->addToCache(info.path, *nar, narAccessor);
+        accessor_->addToCache(printStorePath(info.path), *nar, narAccessor);
 
     /* Optionally write a JSON file containing a listing of the
        contents of the NAR. */
@@ -162,7 +161,7 @@ void BinaryCacheStore::addToStore(const ValidPathInfo & info, const ref<std::str
             }
         }
 
-        upsertFile(storePathToHash(info.path) + ".ls", jsonOut.str(), "application/json");
+        upsertFile(storePathToHash(printStorePath(info.path)) + ".ls", jsonOut.str(), "application/json");
     }
 
     /* Compress the NAR. */
@@ -174,10 +173,10 @@ void BinaryCacheStore::addToStore(const ValidPathInfo & info, const ref<std::str
     narInfo->fileSize = narCompressed->size();
 
     auto duration = std::chrono::duration_cast<std::chrono::milliseconds>(now2 - now1).count();
-    printMsg(lvlTalkative, format("copying path '%1%' (%2% bytes, compressed %3$.1f%% in %4% ms) to binary cache")
-        % narInfo->path % narInfo->narSize
-        % ((1.0 - (double) narCompressed->size() / nar->size()) * 100.0)
-        % duration);
+    printMsg(lvlTalkative, "copying path '%1%' (%2% bytes, compressed %3$.1f%% in %4% ms) to binary cache",
+        printStorePath(narInfo->path), narInfo->narSize,
+        ((1.0 - (double) narCompressed->size() / nar->size()) * 100.0),
+        duration);
 
     narInfo->url = "nar/" + narInfo->fileHash.to_string(Base32, false) + ".nar"
         + (compression == "xz" ? ".xz" :
@@ -254,14 +253,14 @@ void BinaryCacheStore::addToStore(const ValidPathInfo & info, const ref<std::str
     stats.narWriteCompressionTimeMs += duration;
 
     /* Atomically write the NAR info file.*/
-    if (secretKey) narInfo->sign(*secretKey);
+    if (secretKey) narInfo->sign(*this, *secretKey);
 
     writeNarInfo(narInfo);
 
     stats.narInfoWrite++;
 }
 
-bool BinaryCacheStore::isValidPathUncached(const Path & storePath)
+bool BinaryCacheStore::isValidPathUncached(const StorePath & storePath)
 {
     // FIXME: this only checks whether a .narinfo with a matching hash
     // part exists. So ‘f4kb...-foo’ matches ‘f4kb...-bar’, even
@@ -269,7 +268,7 @@ bool BinaryCacheStore::isValidPathUncached(const Path & storePath)
     return fileExists(narInfoFileFor(storePath));
 }
 
-void BinaryCacheStore::narFromPath(const Path & storePath, Sink & sink)
+void BinaryCacheStore::narFromPath(const StorePath & storePath, Sink & sink)
 {
     auto info = queryPathInfo(storePath).cast<const NarInfo>();
 
@@ -295,12 +294,13 @@ void BinaryCacheStore::narFromPath(const Path & storePath, Sink & sink)
     stats.narReadBytes += narSize;
 }
 
-void BinaryCacheStore::queryPathInfoUncached(const Path & storePath,
+void BinaryCacheStore::queryPathInfoUncached(const StorePath & storePath,
     Callback<std::shared_ptr<const ValidPathInfo>> callback) noexcept
 {
     auto uri = getUri();
+    auto storePathS = printStorePath(storePath);
     auto act = std::make_shared<Activity>(*logger, lvlTalkative, actQueryPathInfo,
-        fmt("querying info about '%s' on '%s'", storePath, uri), Logger::Fields{storePath, uri});
+        fmt("querying info about '%s' on '%s'", storePathS, uri), Logger::Fields{storePathS, uri});
     PushActivity pact(act->id);
 
     auto narInfoFile = narInfoFileFor(storePath);
@@ -326,7 +326,7 @@ void BinaryCacheStore::queryPathInfoUncached(const Path & storePath,
         }});
 }
 
-Path BinaryCacheStore::addToStore(const string & name, const Path & srcPath,
+StorePath BinaryCacheStore::addToStore(const string & name, const Path & srcPath,
     bool recursive, HashType hashAlgo, PathFilter & filter, RepairFlag repair)
 {
     // FIXME: some cut&paste from LocalStore::addToStore().
@@ -345,20 +345,18 @@ Path BinaryCacheStore::addToStore(const string & name, const Path & srcPath,
         h = hashString(hashAlgo, s);
     }
 
-    ValidPathInfo info;
-    info.path = makeFixedOutputPath(recursive, h, name);
+    ValidPathInfo info(makeFixedOutputPath(recursive, h, name));
 
     addToStore(info, sink.s, repair, CheckSigs, nullptr);
 
-    return info.path;
+    return std::move(info.path);
 }
 
-Path BinaryCacheStore::addTextToStore(const string & name, const string & s,
-    const PathSet & references, RepairFlag repair)
+StorePath BinaryCacheStore::addTextToStore(const string & name, const string & s,
+    const StorePathSet & references, RepairFlag repair)
 {
-    ValidPathInfo info;
-    info.path = computeStorePathForText(name, s, references);
-    info.references = references;
+    ValidPathInfo info(computeStorePathForText(name, s, references));
+    info.references = cloneStorePathSet(references);
 
     if (repair || !isValidPath(info.path)) {
         StringSink sink;
@@ -366,7 +364,7 @@ Path BinaryCacheStore::addTextToStore(const string & name, const string & s,
         addToStore(info, sink.s, repair, CheckSigs, nullptr);
     }
 
-    return info.path;
+    return std::move(info.path);
 }
 
 ref<FSAccessor> BinaryCacheStore::getFSAccessor()
@@ -374,7 +372,7 @@ ref<FSAccessor> BinaryCacheStore::getFSAccessor()
     return make_ref<RemoteFSAccessor>(ref<Store>(shared_from_this()), localNarCache);
 }
 
-void BinaryCacheStore::addSignatures(const Path & storePath, const StringSet & sigs)
+void BinaryCacheStore::addSignatures(const StorePath & storePath, const StringSet & sigs)
 {
     /* Note: this is inherently racy since there is no locking on
        binary caches. In particular, with S3 this unreliable, even
@@ -390,24 +388,22 @@ void BinaryCacheStore::addSignatures(const Path & storePath, const StringSet & s
     writeNarInfo(narInfo);
 }
 
-std::shared_ptr<std::string> BinaryCacheStore::getBuildLog(const Path & path)
+std::shared_ptr<std::string> BinaryCacheStore::getBuildLog(const StorePath & path)
 {
-    Path drvPath;
+    auto drvPath = path.clone();
 
-    if (isDerivation(path))
-        drvPath = path;
-    else {
+    if (!path.isDerivation()) {
         try {
             auto info = queryPathInfo(path);
             // FIXME: add a "Log" field to .narinfo
-            if (info->deriver == "") return nullptr;
-            drvPath = info->deriver;
+            if (!info->deriver) return nullptr;
+            drvPath = info->deriver->clone();
         } catch (InvalidPath &) {
             return nullptr;
         }
     }
 
-    auto logPath = "log/" + baseNameOf(drvPath);
+    auto logPath = "log/" + std::string(baseNameOf(printStorePath(drvPath)));
 
     debug("fetching build log from binary cache '%s/%s'", getUri(), logPath);
 
diff --git a/src/libstore/binary-cache-store.hh b/src/libstore/binary-cache-store.hh
index 2d7cd1947..fa2200ad8 100644
--- a/src/libstore/binary-cache-store.hh
+++ b/src/libstore/binary-cache-store.hh
@@ -65,18 +65,18 @@ private:
 
     std::string narMagic;
 
-    std::string narInfoFileFor(const Path & storePath);
+    std::string narInfoFileFor(const StorePath & storePath);
 
     void writeNarInfo(ref<NarInfo> narInfo);
 
 public:
 
-    bool isValidPathUncached(const Path & path) override;
+    bool isValidPathUncached(const StorePath & path) override;
 
-    void queryPathInfoUncached(const Path & path,
+    void queryPathInfoUncached(const StorePath & path,
         Callback<std::shared_ptr<const ValidPathInfo>> callback) noexcept override;
 
-    Path queryPathFromHashPart(const string & hashPart) override
+    std::optional<StorePath> queryPathFromHashPart(const std::string & hashPart) override
     { unsupported("queryPathFromHashPart"); }
 
     bool wantMassQuery() override { return wantMassQuery_; }
@@ -85,27 +85,27 @@ public:
         RepairFlag repair, CheckSigsFlag checkSigs,
         std::shared_ptr<FSAccessor> accessor) override;
 
-    Path addToStore(const string & name, const Path & srcPath,
+    StorePath addToStore(const string & name, const Path & srcPath,
         bool recursive, HashType hashAlgo,
         PathFilter & filter, RepairFlag repair) override;
 
-    Path addTextToStore(const string & name, const string & s,
-        const PathSet & references, RepairFlag repair) override;
+    StorePath addTextToStore(const string & name, const string & s,
+        const StorePathSet & references, RepairFlag repair) override;
 
-    void narFromPath(const Path & path, Sink & sink) override;
+    void narFromPath(const StorePath & path, Sink & sink) override;
 
-    BuildResult buildDerivation(const Path & drvPath, const BasicDerivation & drv,
+    BuildResult buildDerivation(const StorePath & drvPath, const BasicDerivation & drv,
         BuildMode buildMode) override
     { unsupported("buildDerivation"); }
 
-    void ensurePath(const Path & path) override
+    void ensurePath(const StorePath & path) override
     { unsupported("ensurePath"); }
 
     ref<FSAccessor> getFSAccessor() override;
 
-    void addSignatures(const Path & storePath, const StringSet & sigs) override;
+    void addSignatures(const StorePath & storePath, const StringSet & sigs) override;
 
-    std::shared_ptr<std::string> getBuildLog(const Path & path) override;
+    std::shared_ptr<std::string> getBuildLog(const StorePath & path) override;
 
     int getPriority() override { return priority; }
 
diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index 69649162e..de0ce9ae1 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -14,6 +14,7 @@
 #include "parsed-derivations.hh"
 #include "machines.hh"
 #include "daemon.hh"
+#include "worker-protocol.hh"
 
 #include <algorithm>
 #include <iostream>
@@ -98,7 +99,7 @@ typedef set<GoalPtr, CompareGoalPtrs> Goals;
 typedef list<WeakGoalPtr> WeakGoals;
 
 /* A map of paths to goals (and the other way around). */
-typedef map<Path, WeakGoalPtr> WeakGoalMap;
+typedef std::map<StorePath, WeakGoalPtr> WeakGoalMap;
 
 
 
@@ -253,7 +254,7 @@ private:
     steady_time_point lastWokenUp;
 
     /* Cache for pathContentsGood(). */
-    std::map<Path, bool> pathContentsGoodCache;
+    std::map<StorePath, bool> pathContentsGoodCache;
 
 public:
 
@@ -300,10 +301,10 @@ public:
     ~Worker();
 
     /* Make a goal (with caching). */
-    GoalPtr makeDerivationGoal(const Path & drvPath, const StringSet & wantedOutputs, BuildMode buildMode = bmNormal);
-    std::shared_ptr<DerivationGoal> makeBasicDerivationGoal(const Path & drvPath,
+    GoalPtr makeDerivationGoal(const StorePath & drvPath, const StringSet & wantedOutputs, BuildMode buildMode = bmNormal);
+    std::shared_ptr<DerivationGoal> makeBasicDerivationGoal(StorePath && drvPath,
         const BasicDerivation & drv, BuildMode buildMode = bmNormal);
-    GoalPtr makeSubstitutionGoal(const Path & storePath, RepairFlag repair = NoRepair);
+    GoalPtr makeSubstitutionGoal(const StorePath & storePath, RepairFlag repair = NoRepair);
 
     /* Remove a dead goal. */
     void removeGoal(GoalPtr goal);
@@ -351,9 +352,9 @@ public:
 
     /* Check whether the given valid path exists and has the right
        contents. */
-    bool pathContentsGood(const Path & path);
+    bool pathContentsGood(const StorePath & path);
 
-    void markContentsGood(const Path & path);
+    void markContentsGood(StorePath && path);
 
     void updateProgress()
     {
@@ -470,7 +471,10 @@ static void commonChildInit(Pipe & logPipe)
     close(fdDevNull);
 }
 
-void handleDiffHook(uid_t uid, uid_t gid, Path tryA, Path tryB, Path drvPath, Path tmpDir)
+void handleDiffHook(
+    uid_t uid, uid_t gid,
+    const Path & tryA, const Path & tryB,
+    const Path & drvPath, const Path & tmpDir)
 {
     auto diffHook = settings.diffHook;
     if (diffHook != "" && settings.runDiffHook) {
@@ -662,7 +666,7 @@ HookInstance::HookInstance()
             throw SysError("dupping builder's stdout/stderr");
 
         Strings args = {
-            baseNameOf(settings.buildHook),
+            std::string(baseNameOf(settings.buildHook.get())),
             std::to_string(verbosity),
         };
 
@@ -709,7 +713,7 @@ private:
     bool useDerivation;
 
     /* The path of the derivation. */
-    Path drvPath;
+    StorePath drvPath;
 
     /* The specific outputs that we need to build.  Empty means all of
        them. */
@@ -734,14 +738,14 @@ private:
 
     /* All input paths (that is, the union of FS closures of the
        immediate input paths). */
-    PathSet inputPaths;
+    StorePathSet inputPaths;
 
     /* Outputs that are already valid.  If we're repairing, these are
        the outputs that are valid *and* not corrupt. */
-    PathSet validPaths;
+    StorePathSet validPaths;
 
     /* Outputs that are corrupt or not valid. */
-    PathSet missingPaths;
+    StorePathSet missingPaths;
 
     /* User selected for running the builder. */
     std::unique_ptr<UserLock> buildUser;
@@ -821,7 +825,7 @@ private:
 
     /* Hash rewriting. */
     StringMap inputRewrites, outputRewrites;
-    typedef map<Path, Path> RedirectedOutputs;
+    typedef map<StorePath, StorePath> RedirectedOutputs;
     RedirectedOutputs redirectedOutputs;
 
     BuildMode buildMode;
@@ -829,7 +833,7 @@ private:
     /* If we're repairing without a chroot, there may be outputs that
        are valid but corrupt.  So we redirect these outputs to
        temporary paths. */
-    PathSet redirectedBadOutputs;
+    StorePathSet redirectedBadOutputs;
 
     BuildResult result;
 
@@ -868,23 +872,23 @@ private:
     std::vector<std::thread> daemonWorkerThreads;
 
     /* Paths that were added via recursive Nix calls. */
-    PathSet addedPaths;
+    StorePathSet addedPaths;
 
     /* Recursive Nix calls are only allowed to build or realize paths
        in the original input closure or added via a recursive Nix call
        (so e.g. you can't do 'nix-store -r /nix/store/<bla>' where
        /nix/store/<bla> is some arbitrary path in a binary cache). */
-    bool isAllowed(const Path & path)
+    bool isAllowed(const StorePath & path)
     {
         return inputPaths.count(path) || addedPaths.count(path);
     }
 
-    friend class RestrictedStore;
+    friend struct RestrictedStore;
 
 public:
-    DerivationGoal(const Path & drvPath, const StringSet & wantedOutputs,
+    DerivationGoal(StorePath && drvPath, const StringSet & wantedOutputs,
         Worker & worker, BuildMode buildMode = bmNormal);
-    DerivationGoal(const Path & drvPath, const BasicDerivation & drv,
+    DerivationGoal(StorePath && drvPath, const BasicDerivation & drv,
         Worker & worker, BuildMode buildMode = bmNormal);
     ~DerivationGoal();
 
@@ -899,14 +903,14 @@ public:
            i.e. a derivation named "aardvark" always comes before
            "baboon". And substitution goals always happen before
            derivation goals (due to "b$"). */
-        return "b$" + storePathToName(drvPath) + "$" + drvPath;
+        return "b$" + std::string(drvPath.name()) + "$" + worker.store.printStorePath(drvPath);
     }
 
     void work() override;
 
-    Path getDrvPath()
+    StorePath getDrvPath()
     {
-        return drvPath;
+        return drvPath.clone();
     }
 
     /* Add wanted outputs to an already existing derivation goal. */
@@ -946,7 +950,7 @@ private:
 
     /* Add 'path' to the set of paths that may be referenced by the
        outputs, and make it appear in the sandbox. */
-    void addDependency(const Path & path);
+    void addDependency(const StorePath & path);
 
     /* Make a file owned by the builder. */
     void chownToBuilder(const Path & path);
@@ -980,15 +984,12 @@ private:
     void flushLine();
 
     /* Return the set of (in)valid paths. */
-    PathSet checkPathValidity(bool returnValid, bool checkHash);
-
-    /* Abort the goal if `path' failed to build. */
-    bool pathFailed(const Path & path);
+    StorePathSet checkPathValidity(bool returnValid, bool checkHash);
 
     /* Forcibly kill the child process, if any. */
     void killChild();
 
-    Path addHashRewrite(const Path & path);
+    void addHashRewrite(const StorePath & path);
 
     void repairClosure();
 
@@ -999,23 +1000,23 @@ private:
 
     void done(BuildResult::Status status, const string & msg = "");
 
-    PathSet exportReferences(PathSet storePaths);
+    StorePathSet exportReferences(const StorePathSet & storePaths);
 };
 
 
 const Path DerivationGoal::homeDir = "/homeless-shelter";
 
 
-DerivationGoal::DerivationGoal(const Path & drvPath, const StringSet & wantedOutputs,
+DerivationGoal::DerivationGoal(StorePath && drvPath, const StringSet & wantedOutputs,
     Worker & worker, BuildMode buildMode)
     : Goal(worker)
     , useDerivation(true)
-    , drvPath(drvPath)
+    , drvPath(std::move(drvPath))
     , wantedOutputs(wantedOutputs)
     , buildMode(buildMode)
 {
     state = &DerivationGoal::getDerivation;
-    name = (format("building of '%1%'") % drvPath).str();
+    name = fmt("building of '%s'", worker.store.printStorePath(drvPath));
     trace("created");
 
     mcExpectedBuilds = std::make_unique<MaintainCount<uint64_t>>(worker.expectedBuilds);
@@ -1023,16 +1024,16 @@ DerivationGoal::DerivationGoal(const Path & drvPath, const StringSet & wantedOut
 }
 
 
-DerivationGoal::DerivationGoal(const Path & drvPath, const BasicDerivation & drv,
+DerivationGoal::DerivationGoal(StorePath && drvPath, const BasicDerivation & drv,
     Worker & worker, BuildMode buildMode)
     : Goal(worker)
     , useDerivation(false)
-    , drvPath(drvPath)
+    , drvPath(std::move(drvPath))
     , buildMode(buildMode)
 {
-    this->drv = std::unique_ptr<BasicDerivation>(new BasicDerivation(drv));
+    this->drv = std::make_unique<BasicDerivation>(BasicDerivation(drv));
     state = &DerivationGoal::haveDerivation;
-    name = (format("building of %1%") % showPaths(drv.outputPaths())).str();
+    name = fmt("building of %s", worker.store.showPaths(drv.outputPaths()));
     trace("created");
 
     mcExpectedBuilds = std::make_unique<MaintainCount<uint64_t>>(worker.expectedBuilds);
@@ -1142,7 +1143,7 @@ void DerivationGoal::loadDerivation()
     trace("loading derivation");
 
     if (nrFailed != 0) {
-        printError(format("cannot build missing derivation '%1%'") % drvPath);
+        printError("cannot build missing derivation '%s'", worker.store.printStorePath(drvPath));
         done(BuildResult::MiscFailure);
         return;
     }
@@ -1171,7 +1172,7 @@ void DerivationGoal::haveDerivation()
         worker.store.addTempRoot(i.second.path);
 
     /* Check what outputs paths are not already valid. */
-    PathSet invalidOutputs = checkPathValidity(false, buildMode == bmRepair);
+    auto invalidOutputs = checkPathValidity(false, buildMode == bmRepair);
 
     /* If they are all valid, then we're done. */
     if (invalidOutputs.size() == 0 && buildMode == bmNormal) {
@@ -1179,7 +1180,7 @@ void DerivationGoal::haveDerivation()
         return;
     }
 
-    parsedDrv = std::make_unique<ParsedDerivation>(drvPath, *drv);
+    parsedDrv = std::make_unique<ParsedDerivation>(drvPath.clone(), *drv);
 
     /* We are first going to try to create the invalid output paths
        through substitutes.  If that doesn't work, we'll build
@@ -1200,7 +1201,9 @@ void DerivationGoal::outputsSubstituted()
     trace("all outputs substituted (maybe)");
 
     if (nrFailed > 0 && nrFailed > nrNoSubstituters + nrIncompleteClosure && !settings.tryFallback) {
-        done(BuildResult::TransientFailure, (format("some substitutes for the outputs of derivation '%1%' failed (usually happens due to networking issues); try '--fallback' to build derivation from source ") % drvPath).str());
+        done(BuildResult::TransientFailure,
+            fmt("some substitutes for the outputs of derivation '%s' failed (usually happens due to networking issues); try '--fallback' to build derivation from source ",
+                worker.store.printStorePath(drvPath)));
         return;
     }
 
@@ -1227,14 +1230,15 @@ void DerivationGoal::outputsSubstituted()
         return;
     }
     if (buildMode == bmCheck && nrInvalid > 0)
-        throw Error(format("some outputs of '%1%' are not valid, so checking is not possible") % drvPath);
+        throw Error("some outputs of '%s' are not valid, so checking is not possible",
+            worker.store.printStorePath(drvPath));
 
     /* Otherwise, at least one of the output paths could not be
        produced using a substitute.  So we have to build instead. */
 
     /* Make sure checkPathValidity() from now on checks all
        outputs. */
-    wantedOutputs = PathSet();
+    wantedOutputs.clear();
 
     /* The inputs must be built before we can build this goal. */
     if (useDerivation)
@@ -1244,8 +1248,8 @@ void DerivationGoal::outputsSubstituted()
     for (auto & i : drv->inputSrcs) {
         if (worker.store.isValidPath(i)) continue;
         if (!settings.useSubstitutes)
-            throw Error(format("dependency '%1%' of '%2%' does not exist, and substitution is disabled")
-                % i % drvPath);
+            throw Error("dependency '%s' of '%s' does not exist, and substitution is disabled",
+                worker.store.printStorePath(i), worker.store.printStorePath(drvPath));
         addWaitee(worker.makeSubstitutionGoal(i));
     }
 
@@ -1264,7 +1268,7 @@ void DerivationGoal::repairClosure()
        that produced those outputs. */
 
     /* Get the output closure. */
-    PathSet outputClosure;
+    StorePathSet outputClosure;
     for (auto & i : drv->outputs) {
         if (!wantOutput(i.first, wantedOutputs)) continue;
         worker.store.computeFSClosure(i.second.path, outputClosure);
@@ -1277,26 +1281,26 @@ void DerivationGoal::repairClosure()
     /* Get all dependencies of this derivation so that we know which
        derivation is responsible for which path in the output
        closure. */
-    PathSet inputClosure;
+    StorePathSet inputClosure;
     if (useDerivation) worker.store.computeFSClosure(drvPath, inputClosure);
-    std::map<Path, Path> outputsToDrv;
+    std::map<StorePath, StorePath> outputsToDrv;
     for (auto & i : inputClosure)
-        if (isDerivation(i)) {
+        if (i.isDerivation()) {
             Derivation drv = worker.store.derivationFromPath(i);
             for (auto & j : drv.outputs)
-                outputsToDrv[j.second.path] = i;
+                outputsToDrv.insert_or_assign(j.second.path.clone(), i.clone());
         }
 
     /* Check each path (slow!). */
-    PathSet broken;
     for (auto & i : outputClosure) {
         if (worker.pathContentsGood(i)) continue;
-        printError(format("found corrupted or missing path '%1%' in the output closure of '%2%'") % i % drvPath);
-        Path drvPath2 = outputsToDrv[i];
-        if (drvPath2 == "")
+        printError("found corrupted or missing path '%s' in the output closure of '%s'",
+            worker.store.printStorePath(i), worker.store.printStorePath(drvPath));
+        auto drvPath2 = outputsToDrv.find(i);
+        if (drvPath2 == outputsToDrv.end())
             addWaitee(worker.makeSubstitutionGoal(i, Repair));
         else
-            addWaitee(worker.makeDerivationGoal(drvPath2, PathSet(), bmRepair));
+            addWaitee(worker.makeDerivationGoal(drvPath2->second, StringSet(), bmRepair));
     }
 
     if (waitees.empty()) {
@@ -1312,7 +1316,8 @@ void DerivationGoal::closureRepaired()
 {
     trace("closure repaired");
     if (nrFailed > 0)
-        throw Error(format("some paths in the output closure of derivation '%1%' could not be repaired") % drvPath);
+        throw Error("some paths in the output closure of derivation '%s' could not be repaired",
+            worker.store.printStorePath(drvPath));
     done(BuildResult::AlreadyValid);
 }
 
@@ -1323,10 +1328,9 @@ void DerivationGoal::inputsRealised()
 
     if (nrFailed != 0) {
         if (!useDerivation)
-            throw Error(format("some dependencies of '%1%' are missing") % drvPath);
-        printError(
-            format("cannot build derivation '%1%': %2% dependencies couldn't be built")
-            % drvPath % nrFailed);
+            throw Error("some dependencies of '%s' are missing", worker.store.printStorePath(drvPath));
+        printError("cannot build derivation '%s': %s dependencies couldn't be built",
+            worker.store.printStorePath(drvPath), nrFailed);
         done(BuildResult::DependencyFailed);
         return;
     }
@@ -1349,19 +1353,21 @@ void DerivationGoal::inputsRealised()
                that are specified as inputs. */
             assert(worker.store.isValidPath(i.first));
             Derivation inDrv = worker.store.derivationFromPath(i.first);
-            for (auto & j : i.second)
-                if (inDrv.outputs.find(j) != inDrv.outputs.end())
-                    worker.store.computeFSClosure(inDrv.outputs[j].path, inputPaths);
+            for (auto & j : i.second) {
+                auto k = inDrv.outputs.find(j);
+                if (k != inDrv.outputs.end())
+                    worker.store.computeFSClosure(k->second.path, inputPaths);
                 else
                     throw Error(
-                        format("derivation '%1%' requires non-existent output '%2%' from input derivation '%3%'")
-                        % drvPath % j % i.first);
+                        "derivation '%s' requires non-existent output '%s' from input derivation '%s'",
+                        worker.store.printStorePath(drvPath), j, worker.store.printStorePath(i.first));
+            }
         }
 
     /* Second, the input sources. */
     worker.store.computeFSClosure(drv->inputSrcs, inputPaths);
 
-    debug(format("added input paths %1%") % showPaths(inputPaths));
+    debug("added input paths %s", worker.store.showPaths(inputPaths));
 
     /* Is this a fixed-output derivation? */
     fixedOutput = drv->isFixedOutput();
@@ -1391,7 +1397,7 @@ void DerivationGoal::tryToBuild()
        few seconds and then retry this goal. */
     PathSet lockFiles;
     for (auto & outPath : drv->outputPaths())
-        lockFiles.insert(worker.store.toRealPath(outPath));
+        lockFiles.insert(worker.store.toRealPath(worker.store.printStorePath(outPath)));
 
     if (!outputLocks.lockPaths(lockFiles, "", false)) {
         worker.waitForAWhile(shared_from_this());
@@ -1407,23 +1413,22 @@ void DerivationGoal::tryToBuild()
        build this derivation, so no further checks are necessary. */
     validPaths = checkPathValidity(true, buildMode == bmRepair);
     if (buildMode != bmCheck && validPaths.size() == drv->outputs.size()) {
-        debug(format("skipping build of derivation '%1%', someone beat us to it") % drvPath);
+        debug("skipping build of derivation '%s', someone beat us to it", worker.store.printStorePath(drvPath));
         outputLocks.setDeletion(true);
         done(BuildResult::AlreadyValid);
         return;
     }
 
-    missingPaths = drv->outputPaths();
+    missingPaths = cloneStorePathSet(drv->outputPaths());
     if (buildMode != bmCheck)
         for (auto & i : validPaths) missingPaths.erase(i);
 
     /* If any of the outputs already exist but are not valid, delete
        them. */
     for (auto & i : drv->outputs) {
-        Path path = i.second.path;
-        if (worker.store.isValidPath(path)) continue;
-        debug(format("removing invalid path '%1%'") % path);
-        deletePath(worker.store.toRealPath(path));
+        if (worker.store.isValidPath(i.second.path)) continue;
+        debug("removing invalid path '%s'", worker.store.printStorePath(i.second.path));
+        deletePath(worker.store.toRealPath(worker.store.printStorePath(i.second.path)));
     }
 
     /* Don't do a remote build if the derivation has the attribute
@@ -1436,11 +1441,11 @@ void DerivationGoal::tryToBuild()
             buildMode == bmRepair ? "repairing outputs of '%s'" :
             buildMode == bmCheck ? "checking outputs of '%s'" :
             nrRounds > 1 ? "building '%s' (round %d/%d)" :
-            "building '%s'", drvPath, curRound, nrRounds);
-        fmt("building '%s'", drvPath);
+            "building '%s'", worker.store.printStorePath(drvPath), curRound, nrRounds);
+        fmt("building '%s'", worker.store.printStorePath(drvPath));
         if (hook) msg += fmt(" on '%s'", machineName);
         act = std::make_unique<Activity>(*logger, lvlInfo, actBuild, msg,
-            Logger::Fields{drvPath, hook ? machineName : "", curRound, nrRounds});
+            Logger::Fields{worker.store.printStorePath(drvPath), hook ? machineName : "", curRound, nrRounds});
         mcRunningBuilds = std::make_unique<MaintainCount<uint64_t>>(worker.runningBuilds);
         worker.updateProgress();
     };
@@ -1509,7 +1514,7 @@ void replaceValidPath(const Path & storePath, const Path tmpPath)
     if (pathExists(storePath))
         rename(storePath.c_str(), oldPath.c_str());
     if (rename(tmpPath.c_str(), storePath.c_str()) == -1)
-        throw SysError(format("moving '%1%' to '%2%'") % tmpPath % storePath);
+        throw SysError("moving '%s' to '%s'", tmpPath, storePath);
     deletePath(oldPath);
 }
 
@@ -1534,7 +1539,7 @@ void DerivationGoal::buildDone()
        kill it. */
     int status = hook ? hook->pid.kill() : pid.kill();
 
-    debug(format("builder process for '%1%' finished") % drvPath);
+    debug("builder process for '%s' finished", worker.store.printStorePath(drvPath));
 
     result.timesBuilt++;
     result.stopTime = time(0);
@@ -1590,12 +1595,15 @@ void DerivationGoal::buildDone()
             /* Move paths out of the chroot for easier debugging of
                build failures. */
             if (useChroot && buildMode == bmNormal)
-                for (auto & i : missingPaths)
-                    if (pathExists(chrootRootDir + i))
-                        rename((chrootRootDir + i).c_str(), i.c_str());
+                for (auto & i : missingPaths) {
+                    auto p = worker.store.printStorePath(i);
+                    if (pathExists(chrootRootDir + p))
+                        rename((chrootRootDir + p).c_str(), p.c_str());
+                }
 
-            std::string msg = (format("builder for '%1%' %2%")
-                % drvPath % statusToString(status)).str();
+            auto msg = fmt("builder for '%s' %s",
+                worker.store.printStorePath(drvPath),
+                statusToString(status));
 
             if (!settings.verboseBuild && !logTail.empty()) {
                 msg += (format("; last %d log lines:") % logTail.size()).str();
@@ -1616,13 +1624,13 @@ void DerivationGoal::buildDone()
         if (settings.postBuildHook != "") {
             Activity act(*logger, lvlInfo, actPostBuildHook,
                 fmt("running post-build-hook '%s'", settings.postBuildHook),
-                Logger::Fields{drvPath});
+                Logger::Fields{worker.store.printStorePath(drvPath)});
             PushActivity pact(act.id);
             auto outputPaths = drv->outputPaths();
             std::map<std::string, std::string> hookEnvironment = getEnv();
 
-            hookEnvironment.emplace("DRV_PATH", drvPath);
-            hookEnvironment.emplace("OUT_PATHS", chomp(concatStringsSep(" ", outputPaths)));
+            hookEnvironment.emplace("DRV_PATH", worker.store.printStorePath(drvPath));
+            hookEnvironment.emplace("OUT_PATHS", chomp(concatStringsSep(" ", worker.store.printStorePathSet(outputPaths))));
 
             RunOptions opts(settings.postBuildHook, {});
             opts.environment = hookEnvironment;
@@ -1675,7 +1683,7 @@ void DerivationGoal::buildDone()
 
         /* Delete unused redirected outputs (when doing hash rewriting). */
         for (auto & i : redirectedOutputs)
-            deletePath(i.second);
+            deletePath(worker.store.toRealPath(worker.store.printStorePath(i.second)));
 
         /* Delete the chroot (if we were using one). */
         autoDelChroot.reset(); /* this runs the destructor */
@@ -1740,7 +1748,7 @@ HookReply DerivationGoal::tryBuildHook()
             << "try"
             << (worker.getNrLocalBuilds() < settings.maxBuildJobs ? 1 : 0)
             << drv->platform
-            << drvPath
+            << worker.store.printStorePath(drvPath)
             << parsedDrv->getRequiredSystemFeatures();
         worker.hook->sink.flush();
 
@@ -1773,7 +1781,7 @@ HookReply DerivationGoal::tryBuildHook()
         else if (reply == "postpone")
             return rpPostpone;
         else if (reply != "accept")
-            throw Error(format("bad hook reply '%1%'") % reply);
+            throw Error("bad hook reply '%s'", reply);
 
     } catch (SysError & e) {
         if (e.errNo == EPIPE) {
@@ -1791,11 +1799,11 @@ HookReply DerivationGoal::tryBuildHook()
 
     /* Tell the hook all the inputs that have to be copied to the
        remote system. */
-    hook->sink << inputPaths;
+    writeStorePaths(worker.store, hook->sink, inputPaths);
 
     /* Tell the hooks the missing outputs that have to be copied back
        from the remote system. */
-    hook->sink << missingPaths;
+    writeStorePaths(worker.store, hook->sink, missingPaths);
 
     hook->sink = FdSink();
     hook->toHook.writeSide = -1;
@@ -1812,10 +1820,10 @@ HookReply DerivationGoal::tryBuildHook()
 }
 
 
-void chmod_(const Path & path, mode_t mode)
+static void chmod_(const Path & path, mode_t mode)
 {
     if (chmod(path.c_str(), mode) == -1)
-        throw SysError(format("setting permissions on '%1%'") % path);
+        throw SysError("setting permissions on '%s'", path);
 }
 
 
@@ -1826,33 +1834,25 @@ int childEntry(void * arg)
 }
 
 
-PathSet DerivationGoal::exportReferences(PathSet storePaths)
+StorePathSet DerivationGoal::exportReferences(const StorePathSet & storePaths)
 {
-    PathSet paths;
-
-    for (auto storePath : storePaths) {
-
-        /* Check that the store path is valid. */
-        if (!worker.store.isInStore(storePath))
-            throw BuildError(format("'exportReferencesGraph' contains a non-store path '%1%'")
-                % storePath);
-
-        storePath = worker.store.toStorePath(storePath);
+    StorePathSet paths;
 
+    for (auto & storePath : storePaths) {
         if (!inputPaths.count(storePath))
-            throw BuildError("cannot export references of path '%s' because it is not in the input closure of the derivation", storePath);
+            throw BuildError("cannot export references of path '%s' because it is not in the input closure of the derivation", worker.store.printStorePath(storePath));
 
-        worker.store.computeFSClosure(storePath, paths);
+        worker.store.computeFSClosure(singleton(storePath), paths);
     }
 
     /* If there are derivations in the graph, then include their
        outputs as well.  This is useful if you want to do things
        like passing all build-time dependencies of some path to a
        derivation that builds a NixOS DVD image. */
-    PathSet paths2(paths);
+    auto paths2 = cloneStorePathSet(paths);
 
     for (auto & j : paths2) {
-        if (isDerivation(j)) {
+        if (j.isDerivation()) {
             Derivation drv = worker.store.derivationFromPath(j);
             for (auto & k : drv.outputs)
                 worker.store.computeFSClosure(k.second.path, paths);
@@ -1900,7 +1900,7 @@ void DerivationGoal::startBuilder()
         throw Error("a '%s' with features {%s} is required to build '%s', but I am a '%s' with features {%s}",
             drv->platform,
             concatStringsSep(", ", parsedDrv->getRequiredSystemFeatures()),
-            drvPath,
+            worker.store.printStorePath(drvPath),
             settings.thisSystem,
             concatStringsSep(", ", settings.systemFeatures));
 
@@ -1916,12 +1916,12 @@ void DerivationGoal::startBuilder()
         auto noChroot = parsedDrv->getBoolAttr("__noChroot");
         if (settings.sandboxMode == smEnabled) {
             if (noChroot)
-                throw Error(format("derivation '%1%' has '__noChroot' set, "
-                    "but that's not allowed when 'sandbox' is 'true'") % drvPath);
+                throw Error("derivation '%s' has '__noChroot' set, "
+                    "but that's not allowed when 'sandbox' is 'true'", worker.store.printStorePath(drvPath));
 #if __APPLE__
             if (additionalSandboxProfile != "")
-                throw Error(format("derivation '%1%' specifies a sandbox profile, "
-                    "but this is only allowed when 'sandbox' is 'relaxed'") % drvPath);
+                throw Error("derivation '%s' specifies a sandbox profile, "
+                    "but this is only allowed when 'sandbox' is 'relaxed'", worker.store.printStorePath(drvPath));
 #endif
             useChroot = true;
         }
@@ -1957,14 +1957,13 @@ void DerivationGoal::startBuilder()
 
     /* Create a temporary directory where the build will take
        place. */
-    auto drvName = storePathToName(drvPath);
-    tmpDir = createTempDir("", "nix-build-" + drvName, false, false, 0700);
+    tmpDir = createTempDir("", "nix-build-" + std::string(drvPath.name()), false, false, 0700);
 
     chownToBuilder(tmpDir);
 
     /* Substitute output placeholders with the actual output paths. */
     for (auto & output : drv->outputs)
-        inputRewrites[hashPlaceholder(output.first)] = output.second.path;
+        inputRewrites[hashPlaceholder(output.first)] = worker.store.printStorePath(output.second.path);
 
     /* Construct the environment passed to the builder. */
     initEnv();
@@ -1980,19 +1979,22 @@ void DerivationGoal::startBuilder()
            temporary build directory.  The text files have the format used
            by `nix-store --register-validity'.  However, the deriver
            fields are left empty. */
-        string s = get(drv->env, "exportReferencesGraph");
+        string s = get(drv->env, "exportReferencesGraph").value_or("");
         Strings ss = tokenizeString<Strings>(s);
         if (ss.size() % 2 != 0)
             throw BuildError(format("odd number of tokens in 'exportReferencesGraph': '%1%'") % s);
         for (Strings::iterator i = ss.begin(); i != ss.end(); ) {
             string fileName = *i++;
-            checkStoreName(fileName); /* !!! abuse of this function */
-            Path storePath = *i++;
+            static std::regex regex("[A-Za-z_][A-Za-z0-9_.]*");
+            if (!std::regex_match(fileName, regex))
+                throw Error("invalid file name '%s' in 'exportReferencesGraph'", fileName);
+
+            auto storePath = worker.store.parseStorePath(*i++);
 
             /* Write closure info to <fileName>. */
             writeFile(tmpDir + "/" + fileName,
                 worker.store.makeValidityRegistration(
-                    exportReferences({storePath}), false, false));
+                    exportReferences(singleton(storePath)), false, false));
         }
     }
 
@@ -2022,17 +2024,19 @@ void DerivationGoal::startBuilder()
         dirsInChroot[tmpDirInSandbox] = tmpDir;
 
         /* Add the closure of store paths to the chroot. */
-        PathSet closure;
+        StorePathSet closure;
         for (auto & i : dirsInChroot)
             try {
                 if (worker.store.isInStore(i.second.source))
-                    worker.store.computeFSClosure(worker.store.toStorePath(i.second.source), closure);
+                    worker.store.computeFSClosure(worker.store.parseStorePath(worker.store.toStorePath(i.second.source)), closure);
             } catch (InvalidPath & e) {
             } catch (Error & e) {
                 throw Error(format("while processing 'sandbox-paths': %s") % e.what());
             }
-        for (auto & i : closure)
-            dirsInChroot[i] = i;
+        for (auto & i : closure) {
+            auto p = worker.store.printStorePath(i);
+            dirsInChroot.insert_or_assign(p, p);
+        }
 
         PathSet allowedPaths = settings.allowedImpureHostPrefixes;
 
@@ -2054,7 +2058,8 @@ void DerivationGoal::startBuilder()
                 }
             }
             if (!found)
-                throw Error(format("derivation '%1%' requested impure path '%2%', but it was not in allowed-impure-host-deps") % drvPath % i);
+                throw Error("derivation '%s' requested impure path '%s', but it was not in allowed-impure-host-deps",
+                    worker.store.printStorePath(drvPath), i);
 
             dirsInChroot[i] = i;
         }
@@ -2064,7 +2069,7 @@ void DerivationGoal::startBuilder()
            environment using bind-mounts.  We put it in the Nix store
            to ensure that we can create hard-links to non-directory
            inputs in the fake Nix store in the chroot (see below). */
-        chrootRootDir = worker.store.toRealPath(drvPath) + ".chroot";
+        chrootRootDir = worker.store.toRealPath(worker.store.printStorePath(drvPath)) + ".chroot";
         deletePath(chrootRootDir);
 
         /* Clean up the chroot directory automatically. */
@@ -2123,14 +2128,15 @@ void DerivationGoal::startBuilder()
             throw SysError(format("cannot change ownership of '%1%'") % chrootStoreDir);
 
         for (auto & i : inputPaths) {
-            Path r = worker.store.toRealPath(i);
+            auto p = worker.store.printStorePath(i);
+            Path r = worker.store.toRealPath(p);
             struct stat st;
             if (lstat(r.c_str(), &st))
-                throw SysError(format("getting attributes of path '%1%'") % i);
+                throw SysError("getting attributes of path '%s'", p);
             if (S_ISDIR(st.st_mode))
-                dirsInChroot[i] = r;
+                dirsInChroot.insert_or_assign(p, r);
             else
-                linkOrCopy(r, chrootRootDir + i);
+                linkOrCopy(r, chrootRootDir + p);
         }
 
         /* If we're repairing, checking or rebuilding part of a
@@ -2139,7 +2145,7 @@ void DerivationGoal::startBuilder()
            (typically the dependencies of /bin/sh).  Throw them
            out. */
         for (auto & i : drv->outputs)
-            dirsInChroot.erase(i.second.path);
+            dirsInChroot.erase(worker.store.printStorePath(i.second.path));
 
 #elif __APPLE__
         /* We don't really have any parent prep work to do (yet?)
@@ -2171,17 +2177,17 @@ void DerivationGoal::startBuilder()
            corrupt outputs in advance.  So rewrite them as well. */
         if (buildMode == bmRepair)
             for (auto & i : missingPaths)
-                if (worker.store.isValidPath(i) && pathExists(i)) {
+                if (worker.store.isValidPath(i) && pathExists(worker.store.printStorePath(i))) {
                     addHashRewrite(i);
-                    redirectedBadOutputs.insert(i);
+                    redirectedBadOutputs.insert(i.clone());
                 }
     }
 
     if (useChroot && settings.preBuildHook != "" && dynamic_cast<Derivation *>(drv.get())) {
         printMsg(lvlChatty, format("executing pre-build hook '%1%'")
             % settings.preBuildHook);
-        auto args = useChroot ? Strings({drvPath, chrootRootDir}) :
-            Strings({ drvPath });
+        auto args = useChroot ? Strings({worker.store.printStorePath(drvPath), chrootRootDir}) :
+            Strings({ worker.store.printStorePath(drvPath) });
         enum BuildHookState {
             stBegin,
             stExtraChrootDirs
@@ -2448,7 +2454,7 @@ void DerivationGoal::initTmpDir() {
        there is no size constraint). */
     if (!parsedDrv->getStructuredAttrs()) {
 
-        StringSet passAsFile = tokenizeString<StringSet>(get(drv->env, "passAsFile"));
+        StringSet passAsFile = tokenizeString<StringSet>(get(drv->env, "passAsFile").value_or(""));
         int fileNr = 0;
         for (auto & i : drv->env) {
             if (passAsFile.find(i.first) == passAsFile.end()) {
@@ -2478,6 +2484,7 @@ void DerivationGoal::initTmpDir() {
     env["PWD"] = tmpDirInSandbox;
 }
 
+
 void DerivationGoal::initEnv()
 {
     env.clear();
@@ -2549,7 +2556,7 @@ void DerivationGoal::writeStructuredAttrs()
     /* Add an "outputs" object containing the output paths. */
     nlohmann::json outputs;
     for (auto & i : drv->outputs)
-        outputs[i.first] = rewriteStrings(i.second.path, inputRewrites);
+        outputs[i.first] = rewriteStrings(worker.store.printStorePath(i.second.path), inputRewrites);
     json["outputs"] = outputs;
 
     /* Handle exportReferencesGraph. */
@@ -2559,9 +2566,9 @@ void DerivationGoal::writeStructuredAttrs()
             std::ostringstream str;
             {
                 JSONPlaceholder jsonRoot(str, true);
-                PathSet storePaths;
+                StorePathSet storePaths;
                 for (auto & p : *i)
-                    storePaths.insert(p.get<std::string>());
+                    storePaths.insert(worker.store.parseStorePath(p.get<std::string>()));
                 worker.store.pathInfoToJSON(jsonRoot,
                     exportReferences(storePaths), false, true);
             }
@@ -2660,22 +2667,22 @@ struct RestrictedStore : public LocalFSStore
     std::string getUri() override
     { return next->getUri(); }
 
-    PathSet queryAllValidPaths() override
+    StorePathSet queryAllValidPaths() override
     {
-        PathSet paths;
-        for (auto & p : goal.inputPaths) paths.insert(p);
-        for (auto & p : goal.addedPaths) paths.insert(p);
+        StorePathSet paths;
+        for (auto & p : goal.inputPaths) paths.insert(p.clone());
+        for (auto & p : goal.addedPaths) paths.insert(p.clone());
         return paths;
     }
 
-    void queryPathInfoUncached(const Path & path,
+    void queryPathInfoUncached(const StorePath & path,
         Callback<std::shared_ptr<const ValidPathInfo>> callback) noexcept override
     {
         if (goal.isAllowed(path)) {
             try {
                 /* Censor impure information. */
                 auto info = std::make_shared<ValidPathInfo>(*next->queryPathInfo(path));
-                info->deriver.clear();
+                info->deriver.reset();
                 info->registrationTime = 0;
                 info->ultimate = false;
                 info->sigs.clear();
@@ -2687,19 +2694,19 @@ struct RestrictedStore : public LocalFSStore
             callback(nullptr);
     };
 
-    void queryReferrers(const Path & path, PathSet & referrers) override
+    void queryReferrers(const StorePath & path, StorePathSet & referrers) override
     { }
 
-    PathSet queryDerivationOutputs(const Path & path) override
+    StorePathSet queryDerivationOutputs(const StorePath & path) override
     { throw Error("queryDerivationOutputs"); }
 
-    StringSet queryDerivationOutputNames(const Path & path) override
+    StringSet queryDerivationOutputNames(const StorePath & path) override
     { throw Error("queryDerivationOutputNames"); }
 
-    Path queryPathFromHashPart(const string & hashPart) override
+    std::optional<StorePath> queryPathFromHashPart(const std::string & hashPart) override
     { throw Error("queryPathFromHashPart"); }
 
-    Path addToStore(const string & name, const Path & srcPath,
+    StorePath addToStore(const string & name, const Path & srcPath,
         bool recursive = true, HashType hashAlgo = htSHA256,
         PathFilter & filter = defaultPathFilter, RepairFlag repair = NoRepair) override
     { throw Error("addToStore"); }
@@ -2712,7 +2719,7 @@ struct RestrictedStore : public LocalFSStore
         goal.addDependency(info.path);
     }
 
-    Path addToStoreFromDump(const string & dump, const string & name,
+    StorePath addToStoreFromDump(const string & dump, const string & name,
         bool recursive = true, HashType hashAlgo = htSHA256, RepairFlag repair = NoRepair) override
     {
         auto path = next->addToStoreFromDump(dump, name, recursive, hashAlgo, repair);
@@ -2720,89 +2727,87 @@ struct RestrictedStore : public LocalFSStore
         return path;
     }
 
-    Path addTextToStore(const string & name, const string & s,
-        const PathSet & references, RepairFlag repair = NoRepair) override
+    StorePath addTextToStore(const string & name, const string & s,
+        const StorePathSet & references, RepairFlag repair = NoRepair) override
     {
         auto path = next->addTextToStore(name, s, references, repair);
         goal.addDependency(path);
         return path;
     }
 
-    void narFromPath(const Path & path, Sink & sink) override 
+    void narFromPath(const StorePath & path, Sink & sink) override
     {
         if (!goal.isAllowed(path))
-            throw InvalidPath("cannot dump unknown path '%s' in recursive Nix", path);
+            throw InvalidPath("cannot dump unknown path '%s' in recursive Nix", printStorePath(path));
         LocalFSStore::narFromPath(path, sink);
     }
 
-    void ensurePath(const Path & path) override
+    void ensurePath(const StorePath & path) override
     {
         if (!goal.isAllowed(path))
-            throw InvalidPath("cannot substitute unknown path '%s' in recursive Nix", path);
+            throw InvalidPath("cannot substitute unknown path '%s' in recursive Nix", printStorePath(path));
         /* Nothing to be done; 'path' must already be valid. */
     }
 
-    void buildPaths(const PathSet & paths, BuildMode buildMode) override
+    void buildPaths(const std::vector<StorePathWithOutputs> & paths, BuildMode buildMode) override
     {
         if (buildMode != bmNormal) throw Error("unsupported build mode");
 
-        PathSet newPaths;
+        StorePathSet newPaths;
 
         for (auto & path : paths) {
-            DrvPathWithOutputs i = parseDrvPathWithOutputs(path);
-            if (isDerivation(i.first)) {
-                if (!goal.isAllowed(i.first))
-                    throw InvalidPath("cannot build unknown path '%s' in recursive Nix", i.first);
-                auto drv = derivationFromPath(i.first);
+            if (path.path.isDerivation()) {
+                if (!goal.isAllowed(path.path))
+                    throw InvalidPath("cannot build unknown path '%s' in recursive Nix", printStorePath(path.path));
+                auto drv = derivationFromPath(path.path);
                 for (auto & output : drv.outputs)
-                    if (wantOutput(output.first, i.second))
-                        newPaths.insert(output.second.path);
-            } else if (!goal.isAllowed(path))
-                throw InvalidPath("cannot build unknown path '%s' in recursive Nix", path);
+                    if (wantOutput(output.first, path.outputs))
+                        newPaths.insert(output.second.path.clone());
+            } else if (!goal.isAllowed(path.path))
+                throw InvalidPath("cannot build unknown path '%s' in recursive Nix", printStorePath(path.path));
         }
 
         next->buildPaths(paths, buildMode);
 
-        PathSet closure;
+        StorePathSet closure;
         next->computeFSClosure(newPaths, closure);
         for (auto & path : closure)
             goal.addDependency(path);
     }
 
-    BuildResult buildDerivation(const Path & drvPath, const BasicDerivation & drv,
+    BuildResult buildDerivation(const StorePath & drvPath, const BasicDerivation & drv,
         BuildMode buildMode = bmNormal) override
     { unsupported("buildDerivation"); }
 
-    void addTempRoot(const Path & path)
+    void addTempRoot(const StorePath & path) override
     { }
 
-    void addIndirectRoot(const Path & path)
+    void addIndirectRoot(const Path & path) override
     { }
 
-    Roots findRoots()
+    Roots findRoots(bool censor) override
     { return Roots(); }
 
-    void collectGarbage(const GCOptions & options, GCResults & results)
+    void collectGarbage(const GCOptions & options, GCResults & results) override
     { }
 
-    void addSignatures(const Path & storePath, const StringSet & sigs)
+    void addSignatures(const StorePath & storePath, const StringSet & sigs) override
     { unsupported("addSignatures"); }
 
-    void queryMissing(const PathSet & targets,
-        PathSet & willBuild, PathSet & willSubstitute, PathSet & unknown,
-        unsigned long long & downloadSize, unsigned long long & narSize)
+    void queryMissing(const std::vector<StorePathWithOutputs> & targets,
+        StorePathSet & willBuild, StorePathSet & willSubstitute, StorePathSet & unknown,
+        unsigned long long & downloadSize, unsigned long long & narSize) override
     {
         /* This is slightly impure since it leaks information to the
            client about what paths will be built/substituted or are
            already present. Probably not a big deal. */
 
-        PathSet allowed;
+        std::vector<StorePathWithOutputs> allowed;
         for (auto & path : targets) {
-            DrvPathWithOutputs i = parseDrvPathWithOutputs(path);
-            if (goal.isAllowed(i.first))
-                allowed.insert(i.first);
+            if (goal.isAllowed(path.path))
+                allowed.emplace_back(path);
             else
-                unknown.insert(i.first);
+                unknown.insert(path.path.clone());
         }
 
         next->queryMissing(allowed, willBuild, willSubstitute,
@@ -2855,7 +2860,7 @@ void DerivationGoal::startDaemon()
 
             debug("received daemon connection");
 
-            auto workerThread = std::thread([this, store, remote{std::move(remote)}]() {
+            auto workerThread = std::thread([store, remote{std::move(remote)}]() {
                 FdSource from(remote.get());
                 FdSink to(remote.get());
                 try {
@@ -2893,28 +2898,26 @@ void DerivationGoal::stopDaemon()
 }
 
 
-void DerivationGoal::addDependency(const Path & path)
+void DerivationGoal::addDependency(const StorePath & path)
 {
-    worker.store.assertStorePath(path);
-
     if (isAllowed(path)) return;
 
-    addedPaths.insert(path);
+    addedPaths.insert(path.clone());
 
     /* If we're doing a sandbox build, then we have to make the path
        appear in the sandbox. */
     if (useChroot) {
 
-        debug("materialising '%s' in the sandbox", path);
+        debug("materialising '%s' in the sandbox", worker.store.printStorePath(path));
 
         #if __linux__
 
-            Path source = worker.store.toRealPath(path);
-            Path target = chrootRootDir + path;
+            Path source = worker.store.toRealPath(worker.store.printStorePath(path));
+            Path target = chrootRootDir + worker.store.printStorePath(path);
             debug("bind-mounting %s -> %s", target, source);
 
             if (pathExists(target))
-                throw Error("store path '%s' already exists in the sandbox", path);
+                throw Error("store path '%s' already exists in the sandbox", worker.store.printStorePath(path));
 
             struct stat st;
             if (lstat(source.c_str(), &st))
@@ -2941,13 +2944,14 @@ void DerivationGoal::addDependency(const Path & path)
 
                 int status = child.wait();
                 if (status != 0)
-                    throw Error("could not add path '%s' to sandbox", path);
+                    throw Error("could not add path '%s' to sandbox", worker.store.printStorePath(path));
 
             } else
                 linkOrCopy(source, target);
 
         #else
-            throw Error("don't know how to make path '%s' (produced by a recursive Nix call) appear in the sandbox", path);
+            throw Error("don't know how to make path '%s' (produced by a recursive Nix call) appear in the sandbox",
+                worker.store.printStorePath(path));
         #endif
 
     }
@@ -3363,8 +3367,10 @@ void DerivationGoal::runChild()
                 }
 
                 /* Add all our input paths to the chroot */
-                for (auto & i : inputPaths)
-                    dirsInChroot[i] = i;
+                for (auto & i : inputPaths) {
+                    auto p = worker.store.printStorePath(i);
+                    dirsInChroot[p] = p;
+                }
 
                 /* Violations will go to the syslog if you set this. Unfortunately the destination does not appear to be configurable */
                 if (settings.darwinLogSandboxViolations) {
@@ -3380,13 +3386,13 @@ void DerivationGoal::runChild()
 
                 /* Our rwx outputs */
                 sandboxProfile += "(allow file-read* file-write* process-exec\n";
-                for (auto & i : missingPaths) {
-                    sandboxProfile += (format("\t(subpath \"%1%\")\n") % i.c_str()).str();
-                }
+                for (auto & i : missingPaths)
+                    sandboxProfile += fmt("\t(subpath \"%s\")\n", worker.store.printStorePath(i));
+
                 /* Also add redirected outputs to the chroot */
-                for (auto & i : redirectedOutputs) {
-                    sandboxProfile += (format("\t(subpath \"%1%\")\n") % i.second.c_str()).str();
-                }
+                for (auto & i : redirectedOutputs)
+                    sandboxProfile += fmt("\t(subpath \"%s\")\n", worker.store.printStorePath(i.second));
+
                 sandboxProfile += ")\n";
 
                 /* Our inputs (transitive dependencies and any impurities computed above)
@@ -3405,19 +3411,19 @@ void DerivationGoal::runChild()
                     if (lstat(path.c_str(), &st)) {
                         if (i.second.optional && errno == ENOENT)
                             continue;
-                        throw SysError(format("getting attributes of path '%1%'") % path);
+                        throw SysError("getting attributes of path '%s", path);
                     }
                     if (S_ISDIR(st.st_mode))
-                        sandboxProfile += (format("\t(subpath \"%1%\")\n") % path).str();
+                        sandboxProfile += fmt("\t(subpath \"%s\")\n", path);
                     else
-                        sandboxProfile += (format("\t(literal \"%1%\")\n") % path).str();
+                        sandboxProfile += fmt("\t(literal \"%s\")\n", path);
                 }
                 sandboxProfile += ")\n";
 
                 /* Allow file-read* on full directory hierarchy to self. Allows realpath() */
                 sandboxProfile += "(allow file-read*\n";
                 for (auto & i : ancestry) {
-                    sandboxProfile += (format("\t(literal \"%1%\")\n") % i.c_str()).str();
+                    sandboxProfile += fmt("\t(literal \"%s\")\n", i);
                 }
                 sandboxProfile += ")\n";
 
@@ -3458,8 +3464,7 @@ void DerivationGoal::runChild()
 #endif
         else {
             builder = drv->builder.c_str();
-            string builderBasename = baseNameOf(drv->builder);
-            args.push_back(builderBasename);
+            args.push_back(std::string(baseNameOf(drv->builder)));
         }
 
         for (auto & i : drv->args)
@@ -3473,7 +3478,7 @@ void DerivationGoal::runChild()
             try {
                 logger = makeJSONLogger(*logger);
 
-                BasicDerivation drv2(*drv);
+                BasicDerivation & drv2(*drv);
                 for (auto & e : drv2.env)
                     e.second = rewriteStrings(e.second, inputRewrites);
 
@@ -3506,16 +3511,15 @@ void DerivationGoal::runChild()
 /* Parse a list of reference specifiers.  Each element must either be
    a store path, or the symbolic name of the output of the derivation
    (such as `out'). */
-PathSet parseReferenceSpecifiers(Store & store, const BasicDerivation & drv, const Strings & paths)
+StorePathSet parseReferenceSpecifiers(Store & store, const BasicDerivation & drv, const Strings & paths)
 {
-    PathSet result;
+    StorePathSet result;
     for (auto & i : paths) {
         if (store.isStorePath(i))
-            result.insert(i);
-        else if (drv.outputs.find(i) != drv.outputs.end())
-            result.insert(drv.outputs.find(i)->second.path);
-        else throw BuildError(
-            format("derivation contains an illegal reference specifier '%1%'") % i);
+            result.insert(store.parseStorePath(i));
+        else if (drv.outputs.count(i))
+            result.insert(drv.outputs.find(i)->second.path.clone());
+        else throw BuildError("derivation contains an illegal reference specifier '%s'", i);
     }
     return result;
 }
@@ -3548,19 +3552,17 @@ void DerivationGoal::registerOutputs()
     /* The paths that can be referenced are the input closures, the
        output paths, and any paths that have been built via recursive
        Nix calls. */
-    PathSet referenceablePaths;
-    for (auto & p : inputPaths) referenceablePaths.insert(p);
-    for (auto & i : drv->outputs) referenceablePaths.insert(i.second.path);
-    for (auto & p : addedPaths) referenceablePaths.insert(p);
+    StorePathSet referenceablePaths;
+    for (auto & p : inputPaths) referenceablePaths.insert(p.clone());
+    for (auto & i : drv->outputs) referenceablePaths.insert(i.second.path.clone());
+    for (auto & p : addedPaths) referenceablePaths.insert(p.clone());
 
     /* Check whether the output paths were created, and grep each
        output path to determine what other paths it references.  Also make all
        output paths read-only. */
     for (auto & i : drv->outputs) {
-        Path path = i.second.path;
-        if (missingPaths.find(path) == missingPaths.end()) continue;
-
-        ValidPathInfo info;
+        auto path = worker.store.printStorePath(i.second.path);
+        if (!missingPaths.count(i.second.path)) continue;
 
         Path actualPath = path;
         if (useChroot) {
@@ -3577,22 +3579,25 @@ void DerivationGoal::registerOutputs()
         }
 
         if (needsHashRewrite()) {
-            Path redirected = redirectedOutputs[path];
-            if (buildMode == bmRepair
-                && redirectedBadOutputs.find(path) != redirectedBadOutputs.end()
-                && pathExists(redirected))
-                replaceValidPath(path, redirected);
-            if (buildMode == bmCheck && redirected != "")
-                actualPath = redirected;
+            auto r = redirectedOutputs.find(i.second.path);
+            if (r != redirectedOutputs.end()) {
+                auto redirected = worker.store.toRealPath(worker.store.printStorePath(r->second));
+                if (buildMode == bmRepair
+                    && redirectedBadOutputs.count(i.second.path)
+                    && pathExists(redirected))
+                    replaceValidPath(path, redirected);
+                if (buildMode == bmCheck)
+                    actualPath = redirected;
+            }
         }
 
         struct stat st;
         if (lstat(actualPath.c_str(), &st) == -1) {
             if (errno == ENOENT)
                 throw BuildError(
-                    format("builder for '%1%' failed to produce output path '%2%'")
-                    % drvPath % path);
-            throw SysError(format("getting attributes of path '%1%'") % actualPath);
+                    "builder for '%s' failed to produce output path '%s'",
+                    worker.store.printStorePath(drvPath), path);
+            throw SysError("getting attributes of path '%s'", actualPath);
         }
 
 #ifndef __CYGWIN__
@@ -3629,6 +3634,8 @@ void DerivationGoal::registerOutputs()
         /* Check that fixed-output derivations produced the right
            outputs (i.e., the content hash should match the specified
            hash). */
+        std::string ca;
+
         if (fixedOutput) {
 
             bool recursive; Hash h;
@@ -3645,7 +3652,7 @@ void DerivationGoal::registerOutputs()
                the derivation to its content-addressed location. */
             Hash h2 = recursive ? hashPath(h.type, actualPath).first : hashFile(h.type, actualPath);
 
-            Path dest = worker.store.makeFixedOutputPath(recursive, h2, storePathToName(path));
+            auto dest = worker.store.makeFixedOutputPath(recursive, h2, i.second.path.name());
 
             if (h != h2) {
 
@@ -3654,9 +3661,9 @@ void DerivationGoal::registerOutputs()
                 worker.hashMismatch = true;
                 delayedException = std::make_exception_ptr(
                     BuildError("hash mismatch in fixed-output derivation '%s':\n  wanted: %s\n  got:    %s",
-                        dest, h.to_string(SRI), h2.to_string(SRI)));
+                        worker.store.printStorePath(dest), h.to_string(SRI), h2.to_string(SRI)));
 
-                Path actualDest = worker.store.toRealPath(dest);
+                Path actualDest = worker.store.toRealPath(worker.store.printStorePath(dest));
 
                 if (worker.store.isValidPath(dest))
                     std::rethrow_exception(delayedException);
@@ -3665,16 +3672,16 @@ void DerivationGoal::registerOutputs()
                     PathLocks outputLocks({actualDest});
                     deletePath(actualDest);
                     if (rename(actualPath.c_str(), actualDest.c_str()) == -1)
-                        throw SysError(format("moving '%1%' to '%2%'") % actualPath % dest);
+                        throw SysError("moving '%s' to '%s'", actualPath, worker.store.printStorePath(dest));
                 }
 
-                path = dest;
+                path = worker.store.printStorePath(dest);
                 actualPath = actualDest;
             }
             else
-                assert(path == dest);
+                assert(worker.store.parseStorePath(path) == dest);
 
-            info.ca = makeFixedOutputCA(recursive, h2);
+            ca = makeFixedOutputCA(recursive, h2);
         }
 
         /* Get rid of all weird permissions.  This also checks that
@@ -3688,11 +3695,11 @@ void DerivationGoal::registerOutputs()
            verify later on whether nobody has messed with the store. */
         debug("scanning for references inside '%1%'", path);
         HashResult hash;
-        PathSet references = scanForReferences(actualPath, referenceablePaths, hash);
+        auto references = worker.store.parseStorePathSet(scanForReferences(actualPath, worker.store.printStorePathSet(referenceablePaths), hash));
 
         if (buildMode == bmCheck) {
-            if (!worker.store.isValidPath(path)) continue;
-            auto info = *worker.store.queryPathInfo(path);
+            if (!worker.store.isValidPath(worker.store.parseStorePath(path))) continue;
+            ValidPathInfo info(*worker.store.queryPathInfo(worker.store.parseStorePath(path)));
             if (hash.first != info.narHash) {
                 worker.checkMismatch = true;
                 if (settings.runDiffHook || settings.keepFailed) {
@@ -3704,20 +3711,22 @@ void DerivationGoal::registerOutputs()
                     handleDiffHook(
                         buildUser ? buildUser->getUID() : getuid(),
                         buildUser ? buildUser->getGID() : getgid(),
-                        path, dst, drvPath, tmpDir);
+                        path, dst, worker.store.printStorePath(drvPath), tmpDir);
 
-                    throw NotDeterministic(format("derivation '%1%' may not be deterministic: output '%2%' differs from '%3%'")
-                        % drvPath % path % dst);
+                    throw NotDeterministic("derivation '%s' may not be deterministic: output '%s' differs from '%s'",
+                        worker.store.printStorePath(drvPath), path, dst);
                 } else
-                    throw NotDeterministic(format("derivation '%1%' may not be deterministic: output '%2%' differs")
-                        % drvPath % path);
+                    throw NotDeterministic("derivation '%s' may not be deterministic: output '%s' differs",
+                        worker.store.printStorePath(drvPath), path);
             }
 
             /* Since we verified the build, it's now ultimately trusted. */
             if (!info.ultimate) {
                 info.ultimate = true;
                 worker.store.signPathInfo(info);
-                worker.store.registerValidPaths({info});
+                ValidPathInfos infos;
+                infos.push_back(std::move(info));
+                worker.store.registerValidPaths(infos);
             }
 
             continue;
@@ -3725,29 +3734,30 @@ void DerivationGoal::registerOutputs()
 
         /* For debugging, print out the referenced and unreferenced paths. */
         for (auto & i : inputPaths) {
-            PathSet::iterator j = references.find(i);
+            auto j = references.find(i);
             if (j == references.end())
-                debug(format("unreferenced input: '%1%'") % i);
+                debug("unreferenced input: '%1%'", worker.store.printStorePath(i));
             else
-                debug(format("referenced input: '%1%'") % i);
+                debug("referenced input: '%1%'", worker.store.printStorePath(i));
         }
 
         if (curRound == nrRounds) {
             worker.store.optimisePath(actualPath); // FIXME: combine with scanForReferences()
-            worker.markContentsGood(path);
+            worker.markContentsGood(worker.store.parseStorePath(path));
         }
 
-        info.path = path;
+        ValidPathInfo info(worker.store.parseStorePath(path));
         info.narHash = hash.first;
         info.narSize = hash.second;
-        info.references = references;
-        info.deriver = drvPath;
+        info.references = std::move(references);
+        info.deriver = drvPath.clone();
         info.ultimate = true;
+        info.ca = ca;
         worker.store.signPathInfo(info);
 
         if (!info.references.empty()) info.ca.clear();
 
-        infos[i.first] = info;
+        infos.emplace(i.first, std::move(info));
     }
 
     if (buildMode == bmCheck) return;
@@ -3762,16 +3772,19 @@ void DerivationGoal::registerOutputs()
         for (auto i = prevInfos.begin(), j = infos.begin(); i != prevInfos.end(); ++i, ++j)
             if (!(*i == *j)) {
                 result.isNonDeterministic = true;
-                Path prev = i->second.path + checkSuffix;
+                Path prev = worker.store.printStorePath(i->second.path) + checkSuffix;
                 bool prevExists = keepPreviousRound && pathExists(prev);
                 auto msg = prevExists
-                    ? fmt("output '%1%' of '%2%' differs from '%3%' from previous round", i->second.path, drvPath, prev)
-                    : fmt("output '%1%' of '%2%' differs from previous round", i->second.path, drvPath);
+                    ? fmt("output '%s' of '%s' differs from '%s' from previous round",
+                        worker.store.printStorePath(i->second.path), worker.store.printStorePath(drvPath), prev)
+                    : fmt("output '%s' of '%s' differs from previous round",
+                        worker.store.printStorePath(i->second.path), worker.store.printStorePath(drvPath));
 
                 handleDiffHook(
                     buildUser ? buildUser->getUID() : getuid(),
                     buildUser ? buildUser->getGID() : getgid(),
-                    prev, i->second.path, drvPath, tmpDir);
+                    prev, worker.store.printStorePath(i->second.path),
+                    worker.store.printStorePath(drvPath), tmpDir);
 
                 if (settings.enforceDeterminism)
                     throw NotDeterministic(msg);
@@ -3784,16 +3797,17 @@ void DerivationGoal::registerOutputs()
     /* If this is the first round of several, then move the output out of the way. */
     if (nrRounds > 1 && curRound == 1 && curRound < nrRounds && keepPreviousRound) {
         for (auto & i : drv->outputs) {
-            Path prev = i.second.path + checkSuffix;
+            auto path = worker.store.printStorePath(i.second.path);
+            Path prev = path + checkSuffix;
             deletePath(prev);
-            Path dst = i.second.path + checkSuffix;
-            if (rename(i.second.path.c_str(), dst.c_str()))
-                throw SysError(format("renaming '%1%' to '%2%'") % i.second.path % dst);
+            Path dst = path + checkSuffix;
+            if (rename(path.c_str(), dst.c_str()))
+                throw SysError("renaming '%s' to '%s'", path, dst);
         }
     }
 
     if (curRound < nrRounds) {
-        prevInfos = infos;
+        prevInfos = std::move(infos);
         return;
     }
 
@@ -3801,7 +3815,7 @@ void DerivationGoal::registerOutputs()
        if the result was not determistic? */
     if (curRound == nrRounds) {
         for (auto & i : drv->outputs) {
-            Path prev = i.second.path + checkSuffix;
+            Path prev = worker.store.printStorePath(i.second.path) + checkSuffix;
             deletePath(prev);
         }
     }
@@ -3826,7 +3840,7 @@ void DerivationGoal::checkOutputs(const std::map<Path, ValidPathInfo> & outputs)
 {
     std::map<Path, const ValidPathInfo &> outputsByPath;
     for (auto & output : outputs)
-        outputsByPath.emplace(output.second.path, output.second);
+        outputsByPath.emplace(worker.store.printStorePath(output.second.path), output.second);
 
     for (auto & output : outputs) {
         auto & outputName = output.first;
@@ -3842,76 +3856,77 @@ void DerivationGoal::checkOutputs(const std::map<Path, ValidPathInfo> & outputs)
         /* Compute the closure and closure size of some output. This
            is slightly tricky because some of its references (namely
            other outputs) may not be valid yet. */
-        auto getClosure = [&](const Path & path)
+        auto getClosure = [&](const StorePath & path)
         {
             uint64_t closureSize = 0;
-            PathSet pathsDone;
-            std::queue<Path> pathsLeft;
-            pathsLeft.push(path);
+            StorePathSet pathsDone;
+            std::queue<StorePath> pathsLeft;
+            pathsLeft.push(path.clone());
 
             while (!pathsLeft.empty()) {
-                auto path = pathsLeft.front();
+                auto path = pathsLeft.front().clone();
                 pathsLeft.pop();
-                if (!pathsDone.insert(path).second) continue;
+                if (!pathsDone.insert(path.clone()).second) continue;
 
-                auto i = outputsByPath.find(path);
+                auto i = outputsByPath.find(worker.store.printStorePath(path));
                 if (i != outputsByPath.end()) {
                     closureSize += i->second.narSize;
                     for (auto & ref : i->second.references)
-                        pathsLeft.push(ref);
+                        pathsLeft.push(ref.clone());
                 } else {
                     auto info = worker.store.queryPathInfo(path);
                     closureSize += info->narSize;
                     for (auto & ref : info->references)
-                        pathsLeft.push(ref);
+                        pathsLeft.push(ref.clone());
                 }
             }
 
-            return std::make_pair(pathsDone, closureSize);
+            return std::make_pair(std::move(pathsDone), closureSize);
         };
 
         auto applyChecks = [&](const Checks & checks)
         {
             if (checks.maxSize && info.narSize > *checks.maxSize)
                 throw BuildError("path '%s' is too large at %d bytes; limit is %d bytes",
-                    info.path, info.narSize, *checks.maxSize);
+                    worker.store.printStorePath(info.path), info.narSize, *checks.maxSize);
 
             if (checks.maxClosureSize) {
                 uint64_t closureSize = getClosure(info.path).second;
                 if (closureSize > *checks.maxClosureSize)
                     throw BuildError("closure of path '%s' is too large at %d bytes; limit is %d bytes",
-                        info.path, closureSize, *checks.maxClosureSize);
+                        worker.store.printStorePath(info.path), closureSize, *checks.maxClosureSize);
             }
 
             auto checkRefs = [&](const std::optional<Strings> & value, bool allowed, bool recursive)
             {
                 if (!value) return;
 
-                PathSet spec = parseReferenceSpecifiers(worker.store, *drv, *value);
+                auto spec = parseReferenceSpecifiers(worker.store, *drv, *value);
 
-                PathSet used = recursive ? getClosure(info.path).first : info.references;
+                auto used = recursive ? cloneStorePathSet(getClosure(info.path).first) : cloneStorePathSet(info.references);
 
                 if (recursive && checks.ignoreSelfRefs)
                     used.erase(info.path);
 
-                PathSet badPaths;
+                StorePathSet badPaths;
 
                 for (auto & i : used)
                     if (allowed) {
                         if (!spec.count(i))
-                            badPaths.insert(i);
+                            badPaths.insert(i.clone());
                     } else {
                         if (spec.count(i))
-                            badPaths.insert(i);
+                            badPaths.insert(i.clone());
                     }
 
                 if (!badPaths.empty()) {
                     string badPathsStr;
                     for (auto & i : badPaths) {
                         badPathsStr += "\n  ";
-                        badPathsStr += i;
+                        badPathsStr += worker.store.printStorePath(i);
                     }
-                    throw BuildError("output '%s' is not allowed to refer to the following paths:%s", info.path, badPathsStr);
+                    throw BuildError("output '%s' is not allowed to refer to the following paths:%s",
+                        worker.store.printStorePath(info.path), badPathsStr);
                 }
             };
 
@@ -3943,7 +3958,7 @@ void DerivationGoal::checkOutputs(const std::map<Path, ValidPathInfo> & outputs)
                             Strings res;
                             for (auto j = i->begin(); j != i->end(); ++j) {
                                 if (!j->is_string())
-                                    throw Error("attribute '%s' of derivation '%s' must be a list of strings", name, drvPath);
+                                    throw Error("attribute '%s' of derivation '%s' must be a list of strings", name, worker.store.printStorePath(drvPath));
                                 res.push_back(j->get<std::string>());
                             }
                             checks.disallowedRequisites = res;
@@ -3980,7 +3995,7 @@ Path DerivationGoal::openLogFile()
 
     if (!settings.keepLog) return "";
 
-    string baseName = baseNameOf(drvPath);
+    auto baseName = std::string(baseNameOf(worker.store.printStorePath(drvPath)));
 
     /* Create a log file. */
     Path dir = fmt("%s/%s/%s/", worker.store.logDir, worker.store.drvsLogDir, string(baseName, 0, 2));
@@ -4019,9 +4034,7 @@ void DerivationGoal::deleteTmpDir(bool force)
         /* Don't keep temporary directories for builtins because they
            might have privileged stuff (like a copy of netrc). */
         if (settings.keepFailed && !force && !drv->isBuiltin()) {
-            printError(
-                format("note: keeping build directory '%2%'")
-                % drvPath % tmpDir);
+            printError("note: keeping build directory '%s'", tmpDir);
             chmod(tmpDir.c_str(), 0755);
         }
         else
@@ -4100,31 +4113,31 @@ void DerivationGoal::flushLine()
 }
 
 
-PathSet DerivationGoal::checkPathValidity(bool returnValid, bool checkHash)
+StorePathSet DerivationGoal::checkPathValidity(bool returnValid, bool checkHash)
 {
-    PathSet result;
+    StorePathSet result;
     for (auto & i : drv->outputs) {
         if (!wantOutput(i.first, wantedOutputs)) continue;
         bool good =
             worker.store.isValidPath(i.second.path) &&
             (!checkHash || worker.pathContentsGood(i.second.path));
-        if (good == returnValid) result.insert(i.second.path);
+        if (good == returnValid) result.insert(i.second.path.clone());
     }
     return result;
 }
 
 
-Path DerivationGoal::addHashRewrite(const Path & path)
+void DerivationGoal::addHashRewrite(const StorePath & path)
 {
-    string h1 = string(path, worker.store.storeDir.size() + 1, 32);
-    string h2 = string(hashString(htSHA256, "rewrite:" + drvPath + ":" + path).to_string(Base32, false), 0, 32);
-    Path p = worker.store.storeDir + "/" + h2 + string(path, worker.store.storeDir.size() + 33);
-    deletePath(p);
-    assert(path.size() == p.size());
+    auto h1 = std::string(((std::string_view) path.to_string()).substr(0, 32));
+    auto p = worker.store.makeStorePath(
+        "rewrite:" + std::string(drvPath.to_string()) + ":" + std::string(path.to_string()),
+        Hash(htSHA256), path.name());
+    auto h2 = std::string(((std::string_view) p.to_string()).substr(0, 32));
+    deletePath(worker.store.printStorePath(p));
     inputRewrites[h1] = h2;
     outputRewrites[h2] = h1;
-    redirectedOutputs[path] = p;
-    return p;
+    redirectedOutputs.insert_or_assign(path.clone(), std::move(p));
 }
 
 
@@ -4162,7 +4175,7 @@ class SubstitutionGoal : public Goal
 
 private:
     /* The store path that should be realised through a substitute. */
-    Path storePath;
+    StorePath storePath;
 
     /* The remaining substituters. */
     std::list<ref<Store>> subs;
@@ -4198,7 +4211,7 @@ private:
     GoalState state;
 
 public:
-    SubstitutionGoal(const Path & storePath, Worker & worker, RepairFlag repair = NoRepair);
+    SubstitutionGoal(StorePath && storePath, Worker & worker, RepairFlag repair = NoRepair);
     ~SubstitutionGoal();
 
     void timedOut() override { abort(); };
@@ -4207,7 +4220,7 @@ public:
     {
         /* "a$" ensures substitution goals happen before derivation
            goals. */
-        return "a$" + storePathToName(storePath) + "$" + storePath;
+        return "a$" + std::string(storePath.name()) + "$" + worker.store.printStorePath(storePath);
     }
 
     void work() override;
@@ -4224,7 +4237,7 @@ public:
     void handleChildOutput(int fd, const string & data) override;
     void handleEOF(int fd) override;
 
-    Path getStorePath() { return storePath; }
+    StorePath getStorePath() { return storePath.clone(); }
 
     void amDone(ExitCode result) override
     {
@@ -4233,13 +4246,13 @@ public:
 };
 
 
-SubstitutionGoal::SubstitutionGoal(const Path & storePath, Worker & worker, RepairFlag repair)
+SubstitutionGoal::SubstitutionGoal(StorePath && storePath, Worker & worker, RepairFlag repair)
     : Goal(worker)
+    , storePath(std::move(storePath))
     , repair(repair)
 {
-    this->storePath = storePath;
     state = &SubstitutionGoal::init;
-    name = (format("substitution of '%1%'") % storePath).str();
+    name = fmt("substitution of '%s'", worker.store.printStorePath(storePath));
     trace("created");
     maintainExpectedSubstitutions = std::make_unique<MaintainCount<uint64_t>>(worker.expectedSubstitutions);
 }
@@ -4278,7 +4291,7 @@ void SubstitutionGoal::init()
     }
 
     if (settings.readOnlyMode)
-        throw Error(format("cannot substitute path '%1%' - no write access to the Nix store") % storePath);
+        throw Error("cannot substitute path '%s' - no write access to the Nix store", worker.store.printStorePath(storePath));
 
     subs = settings.useSubstitutes ? getDefaultSubstituters() : std::list<ref<Store>>();
 
@@ -4293,7 +4306,7 @@ void SubstitutionGoal::tryNext()
     if (subs.size() == 0) {
         /* None left.  Terminate this goal and let someone else deal
            with it. */
-        debug(format("path '%1%' is required, but there is no substituter that can build it") % storePath);
+        debug("path '%s' is required, but there is no substituter that can build it", worker.store.printStorePath(storePath));
 
         /* Hack: don't indicate failure if there were no substituters.
            In that case the calling derivation should just do a
@@ -4357,7 +4370,7 @@ void SubstitutionGoal::tryNext()
         && !info->checkSignatures(worker.store, worker.store.getPublicKeys()))
     {
         printError("warning: substituter '%s' does not have a valid signature for path '%s'",
-            sub->getUri(), storePath);
+            sub->getUri(), worker.store.printStorePath(storePath));
         tryNext();
         return;
     }
@@ -4380,7 +4393,7 @@ void SubstitutionGoal::referencesValid()
     trace("all references realised");
 
     if (nrFailed > 0) {
-        debug(format("some references of path '%1%' could not be realised") % storePath);
+        debug("some references of path '%s' could not be realised", worker.store.printStorePath(storePath));
         amDone(nrNoSubstituters > 0 || nrIncompleteClosure > 0 ? ecIncompleteClosure : ecFailed);
         return;
     }
@@ -4419,7 +4432,7 @@ void SubstitutionGoal::tryToRun()
             /* Wake up the worker loop when we're done. */
             Finally updateStats([this]() { outPipe.writeSide = -1; });
 
-            Activity act(*logger, actSubstitute, Logger::Fields{storePath, sub->getUri()});
+            Activity act(*logger, actSubstitute, Logger::Fields{worker.store.printStorePath(storePath), sub->getUri()});
             PushActivity pact(act.id);
 
             copyStorePath(ref<Store>(sub), ref<Store>(worker.store.shared_from_this()),
@@ -4466,10 +4479,9 @@ void SubstitutionGoal::finished()
         return;
     }
 
-    worker.markContentsGood(storePath);
+    worker.markContentsGood(storePath.clone());
 
-    printMsg(lvlChatty,
-        format("substitution of path '%1%' succeeded") % storePath);
+    printMsg(lvlChatty, "substitution of path '%s' succeeded", worker.store.printStorePath(storePath));
 
     maintainRunningSubstitutions.reset();
 
@@ -4535,13 +4547,13 @@ Worker::~Worker()
 }
 
 
-GoalPtr Worker::makeDerivationGoal(const Path & path,
+GoalPtr Worker::makeDerivationGoal(const StorePath & path,
     const StringSet & wantedOutputs, BuildMode buildMode)
 {
-    GoalPtr goal = derivationGoals[path].lock();
+    GoalPtr goal = derivationGoals[path.clone()].lock(); // FIXME
     if (!goal) {
-        goal = std::make_shared<DerivationGoal>(path, wantedOutputs, *this, buildMode);
-        derivationGoals[path] = goal;
+        goal = std::make_shared<DerivationGoal>(path.clone(), wantedOutputs, *this, buildMode);
+        derivationGoals.insert_or_assign(path.clone(), goal);
         wakeUp(goal);
     } else
         (dynamic_cast<DerivationGoal *>(goal.get()))->addWantedOutputs(wantedOutputs);
@@ -4549,21 +4561,21 @@ GoalPtr Worker::makeDerivationGoal(const Path & path,
 }
 
 
-std::shared_ptr<DerivationGoal> Worker::makeBasicDerivationGoal(const Path & drvPath,
+std::shared_ptr<DerivationGoal> Worker::makeBasicDerivationGoal(StorePath && drvPath,
     const BasicDerivation & drv, BuildMode buildMode)
 {
-    auto goal = std::make_shared<DerivationGoal>(drvPath, drv, *this, buildMode);
+    auto goal = std::make_shared<DerivationGoal>(std::move(drvPath), drv, *this, buildMode);
     wakeUp(goal);
     return goal;
 }
 
 
-GoalPtr Worker::makeSubstitutionGoal(const Path & path, RepairFlag repair)
+GoalPtr Worker::makeSubstitutionGoal(const StorePath & path, RepairFlag repair)
 {
-    GoalPtr goal = substitutionGoals[path].lock();
+    GoalPtr goal = substitutionGoals[path.clone()].lock(); // FIXME
     if (!goal) {
-        goal = std::make_shared<SubstitutionGoal>(path, *this, repair);
-        substitutionGoals[path] = goal;
+        goal = std::make_shared<SubstitutionGoal>(path.clone(), *this, repair);
+        substitutionGoals.insert_or_assign(path.clone(), goal);
         wakeUp(goal);
     }
     return goal;
@@ -4902,38 +4914,38 @@ unsigned int Worker::exitStatus()
 }
 
 
-bool Worker::pathContentsGood(const Path & path)
+bool Worker::pathContentsGood(const StorePath & path)
 {
-    std::map<Path, bool>::iterator i = pathContentsGoodCache.find(path);
+    auto i = pathContentsGoodCache.find(path);
     if (i != pathContentsGoodCache.end()) return i->second;
-    printInfo(format("checking path '%1%'...") % path);
+    printInfo("checking path '%s'...", store.printStorePath(path));
     auto info = store.queryPathInfo(path);
     bool res;
-    if (!pathExists(path))
+    if (!pathExists(store.printStorePath(path)))
         res = false;
     else {
-        HashResult current = hashPath(info->narHash.type, path);
+        HashResult current = hashPath(info->narHash.type, store.printStorePath(path));
         Hash nullHash(htSHA256);
         res = info->narHash == nullHash || info->narHash == current.first;
     }
-    pathContentsGoodCache[path] = res;
-    if (!res) printError(format("path '%1%' is corrupted or missing!") % path);
+    pathContentsGoodCache.insert_or_assign(path.clone(), res);
+    if (!res) printError("path '%s' is corrupted or missing!", store.printStorePath(path));
     return res;
 }
 
 
-void Worker::markContentsGood(const Path & path)
+void Worker::markContentsGood(StorePath && path)
 {
-    pathContentsGoodCache[path] = true;
+    pathContentsGoodCache.insert_or_assign(std::move(path), true);
 }
 
 
 //////////////////////////////////////////////////////////////////////
 
 
-static void primeCache(Store & store, const PathSet & paths)
+static void primeCache(Store & store, const std::vector<StorePathWithOutputs> & paths)
 {
-    PathSet willBuild, willSubstitute, unknown;
+    StorePathSet willBuild, willSubstitute, unknown;
     unsigned long long downloadSize, narSize;
     store.queryMissing(paths, willBuild, willSubstitute, unknown, downloadSize, narSize);
 
@@ -4944,24 +4956,23 @@ static void primeCache(Store & store, const PathSet & paths)
 }
 
 
-void LocalStore::buildPaths(const PathSet & drvPaths, BuildMode buildMode)
+void LocalStore::buildPaths(const std::vector<StorePathWithOutputs> & drvPaths, BuildMode buildMode)
 {
     Worker worker(*this);
 
     primeCache(*this, drvPaths);
 
     Goals goals;
-    for (auto & i : drvPaths) {
-        DrvPathWithOutputs i2 = parseDrvPathWithOutputs(i);
-        if (isDerivation(i2.first))
-            goals.insert(worker.makeDerivationGoal(i2.first, i2.second, buildMode));
+    for (auto & path : drvPaths) {
+        if (path.path.isDerivation())
+            goals.insert(worker.makeDerivationGoal(path.path, path.outputs, buildMode));
         else
-            goals.insert(worker.makeSubstitutionGoal(i, buildMode == bmRepair ? Repair : NoRepair));
+            goals.insert(worker.makeSubstitutionGoal(path.path, buildMode == bmRepair ? Repair : NoRepair));
     }
 
     worker.run(goals);
 
-    PathSet failed;
+    StorePathSet failed;
     for (auto & i : goals) {
         if (i->getExitCode() != Goal::ecSuccess) {
             DerivationGoal * i2 = dynamic_cast<DerivationGoal *>(i.get());
@@ -4975,11 +4986,11 @@ void LocalStore::buildPaths(const PathSet & drvPaths, BuildMode buildMode)
 }
 
 
-BuildResult LocalStore::buildDerivation(const Path & drvPath, const BasicDerivation & drv,
+BuildResult LocalStore::buildDerivation(const StorePath & drvPath, const BasicDerivation & drv,
     BuildMode buildMode)
 {
     Worker worker(*this);
-    auto goal = worker.makeBasicDerivationGoal(drvPath, drv, buildMode);
+    auto goal = worker.makeBasicDerivationGoal(drvPath.clone(), drv, buildMode);
 
     BuildResult result;
 
@@ -4995,12 +5006,12 @@ BuildResult LocalStore::buildDerivation(const Path & drvPath, const BasicDerivat
 }
 
 
-void LocalStore::ensurePath(const Path & path)
+void LocalStore::ensurePath(const StorePath & path)
 {
     /* If the path is already valid, we're done. */
     if (isValidPath(path)) return;
 
-    primeCache(*this, {path});
+    primeCache(*this, {StorePathWithOutputs(path)});
 
     Worker worker(*this);
     GoalPtr goal = worker.makeSubstitutionGoal(path);
@@ -5009,11 +5020,11 @@ void LocalStore::ensurePath(const Path & path)
     worker.run(goals);
 
     if (goal->getExitCode() != Goal::ecSuccess)
-        throw Error(worker.exitStatus(), "path '%s' does not exist and cannot be created", path);
+        throw Error(worker.exitStatus(), "path '%s' does not exist and cannot be created", printStorePath(path));
 }
 
 
-void LocalStore::repairPath(const Path & path)
+void LocalStore::repairPath(const StorePath & path)
 {
     Worker worker(*this);
     GoalPtr goal = worker.makeSubstitutionGoal(path, Repair);
@@ -5024,13 +5035,13 @@ void LocalStore::repairPath(const Path & path)
     if (goal->getExitCode() != Goal::ecSuccess) {
         /* Since substituting the path didn't work, if we have a valid
            deriver, then rebuild the deriver. */
-        auto deriver = queryPathInfo(path)->deriver;
-        if (deriver != "" && isValidPath(deriver)) {
+        auto info = queryPathInfo(path);
+        if (info->deriver && isValidPath(*info->deriver)) {
             goals.clear();
-            goals.insert(worker.makeDerivationGoal(deriver, StringSet(), bmRepair));
+            goals.insert(worker.makeDerivationGoal(*info->deriver, StringSet(), bmRepair));
             worker.run(goals);
         } else
-            throw Error(worker.exitStatus(), "cannot repair path '%s'", path);
+            throw Error(worker.exitStatus(), "cannot repair path '%s'", printStorePath(path));
     }
 }
 
diff --git a/src/libstore/builtins/fetchurl.cc b/src/libstore/builtins/fetchurl.cc
index b1af3b4fc..f6ae5d2e6 100644
--- a/src/libstore/builtins/fetchurl.cc
+++ b/src/libstore/builtins/fetchurl.cc
@@ -24,7 +24,7 @@ void builtinFetchurl(const BasicDerivation & drv, const std::string & netrcData)
 
     Path storePath = getAttr("out");
     auto mainUrl = getAttr("url");
-    bool unpack = get(drv.env, "unpack", "") == "1";
+    bool unpack = get(drv.env, "unpack").value_or("") == "1";
 
     /* Note: have to use a fresh downloader here because we're in
        a forked process. */
diff --git a/src/libstore/daemon.cc b/src/libstore/daemon.cc
index d3c17e772..c53dfdd56 100644
--- a/src/libstore/daemon.cc
+++ b/src/libstore/daemon.cc
@@ -260,14 +260,8 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
     switch (op) {
 
     case wopIsValidPath: {
-        /* 'readStorePath' could raise an error leading to the connection
-           being closed.  To be able to recover from an invalid path error,
-           call 'startWork' early, and do 'assertStorePath' afterwards so
-           that the 'Error' exception handler doesn't close the
-           connection.  */
-        Path path = readString(from);
+        auto path = store->parseStorePath(readString(from));
         logger->startWork();
-        store->assertStorePath(path);
         bool result = store->isValidPath(path);
         logger->stopWork();
         to << result;
@@ -275,34 +269,36 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
     }
 
     case wopQueryValidPaths: {
-        PathSet paths = readStorePaths<PathSet>(*store, from);
+        auto paths = readStorePaths<StorePathSet>(*store, from);
         logger->startWork();
-        PathSet res = store->queryValidPaths(paths);
+        auto res = store->queryValidPaths(paths);
         logger->stopWork();
-        to << res;
+        writeStorePaths(*store, to, res);
         break;
     }
 
     case wopHasSubstitutes: {
-        Path path = readStorePath(*store, from);
+        auto path = store->parseStorePath(readString(from));
         logger->startWork();
-        PathSet res = store->querySubstitutablePaths({path});
+        StorePathSet paths; // FIXME
+        paths.insert(path.clone());
+        auto res = store->querySubstitutablePaths(paths);
         logger->stopWork();
-        to << (res.find(path) != res.end());
+        to << (res.count(path) != 0);
         break;
     }
 
     case wopQuerySubstitutablePaths: {
-        PathSet paths = readStorePaths<PathSet>(*store, from);
+        auto paths = readStorePaths<StorePathSet>(*store, from);
         logger->startWork();
-        PathSet res = store->querySubstitutablePaths(paths);
+        auto res = store->querySubstitutablePaths(paths);
         logger->stopWork();
-        to << res;
+        writeStorePaths(*store, to, res);
         break;
     }
 
     case wopQueryPathHash: {
-        Path path = readStorePath(*store, from);
+        auto path = store->parseStorePath(readString(from));
         logger->startWork();
         auto hash = store->queryPathInfo(path)->narHash;
         logger->stopWork();
@@ -314,23 +310,24 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
     case wopQueryReferrers:
     case wopQueryValidDerivers:
     case wopQueryDerivationOutputs: {
-        Path path = readStorePath(*store, from);
+        auto path = store->parseStorePath(readString(from));
         logger->startWork();
-        PathSet paths;
+        StorePathSet paths;
         if (op == wopQueryReferences)
-            paths = store->queryPathInfo(path)->references;
+            for (auto & i : store->queryPathInfo(path)->references)
+                paths.insert(i.clone());
         else if (op == wopQueryReferrers)
             store->queryReferrers(path, paths);
         else if (op == wopQueryValidDerivers)
             paths = store->queryValidDerivers(path);
         else paths = store->queryDerivationOutputs(path);
         logger->stopWork();
-        to << paths;
+        writeStorePaths(*store, to, paths);
         break;
     }
 
     case wopQueryDerivationOutputNames: {
-        Path path = readStorePath(*store, from);
+        auto path = store->parseStorePath(readString(from));
         logger->startWork();
         StringSet names;
         names = store->queryDerivationOutputNames(path);
@@ -340,20 +337,20 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
     }
 
     case wopQueryDeriver: {
-        Path path = readStorePath(*store, from);
+        auto path = store->parseStorePath(readString(from));
         logger->startWork();
-        auto deriver = store->queryPathInfo(path)->deriver;
+        auto info = store->queryPathInfo(path);
         logger->stopWork();
-        to << deriver;
+        to << (info->deriver ? store->printStorePath(*info->deriver) : "");
         break;
     }
 
     case wopQueryPathFromHashPart: {
-        string hashPart = readString(from);
+        auto hashPart = readString(from);
         logger->startWork();
-        Path path = store->queryPathFromHashPart(hashPart);
+        auto path = store->queryPathFromHashPart(hashPart);
         logger->stopWork();
-        to << path;
+        to << (path ? store->printStorePath(*path) : "");
         break;
     }
 
@@ -383,26 +380,26 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         logger->startWork();
         if (!savedRegular.regular) throw Error("regular file expected");
 
-        Path path = store->addToStoreFromDump(recursive ? *savedNAR.data : savedRegular.s, baseName, recursive, hashAlgo);
+        auto path = store->addToStoreFromDump(recursive ? *savedNAR.data : savedRegular.s, baseName, recursive, hashAlgo);
         logger->stopWork();
 
-        to << path;
+        to << store->printStorePath(path);
         break;
     }
 
     case wopAddTextToStore: {
         string suffix = readString(from);
         string s = readString(from);
-        PathSet refs = readStorePaths<PathSet>(*store, from);
+        auto refs = readStorePaths<StorePathSet>(*store, from);
         logger->startWork();
-        Path path = store->addTextToStore(suffix, s, refs, NoRepair);
+        auto path = store->addTextToStore(suffix, s, refs, NoRepair);
         logger->stopWork();
-        to << path;
+        to << store->printStorePath(path);
         break;
     }
 
     case wopExportPath: {
-        Path path = readStorePath(*store, from);
+        auto path = store->parseStorePath(readString(from));
         readInt(from); // obsolete
         logger->startWork();
         TunnelSink sink(to);
@@ -415,15 +412,19 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
     case wopImportPaths: {
         logger->startWork();
         TunnelSource source(from, to);
-        Paths paths = store->importPaths(source, nullptr,
+        auto paths = store->importPaths(source, nullptr,
             trusted ? NoCheckSigs : CheckSigs);
         logger->stopWork();
-        to << paths;
+        Strings paths2;
+        for (auto & i : paths) paths2.push_back(store->printStorePath(i));
+        to << paths2;
         break;
     }
 
     case wopBuildPaths: {
-        PathSet drvs = readStorePaths<PathSet>(*store, from);
+        std::vector<StorePathWithOutputs> drvs;
+        for (auto & s : readStrings<Strings>(from))
+            drvs.push_back(store->parseDrvPathWithOutputs(s));
         BuildMode mode = bmNormal;
         if (GET_PROTOCOL_MINOR(clientVersion) >= 15) {
             mode = (BuildMode) readInt(from);
@@ -441,7 +442,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
     }
 
     case wopBuildDerivation: {
-        Path drvPath = readStorePath(*store, from);
+        auto drvPath = store->parseStorePath(readString(from));
         BasicDerivation drv;
         readDerivation(from, *store, drv);
         BuildMode buildMode = (BuildMode) readInt(from);
@@ -455,7 +456,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
     }
 
     case wopEnsurePath: {
-        Path path = readStorePath(*store, from);
+        auto path = store->parseStorePath(readString(from));
         logger->startWork();
         store->ensurePath(path);
         logger->stopWork();
@@ -464,7 +465,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
     }
 
     case wopAddTempRoot: {
-        Path path = readStorePath(*store, from);
+        auto path = store->parseStorePath(readString(from));
         logger->startWork();
         store->addTempRoot(path);
         logger->stopWork();
@@ -502,7 +503,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
 
         for (auto & [target, links] : roots)
             for (auto & link : links)
-                to << link << target;
+                to << link << store->printStorePath(target);
 
         break;
     }
@@ -510,7 +511,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
     case wopCollectGarbage: {
         GCOptions options;
         options.action = (GCOptions::GCAction) readInt(from);
-        options.pathsToDelete = readStorePaths<PathSet>(*store, from);
+        options.pathsToDelete = readStorePaths<StorePathSet>(*store, from);
         from >> options.ignoreLiveness >> options.maxFreed;
         // obsolete fields
         readInt(from);
@@ -568,44 +569,52 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
     }
 
     case wopQuerySubstitutablePathInfo: {
-        Path path = absPath(readString(from));
+        auto path = store->parseStorePath(readString(from));
         logger->startWork();
         SubstitutablePathInfos infos;
-        store->querySubstitutablePathInfos({path}, infos);
+        StorePathSet paths;
+        paths.insert(path.clone()); // FIXME
+        store->querySubstitutablePathInfos(paths, infos);
         logger->stopWork();
-        SubstitutablePathInfos::iterator i = infos.find(path);
+        auto i = infos.find(path);
         if (i == infos.end())
             to << 0;
         else {
-            to << 1 << i->second.deriver << i->second.references << i->second.downloadSize << i->second.narSize;
+            to << 1
+               << (i->second.deriver ? store->printStorePath(*i->second.deriver) : "");
+            writeStorePaths(*store, to, i->second.references);
+            to << i->second.downloadSize
+               << i->second.narSize;
         }
         break;
     }
 
     case wopQuerySubstitutablePathInfos: {
-        PathSet paths = readStorePaths<PathSet>(*store, from);
+        auto paths = readStorePaths<StorePathSet>(*store, from);
         logger->startWork();
         SubstitutablePathInfos infos;
         store->querySubstitutablePathInfos(paths, infos);
         logger->stopWork();
         to << infos.size();
         for (auto & i : infos) {
-            to << i.first << i.second.deriver << i.second.references
-               << i.second.downloadSize << i.second.narSize;
+            to << store->printStorePath(i.first)
+               << (i.second.deriver ? store->printStorePath(*i.second.deriver) : "");
+            writeStorePaths(*store, to, i.second.references);
+            to << i.second.downloadSize << i.second.narSize;
         }
         break;
     }
 
     case wopQueryAllValidPaths: {
         logger->startWork();
-        PathSet paths = store->queryAllValidPaths();
+        auto paths = store->queryAllValidPaths();
         logger->stopWork();
-        to << paths;
+        writeStorePaths(*store, to, paths);
         break;
     }
 
     case wopQueryPathInfo: {
-        Path path = readStorePath(*store, from);
+        auto path = store->parseStorePath(readString(from));
         std::shared_ptr<const ValidPathInfo> info;
         logger->startWork();
         try {
@@ -617,8 +626,10 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         if (info) {
             if (GET_PROTOCOL_MINOR(clientVersion) >= 17)
                 to << 1;
-            to << info->deriver << info->narHash.to_string(Base16, false) << info->references
-               << info->registrationTime << info->narSize;
+            to << (info->deriver ? store->printStorePath(*info->deriver) : "")
+               << info->narHash.to_string(Base16, false);
+            writeStorePaths(*store, to, info->references);
+            to << info->registrationTime << info->narSize;
             if (GET_PROTOCOL_MINOR(clientVersion) >= 16) {
                 to << info->ultimate
                    << info->sigs
@@ -651,7 +662,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
     }
 
     case wopAddSignatures: {
-        Path path = readStorePath(*store, from);
+        auto path = store->parseStorePath(readString(from));
         StringSet sigs = readStrings<StringSet>(from);
         logger->startWork();
         if (!trusted)
@@ -663,22 +674,21 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
     }
 
     case wopNarFromPath: {
-        auto path = readStorePath(*store, from);
+        auto path = store->parseStorePath(readString(from));
         logger->startWork();
         logger->stopWork();
-        dumpPath(path, to);
+        dumpPath(store->printStorePath(path), to);
         break;
     }
 
     case wopAddToStoreNar: {
         bool repair, dontCheckSigs;
-        ValidPathInfo info;
-        info.path = readStorePath(*store, from);
-        from >> info.deriver;
-        if (!info.deriver.empty())
-            store->assertStorePath(info.deriver);
+        ValidPathInfo info(store->parseStorePath(readString(from)));
+        auto deriver = readString(from);
+        if (deriver != "")
+            info.deriver = store->parseStorePath(deriver);
         info.narHash = Hash(readString(from), htSHA256);
-        info.references = readStorePaths<PathSet>(*store, from);
+        info.references = readStorePaths<StorePathSet>(*store, from);
         from >> info.registrationTime >> info.narSize >> info.ultimate;
         info.sigs = readStrings<StringSet>(from);
         from >> info.ca >> repair >> dontCheckSigs;
@@ -709,13 +719,18 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
     }
 
     case wopQueryMissing: {
-        PathSet targets = readStorePaths<PathSet>(*store, from);
+        std::vector<StorePathWithOutputs> targets;
+        for (auto & s : readStrings<Strings>(from))
+            targets.push_back(store->parseDrvPathWithOutputs(s));
         logger->startWork();
-        PathSet willBuild, willSubstitute, unknown;
+        StorePathSet willBuild, willSubstitute, unknown;
         unsigned long long downloadSize, narSize;
         store->queryMissing(targets, willBuild, willSubstitute, unknown, downloadSize, narSize);
         logger->stopWork();
-        to << willBuild << willSubstitute << unknown << downloadSize << narSize;
+        writeStorePaths(*store, to, willBuild);
+        writeStorePaths(*store, to, willSubstitute);
+        writeStorePaths(*store, to, unknown);
+        to << downloadSize << narSize;
         break;
     }
 
diff --git a/src/libstore/derivations.cc b/src/libstore/derivations.cc
index 23fcfb281..726e34479 100644
--- a/src/libstore/derivations.cc
+++ b/src/libstore/derivations.cc
@@ -21,17 +21,39 @@ void DerivationOutput::parseHashInfo(bool & recursive, Hash & hash) const
 
     HashType hashType = parseHashType(algo);
     if (hashType == htUnknown)
-        throw Error(format("unknown hash algorithm '%1%'") % algo);
+        throw Error("unknown hash algorithm '%s'", algo);
 
     hash = Hash(this->hash, hashType);
 }
 
 
-Path BasicDerivation::findOutput(const string & id) const
+BasicDerivation::BasicDerivation(const BasicDerivation & other)
+    : platform(other.platform)
+    , builder(other.builder)
+    , args(other.args)
+    , env(other.env)
+{
+    for (auto & i : other.outputs)
+        outputs.insert_or_assign(i.first,
+            DerivationOutput(i.second.path.clone(), std::string(i.second.hashAlgo), std::string(i.second.hash)));
+    for (auto & i : other.inputSrcs)
+        inputSrcs.insert(i.clone());
+}
+
+
+Derivation::Derivation(const Derivation & other)
+    : BasicDerivation(other)
+{
+    for (auto & i : other.inputDrvs)
+        inputDrvs.insert_or_assign(i.first.clone(), i.second);
+}
+
+
+const StorePath & BasicDerivation::findOutput(const string & id) const
 {
     auto i = outputs.find(id);
     if (i == outputs.end())
-        throw Error(format("derivation has no output '%1%'") % id);
+        throw Error("derivation has no output '%s'", id);
     return i->second.path;
 }
 
@@ -42,18 +64,17 @@ bool BasicDerivation::isBuiltin() const
 }
 
 
-Path writeDerivation(ref<Store> store,
+StorePath writeDerivation(ref<Store> store,
     const Derivation & drv, const string & name, RepairFlag repair)
 {
-    PathSet references;
-    references.insert(drv.inputSrcs.begin(), drv.inputSrcs.end());
+    auto references = cloneStorePathSet(drv.inputSrcs);
     for (auto & i : drv.inputDrvs)
-        references.insert(i.first);
+        references.insert(i.first.clone());
     /* Note that the outputs of a derivation are *not* references
        (that can be missing (of course) and should not necessarily be
        held during a garbage collection). */
     string suffix = name + drvExtension;
-    string contents = drv.unparse();
+    string contents = drv.unparse(*store, false);
     return settings.readOnlyMode
         ? store->computeStorePathForText(suffix, contents, references)
         : store->addTextToStore(suffix, contents, references, repair);
@@ -121,7 +142,7 @@ static StringSet parseStrings(std::istream & str, bool arePaths)
 }
 
 
-static Derivation parseDerivation(const string & s)
+static Derivation parseDerivation(const Store & store, const string & s)
 {
     Derivation drv;
     istringstream_nocopy str(s);
@@ -129,13 +150,12 @@ static Derivation parseDerivation(const string & s)
 
     /* Parse the list of outputs. */
     while (!endOfList(str)) {
-        DerivationOutput out;
-        expect(str, "("); string id = parseString(str);
-        expect(str, ","); out.path = parsePath(str);
-        expect(str, ","); out.hashAlgo = parseString(str);
-        expect(str, ","); out.hash = parseString(str);
+        expect(str, "("); std::string id = parseString(str);
+        expect(str, ","); auto path = store.parseStorePath(parsePath(str));
+        expect(str, ","); auto hashAlgo = parseString(str);
+        expect(str, ","); auto hash = parseString(str);
         expect(str, ")");
-        drv.outputs[id] = out;
+        drv.outputs.emplace(id, DerivationOutput(std::move(path), std::move(hashAlgo), std::move(hash)));
     }
 
     /* Parse the list of input derivations. */
@@ -144,11 +164,11 @@ static Derivation parseDerivation(const string & s)
         expect(str, "(");
         Path drvPath = parsePath(str);
         expect(str, ",[");
-        drv.inputDrvs[drvPath] = parseStrings(str, false);
+        drv.inputDrvs.insert_or_assign(store.parseStorePath(drvPath), parseStrings(str, false));
         expect(str, ")");
     }
 
-    expect(str, ",["); drv.inputSrcs = parseStrings(str, true);
+    expect(str, ",["); drv.inputSrcs = store.parseStorePathSet(parseStrings(str, true));
     expect(str, ","); drv.platform = parseString(str);
     expect(str, ","); drv.builder = parseString(str);
 
@@ -171,25 +191,24 @@ static Derivation parseDerivation(const string & s)
 }
 
 
-Derivation readDerivation(const Path & drvPath)
+Derivation readDerivation(const Store & store, const Path & drvPath)
 {
     try {
-        return parseDerivation(readFile(drvPath));
+        return parseDerivation(store, readFile(drvPath));
     } catch (FormatError & e) {
         throw Error(format("error parsing derivation '%1%': %2%") % drvPath % e.msg());
     }
 }
 
 
-Derivation Store::derivationFromPath(const Path & drvPath)
+Derivation Store::derivationFromPath(const StorePath & drvPath)
 {
-    assertStorePath(drvPath);
     ensurePath(drvPath);
     auto accessor = getFSAccessor();
     try {
-        return parseDerivation(accessor->readFile(drvPath));
+        return parseDerivation(*this, accessor->readFile(printStorePath(drvPath)));
     } catch (FormatError & e) {
-        throw Error(format("error parsing derivation '%1%': %2%") % drvPath % e.msg());
+        throw Error("error parsing derivation '%s': %s", printStorePath(drvPath), e.msg());
     }
 }
 
@@ -220,33 +239,56 @@ static void printStrings(string & res, ForwardIterator i, ForwardIterator j)
 }
 
 
-string Derivation::unparse() const
+string Derivation::unparse(const Store & store, bool maskOutputs,
+    std::map<std::string, StringSet> * actualInputs) const
 {
     string s;
     s.reserve(65536);
     s += "Derive([";
 
-    bool first = true;
-    for (auto & i : outputs) {
-        if (first) first = false; else s += ',';
-        s += '('; printString(s, i.first);
-        s += ','; printString(s, i.second.path);
-        s += ','; printString(s, i.second.hashAlgo);
-        s += ','; printString(s, i.second.hash);
-        s += ')';
+    StringSet maskedOutputs;
+
+    if (maskOutputs) {
+        bool first = true;
+        maskedOutputs = tokenizeString<StringSet>(get(env, "outputs").value_or("out"), " ");
+        for (auto & i : maskedOutputs) {
+            if (first) first = false; else s += ',';
+            s += '('; printString(s, i);
+            s += ",\"\",\"\",\"\")";
+        }
+    } else {
+        bool first = true;
+        for (auto & i : outputs) {
+            if (first) first = false; else s += ',';
+            s += '('; printString(s, i.first);
+            s += ','; printString(s, store.printStorePath(i.second.path));
+            s += ','; printString(s, i.second.hashAlgo);
+            s += ','; printString(s, i.second.hash);
+            s += ')';
+        }
     }
 
     s += "],[";
-    first = true;
-    for (auto & i : inputDrvs) {
-        if (first) first = false; else s += ',';
-        s += '('; printString(s, i.first);
-        s += ','; printStrings(s, i.second.begin(), i.second.end());
-        s += ')';
+    bool first = true;
+    if (actualInputs) {
+        for (auto & i : *actualInputs) {
+            if (first) first = false; else s += ',';
+            s += '('; printString(s, i.first);
+            s += ','; printStrings(s, i.second.begin(), i.second.end());
+            s += ')';
+        }
+    } else {
+        for (auto & i : inputDrvs) {
+            if (first) first = false; else s += ',';
+            s += '('; printString(s, store.printStorePath(i.first));
+            s += ','; printStrings(s, i.second.begin(), i.second.end());
+            s += ')';
+        }
     }
 
     s += "],";
-    printStrings(s, inputSrcs.begin(), inputSrcs.end());
+    auto paths = store.printStorePathSet(inputSrcs); // FIXME: slow
+    printStrings(s, paths.begin(), paths.end());
 
     s += ','; printString(s, platform);
     s += ','; printString(s, builder);
@@ -257,7 +299,7 @@ string Derivation::unparse() const
     for (auto & i : env) {
         if (first) first = false; else s += ',';
         s += '('; printString(s, i.first);
-        s += ','; printString(s, i.second);
+        s += ','; printString(s, maskOutputs && maskedOutputs.count(i.first) ? "" : i.second);
         s += ')';
     }
 
@@ -267,6 +309,7 @@ string Derivation::unparse() const
 }
 
 
+// FIXME: remove
 bool isDerivation(const string & fileName)
 {
     return hasSuffix(fileName, drvExtension);
@@ -304,7 +347,7 @@ DrvHashes drvHashes;
    paths have been replaced by the result of a recursive call to this
    function, and that for fixed-output derivations we return a hash of
    its output path. */
-Hash hashDerivationModulo(Store & store, Derivation drv)
+Hash hashDerivationModulo(Store & store, const Derivation & drv, bool maskOutputs)
 {
     /* Return a fixed hash for fixed-output derivations. */
     if (drv.isFixedOutput()) {
@@ -312,42 +355,41 @@ Hash hashDerivationModulo(Store & store, Derivation drv)
         return hashString(htSHA256, "fixed:out:"
             + i->second.hashAlgo + ":"
             + i->second.hash + ":"
-            + i->second.path);
+            + store.printStorePath(i->second.path));
     }
 
     /* For other derivations, replace the inputs paths with recursive
        calls to this function.*/
-    DerivationInputs inputs2;
+    std::map<std::string, StringSet> inputs2;
     for (auto & i : drv.inputDrvs) {
-        Hash h = drvHashes[i.first];
-        if (!h) {
+        auto h = drvHashes.find(i.first);
+        if (h == drvHashes.end()) {
             assert(store.isValidPath(i.first));
-            Derivation drv2 = readDerivation(store.toRealPath(i.first));
-            h = hashDerivationModulo(store, drv2);
-            drvHashes[i.first] = h;
+            h = drvHashes.insert_or_assign(i.first.clone(), hashDerivationModulo(store,
+                readDerivation(store, store.toRealPath(store.printStorePath(i.first))), false)).first;
         }
-        inputs2[h.to_string(Base16, false)] = i.second;
+        inputs2.insert_or_assign(h->second.to_string(Base16, false), i.second);
     }
-    drv.inputDrvs = inputs2;
 
-    return hashString(htSHA256, drv.unparse());
+    return hashString(htSHA256, drv.unparse(store, maskOutputs, &inputs2));
 }
 
 
-DrvPathWithOutputs parseDrvPathWithOutputs(const string & s)
+StorePathWithOutputs Store::parseDrvPathWithOutputs(const std::string & s)
 {
     size_t n = s.find("!");
     return n == s.npos
-        ? DrvPathWithOutputs(s, std::set<string>())
-        : DrvPathWithOutputs(string(s, 0, n), tokenizeString<std::set<string> >(string(s, n + 1), ","));
+        ? StorePathWithOutputs{parseStorePath(s), std::set<string>()}
+        : StorePathWithOutputs{parseStorePath(std::string_view(s.data(), n)),
+            tokenizeString<std::set<string>>(string(s, n + 1), ",")};
 }
 
 
-Path makeDrvPathWithOutputs(const Path & drvPath, const std::set<string> & outputs)
+std::string StorePathWithOutputs::to_string(const Store & store) const
 {
     return outputs.empty()
-        ? drvPath
-        : drvPath + "!" + concatStringsSep(",", outputs);
+        ? store.printStorePath(path)
+        : store.printStorePath(path) + "!" + concatStringsSep(",", outputs);
 }
 
 
@@ -357,28 +399,28 @@ bool wantOutput(const string & output, const std::set<string> & wanted)
 }
 
 
-PathSet BasicDerivation::outputPaths() const
+StorePathSet BasicDerivation::outputPaths() const
 {
-    PathSet paths;
+    StorePathSet paths;
     for (auto & i : outputs)
-        paths.insert(i.second.path);
+        paths.insert(i.second.path.clone());
     return paths;
 }
 
 
-Source & readDerivation(Source & in, Store & store, BasicDerivation & drv)
+Source & readDerivation(Source & in, const Store & store, BasicDerivation & drv)
 {
     drv.outputs.clear();
     auto nr = readNum<size_t>(in);
     for (size_t n = 0; n < nr; n++) {
         auto name = readString(in);
-        DerivationOutput o;
-        in >> o.path >> o.hashAlgo >> o.hash;
-        store.assertStorePath(o.path);
-        drv.outputs[name] = o;
+        auto path = store.parseStorePath(readString(in));
+        auto hashAlgo = readString(in);
+        auto hash = readString(in);
+        drv.outputs.emplace(name, DerivationOutput(std::move(path), std::move(hashAlgo), std::move(hash)));
     }
 
-    drv.inputSrcs = readStorePaths<PathSet>(store, in);
+    drv.inputSrcs = readStorePaths<StorePathSet>(store, in);
     in >> drv.platform >> drv.builder;
     drv.args = readStrings<Strings>(in);
 
@@ -393,16 +435,16 @@ Source & readDerivation(Source & in, Store & store, BasicDerivation & drv)
 }
 
 
-Sink & operator << (Sink & out, const BasicDerivation & drv)
+void writeDerivation(Sink & out, const Store & store, const BasicDerivation & drv)
 {
     out << drv.outputs.size();
     for (auto & i : drv.outputs)
-        out << i.first << i.second.path << i.second.hashAlgo << i.second.hash;
-    out << drv.inputSrcs << drv.platform << drv.builder << drv.args;
+        out << i.first << store.printStorePath(i.second.path) << i.second.hashAlgo << i.second.hash;
+    writeStorePaths(store, out, drv.inputSrcs);
+    out << drv.platform << drv.builder << drv.args;
     out << drv.env.size();
     for (auto & i : drv.env)
         out << i.first << i.second;
-    return out;
 }
 
 
diff --git a/src/libstore/derivations.hh b/src/libstore/derivations.hh
index 8e02c9bc5..c2df66229 100644
--- a/src/libstore/derivations.hh
+++ b/src/libstore/derivations.hh
@@ -10,26 +10,18 @@
 namespace nix {
 
 
-/* Extension of derivations in the Nix store. */
-const string drvExtension = ".drv";
-
-
 /* Abstract syntax of derivations. */
 
 struct DerivationOutput
 {
-    Path path;
-    string hashAlgo; /* hash used for expected hash computation */
-    string hash; /* expected hash, may be null */
-    DerivationOutput()
-    {
-    }
-    DerivationOutput(Path path, string hashAlgo, string hash)
-    {
-        this->path = path;
-        this->hashAlgo = hashAlgo;
-        this->hash = hash;
-    }
+    StorePath path;
+    std::string hashAlgo; /* hash used for expected hash computation */
+    std::string hash; /* expected hash, may be null */
+    DerivationOutput(StorePath && path, std::string && hashAlgo, std::string && hash)
+        : path(std::move(path))
+        , hashAlgo(std::move(hashAlgo))
+        , hash(std::move(hash))
+    { }
     void parseHashInfo(bool & recursive, Hash & hash) const;
 };
 
@@ -37,24 +29,26 @@ typedef std::map<string, DerivationOutput> DerivationOutputs;
 
 /* For inputs that are sub-derivations, we specify exactly which
    output IDs we are interested in. */
-typedef std::map<Path, StringSet> DerivationInputs;
+typedef std::map<StorePath, StringSet> DerivationInputs;
 
 typedef std::map<string, string> StringPairs;
 
 struct BasicDerivation
 {
     DerivationOutputs outputs; /* keyed on symbolic IDs */
-    PathSet inputSrcs; /* inputs that are sources */
+    StorePathSet inputSrcs; /* inputs that are sources */
     string platform;
     Path builder;
     Strings args;
     StringPairs env;
 
+    BasicDerivation() { }
+    explicit BasicDerivation(const BasicDerivation & other);
     virtual ~BasicDerivation() { };
 
     /* Return the path corresponding to the output identifier `id' in
        the given derivation. */
-    Path findOutput(const string & id) const;
+    const StorePath & findOutput(const std::string & id) const;
 
     bool isBuiltin() const;
 
@@ -62,7 +56,7 @@ struct BasicDerivation
     bool isFixedOutput() const;
 
     /* Return the output paths of a derivation. */
-    PathSet outputPaths() const;
+    StorePathSet outputPaths() const;
 
 };
 
@@ -71,7 +65,12 @@ struct Derivation : BasicDerivation
     DerivationInputs inputDrvs; /* inputs that are sub-derivations */
 
     /* Print a derivation. */
-    std::string unparse() const;
+    std::string unparse(const Store & store, bool maskOutputs,
+        std::map<std::string, StringSet> * actualInputs = nullptr) const;
+
+    Derivation() { }
+    Derivation(Derivation && other) = default;
+    explicit Derivation(const Derivation & other);
 };
 
 
@@ -79,38 +78,29 @@ class Store;
 
 
 /* Write a derivation to the Nix store, and return its path. */
-Path writeDerivation(ref<Store> store,
+StorePath writeDerivation(ref<Store> store,
     const Derivation & drv, const string & name, RepairFlag repair = NoRepair);
 
 /* Read a derivation from a file. */
-Derivation readDerivation(const Path & drvPath);
+Derivation readDerivation(const Store & store, const Path & drvPath);
 
-/* Check whether a file name ends with the extension for
-   derivations. */
+// FIXME: remove
 bool isDerivation(const string & fileName);
 
-Hash hashDerivationModulo(Store & store, Derivation drv);
+Hash hashDerivationModulo(Store & store, const Derivation & drv, bool maskOutputs);
 
 /* Memoisation of hashDerivationModulo(). */
-typedef std::map<Path, Hash> DrvHashes;
+typedef std::map<StorePath, Hash> DrvHashes;
 
 extern DrvHashes drvHashes; // FIXME: global, not thread-safe
 
-/* Split a string specifying a derivation and a set of outputs
-   (/nix/store/hash-foo!out1,out2,...) into the derivation path and
-   the outputs. */
-typedef std::pair<string, std::set<string> > DrvPathWithOutputs;
-DrvPathWithOutputs parseDrvPathWithOutputs(const string & s);
-
-Path makeDrvPathWithOutputs(const Path & drvPath, const std::set<string> & outputs);
-
 bool wantOutput(const string & output, const std::set<string> & wanted);
 
 struct Source;
 struct Sink;
 
-Source & readDerivation(Source & in, Store & store, BasicDerivation & drv);
-Sink & operator << (Sink & out, const BasicDerivation & drv);
+Source & readDerivation(Source & in, const Store & store, BasicDerivation & drv);
+void writeDerivation(Sink & out, const Store & store, const BasicDerivation & drv);
 
 std::string hashPlaceholder(const std::string & outputName);
 
diff --git a/src/libstore/download.cc b/src/libstore/download.cc
index 61e88c5c1..af058ba42 100644
--- a/src/libstore/download.cc
+++ b/src/libstore/download.cc
@@ -650,10 +650,10 @@ struct CurlDownloader : public Downloader
 #ifdef ENABLE_S3
                 auto [bucketName, key, params] = parseS3Uri(request.uri);
 
-                std::string profile = get(params, "profile", "");
-                std::string region = get(params, "region", Aws::Region::US_EAST_1);
-                std::string scheme = get(params, "scheme", "");
-                std::string endpoint = get(params, "endpoint", "");
+                std::string profile = get(params, "profile").value_or("");
+                std::string region = get(params, "region").value_or(Aws::Region::US_EAST_1);
+                std::string scheme = get(params, "scheme").value_or("");
+                std::string endpoint = get(params, "endpoint").value_or("");
 
                 S3Helper s3Helper(profile, region, scheme, endpoint);
 
@@ -811,13 +811,13 @@ CachedDownloadResult Downloader::downloadCached(
         if (p != string::npos) name = string(url, p + 1);
     }
 
-    Path expectedStorePath;
+    std::optional<StorePath> expectedStorePath;
     if (request.expectedHash) {
         expectedStorePath = store->makeFixedOutputPath(request.unpack, request.expectedHash, name);
-        if (store->isValidPath(expectedStorePath)) {
+        if (store->isValidPath(*expectedStorePath)) {
             CachedDownloadResult result;
-            result.storePath = expectedStorePath;
-            result.path = store->toRealPath(expectedStorePath);
+            result.storePath = store->printStorePath(*expectedStorePath);
+            result.path = store->toRealPath(result.storePath);
             return result;
         }
     }
@@ -832,7 +832,7 @@ CachedDownloadResult Downloader::downloadCached(
 
     PathLocks lock({fileLink}, fmt("waiting for lock on '%1%'...", fileLink));
 
-    Path storePath;
+    std::optional<StorePath> storePath;
 
     string expectedETag;
 
@@ -841,9 +841,10 @@ CachedDownloadResult Downloader::downloadCached(
     CachedDownloadResult result;
 
     if (pathExists(fileLink) && pathExists(dataFile)) {
-        storePath = readLink(fileLink);
-        store->addTempRoot(storePath);
-        if (store->isValidPath(storePath)) {
+        storePath = store->parseStorePath(readLink(fileLink));
+        // FIXME
+        store->addTempRoot(*storePath);
+        if (store->isValidPath(*storePath)) {
             auto ss = tokenizeString<vector<string>>(readFile(dataFile), "\n");
             if (ss.size() >= 3 && ss[0] == url) {
                 time_t lastChecked;
@@ -857,7 +858,7 @@ CachedDownloadResult Downloader::downloadCached(
                 }
             }
         } else
-            storePath = "";
+            storePath.reset();
     }
 
     if (!skip) {
@@ -870,65 +871,65 @@ CachedDownloadResult Downloader::downloadCached(
             result.etag = res.etag;
 
             if (!res.cached) {
-                ValidPathInfo info;
                 StringSink sink;
                 dumpString(*res.data, sink);
                 Hash hash = hashString(request.expectedHash ? request.expectedHash.type : htSHA256, *res.data);
-                info.path = store->makeFixedOutputPath(false, hash, name);
+                ValidPathInfo info(store->makeFixedOutputPath(false, hash, name));
                 info.narHash = hashString(htSHA256, *sink.s);
                 info.narSize = sink.s->size();
                 info.ca = makeFixedOutputCA(false, hash);
                 store->addToStore(info, sink.s, NoRepair, NoCheckSigs);
-                storePath = info.path;
+                storePath = info.path.clone();
             }
 
-            assert(!storePath.empty());
-            replaceSymlink(storePath, fileLink);
+            assert(storePath);
+            replaceSymlink(store->printStorePath(*storePath), fileLink);
 
             writeFile(dataFile, url + "\n" + res.etag + "\n" + std::to_string(time(0)) + "\n");
         } catch (DownloadError & e) {
-            if (storePath.empty()) throw;
+            if (!storePath) throw;
             warn("warning: %s; using cached result", e.msg());
             result.etag = expectedETag;
         }
     }
 
     if (request.unpack) {
-        Path unpackedLink = cacheDir + "/" + baseNameOf(storePath) + "-unpacked";
+        Path unpackedLink = cacheDir + "/" + ((std::string) storePath->to_string()) + "-unpacked";
         PathLocks lock2({unpackedLink}, fmt("waiting for lock on '%1%'...", unpackedLink));
-        Path unpackedStorePath;
+        std::optional<StorePath> unpackedStorePath;
         if (pathExists(unpackedLink)) {
-            unpackedStorePath = readLink(unpackedLink);
-            store->addTempRoot(unpackedStorePath);
-            if (!store->isValidPath(unpackedStorePath))
-                unpackedStorePath = "";
+            unpackedStorePath = store->parseStorePath(readLink(unpackedLink));
+            // FIXME
+            store->addTempRoot(*unpackedStorePath);
+            if (!store->isValidPath(*unpackedStorePath))
+                unpackedStorePath.reset();
         }
-        if (unpackedStorePath.empty()) {
+        if (!unpackedStorePath) {
             printInfo("unpacking '%s'...", url);
             Path tmpDir = createTempDir();
             AutoDelete autoDelete(tmpDir, true);
-            unpackTarfile(store->toRealPath(storePath), tmpDir, baseNameOf(url));
+            unpackTarfile(store->toRealPath(store->printStorePath(*storePath)), tmpDir, std::string(baseNameOf(url)));
             auto members = readDirectory(tmpDir);
             if (members.size() != 1)
                 throw nix::Error("tarball '%s' contains an unexpected number of top-level files", url);
             auto topDir = tmpDir + "/" + members.begin()->name;
             unpackedStorePath = store->addToStore(name, topDir, true, htSHA256, defaultPathFilter, NoRepair);
         }
-        replaceSymlink(unpackedStorePath, unpackedLink);
-        storePath = unpackedStorePath;
+        replaceSymlink(store->printStorePath(*unpackedStorePath), unpackedLink);
+        storePath = std::move(*unpackedStorePath);
     }
 
-    if (expectedStorePath != "" && storePath != expectedStorePath) {
+    if (expectedStorePath && *storePath != *expectedStorePath) {
         unsigned int statusCode = 102;
         Hash gotHash = request.unpack
-            ? hashPath(request.expectedHash.type, store->toRealPath(storePath)).first
-            : hashFile(request.expectedHash.type, store->toRealPath(storePath));
+            ? hashPath(request.expectedHash.type, store->toRealPath(store->printStorePath(*storePath))).first
+            : hashFile(request.expectedHash.type, store->toRealPath(store->printStorePath(*storePath)));
         throw nix::Error(statusCode, "hash mismatch in file downloaded from '%s':\n  wanted: %s\n  got:    %s",
             url, request.expectedHash.to_string(), gotHash.to_string());
     }
 
-    result.storePath = storePath;
-    result.path = store->toRealPath(storePath);
+    result.storePath = store->printStorePath(*storePath);
+    result.path = store->toRealPath(result.storePath);
     return result;
 }
 
diff --git a/src/libstore/export-import.cc b/src/libstore/export-import.cc
index ef3fea7c8..4692d1a7b 100644
--- a/src/libstore/export-import.cc
+++ b/src/libstore/export-import.cc
@@ -24,9 +24,9 @@ struct HashAndWriteSink : Sink
     }
 };
 
-void Store::exportPaths(const Paths & paths, Sink & sink)
+void Store::exportPaths(const StorePathSet & paths, Sink & sink)
 {
-    Paths sorted = topoSortPaths(PathSet(paths.begin(), paths.end()));
+    auto sorted = topoSortPaths(paths);
     std::reverse(sorted.begin(), sorted.end());
 
     std::string doneLabel("paths exported");
@@ -42,7 +42,7 @@ void Store::exportPaths(const Paths & paths, Sink & sink)
     sink << 0;
 }
 
-void Store::exportPath(const Path & path, Sink & sink)
+void Store::exportPath(const StorePath & path, Sink & sink)
 {
     auto info = queryPathInfo(path);
 
@@ -55,15 +55,21 @@ void Store::exportPath(const Path & path, Sink & sink)
        Don't complain if the stored hash is zero (unknown). */
     Hash hash = hashAndWriteSink.currentHash();
     if (hash != info->narHash && info->narHash != Hash(info->narHash.type))
-        throw Error(format("hash of path '%1%' has changed from '%2%' to '%3%'!") % path
-            % info->narHash.to_string() % hash.to_string());
+        throw Error("hash of path '%s' has changed from '%s' to '%s'!",
+            printStorePath(path), info->narHash.to_string(), hash.to_string());
 
-    hashAndWriteSink << exportMagic << path << info->references << info->deriver << 0;
+    hashAndWriteSink
+        << exportMagic
+        << printStorePath(path);
+    writeStorePaths(*this, hashAndWriteSink, info->references);
+    hashAndWriteSink
+        << (info->deriver ? printStorePath(*info->deriver) : "")
+        << 0;
 }
 
-Paths Store::importPaths(Source & source, std::shared_ptr<FSAccessor> accessor, CheckSigsFlag checkSigs)
+StorePaths Store::importPaths(Source & source, std::shared_ptr<FSAccessor> accessor, CheckSigsFlag checkSigs)
 {
-    Paths res;
+    StorePaths res;
     while (true) {
         auto n = readNum<uint64_t>(source);
         if (n == 0) break;
@@ -77,16 +83,15 @@ Paths Store::importPaths(Source & source, std::shared_ptr<FSAccessor> accessor,
         if (magic != exportMagic)
             throw Error("Nix archive cannot be imported; wrong format");
 
-        ValidPathInfo info;
-
-        info.path = readStorePath(*this, source);
+        ValidPathInfo info(parseStorePath(readString(source)));
 
         //Activity act(*logger, lvlInfo, format("importing path '%s'") % info.path);
 
-        info.references = readStorePaths<PathSet>(*this, source);
+        info.references = readStorePaths<StorePathSet>(*this, source);
 
-        info.deriver = readString(source);
-        if (info.deriver != "") assertStorePath(info.deriver);
+        auto deriver = readString(source);
+        if (deriver != "")
+            info.deriver = parseStorePath(deriver);
 
         info.narHash = hashString(htSHA256, *tee.source.data);
         info.narSize = tee.source.data->size();
@@ -97,7 +102,7 @@ Paths Store::importPaths(Source & source, std::shared_ptr<FSAccessor> accessor,
 
         addToStore(info, tee.source.data, NoRepair, checkSigs, accessor);
 
-        res.push_back(info.path);
+        res.push_back(info.path.clone());
     }
 
     return res;
diff --git a/src/libstore/gc.cc b/src/libstore/gc.cc
index 842980fb7..ed81186af 100644
--- a/src/libstore/gc.cc
+++ b/src/libstore/gc.cc
@@ -85,12 +85,10 @@ void LocalStore::addIndirectRoot(const Path & path)
 }
 
 
-Path LocalFSStore::addPermRoot(const Path & _storePath,
+Path LocalFSStore::addPermRoot(const StorePath & storePath,
     const Path & _gcRoot, bool indirect, bool allowOutsideRootsDir)
 {
-    Path storePath(canonPath(_storePath));
     Path gcRoot(canonPath(_gcRoot));
-    assertStorePath(storePath);
 
     if (isInStore(gcRoot))
         throw Error(format(
@@ -102,7 +100,7 @@ Path LocalFSStore::addPermRoot(const Path & _storePath,
            point to the Nix store. */
         if (pathExists(gcRoot) && (!isLink(gcRoot) || !isInStore(readLink(gcRoot))))
             throw Error(format("cannot create symlink '%1%'; already exists") % gcRoot);
-        makeSymlink(gcRoot, storePath);
+        makeSymlink(gcRoot, printStorePath(storePath));
         addIndirectRoot(gcRoot);
     }
 
@@ -117,10 +115,10 @@ Path LocalFSStore::addPermRoot(const Path & _storePath,
                     % gcRoot % rootsDir);
         }
 
-        if (baseNameOf(gcRoot) == baseNameOf(storePath))
+        if (baseNameOf(gcRoot) == std::string(storePath.to_string()))
             writeFile(gcRoot, "");
         else
-            makeSymlink(gcRoot, storePath);
+            makeSymlink(gcRoot, printStorePath(storePath));
     }
 
     /* Check that the root can be found by the garbage collector.
@@ -129,13 +127,12 @@ Path LocalFSStore::addPermRoot(const Path & _storePath,
        check if the root is in a directory in or linked from the
        gcroots directory. */
     if (settings.checkRootReachability) {
-        Roots roots = findRoots(false);
-        if (roots[storePath].count(gcRoot) == 0)
+        auto roots = findRoots(false);
+        if (roots[storePath.clone()].count(gcRoot) == 0)
             printError(
-                format(
-                    "warning: '%1%' is not in a directory where the garbage collector looks for roots; "
-                    "therefore, '%2%' might be removed by the garbage collector")
-                % gcRoot % storePath);
+                "warning: '%1%' is not in a directory where the garbage collector looks for roots; "
+                "therefore, '%2%' might be removed by the garbage collector",
+                gcRoot, printStorePath(storePath));
     }
 
     /* Grab the global GC root, causing us to block while a GC is in
@@ -147,7 +144,7 @@ Path LocalFSStore::addPermRoot(const Path & _storePath,
 }
 
 
-void LocalStore::addTempRoot(const Path & path)
+void LocalStore::addTempRoot(const StorePath & path)
 {
     auto state(_state.lock());
 
@@ -188,7 +185,7 @@ void LocalStore::addTempRoot(const Path & path)
     debug(format("acquiring write lock on '%1%'") % fnTempRoots);
     lockFile(state->fdTempRoots.get(), ltWrite, true);
 
-    string s = path + '\0';
+    string s = printStorePath(path) + '\0';
     writeFull(state->fdTempRoots.get(), s);
 
     /* Downgrade to a read lock. */
@@ -246,8 +243,7 @@ void LocalStore::findTempRoots(FDs & fds, Roots & tempRoots, bool censor)
         while ((end = contents.find((char) 0, pos)) != string::npos) {
             Path root(contents, pos, end - pos);
             debug("got temporary root '%s'", root);
-            assertStorePath(root);
-            tempRoots[root].emplace(censor ? censored : fmt("{temp:%d}", pid));
+            tempRoots[parseStorePath(root)].emplace(censor ? censored : fmt("{temp:%d}", pid));
             pos = end + 1;
         }
 
@@ -260,10 +256,11 @@ void LocalStore::findRoots(const Path & path, unsigned char type, Roots & roots)
 {
     auto foundRoot = [&](const Path & path, const Path & target) {
         Path storePath = toStorePath(target);
-        if (isStorePath(storePath) && isValidPath(storePath))
-            roots[storePath].emplace(path);
+        // FIXME
+        if (isStorePath(storePath) && isValidPath(parseStorePath(storePath)))
+            roots[parseStorePath(storePath)].emplace(path);
         else
-            printInfo(format("skipping invalid root from '%1%' to '%2%'") % path % storePath);
+            printInfo("skipping invalid root from '%1%' to '%2%'", path, storePath);
     };
 
     try {
@@ -299,9 +296,10 @@ void LocalStore::findRoots(const Path & path, unsigned char type, Roots & roots)
         }
 
         else if (type == DT_REG) {
-            Path storePath = storeDir + "/" + baseNameOf(path);
-            if (isStorePath(storePath) && isValidPath(storePath))
-                roots[storePath].emplace(path);
+            Path storePath = storeDir + "/" + std::string(baseNameOf(path));
+            // FIXME
+            if (isStorePath(storePath) && isValidPath(parseStorePath(storePath)))
+                roots[parseStorePath(storePath)].emplace(path);
         }
 
     }
@@ -309,7 +307,7 @@ void LocalStore::findRoots(const Path & path, unsigned char type, Roots & roots)
     catch (SysError & e) {
         /* We only ignore permanent failures. */
         if (e.errNo == EACCES || e.errNo == ENOENT || e.errNo == ENOTDIR)
-            printInfo(format("cannot read potential root '%1%'") % path);
+            printInfo("cannot read potential root '%1%'", path);
         else
             throw;
     }
@@ -340,7 +338,9 @@ Roots LocalStore::findRoots(bool censor)
     return roots;
 }
 
-static void readProcLink(const string & file, Roots & roots)
+typedef std::unordered_map<Path, std::unordered_set<std::string>> UncheckedRoots;
+
+static void readProcLink(const string & file, UncheckedRoots & roots)
 {
     /* 64 is the starting buffer size gnu readlink uses... */
     auto bufsiz = ssize_t{64};
@@ -369,7 +369,7 @@ static string quoteRegexChars(const string & raw)
     return std::regex_replace(raw, specialRegex, R"(\$&)");
 }
 
-static void readFileRoots(const char * path, Roots & roots)
+static void readFileRoots(const char * path, UncheckedRoots & roots)
 {
     try {
         roots[readFile(path)].emplace(path);
@@ -381,7 +381,7 @@ static void readFileRoots(const char * path, Roots & roots)
 
 void LocalStore::findRuntimeRoots(Roots & roots, bool censor)
 {
-    Roots unchecked;
+    UncheckedRoots unchecked;
 
     auto procDir = AutoCloseDir{opendir("/proc")};
     if (procDir) {
@@ -466,16 +466,16 @@ void LocalStore::findRuntimeRoots(Roots & roots, bool censor)
 #endif
 
     for (auto & [target, links] : unchecked) {
-        if (isInStore(target)) {
-            Path path = toStorePath(target);
-            if (isStorePath(path) && isValidPath(path)) {
-                debug(format("got additional root '%1%'") % path);
-                if (censor)
-                    roots[path].insert(censored);
-                else
-                    roots[path].insert(links.begin(), links.end());
-            }
-        }
+        if (!isInStore(target)) continue;
+        Path pathS = toStorePath(target);
+        if (!isStorePath(pathS)) continue;
+        auto path = parseStorePath(pathS);
+        if (!isValidPath(path)) continue;
+        debug("got additional root '%1%'", pathS);
+        if (censor)
+            roots[path.clone()].insert(censored);
+        else
+            roots[path.clone()].insert(links.begin(), links.end());
     }
 }
 
@@ -485,18 +485,19 @@ struct GCLimitReached { };
 
 struct LocalStore::GCState
 {
-    GCOptions options;
+    const GCOptions & options;
     GCResults & results;
-    PathSet roots;
-    PathSet tempRoots;
-    PathSet dead;
-    PathSet alive;
+    StorePathSet roots;
+    StorePathSet tempRoots;
+    StorePathSet dead;
+    StorePathSet alive;
     bool gcKeepOutputs;
     bool gcKeepDerivations;
     unsigned long long bytesInvalidated;
     bool moveToTrash = true;
     bool shouldDelete;
-    GCState(GCResults & results_) : results(results_), bytesInvalidated(0) { }
+    GCState(const GCOptions & options, GCResults & results)
+        : options(options), results(results), bytesInvalidated(0) { }
 };
 
 
@@ -504,7 +505,7 @@ bool LocalStore::isActiveTempFile(const GCState & state,
     const Path & path, const string & suffix)
 {
     return hasSuffix(path, suffix)
-        && state.tempRoots.find(string(path, 0, path.size() - suffix.size())) != state.tempRoots.end();
+        && state.tempRoots.count(parseStorePath(string(path, 0, path.size() - suffix.size())));
 }
 
 
@@ -522,16 +523,17 @@ void LocalStore::deletePathRecursive(GCState & state, const Path & path)
 
     unsigned long long size = 0;
 
-    if (isStorePath(path) && isValidPath(path)) {
-        PathSet referrers;
-        queryReferrers(path, referrers);
+    // FIXME
+    if (isStorePath(path) && isValidPath(parseStorePath(path))) {
+        StorePathSet referrers;
+        queryReferrers(parseStorePath(path), referrers);
         for (auto & i : referrers)
-            if (i != path) deletePathRecursive(state, i);
-        size = queryPathInfo(path)->narSize;
-        invalidatePathChecked(path);
+            if (printStorePath(i) != path) deletePathRecursive(state, printStorePath(i));
+        size = queryPathInfo(parseStorePath(path))->narSize;
+        invalidatePathChecked(parseStorePath(path));
     }
 
-    Path realPath = realStoreDir + "/" + baseNameOf(path);
+    Path realPath = realStoreDir + "/" + std::string(baseNameOf(path));
 
     struct stat st;
     if (lstat(realPath.c_str(), &st)) {
@@ -555,7 +557,7 @@ void LocalStore::deletePathRecursive(GCState & state, const Path & path)
         try {
             if (chmod(realPath.c_str(), st.st_mode | S_IWUSR) == -1)
                 throw SysError(format("making '%1%' writable") % realPath);
-            Path tmp = trashDir + "/" + baseNameOf(path);
+            Path tmp = trashDir + "/" + std::string(baseNameOf(path));
             if (rename(realPath.c_str(), tmp.c_str()))
                 throw SysError(format("unable to rename '%1%' to '%2%'") % realPath % tmp);
             state.bytesInvalidated += size;
@@ -575,7 +577,7 @@ void LocalStore::deletePathRecursive(GCState & state, const Path & path)
 }
 
 
-bool LocalStore::canReachRoot(GCState & state, PathSet & visited, const Path & path)
+bool LocalStore::canReachRoot(GCState & state, StorePathSet & visited, const StorePath & path)
 {
     if (visited.count(path)) return false;
 
@@ -584,41 +586,41 @@ bool LocalStore::canReachRoot(GCState & state, PathSet & visited, const Path & p
     if (state.dead.count(path)) return false;
 
     if (state.roots.count(path)) {
-        debug(format("cannot delete '%1%' because it's a root") % path);
-        state.alive.insert(path);
+        debug("cannot delete '%1%' because it's a root", printStorePath(path));
+        state.alive.insert(path.clone());
         return true;
     }
 
-    visited.insert(path);
+    visited.insert(path.clone());
 
-    if (!isStorePath(path) || !isValidPath(path)) return false;
+    //FIXME
+    if (!isStorePath(printStorePath(path)) || !isValidPath(path)) return false;
 
-    PathSet incoming;
+    StorePathSet incoming;
 
     /* Don't delete this path if any of its referrers are alive. */
     queryReferrers(path, incoming);
 
     /* If keep-derivations is set and this is a derivation, then
        don't delete the derivation if any of the outputs are alive. */
-    if (state.gcKeepDerivations && isDerivation(path)) {
-        PathSet outputs = queryDerivationOutputs(path);
-        for (auto & i : outputs)
+    if (state.gcKeepDerivations && path.isDerivation()) {
+        for (auto & i : queryDerivationOutputs(path))
             if (isValidPath(i) && queryPathInfo(i)->deriver == path)
-                incoming.insert(i);
+                incoming.insert(i.clone());
     }
 
     /* If keep-outputs is set, then don't delete this path if there
        are derivers of this path that are not garbage. */
     if (state.gcKeepOutputs) {
-        PathSet derivers = queryValidDerivers(path);
+        auto derivers = queryValidDerivers(path);
         for (auto & i : derivers)
-            incoming.insert(i);
+            incoming.insert(i.clone());
     }
 
     for (auto & i : incoming)
         if (i != path)
             if (canReachRoot(state, visited, i)) {
-                state.alive.insert(path);
+                state.alive.insert(path.clone());
                 return true;
             }
 
@@ -630,12 +632,13 @@ void LocalStore::tryToDelete(GCState & state, const Path & path)
 {
     checkInterrupt();
 
-    auto realPath = realStoreDir + "/" + baseNameOf(path);
+    auto realPath = realStoreDir + "/" + std::string(baseNameOf(path));
     if (realPath == linksDir || realPath == trashDir) return;
 
     //Activity act(*logger, lvlDebug, format("considering whether to delete '%1%'") % path);
 
-    if (!isStorePath(path) || !isValidPath(path)) {
+    // FIXME
+    if (!isStorePath(path) || !isValidPath(parseStorePath(path))) {
         /* A lock file belonging to a path that we're building right
            now isn't garbage. */
         if (isActiveTempFile(state, path, ".lock")) return;
@@ -650,16 +653,17 @@ void LocalStore::tryToDelete(GCState & state, const Path & path)
         if (isActiveTempFile(state, path, ".check")) return;
     }
 
-    PathSet visited;
+    StorePathSet visited;
 
-    if (canReachRoot(state, visited, path)) {
-        debug(format("cannot delete '%1%' because it's still reachable") % path);
+    if (canReachRoot(state, visited, parseStorePath(path))) {
+        debug("cannot delete '%s' because it's still reachable", path);
     } else {
         /* No path we visited was a root, so everything is garbage.
            But we only delete ‘path’ and its referrers here so that
            ‘nix-store --delete’ doesn't have the unexpected effect of
            recursing into derivations and outputs. */
-        state.dead.insert(visited.begin(), visited.end());
+        for (auto & i : visited)
+            state.dead.insert(i.clone());
         if (state.shouldDelete)
             deletePathRecursive(state, path);
     }
@@ -715,8 +719,7 @@ void LocalStore::removeUnusedLinks(const GCState & state)
 
 void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
 {
-    GCState state(results);
-    state.options = options;
+    GCState state(options, results);
     state.gcKeepOutputs = settings.gcKeepOutputs;
     state.gcKeepDerivations = settings.gcKeepDerivations;
 
@@ -741,12 +744,12 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
 
     /* Find the roots.  Since we've grabbed the GC lock, the set of
        permanent roots cannot increase now. */
-    printError(format("finding garbage collector roots..."));
+    printError("finding garbage collector roots...");
     Roots rootMap;
     if (!options.ignoreLiveness)
         findRootsNoTemp(rootMap, true);
 
-    for (auto & i : rootMap) state.roots.insert(i.first);
+    for (auto & i : rootMap) state.roots.insert(i.first.clone());
 
     /* Read the temporary roots.  This acquires read locks on all
        per-process temporary root files.  So after this point no paths
@@ -754,9 +757,10 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
     FDs fds;
     Roots tempRoots;
     findTempRoots(fds, tempRoots, true);
-    for (auto & root : tempRoots)
-        state.tempRoots.insert(root.first);
-    state.roots.insert(state.tempRoots.begin(), state.tempRoots.end());
+    for (auto & root : tempRoots) {
+        state.tempRoots.insert(root.first.clone());
+        state.roots.insert(root.first.clone());
+    }
 
     /* After this point the set of roots or temporary roots cannot
        increase, since we hold locks on everything.  So everything
@@ -768,7 +772,7 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
             createDirs(trashDir);
         } catch (SysError & e) {
             if (e.errNo == ENOSPC) {
-                printInfo(format("note: can't create trash directory: %1%") % e.msg());
+                printInfo("note: can't create trash directory: %s", e.msg());
                 state.moveToTrash = false;
             }
         }
@@ -780,22 +784,21 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
     if (options.action == GCOptions::gcDeleteSpecific) {
 
         for (auto & i : options.pathsToDelete) {
-            assertStorePath(i);
-            tryToDelete(state, i);
+            tryToDelete(state, printStorePath(i));
             if (state.dead.find(i) == state.dead.end())
-                throw Error(format(
+                throw Error(
                     "cannot delete path '%1%' since it is still alive. "
                     "To find out why use: "
-                    "nix-store --query --roots"
-                    ) % i);
+                    "nix-store --query --roots",
+                    printStorePath(i));
         }
 
     } else if (options.maxFreed > 0) {
 
         if (state.shouldDelete)
-            printError(format("deleting garbage..."));
+            printError("deleting garbage...");
         else
-            printError(format("determining live/dead paths..."));
+            printError("determining live/dead paths...");
 
         try {
 
@@ -815,7 +818,8 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
                 string name = dirent->d_name;
                 if (name == "." || name == "..") continue;
                 Path path = storeDir + "/" + name;
-                if (isStorePath(path) && isValidPath(path))
+                // FIXME
+                if (isStorePath(path) && isValidPath(parseStorePath(path)))
                     entries.push_back(path);
                 else
                     tryToDelete(state, path);
@@ -840,12 +844,14 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
     }
 
     if (state.options.action == GCOptions::gcReturnLive) {
-        state.results.paths = state.alive;
+        for (auto & i : state.alive)
+            state.results.paths.insert(printStorePath(i));
         return;
     }
 
     if (state.options.action == GCOptions::gcReturnDead) {
-        state.results.paths = state.dead;
+        for (auto & i : state.dead)
+            state.results.paths.insert(printStorePath(i));
         return;
     }
 
@@ -859,7 +865,7 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
 
     /* Clean up the links directory. */
     if (options.action == GCOptions::gcDeleteDead || options.action == GCOptions::gcDeleteSpecific) {
-        printError(format("deleting unused links..."));
+        printError("deleting unused links...");
         removeUnusedLinks(state);
     }
 
diff --git a/src/libstore/legacy-ssh-store.cc b/src/libstore/legacy-ssh-store.cc
index 1b8b5908c..458266be0 100644
--- a/src/libstore/legacy-ssh-store.cc
+++ b/src/libstore/legacy-ssh-store.cc
@@ -87,25 +87,27 @@ struct LegacySSHStore : public Store
         return uriScheme + host;
     }
 
-    void queryPathInfoUncached(const Path & path,
+    void queryPathInfoUncached(const StorePath & path,
         Callback<std::shared_ptr<const ValidPathInfo>> callback) noexcept override
     {
         try {
             auto conn(connections->get());
 
-            debug("querying remote host '%s' for info on '%s'", host, path);
+            debug("querying remote host '%s' for info on '%s'", host, printStorePath(path));
 
-            conn->to << cmdQueryPathInfos << PathSet{path};
+            conn->to << cmdQueryPathInfos << PathSet{printStorePath(path)};
             conn->to.flush();
 
-            auto info = std::make_shared<ValidPathInfo>();
-            conn->from >> info->path;
-            if (info->path.empty()) return callback(nullptr);
+            auto p = readString(conn->from);
+            if (p.empty()) return callback(nullptr);
+            auto info = std::make_shared<ValidPathInfo>(parseStorePath(p));
             assert(path == info->path);
 
             PathSet references;
-            conn->from >> info->deriver;
-            info->references = readStorePaths<PathSet>(*this, conn->from);
+            auto deriver = readString(conn->from);
+            if (deriver != "")
+                info->deriver = parseStorePath(deriver);
+            info->references = readStorePaths<StorePathSet>(*this, conn->from);
             readLongLong(conn->from); // download size
             info->narSize = readLongLong(conn->from);
 
@@ -127,7 +129,7 @@ struct LegacySSHStore : public Store
         RepairFlag repair, CheckSigsFlag checkSigs,
         std::shared_ptr<FSAccessor> accessor) override
     {
-        debug("adding path '%s' to remote host '%s'", info.path, host);
+        debug("adding path '%s' to remote host '%s'", printStorePath(info.path), host);
 
         auto conn(connections->get());
 
@@ -135,10 +137,11 @@ struct LegacySSHStore : public Store
 
             conn->to
                 << cmdAddToStoreNar
-                << info.path
-                << info.deriver
-                << info.narHash.to_string(Base16, false)
-                << info.references
+                << printStorePath(info.path)
+                << (info.deriver ? printStorePath(*info.deriver) : "")
+                << info.narHash.to_string(Base16, false);
+            writeStorePaths(*this, conn->to, info.references);
+            conn->to
                 << info.registrationTime
                 << info.narSize
                 << info.ultimate
@@ -165,9 +168,10 @@ struct LegacySSHStore : public Store
             }
             conn->to
                 << exportMagic
-                << info.path
-                << info.references
-                << info.deriver
+                << printStorePath(info.path);
+            writeStorePaths(*this, conn->to, info.references);
+            conn->to
+                << (info.deriver ? printStorePath(*info.deriver) : "")
                 << 0
                 << 0;
             conn->to.flush();
@@ -175,39 +179,40 @@ struct LegacySSHStore : public Store
         }
 
         if (readInt(conn->from) != 1)
-            throw Error("failed to add path '%s' to remote host '%s', info.path, host");
+            throw Error("failed to add path '%s' to remote host '%s'", printStorePath(info.path), host);
     }
 
-    void narFromPath(const Path & path, Sink & sink) override
+    void narFromPath(const StorePath & path, Sink & sink) override
     {
         auto conn(connections->get());
 
-        conn->to << cmdDumpStorePath << path;
+        conn->to << cmdDumpStorePath << printStorePath(path);
         conn->to.flush();
         copyNAR(conn->from, sink);
     }
 
-    Path queryPathFromHashPart(const string & hashPart) override
+    std::optional<StorePath> queryPathFromHashPart(const std::string & hashPart) override
     { unsupported("queryPathFromHashPart"); }
 
-    Path addToStore(const string & name, const Path & srcPath,
+    StorePath addToStore(const string & name, const Path & srcPath,
         bool recursive, HashType hashAlgo,
         PathFilter & filter, RepairFlag repair) override
     { unsupported("addToStore"); }
 
-    Path addTextToStore(const string & name, const string & s,
-        const PathSet & references, RepairFlag repair) override
+    StorePath addTextToStore(const string & name, const string & s,
+        const StorePathSet & references, RepairFlag repair) override
     { unsupported("addTextToStore"); }
 
-    BuildResult buildDerivation(const Path & drvPath, const BasicDerivation & drv,
+    BuildResult buildDerivation(const StorePath & drvPath, const BasicDerivation & drv,
         BuildMode buildMode) override
     {
         auto conn(connections->get());
 
         conn->to
             << cmdBuildDerivation
-            << drvPath
-            << drv
+            << printStorePath(drvPath);
+        writeDerivation(conn->to, *this, drv);
+        conn->to
             << settings.maxSilentTime
             << settings.buildTimeout;
         if (GET_PROTOCOL_MINOR(conn->remoteVersion) >= 2)
@@ -230,11 +235,11 @@ struct LegacySSHStore : public Store
         return status;
     }
 
-    void ensurePath(const Path & path) override
+    void ensurePath(const StorePath & path) override
     { unsupported("ensurePath"); }
 
-    void computeFSClosure(const PathSet & paths,
-        PathSet & out, bool flipDirection = false,
+    void computeFSClosure(const StorePathSet & paths,
+        StorePathSet & out, bool flipDirection = false,
         bool includeOutputs = false, bool includeDerivers = false) override
     {
         if (flipDirection || includeDerivers) {
@@ -246,16 +251,15 @@ struct LegacySSHStore : public Store
 
         conn->to
             << cmdQueryClosure
-            << includeOutputs
-            << paths;
+            << includeOutputs;
+        writeStorePaths(*this, conn->to, paths);
         conn->to.flush();
 
-        auto res = readStorePaths<PathSet>(*this, conn->from);
-
-        out.insert(res.begin(), res.end());
+        for (auto & i : readStorePaths<StorePathSet>(*this, conn->from))
+            out.insert(i.clone());
     }
 
-    PathSet queryValidPaths(const PathSet & paths,
+    StorePathSet queryValidPaths(const StorePathSet & paths,
         SubstituteFlag maybeSubstitute = NoSubstitute) override
     {
         auto conn(connections->get());
@@ -263,11 +267,11 @@ struct LegacySSHStore : public Store
         conn->to
             << cmdQueryValidPaths
             << false // lock
-            << maybeSubstitute
-            << paths;
+            << maybeSubstitute;
+        writeStorePaths(*this, conn->to, paths);
         conn->to.flush();
 
-        return readStorePaths<PathSet>(*this, conn->from);
+        return readStorePaths<StorePathSet>(*this, conn->from);
     }
 
     void connect() override
diff --git a/src/libstore/local-binary-cache-store.cc b/src/libstore/local-binary-cache-store.cc
index 9f99ee76d..363be1443 100644
--- a/src/libstore/local-binary-cache-store.cc
+++ b/src/libstore/local-binary-cache-store.cc
@@ -44,15 +44,15 @@ protected:
         }
     }
 
-    PathSet queryAllValidPaths() override
+    StorePathSet queryAllValidPaths() override
     {
-        PathSet paths;
+        StorePathSet paths;
 
         for (auto & entry : readDirectory(binaryCacheDir)) {
             if (entry.name.size() != 40 ||
                 !hasSuffix(entry.name, ".narinfo"))
                 continue;
-            paths.insert(storeDir + "/" + entry.name.substr(0, entry.name.size() - 8));
+            paths.insert(parseStorePath(storeDir + "/" + entry.name.substr(0, entry.name.size() - 8)));
         }
 
         return paths;
diff --git a/src/libstore/local-fs-store.cc b/src/libstore/local-fs-store.cc
index 642e4070d..aa5abd835 100644
--- a/src/libstore/local-fs-store.cc
+++ b/src/libstore/local-fs-store.cc
@@ -21,7 +21,7 @@ struct LocalStoreAccessor : public FSAccessor
     Path toRealPath(const Path & path)
     {
         Path storePath = store->toStorePath(path);
-        if (!store->isValidPath(storePath))
+        if (!store->isValidPath(store->parseStorePath(storePath)))
             throw InvalidPath(format("path '%1%' is not a valid store path") % storePath);
         return store->getRealStoreDir() + std::string(path, store->storeDir.size());
     }
@@ -77,34 +77,32 @@ ref<FSAccessor> LocalFSStore::getFSAccessor()
             std::dynamic_pointer_cast<LocalFSStore>(shared_from_this())));
 }
 
-void LocalFSStore::narFromPath(const Path & path, Sink & sink)
+void LocalFSStore::narFromPath(const StorePath & path, Sink & sink)
 {
     if (!isValidPath(path))
-        throw Error(format("path '%s' is not valid") % path);
-    dumpPath(getRealStoreDir() + std::string(path, storeDir.size()), sink);
+        throw Error("path '%s' is not valid", printStorePath(path));
+    dumpPath(getRealStoreDir() + std::string(printStorePath(path), storeDir.size()), sink);
 }
 
 const string LocalFSStore::drvsLogDir = "drvs";
 
 
 
-std::shared_ptr<std::string> LocalFSStore::getBuildLog(const Path & path_)
+std::shared_ptr<std::string> LocalFSStore::getBuildLog(const StorePath & path_)
 {
-    auto path(path_);
+    auto path = path_.clone();
 
-    assertStorePath(path);
-
-
-    if (!isDerivation(path)) {
+    if (!path.isDerivation()) {
         try {
-            path = queryPathInfo(path)->deriver;
+            auto info = queryPathInfo(path);
+            if (!info->deriver) return nullptr;
+            path = info->deriver->clone();
         } catch (InvalidPath &) {
             return nullptr;
         }
-        if (path == "") return nullptr;
     }
 
-    string baseName = baseNameOf(path);
+    auto baseName = std::string(baseNameOf(printStorePath(path)));
 
     for (int j = 0; j < 2; j++) {
 
diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
index 60e7bb7af..c1380ef09 100644
--- a/src/libstore/local-store.cc
+++ b/src/libstore/local-store.cc
@@ -541,42 +541,36 @@ void canonicalisePathMetaData(const Path & path, uid_t fromUid)
 }
 
 
-void LocalStore::checkDerivationOutputs(const Path & drvPath, const Derivation & drv)
+void LocalStore::checkDerivationOutputs(const StorePath & drvPath, const Derivation & drv)
 {
-    string drvName = storePathToName(drvPath);
-    assert(isDerivation(drvName));
+    assert(drvPath.isDerivation());
+    std::string drvName(drvPath.name());
     drvName = string(drvName, 0, drvName.size() - drvExtension.size());
 
     if (drv.isFixedOutput()) {
         DerivationOutputs::const_iterator out = drv.outputs.find("out");
         if (out == drv.outputs.end())
-            throw Error(format("derivation '%1%' does not have an output named 'out'") % drvPath);
+            throw Error("derivation '%s' does not have an output named 'out'", printStorePath(drvPath));
 
         bool recursive; Hash h;
         out->second.parseHashInfo(recursive, h);
-        Path outPath = makeFixedOutputPath(recursive, h, drvName);
+        auto outPath = makeFixedOutputPath(recursive, h, drvName);
 
         StringPairs::const_iterator j = drv.env.find("out");
-        if (out->second.path != outPath || j == drv.env.end() || j->second != outPath)
-            throw Error(format("derivation '%1%' has incorrect output '%2%', should be '%3%'")
-                % drvPath % out->second.path % outPath);
+        if (out->second.path != outPath || j == drv.env.end() || parseStorePath(j->second) != outPath)
+            throw Error("derivation '%s' has incorrect output '%s', should be '%s'",
+                printStorePath(drvPath), printStorePath(out->second.path), printStorePath(outPath));
     }
 
     else {
-        Derivation drvCopy(drv);
-        for (auto & i : drvCopy.outputs) {
-            i.second.path = "";
-            drvCopy.env[i.first] = "";
-        }
-
-        Hash h = hashDerivationModulo(*this, drvCopy);
+        Hash h = hashDerivationModulo(*this, drv, true);
 
         for (auto & i : drv.outputs) {
-            Path outPath = makeOutputPath(i.first, h, drvName);
+            auto outPath = makeOutputPath(i.first, h, drvName);
             StringPairs::const_iterator j = drv.env.find(i.first);
-            if (i.second.path != outPath || j == drv.env.end() || j->second != outPath)
-                throw Error(format("derivation '%1%' has incorrect output '%2%', should be '%3%'")
-                    % drvPath % i.second.path % outPath);
+            if (i.second.path != outPath || j == drv.env.end() || parseStorePath(j->second) != outPath)
+                throw Error("derivation '%s' has incorrect output '%s', should be '%s'",
+                    printStorePath(drvPath), printStorePath(i.second.path), printStorePath(outPath));
         }
     }
 }
@@ -585,16 +579,15 @@ void LocalStore::checkDerivationOutputs(const Path & drvPath, const Derivation &
 uint64_t LocalStore::addValidPath(State & state,
     const ValidPathInfo & info, bool checkOutputs)
 {
-    checkStoreName(storePathToName(info.path));
-
     if (info.ca != "" && !info.isContentAddressed(*this))
-        throw Error("cannot add path '%s' to the Nix store because it claims to be content-addressed but isn't", info.path);
+        throw Error("cannot add path '%s' to the Nix store because it claims to be content-addressed but isn't",
+            printStorePath(info.path));
 
     state.stmtRegisterValidPath.use()
-        (info.path)
+        (printStorePath(info.path))
         (info.narHash.to_string(Base16))
         (info.registrationTime == 0 ? time(0) : info.registrationTime)
-        (info.deriver, info.deriver != "")
+        (info.deriver ? printStorePath(*info.deriver) : "", (bool) info.deriver)
         (info.narSize, info.narSize != 0)
         (info.ultimate ? 1 : 0, info.ultimate)
         (concatStringsSep(" ", info.sigs), !info.sigs.empty())
@@ -606,8 +599,8 @@ uint64_t LocalStore::addValidPath(State & state,
        the database.  This is useful for the garbage collector: it can
        efficiently query whether a path is an output of some
        derivation. */
-    if (isDerivation(info.path)) {
-        Derivation drv = readDerivation(realStoreDir + "/" + baseNameOf(info.path));
+    if (info.path.isDerivation()) {
+        auto drv = readDerivation(*this, realStoreDir + "/" + std::string(info.path.to_string()));
 
         /* Verify that the output paths in the derivation are correct
            (i.e., follow the scheme for computing output paths from
@@ -620,34 +613,31 @@ uint64_t LocalStore::addValidPath(State & state,
             state.stmtAddDerivationOutput.use()
                 (id)
                 (i.first)
-                (i.second.path)
+                (printStorePath(i.second.path))
                 .exec();
         }
     }
 
     {
         auto state_(Store::state.lock());
-        state_->pathInfoCache.upsert(storePathToHash(info.path), std::make_shared<ValidPathInfo>(info));
+        state_->pathInfoCache.upsert(storePathToHash(printStorePath(info.path)), std::make_shared<ValidPathInfo>(info));
     }
 
     return id;
 }
 
 
-void LocalStore::queryPathInfoUncached(const Path & path,
+void LocalStore::queryPathInfoUncached(const StorePath & path,
     Callback<std::shared_ptr<const ValidPathInfo>> callback) noexcept
 {
     try {
-        auto info = std::make_shared<ValidPathInfo>();
-        info->path = path;
-
-        assertStorePath(path);
+        auto info = std::make_shared<ValidPathInfo>(path.clone());
 
         callback(retrySQLite<std::shared_ptr<ValidPathInfo>>([&]() {
             auto state(_state.lock());
 
             /* Get the path info. */
-            auto useQueryPathInfo(state->stmtQueryPathInfo.use()(path));
+            auto useQueryPathInfo(state->stmtQueryPathInfo.use()(printStorePath(info->path)));
 
             if (!useQueryPathInfo.next())
                 return std::shared_ptr<ValidPathInfo>();
@@ -657,13 +647,13 @@ void LocalStore::queryPathInfoUncached(const Path & path,
             try {
                 info->narHash = Hash(useQueryPathInfo.getStr(1));
             } catch (BadHash & e) {
-                throw Error("in valid-path entry for '%s': %s", path, e.what());
+                throw Error("in valid-path entry for '%s': %s", printStorePath(path), e.what());
             }
 
             info->registrationTime = useQueryPathInfo.getInt(2);
 
             auto s = (const char *) sqlite3_column_text(state->stmtQueryPathInfo, 3);
-            if (s) info->deriver = s;
+            if (s) info->deriver = parseStorePath(s);
 
             /* Note that narSize = NULL yields 0. */
             info->narSize = useQueryPathInfo.getInt(4);
@@ -680,7 +670,7 @@ void LocalStore::queryPathInfoUncached(const Path & path,
             auto useQueryReferences(state->stmtQueryReferences.use()(info->id));
 
             while (useQueryReferences.next())
-                info->references.insert(useQueryReferences.getStr(0));
+                info->references.insert(parseStorePath(useQueryReferences.getStr(0)));
 
             return info;
         }));
@@ -698,27 +688,27 @@ void LocalStore::updatePathInfo(State & state, const ValidPathInfo & info)
         (info.ultimate ? 1 : 0, info.ultimate)
         (concatStringsSep(" ", info.sigs), !info.sigs.empty())
         (info.ca, !info.ca.empty())
-        (info.path)
+        (printStorePath(info.path))
         .exec();
 }
 
 
-uint64_t LocalStore::queryValidPathId(State & state, const Path & path)
+uint64_t LocalStore::queryValidPathId(State & state, const StorePath & path)
 {
-    auto use(state.stmtQueryPathInfo.use()(path));
+    auto use(state.stmtQueryPathInfo.use()(printStorePath(path)));
     if (!use.next())
-        throw Error(format("path '%1%' is not valid") % path);
+        throw Error("path '%s' is not valid", printStorePath(path));
     return use.getInt(0);
 }
 
 
-bool LocalStore::isValidPath_(State & state, const Path & path)
+bool LocalStore::isValidPath_(State & state, const StorePath & path)
 {
-    return state.stmtQueryPathInfo.use()(path).next();
+    return state.stmtQueryPathInfo.use()(printStorePath(path)).next();
 }
 
 
-bool LocalStore::isValidPathUncached(const Path & path)
+bool LocalStore::isValidPathUncached(const StorePath & path)
 {
     return retrySQLite<bool>([&]() {
         auto state(_state.lock());
@@ -727,39 +717,38 @@ bool LocalStore::isValidPathUncached(const Path & path)
 }
 
 
-PathSet LocalStore::queryValidPaths(const PathSet & paths, SubstituteFlag maybeSubstitute)
+StorePathSet LocalStore::queryValidPaths(const StorePathSet & paths, SubstituteFlag maybeSubstitute)
 {
-    PathSet res;
+    StorePathSet res;
     for (auto & i : paths)
-        if (isValidPath(i)) res.insert(i);
+        if (isValidPath(i)) res.insert(i.clone());
     return res;
 }
 
 
-PathSet LocalStore::queryAllValidPaths()
+StorePathSet LocalStore::queryAllValidPaths()
 {
-    return retrySQLite<PathSet>([&]() {
+    return retrySQLite<StorePathSet>([&]() {
         auto state(_state.lock());
         auto use(state->stmtQueryValidPaths.use());
-        PathSet res;
-        while (use.next()) res.insert(use.getStr(0));
+        StorePathSet res;
+        while (use.next()) res.insert(parseStorePath(use.getStr(0)));
         return res;
     });
 }
 
 
-void LocalStore::queryReferrers(State & state, const Path & path, PathSet & referrers)
+void LocalStore::queryReferrers(State & state, const StorePath & path, StorePathSet & referrers)
 {
-    auto useQueryReferrers(state.stmtQueryReferrers.use()(path));
+    auto useQueryReferrers(state.stmtQueryReferrers.use()(printStorePath(path)));
 
     while (useQueryReferrers.next())
-        referrers.insert(useQueryReferrers.getStr(0));
+        referrers.insert(parseStorePath(useQueryReferrers.getStr(0)));
 }
 
 
-void LocalStore::queryReferrers(const Path & path, PathSet & referrers)
+void LocalStore::queryReferrers(const StorePath & path, StorePathSet & referrers)
 {
-    assertStorePath(path);
     return retrySQLite<void>([&]() {
         auto state(_state.lock());
         queryReferrers(*state, path, referrers);
@@ -767,42 +756,40 @@ void LocalStore::queryReferrers(const Path & path, PathSet & referrers)
 }
 
 
-PathSet LocalStore::queryValidDerivers(const Path & path)
+StorePathSet LocalStore::queryValidDerivers(const StorePath & path)
 {
-    assertStorePath(path);
-
-    return retrySQLite<PathSet>([&]() {
+    return retrySQLite<StorePathSet>([&]() {
         auto state(_state.lock());
 
-        auto useQueryValidDerivers(state->stmtQueryValidDerivers.use()(path));
+        auto useQueryValidDerivers(state->stmtQueryValidDerivers.use()(printStorePath(path)));
 
-        PathSet derivers;
+        StorePathSet derivers;
         while (useQueryValidDerivers.next())
-            derivers.insert(useQueryValidDerivers.getStr(1));
+            derivers.insert(parseStorePath(useQueryValidDerivers.getStr(1)));
 
         return derivers;
     });
 }
 
 
-PathSet LocalStore::queryDerivationOutputs(const Path & path)
+StorePathSet LocalStore::queryDerivationOutputs(const StorePath & path)
 {
-    return retrySQLite<PathSet>([&]() {
+    return retrySQLite<StorePathSet>([&]() {
         auto state(_state.lock());
 
         auto useQueryDerivationOutputs(state->stmtQueryDerivationOutputs.use()
             (queryValidPathId(*state, path)));
 
-        PathSet outputs;
+        StorePathSet outputs;
         while (useQueryDerivationOutputs.next())
-            outputs.insert(useQueryDerivationOutputs.getStr(1));
+            outputs.insert(parseStorePath(useQueryDerivationOutputs.getStr(1)));
 
         return outputs;
     });
 }
 
 
-StringSet LocalStore::queryDerivationOutputNames(const Path & path)
+StringSet LocalStore::queryDerivationOutputNames(const StorePath & path)
 {
     return retrySQLite<StringSet>([&]() {
         auto state(_state.lock());
@@ -819,31 +806,36 @@ StringSet LocalStore::queryDerivationOutputNames(const Path & path)
 }
 
 
-Path LocalStore::queryPathFromHashPart(const string & hashPart)
+std::optional<StorePath> LocalStore::queryPathFromHashPart(const std::string & hashPart)
 {
     if (hashPart.size() != storePathHashLen) throw Error("invalid hash part");
 
     Path prefix = storeDir + "/" + hashPart;
 
-    return retrySQLite<Path>([&]() -> std::string {
+    return retrySQLite<std::optional<StorePath>>([&]() -> std::optional<StorePath> {
         auto state(_state.lock());
 
         auto useQueryPathFromHashPart(state->stmtQueryPathFromHashPart.use()(prefix));
 
-        if (!useQueryPathFromHashPart.next()) return "";
+        if (!useQueryPathFromHashPart.next()) return {};
 
         const char * s = (const char *) sqlite3_column_text(state->stmtQueryPathFromHashPart, 0);
-        return s && prefix.compare(0, prefix.size(), s, prefix.size()) == 0 ? s : "";
+        if (s && prefix.compare(0, prefix.size(), s, prefix.size()) == 0)
+            return parseStorePath(s);
+        return {};
     });
 }
 
 
-PathSet LocalStore::querySubstitutablePaths(const PathSet & paths)
+StorePathSet LocalStore::querySubstitutablePaths(const StorePathSet & paths)
 {
-    if (!settings.useSubstitutes) return PathSet();
+    if (!settings.useSubstitutes) return StorePathSet();
 
-    auto remaining = paths;
-    PathSet res;
+    StorePathSet remaining;
+    for (auto & i : paths)
+        remaining.insert(i.clone());
+
+    StorePathSet res;
 
     for (auto & sub : getDefaultSubstituters()) {
         if (remaining.empty()) break;
@@ -852,12 +844,12 @@ PathSet LocalStore::querySubstitutablePaths(const PathSet & paths)
 
         auto valid = sub->queryValidPaths(remaining);
 
-        PathSet remaining2;
+        StorePathSet remaining2;
         for (auto & path : remaining)
             if (valid.count(path))
-                res.insert(path);
+                res.insert(path.clone());
             else
-                remaining2.insert(path);
+                remaining2.insert(path.clone());
 
         std::swap(remaining, remaining2);
     }
@@ -866,7 +858,7 @@ PathSet LocalStore::querySubstitutablePaths(const PathSet & paths)
 }
 
 
-void LocalStore::querySubstitutablePathInfos(const PathSet & paths,
+void LocalStore::querySubstitutablePathInfos(const StorePathSet & paths,
     SubstitutablePathInfos & infos)
 {
     if (!settings.useSubstitutes) return;
@@ -874,17 +866,16 @@ void LocalStore::querySubstitutablePathInfos(const PathSet & paths,
         if (sub->storeDir != storeDir) continue;
         for (auto & path : paths) {
             if (infos.count(path)) continue;
-            debug(format("checking substituter '%s' for path '%s'")
-                % sub->getUri() % path);
+            debug("checking substituter '%s' for path '%s'", sub->getUri(), printStorePath(path));
             try {
                 auto info = sub->queryPathInfo(path);
                 auto narInfo = std::dynamic_pointer_cast<const NarInfo>(
                     std::shared_ptr<const ValidPathInfo>(info));
-                infos[path] = SubstitutablePathInfo{
-                    info->deriver,
-                    info->references,
+                infos.insert_or_assign(path.clone(), SubstitutablePathInfo{
+                    info->deriver ? info->deriver->clone() : std::optional<StorePath>(),
+                    cloneStorePathSet(info->references),
                     narInfo ? narInfo->fileSize : 0,
-                    info->narSize};
+                    info->narSize});
             } catch (InvalidPath &) {
             } catch (SubstituterDisabled &) {
             } catch (Error & e) {
@@ -918,7 +909,7 @@ void LocalStore::registerValidPaths(const ValidPathInfos & infos)
         auto state(_state.lock());
 
         SQLiteTxn txn(state->db);
-        PathSet paths;
+        StorePathSet paths;
 
         for (auto & i : infos) {
             assert(i.narHash.type == htSHA256);
@@ -926,7 +917,7 @@ void LocalStore::registerValidPaths(const ValidPathInfos & infos)
                 updatePathInfo(*state, i);
             else
                 addValidPath(*state, i, false);
-            paths.insert(i.path);
+            paths.insert(i.path.clone());
         }
 
         for (auto & i : infos) {
@@ -939,10 +930,10 @@ void LocalStore::registerValidPaths(const ValidPathInfos & infos)
            this in addValidPath() above, because the references might
            not be valid yet. */
         for (auto & i : infos)
-            if (isDerivation(i.path)) {
+            if (i.path.isDerivation()) {
                 // FIXME: inefficient; we already loaded the derivation in addValidPath().
-                Derivation drv = readDerivation(realStoreDir + "/" + baseNameOf(i.path));
-                checkDerivationOutputs(i.path, drv);
+                checkDerivationOutputs(i.path,
+                    readDerivation(*this, realStoreDir + "/" + std::string(i.path.to_string())));
             }
 
         /* Do a topological sort of the paths.  This will throw an
@@ -958,18 +949,18 @@ void LocalStore::registerValidPaths(const ValidPathInfos & infos)
 
 /* Invalidate a path.  The caller is responsible for checking that
    there are no referrers. */
-void LocalStore::invalidatePath(State & state, const Path & path)
+void LocalStore::invalidatePath(State & state, const StorePath & path)
 {
-    debug(format("invalidating path '%1%'") % path);
+    debug("invalidating path '%s'", printStorePath(path));
 
-    state.stmtInvalidatePath.use()(path).exec();
+    state.stmtInvalidatePath.use()(printStorePath(path)).exec();
 
     /* Note that the foreign key constraints on the Refs table take
        care of deleting the references entries for `path'. */
 
     {
         auto state_(Store::state.lock());
-        state_->pathInfoCache.erase(storePathToHash(path));
+        state_->pathInfoCache.erase(storePathToHash(printStorePath(path)));
     }
 }
 
@@ -987,10 +978,10 @@ void LocalStore::addToStore(const ValidPathInfo & info, Source & source,
     RepairFlag repair, CheckSigsFlag checkSigs, std::shared_ptr<FSAccessor> accessor)
 {
     if (!info.narHash)
-        throw Error("cannot add path '%s' because it lacks a hash", info.path);
+        throw Error("cannot add path '%s' because it lacks a hash", printStorePath(info.path));
 
     if (requireSigs && checkSigs && !info.checkSignatures(*this, getPublicKeys()))
-        throw Error("cannot add path '%s' because it lacks a valid signature", info.path);
+        throw Error("cannot add path '%s' because it lacks a valid signature", printStorePath(info.path));
 
     addTempRoot(info.path);
 
@@ -998,12 +989,12 @@ void LocalStore::addToStore(const ValidPathInfo & info, Source & source,
 
         PathLocks outputLock;
 
-        Path realPath = realStoreDir + "/" + baseNameOf(info.path);
+        Path realPath = realStoreDir + "/" + std::string(info.path.to_string());
 
         /* Lock the output path.  But don't lock if we're being called
            from a build hook (whose parent process already acquired a
            lock on this path). */
-        if (!locksHeld.count(info.path))
+        if (!locksHeld.count(printStorePath(info.path)))
             outputLock.lockPaths({realPath});
 
         if (repair || !isValidPath(info.path)) {
@@ -1018,7 +1009,7 @@ void LocalStore::addToStore(const ValidPathInfo & info, Source & source,
             else {
                 if (!info.references.empty())
                     settings.requireExperimentalFeature("ca-references");
-                hashSink = std::make_unique<HashModuloSink>(htSHA256, storePathToHash(info.path));
+                hashSink = std::make_unique<HashModuloSink>(htSHA256, storePathToHash(printStorePath(info.path)));
             }
 
             LambdaSource wrapperSource([&](unsigned char * data, size_t len) -> size_t {
@@ -1033,11 +1024,11 @@ void LocalStore::addToStore(const ValidPathInfo & info, Source & source,
 
             if (hashResult.first != info.narHash)
                 throw Error("hash mismatch importing path '%s';\n  wanted: %s\n  got:    %s",
-                    info.path, info.narHash.to_string(), hashResult.first.to_string());
+                    printStorePath(info.path), info.narHash.to_string(), hashResult.first.to_string());
 
             if (hashResult.second != info.narSize)
                 throw Error("size mismatch importing path '%s';\n  wanted: %s\n  got:   %s",
-                    info.path, info.narSize, hashResult.second);
+                    printStorePath(info.path), info.narSize, hashResult.second);
 
             autoGC();
 
@@ -1053,12 +1044,12 @@ void LocalStore::addToStore(const ValidPathInfo & info, Source & source,
 }
 
 
-Path LocalStore::addToStoreFromDump(const string & dump, const string & name,
+StorePath LocalStore::addToStoreFromDump(const string & dump, const string & name,
     bool recursive, HashType hashAlgo, RepairFlag repair)
 {
     Hash h = hashString(hashAlgo, dump);
 
-    Path dstPath = makeFixedOutputPath(recursive, h, name);
+    auto dstPath = makeFixedOutputPath(recursive, h, name);
 
     addTempRoot(dstPath);
 
@@ -1067,7 +1058,8 @@ Path LocalStore::addToStoreFromDump(const string & dump, const string & name,
         /* The first check above is an optimisation to prevent
            unnecessary lock acquisition. */
 
-        Path realPath = realStoreDir + "/" + baseNameOf(dstPath);
+        Path realPath = realStoreDir + "/";
+        realPath += dstPath.to_string();
 
         PathLocks outputLock({realPath});
 
@@ -1098,8 +1090,7 @@ Path LocalStore::addToStoreFromDump(const string & dump, const string & name,
 
             optimisePath(realPath); // FIXME: combine with hashPath()
 
-            ValidPathInfo info;
-            info.path = dstPath;
+            ValidPathInfo info(dstPath.clone());
             info.narHash = hash.first;
             info.narSize = hash.second;
             info.ca = makeFixedOutputCA(recursive, h);
@@ -1113,7 +1104,7 @@ Path LocalStore::addToStoreFromDump(const string & dump, const string & name,
 }
 
 
-Path LocalStore::addToStore(const string & name, const Path & _srcPath,
+StorePath LocalStore::addToStore(const string & name, const Path & _srcPath,
     bool recursive, HashType hashAlgo, PathFilter & filter, RepairFlag repair)
 {
     Path srcPath(absPath(_srcPath));
@@ -1131,8 +1122,8 @@ Path LocalStore::addToStore(const string & name, const Path & _srcPath,
 }
 
 
-Path LocalStore::addTextToStore(const string & name, const string & s,
-    const PathSet & references, RepairFlag repair)
+StorePath LocalStore::addTextToStore(const string & name, const string & s,
+    const StorePathSet & references, RepairFlag repair)
 {
     auto hash = hashString(htSHA256, s);
     auto dstPath = makeTextPath(name, hash, references);
@@ -1141,7 +1132,8 @@ Path LocalStore::addTextToStore(const string & name, const string & s,
 
     if (repair || !isValidPath(dstPath)) {
 
-        Path realPath = realStoreDir + "/" + baseNameOf(dstPath);
+        Path realPath = realStoreDir + "/";
+        realPath += dstPath.to_string();
 
         PathLocks outputLock({realPath});
 
@@ -1161,11 +1153,10 @@ Path LocalStore::addTextToStore(const string & name, const string & s,
 
             optimisePath(realPath);
 
-            ValidPathInfo info;
-            info.path = dstPath;
+            ValidPathInfo info(dstPath.clone());
             info.narHash = narHash;
             info.narSize = sink.s->size();
-            info.references = references;
+            info.references = cloneStorePathSet(references);
             info.ca = "text:" + hash.to_string();
             registerValidPath(info);
         }
@@ -1187,27 +1178,25 @@ Path LocalStore::createTempDirInStore()
            the GC between createTempDir() and addTempRoot(), so repeat
            until `tmpDir' exists. */
         tmpDir = createTempDir(realStoreDir);
-        addTempRoot(tmpDir);
+        addTempRoot(parseStorePath(tmpDir));
     } while (!pathExists(tmpDir));
     return tmpDir;
 }
 
 
-void LocalStore::invalidatePathChecked(const Path & path)
+void LocalStore::invalidatePathChecked(const StorePath & path)
 {
-    assertStorePath(path);
-
     retrySQLite<void>([&]() {
         auto state(_state.lock());
 
         SQLiteTxn txn(state->db);
 
         if (isValidPath_(*state, path)) {
-            PathSet referrers; queryReferrers(*state, path, referrers);
+            StorePathSet referrers; queryReferrers(*state, path, referrers);
             referrers.erase(path); /* ignore self-references */
             if (!referrers.empty())
-                throw PathInUse(format("cannot delete path '%1%' because it is in use by %2%")
-                    % path % showPaths(referrers));
+                throw PathInUse("cannot delete path '%s' because it is in use by %s",
+                    printStorePath(path), showPaths(referrers));
             invalidatePath(*state, path);
         }
 
@@ -1226,18 +1215,19 @@ bool LocalStore::verifyStore(bool checkContents, RepairFlag repair)
        existing and valid paths. */
     AutoCloseFD fdGCLock = openGCLock(ltWrite);
 
-    PathSet store;
+    StringSet store;
     for (auto & i : readDirectory(realStoreDir)) store.insert(i.name);
 
     /* Check whether all valid paths actually exist. */
     printInfo("checking path existence...");
 
-    PathSet validPaths2 = queryAllValidPaths(), validPaths, done;
+    StorePathSet validPaths;
+    PathSet done;
 
     fdGCLock = -1;
 
-    for (auto & i : validPaths2)
-        verifyPath(i, store, done, validPaths, repair, errors);
+    for (auto & i : queryAllValidPaths())
+        verifyPath(printStorePath(i), store, done, validPaths, repair, errors);
 
     /* Optionally, check the content hashes (slow). */
     if (checkContents) {
@@ -1272,21 +1262,20 @@ bool LocalStore::verifyStore(bool checkContents, RepairFlag repair)
                 auto info = std::const_pointer_cast<ValidPathInfo>(std::shared_ptr<const ValidPathInfo>(queryPathInfo(i)));
 
                 /* Check the content hash (optionally - slow). */
-                printMsg(lvlTalkative, format("checking contents of '%1%'") % i);
+                printMsg(lvlTalkative, "checking contents of '%s'", printStorePath(i));
 
                 std::unique_ptr<AbstractHashSink> hashSink;
                 if (info->ca == "")
                     hashSink = std::make_unique<HashSink>(info->narHash.type);
                 else
-                    hashSink = std::make_unique<HashModuloSink>(info->narHash.type, storePathToHash(info->path));
+                    hashSink = std::make_unique<HashModuloSink>(info->narHash.type, storePathToHash(printStorePath(info->path)));
 
-                dumpPath(toRealPath(i), *hashSink);
+                dumpPath(toRealPath(printStorePath(i)), *hashSink);
                 auto current = hashSink->finish();
 
                 if (info->narHash != nullHash && info->narHash != current.first) {
-                    printError(format("path '%1%' was modified! "
-                            "expected hash '%2%', got '%3%'")
-                        % i % info->narHash.to_string() % current.first.to_string());
+                    printError("path '%s' was modified! expected hash '%s', got '%s'",
+                        printStorePath(i), info->narHash.to_string(), current.first.to_string());
                     if (repair) repairPath(i); else errors = true;
                 } else {
 
@@ -1294,14 +1283,14 @@ bool LocalStore::verifyStore(bool checkContents, RepairFlag repair)
 
                     /* Fill in missing hashes. */
                     if (info->narHash == nullHash) {
-                        printError(format("fixing missing hash on '%1%'") % i);
+                        printError("fixing missing hash on '%s'", printStorePath(i));
                         info->narHash = current.first;
                         update = true;
                     }
 
                     /* Fill in missing narSize fields (from old stores). */
                     if (info->narSize == 0) {
-                        printError(format("updating size field on '%1%' to %2%") % i % current.second);
+                        printError("updating size field on '%s' to %s", printStorePath(i), current.second);
                         info->narSize = current.second;
                         update = true;
                     }
@@ -1317,9 +1306,9 @@ bool LocalStore::verifyStore(bool checkContents, RepairFlag repair)
                 /* It's possible that the path got GC'ed, so ignore
                    errors on invalid paths. */
                 if (isValidPath(i))
-                    printError(format("error: %1%") % e.msg());
+                    printError("error: %s", e.msg());
                 else
-                    printError(format("warning: %1%") % e.msg());
+                    warn(e.msg());
                 errors = true;
             }
         }
@@ -1329,43 +1318,43 @@ bool LocalStore::verifyStore(bool checkContents, RepairFlag repair)
 }
 
 
-void LocalStore::verifyPath(const Path & path, const PathSet & store,
-    PathSet & done, PathSet & validPaths, RepairFlag repair, bool & errors)
+void LocalStore::verifyPath(const Path & pathS, const StringSet & store,
+    PathSet & done, StorePathSet & validPaths, RepairFlag repair, bool & errors)
 {
     checkInterrupt();
 
-    if (!done.insert(path).second) return;
+    if (!done.insert(pathS).second) return;
 
-    if (!isStorePath(path)) {
-        printError(format("path '%1%' is not in the Nix store") % path);
-        auto state(_state.lock());
-        invalidatePath(*state, path);
+    if (!isStorePath(pathS)) {
+        printError("path '%s' is not in the Nix store", pathS);
         return;
     }
 
-    if (store.find(baseNameOf(path)) == store.end()) {
+    auto path = parseStorePath(pathS);
+
+    if (!store.count(std::string(path.to_string()))) {
         /* Check any referrers first.  If we can invalidate them
            first, then we can invalidate this path as well. */
         bool canInvalidate = true;
-        PathSet referrers; queryReferrers(path, referrers);
+        StorePathSet referrers; queryReferrers(path, referrers);
         for (auto & i : referrers)
             if (i != path) {
-                verifyPath(i, store, done, validPaths, repair, errors);
-                if (validPaths.find(i) != validPaths.end())
+                verifyPath(printStorePath(i), store, done, validPaths, repair, errors);
+                if (validPaths.count(i))
                     canInvalidate = false;
             }
 
         if (canInvalidate) {
-            printError(format("path '%1%' disappeared, removing from database...") % path);
+            printError("path '%s' disappeared, removing from database...", pathS);
             auto state(_state.lock());
             invalidatePath(*state, path);
         } else {
-            printError(format("path '%1%' disappeared, but it still has valid referrers!") % path);
+            printError("path '%s' disappeared, but it still has valid referrers!", pathS);
             if (repair)
                 try {
                     repairPath(path);
                 } catch (Error & e) {
-                    printError(format("warning: %1%") % e.msg());
+                    warn(e.msg());
                     errors = true;
                 }
             else errors = true;
@@ -1374,7 +1363,7 @@ void LocalStore::verifyPath(const Path & path, const PathSet & store,
         return;
     }
 
-    validPaths.insert(path);
+    validPaths.insert(std::move(path));
 }
 
 
@@ -1443,7 +1432,7 @@ void LocalStore::vacuumDB()
 }
 
 
-void LocalStore::addSignatures(const Path & storePath, const StringSet & sigs)
+void LocalStore::addSignatures(const StorePath & storePath, const StringSet & sigs)
 {
     retrySQLite<void>([&]() {
         auto state(_state.lock());
@@ -1469,7 +1458,7 @@ void LocalStore::signPathInfo(ValidPathInfo & info)
 
     for (auto & secretKeyFile : secretKeyFiles.get()) {
         SecretKey secretKey(readFile(secretKeyFile));
-        info.sign(secretKey);
+        info.sign(*this, secretKey);
     }
 }
 
diff --git a/src/libstore/local-store.hh b/src/libstore/local-store.hh
index 1d4b88898..16aeab0ad 100644
--- a/src/libstore/local-store.hh
+++ b/src/libstore/local-store.hh
@@ -119,36 +119,36 @@ public:
 
     std::string getUri() override;
 
-    bool isValidPathUncached(const Path & path) override;
+    bool isValidPathUncached(const StorePath & path) override;
 
-    PathSet queryValidPaths(const PathSet & paths,
+    StorePathSet queryValidPaths(const StorePathSet & paths,
         SubstituteFlag maybeSubstitute = NoSubstitute) override;
 
-    PathSet queryAllValidPaths() override;
+    StorePathSet queryAllValidPaths() override;
 
-    void queryPathInfoUncached(const Path & path,
+    void queryPathInfoUncached(const StorePath & path,
         Callback<std::shared_ptr<const ValidPathInfo>> callback) noexcept override;
 
-    void queryReferrers(const Path & path, PathSet & referrers) override;
+    void queryReferrers(const StorePath & path, StorePathSet & referrers) override;
 
-    PathSet queryValidDerivers(const Path & path) override;
+    StorePathSet queryValidDerivers(const StorePath & path) override;
 
-    PathSet queryDerivationOutputs(const Path & path) override;
+    StorePathSet queryDerivationOutputs(const StorePath & path) override;
 
-    StringSet queryDerivationOutputNames(const Path & path) override;
+    StringSet queryDerivationOutputNames(const StorePath & path) override;
 
-    Path queryPathFromHashPart(const string & hashPart) override;
+    std::optional<StorePath> queryPathFromHashPart(const std::string & hashPart) override;
 
-    PathSet querySubstitutablePaths(const PathSet & paths) override;
+    StorePathSet querySubstitutablePaths(const StorePathSet & paths) override;
 
-    void querySubstitutablePathInfos(const PathSet & paths,
+    void querySubstitutablePathInfos(const StorePathSet & paths,
         SubstitutablePathInfos & infos) override;
 
     void addToStore(const ValidPathInfo & info, Source & source,
         RepairFlag repair, CheckSigsFlag checkSigs,
         std::shared_ptr<FSAccessor> accessor) override;
 
-    Path addToStore(const string & name, const Path & srcPath,
+    StorePath addToStore(const string & name, const Path & srcPath,
         bool recursive, HashType hashAlgo,
         PathFilter & filter, RepairFlag repair) override;
 
@@ -156,20 +156,22 @@ public:
        in `dump', which is either a NAR serialisation (if recursive ==
        true) or simply the contents of a regular file (if recursive ==
        false). */
-    Path addToStoreFromDump(const string & dump, const string & name,
+    StorePath addToStoreFromDump(const string & dump, const string & name,
         bool recursive = true, HashType hashAlgo = htSHA256, RepairFlag repair = NoRepair) override;
 
-    Path addTextToStore(const string & name, const string & s,
-        const PathSet & references, RepairFlag repair) override;
+    StorePath addTextToStore(const string & name, const string & s,
+        const StorePathSet & references, RepairFlag repair) override;
 
-    void buildPaths(const PathSet & paths, BuildMode buildMode) override;
-
-    BuildResult buildDerivation(const Path & drvPath, const BasicDerivation & drv,
+    void buildPaths(
+        const std::vector<StorePathWithOutputs> & paths,
         BuildMode buildMode) override;
 
-    void ensurePath(const Path & path) override;
+    BuildResult buildDerivation(const StorePath & drvPath, const BasicDerivation & drv,
+        BuildMode buildMode) override;
 
-    void addTempRoot(const Path & path) override;
+    void ensurePath(const StorePath & path) override;
+
+    void addTempRoot(const StorePath & path) override;
 
     void addIndirectRoot(const Path & path) override;
 
@@ -215,9 +217,9 @@ public:
 
     /* Repair the contents of the given path by redownloading it using
        a substituter (if available). */
-    void repairPath(const Path & path);
+    void repairPath(const StorePath & path);
 
-    void addSignatures(const Path & storePath, const StringSet & sigs) override;
+    void addSignatures(const StorePath & storePath, const StringSet & sigs) override;
 
     /* If free disk space in /nix/store if below minFree, delete
        garbage until it exceeds maxFree. */
@@ -231,17 +233,17 @@ private:
 
     void makeStoreWritable();
 
-    uint64_t queryValidPathId(State & state, const Path & path);
+    uint64_t queryValidPathId(State & state, const StorePath & path);
 
     uint64_t addValidPath(State & state, const ValidPathInfo & info, bool checkOutputs = true);
 
-    void invalidatePath(State & state, const Path & path);
+    void invalidatePath(State & state, const StorePath & path);
 
     /* Delete a path from the Nix store. */
-    void invalidatePathChecked(const Path & path);
+    void invalidatePathChecked(const StorePath & path);
 
-    void verifyPath(const Path & path, const PathSet & store,
-        PathSet & done, PathSet & validPaths, RepairFlag repair, bool & errors);
+    void verifyPath(const Path & path, const StringSet & store,
+        PathSet & done, StorePathSet & validPaths, RepairFlag repair, bool & errors);
 
     void updatePathInfo(State & state, const ValidPathInfo & info);
 
@@ -256,7 +258,7 @@ private:
 
     void tryToDelete(GCState & state, const Path & path);
 
-    bool canReachRoot(GCState & state, PathSet & visited, const Path & path);
+    bool canReachRoot(GCState & state, StorePathSet & visited, const StorePath & path);
 
     void deletePathRecursive(GCState & state, const Path & path);
 
@@ -275,7 +277,7 @@ private:
 
     Path createTempDirInStore();
 
-    void checkDerivationOutputs(const Path & drvPath, const Derivation & drv);
+    void checkDerivationOutputs(const StorePath & drvPath, const Derivation & drv);
 
     typedef std::unordered_set<ino_t> InodeHash;
 
@@ -284,8 +286,8 @@ private:
     void optimisePath_(Activity * act, OptimiseStats & stats, const Path & path, InodeHash & inodeHash);
 
     // Internal versions that are not wrapped in retry_sqlite.
-    bool isValidPath_(State & state, const Path & path);
-    void queryReferrers(State & state, const Path & path, PathSet & referrers);
+    bool isValidPath_(State & state, const StorePath & path);
+    void queryReferrers(State & state, const StorePath & path, StorePathSet & referrers);
 
     /* Add signatures to a ValidPathInfo using the secret keys
        specified by the ‘secret-key-files’ option. */
diff --git a/src/libstore/local.mk b/src/libstore/local.mk
index d690fea28..d3254554d 100644
--- a/src/libstore/local.mk
+++ b/src/libstore/local.mk
@@ -6,7 +6,7 @@ libstore_DIR := $(d)
 
 libstore_SOURCES := $(wildcard $(d)/*.cc $(d)/builtins/*.cc)
 
-libstore_LIBS = libutil
+libstore_LIBS = libutil libnixrust
 
 libstore_LDFLAGS = $(SQLITE3_LIBS) -lbz2 $(LIBCURL_LIBS) $(SODIUM_LIBS) -pthread
 ifneq ($(OS), FreeBSD)
diff --git a/src/libstore/misc.cc b/src/libstore/misc.cc
index 2fceb9b9a..9c47fe524 100644
--- a/src/libstore/misc.cc
+++ b/src/libstore/misc.cc
@@ -9,13 +9,13 @@
 namespace nix {
 
 
-void Store::computeFSClosure(const PathSet & startPaths,
-    PathSet & paths_, bool flipDirection, bool includeOutputs, bool includeDerivers)
+void Store::computeFSClosure(const StorePathSet & startPaths,
+    StorePathSet & paths_, bool flipDirection, bool includeOutputs, bool includeDerivers)
 {
     struct State
     {
         size_t pending;
-        PathSet & paths;
+        StorePathSet & paths;
         std::exception_ptr exc;
     };
 
@@ -29,45 +29,47 @@ void Store::computeFSClosure(const PathSet & startPaths,
         {
             auto state(state_.lock());
             if (state->exc) return;
-            if (!state->paths.insert(path).second) return;
+            if (!state->paths.insert(parseStorePath(path)).second) return;
             state->pending++;
         }
 
-        queryPathInfo(path, {[&, path](std::future<ref<const ValidPathInfo>> fut) {
+        queryPathInfo(parseStorePath(path), {[&, pathS(path)](std::future<ref<const ValidPathInfo>> fut) {
             // FIXME: calls to isValidPath() should be async
 
             try {
                 auto info = fut.get();
 
+                auto path = parseStorePath(pathS);
+
                 if (flipDirection) {
 
-                    PathSet referrers;
+                    StorePathSet referrers;
                     queryReferrers(path, referrers);
                     for (auto & ref : referrers)
                         if (ref != path)
-                            enqueue(ref);
+                            enqueue(printStorePath(ref));
 
                     if (includeOutputs)
                         for (auto & i : queryValidDerivers(path))
-                            enqueue(i);
+                            enqueue(printStorePath(i));
 
-                    if (includeDerivers && isDerivation(path))
+                    if (includeDerivers && path.isDerivation())
                         for (auto & i : queryDerivationOutputs(path))
                             if (isValidPath(i) && queryPathInfo(i)->deriver == path)
-                                enqueue(i);
+                                enqueue(printStorePath(i));
 
                 } else {
 
                     for (auto & ref : info->references)
                         if (ref != path)
-                            enqueue(ref);
+                            enqueue(printStorePath(ref));
 
-                    if (includeOutputs && isDerivation(path))
+                    if (includeOutputs && path.isDerivation())
                         for (auto & i : queryDerivationOutputs(path))
-                            if (isValidPath(i)) enqueue(i);
+                            if (isValidPath(i)) enqueue(printStorePath(i));
 
-                    if (includeDerivers && isValidPath(info->deriver))
-                        enqueue(info->deriver);
+                    if (includeDerivers && info->deriver && isValidPath(*info->deriver))
+                        enqueue(printStorePath(*info->deriver));
 
                 }
 
@@ -87,7 +89,7 @@ void Store::computeFSClosure(const PathSet & startPaths,
     };
 
     for (auto & startPath : startPaths)
-        enqueue(startPath);
+        enqueue(printStorePath(startPath));
 
     {
         auto state(state_.lock());
@@ -97,15 +99,17 @@ void Store::computeFSClosure(const PathSet & startPaths,
 }
 
 
-void Store::computeFSClosure(const Path & startPath,
-    PathSet & paths_, bool flipDirection, bool includeOutputs, bool includeDerivers)
+void Store::computeFSClosure(const StorePath & startPath,
+    StorePathSet & paths_, bool flipDirection, bool includeOutputs, bool includeDerivers)
 {
-    computeFSClosure(PathSet{startPath}, paths_, flipDirection, includeOutputs, includeDerivers);
+    StorePathSet paths;
+    paths.insert(startPath.clone());
+    computeFSClosure(paths, paths_, flipDirection, includeOutputs, includeDerivers);
 }
 
 
-void Store::queryMissing(const PathSet & targets,
-    PathSet & willBuild_, PathSet & willSubstitute_, PathSet & unknown_,
+void Store::queryMissing(const std::vector<StorePathWithOutputs> & targets,
+    StorePathSet & willBuild_, StorePathSet & willSubstitute_, StorePathSet & unknown_,
     unsigned long long & downloadSize_, unsigned long long & narSize_)
 {
     Activity act(*logger, lvlDebug, actUnknown, "querying info about missing paths");
@@ -116,8 +120,8 @@ void Store::queryMissing(const PathSet & targets,
 
     struct State
     {
-        PathSet done;
-        PathSet & unknown, & willSubstitute, & willBuild;
+        std::unordered_set<std::string> done;
+        StorePathSet & unknown, & willSubstitute, & willBuild;
         unsigned long long & downloadSize;
         unsigned long long & narSize;
     };
@@ -126,31 +130,36 @@ void Store::queryMissing(const PathSet & targets,
     {
         size_t left;
         bool done = false;
-        PathSet outPaths;
+        StorePathSet outPaths;
         DrvState(size_t left) : left(left) { }
     };
 
-    Sync<State> state_(State{PathSet(), unknown_, willSubstitute_, willBuild_, downloadSize_, narSize_});
+    Sync<State> state_(State{{}, unknown_, willSubstitute_, willBuild_, downloadSize_, narSize_});
 
-    std::function<void(Path)> doPath;
+    std::function<void(StorePathWithOutputs)> doPath;
 
-    auto mustBuildDrv = [&](const Path & drvPath, const Derivation & drv) {
+    auto mustBuildDrv = [&](const StorePath & drvPath, const Derivation & drv) {
         {
             auto state(state_.lock());
-            state->willBuild.insert(drvPath);
+            state->willBuild.insert(drvPath.clone());
         }
 
         for (auto & i : drv.inputDrvs)
-            pool.enqueue(std::bind(doPath, makeDrvPathWithOutputs(i.first, i.second)));
+            pool.enqueue(std::bind(doPath, StorePathWithOutputs(i.first, i.second)));
     };
 
     auto checkOutput = [&](
-        const Path & drvPath, ref<Derivation> drv, const Path & outPath, ref<Sync<DrvState>> drvState_)
+        const Path & drvPathS, ref<Derivation> drv, const Path & outPathS, ref<Sync<DrvState>> drvState_)
     {
         if (drvState_->lock()->done) return;
 
+        auto drvPath = parseStorePath(drvPathS);
+        auto outPath = parseStorePath(outPathS);
+
         SubstitutablePathInfos infos;
-        querySubstitutablePathInfos({outPath}, infos);
+        StorePathSet paths; // FIXME
+        paths.insert(outPath.clone());
+        querySubstitutablePathInfos(paths, infos);
 
         if (infos.empty()) {
             drvState_->lock()->done = true;
@@ -161,74 +170,74 @@ void Store::queryMissing(const PathSet & targets,
                 if (drvState->done) return;
                 assert(drvState->left);
                 drvState->left--;
-                drvState->outPaths.insert(outPath);
+                drvState->outPaths.insert(outPath.clone());
                 if (!drvState->left) {
                     for (auto & path : drvState->outPaths)
-                        pool.enqueue(std::bind(doPath, path));
+                        pool.enqueue(std::bind(doPath, StorePathWithOutputs(path.clone())));
                 }
             }
         }
     };
 
-    doPath = [&](const Path & path) {
+    doPath = [&](const StorePathWithOutputs & path) {
 
         {
             auto state(state_.lock());
-            if (!state->done.insert(path).second) return;
+            if (!state->done.insert(path.to_string(*this)).second) return;
         }
 
-        DrvPathWithOutputs i2 = parseDrvPathWithOutputs(path);
-
-        if (isDerivation(i2.first)) {
-            if (!isValidPath(i2.first)) {
+        if (path.path.isDerivation()) {
+            if (!isValidPath(path.path)) {
                 // FIXME: we could try to substitute the derivation.
                 auto state(state_.lock());
-                state->unknown.insert(path);
+                state->unknown.insert(path.path.clone());
                 return;
             }
 
-            Derivation drv = derivationFromPath(i2.first);
-            ParsedDerivation parsedDrv(i2.first, drv);
+            auto drv = make_ref<Derivation>(derivationFromPath(path.path));
+            ParsedDerivation parsedDrv(path.path.clone(), *drv);
 
             PathSet invalid;
-            for (auto & j : drv.outputs)
-                if (wantOutput(j.first, i2.second)
+            for (auto & j : drv->outputs)
+                if (wantOutput(j.first, path.outputs)
                     && !isValidPath(j.second.path))
-                    invalid.insert(j.second.path);
+                    invalid.insert(printStorePath(j.second.path));
             if (invalid.empty()) return;
 
             if (settings.useSubstitutes && parsedDrv.substitutesAllowed()) {
                 auto drvState = make_ref<Sync<DrvState>>(DrvState(invalid.size()));
                 for (auto & output : invalid)
-                    pool.enqueue(std::bind(checkOutput, i2.first, make_ref<Derivation>(drv), output, drvState));
+                    pool.enqueue(std::bind(checkOutput, printStorePath(path.path), drv, output, drvState));
             } else
-                mustBuildDrv(i2.first, drv);
+                mustBuildDrv(path.path, *drv);
 
         } else {
 
-            if (isValidPath(path)) return;
+            if (isValidPath(path.path)) return;
 
             SubstitutablePathInfos infos;
-            querySubstitutablePathInfos({path}, infos);
+            StorePathSet paths; // FIXME
+            paths.insert(path.path.clone());
+            querySubstitutablePathInfos(paths, infos);
 
             if (infos.empty()) {
                 auto state(state_.lock());
-                state->unknown.insert(path);
+                state->unknown.insert(path.path.clone());
                 return;
             }
 
-            auto info = infos.find(path);
+            auto info = infos.find(path.path);
             assert(info != infos.end());
 
             {
                 auto state(state_.lock());
-                state->willSubstitute.insert(path);
+                state->willSubstitute.insert(path.path.clone());
                 state->downloadSize += info->second.downloadSize;
                 state->narSize += info->second.narSize;
             }
 
             for (auto & ref : info->second.references)
-                pool.enqueue(std::bind(doPath, ref));
+                pool.enqueue(std::bind(doPath, StorePathWithOutputs(ref)));
         }
     };
 
@@ -239,39 +248,42 @@ void Store::queryMissing(const PathSet & targets,
 }
 
 
-Paths Store::topoSortPaths(const PathSet & paths)
+StorePaths Store::topoSortPaths(const StorePathSet & paths)
 {
-    Paths sorted;
-    PathSet visited, parents;
+    StorePaths sorted;
+    StorePathSet visited, parents;
 
-    std::function<void(const Path & path, const Path * parent)> dfsVisit;
+    std::function<void(const StorePath & path, const StorePath * parent)> dfsVisit;
 
-    dfsVisit = [&](const Path & path, const Path * parent) {
-        if (parents.find(path) != parents.end())
-            throw BuildError(format("cycle detected in the references of '%1%' from '%2%'") % path % *parent);
+    dfsVisit = [&](const StorePath & path, const StorePath * parent) {
+        if (parents.count(path))
+            throw BuildError("cycle detected in the references of '%s' from '%s'",
+                printStorePath(path), printStorePath(*parent));
 
-        if (!visited.insert(path).second) return;
-        parents.insert(path);
+        if (!visited.insert(path.clone()).second) return;
+        parents.insert(path.clone());
 
-        PathSet references;
+        StorePathSet references;
         try {
-            references = queryPathInfo(path)->references;
+            references = cloneStorePathSet(queryPathInfo(path)->references);
         } catch (InvalidPath &) {
         }
 
         for (auto & i : references)
             /* Don't traverse into paths that don't exist.  That can
                happen due to substitutes for non-existent paths. */
-            if (i != path && paths.find(i) != paths.end())
+            if (i != path && paths.count(i))
                 dfsVisit(i, &path);
 
-        sorted.push_front(path);
+        sorted.push_back(path.clone());
         parents.erase(path);
     };
 
     for (auto & i : paths)
         dfsVisit(i, nullptr);
 
+    std::reverse(sorted.begin(), sorted.end());
+
     return sorted;
 }
 
diff --git a/src/libstore/nar-info-disk-cache.cc b/src/libstore/nar-info-disk-cache.cc
index 5bf982195..3a2cde55f 100644
--- a/src/libstore/nar-info-disk-cache.cc
+++ b/src/libstore/nar-info-disk-cache.cc
@@ -193,11 +193,8 @@ public:
             if (!queryNAR.getInt(0))
                 return {oInvalid, 0};
 
-            auto narInfo = make_ref<NarInfo>();
-
             auto namePart = queryNAR.getStr(1);
-            narInfo->path = cache.storeDir + "/" +
-                hashPart + (namePart.empty() ? "" : "-" + namePart);
+            auto narInfo = make_ref<NarInfo>(StorePath::fromBaseName(hashPart + "-" + namePart));
             narInfo->url = queryNAR.getStr(2);
             narInfo->compression = queryNAR.getStr(3);
             if (!queryNAR.isNull(4))
@@ -206,9 +203,9 @@ public:
             narInfo->narHash = Hash(queryNAR.getStr(6));
             narInfo->narSize = queryNAR.getInt(7);
             for (auto & r : tokenizeString<Strings>(queryNAR.getStr(8), " "))
-                narInfo->references.insert(cache.storeDir + "/" + r);
+                narInfo->references.insert(StorePath::fromBaseName(r));
             if (!queryNAR.isNull(9))
-                narInfo->deriver = cache.storeDir + "/" + queryNAR.getStr(9);
+                narInfo->deriver = StorePath::fromBaseName(queryNAR.getStr(9));
             for (auto & sig : tokenizeString<Strings>(queryNAR.getStr(10), " "))
                 narInfo->sigs.insert(sig);
             narInfo->ca = queryNAR.getStr(11);
@@ -230,12 +227,12 @@ public:
 
                 auto narInfo = std::dynamic_pointer_cast<const NarInfo>(info);
 
-                assert(hashPart == storePathToHash(info->path));
+                //assert(hashPart == storePathToHash(info->path));
 
                 state->insertNAR.use()
                     (cache.id)
                     (hashPart)
-                    (storePathToName(info->path))
+                    (std::string(info->path.name()))
                     (narInfo ? narInfo->url : "", narInfo != 0)
                     (narInfo ? narInfo->compression : "", narInfo != 0)
                     (narInfo && narInfo->fileHash ? narInfo->fileHash.to_string() : "", narInfo && narInfo->fileHash)
@@ -243,7 +240,7 @@ public:
                     (info->narHash.to_string())
                     (info->narSize)
                     (concatStringsSep(" ", info->shortRefs()))
-                    (info->deriver != "" ? baseNameOf(info->deriver) : "", info->deriver != "")
+                    (info->deriver ? std::string(info->deriver->to_string()) : "", (bool) info->deriver)
                     (concatStringsSep(" ", info->sigs))
                     (info->ca)
                     (time(0)).exec();
diff --git a/src/libstore/nar-info.cc b/src/libstore/nar-info.cc
index cb568ccdc..fb02cf3fd 100644
--- a/src/libstore/nar-info.cc
+++ b/src/libstore/nar-info.cc
@@ -4,6 +4,7 @@
 namespace nix {
 
 NarInfo::NarInfo(const Store & store, const std::string & s, const std::string & whence)
+    : ValidPathInfo(StorePath::make((unsigned char *) "xxxxxxxxxxxxxxxxxxxx", "x")) // FIXME: hack
 {
     auto corrupt = [&]() {
         throw Error(format("NAR info file '%1%' is corrupt") % whence);
@@ -18,6 +19,8 @@ NarInfo::NarInfo(const Store & store, const std::string & s, const std::string &
         }
     };
 
+    bool havePath = false;
+
     size_t pos = 0;
     while (pos < s.size()) {
 
@@ -32,8 +35,8 @@ NarInfo::NarInfo(const Store & store, const std::string & s, const std::string &
         std::string value(s, colon + 2, eol - colon - 2);
 
         if (name == "StorePath") {
-            if (!store.isStorePath(value)) corrupt();
-            path = value;
+            path = store.parseStorePath(value);
+            havePath = true;
         }
         else if (name == "URL")
             url = value;
@@ -52,18 +55,12 @@ NarInfo::NarInfo(const Store & store, const std::string & s, const std::string &
         else if (name == "References") {
             auto refs = tokenizeString<Strings>(value, " ");
             if (!references.empty()) corrupt();
-            for (auto & r : refs) {
-                auto r2 = store.storeDir + "/" + r;
-                if (!store.isStorePath(r2)) corrupt();
-                references.insert(r2);
-            }
+            for (auto & r : refs)
+                references.insert(StorePath::fromBaseName(r));
         }
         else if (name == "Deriver") {
-            if (value != "unknown-deriver") {
-                auto p = store.storeDir + "/" + value;
-                if (!store.isStorePath(p)) corrupt();
-                deriver = p;
-            }
+            if (value != "unknown-deriver")
+                deriver = StorePath::fromBaseName(value);
         }
         else if (name == "System")
             system = value;
@@ -79,13 +76,13 @@ NarInfo::NarInfo(const Store & store, const std::string & s, const std::string &
 
     if (compression == "") compression = "bzip2";
 
-    if (path.empty() || url.empty() || narSize == 0 || !narHash) corrupt();
+    if (!havePath || url.empty() || narSize == 0 || !narHash) corrupt();
 }
 
-std::string NarInfo::to_string() const
+std::string NarInfo::to_string(const Store & store) const
 {
     std::string res;
-    res += "StorePath: " + path + "\n";
+    res += "StorePath: " + store.printStorePath(path) + "\n";
     res += "URL: " + url + "\n";
     assert(compression != "");
     res += "Compression: " + compression + "\n";
@@ -98,8 +95,8 @@ std::string NarInfo::to_string() const
 
     res += "References: " + concatStringsSep(" ", shortRefs()) + "\n";
 
-    if (!deriver.empty())
-        res += "Deriver: " + baseNameOf(deriver) + "\n";
+    if (deriver)
+        res += "Deriver: " + std::string(deriver->to_string()) + "\n";
 
     if (!system.empty())
         res += "System: " + system + "\n";
diff --git a/src/libstore/nar-info.hh b/src/libstore/nar-info.hh
index 4995061fb..373c33427 100644
--- a/src/libstore/nar-info.hh
+++ b/src/libstore/nar-info.hh
@@ -14,11 +14,12 @@ struct NarInfo : ValidPathInfo
     uint64_t fileSize = 0;
     std::string system;
 
-    NarInfo() { }
+    NarInfo() = delete;
+    NarInfo(StorePath && path) : ValidPathInfo(std::move(path)) { }
     NarInfo(const ValidPathInfo & info) : ValidPathInfo(info) { }
     NarInfo(const Store & store, const std::string & s, const std::string & whence);
 
-    std::string to_string() const;
+    std::string to_string(const Store & store) const;
 };
 
 }
diff --git a/src/libstore/optimise-store.cc b/src/libstore/optimise-store.cc
index 991512f21..8ac382e9d 100644
--- a/src/libstore/optimise-store.cc
+++ b/src/libstore/optimise-store.cc
@@ -254,7 +254,7 @@ void LocalStore::optimiseStore(OptimiseStats & stats)
 {
     Activity act(*logger, actOptimiseStore);
 
-    PathSet paths = queryAllValidPaths();
+    auto paths = queryAllValidPaths();
     InodeHash inodeHash = loadInodeHash();
 
     act.progress(0, paths.size());
@@ -265,8 +265,8 @@ void LocalStore::optimiseStore(OptimiseStats & stats)
         addTempRoot(i);
         if (!isValidPath(i)) continue; /* path was GC'ed, probably */
         {
-            Activity act(*logger, lvlTalkative, actUnknown, fmt("optimising path '%s'", i));
-            optimisePath_(&act, stats, realStoreDir + "/" + baseNameOf(i), inodeHash);
+            Activity act(*logger, lvlTalkative, actUnknown, fmt("optimising path '%s'", printStorePath(i)));
+            optimisePath_(&act, stats, realStoreDir + "/" + std::string(i.to_string()), inodeHash);
         }
         done++;
         act.progress(done, paths.size());
diff --git a/src/libstore/parsed-derivations.cc b/src/libstore/parsed-derivations.cc
index 87be8a24e..d0f289a0f 100644
--- a/src/libstore/parsed-derivations.cc
+++ b/src/libstore/parsed-derivations.cc
@@ -2,8 +2,8 @@
 
 namespace nix {
 
-ParsedDerivation::ParsedDerivation(const Path & drvPath, BasicDerivation & drv)
-    : drvPath(drvPath), drv(drv)
+ParsedDerivation::ParsedDerivation(StorePath && drvPath, BasicDerivation & drv)
+    : drvPath(std::move(drvPath)), drv(drv)
 {
     /* Parse the __json attribute, if any. */
     auto jsonAttr = drv.env.find("__json");
@@ -11,7 +11,7 @@ ParsedDerivation::ParsedDerivation(const Path & drvPath, BasicDerivation & drv)
         try {
             structuredAttrs = nlohmann::json::parse(jsonAttr->second);
         } catch (std::exception & e) {
-            throw Error("cannot process __json attribute of '%s': %s", drvPath, e.what());
+            throw Error("cannot process __json attribute of '%s': %s", drvPath.to_string(), e.what());
         }
     }
 }
@@ -24,7 +24,7 @@ std::optional<std::string> ParsedDerivation::getStringAttr(const std::string & n
             return {};
         else {
             if (!i->is_string())
-                throw Error("attribute '%s' of derivation '%s' must be a string", name, drvPath);
+                throw Error("attribute '%s' of derivation '%s' must be a string", name, drvPath.to_string());
             return i->get<std::string>();
         }
     } else {
@@ -44,7 +44,7 @@ bool ParsedDerivation::getBoolAttr(const std::string & name, bool def) const
             return def;
         else {
             if (!i->is_boolean())
-                throw Error("attribute '%s' of derivation '%s' must be a Boolean", name, drvPath);
+                throw Error("attribute '%s' of derivation '%s' must be a Boolean", name, drvPath.to_string());
             return i->get<bool>();
         }
     } else {
@@ -64,11 +64,11 @@ std::optional<Strings> ParsedDerivation::getStringsAttr(const std::string & name
             return {};
         else {
             if (!i->is_array())
-                throw Error("attribute '%s' of derivation '%s' must be a list of strings", name, drvPath);
+                throw Error("attribute '%s' of derivation '%s' must be a list of strings", name, drvPath.to_string());
             Strings res;
             for (auto j = i->begin(); j != i->end(); ++j) {
                 if (!j->is_string())
-                    throw Error("attribute '%s' of derivation '%s' must be a list of strings", name, drvPath);
+                    throw Error("attribute '%s' of derivation '%s' must be a list of strings", name, drvPath.to_string());
                 res.push_back(j->get<std::string>());
             }
             return res;
diff --git a/src/libstore/parsed-derivations.hh b/src/libstore/parsed-derivations.hh
index 9bde4b4dc..cec868754 100644
--- a/src/libstore/parsed-derivations.hh
+++ b/src/libstore/parsed-derivations.hh
@@ -6,13 +6,13 @@ namespace nix {
 
 class ParsedDerivation
 {
-    Path drvPath;
+    StorePath drvPath;
     BasicDerivation & drv;
     std::optional<nlohmann::json> structuredAttrs;
 
 public:
 
-    ParsedDerivation(const Path & drvPath, BasicDerivation & drv);
+    ParsedDerivation(StorePath && drvPath, BasicDerivation & drv);
 
     const std::optional<nlohmann::json> & getStructuredAttrs() const
     {
diff --git a/src/libstore/path.cc b/src/libstore/path.cc
new file mode 100644
index 000000000..81ae495a1
--- /dev/null
+++ b/src/libstore/path.cc
@@ -0,0 +1,99 @@
+#include "store-api.hh"
+
+namespace nix {
+
+extern "C" {
+    rust::Result<StorePath> ffi_StorePath_new(rust::StringSlice path, rust::StringSlice storeDir);
+    rust::Result<StorePath> ffi_StorePath_new2(unsigned char hash[20], rust::StringSlice storeDir);
+    rust::Result<StorePath> ffi_StorePath_fromBaseName(rust::StringSlice baseName);
+    rust::String ffi_StorePath_to_string(const StorePath & _this);
+    StorePath ffi_StorePath_clone(const StorePath & _this);
+    rust::StringSlice ffi_StorePath_name(const StorePath & _this);
+}
+
+StorePath StorePath::make(std::string_view path, std::string_view storeDir)
+{
+    return ffi_StorePath_new((rust::StringSlice) path, (rust::StringSlice) storeDir).unwrap();
+}
+
+StorePath StorePath::make(unsigned char hash[20], std::string_view name)
+{
+    return ffi_StorePath_new2(hash, (rust::StringSlice) name).unwrap();
+}
+
+StorePath StorePath::fromBaseName(std::string_view baseName)
+{
+    return ffi_StorePath_fromBaseName((rust::StringSlice) baseName).unwrap();
+}
+
+rust::String StorePath::to_string() const
+{
+    return ffi_StorePath_to_string(*this);
+}
+
+StorePath StorePath::clone() const
+{
+    return ffi_StorePath_clone(*this);
+}
+
+bool StorePath::isDerivation() const
+{
+    return hasSuffix(name(), drvExtension);
+}
+
+std::string_view StorePath::name() const
+{
+    return ffi_StorePath_name(*this);
+}
+
+StorePath Store::parseStorePath(std::string_view path) const
+{
+    return StorePath::make(path, storeDir);
+}
+
+
+StorePathSet Store::parseStorePathSet(const PathSet & paths) const
+{
+    StorePathSet res;
+    for (auto & i : paths) res.insert(parseStorePath(i));
+    return res;
+}
+
+std::string Store::printStorePath(const StorePath & path) const
+{
+    auto s = storeDir + "/";
+    s += (std::string_view) path.to_string();
+    return s;
+}
+
+PathSet Store::printStorePathSet(const StorePathSet & paths) const
+{
+    PathSet res;
+    for (auto & i : paths) res.insert(printStorePath(i));
+    return res;
+}
+
+StorePathSet cloneStorePathSet(const StorePathSet & paths)
+{
+    StorePathSet res;
+    for (auto & p : paths)
+        res.insert(p.clone());
+    return res;
+}
+
+StorePathSet storePathsToSet(const StorePaths & paths)
+{
+    StorePathSet res;
+    for (auto & p : paths)
+        res.insert(p.clone());
+    return res;
+}
+
+StorePathSet singleton(const StorePath & path)
+{
+    StorePathSet res;
+    res.insert(path.clone());
+    return res;
+}
+
+}
diff --git a/src/libstore/path.hh b/src/libstore/path.hh
new file mode 100644
index 000000000..273808f02
--- /dev/null
+++ b/src/libstore/path.hh
@@ -0,0 +1,81 @@
+#pragma once
+
+#include "rust-ffi.hh"
+
+namespace nix {
+
+/* See path.rs. */
+struct StorePath;
+
+extern "C" {
+    void ffi_StorePath_drop(void *);
+    bool ffi_StorePath_less_than(const StorePath & a, const StorePath & b);
+    bool ffi_StorePath_eq(const StorePath & a, const StorePath & b);
+    unsigned char * ffi_StorePath_hash_data(const StorePath & p);
+}
+
+struct StorePath : rust::Value<3 * sizeof(void *) + 24, ffi_StorePath_drop>
+{
+    static StorePath make(std::string_view path, std::string_view storeDir);
+
+    static StorePath make(unsigned char hash[20], std::string_view name);
+
+    static StorePath fromBaseName(std::string_view baseName);
+
+    rust::String to_string() const;
+
+    bool operator < (const StorePath & other) const
+    {
+        return ffi_StorePath_less_than(*this, other);
+    }
+
+    bool operator == (const StorePath & other) const
+    {
+        return ffi_StorePath_eq(*this, other);
+    }
+
+    bool operator != (const StorePath & other) const
+    {
+        return !(*this == other);
+    }
+
+    StorePath clone() const;
+
+    /* Check whether a file name ends with the extension for
+       derivations. */
+    bool isDerivation() const;
+
+    std::string_view name() const;
+
+    unsigned char * hashData() const
+    {
+        return ffi_StorePath_hash_data(*this);
+    }
+};
+
+typedef std::set<StorePath> StorePathSet;
+typedef std::vector<StorePath> StorePaths;
+
+StorePathSet cloneStorePathSet(const StorePathSet & paths);
+StorePathSet storePathsToSet(const StorePaths & paths);
+
+StorePathSet singleton(const StorePath & path);
+
+/* Size of the hash part of store paths, in base-32 characters. */
+const size_t storePathHashLen = 32; // i.e. 160 bits
+
+/* Extension of derivations in the Nix store. */
+const std::string drvExtension = ".drv";
+
+}
+
+namespace std {
+
+template<> struct hash<nix::StorePath> {
+    std::size_t operator()(const nix::StorePath & path) const noexcept
+    {
+        return * (std::size_t *) path.hashData();
+    }
+};
+
+}
diff --git a/src/libstore/profiles.cc b/src/libstore/profiles.cc
index 4c6af567a..dae3f2d32 100644
--- a/src/libstore/profiles.cc
+++ b/src/libstore/profiles.cc
@@ -40,7 +40,7 @@ Generations findGenerations(Path profile, int & curGen)
     Generations gens;
 
     Path profileDir = dirOf(profile);
-    string profileName = baseNameOf(profile);
+    auto profileName = std::string(baseNameOf(profile));
 
     for (auto & i : readDirectory(profileDir)) {
         int n;
@@ -108,7 +108,7 @@ Path createGeneration(ref<LocalFSStore> store, Path profile, Path outPath)
        user environment etc. we've just built. */
     Path generation;
     makeName(profile, num + 1, generation);
-    store->addPermRoot(outPath, generation, false, true);
+    store->addPermRoot(store->parseStorePath(outPath), generation, false, true);
 
     return generation;
 }
diff --git a/src/libstore/references.cc b/src/libstore/references.cc
index 605ca9815..102e15921 100644
--- a/src/libstore/references.cc
+++ b/src/libstore/references.cc
@@ -89,7 +89,7 @@ PathSet scanForReferences(const string & path,
        hash part of the file name.  (This assumes that all references
        have the form `HASH-bla'). */
     for (auto & i : refs) {
-        string baseName = baseNameOf(i);
+        auto baseName = std::string(baseNameOf(i));
         string::size_type pos = baseName.find('-');
         if (pos == string::npos)
             throw Error(format("bad reference '%1%'") % i);
diff --git a/src/libstore/remote-fs-accessor.cc b/src/libstore/remote-fs-accessor.cc
index 5233fb2c2..5a2d103b9 100644
--- a/src/libstore/remote-fs-accessor.cc
+++ b/src/libstore/remote-fs-accessor.cc
@@ -50,7 +50,7 @@ std::pair<ref<FSAccessor>, Path> RemoteFSAccessor::fetch(const Path & path_)
     auto storePath = store->toStorePath(path);
     std::string restPath = std::string(path, storePath.size());
 
-    if (!store->isValidPath(storePath))
+    if (!store->isValidPath(store->parseStorePath(storePath)))
         throw InvalidPath(format("path '%1%' is not a valid store path") % storePath);
 
     auto i = nars.find(storePath);
@@ -96,7 +96,7 @@ std::pair<ref<FSAccessor>, Path> RemoteFSAccessor::fetch(const Path & path_)
         } catch (SysError &) { }
     }
 
-    store->narFromPath(storePath, sink);
+    store->narFromPath(store->parseStorePath(storePath), sink);
     auto narAccessor = makeNarAccessor(sink.s);
     addToCache(storePath, *sink.s, narAccessor);
     return {narAccessor, restPath};
diff --git a/src/libstore/remote-store.cc b/src/libstore/remote-store.cc
index 2a89b7c98..8c55da268 100644
--- a/src/libstore/remote-store.cc
+++ b/src/libstore/remote-store.cc
@@ -22,23 +22,22 @@
 namespace nix {
 
 
-Path readStorePath(Store & store, Source & from)
+template<> StorePathSet readStorePaths(const Store & store, Source & from)
 {
-    Path path = readString(from);
-    store.assertStorePath(path);
-    return path;
-}
-
-
-template<class T> T readStorePaths(Store & store, Source & from)
-{
-    T paths = readStrings<T>(from);
-    for (auto & i : paths) store.assertStorePath(i);
+    StorePathSet paths;
+    for (auto & i : readStrings<Strings>(from))
+        paths.insert(store.parseStorePath(i));
     return paths;
 }
 
-template PathSet readStorePaths(Store & store, Source & from);
-template Paths readStorePaths(Store & store, Source & from);
+
+void writeStorePaths(const Store & store, Sink & out, const StorePathSet & paths)
+{
+    out << paths.size();
+    for (auto & i : paths)
+        out << store.printStorePath(i);
+}
+
 
 /* TODO: Separate these store impls into different files, give them better names */
 RemoteStore::RemoteStore(const Params & params)
@@ -254,60 +253,62 @@ ConnectionHandle RemoteStore::getConnection()
 }
 
 
-bool RemoteStore::isValidPathUncached(const Path & path)
+bool RemoteStore::isValidPathUncached(const StorePath & path)
 {
     auto conn(getConnection());
-    conn->to << wopIsValidPath << path;
+    conn->to << wopIsValidPath << printStorePath(path);
     conn.processStderr();
     return readInt(conn->from);
 }
 
 
-PathSet RemoteStore::queryValidPaths(const PathSet & paths, SubstituteFlag maybeSubstitute)
+StorePathSet RemoteStore::queryValidPaths(const StorePathSet & paths, SubstituteFlag maybeSubstitute)
 {
     auto conn(getConnection());
     if (GET_PROTOCOL_MINOR(conn->daemonVersion) < 12) {
-        PathSet res;
+        StorePathSet res;
         for (auto & i : paths)
-            if (isValidPath(i)) res.insert(i);
+            if (isValidPath(i)) res.insert(i.clone());
         return res;
     } else {
-        conn->to << wopQueryValidPaths << paths;
+        conn->to << wopQueryValidPaths;
+        writeStorePaths(*this, conn->to, paths);
         conn.processStderr();
-        return readStorePaths<PathSet>(*this, conn->from);
+        return readStorePaths<StorePathSet>(*this, conn->from);
     }
 }
 
 
-PathSet RemoteStore::queryAllValidPaths()
+StorePathSet RemoteStore::queryAllValidPaths()
 {
     auto conn(getConnection());
     conn->to << wopQueryAllValidPaths;
     conn.processStderr();
-    return readStorePaths<PathSet>(*this, conn->from);
+    return readStorePaths<StorePathSet>(*this, conn->from);
 }
 
 
-PathSet RemoteStore::querySubstitutablePaths(const PathSet & paths)
+StorePathSet RemoteStore::querySubstitutablePaths(const StorePathSet & paths)
 {
     auto conn(getConnection());
     if (GET_PROTOCOL_MINOR(conn->daemonVersion) < 12) {
-        PathSet res;
+        StorePathSet res;
         for (auto & i : paths) {
-            conn->to << wopHasSubstitutes << i;
+            conn->to << wopHasSubstitutes << printStorePath(i);
             conn.processStderr();
-            if (readInt(conn->from)) res.insert(i);
+            if (readInt(conn->from)) res.insert(i.clone());
         }
         return res;
     } else {
-        conn->to << wopQuerySubstitutablePaths << paths;
+        conn->to << wopQuerySubstitutablePaths;
+        writeStorePaths(*this, conn->to, paths);
         conn.processStderr();
-        return readStorePaths<PathSet>(*this, conn->from);
+        return readStorePaths<StorePathSet>(*this, conn->from);
     }
 }
 
 
-void RemoteStore::querySubstitutablePathInfos(const PathSet & paths,
+void RemoteStore::querySubstitutablePathInfos(const StorePathSet & paths,
     SubstitutablePathInfos & infos)
 {
     if (paths.empty()) return;
@@ -318,29 +319,31 @@ void RemoteStore::querySubstitutablePathInfos(const PathSet & paths,
 
         for (auto & i : paths) {
             SubstitutablePathInfo info;
-            conn->to << wopQuerySubstitutablePathInfo << i;
+            conn->to << wopQuerySubstitutablePathInfo << printStorePath(i);
             conn.processStderr();
             unsigned int reply = readInt(conn->from);
             if (reply == 0) continue;
-            info.deriver = readString(conn->from);
-            if (info.deriver != "") assertStorePath(info.deriver);
-            info.references = readStorePaths<PathSet>(*this, conn->from);
+            auto deriver = readString(conn->from);
+            if (deriver != "")
+                info.deriver = parseStorePath(deriver);
+            info.references = readStorePaths<StorePathSet>(*this, conn->from);
             info.downloadSize = readLongLong(conn->from);
             info.narSize = readLongLong(conn->from);
-            infos[i] = info;
+            infos.insert_or_assign(i.clone(), std::move(info));
         }
 
     } else {
 
-        conn->to << wopQuerySubstitutablePathInfos << paths;
+        conn->to << wopQuerySubstitutablePathInfos;
+        writeStorePaths(*this, conn->to, paths);
         conn.processStderr();
         size_t count = readNum<size_t>(conn->from);
         for (size_t n = 0; n < count; n++) {
-            Path path = readStorePath(*this, conn->from);
-            SubstitutablePathInfo & info(infos[path]);
-            info.deriver = readString(conn->from);
-            if (info.deriver != "") assertStorePath(info.deriver);
-            info.references = readStorePaths<PathSet>(*this, conn->from);
+            SubstitutablePathInfo & info(infos[parseStorePath(readString(conn->from))]);
+            auto deriver = readString(conn->from);
+            if (deriver != "")
+                info.deriver = parseStorePath(deriver);
+            info.references = readStorePaths<StorePathSet>(*this, conn->from);
             info.downloadSize = readLongLong(conn->from);
             info.narSize = readLongLong(conn->from);
         }
@@ -349,14 +352,14 @@ void RemoteStore::querySubstitutablePathInfos(const PathSet & paths,
 }
 
 
-void RemoteStore::queryPathInfoUncached(const Path & path,
+void RemoteStore::queryPathInfoUncached(const StorePath & path,
     Callback<std::shared_ptr<const ValidPathInfo>> callback) noexcept
 {
     try {
         std::shared_ptr<ValidPathInfo> info;
         {
             auto conn(getConnection());
-            conn->to << wopQueryPathInfo << path;
+            conn->to << wopQueryPathInfo << printStorePath(path);
             try {
                 conn.processStderr();
             } catch (Error & e) {
@@ -367,14 +370,13 @@ void RemoteStore::queryPathInfoUncached(const Path & path,
             }
             if (GET_PROTOCOL_MINOR(conn->daemonVersion) >= 17) {
                 bool valid; conn->from >> valid;
-                if (!valid) throw InvalidPath(format("path '%s' is not valid") % path);
+                if (!valid) throw InvalidPath("path '%s' is not valid", printStorePath(path));
             }
-            info = std::make_shared<ValidPathInfo>();
-            info->path = path;
-            info->deriver = readString(conn->from);
-            if (info->deriver != "") assertStorePath(info->deriver);
+            info = std::make_shared<ValidPathInfo>(path.clone());
+            auto deriver = readString(conn->from);
+            if (deriver != "") info->deriver = parseStorePath(deriver);
             info->narHash = Hash(readString(conn->from), htSHA256);
-            info->references = readStorePaths<PathSet>(*this, conn->from);
+            info->references = readStorePaths<StorePathSet>(*this, conn->from);
             conn->from >> info->registrationTime >> info->narSize;
             if (GET_PROTOCOL_MINOR(conn->daemonVersion) >= 16) {
                 conn->from >> info->ultimate;
@@ -387,52 +389,52 @@ void RemoteStore::queryPathInfoUncached(const Path & path,
 }
 
 
-void RemoteStore::queryReferrers(const Path & path,
-    PathSet & referrers)
+void RemoteStore::queryReferrers(const StorePath & path,
+    StorePathSet & referrers)
 {
     auto conn(getConnection());
-    conn->to << wopQueryReferrers << path;
+    conn->to << wopQueryReferrers << printStorePath(path);
     conn.processStderr();
-    PathSet referrers2 = readStorePaths<PathSet>(*this, conn->from);
-    referrers.insert(referrers2.begin(), referrers2.end());
+    for (auto & i : readStorePaths<StorePathSet>(*this, conn->from))
+        referrers.insert(i.clone());
 }
 
 
-PathSet RemoteStore::queryValidDerivers(const Path & path)
+StorePathSet RemoteStore::queryValidDerivers(const StorePath & path)
 {
     auto conn(getConnection());
-    conn->to << wopQueryValidDerivers << path;
+    conn->to << wopQueryValidDerivers << printStorePath(path);
     conn.processStderr();
-    return readStorePaths<PathSet>(*this, conn->from);
+    return readStorePaths<StorePathSet>(*this, conn->from);
 }
 
 
-PathSet RemoteStore::queryDerivationOutputs(const Path & path)
+StorePathSet RemoteStore::queryDerivationOutputs(const StorePath & path)
 {
     auto conn(getConnection());
-    conn->to << wopQueryDerivationOutputs << path;
+    conn->to << wopQueryDerivationOutputs << printStorePath(path);
     conn.processStderr();
-    return readStorePaths<PathSet>(*this, conn->from);
+    return readStorePaths<StorePathSet>(*this, conn->from);
 }
 
 
-PathSet RemoteStore::queryDerivationOutputNames(const Path & path)
+PathSet RemoteStore::queryDerivationOutputNames(const StorePath & path)
 {
     auto conn(getConnection());
-    conn->to << wopQueryDerivationOutputNames << path;
+    conn->to << wopQueryDerivationOutputNames << printStorePath(path);
     conn.processStderr();
     return readStrings<PathSet>(conn->from);
 }
 
 
-Path RemoteStore::queryPathFromHashPart(const string & hashPart)
+std::optional<StorePath> RemoteStore::queryPathFromHashPart(const std::string & hashPart)
 {
     auto conn(getConnection());
     conn->to << wopQueryPathFromHashPart << hashPart;
     conn.processStderr();
     Path path = readString(conn->from);
-    if (!path.empty()) assertStorePath(path);
-    return path;
+    if (path.empty()) return {};
+    return parseStorePath(path);
 }
 
 
@@ -450,9 +452,10 @@ void RemoteStore::addToStore(const ValidPathInfo & info, Source & source,
             copyNAR(source, sink);
             sink
                 << exportMagic
-                << info.path
-                << info.references
-                << info.deriver
+                << printStorePath(info.path);
+            writeStorePaths(*this, sink, info.references);
+            sink
+                << (info.deriver ? printStorePath(*info.deriver) : "")
                 << 0 // == no legacy signature
                 << 0 // == no path follows
                 ;
@@ -460,14 +463,17 @@ void RemoteStore::addToStore(const ValidPathInfo & info, Source & source,
 
         conn.processStderr(0, source2.get());
 
-        auto importedPaths = readStorePaths<PathSet>(*this, conn->from);
+        auto importedPaths = readStorePaths<StorePathSet>(*this, conn->from);
         assert(importedPaths.size() <= 1);
     }
 
     else {
         conn->to << wopAddToStoreNar
-                 << info.path << info.deriver << info.narHash.to_string(Base16, false)
-                 << info.references << info.registrationTime << info.narSize
+                 << printStorePath(info.path)
+                 << (info.deriver ? printStorePath(*info.deriver) : "")
+                 << info.narHash.to_string(Base16, false);
+        writeStorePaths(*this, conn->to, info.references);
+        conn->to << info.registrationTime << info.narSize
                  << info.ultimate << info.sigs << info.ca
                  << repair << !checkSigs;
         bool tunnel = GET_PROTOCOL_MINOR(conn->daemonVersion) >= 21;
@@ -477,7 +483,7 @@ void RemoteStore::addToStore(const ValidPathInfo & info, Source & source,
 }
 
 
-Path RemoteStore::addToStore(const string & name, const Path & _srcPath,
+StorePath RemoteStore::addToStore(const string & name, const Path & _srcPath,
     bool recursive, HashType hashAlgo, PathFilter & filter, RepairFlag repair)
 {
     if (repair) throw Error("repairing is not supported when building through the Nix daemon");
@@ -511,54 +517,52 @@ Path RemoteStore::addToStore(const string & name, const Path & _srcPath,
         throw;
     }
 
-    return readStorePath(*this, conn->from);
+    return parseStorePath(readString(conn->from));
 }
 
 
-Path RemoteStore::addTextToStore(const string & name, const string & s,
-    const PathSet & references, RepairFlag repair)
+StorePath RemoteStore::addTextToStore(const string & name, const string & s,
+    const StorePathSet & references, RepairFlag repair)
 {
     if (repair) throw Error("repairing is not supported when building through the Nix daemon");
 
     auto conn(getConnection());
-    conn->to << wopAddTextToStore << name << s << references;
+    conn->to << wopAddTextToStore << name << s;
+    writeStorePaths(*this, conn->to, references);
 
     conn.processStderr();
-    return readStorePath(*this, conn->from);
+    return parseStorePath(readString(conn->from));
 }
 
 
-void RemoteStore::buildPaths(const PathSet & drvPaths, BuildMode buildMode)
+void RemoteStore::buildPaths(const std::vector<StorePathWithOutputs> & drvPaths, BuildMode buildMode)
 {
     auto conn(getConnection());
     conn->to << wopBuildPaths;
-    if (GET_PROTOCOL_MINOR(conn->daemonVersion) >= 13) {
-        conn->to << drvPaths;
-        if (GET_PROTOCOL_MINOR(conn->daemonVersion) >= 15)
-            conn->to << buildMode;
-        else
-            /* Old daemons did not take a 'buildMode' parameter, so we
-               need to validate it here on the client side.  */
-            if (buildMode != bmNormal)
-                throw Error("repairing or checking is not supported when building through the Nix daemon");
-    } else {
-        /* For backwards compatibility with old daemons, strip output
-           identifiers. */
-        PathSet drvPaths2;
-        for (auto & i : drvPaths)
-            drvPaths2.insert(string(i, 0, i.find('!')));
-        conn->to << drvPaths2;
-    }
+    assert(GET_PROTOCOL_MINOR(conn->daemonVersion) >= 13);
+    Strings ss;
+    for (auto & p : drvPaths)
+        ss.push_back(p.to_string(*this));
+    conn->to << ss;
+    if (GET_PROTOCOL_MINOR(conn->daemonVersion) >= 15)
+        conn->to << buildMode;
+    else
+        /* Old daemons did not take a 'buildMode' parameter, so we
+           need to validate it here on the client side.  */
+        if (buildMode != bmNormal)
+            throw Error("repairing or checking is not supported when building through the Nix daemon");
     conn.processStderr();
     readInt(conn->from);
 }
 
 
-BuildResult RemoteStore::buildDerivation(const Path & drvPath, const BasicDerivation & drv,
+BuildResult RemoteStore::buildDerivation(const StorePath & drvPath, const BasicDerivation & drv,
     BuildMode buildMode)
 {
     auto conn(getConnection());
-    conn->to << wopBuildDerivation << drvPath << drv << buildMode;
+    conn->to << wopBuildDerivation << printStorePath(drvPath);
+    writeDerivation(conn->to, *this, drv);
+    conn->to << buildMode;
     conn.processStderr();
     BuildResult res;
     unsigned int status;
@@ -568,19 +572,19 @@ BuildResult RemoteStore::buildDerivation(const Path & drvPath, const BasicDeriva
 }
 
 
-void RemoteStore::ensurePath(const Path & path)
+void RemoteStore::ensurePath(const StorePath & path)
 {
     auto conn(getConnection());
-    conn->to << wopEnsurePath << path;
+    conn->to << wopEnsurePath << printStorePath(path);
     conn.processStderr();
     readInt(conn->from);
 }
 
 
-void RemoteStore::addTempRoot(const Path & path)
+void RemoteStore::addTempRoot(const StorePath & path)
 {
     auto conn(getConnection());
-    conn->to << wopAddTempRoot << path;
+    conn->to << wopAddTempRoot << printStorePath(path);
     conn.processStderr();
     readInt(conn->from);
 }
@@ -613,8 +617,8 @@ Roots RemoteStore::findRoots(bool censor)
     Roots result;
     while (count--) {
         Path link = readString(conn->from);
-        Path target = readStorePath(*this, conn->from);
-        result[target].emplace(link);
+        auto target = parseStorePath(readString(conn->from));
+        result[std::move(target)].emplace(link);
     }
     return result;
 }
@@ -625,7 +629,9 @@ void RemoteStore::collectGarbage(const GCOptions & options, GCResults & results)
     auto conn(getConnection());
 
     conn->to
-        << wopCollectGarbage << options.action << options.pathsToDelete << options.ignoreLiveness
+        << wopCollectGarbage << options.action;
+    writeStorePaths(*this, conn->to, options.pathsToDelete);
+    conn->to << options.ignoreLiveness
         << options.maxFreed
         /* removed options */
         << 0 << 0 << 0;
@@ -661,17 +667,17 @@ bool RemoteStore::verifyStore(bool checkContents, RepairFlag repair)
 }
 
 
-void RemoteStore::addSignatures(const Path & storePath, const StringSet & sigs)
+void RemoteStore::addSignatures(const StorePath & storePath, const StringSet & sigs)
 {
     auto conn(getConnection());
-    conn->to << wopAddSignatures << storePath << sigs;
+    conn->to << wopAddSignatures << printStorePath(storePath) << sigs;
     conn.processStderr();
     readInt(conn->from);
 }
 
 
-void RemoteStore::queryMissing(const PathSet & targets,
-    PathSet & willBuild, PathSet & willSubstitute, PathSet & unknown,
+void RemoteStore::queryMissing(const std::vector<StorePathWithOutputs> & targets,
+    StorePathSet & willBuild, StorePathSet & willSubstitute, StorePathSet & unknown,
     unsigned long long & downloadSize, unsigned long long & narSize)
 {
     {
@@ -680,11 +686,15 @@ void RemoteStore::queryMissing(const PathSet & targets,
             // Don't hold the connection handle in the fallback case
             // to prevent a deadlock.
             goto fallback;
-        conn->to << wopQueryMissing << targets;
+        conn->to << wopQueryMissing;
+        Strings ss;
+        for (auto & p : targets)
+            ss.push_back(p.to_string(*this));
+        conn->to << ss;
         conn.processStderr();
-        willBuild = readStorePaths<PathSet>(*this, conn->from);
-        willSubstitute = readStorePaths<PathSet>(*this, conn->from);
-        unknown = readStorePaths<PathSet>(*this, conn->from);
+        willBuild = readStorePaths<StorePathSet>(*this, conn->from);
+        willSubstitute = readStorePaths<StorePathSet>(*this, conn->from);
+        unknown = readStorePaths<StorePathSet>(*this, conn->from);
         conn->from >> downloadSize >> narSize;
         return;
     }
diff --git a/src/libstore/remote-store.hh b/src/libstore/remote-store.hh
index 728df8b00..f301a97d8 100644
--- a/src/libstore/remote-store.hh
+++ b/src/libstore/remote-store.hh
@@ -35,50 +35,50 @@ public:
 
     /* Implementations of abstract store API methods. */
 
-    bool isValidPathUncached(const Path & path) override;
+    bool isValidPathUncached(const StorePath & path) override;
 
-    PathSet queryValidPaths(const PathSet & paths,
+    StorePathSet queryValidPaths(const StorePathSet & paths,
         SubstituteFlag maybeSubstitute = NoSubstitute) override;
 
-    PathSet queryAllValidPaths() override;
+    StorePathSet queryAllValidPaths() override;
 
-    void queryPathInfoUncached(const Path & path,
+    void queryPathInfoUncached(const StorePath & path,
         Callback<std::shared_ptr<const ValidPathInfo>> callback) noexcept override;
 
-    void queryReferrers(const Path & path, PathSet & referrers) override;
+    void queryReferrers(const StorePath & path, StorePathSet & referrers) override;
 
-    PathSet queryValidDerivers(const Path & path) override;
+    StorePathSet queryValidDerivers(const StorePath & path) override;
 
-    PathSet queryDerivationOutputs(const Path & path) override;
+    StorePathSet queryDerivationOutputs(const StorePath & path) override;
 
-    StringSet queryDerivationOutputNames(const Path & path) override;
+    StringSet queryDerivationOutputNames(const StorePath & path) override;
 
-    Path queryPathFromHashPart(const string & hashPart) override;
+    std::optional<StorePath> queryPathFromHashPart(const std::string & hashPart) override;
 
-    PathSet querySubstitutablePaths(const PathSet & paths) override;
+    StorePathSet querySubstitutablePaths(const StorePathSet & paths) override;
 
-    void querySubstitutablePathInfos(const PathSet & paths,
+    void querySubstitutablePathInfos(const StorePathSet & paths,
         SubstitutablePathInfos & infos) override;
 
     void addToStore(const ValidPathInfo & info, Source & nar,
         RepairFlag repair, CheckSigsFlag checkSigs,
         std::shared_ptr<FSAccessor> accessor) override;
 
-    Path addToStore(const string & name, const Path & srcPath,
+    StorePath addToStore(const string & name, const Path & srcPath,
         bool recursive = true, HashType hashAlgo = htSHA256,
         PathFilter & filter = defaultPathFilter, RepairFlag repair = NoRepair) override;
 
-    Path addTextToStore(const string & name, const string & s,
-        const PathSet & references, RepairFlag repair) override;
+    StorePath addTextToStore(const string & name, const string & s,
+        const StorePathSet & references, RepairFlag repair) override;
 
-    void buildPaths(const PathSet & paths, BuildMode buildMode) override;
+    void buildPaths(const std::vector<StorePathWithOutputs> & paths, BuildMode buildMode) override;
 
-    BuildResult buildDerivation(const Path & drvPath, const BasicDerivation & drv,
+    BuildResult buildDerivation(const StorePath & drvPath, const BasicDerivation & drv,
         BuildMode buildMode) override;
 
-    void ensurePath(const Path & path) override;
+    void ensurePath(const StorePath & path) override;
 
-    void addTempRoot(const Path & path) override;
+    void addTempRoot(const StorePath & path) override;
 
     void addIndirectRoot(const Path & path) override;
 
@@ -92,10 +92,10 @@ public:
 
     bool verifyStore(bool checkContents, RepairFlag repair) override;
 
-    void addSignatures(const Path & storePath, const StringSet & sigs) override;
+    void addSignatures(const StorePath & storePath, const StringSet & sigs) override;
 
-    void queryMissing(const PathSet & targets,
-        PathSet & willBuild, PathSet & willSubstitute, PathSet & unknown,
+    void queryMissing(const std::vector<StorePathWithOutputs> & targets,
+        StorePathSet & willBuild, StorePathSet & willSubstitute, StorePathSet & unknown,
         unsigned long long & downloadSize, unsigned long long & narSize) override;
 
     void connect() override;
diff --git a/src/libstore/s3-binary-cache-store.cc b/src/libstore/s3-binary-cache-store.cc
index cd547a964..58966a5b7 100644
--- a/src/libstore/s3-binary-cache-store.cc
+++ b/src/libstore/s3-binary-cache-store.cc
@@ -222,7 +222,7 @@ struct S3BinaryCacheStoreImpl : public S3BinaryCacheStore
        fetches the .narinfo file, rather than first checking for its
        existence via a HEAD request. Since .narinfos are small, doing
        a GET is unlikely to be slower than HEAD. */
-    bool isValidPathUncached(const Path & storePath) override
+    bool isValidPathUncached(const StorePath & storePath) override
     {
         try {
             queryPathInfo(storePath);
@@ -382,9 +382,9 @@ struct S3BinaryCacheStoreImpl : public S3BinaryCacheStore
             throw NoSuchBinaryCacheFile("file '%s' does not exist in binary cache '%s'", path, getUri());
     }
 
-    PathSet queryAllValidPaths() override
+    StorePathSet queryAllValidPaths() override
     {
-        PathSet paths;
+        StorePathSet paths;
         std::string marker;
 
         do {
@@ -405,7 +405,7 @@ struct S3BinaryCacheStoreImpl : public S3BinaryCacheStore
             for (auto object : contents) {
                 auto & key = object.GetKey();
                 if (key.size() != 40 || !hasSuffix(key, ".narinfo")) continue;
-                paths.insert(storeDir + "/" + key.substr(0, key.size() - 8));
+                paths.insert(parseStorePath(storeDir + "/" + key.substr(0, key.size() - 8) + "-unknown"));
             }
 
             marker = res.GetNextMarker();
diff --git a/src/libstore/ssh-store.cc b/src/libstore/ssh-store.cc
index b9d0c41ea..42ee06501 100644
--- a/src/libstore/ssh-store.cc
+++ b/src/libstore/ssh-store.cc
@@ -38,7 +38,7 @@ public:
     bool sameMachine() override
     { return false; }
 
-    void narFromPath(const Path & path, Sink & sink) override;
+    void narFromPath(const StorePath & path, Sink & sink) override;
 
     ref<FSAccessor> getFSAccessor() override;
 
@@ -66,10 +66,10 @@ private:
     };
 };
 
-void SSHStore::narFromPath(const Path & path, Sink & sink)
+void SSHStore::narFromPath(const StorePath & path, Sink & sink)
 {
     auto conn(connections->get());
-    conn->to << wopNarFromPath << path;
+    conn->to << wopNarFromPath << printStorePath(path);
     conn->processStderr();
     copyNAR(conn->from, sink);
 }
diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index 7e548ecd2..c98931885 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -27,13 +27,6 @@ bool Store::isStorePath(const Path & path) const
 }
 
 
-void Store::assertStorePath(const Path & path) const
-{
-    if (!isStorePath(path))
-        throw Error(format("path '%1%' is not in the Nix store") % path);
-}
-
-
 Path Store::toStorePath(const Path & path) const
 {
     if (!isInStore(path))
@@ -60,17 +53,9 @@ Path Store::followLinksToStore(const Path & _path) const
 }
 
 
-Path Store::followLinksToStorePath(const Path & path) const
+StorePath Store::followLinksToStorePath(const Path & path) const
 {
-    return toStorePath(followLinksToStore(path));
-}
-
-
-string storePathToName(const Path & path)
-{
-    auto base = baseNameOf(path);
-    assert(base.size() == storePathHashLen || (base.size() > storePathHashLen && base[storePathHashLen] == '-'));
-    return base.size() == storePathHashLen ? "" : string(base, storePathHashLen + 1);
+    return parseStorePath(toStorePath(followLinksToStore(path)));
 }
 
 
@@ -82,41 +67,6 @@ string storePathToHash(const Path & path)
 }
 
 
-void checkStoreName(const string & name)
-{
-    string validChars = "+-._?=";
-
-    auto baseError = format("The path name '%2%' is invalid: %3%. "
-        "Path names are alphanumeric and can include the symbols %1% "
-        "and must not begin with a period. "
-        "Note: If '%2%' is a source file and you cannot rename it on "
-        "disk, 'builtins.path { name = ... }' can be used to give it an "
-        "alternative name.") % validChars % name;
-
-    if (name.empty())
-        throw Error(baseError % "it is an empty string");
-
-    /* Disallow names starting with a dot for possible security
-       reasons (e.g., "." and ".."). */
-    if (name[0] == '.')
-        throw Error(baseError % "it is illegal to start the name with a period");
-
-    /* Disallow names longer than 211 characters. ext4’s max is 256,
-       but we need extra space for the hash and .chroot extensions. */
-    if (name.length() > 211)
-        throw Error(baseError % "name must be less than 212 characters");
-
-    for (auto & i : name)
-        if (!((i >= 'A' && i <= 'Z') ||
-              (i >= 'a' && i <= 'z') ||
-              (i >= '0' && i <= '9') ||
-              validChars.find(i) != string::npos))
-        {
-            throw Error(baseError % (format("the '%1%' character is invalid") % i));
-        }
-}
-
-
 /* Store paths have the following form:
 
    <store>/<h>-<name>
@@ -188,43 +138,48 @@ void checkStoreName(const string & name)
 */
 
 
-Path Store::makeStorePath(const string & type,
-    const Hash & hash, const string & name) const
+StorePath Store::makeStorePath(const string & type,
+    const Hash & hash, std::string_view name) const
 {
     /* e.g., "source:sha256:1abc...:/nix/store:foo.tar.gz" */
-    string s = type + ":" + hash.to_string(Base16) + ":" + storeDir + ":" + name;
-
-    checkStoreName(name);
-
-    return storeDir + "/"
-        + compressHash(hashString(htSHA256, s), 20).to_string(Base32, false)
-        + "-" + name;
+    string s = type + ":" + hash.to_string(Base16) + ":" + storeDir + ":" + std::string(name);
+    auto h = compressHash(hashString(htSHA256, s), 20);
+    return StorePath::make(h.hash, name);
 }
 
 
-Path Store::makeOutputPath(const string & id,
-    const Hash & hash, const string & name) const
+StorePath Store::makeOutputPath(const string & id,
+    const Hash & hash, std::string_view name) const
 {
     return makeStorePath("output:" + id, hash,
-        name + (id == "out" ? "" : "-" + id));
+        std::string(name) + (id == "out" ? "" : "-" + id));
 }
 
 
-static std::string makeType(string && type, const PathSet & references)
+static std::string makeType(
+    const Store & store,
+    string && type,
+    const StorePathSet & references,
+    bool hasSelfReference = false)
 {
     for (auto & i : references) {
         type += ":";
-        type += i;
+        type += store.printStorePath(i);
     }
+    if (hasSelfReference) type += ":self";
     return std::move(type);
 }
 
 
-Path Store::makeFixedOutputPath(bool recursive,
-    const Hash & hash, const string & name, const PathSet & references) const
+StorePath Store::makeFixedOutputPath(
+    bool recursive,
+    const Hash & hash,
+    std::string_view name,
+    const StorePathSet & references,
+    bool hasSelfReference) const
 {
     if (hash.type == htSHA256 && recursive) {
-        return makeStorePath(makeType("source", references), hash, name);
+        return makeStorePath(makeType(*this, "source", references, hasSelfReference), hash, name);
     } else {
         assert(references.empty());
         return makeStorePath("output:out", hashString(htSHA256,
@@ -234,28 +189,27 @@ Path Store::makeFixedOutputPath(bool recursive,
 }
 
 
-Path Store::makeTextPath(const string & name, const Hash & hash,
-    const PathSet & references) const
+StorePath Store::makeTextPath(std::string_view name, const Hash & hash,
+    const StorePathSet & references) const
 {
     assert(hash.type == htSHA256);
     /* Stuff the references (if any) into the type.  This is a bit
        hacky, but we can't put them in `s' since that would be
        ambiguous. */
-    return makeStorePath(makeType("text", references), hash, name);
+    return makeStorePath(makeType(*this, "text", references), hash, name);
 }
 
 
-std::pair<Path, Hash> Store::computeStorePathForPath(const string & name,
+std::pair<StorePath, Hash> Store::computeStorePathForPath(std::string_view name,
     const Path & srcPath, bool recursive, HashType hashAlgo, PathFilter & filter) const
 {
     Hash h = recursive ? hashPath(hashAlgo, srcPath, filter).first : hashFile(hashAlgo, srcPath);
-    Path dstPath = makeFixedOutputPath(recursive, h, name);
-    return std::pair<Path, Hash>(dstPath, h);
+    return std::make_pair(makeFixedOutputPath(recursive, h, name), h);
 }
 
 
-Path Store::computeStorePathForText(const string & name, const string & s,
-    const PathSet & references) const
+StorePath Store::computeStorePathForText(const string & name, const string & s,
+    const StorePathSet & references) const
 {
     return makeTextPath(name, hashString(htSHA256, s), references);
 }
@@ -274,11 +228,9 @@ std::string Store::getUri()
 }
 
 
-bool Store::isValidPath(const Path & storePath)
+bool Store::isValidPath(const StorePath & storePath)
 {
-    assertStorePath(storePath);
-
-    auto hashPart = storePathToHash(storePath);
+    auto hashPart = storePathToHash(printStorePath(storePath));
 
     {
         auto state_(state.lock());
@@ -312,7 +264,7 @@ bool Store::isValidPath(const Path & storePath)
 
 /* Default implementation for stores that only implement
    queryPathInfoUncached(). */
-bool Store::isValidPathUncached(const Path & path)
+bool Store::isValidPathUncached(const StorePath & path)
 {
     try {
         queryPathInfo(path);
@@ -323,7 +275,7 @@ bool Store::isValidPathUncached(const Path & path)
 }
 
 
-ref<const ValidPathInfo> Store::queryPathInfo(const Path & storePath)
+ref<const ValidPathInfo> Store::queryPathInfo(const StorePath & storePath)
 {
     std::promise<ref<const ValidPathInfo>> promise;
 
@@ -340,22 +292,20 @@ ref<const ValidPathInfo> Store::queryPathInfo(const Path & storePath)
 }
 
 
-void Store::queryPathInfo(const Path & storePath,
+void Store::queryPathInfo(const StorePath & storePath,
     Callback<ref<const ValidPathInfo>> callback) noexcept
 {
     std::string hashPart;
 
     try {
-        assertStorePath(storePath);
-
-        hashPart = storePathToHash(storePath);
+        hashPart = storePathToHash(printStorePath(storePath));
 
         {
             auto res = state.lock()->pathInfoCache.get(hashPart);
             if (res) {
                 stats.narInfoReadAverted++;
                 if (!*res)
-                    throw InvalidPath(format("path '%s' is not valid") % storePath);
+                    throw InvalidPath("path '%s' is not valid", printStorePath(storePath));
                 return callback(ref<const ValidPathInfo>(*res));
             }
         }
@@ -369,8 +319,8 @@ void Store::queryPathInfo(const Path & storePath,
                     state_->pathInfoCache.upsert(hashPart,
                         res.first == NarInfoDiskCache::oInvalid ? 0 : res.second);
                     if (res.first == NarInfoDiskCache::oInvalid ||
-                        (res.second->path != storePath && storePathToName(storePath) != ""))
-                        throw InvalidPath(format("path '%s' is not valid") % storePath);
+                        res.second->path != storePath)
+                        throw InvalidPath("path '%s' is not valid", printStorePath(storePath));
                 }
                 return callback(ref<const ValidPathInfo>(res.second));
             }
@@ -381,7 +331,7 @@ void Store::queryPathInfo(const Path & storePath,
     auto callbackPtr = std::make_shared<decltype(callback)>(std::move(callback));
 
     queryPathInfoUncached(storePath,
-        {[this, storePath, hashPart, callbackPtr](std::future<std::shared_ptr<const ValidPathInfo>> fut) {
+        {[this, storePath{printStorePath(storePath)}, hashPart, callbackPtr](std::future<std::shared_ptr<const ValidPathInfo>> fut) {
 
             try {
                 auto info = fut.get();
@@ -394,9 +344,7 @@ void Store::queryPathInfo(const Path & storePath,
                     state_->pathInfoCache.upsert(hashPart, info);
                 }
 
-                if (!info
-                    || (info->path != storePath && storePathToName(storePath) != ""))
-                {
+                if (!info || info->path != parseStorePath(storePath)) {
                     stats.narInfoMissing++;
                     throw InvalidPath("path '%s' is not valid", storePath);
                 }
@@ -407,27 +355,27 @@ void Store::queryPathInfo(const Path & storePath,
 }
 
 
-PathSet Store::queryValidPaths(const PathSet & paths, SubstituteFlag maybeSubstitute)
+StorePathSet Store::queryValidPaths(const StorePathSet & paths, SubstituteFlag maybeSubstitute)
 {
     struct State
     {
         size_t left;
-        PathSet valid;
+        StorePathSet valid;
         std::exception_ptr exc;
     };
 
-    Sync<State> state_(State{paths.size(), PathSet()});
+    Sync<State> state_(State{paths.size(), StorePathSet()});
 
     std::condition_variable wakeup;
     ThreadPool pool;
 
-    auto doQuery = [&](const Path & path ) {
+    auto doQuery = [&](const Path & path) {
         checkInterrupt();
-        queryPathInfo(path, {[path, &state_, &wakeup](std::future<ref<const ValidPathInfo>> fut) {
+        queryPathInfo(parseStorePath(path), {[path, this, &state_, &wakeup](std::future<ref<const ValidPathInfo>> fut) {
             auto state(state_.lock());
             try {
                 auto info = fut.get();
-                state->valid.insert(path);
+                state->valid.insert(parseStorePath(path));
             } catch (InvalidPath &) {
             } catch (...) {
                 state->exc = std::current_exception();
@@ -439,7 +387,7 @@ PathSet Store::queryValidPaths(const PathSet & paths, SubstituteFlag maybeSubsti
     };
 
     for (auto & path : paths)
-        pool.enqueue(std::bind(doQuery, path));
+        pool.enqueue(std::bind(doQuery, printStorePath(path))); // FIXME
 
     pool.process();
 
@@ -447,7 +395,7 @@ PathSet Store::queryValidPaths(const PathSet & paths, SubstituteFlag maybeSubsti
         auto state(state_.lock());
         if (!state->left) {
             if (state->exc) std::rethrow_exception(state->exc);
-            return state->valid;
+            return std::move(state->valid);
         }
         state.wait(wakeup);
     }
@@ -457,13 +405,13 @@ PathSet Store::queryValidPaths(const PathSet & paths, SubstituteFlag maybeSubsti
 /* Return a string accepted by decodeValidPathInfo() that
    registers the specified paths as valid.  Note: it's the
    responsibility of the caller to provide a closure. */
-string Store::makeValidityRegistration(const PathSet & paths,
+string Store::makeValidityRegistration(const StorePathSet & paths,
     bool showDerivers, bool showHash)
 {
     string s = "";
 
     for (auto & i : paths) {
-        s += i + "\n";
+        s += printStorePath(i) + "\n";
 
         auto info = queryPathInfo(i);
 
@@ -472,31 +420,30 @@ string Store::makeValidityRegistration(const PathSet & paths,
             s += (format("%1%\n") % info->narSize).str();
         }
 
-        Path deriver = showDerivers ? info->deriver : "";
+        auto deriver = showDerivers && info->deriver ? printStorePath(*info->deriver) : "";
         s += deriver + "\n";
 
         s += (format("%1%\n") % info->references.size()).str();
 
         for (auto & j : info->references)
-            s += j + "\n";
+            s += printStorePath(j) + "\n";
     }
 
     return s;
 }
 
 
-void Store::pathInfoToJSON(JSONPlaceholder & jsonOut, const PathSet & storePaths,
+void Store::pathInfoToJSON(JSONPlaceholder & jsonOut, const StorePathSet & storePaths,
     bool includeImpureInfo, bool showClosureSize, AllowInvalidFlag allowInvalid)
 {
     auto jsonList = jsonOut.list();
 
-    for (auto storePath : storePaths) {
+    for (auto & storePath : storePaths) {
         auto jsonPath = jsonList.object();
-        jsonPath.attr("path", storePath);
+        jsonPath.attr("path", printStorePath(storePath));
 
         try {
             auto info = queryPathInfo(storePath);
-            storePath = info->path;
 
             jsonPath
                 .attr("narHash", info->narHash.to_string())
@@ -505,7 +452,7 @@ void Store::pathInfoToJSON(JSONPlaceholder & jsonOut, const PathSet & storePaths
             {
                 auto jsonRefs = jsonPath.list("references");
                 for (auto & ref : info->references)
-                    jsonRefs.elem(ref);
+                    jsonRefs.elem(printStorePath(ref));
             }
 
             if (info->ca != "")
@@ -514,14 +461,14 @@ void Store::pathInfoToJSON(JSONPlaceholder & jsonOut, const PathSet & storePaths
             std::pair<uint64_t, uint64_t> closureSizes;
 
             if (showClosureSize) {
-                closureSizes = getClosureSize(storePath);
+                closureSizes = getClosureSize(info->path);
                 jsonPath.attr("closureSize", closureSizes.first);
             }
 
             if (includeImpureInfo) {
 
-                if (info->deriver != "")
-                    jsonPath.attr("deriver", info->deriver);
+                if (info->deriver)
+                    jsonPath.attr("deriver", printStorePath(*info->deriver));
 
                 if (info->registrationTime)
                     jsonPath.attr("registrationTime", info->registrationTime);
@@ -557,10 +504,10 @@ void Store::pathInfoToJSON(JSONPlaceholder & jsonOut, const PathSet & storePaths
 }
 
 
-std::pair<uint64_t, uint64_t> Store::getClosureSize(const Path & storePath)
+std::pair<uint64_t, uint64_t> Store::getClosureSize(const StorePath & storePath)
 {
     uint64_t totalNarSize = 0, totalDownloadSize = 0;
-    PathSet closure;
+    StorePathSet closure;
     computeFSClosure(storePath, closure, false, false);
     for (auto & p : closure) {
         auto info = queryPathInfo(p);
@@ -584,30 +531,34 @@ const Store::Stats & Store::getStats()
 }
 
 
-void Store::buildPaths(const PathSet & paths, BuildMode buildMode)
+void Store::buildPaths(const std::vector<StorePathWithOutputs> & paths, BuildMode buildMode)
 {
-    for (auto & path : paths)
-        if (isDerivation(path))
-            unsupported("buildPaths");
+    StorePathSet paths2;
 
-    if (queryValidPaths(paths).size() != paths.size())
+    for (auto & path : paths) {
+        if (path.path.isDerivation())
+            unsupported("buildPaths");
+        paths2.insert(path.path.clone());
+    }
+
+    if (queryValidPaths(paths2).size() != paths2.size())
         unsupported("buildPaths");
 }
 
 
 void copyStorePath(ref<Store> srcStore, ref<Store> dstStore,
-    const Path & storePath, RepairFlag repair, CheckSigsFlag checkSigs)
+    const StorePath & storePath, RepairFlag repair, CheckSigsFlag checkSigs)
 {
     auto srcUri = srcStore->getUri();
     auto dstUri = dstStore->getUri();
 
     Activity act(*logger, lvlInfo, actCopyPath,
         srcUri == "local" || srcUri == "daemon"
-          ? fmt("copying path '%s' to '%s'", storePath, dstUri)
+        ? fmt("copying path '%s' to '%s'", srcStore->printStorePath(storePath), dstUri)
           : dstUri == "local" || dstUri == "daemon"
-            ? fmt("copying path '%s' from '%s'", storePath, srcUri)
-            : fmt("copying path '%s' from '%s' to '%s'", storePath, srcUri, dstUri),
-        {storePath, srcUri, dstUri});
+        ? fmt("copying path '%s' from '%s'", srcStore->printStorePath(storePath), srcUri)
+          : fmt("copying path '%s' from '%s' to '%s'", srcStore->printStorePath(storePath), srcUri, dstUri),
+        {srcStore->printStorePath(storePath), srcUri, dstUri});
     PushActivity pact(act.id);
 
     auto info = srcStore->queryPathInfo(storePath);
@@ -640,23 +591,23 @@ void copyStorePath(ref<Store> srcStore, ref<Store> dstStore,
             total += len;
             act.progress(total, info->narSize);
         });
-        srcStore->narFromPath({storePath}, wrapperSink);
+        srcStore->narFromPath(storePath, wrapperSink);
     }, [&]() {
-        throw EndOfFile("NAR for '%s' fetched from '%s' is incomplete", storePath, srcStore->getUri());
+           throw EndOfFile("NAR for '%s' fetched from '%s' is incomplete", srcStore->printStorePath(storePath), srcStore->getUri());
     });
 
     dstStore->addToStore(*info, *source, repair, checkSigs);
 }
 
 
-void copyPaths(ref<Store> srcStore, ref<Store> dstStore, const PathSet & storePaths,
+void copyPaths(ref<Store> srcStore, ref<Store> dstStore, const StorePathSet & storePaths,
     RepairFlag repair, CheckSigsFlag checkSigs, SubstituteFlag substitute)
 {
-    PathSet valid = dstStore->queryValidPaths(storePaths, substitute);
+    auto valid = dstStore->queryValidPaths(storePaths, substitute);
 
     PathSet missing;
     for (auto & path : storePaths)
-        if (!valid.count(path)) missing.insert(path);
+        if (!valid.count(path)) missing.insert(srcStore->printStorePath(path));
 
     if (missing.empty()) return;
 
@@ -677,23 +628,25 @@ void copyPaths(ref<Store> srcStore, ref<Store> dstStore, const PathSet & storePa
         PathSet(missing.begin(), missing.end()),
 
         [&](const Path & storePath) {
-            if (dstStore->isValidPath(storePath)) {
+            if (dstStore->isValidPath(dstStore->parseStorePath(storePath))) {
                 nrDone++;
                 showProgress();
                 return PathSet();
             }
 
-            auto info = srcStore->queryPathInfo(storePath);
+            auto info = srcStore->queryPathInfo(srcStore->parseStorePath(storePath));
 
             bytesExpected += info->narSize;
             act.setExpected(actCopyPath, bytesExpected);
 
-            return info->references;
+            return srcStore->printStorePathSet(info->references);
         },
 
-        [&](const Path & storePath) {
+        [&](const Path & storePathS) {
             checkInterrupt();
 
+            auto storePath = dstStore->parseStorePath(storePathS);
+
             if (!dstStore->isValidPath(storePath)) {
                 MaintainCount<decltype(nrRunning)> mc(nrRunning);
                 showProgress();
@@ -703,7 +656,7 @@ void copyPaths(ref<Store> srcStore, ref<Store> dstStore, const PathSet & storePa
                     nrFailed++;
                     if (!settings.keepGoing)
                         throw e;
-                    logger->log(lvlError, format("could not copy %s: %s") % storePath % e.what());
+                    logger->log(lvlError, fmt("could not copy %s: %s", storePathS, e.what()));
                     showProgress();
                     return;
                 }
@@ -716,20 +669,36 @@ void copyPaths(ref<Store> srcStore, ref<Store> dstStore, const PathSet & storePa
 
 
 void copyClosure(ref<Store> srcStore, ref<Store> dstStore,
-    const PathSet & storePaths, RepairFlag repair, CheckSigsFlag checkSigs,
+    const StorePathSet & storePaths, RepairFlag repair, CheckSigsFlag checkSigs,
     SubstituteFlag substitute)
 {
-    PathSet closure;
-    srcStore->computeFSClosure({storePaths}, closure);
+    StorePathSet closure;
+    srcStore->computeFSClosure(storePaths, closure);
     copyPaths(srcStore, dstStore, closure, repair, checkSigs, substitute);
 }
 
 
-ValidPathInfo decodeValidPathInfo(std::istream & str, bool hashGiven)
+ValidPathInfo::ValidPathInfo(const ValidPathInfo & other)
+    : path(other.path.clone())
+    , deriver(other.deriver ? other.deriver->clone(): std::optional<StorePath>{})
+    , narHash(other.narHash)
+    , references(cloneStorePathSet(other.references))
+    , registrationTime(other.registrationTime)
+    , narSize(other.narSize)
+    , id(other.id)
+    , ultimate(other.ultimate)
+    , sigs(other.sigs)
+    , ca(other.ca)
 {
-    ValidPathInfo info;
-    getline(str, info.path);
-    if (str.eof()) { info.path = ""; return info; }
+}
+
+
+std::optional<ValidPathInfo> decodeValidPathInfo(const Store & store, std::istream & str, bool hashGiven)
+{
+    std::string path;
+    getline(str, path);
+    if (str.eof()) { return {}; }
+    ValidPathInfo info(store.parseStorePath(path));
     if (hashGiven) {
         string s;
         getline(str, s);
@@ -737,16 +706,29 @@ ValidPathInfo decodeValidPathInfo(std::istream & str, bool hashGiven)
         getline(str, s);
         if (!string2Int(s, info.narSize)) throw Error("number expected");
     }
-    getline(str, info.deriver);
+    std::string deriver;
+    getline(str, deriver);
+    if (deriver != "") info.deriver = store.parseStorePath(deriver);
     string s; int n;
     getline(str, s);
     if (!string2Int(s, n)) throw Error("number expected");
     while (n--) {
         getline(str, s);
-        info.references.insert(s);
+        info.references.insert(store.parseStorePath(s));
     }
     if (!str || str.eof()) throw Error("missing input");
-    return info;
+    return std::optional<ValidPathInfo>(std::move(info));
+}
+
+
+std::string Store::showPaths(const StorePathSet & paths)
+{
+    std::string s;
+    for (auto & i : paths) {
+        if (s.size() != 0) s += ", ";
+        s += "'" + printStorePath(i) + "'";
+    }
+    return s;
 }
 
 
@@ -761,34 +743,34 @@ string showPaths(const PathSet & paths)
 }
 
 
-std::string ValidPathInfo::fingerprint() const
+std::string ValidPathInfo::fingerprint(const Store & store) const
 {
     if (narSize == 0 || !narHash)
-        throw Error(format("cannot calculate fingerprint of path '%s' because its size/hash is not known")
-            % path);
+        throw Error("cannot calculate fingerprint of path '%s' because its size/hash is not known",
+            store.printStorePath(path));
     return
-        "1;" + path + ";"
+        "1;" + store.printStorePath(path) + ";"
         + narHash.to_string(Base32) + ";"
         + std::to_string(narSize) + ";"
-        + concatStringsSep(",", references);
+        + concatStringsSep(",", store.printStorePathSet(references));
 }
 
 
-void ValidPathInfo::sign(const SecretKey & secretKey)
+void ValidPathInfo::sign(const Store & store, const SecretKey & secretKey)
 {
-    sigs.insert(secretKey.signDetached(fingerprint()));
+    sigs.insert(secretKey.signDetached(fingerprint(store)));
 }
 
 
 bool ValidPathInfo::isContentAddressed(const Store & store) const
 {
     auto warn = [&]() {
-        printError(format("warning: path '%s' claims to be content-addressed but isn't") % path);
+        printError("warning: path '%s' claims to be content-addressed but isn't", store.printStorePath(path));
     };
 
     if (hasPrefix(ca, "text:")) {
         Hash hash(std::string(ca, 5));
-        if (store.makeTextPath(storePathToName(path), hash, references) == path)
+        if (store.makeTextPath(path.name(), hash, references) == path)
             return true;
         else
             warn();
@@ -797,9 +779,13 @@ bool ValidPathInfo::isContentAddressed(const Store & store) const
     else if (hasPrefix(ca, "fixed:")) {
         bool recursive = ca.compare(6, 2, "r:") == 0;
         Hash hash(std::string(ca, recursive ? 8 : 6));
-        auto refs = references;
-        replaceInSet(refs, path, std::string("self"));
-        if (store.makeFixedOutputPath(recursive, hash, storePathToName(path), refs) == path)
+        auto refs = cloneStorePathSet(references);
+        bool hasSelfReference = false;
+        if (refs.count(path)) {
+            hasSelfReference = true;
+            refs.erase(path);
+        }
+        if (store.makeFixedOutputPath(recursive, hash, path.name(), refs, hasSelfReference) == path)
             return true;
         else
             warn();
@@ -815,15 +801,15 @@ size_t ValidPathInfo::checkSignatures(const Store & store, const PublicKeys & pu
 
     size_t good = 0;
     for (auto & sig : sigs)
-        if (checkSignature(publicKeys, sig))
+        if (checkSignature(store, publicKeys, sig))
             good++;
     return good;
 }
 
 
-bool ValidPathInfo::checkSignature(const PublicKeys & publicKeys, const std::string & sig) const
+bool ValidPathInfo::checkSignature(const Store & store, const PublicKeys & publicKeys, const std::string & sig) const
 {
-    return verifyDetached(fingerprint(), sig, publicKeys);
+    return verifyDetached(fingerprint(store), sig, publicKeys);
 }
 
 
@@ -831,7 +817,7 @@ Strings ValidPathInfo::shortRefs() const
 {
     Strings refs;
     for (auto & r : references)
-        refs.push_back(baseNameOf(r));
+        refs.push_back(std::string(r.to_string()));
     return refs;
 }
 
@@ -944,7 +930,7 @@ static RegisterStoreImplementation regStore([](
     const std::string & uri, const Store::Params & params)
     -> std::shared_ptr<Store>
 {
-    switch (getStoreType(uri, get(params, "state", settings.nixStateDir))) {
+    switch (getStoreType(uri, get(params, "state").value_or(settings.nixStateDir))) {
         case tDaemon:
             return std::shared_ptr<Store>(std::make_shared<UDSRemoteStore>(params));
         case tLocal: {
diff --git a/src/libstore/store-api.hh b/src/libstore/store-api.hh
index 8e4b133d5..552bbd67d 100644
--- a/src/libstore/store-api.hh
+++ b/src/libstore/store-api.hh
@@ -1,5 +1,6 @@
 #pragma once
 
+#include "path.hh"
 #include "hash.hh"
 #include "serialise.hh"
 #include "crypto.hh"
@@ -42,14 +43,11 @@ enum SubstituteFlag : bool { NoSubstitute = false, Substitute = true };
 enum AllowInvalidFlag : bool { DisallowInvalid = false, AllowInvalid = true };
 
 
-/* Size of the hash part of store paths, in base-32 characters. */
-const size_t storePathHashLen = 32; // i.e. 160 bits
-
 /* Magic header of exportPath() output (obsolete). */
 const uint32_t exportMagic = 0x4558494e;
 
 
-typedef std::unordered_map<Path, std::unordered_set<std::string>> Roots;
+typedef std::unordered_map<StorePath, std::unordered_set<std::string>> Roots;
 
 
 struct GCOptions
@@ -83,7 +81,7 @@ struct GCOptions
     bool ignoreLiveness{false};
 
     /* For `gcDeleteSpecific', the paths to delete. */
-    PathSet pathsToDelete;
+    StorePathSet pathsToDelete;
 
     /* Stop after at least `maxFreed' bytes have been freed. */
     unsigned long long maxFreed{std::numeric_limits<unsigned long long>::max()};
@@ -104,21 +102,21 @@ struct GCResults
 
 struct SubstitutablePathInfo
 {
-    Path deriver;
-    PathSet references;
+    std::optional<StorePath> deriver;
+    StorePathSet references;
     unsigned long long downloadSize; /* 0 = unknown or inapplicable */
     unsigned long long narSize; /* 0 = unknown */
 };
 
-typedef std::map<Path, SubstitutablePathInfo> SubstitutablePathInfos;
+typedef std::map<StorePath, SubstitutablePathInfo> SubstitutablePathInfos;
 
 
 struct ValidPathInfo
 {
-    Path path;
-    Path deriver;
+    StorePath path;
+    std::optional<StorePath> deriver;
     Hash narHash;
-    PathSet references;
+    StorePathSet references;
     time_t registrationTime = 0;
     uint64_t narSize = 0; // 0 = unknown
     uint64_t id; // internal use only
@@ -143,7 +141,7 @@ struct ValidPathInfo
 
        Ideally, the content-addressability assertion would just be a
        Boolean, and the store path would be computed from
-       ‘storePathToName(path)’, ‘narHash’ and ‘references’. However,
+       the name component, ‘narHash’ and ‘references’. However,
        1) we've accumulated several types of content-addressed paths
        over the years; and 2) fixed-output derivations support
        multiple hash algorithms and serialisation methods (flat file
@@ -171,9 +169,9 @@ struct ValidPathInfo
        the NAR, and the sorted references. The size field is strictly
        speaking superfluous, but might prevent endless/excessive data
        attacks. */
-    std::string fingerprint() const;
+    std::string fingerprint(const Store & store) const;
 
-    void sign(const SecretKey & secretKey);
+    void sign(const Store & store, const SecretKey & secretKey);
 
     /* Return true iff the path is verifiably content-addressed. */
     bool isContentAddressed(const Store & store) const;
@@ -186,10 +184,13 @@ struct ValidPathInfo
     size_t checkSignatures(const Store & store, const PublicKeys & publicKeys) const;
 
     /* Verify a single signature. */
-    bool checkSignature(const PublicKeys & publicKeys, const std::string & sig) const;
+    bool checkSignature(const Store & store, const PublicKeys & publicKeys, const std::string & sig) const;
 
     Strings shortRefs() const;
 
+    ValidPathInfo(StorePath && path) : path(std::move(path)) { }
+    explicit ValidPathInfo(const ValidPathInfo & other);
+
     virtual ~ValidPathInfo() { }
 };
 
@@ -240,6 +241,23 @@ struct BuildResult
 };
 
 
+struct StorePathWithOutputs
+{
+    StorePath path;
+    std::set<std::string> outputs;
+
+    StorePathWithOutputs(const StorePath & path, const std::set<std::string> & outputs = {})
+        : path(path.clone()), outputs(outputs)
+    { }
+
+    StorePathWithOutputs(const StorePathWithOutputs & other)
+        : path(other.path.clone()), outputs(other.outputs)
+    { }
+
+    std::string to_string(const Store & store) const;
+};
+
+
 class Store : public std::enable_shared_from_this<Store>, public Config
 {
 public:
@@ -258,6 +276,7 @@ protected:
 
     struct State
     {
+        // FIXME: fix key
         LRUCache<std::string, std::shared_ptr<const ValidPathInfo>> pathInfoCache;
     };
 
@@ -273,6 +292,24 @@ public:
 
     virtual std::string getUri() = 0;
 
+    StorePath parseStorePath(std::string_view path) const;
+
+    std::string printStorePath(const StorePath & path) const;
+
+    // FIXME: remove
+    StorePathSet parseStorePathSet(const PathSet & paths) const;
+
+    PathSet printStorePathSet(const StorePathSet & path) const;
+
+    /* Split a string specifying a derivation and a set of outputs
+       (/nix/store/hash-foo!out1,out2,...) into the derivation path
+       and the outputs. */
+    StorePathWithOutputs parseDrvPathWithOutputs(const string & s);
+
+    /* Display a set of paths in human-readable form (i.e., between quotes
+       and separated by commas). */
+    std::string showPaths(const StorePathSet & paths);
+
     /* Return true if ‘path’ is in the Nix store (but not the Nix
        store itself). */
     bool isInStore(const Path & path) const;
@@ -281,9 +318,6 @@ public:
        the Nix store. */
     bool isStorePath(const Path & path) const;
 
-    /* Throw an exception if ‘path’ is not a store path. */
-    void assertStorePath(const Path & path) const;
-
     /* Chop off the parts after the top-level store name, e.g.,
        /nix/store/abcd-foo/bar => /nix/store/abcd-foo. */
     Path toStorePath(const Path & path) const;
@@ -293,26 +327,27 @@ public:
 
     /* Same as followLinksToStore(), but apply toStorePath() to the
        result. */
-    Path followLinksToStorePath(const Path & path) const;
+    StorePath followLinksToStorePath(const Path & path) const;
 
     /* Constructs a unique store path name. */
-    Path makeStorePath(const string & type,
-        const Hash & hash, const string & name) const;
+    StorePath makeStorePath(const string & type,
+        const Hash & hash, std::string_view name) const;
 
-    Path makeOutputPath(const string & id,
-        const Hash & hash, const string & name) const;
+    StorePath makeOutputPath(const string & id,
+        const Hash & hash, std::string_view name) const;
 
-    Path makeFixedOutputPath(bool recursive,
-        const Hash & hash, const string & name,
-        const PathSet & references = {}) const;
+    StorePath makeFixedOutputPath(bool recursive,
+        const Hash & hash, std::string_view name,
+        const StorePathSet & references = {},
+        bool hasSelfReference = false) const;
 
-    Path makeTextPath(const string & name, const Hash & hash,
-        const PathSet & references) const;
+    StorePath makeTextPath(std::string_view name, const Hash & hash,
+        const StorePathSet & references) const;
 
     /* This is the preparatory part of addToStore(); it computes the
        store path to which srcPath is to be copied.  Returns the store
        path and the cryptographic hash of the contents of srcPath. */
-    std::pair<Path, Hash> computeStorePathForPath(const string & name,
+    std::pair<StorePath, Hash> computeStorePathForPath(std::string_view name,
         const Path & srcPath, bool recursive = true,
         HashType hashAlgo = htSHA256, PathFilter & filter = defaultPathFilter) const;
 
@@ -330,21 +365,21 @@ public:
        simply yield a different store path, so other users wouldn't be
        affected), but it has some backwards compatibility issues (the
        hashing scheme changes), so I'm not doing that for now. */
-    Path computeStorePathForText(const string & name, const string & s,
-        const PathSet & references) const;
+    StorePath computeStorePathForText(const string & name, const string & s,
+        const StorePathSet & references) const;
 
     /* Check whether a path is valid. */
-    bool isValidPath(const Path & path);
+    bool isValidPath(const StorePath & path);
 
 protected:
 
-    virtual bool isValidPathUncached(const Path & path);
+    virtual bool isValidPathUncached(const StorePath & path);
 
 public:
 
     /* Query which of the given paths is valid. Optionally, try to
        substitute missing paths. */
-    virtual PathSet queryValidPaths(const PathSet & paths,
+    virtual StorePathSet queryValidPaths(const StorePathSet & paths,
         SubstituteFlag maybeSubstitute = NoSubstitute);
 
     /* Query the set of all valid paths. Note that for some store
@@ -352,54 +387,54 @@ public:
        (i.e. you'll get /nix/store/<hash> rather than
        /nix/store/<hash>-<name>). Use queryPathInfo() to obtain the
        full store path. */
-    virtual PathSet queryAllValidPaths()
+    virtual StorePathSet queryAllValidPaths()
     { unsupported("queryAllValidPaths"); }
 
     /* Query information about a valid path. It is permitted to omit
        the name part of the store path. */
-    ref<const ValidPathInfo> queryPathInfo(const Path & path);
+    ref<const ValidPathInfo> queryPathInfo(const StorePath & path);
 
     /* Asynchronous version of queryPathInfo(). */
-    void queryPathInfo(const Path & path,
+    void queryPathInfo(const StorePath & path,
         Callback<ref<const ValidPathInfo>> callback) noexcept;
 
 protected:
 
-    virtual void queryPathInfoUncached(const Path & path,
+    virtual void queryPathInfoUncached(const StorePath & path,
         Callback<std::shared_ptr<const ValidPathInfo>> callback) noexcept = 0;
 
 public:
 
     /* Queries the set of incoming FS references for a store path.
        The result is not cleared. */
-    virtual void queryReferrers(const Path & path, PathSet & referrers)
+    virtual void queryReferrers(const StorePath & path, StorePathSet & referrers)
     { unsupported("queryReferrers"); }
 
     /* Return all currently valid derivations that have `path' as an
        output.  (Note that the result of `queryDeriver()' is the
        derivation that was actually used to produce `path', which may
        not exist anymore.) */
-    virtual PathSet queryValidDerivers(const Path & path) { return {}; };
+    virtual StorePathSet queryValidDerivers(const StorePath & path) { return {}; };
 
     /* Query the outputs of the derivation denoted by `path'. */
-    virtual PathSet queryDerivationOutputs(const Path & path)
+    virtual StorePathSet queryDerivationOutputs(const StorePath & path)
     { unsupported("queryDerivationOutputs"); }
 
     /* Query the output names of the derivation denoted by `path'. */
-    virtual StringSet queryDerivationOutputNames(const Path & path)
+    virtual StringSet queryDerivationOutputNames(const StorePath & path)
     { unsupported("queryDerivationOutputNames"); }
 
     /* Query the full store path given the hash part of a valid store
-       path, or "" if the path doesn't exist. */
-    virtual Path queryPathFromHashPart(const string & hashPart) = 0;
+       path, or empty if the path doesn't exist. */
+    virtual std::optional<StorePath> queryPathFromHashPart(const std::string & hashPart) = 0;
 
     /* Query which of the given paths have substitutes. */
-    virtual PathSet querySubstitutablePaths(const PathSet & paths) { return {}; };
+    virtual StorePathSet querySubstitutablePaths(const StorePathSet & paths) { return {}; };
 
     /* Query substitute info (i.e. references, derivers and download
        sizes) of a set of paths.  If a path does not have substitute
        info, it's omitted from the resulting ‘infos’ map. */
-    virtual void querySubstitutablePathInfos(const PathSet & paths,
+    virtual void querySubstitutablePathInfos(const StorePathSet & paths,
         SubstitutablePathInfos & infos) { return; };
 
     virtual bool wantMassQuery() { return false; }
@@ -418,12 +453,12 @@ public:
        validity the resulting path.  The resulting path is returned.
        The function object `filter' can be used to exclude files (see
        libutil/archive.hh). */
-    virtual Path addToStore(const string & name, const Path & srcPath,
+    virtual StorePath addToStore(const string & name, const Path & srcPath,
         bool recursive = true, HashType hashAlgo = htSHA256,
         PathFilter & filter = defaultPathFilter, RepairFlag repair = NoRepair) = 0;
 
     // FIXME: remove?
-    virtual Path addToStoreFromDump(const string & dump, const string & name,
+    virtual StorePath addToStoreFromDump(const string & dump, const string & name,
         bool recursive = true, HashType hashAlgo = htSHA256, RepairFlag repair = NoRepair)
     {
         throw Error("addToStoreFromDump() is not supported by this store");
@@ -431,11 +466,11 @@ public:
 
     /* Like addToStore, but the contents written to the output path is
        a regular file containing the given string. */
-    virtual Path addTextToStore(const string & name, const string & s,
-        const PathSet & references, RepairFlag repair = NoRepair) = 0;
+    virtual StorePath addTextToStore(const string & name, const string & s,
+        const StorePathSet & references, RepairFlag repair = NoRepair) = 0;
 
     /* Write a NAR dump of a store path. */
-    virtual void narFromPath(const Path & path, Sink & sink) = 0;
+    virtual void narFromPath(const StorePath & path, Sink & sink) = 0;
 
     /* For each path, if it's a derivation, build it.  Building a
        derivation means ensuring that the output paths are valid.  If
@@ -445,22 +480,24 @@ public:
        output paths can be created by running the builder, after
        recursively building any sub-derivations. For inputs that are
        not derivations, substitute them. */
-    virtual void buildPaths(const PathSet & paths, BuildMode buildMode = bmNormal);
+    virtual void buildPaths(
+        const std::vector<StorePathWithOutputs> & paths,
+        BuildMode buildMode = bmNormal);
 
     /* Build a single non-materialized derivation (i.e. not from an
        on-disk .drv file). Note that ‘drvPath’ is only used for
        informational purposes. */
-    virtual BuildResult buildDerivation(const Path & drvPath, const BasicDerivation & drv,
+    virtual BuildResult buildDerivation(const StorePath & drvPath, const BasicDerivation & drv,
         BuildMode buildMode = bmNormal) = 0;
 
     /* Ensure that a path is valid.  If it is not currently valid, it
        may be made valid by running a substitute (if defined for the
        path). */
-    virtual void ensurePath(const Path & path) = 0;
+    virtual void ensurePath(const StorePath & path) = 0;
 
     /* Add a store path as a temporary root of the garbage collector.
        The root disappears as soon as we exit. */
-    virtual void addTempRoot(const Path & path)
+    virtual void addTempRoot(const StorePath & path)
     { unsupported("addTempRoot"); }
 
     /* Add an indirect root, which is merely a symlink to `path' from
@@ -506,7 +543,7 @@ public:
     /* Return a string representing information about the path that
        can be loaded into the database using `nix-store --load-db' or
        `nix-store --register-validity'. */
-    string makeValidityRegistration(const PathSet & paths,
+    string makeValidityRegistration(const StorePathSet & paths,
         bool showDerivers, bool showHash);
 
     /* Write a JSON representation of store path metadata, such as the
@@ -514,14 +551,14 @@ public:
        variable elements such as the registration time are
        included. If ‘showClosureSize’ is true, the closure size of
        each path is included. */
-    void pathInfoToJSON(JSONPlaceholder & jsonOut, const PathSet & storePaths,
+    void pathInfoToJSON(JSONPlaceholder & jsonOut, const StorePathSet & storePaths,
         bool includeImpureInfo, bool showClosureSize,
         AllowInvalidFlag allowInvalid = DisallowInvalid);
 
     /* Return the size of the closure of the specified path, that is,
        the sum of the size of the NAR serialisation of each path in
        the closure. */
-    std::pair<uint64_t, uint64_t> getClosureSize(const Path & storePath);
+    std::pair<uint64_t, uint64_t> getClosureSize(const StorePath & storePath);
 
     /* Optimise the disk space usage of the Nix store by hard-linking files
        with the same contents. */
@@ -537,14 +574,14 @@ public:
 
     /* Add signatures to the specified store path. The signatures are
        not verified. */
-    virtual void addSignatures(const Path & storePath, const StringSet & sigs)
+    virtual void addSignatures(const StorePath & storePath, const StringSet & sigs)
     { unsupported("addSignatures"); }
 
     /* Utility functions. */
 
     /* Read a derivation, after ensuring its existence through
        ensurePath(). */
-    Derivation derivationFromPath(const Path & drvPath);
+    Derivation derivationFromPath(const StorePath & drvPath);
 
     /* Place in `out' the set of all store paths in the file system
        closure of `storePath'; that is, all paths than can be directly
@@ -553,36 +590,36 @@ public:
        `storePath' is returned; that is, the closures under the
        `referrers' relation instead of the `references' relation is
        returned. */
-    virtual void computeFSClosure(const PathSet & paths,
-        PathSet & out, bool flipDirection = false,
+    virtual void computeFSClosure(const StorePathSet & paths,
+        StorePathSet & out, bool flipDirection = false,
         bool includeOutputs = false, bool includeDerivers = false);
 
-    void computeFSClosure(const Path & path,
-        PathSet & out, bool flipDirection = false,
+    void computeFSClosure(const StorePath & path,
+        StorePathSet & out, bool flipDirection = false,
         bool includeOutputs = false, bool includeDerivers = false);
 
     /* Given a set of paths that are to be built, return the set of
        derivations that will be built, and the set of output paths
        that will be substituted. */
-    virtual void queryMissing(const PathSet & targets,
-        PathSet & willBuild, PathSet & willSubstitute, PathSet & unknown,
+    virtual void queryMissing(const std::vector<StorePathWithOutputs> & targets,
+        StorePathSet & willBuild, StorePathSet & willSubstitute, StorePathSet & unknown,
         unsigned long long & downloadSize, unsigned long long & narSize);
 
     /* Sort a set of paths topologically under the references
        relation.  If p refers to q, then p precedes q in this list. */
-    Paths topoSortPaths(const PathSet & paths);
+    StorePaths topoSortPaths(const StorePathSet & paths);
 
     /* Export multiple paths in the format expected by ‘nix-store
        --import’. */
-    void exportPaths(const Paths & paths, Sink & sink);
+    void exportPaths(const StorePathSet & paths, Sink & sink);
 
-    void exportPath(const Path & path, Sink & sink);
+    void exportPath(const StorePath & path, Sink & sink);
 
     /* Import a sequence of NAR dumps created by exportPaths() into
        the Nix store. Optionally, the contents of the NARs are
        preloaded into the specified FS accessor to speed up subsequent
        access. */
-    Paths importPaths(Source & source, std::shared_ptr<FSAccessor> accessor,
+    StorePaths importPaths(Source & source, std::shared_ptr<FSAccessor> accessor,
         CheckSigsFlag checkSigs = CheckSigs);
 
     struct Stats
@@ -606,7 +643,7 @@ public:
 
     /* Return the build log of the specified store path, if available,
        or null otherwise. */
-    virtual std::shared_ptr<std::string> getBuildLog(const Path & path)
+    virtual std::shared_ptr<std::string> getBuildLog(const StorePath & path)
     { return nullptr; }
 
     /* Hack to allow long-running processes like hydra-queue-runner to
@@ -672,11 +709,11 @@ public:
 
     LocalFSStore(const Params & params);
 
-    void narFromPath(const Path & path, Sink & sink) override;
+    void narFromPath(const StorePath & path, Sink & sink) override;
     ref<FSAccessor> getFSAccessor() override;
 
     /* Register a permanent GC root. */
-    Path addPermRoot(const Path & storePath,
+    Path addPermRoot(const StorePath & storePath,
         const Path & gcRoot, bool indirect, bool allowOutsideRootsDir = false);
 
     virtual Path getRealStoreDir() { return storeDir; }
@@ -687,25 +724,17 @@ public:
         return getRealStoreDir() + "/" + std::string(storePath, storeDir.size() + 1);
     }
 
-    std::shared_ptr<std::string> getBuildLog(const Path & path) override;
+    std::shared_ptr<std::string> getBuildLog(const StorePath & path) override;
 };
 
 
-/* Extract the name part of the given store path. */
-string storePathToName(const Path & path);
-
 /* Extract the hash part of the given store path. */
 string storePathToHash(const Path & path);
 
-/* Check whether ‘name’ is a valid store path name part, i.e. contains
-   only the characters [a-zA-Z0-9\+\-\.\_\?\=] and doesn't start with
-   a dot. */
-void checkStoreName(const string & name);
-
 
 /* Copy a path from one store to another. */
 void copyStorePath(ref<Store> srcStore, ref<Store> dstStore,
-    const Path & storePath, RepairFlag repair = NoRepair, CheckSigsFlag checkSigs = CheckSigs);
+    const StorePath & storePath, RepairFlag repair = NoRepair, CheckSigsFlag checkSigs = CheckSigs);
 
 
 /* Copy store paths from one store to another. The paths may be copied
@@ -713,7 +742,7 @@ void copyStorePath(ref<Store> srcStore, ref<Store> dstStore,
    (i.e. if A is a reference of B, then A is copied before B), but
    the set of store paths is not automatically closed; use
    copyClosure() for that. */
-void copyPaths(ref<Store> srcStore, ref<Store> dstStore, const PathSet & storePaths,
+void copyPaths(ref<Store> srcStore, ref<Store> dstStore, const StorePathSet & storePaths,
     RepairFlag repair = NoRepair,
     CheckSigsFlag checkSigs = CheckSigs,
     SubstituteFlag substitute = NoSubstitute);
@@ -721,7 +750,7 @@ void copyPaths(ref<Store> srcStore, ref<Store> dstStore, const PathSet & storePa
 
 /* Copy the closure of the specified paths from one store to another. */
 void copyClosure(ref<Store> srcStore, ref<Store> dstStore,
-    const PathSet & storePaths,
+    const StorePathSet & storePaths,
     RepairFlag repair = NoRepair,
     CheckSigsFlag checkSigs = CheckSigs,
     SubstituteFlag substitute = NoSubstitute);
@@ -804,7 +833,9 @@ struct RegisterStoreImplementation
 string showPaths(const PathSet & paths);
 
 
-ValidPathInfo decodeValidPathInfo(std::istream & str,
+std::optional<ValidPathInfo> decodeValidPathInfo(
+    const Store & store,
+    std::istream & str,
     bool hashGiven = false);
 
 
diff --git a/src/libstore/worker-protocol.hh b/src/libstore/worker-protocol.hh
index 6762b609d..857d54d99 100644
--- a/src/libstore/worker-protocol.hh
+++ b/src/libstore/worker-protocol.hh
@@ -65,8 +65,9 @@ typedef enum {
 class Store;
 struct Source;
 
-Path readStorePath(Store & store, Source & from);
-template<class T> T readStorePaths(Store & store, Source & from);
+template<class T> T readStorePaths(const Store & store, Source & from);
+
+void writeStorePaths(const Store & store, Sink & out, const StorePathSet & paths);
 
 
 }
diff --git a/src/libutil/rust-ffi.cc b/src/libutil/rust-ffi.cc
index 931d29542..accc5e22b 100644
--- a/src/libutil/rust-ffi.cc
+++ b/src/libutil/rust-ffi.cc
@@ -1,12 +1,18 @@
 #include "logging.hh"
 #include "rust-ffi.hh"
 
-namespace nix {
-
 extern "C" std::exception_ptr * make_error(rust::StringSlice s)
 {
     // FIXME: leak
-    return new std::exception_ptr(std::make_exception_ptr(Error(std::string(s.ptr, s.size))));
+    return new std::exception_ptr(std::make_exception_ptr(nix::Error(std::string(s.ptr, s.size))));
+}
+
+namespace rust {
+
+std::ostream & operator << (std::ostream & str, const String & s)
+{
+    str << (std::string_view) s;
+    return str;
 }
 
 }
diff --git a/src/libutil/rust-ffi.hh b/src/libutil/rust-ffi.hh
index 663758bfc..a77f83ac5 100644
--- a/src/libutil/rust-ffi.hh
+++ b/src/libutil/rust-ffi.hh
@@ -1,16 +1,91 @@
+#pragma once
+
 #include "serialise.hh"
 
+#include <string_view>
+#include <cstring>
+#include <array>
+
 namespace rust {
 
-// Depending on the internal representation of Rust slices is slightly
-// evil...
+typedef void (*DropFun)(void *);
+
+/* A Rust value of N bytes. It can be moved but not copied. When it
+   goes out of scope, the C++ destructor will run the drop
+   function. */
+template<std::size_t N, DropFun drop>
+struct Value
+{
+protected:
+
+    std::array<char, N> raw;
+
+    ~Value()
+    {
+        if (!isEvacuated()) {
+            drop(this);
+            evacuate();
+        }
+    }
+
+    // Must not be called directly.
+    Value()
+    { }
+
+    Value(Value && other)
+        : raw(other.raw)
+    {
+        other.evacuate();
+    }
+
+    void operator =(Value && other)
+    {
+        if (!isEvacuated())
+            drop(this);
+        raw = other.raw;
+        other.evacuate();
+    }
+
+private:
+
+    /* FIXME: optimize these (ideally in such a way that the compiler
+       can elide most calls to evacuate() / isEvacuated(). */
+    inline void evacuate()
+    {
+        for (auto & i : raw) i = 0;
+    }
+
+    inline bool isEvacuated()
+    {
+        for (auto & i : raw)
+            if (i != 0) return false;
+        return true;
+    }
+};
+
+/* A Rust vector. */
+template<typename T, DropFun drop>
+struct Vec : Value<3 * sizeof(void *), drop>
+{
+    inline size_t size() const
+    {
+        return ((const size_t *) &this->raw)[2];
+    }
+
+    const T * data() const
+    {
+        return ((const T * *) &this->raw)[0];
+    }
+};
+
+/* A Rust slice. */
 template<typename T>
 struct Slice
 {
-    T * ptr;
+    const T * ptr;
     size_t size;
 
-    Slice(T * ptr, size_t size) : ptr(ptr), size(size)
+    Slice(const T * ptr, size_t size) : ptr(ptr), size(size)
     {
         assert(ptr);
     }
@@ -18,9 +93,44 @@ struct Slice
 
 struct StringSlice : Slice<char>
 {
-    StringSlice(const std::string & s): Slice((char *) s.data(), s.size()) {}
+    StringSlice(const std::string & s): Slice(s.data(), s.size()) {}
+    explicit StringSlice(std::string_view s): Slice(s.data(), s.size()) {}
+    StringSlice(const char * s): Slice(s, strlen(s)) {}
+
+    operator std::string_view() const
+    {
+        return std::string_view(ptr, size);
+    }
 };
 
+/* A Rust string. */
+struct String;
+
+extern "C" {
+    void ffi_String_new(StringSlice s, String * out);
+    void ffi_String_drop(void * s);
+}
+
+struct String : Vec<char, ffi_String_drop>
+{
+    String(std::string_view s)
+    {
+        ffi_String_new(StringSlice(s), this);
+    }
+
+    String(const char * s)
+        : String({s, std::strlen(s)})
+    {
+    }
+
+    operator std::string_view() const
+    {
+        return std::string_view(data(), size());
+    }
+};
+
+std::ostream & operator << (std::ostream & str, const String & s);
+
 struct Source
 {
     size_t (*fun)(void * source_this, rust::Slice<uint8_t> data);
@@ -33,7 +143,7 @@ struct Source
     // FIXME: how to propagate exceptions?
     static size_t sourceWrapper(void * _this, rust::Slice<uint8_t> data)
     {
-        auto n = ((nix::Source *) _this)->read(data.ptr, data.size);
+        auto n = ((nix::Source *) _this)->read((unsigned char *) data.ptr, data.size);
         return n;
     }
 };
@@ -49,11 +159,20 @@ struct Result
         std::exception_ptr * exc;
     };
 
+    ~Result()
+    {
+        if (tag == 0)
+            data.~T();
+        else if (tag == 1)
+            // FIXME: don't leak exc
+            ;
+    }
+
     /* Rethrow the wrapped exception or return the wrapped value. */
     T unwrap()
     {
         if (tag == 0)
-            return data;
+            return std::move(data);
         else if (tag == 1)
             std::rethrow_exception(*exc);
         else
diff --git a/src/libutil/tarfile.cc b/src/libutil/tarfile.cc
index 2cc7793fd..262bc655f 100644
--- a/src/libutil/tarfile.cc
+++ b/src/libutil/tarfile.cc
@@ -17,7 +17,7 @@ void unpackTarfile(Source & source, const Path & destDir)
 void unpackTarfile(const Path & tarFile, const Path & destDir,
     std::optional<std::string> baseName)
 {
-    if (!baseName) baseName = baseNameOf(tarFile);
+    if (!baseName) baseName = std::string(baseNameOf(tarFile));
 
     auto source = sinkToSource([&](Sink & sink) {
         // FIXME: look at first few bytes to determine compression type.
diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index b4d444a67..e67bdcdeb 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -188,22 +188,22 @@ Path dirOf(const Path & path)
 }
 
 
-string baseNameOf(const Path & path)
+std::string_view baseNameOf(std::string_view path)
 {
     if (path.empty())
         return "";
 
-    Path::size_type last = path.length() - 1;
+    auto last = path.size() - 1;
     if (path[last] == '/' && last > 0)
         last -= 1;
 
-    Path::size_type pos = path.rfind('/', last);
+    auto pos = path.rfind('/', last);
     if (pos == string::npos)
         pos = 0;
     else
         pos += 1;
 
-    return string(path, pos, last - pos + 1);
+    return path.substr(pos, last - pos + 1);
 }
 
 
@@ -1302,9 +1302,10 @@ bool hasPrefix(const string & s, const string & prefix)
 }
 
 
-bool hasSuffix(const string & s, const string & suffix)
+bool hasSuffix(std::string_view s, std::string_view suffix)
 {
-    return s.size() >= suffix.size() && string(s, s.size() - suffix.size()) == suffix;
+    return s.size() >= suffix.size()
+        && s.substr(s.size() - suffix.size()) == suffix;
 }
 
 
diff --git a/src/libutil/util.hh b/src/libutil/util.hh
index a1acb49b5..abd91b81c 100644
--- a/src/libutil/util.hh
+++ b/src/libutil/util.hh
@@ -62,7 +62,7 @@ Path dirOf(const Path & path);
 
 /* Return the base name of the given canonical path, i.e., everything
    following the final `/'. */
-string baseNameOf(const Path & path);
+std::string_view baseNameOf(std::string_view path);
 
 /* Check whether 'path' is a descendant of 'dir'. */
 bool isInDir(const Path & path, const Path & dir);
@@ -407,7 +407,7 @@ bool hasPrefix(const string & s, const string & prefix);
 
 
 /* Return true iff `s' ends in `suffix'. */
-bool hasSuffix(const string & s, const string & suffix);
+bool hasSuffix(std::string_view s, std::string_view suffix);
 
 
 /* Convert a string to lower case. */
@@ -450,10 +450,10 @@ string base64Decode(const string & s);
 /* Get a value for the specified key from an associate container, or a
    default value if the key doesn't exist. */
 template <class T>
-string get(const T & map, const string & key, const string & def = "")
+std::optional<std::string> get(const T & map, const std::string & key)
 {
     auto i = map.find(key);
-    return i == map.end() ? def : i->second;
+    return i == map.end() ? std::optional<std::string>() : i->second;
 }
 
 
diff --git a/src/nix-build/nix-build.cc b/src/nix-build/nix-build.cc
index c506f9b0a..73e3a347b 100755
--- a/src/nix-build/nix-build.cc
+++ b/src/nix-build/nix-build.cc
@@ -317,11 +317,11 @@ static void _main(int argc, char * * argv)
 
     state->printStats();
 
-    auto buildPaths = [&](const PathSet & paths) {
+    auto buildPaths = [&](const std::vector<StorePathWithOutputs> & paths) {
         /* Note: we do this even when !printMissing to efficiently
            fetch binary cache data. */
         unsigned long long downloadSize, narSize;
-        PathSet willBuild, willSubstitute, unknown;
+        StorePathSet willBuild, willSubstitute, unknown;
         store->queryMissing(paths,
             willBuild, willSubstitute, unknown, downloadSize, narSize);
 
@@ -337,9 +337,9 @@ static void _main(int argc, char * * argv)
             throw UsageError("nix-shell requires a single derivation");
 
         auto & drvInfo = drvs.front();
-        auto drv = store->derivationFromPath(drvInfo.queryDrvPath());
+        auto drv = store->derivationFromPath(store->parseStorePath(drvInfo.queryDrvPath()));
 
-        PathSet pathsToBuild;
+        std::vector<StorePathWithOutputs> pathsToBuild;
 
         /* Figure out what bash shell to use. If $NIX_BUILD_SHELL
            is not set, then build bashInteractive from
@@ -358,7 +358,7 @@ static void _main(int argc, char * * argv)
                 if (!drv)
                     throw Error("the 'bashInteractive' attribute in <nixpkgs> did not evaluate to a derivation");
 
-                pathsToBuild.insert(drv->queryDrvPath());
+                pathsToBuild.emplace_back(store->parseStorePath(drv->queryDrvPath()));
 
                 shell = drv->queryOutPath() + "/bin/bash";
 
@@ -370,10 +370,11 @@ static void _main(int argc, char * * argv)
 
         // Build or fetch all dependencies of the derivation.
         for (const auto & input : drv.inputDrvs)
-            if (std::all_of(envExclude.cbegin(), envExclude.cend(), [&](const string & exclude) { return !std::regex_search(input.first, std::regex(exclude)); }))
-                pathsToBuild.insert(makeDrvPathWithOutputs(input.first, input.second));
+            if (std::all_of(envExclude.cbegin(), envExclude.cend(),
+                    [&](const string & exclude) { return !std::regex_search(store->printStorePath(input.first), std::regex(exclude)); }))
+                pathsToBuild.emplace_back(input.first, input.second);
         for (const auto & src : drv.inputSrcs)
-            pathsToBuild.insert(src);
+            pathsToBuild.emplace_back(src);
 
         buildPaths(pathsToBuild);
 
@@ -399,7 +400,7 @@ static void _main(int argc, char * * argv)
         env["NIX_STORE"] = store->storeDir;
         env["NIX_BUILD_CORES"] = std::to_string(settings.buildCores);
 
-        auto passAsFile = tokenizeString<StringSet>(get(drv.env, "passAsFile", ""));
+        auto passAsFile = tokenizeString<StringSet>(get(drv.env, "passAsFile").value_or(""));
 
         bool keepTmp = false;
         int fileNr = 0;
@@ -468,7 +469,7 @@ static void _main(int argc, char * * argv)
 
     else {
 
-        PathSet pathsToBuild;
+        std::vector<StorePathWithOutputs> pathsToBuild;
 
         std::map<Path, Path> drvPrefixes;
         std::map<Path, Path> resultSymlinks;
@@ -482,7 +483,7 @@ static void _main(int argc, char * * argv)
             if (outputName == "")
                 throw Error("derivation '%s' lacks an 'outputName' attribute", drvPath);
 
-            pathsToBuild.insert(drvPath + "!" + outputName);
+            pathsToBuild.emplace_back(store->parseStorePath(drvPath), StringSet{outputName});
 
             std::string drvPrefix;
             auto i = drvPrefixes.find(drvPath);
@@ -508,7 +509,7 @@ static void _main(int argc, char * * argv)
 
         for (auto & symlink : resultSymlinks)
             if (auto store2 = store.dynamic_pointer_cast<LocalFSStore>())
-                store2->addPermRoot(symlink.second, absPath(symlink.first), true);
+                store2->addPermRoot(store->parseStorePath(symlink.second), absPath(symlink.first), true);
 
         for (auto & path : outPaths)
             std::cout << path << '\n';
diff --git a/src/nix-channel/nix-channel.cc b/src/nix-channel/nix-channel.cc
index 70aa5c966..1b337a712 100755
--- a/src/nix-channel/nix-channel.cc
+++ b/src/nix-channel/nix-channel.cc
@@ -27,7 +27,7 @@ static void readChannels()
             continue;
         auto split = tokenizeString<std::vector<string>>(line, " ");
         auto url = std::regex_replace(split[0], std::regex("/*$"), "");
-        auto name = split.size() > 1 ? split[1] : baseNameOf(url);
+        auto name = split.size() > 1 ? split[1] : std::string(baseNameOf(url));
         channels[name] = url;
     }
 }
@@ -98,10 +98,9 @@ static void update(const StringSet & channelNames)
         // shows something useful).
         auto cname = name;
         std::smatch match;
-        auto urlBase = baseNameOf(url);
-        if (std::regex_search(urlBase, match, std::regex("(-\\d.*)$"))) {
+        auto urlBase = std::string(baseNameOf(url));
+        if (std::regex_search(urlBase, match, std::regex("(-\\d.*)$")))
             cname = cname + (string) match[1];
-        }
 
         std::string extraAttrs;
 
diff --git a/src/nix-copy-closure/nix-copy-closure.cc b/src/nix-copy-closure/nix-copy-closure.cc
index fdcde8b07..f87035760 100755
--- a/src/nix-copy-closure/nix-copy-closure.cc
+++ b/src/nix-copy-closure/nix-copy-closure.cc
@@ -52,11 +52,11 @@ static int _main(int argc, char ** argv)
         auto to = toMode ? openStore(remoteUri) : openStore();
         auto from = toMode ? openStore() : openStore(remoteUri);
 
-        PathSet storePaths2;
+        StorePathSet storePaths2;
         for (auto & path : storePaths)
             storePaths2.insert(from->followLinksToStorePath(path));
 
-        PathSet closure;
+        StorePathSet closure;
         from->computeFSClosure(storePaths2, closure, false, includeOutputs);
 
         copyPaths(from, to, closure, NoRepair, NoCheckSigs, useSubstitutes);
diff --git a/src/nix-daemon/nix-daemon.cc b/src/nix-daemon/nix-daemon.cc
index 73d1d1127..134898561 100644
--- a/src/nix-daemon/nix-daemon.cc
+++ b/src/nix-daemon/nix-daemon.cc
@@ -286,7 +286,7 @@ static int _main(int argc, char * * argv)
                 if (chdir(socketDir.c_str()) == -1)
                     throw SysError(format("changing to socket directory '%1%'") % socketDir);
 
-                auto socketName = baseNameOf(socketPath);
+                auto socketName = std::string(baseNameOf(socketPath));
                 auto addr = sockaddr_un{};
                 addr.sun_family = AF_UNIX;
                 if (socketName.size() + 1 >= sizeof(addr.sun_path))
diff --git a/src/nix-env/nix-env.cc b/src/nix-env/nix-env.cc
index a9c743955..a40d0c7e6 100644
--- a/src/nix-env/nix-env.cc
+++ b/src/nix-env/nix-env.cc
@@ -208,10 +208,11 @@ static long comparePriorities(EvalState & state, DrvInfo & drv1, DrvInfo & drv2)
 // at a time.
 static bool isPrebuilt(EvalState & state, DrvInfo & elem)
 {
-    Path path = elem.queryOutPath();
+    auto path = state.store->parseStorePath(elem.queryOutPath());
     if (state.store->isValidPath(path)) return true;
-    PathSet ps = state.store->querySubstitutablePaths({path});
-    return ps.find(path) != ps.end();
+    StorePathSet paths;
+    paths.insert(path.clone()); // FIXME: why doesn't StorePathSet{path.clone()} work?
+    return state.store->querySubstitutablePaths(paths).count(path);
 }
 
 
@@ -371,24 +372,21 @@ static void queryInstSources(EvalState & state,
         case srcStorePaths: {
 
             for (auto & i : args) {
-                Path path = state.store->followLinksToStorePath(i);
+                auto path = state.store->followLinksToStorePath(i);
 
-                string name = baseNameOf(path);
-                string::size_type dash = name.find('-');
-                if (dash != string::npos)
-                    name = string(name, dash + 1);
+                std::string name(path.name());
 
                 DrvInfo elem(state, "", nullptr);
                 elem.setName(name);
 
-                if (isDerivation(path)) {
-                    elem.setDrvPath(path);
-                    elem.setOutPath(state.store->derivationFromPath(path).findOutput("out"));
+                if (path.isDerivation()) {
+                    elem.setDrvPath(state.store->printStorePath(path));
+                    elem.setOutPath(state.store->printStorePath(state.store->derivationFromPath(path).findOutput("out")));
                     if (name.size() >= drvExtension.size() &&
                         string(name, name.size() - drvExtension.size()) == drvExtension)
                         name = string(name, 0, name.size() - drvExtension.size());
                 }
-                else elem.setOutPath(path);
+                else elem.setOutPath(state.store->printStorePath(path));
 
                 elems.push_back(elem);
             }
@@ -421,13 +419,13 @@ static void queryInstSources(EvalState & state,
 
 static void printMissing(EvalState & state, DrvInfos & elems)
 {
-    PathSet targets;
+    std::vector<StorePathWithOutputs> targets;
     for (auto & i : elems) {
         Path drvPath = i.queryDrvPath();
         if (drvPath != "")
-            targets.insert(drvPath);
+            targets.emplace_back(state.store->parseStorePath(drvPath));
         else
-            targets.insert(i.queryOutPath());
+            targets.emplace_back(state.store->parseStorePath(i.queryOutPath()));
     }
 
     printMissing(state.store, targets);
@@ -697,15 +695,15 @@ static void opSet(Globals & globals, Strings opFlags, Strings opArgs)
         drv.setName(globals.forceName);
 
     if (drv.queryDrvPath() != "") {
-        PathSet paths = {drv.queryDrvPath()};
+        std::vector<StorePathWithOutputs> paths{globals.state->store->parseStorePath(drv.queryDrvPath())};
         printMissing(globals.state->store, paths);
         if (globals.dryRun) return;
         globals.state->store->buildPaths(paths, globals.state->repair ? bmRepair : bmNormal);
-    }
-    else {
-        printMissing(globals.state->store, {drv.queryOutPath()});
+    } else {
+        printMissing(globals.state->store,
+            {globals.state->store->parseStorePath(drv.queryOutPath())});
         if (globals.dryRun) return;
-        globals.state->store->ensurePath(drv.queryOutPath());
+        globals.state->store->ensurePath(globals.state->store->parseStorePath(drv.queryOutPath()));
     }
 
     debug(format("switching to new user environment"));
@@ -729,7 +727,7 @@ static void uninstallDerivations(Globals & globals, Strings & selectors,
             for (auto & j : selectors)
                 /* !!! the repeated calls to followLinksToStorePath()
                    are expensive, should pre-compute them. */
-                if ((isPath(j) && i.queryOutPath() == globals.state->store->followLinksToStorePath(j))
+                if ((isPath(j) && globals.state->store->parseStorePath(i.queryOutPath()) == globals.state->store->followLinksToStorePath(j))
                     || DrvName(j).matches(drvName))
                 {
                     printInfo("uninstalling '%s'", i.queryName());
@@ -953,12 +951,13 @@ static void opQuery(Globals & globals, Strings opFlags, Strings opArgs)
 
 
     /* Query which paths have substitutes. */
-    PathSet validPaths, substitutablePaths;
+    StorePathSet validPaths;
+    StorePathSet substitutablePaths;
     if (printStatus || globals.prebuiltOnly) {
-        PathSet paths;
+        StorePathSet paths;
         for (auto & i : elems)
             try {
-                paths.insert(i.queryOutPath());
+                paths.insert(globals.state->store->parseStorePath(i.queryOutPath()));
             } catch (AssertionError & e) {
                 printMsg(lvlTalkative, "skipping derivation named '%s' which gives an assertion failure", i.queryName());
                 i.setFailed();
@@ -989,8 +988,8 @@ static void opQuery(Globals & globals, Strings opFlags, Strings opArgs)
             //Activity act(*logger, lvlDebug, format("outputting query result '%1%'") % i.attrPath);
 
             if (globals.prebuiltOnly &&
-                validPaths.find(i.queryOutPath()) == validPaths.end() &&
-                substitutablePaths.find(i.queryOutPath()) == substitutablePaths.end())
+                !validPaths.count(globals.state->store->parseStorePath(i.queryOutPath())) &&
+                !substitutablePaths.count(globals.state->store->parseStorePath(i.queryOutPath())))
                 continue;
 
             /* For table output. */
@@ -1001,9 +1000,9 @@ static void opQuery(Globals & globals, Strings opFlags, Strings opArgs)
 
             if (printStatus) {
                 Path outPath = i.queryOutPath();
-                bool hasSubs = substitutablePaths.find(outPath) != substitutablePaths.end();
+                bool hasSubs = substitutablePaths.count(globals.state->store->parseStorePath(outPath));
                 bool isInstalled = installed.find(outPath) != installed.end();
-                bool isValid = validPaths.find(outPath) != validPaths.end();
+                bool isValid = validPaths.count(globals.state->store->parseStorePath(outPath));
                 if (xmlOutput) {
                     attrs["installed"] = isInstalled ? "1" : "0";
                     attrs["valid"] = isValid ? "1" : "0";
@@ -1347,7 +1346,7 @@ static int _main(int argc, char * * argv)
             using LegacyArgs::LegacyArgs;
         };
 
-        MyArgs myArgs(baseNameOf(argv[0]), [&](Strings::iterator & arg, const Strings::iterator & end) {
+        MyArgs myArgs(std::string(baseNameOf(argv[0])), [&](Strings::iterator & arg, const Strings::iterator & end) {
             Operation oldOp = op;
 
             if (*arg == "--help")
diff --git a/src/nix-env/user-env.cc b/src/nix-env/user-env.cc
index 7b9a88281..8e4ecda4e 100644
--- a/src/nix-env/user-env.cc
+++ b/src/nix-env/user-env.cc
@@ -32,16 +32,16 @@ bool createUserEnv(EvalState & state, DrvInfos & elems,
 {
     /* Build the components in the user environment, if they don't
        exist already. */
-    PathSet drvsToBuild;
+    std::vector<StorePathWithOutputs> drvsToBuild;
     for (auto & i : elems)
         if (i.queryDrvPath() != "")
-            drvsToBuild.insert(i.queryDrvPath());
+            drvsToBuild.push_back({state.store->parseStorePath(i.queryDrvPath())});
 
     debug(format("building user environment dependencies"));
     state.store->buildPaths(drvsToBuild, state.repair ? bmRepair : bmNormal);
 
     /* Construct the whole top level derivation. */
-    PathSet references;
+    StorePathSet references;
     Value manifest;
     state.mkList(manifest, elems.size());
     unsigned int n = 0;
@@ -77,10 +77,10 @@ bool createUserEnv(EvalState & state, DrvInfos & elems,
 
             /* This is only necessary when installing store paths, e.g.,
                `nix-env -i /nix/store/abcd...-foo'. */
-            state.store->addTempRoot(j.second);
-            state.store->ensurePath(j.second);
+            state.store->addTempRoot(state.store->parseStorePath(j.second));
+            state.store->ensurePath(state.store->parseStorePath(j.second));
 
-            references.insert(j.second);
+            references.insert(state.store->parseStorePath(j.second));
         }
 
         // Copy the meta attributes.
@@ -95,14 +95,14 @@ bool createUserEnv(EvalState & state, DrvInfos & elems,
         vMeta.attrs->sort();
         v.attrs->sort();
 
-        if (drvPath != "") references.insert(drvPath);
+        if (drvPath != "") references.insert(state.store->parseStorePath(drvPath));
     }
 
     /* Also write a copy of the list of user environment elements to
        the store; we need it for future modifications of the
        environment. */
-    Path manifestFile = state.store->addTextToStore("env-manifest.nix",
-        (format("%1%") % manifest).str(), references);
+    auto manifestFile = state.store->addTextToStore("env-manifest.nix",
+        fmt("%s", manifest), references);
 
     /* Get the environment builder expression. */
     Value envBuilder;
@@ -113,7 +113,7 @@ bool createUserEnv(EvalState & state, DrvInfos & elems,
     Value args, topLevel;
     state.mkAttrs(args, 3);
     mkString(*state.allocAttr(args, state.symbols.create("manifest")),
-        manifestFile, {manifestFile});
+        state.store->printStorePath(manifestFile), {state.store->printStorePath(manifestFile)});
     args.attrs->push_back(Attr(state.symbols.create("derivations"), &manifest));
     args.attrs->sort();
     mkApp(topLevel, envBuilder, args);
@@ -123,13 +123,15 @@ bool createUserEnv(EvalState & state, DrvInfos & elems,
     state.forceValue(topLevel);
     PathSet context;
     Attr & aDrvPath(*topLevel.attrs->find(state.sDrvPath));
-    Path topLevelDrv = state.coerceToPath(aDrvPath.pos ? *(aDrvPath.pos) : noPos, *(aDrvPath.value), context);
+    auto topLevelDrv = state.store->parseStorePath(state.coerceToPath(aDrvPath.pos ? *(aDrvPath.pos) : noPos, *(aDrvPath.value), context));
     Attr & aOutPath(*topLevel.attrs->find(state.sOutPath));
     Path topLevelOut = state.coerceToPath(aOutPath.pos ? *(aOutPath.pos) : noPos, *(aOutPath.value), context);
 
     /* Realise the resulting store expression. */
     debug("building user environment");
-    state.store->buildPaths({topLevelDrv}, state.repair ? bmRepair : bmNormal);
+    std::vector<StorePathWithOutputs> topLevelDrvs;
+    topLevelDrvs.push_back(StorePathWithOutputs{topLevelDrv.clone()});
+    state.store->buildPaths(topLevelDrvs, state.repair ? bmRepair : bmNormal);
 
     /* Switch the current user environment to the output path. */
     auto store2 = state.store.dynamic_pointer_cast<LocalFSStore>();
diff --git a/src/nix-instantiate/nix-instantiate.cc b/src/nix-instantiate/nix-instantiate.cc
index a736caa8f..5a886d69d 100644
--- a/src/nix-instantiate/nix-instantiate.cc
+++ b/src/nix-instantiate/nix-instantiate.cc
@@ -75,9 +75,9 @@ void processExpr(EvalState & state, const Strings & attrPaths,
                     if (++rootNr > 1) rootName += "-" + std::to_string(rootNr);
                     auto store2 = state.store.dynamic_pointer_cast<LocalFSStore>();
                     if (store2)
-                        drvPath = store2->addPermRoot(drvPath, rootName, indirectRoot);
+                        drvPath = store2->addPermRoot(store2->parseStorePath(drvPath), rootName, indirectRoot);
                 }
-                std::cout << format("%1%%2%\n") % drvPath % (outputName != "out" ? "!" + outputName : "");
+                std::cout << fmt("%s%s\n", drvPath, (outputName != "out" ? "!" + outputName : ""));
             }
         }
     }
@@ -105,7 +105,7 @@ static int _main(int argc, char * * argv)
             using LegacyArgs::LegacyArgs;
         };
 
-        MyArgs myArgs(baseNameOf(argv[0]), [&](Strings::iterator & arg, const Strings::iterator & end) {
+        MyArgs myArgs(std::string(baseNameOf(argv[0])), [&](Strings::iterator & arg, const Strings::iterator & end) {
             if (*arg == "--help")
                 showManPage("nix-instantiate");
             else if (*arg == "--version")
diff --git a/src/nix-prefetch-url/nix-prefetch-url.cc b/src/nix-prefetch-url/nix-prefetch-url.cc
index 78c883833..5040b6fb8 100644
--- a/src/nix-prefetch-url/nix-prefetch-url.cc
+++ b/src/nix-prefetch-url/nix-prefetch-url.cc
@@ -64,7 +64,7 @@ static int _main(int argc, char * * argv)
             using LegacyArgs::LegacyArgs;
         };
 
-        MyArgs myArgs(baseNameOf(argv[0]), [&](Strings::iterator & arg, const Strings::iterator & end) {
+        MyArgs myArgs(std::string(baseNameOf(argv[0])), [&](Strings::iterator & arg, const Strings::iterator & end) {
             if (*arg == "--help")
                 showManPage("nix-prefetch-url");
             else if (*arg == "--version")
@@ -156,17 +156,17 @@ static int _main(int argc, char * * argv)
         /* If an expected hash is given, the file may already exist in
            the store. */
         Hash hash, expectedHash(ht);
-        Path storePath;
+        std::optional<StorePath> storePath;
         if (args.size() == 2) {
             expectedHash = Hash(args[1], ht);
             storePath = store->makeFixedOutputPath(unpack, expectedHash, name);
-            if (store->isValidPath(storePath))
+            if (store->isValidPath(*storePath))
                 hash = expectedHash;
             else
-                storePath.clear();
+                storePath.reset();
         }
 
-        if (storePath.empty()) {
+        if (!storePath) {
 
             auto actualUri = resolveMirrorUri(*state, uri);
 
@@ -193,7 +193,7 @@ static int _main(int argc, char * * argv)
                 if (hasSuffix(baseNameOf(uri), ".zip"))
                     runProgram("unzip", true, {"-qq", tmpFile, "-d", unpacked});
                 else
-                    unpackTarfile(tmpFile, unpacked, baseNameOf(uri));
+                    unpackTarfile(tmpFile, unpacked, std::string(baseNameOf(uri)));
 
                 /* If the archive unpacks to a single file/directory, then use
                    that as the top-level. */
@@ -217,17 +217,17 @@ static int _main(int argc, char * * argv)
                into the Nix store. */
             storePath = store->addToStore(name, tmpFile, unpack, ht);
 
-            assert(storePath == store->makeFixedOutputPath(unpack, hash, name));
+            assert(*storePath == store->makeFixedOutputPath(unpack, hash, name));
         }
 
         stopProgressBar();
 
         if (!printPath)
-            printInfo(format("path is '%1%'") % storePath);
+            printInfo("path is '%s'", store->printStorePath(*storePath));
 
         std::cout << printHash16or32(hash) << std::endl;
         if (printPath)
-            std::cout << storePath << std::endl;
+            std::cout << store->printStorePath(*storePath) << std::endl;
 
         return 0;
     }
diff --git a/src/nix-store/dotgraph.cc b/src/nix-store/dotgraph.cc
index d448654fe..a9d0dbbed 100644
--- a/src/nix-store/dotgraph.cc
+++ b/src/nix-store/dotgraph.cc
@@ -10,9 +10,9 @@ using std::cout;
 namespace nix {
 
 
-static string dotQuote(const string & s)
+static string dotQuote(std::string_view s)
 {
-    return "\"" + s + "\"";
+    return "\"" + std::string(s) + "\"";
 }
 
 
@@ -34,7 +34,7 @@ static string makeEdge(const string & src, const string & dst)
 }
 
 
-static string makeNode(const string & id, const string & label,
+static string makeNode(const string & id, std::string_view label,
     const string & colour)
 {
     format f = format("%1% [label = %2%, shape = box, "
@@ -44,13 +44,6 @@ static string makeNode(const string & id, const string & label,
 }
 
 
-static string symbolicName(const string & path)
-{
-    string p = baseNameOf(path);
-    return string(p, p.find('-') + 1);
-}
-
-
 #if 0
 string pathLabel(const Path & nePath, const string & elemPath)
 {
@@ -91,25 +84,24 @@ void printClosure(const Path & nePath, const StoreExpr & fs)
 #endif
 
 
-void printDotGraph(ref<Store> store, const PathSet & roots)
+void printDotGraph(ref<Store> store, StorePathSet && roots)
 {
-    PathSet workList(roots);
-    PathSet doneSet;
+    StorePathSet workList(std::move(roots));
+    StorePathSet doneSet;
 
     cout << "digraph G {\n";
 
     while (!workList.empty()) {
-        Path path = *(workList.begin());
-        workList.erase(path);
+        auto path = std::move(workList.extract(workList.begin()).value());
 
-        if (!doneSet.insert(path).second) continue;
+        if (!doneSet.insert(path.clone()).second) continue;
 
-        cout << makeNode(path, symbolicName(path), "#ff0000");
+        cout << makeNode(std::string(path.to_string()), path.name(), "#ff0000");
 
         for (auto & p : store->queryPathInfo(path)->references) {
             if (p != path) {
-                workList.insert(p);
-                cout << makeEdge(p, path);
+                workList.insert(p.clone());
+                cout << makeEdge(std::string(p.to_string()), std::string(p.to_string()));
             }
         }
 
diff --git a/src/nix-store/dotgraph.hh b/src/nix-store/dotgraph.hh
index e2b5fc72f..73b8d06b9 100644
--- a/src/nix-store/dotgraph.hh
+++ b/src/nix-store/dotgraph.hh
@@ -1,11 +1,9 @@
 #pragma once
 
-#include "types.hh"
+#include "store-api.hh"
 
 namespace nix {
 
-class Store;
-
-void printDotGraph(ref<Store> store, const PathSet & roots);
+void printDotGraph(ref<Store> store, StorePathSet && roots);
 
 }
diff --git a/src/nix-store/graphml.cc b/src/nix-store/graphml.cc
index 670fbe227..347708851 100644
--- a/src/nix-store/graphml.cc
+++ b/src/nix-store/graphml.cc
@@ -11,7 +11,7 @@ using std::cout;
 namespace nix {
 
 
-static inline const string & xmlQuote(const string & s)
+static inline std::string_view xmlQuote(std::string_view s)
 {
     // Luckily, store paths shouldn't contain any character that needs to be
     // quoted.
@@ -19,14 +19,13 @@ static inline const string & xmlQuote(const string & s)
 }
 
 
-static string symbolicName(const string & path)
+static string symbolicName(const std::string & p)
 {
-    string p = baseNameOf(path);
     return string(p, p.find('-') + 1);
 }
 
 
-static string makeEdge(const string & src, const string & dst)
+static string makeEdge(std::string_view src, std::string_view dst)
 {
     return fmt("  <edge source=\"%1%\" target=\"%2%\"/>\n",
         xmlQuote(src), xmlQuote(dst));
@@ -41,18 +40,18 @@ static string makeNode(const ValidPathInfo & info)
         "    <data key=\"name\">%3%</data>\n"
         "    <data key=\"type\">%4%</data>\n"
         "  </node>\n",
-        info.path,
+        info.path.to_string(),
         info.narSize,
-        symbolicName(info.path),
-        (isDerivation(info.path) ? "derivation" : "output-path"));
+        symbolicName(std::string(info.path.name())),
+        (info.path.isDerivation() ? "derivation" : "output-path"));
 }
 
 
-void printGraphML(ref<Store> store, const PathSet & roots)
+void printGraphML(ref<Store> store, StorePathSet && roots)
 {
-    PathSet workList(roots);
-    PathSet doneSet;
-    std::pair<PathSet::iterator,bool> ret;
+    StorePathSet workList(std::move(roots));
+    StorePathSet doneSet;
+    std::pair<StorePathSet::iterator, bool> ret;
 
     cout << "<?xml version='1.0' encoding='utf-8'?>\n"
          << "<graphml xmlns='http://graphml.graphdrawing.org/xmlns'\n"
@@ -64,19 +63,18 @@ void printGraphML(ref<Store> store, const PathSet & roots)
          << "<graph id='G' edgedefault='directed'>\n";
 
     while (!workList.empty()) {
-        Path path = *(workList.begin());
-        workList.erase(path);
+        auto path = std::move(workList.extract(workList.begin()).value());
 
-        ret = doneSet.insert(path);
+        ret = doneSet.insert(path.clone());
         if (ret.second == false) continue;
 
-        ValidPathInfo info = *(store->queryPathInfo(path));
-        cout << makeNode(info);
+        auto info = store->queryPathInfo(path);
+        cout << makeNode(*info);
 
-        for (auto & p : store->queryPathInfo(path)->references) {
+        for (auto & p : info->references) {
             if (p != path) {
-                workList.insert(p);
-                cout << makeEdge(path, p);
+                workList.insert(p.clone());
+                cout << makeEdge(path.to_string(), p.to_string());
             }
         }
 
diff --git a/src/nix-store/graphml.hh b/src/nix-store/graphml.hh
index b78df1e49..78be8a367 100644
--- a/src/nix-store/graphml.hh
+++ b/src/nix-store/graphml.hh
@@ -1,11 +1,9 @@
 #pragma once
 
-#include "types.hh"
+#include "store-api.hh"
 
 namespace nix {
 
-class Store;
-
-void printGraphML(ref<Store> store, const PathSet & roots);
+void printGraphML(ref<Store> store, StorePathSet && roots);
 
 }
diff --git a/src/nix-store/nix-store.cc b/src/nix-store/nix-store.cc
index dfa473db5..e2e2939f4 100644
--- a/src/nix-store/nix-store.cc
+++ b/src/nix-store/nix-store.cc
@@ -47,38 +47,37 @@ ref<LocalStore> ensureLocalStore()
 }
 
 
-static Path useDeriver(Path path)
+static StorePath useDeriver(const StorePath & path)
 {
-    if (isDerivation(path)) return path;
-    Path drvPath = store->queryPathInfo(path)->deriver;
-    if (drvPath == "")
-        throw Error(format("deriver of path '%1%' is not known") % path);
-    return drvPath;
+    if (path.isDerivation()) return path.clone();
+    auto info = store->queryPathInfo(path);
+    if (!info->deriver)
+        throw Error("deriver of path '%s' is not known", store->printStorePath(path));
+    return info->deriver->clone();
 }
 
 
 /* Realise the given path.  For a derivation that means build it; for
    other paths it means ensure their validity. */
-static PathSet realisePath(Path path, bool build = true)
+static PathSet realisePath(StorePathWithOutputs path, bool build = true)
 {
-    DrvPathWithOutputs p = parseDrvPathWithOutputs(path);
-
     auto store2 = std::dynamic_pointer_cast<LocalFSStore>(store);
 
-    if (isDerivation(p.first)) {
+    if (path.path.isDerivation()) {
         if (build) store->buildPaths({path});
-        Derivation drv = store->derivationFromPath(p.first);
+        Derivation drv = store->derivationFromPath(path.path);
         rootNr++;
 
-        if (p.second.empty())
-            for (auto & i : drv.outputs) p.second.insert(i.first);
+        if (path.outputs.empty())
+            for (auto & i : drv.outputs) path.outputs.insert(i.first);
 
         PathSet outputs;
-        for (auto & j : p.second) {
+        for (auto & j : path.outputs) {
             DerivationOutputs::iterator i = drv.outputs.find(j);
             if (i == drv.outputs.end())
-                throw Error(format("derivation '%1%' does not have an output named '%2%'") % p.first % j);
-            Path outPath = i->second.path;
+                throw Error("derivation '%s' does not have an output named '%s'",
+                    store2->printStorePath(path.path), j);
+            auto outPath = store2->printStorePath(i->second.path);
             if (store2) {
                 if (gcRoot == "")
                     printGCWarning();
@@ -86,7 +85,7 @@ static PathSet realisePath(Path path, bool build = true)
                     Path rootName = gcRoot;
                     if (rootNr > 1) rootName += "-" + std::to_string(rootNr);
                     if (i->first != "out") rootName += "-" + i->first;
-                    outPath = store2->addPermRoot(outPath, rootName, indirectRoot);
+                    outPath = store2->addPermRoot(store->parseStorePath(outPath), rootName, indirectRoot);
                 }
             }
             outputs.insert(outPath);
@@ -95,8 +94,9 @@ static PathSet realisePath(Path path, bool build = true)
     }
 
     else {
-        if (build) store->ensurePath(path);
-        else if (!store->isValidPath(path)) throw Error(format("path '%1%' does not exist and cannot be created") % path);
+        if (build) store->ensurePath(path.path);
+        else if (!store->isValidPath(path.path))
+            throw Error("path '%s' does not exist and cannot be created", store->printStorePath(path.path));
         if (store2) {
             if (gcRoot == "")
                 printGCWarning();
@@ -104,10 +104,10 @@ static PathSet realisePath(Path path, bool build = true)
                 Path rootName = gcRoot;
                 rootNr++;
                 if (rootNr > 1) rootName += "-" + std::to_string(rootNr);
-                path = store2->addPermRoot(path, rootName, indirectRoot);
+                return {store2->addPermRoot(path.path, rootName, indirectRoot)};
             }
         }
-        return {path};
+        return {store->printStorePath(path.path)};
     }
 }
 
@@ -126,23 +126,20 @@ static void opRealise(Strings opFlags, Strings opArgs)
         else if (i == "--ignore-unknown") ignoreUnknown = true;
         else throw UsageError(format("unknown flag '%1%'") % i);
 
-    Paths paths;
-    for (auto & i : opArgs) {
-        DrvPathWithOutputs p = parseDrvPathWithOutputs(i);
-        paths.push_back(makeDrvPathWithOutputs(store->followLinksToStorePath(p.first), p.second));
-    }
+    std::vector<StorePathWithOutputs> paths;
+    for (auto & i : opArgs)
+        paths.push_back(store->parseDrvPathWithOutputs(i));
 
     unsigned long long downloadSize, narSize;
-    PathSet willBuild, willSubstitute, unknown;
-    store->queryMissing(PathSet(paths.begin(), paths.end()),
-        willBuild, willSubstitute, unknown, downloadSize, narSize);
+    StorePathSet willBuild, willSubstitute, unknown;
+    store->queryMissing(paths, willBuild, willSubstitute, unknown, downloadSize, narSize);
 
     if (ignoreUnknown) {
-        Paths paths2;
+        std::vector<StorePathWithOutputs> paths2;
         for (auto & i : paths)
-            if (unknown.find(i) == unknown.end()) paths2.push_back(i);
-        paths = paths2;
-        unknown = PathSet();
+            if (!unknown.count(i.path)) paths2.push_back(i);
+        paths = std::move(paths2);
+        unknown = StorePathSet();
     }
 
     if (settings.printMissing)
@@ -151,14 +148,14 @@ static void opRealise(Strings opFlags, Strings opArgs)
     if (dryRun) return;
 
     /* Build all paths at the same time to exploit parallelism. */
-    store->buildPaths(PathSet(paths.begin(), paths.end()), buildMode);
+    store->buildPaths(paths, buildMode);
 
     if (!ignoreUnknown)
         for (auto & i : paths) {
-            PathSet paths = realisePath(i, false);
+            auto paths2 = realisePath(i, false);
             if (!noOutput)
-                for (auto & j : paths)
-                    cout << format("%1%\n") % j;
+                for (auto & j : paths2)
+                    cout << fmt("%1%\n", j);
         }
 }
 
@@ -169,7 +166,7 @@ static void opAdd(Strings opFlags, Strings opArgs)
     if (!opFlags.empty()) throw UsageError("unknown flag");
 
     for (auto & i : opArgs)
-        cout << format("%1%\n") % store->addToStore(baseNameOf(i), i);
+        cout << fmt("%s\n", store->printStorePath(store->addToStore(std::string(baseNameOf(i)), i)));
 }
 
 
@@ -190,7 +187,7 @@ static void opAddFixed(Strings opFlags, Strings opArgs)
     opArgs.pop_front();
 
     for (auto & i : opArgs)
-        cout << format("%1%\n") % store->addToStore(baseNameOf(i), i, recursive, hashAlgo);
+        cout << fmt("%s\n", store->printStorePath(store->addToStore(std::string(baseNameOf(i)), i, recursive, hashAlgo)));
 }
 
 
@@ -211,22 +208,21 @@ static void opPrintFixedPath(Strings opFlags, Strings opArgs)
     string hash = *i++;
     string name = *i++;
 
-    cout << format("%1%\n") %
-        store->makeFixedOutputPath(recursive, Hash(hash, hashAlgo), name);
+    cout << fmt("%s\n", store->printStorePath(store->makeFixedOutputPath(recursive, Hash(hash, hashAlgo), name)));
 }
 
 
-static PathSet maybeUseOutputs(const Path & storePath, bool useOutput, bool forceRealise)
+static StorePathSet maybeUseOutputs(const StorePath & storePath, bool useOutput, bool forceRealise)
 {
     if (forceRealise) realisePath(storePath);
-    if (useOutput && isDerivation(storePath)) {
-        Derivation drv = store->derivationFromPath(storePath);
-        PathSet outputs;
+    if (useOutput && storePath.isDerivation()) {
+        auto drv = store->derivationFromPath(storePath);
+        StorePathSet outputs;
         for (auto & i : drv.outputs)
-            outputs.insert(i.second.path);
+            outputs.insert(i.second.path.clone());
         return outputs;
     }
-    else return {storePath};
+    else return singleton(storePath.clone());
 }
 
 
@@ -239,23 +235,23 @@ const string treeLine = "|   ";
 const string treeNull = "    ";
 
 
-static void printTree(const Path & path,
-    const string & firstPad, const string & tailPad, PathSet & done)
+static void printTree(const StorePath & path,
+    const string & firstPad, const string & tailPad, StorePathSet & done)
 {
-    if (!done.insert(path).second) {
-        cout << format("%1%%2% [...]\n") % firstPad % path;
+    if (!done.insert(path.clone()).second) {
+        cout << fmt("%s%s [...]\n", firstPad, store->printStorePath(path));
         return;
     }
 
-    cout << format("%1%%2%\n") % firstPad % path;
+    cout << fmt("%s%s\n", firstPad, store->printStorePath(path));
 
-    auto references = store->queryPathInfo(path)->references;
+    auto info = store->queryPathInfo(path);
 
     /* Topologically sort under the relation A < B iff A \in
        closure(B).  That is, if derivation A is an (possibly indirect)
        input of B, then A is printed first.  This has the effect of
        flattening the tree, preventing deeply nested structures.  */
-    Paths sorted = store->topoSortPaths(references);
+    auto sorted = store->topoSortPaths(info->references);
     reverse(sorted.begin(), sorted.end());
 
     for (auto i = sorted.begin(); i != sorted.end(); ++i) {
@@ -318,11 +314,11 @@ static void opQuery(Strings opFlags, Strings opArgs)
 
         case qOutputs: {
             for (auto & i : opArgs) {
-                i = store->followLinksToStorePath(i);
-                if (forceRealise) realisePath(i);
-                Derivation drv = store->derivationFromPath(i);
+                auto i2 = store->followLinksToStorePath(i);
+                if (forceRealise) realisePath(i2);
+                Derivation drv = store->derivationFromPath(i2);
                 for (auto & j : drv.outputs)
-                    cout << format("%1%\n") % j.second.path;
+                    cout << fmt("%1%\n", store->printStorePath(j.second.path));
             }
             break;
         }
@@ -331,51 +327,54 @@ static void opQuery(Strings opFlags, Strings opArgs)
         case qReferences:
         case qReferrers:
         case qReferrersClosure: {
-            PathSet paths;
+            StorePathSet paths;
             for (auto & i : opArgs) {
-                PathSet ps = maybeUseOutputs(store->followLinksToStorePath(i), useOutput, forceRealise);
+                auto ps = maybeUseOutputs(store->followLinksToStorePath(i), useOutput, forceRealise);
                 for (auto & j : ps) {
                     if (query == qRequisites) store->computeFSClosure(j, paths, false, includeOutputs);
                     else if (query == qReferences) {
                         for (auto & p : store->queryPathInfo(j)->references)
-                            paths.insert(p);
+                            paths.insert(p.clone());
+                    }
+                    else if (query == qReferrers) {
+                        StorePathSet tmp;
+                        store->queryReferrers(j, tmp);
+                        for (auto & i : tmp)
+                            paths.insert(i.clone());
                     }
-                    else if (query == qReferrers) store->queryReferrers(j, paths);
                     else if (query == qReferrersClosure) store->computeFSClosure(j, paths, true);
                 }
             }
-            Paths sorted = store->topoSortPaths(paths);
-            for (Paths::reverse_iterator i = sorted.rbegin();
+            auto sorted = store->topoSortPaths(paths);
+            for (StorePaths::reverse_iterator i = sorted.rbegin();
                  i != sorted.rend(); ++i)
-                cout << format("%s\n") % *i;
+                cout << fmt("%s\n", store->printStorePath(*i));
             break;
         }
 
         case qDeriver:
             for (auto & i : opArgs) {
-                Path deriver = store->queryPathInfo(store->followLinksToStorePath(i))->deriver;
-                cout << format("%1%\n") %
-                    (deriver == "" ? "unknown-deriver" : deriver);
+                auto info = store->queryPathInfo(store->followLinksToStorePath(i));
+                cout << fmt("%s\n", info->deriver ? store->printStorePath(*info->deriver) : "unknown-deriver");
             }
             break;
 
         case qBinding:
             for (auto & i : opArgs) {
-                Path path = useDeriver(store->followLinksToStorePath(i));
+                auto path = useDeriver(store->followLinksToStorePath(i));
                 Derivation drv = store->derivationFromPath(path);
                 StringPairs::iterator j = drv.env.find(bindingName);
                 if (j == drv.env.end())
-                    throw Error(format("derivation '%1%' has no environment binding named '%2%'")
-                        % path % bindingName);
-                cout << format("%1%\n") % j->second;
+                    throw Error("derivation '%s' has no environment binding named '%s'",
+                        store->printStorePath(path), bindingName);
+                cout << fmt("%s\n", j->second);
             }
             break;
 
         case qHash:
         case qSize:
             for (auto & i : opArgs) {
-                PathSet paths = maybeUseOutputs(store->followLinksToStorePath(i), useOutput, forceRealise);
-                for (auto & j : paths) {
+                for (auto & j : maybeUseOutputs(store->followLinksToStorePath(i), useOutput, forceRealise)) {
                     auto info = store->queryPathInfo(j);
                     if (query == qHash) {
                         assert(info->narHash.type == htSHA256);
@@ -387,50 +386,51 @@ static void opQuery(Strings opFlags, Strings opArgs)
             break;
 
         case qTree: {
-            PathSet done;
+            StorePathSet done;
             for (auto & i : opArgs)
                 printTree(store->followLinksToStorePath(i), "", "", done);
             break;
         }
 
         case qGraph: {
-            PathSet roots;
-            for (auto & i : opArgs) {
-                PathSet paths = maybeUseOutputs(store->followLinksToStorePath(i), useOutput, forceRealise);
-                roots.insert(paths.begin(), paths.end());
-            }
-            printDotGraph(ref<Store>(store), roots);
+            StorePathSet roots;
+            for (auto & i : opArgs)
+                for (auto & j : maybeUseOutputs(store->followLinksToStorePath(i), useOutput, forceRealise))
+                    roots.insert(j.clone());
+            printDotGraph(ref<Store>(store), std::move(roots));
             break;
         }
 
         case qGraphML: {
-            PathSet roots;
-            for (auto & i : opArgs) {
-                PathSet paths = maybeUseOutputs(store->followLinksToStorePath(i), useOutput, forceRealise);
-                roots.insert(paths.begin(), paths.end());
-            }
-            printGraphML(ref<Store>(store), roots);
+            StorePathSet roots;
+            for (auto & i : opArgs)
+                for (auto & j : maybeUseOutputs(store->followLinksToStorePath(i), useOutput, forceRealise))
+                    roots.insert(j.clone());
+            printGraphML(ref<Store>(store), std::move(roots));
             break;
         }
 
         case qResolve: {
             for (auto & i : opArgs)
-                cout << format("%1%\n") % store->followLinksToStorePath(i);
+                cout << fmt("%s\n", store->printStorePath(store->followLinksToStorePath(i)));
             break;
         }
 
         case qRoots: {
-            PathSet referrers;
-            for (auto & i : opArgs) {
-                store->computeFSClosure(
-                    maybeUseOutputs(store->followLinksToStorePath(i), useOutput, forceRealise),
-                    referrers, true, settings.gcKeepOutputs, settings.gcKeepDerivations);
-            }
+            StorePathSet args;
+            for (auto & i : opArgs)
+                for (auto & p : maybeUseOutputs(store->followLinksToStorePath(i), useOutput, forceRealise))
+                    args.insert(p.clone());
+
+            StorePathSet referrers;
+            store->computeFSClosure(
+                args, referrers, true, settings.gcKeepOutputs, settings.gcKeepDerivations);
+
             Roots roots = store->findRoots(false);
             for (auto & [target, links] : roots)
                 if (referrers.find(target) != referrers.end())
                     for (auto & link : links)
-                        cout << format("%1% -> %2%\n") % link % target;
+                        cout << fmt("%1% -> %2%\n", link, store->printStorePath(target));
             break;
         }
 
@@ -446,7 +446,7 @@ static void opPrintEnv(Strings opFlags, Strings opArgs)
     if (opArgs.size() != 1) throw UsageError("'--print-env' requires one derivation store path");
 
     Path drvPath = opArgs.front();
-    Derivation drv = store->derivationFromPath(drvPath);
+    Derivation drv = store->derivationFromPath(store->parseStorePath(drvPath));
 
     /* Print each environment variable in the derivation in a format
        that can be sourced by the shell. */
@@ -476,7 +476,7 @@ static void opReadLog(Strings opFlags, Strings opArgs)
         auto path = store->followLinksToStorePath(i);
         auto log = store->getBuildLog(path);
         if (!log)
-            throw Error("build log of derivation '%s' is not available", path);
+            throw Error("build log of derivation '%s' is not available", store->printStorePath(path));
         std::cout << *log;
     }
 }
@@ -487,13 +487,10 @@ static void opDumpDB(Strings opFlags, Strings opArgs)
     if (!opFlags.empty()) throw UsageError("unknown flag");
     if (!opArgs.empty()) {
         for (auto & i : opArgs)
-            i = store->followLinksToStorePath(i);
-        for (auto & i : opArgs)
-            cout << store->makeValidityRegistration({i}, true, true);
+            cout << store->makeValidityRegistration(singleton(store->followLinksToStorePath(i)), true, true);
     } else {
-        PathSet validPaths = store->queryAllValidPaths();
-        for (auto & i : validPaths)
-            cout << store->makeValidityRegistration({i}, true, true);
+        for (auto & i : store->queryAllValidPaths())
+            cout << store->makeValidityRegistration(singleton(i), true, true);
     }
 }
 
@@ -503,18 +500,18 @@ static void registerValidity(bool reregister, bool hashGiven, bool canonicalise)
     ValidPathInfos infos;
 
     while (1) {
-        ValidPathInfo info = decodeValidPathInfo(cin, hashGiven);
-        if (info.path == "") break;
-        if (!store->isValidPath(info.path) || reregister) {
+        auto info = decodeValidPathInfo(*store, cin, hashGiven);
+        if (!info) break;
+        if (!store->isValidPath(info->path) || reregister) {
             /* !!! races */
             if (canonicalise)
-                canonicalisePathMetaData(info.path, -1);
+                canonicalisePathMetaData(store->printStorePath(info->path), -1);
             if (!hashGiven) {
-                HashResult hash = hashPath(htSHA256, info.path);
-                info.narHash = hash.first;
-                info.narSize = hash.second;
+                HashResult hash = hashPath(htSHA256, store->printStorePath(info->path));
+                info->narHash = hash.first;
+                info->narSize = hash.second;
             }
-            infos.push_back(info);
+            infos.push_back(std::move(*info));
         }
     }
 
@@ -556,12 +553,12 @@ static void opCheckValidity(Strings opFlags, Strings opArgs)
         else throw UsageError(format("unknown flag '%1%'") % i);
 
     for (auto & i : opArgs) {
-        Path path = store->followLinksToStorePath(i);
+        auto path = store->followLinksToStorePath(i);
         if (!store->isValidPath(path)) {
             if (printInvalid)
-                cout << format("%1%\n") % path;
+                cout << fmt("%s\n", store->printStorePath(path));
             else
-                throw Error(format("path '%1%' is not valid") % path);
+                throw Error("path '%s' is not valid", store->printStorePath(path));
         }
     }
 }
@@ -591,13 +588,13 @@ static void opGC(Strings opFlags, Strings opArgs)
 
     if (printRoots) {
         Roots roots = store->findRoots(false);
-        std::set<std::pair<Path, Path>> roots2;
+        std::set<std::pair<Path, StorePath>> roots2;
         // Transpose and sort the roots.
         for (auto & [target, links] : roots)
             for (auto & link : links)
-                roots2.emplace(link, target);
+                roots2.emplace(link, target.clone());
         for (auto & [link, target] : roots2)
-            std::cout << link << " -> " << target << "\n";
+            std::cout << link << " -> " << store->printStorePath(target) << "\n";
     }
 
     else {
@@ -661,11 +658,13 @@ static void opExport(Strings opFlags, Strings opArgs)
     for (auto & i : opFlags)
         throw UsageError(format("unknown flag '%1%'") % i);
 
+    StorePathSet paths;
+
     for (auto & i : opArgs)
-        i = store->followLinksToStorePath(i);
+        paths.insert(store->followLinksToStorePath(i));
 
     FdSink sink(STDOUT_FILENO);
-    store->exportPaths(opArgs, sink);
+    store->exportPaths(paths, sink);
     sink.flush();
 }
 
@@ -678,10 +677,10 @@ static void opImport(Strings opFlags, Strings opArgs)
     if (!opArgs.empty()) throw UsageError("no arguments expected");
 
     FdSource source(STDIN_FILENO);
-    Paths paths = store->importPaths(source, nullptr, NoCheckSigs);
+    auto paths = store->importPaths(source, nullptr, NoCheckSigs);
 
     for (auto & i : paths)
-        cout << format("%1%\n") % i << std::flush;
+        cout << fmt("%s\n", store->printStorePath(i)) << std::flush;
 }
 
 
@@ -726,16 +725,16 @@ static void opVerifyPath(Strings opFlags, Strings opArgs)
     int status = 0;
 
     for (auto & i : opArgs) {
-        Path path = store->followLinksToStorePath(i);
-        printMsg(lvlTalkative, format("checking path '%1%'...") % path);
+        auto path = store->followLinksToStorePath(i);
+        printMsg(lvlTalkative, "checking path '%s'...", store->printStorePath(path));
         auto info = store->queryPathInfo(path);
         HashSink sink(info->narHash.type);
         store->narFromPath(path, sink);
         auto current = sink.finish();
         if (current.first != info->narHash) {
             printError(
-                format("path '%1%' was modified! expected hash '%2%', got '%3%'")
-                % path % info->narHash.to_string() % current.first.to_string());
+                "path '%s' was modified! expected hash '%s', got '%s'",
+                store->printStorePath(path), info->narHash.to_string(), current.first.to_string());
             status = 1;
         }
     }
@@ -751,10 +750,8 @@ static void opRepairPath(Strings opFlags, Strings opArgs)
     if (!opFlags.empty())
         throw UsageError("no flags expected");
 
-    for (auto & i : opArgs) {
-        Path path = store->followLinksToStorePath(i);
-        ensureLocalStore()->repairPath(path);
-    }
+    for (auto & i : opArgs)
+        ensureLocalStore()->repairPath(store->followLinksToStorePath(i));
 }
 
 /* Optimise the disk space usage of the Nix store by hard-linking
@@ -818,7 +815,7 @@ static void opServe(Strings opFlags, Strings opArgs)
             case cmdQueryValidPaths: {
                 bool lock = readInt(in);
                 bool substitute = readInt(in);
-                PathSet paths = readStorePaths<PathSet>(*store, in);
+                auto paths = readStorePaths<StorePathSet>(*store, in);
                 if (lock && writeAllowed)
                     for (auto & path : paths)
                         store->addTempRoot(path);
@@ -828,34 +825,39 @@ static void opServe(Strings opFlags, Strings opArgs)
                    flag. */
                 if (substitute && writeAllowed) {
                     /* Filter out .drv files (we don't want to build anything). */
-                    PathSet paths2;
+                    std::vector<StorePathWithOutputs> paths2;
                     for (auto & path : paths)
-                        if (!isDerivation(path)) paths2.insert(path);
+                        if (!path.isDerivation())
+                            paths2.emplace_back(path.clone());
                     unsigned long long downloadSize, narSize;
-                    PathSet willBuild, willSubstitute, unknown;
-                    store->queryMissing(PathSet(paths2.begin(), paths2.end()),
+                    StorePathSet willBuild, willSubstitute, unknown;
+                    store->queryMissing(paths2,
                         willBuild, willSubstitute, unknown, downloadSize, narSize);
                     /* FIXME: should use ensurePath(), but it only
                        does one path at a time. */
                     if (!willSubstitute.empty())
                         try {
-                            store->buildPaths(willSubstitute);
+                            std::vector<StorePathWithOutputs> subs;
+                            for (auto & p : willSubstitute) subs.emplace_back(p.clone());
+                            store->buildPaths(subs);
                         } catch (Error & e) {
                             printError(format("warning: %1%") % e.msg());
                         }
                 }
 
-                out << store->queryValidPaths(paths);
+                writeStorePaths(*store, out, store->queryValidPaths(paths));
                 break;
             }
 
             case cmdQueryPathInfos: {
-                PathSet paths = readStorePaths<PathSet>(*store, in);
+                auto paths = readStorePaths<StorePathSet>(*store, in);
                 // !!! Maybe we want a queryPathInfos?
                 for (auto & i : paths) {
                     try {
                         auto info = store->queryPathInfo(i);
-                        out << info->path << info->deriver << info->references;
+                        out << store->printStorePath(info->path)
+                            << (info->deriver ? store->printStorePath(*info->deriver) : "");
+                        writeStorePaths(*store, out, info->references);
                         // !!! Maybe we want compression?
                         out << info->narSize // downloadSize
                             << info->narSize;
@@ -869,7 +871,7 @@ static void opServe(Strings opFlags, Strings opArgs)
             }
 
             case cmdDumpStorePath:
-                store->narFromPath(readStorePath(*store, in), out);
+                store->narFromPath(store->parseStorePath(readString(in)), out);
                 break;
 
             case cmdImportPaths: {
@@ -881,14 +883,17 @@ static void opServe(Strings opFlags, Strings opArgs)
 
             case cmdExportPaths: {
                 readInt(in); // obsolete
-                store->exportPaths(readStorePaths<Paths>(*store, in), out);
+                store->exportPaths(readStorePaths<StorePathSet>(*store, in), out);
                 break;
             }
 
             case cmdBuildPaths: {
 
                 if (!writeAllowed) throw Error("building paths is not allowed");
-                PathSet paths = readStorePaths<PathSet>(*store, in);
+
+                std::vector<StorePathWithOutputs> paths;
+                for (auto & s : readStrings<Strings>(in))
+                    paths.emplace_back(store->parseDrvPathWithOutputs(s));
 
                 getBuildSettings();
 
@@ -907,7 +912,7 @@ static void opServe(Strings opFlags, Strings opArgs)
 
                 if (!writeAllowed) throw Error("building paths is not allowed");
 
-                Path drvPath = readStorePath(*store, in); // informational only
+                auto drvPath = store->parseStorePath(readString(in)); // informational only
                 BasicDerivation drv;
                 readDerivation(in, *store, drv);
 
@@ -926,30 +931,29 @@ static void opServe(Strings opFlags, Strings opArgs)
 
             case cmdQueryClosure: {
                 bool includeOutputs = readInt(in);
-                PathSet closure;
-                store->computeFSClosure(readStorePaths<PathSet>(*store, in),
+                StorePathSet closure;
+                store->computeFSClosure(readStorePaths<StorePathSet>(*store, in),
                     closure, false, includeOutputs);
-                out << closure;
+                writeStorePaths(*store, out, closure);
                 break;
             }
 
             case cmdAddToStoreNar: {
                 if (!writeAllowed) throw Error("importing paths is not allowed");
 
-                ValidPathInfo info;
-                info.path = readStorePath(*store, in);
-                in >> info.deriver;
-                if (!info.deriver.empty())
-                    store->assertStorePath(info.deriver);
+                auto path = readString(in);
+                ValidPathInfo info(store->parseStorePath(path));
+                auto deriver = readString(in);
+                if (deriver != "")
+                    info.deriver = store->parseStorePath(deriver);
                 info.narHash = Hash(readString(in), htSHA256);
-                info.references = readStorePaths<PathSet>(*store, in);
+                info.references = readStorePaths<StorePathSet>(*store, in);
                 in >> info.registrationTime >> info.narSize >> info.ultimate;
                 info.sigs = readStrings<StringSet>(in);
                 in >> info.ca;
 
-                if (info.narSize == 0) {
+                if (info.narSize == 0)
                     throw Error("narInfo is too old and missing the narSize field");
-                }
 
                 SizedSource sizedSource(in, info.narSize);
 
diff --git a/src/nix/add-to-store.cc b/src/nix/add-to-store.cc
index 296b2c7e4..139db3657 100644
--- a/src/nix/add-to-store.cc
+++ b/src/nix/add-to-store.cc
@@ -40,16 +40,17 @@ struct CmdAddToStore : MixDryRun, StoreCommand
         StringSink sink;
         dumpPath(path, sink);
 
-        ValidPathInfo info;
-        info.narHash = hashString(htSHA256, *sink.s);
+        auto narHash = hashString(htSHA256, *sink.s);
+
+        ValidPathInfo info(store->makeFixedOutputPath(true, narHash, *namePart));
+        info.narHash = narHash;
         info.narSize = sink.s->size();
-        info.path = store->makeFixedOutputPath(true, info.narHash, *namePart);
         info.ca = makeFixedOutputCA(true, info.narHash);
 
         if (!dryRun)
             store->addToStore(info, sink.s);
 
-        std::cout << fmt("%s\n", info.path);
+        std::cout << fmt("%s\n", store->printStorePath(info.path));
     }
 };
 
diff --git a/src/nix/command.cc b/src/nix/command.cc
index 9dbc3685a..442bc6c53 100644
--- a/src/nix/command.cc
+++ b/src/nix/command.cc
@@ -48,28 +48,29 @@ StorePathsCommand::StorePathsCommand(bool recursive)
 
 void StorePathsCommand::run(ref<Store> store)
 {
-    Paths storePaths;
+    StorePaths storePaths;
 
     if (all) {
         if (installables.size())
             throw UsageError("'--all' does not expect arguments");
         for (auto & p : store->queryAllValidPaths())
-            storePaths.push_back(p);
+            storePaths.push_back(p.clone());
     }
 
     else {
         for (auto & p : toStorePaths(store, realiseMode, installables))
-            storePaths.push_back(p);
+            storePaths.push_back(p.clone());
 
         if (recursive) {
-            PathSet closure;
-            store->computeFSClosure(PathSet(storePaths.begin(), storePaths.end()),
-                closure, false, false);
-            storePaths = Paths(closure.begin(), closure.end());
+            StorePathSet closure;
+            store->computeFSClosure(storePathsToSet(storePaths), closure, false, false);
+            storePaths.clear();
+            for (auto & p : closure)
+                storePaths.push_back(p.clone());
         }
     }
 
-    run(store, storePaths);
+    run(store, std::move(storePaths));
 }
 
 void StorePathCommand::run(ref<Store> store)
diff --git a/src/nix/command.hh b/src/nix/command.hh
index 7474c5eae..00eb46903 100644
--- a/src/nix/command.hh
+++ b/src/nix/command.hh
@@ -2,6 +2,7 @@
 
 #include "args.hh"
 #include "common-eval-args.hh"
+#include "path.hh"
 
 namespace nix {
 
@@ -28,8 +29,8 @@ private:
 
 struct Buildable
 {
-    Path drvPath; // may be empty
-    std::map<std::string, Path> outputs;
+    std::optional<StorePath> drvPath;
+    std::map<std::string, StorePath> outputs;
 };
 
 typedef std::vector<Buildable> Buildables;
@@ -131,7 +132,7 @@ public:
 
     using StoreCommand::run;
 
-    virtual void run(ref<Store> store, Paths storePaths) = 0;
+    virtual void run(ref<Store> store, std::vector<StorePath> storePaths) = 0;
 
     void run(ref<Store> store) override;
 
@@ -143,7 +144,7 @@ struct StorePathCommand : public InstallablesCommand
 {
     using StoreCommand::run;
 
-    virtual void run(ref<Store> store, const Path & storePath) = 0;
+    virtual void run(ref<Store> store, const StorePath & storePath) = 0;
 
     void run(ref<Store> store) override;
 };
@@ -174,13 +175,13 @@ std::shared_ptr<Installable> parseInstallable(
 Buildables build(ref<Store> store, RealiseMode mode,
     std::vector<std::shared_ptr<Installable>> installables);
 
-PathSet toStorePaths(ref<Store> store, RealiseMode mode,
+std::set<StorePath> toStorePaths(ref<Store> store, RealiseMode mode,
     std::vector<std::shared_ptr<Installable>> installables);
 
-Path toStorePath(ref<Store> store, RealiseMode mode,
+StorePath toStorePath(ref<Store> store, RealiseMode mode,
     std::shared_ptr<Installable> installable);
 
-PathSet toDerivations(ref<Store> store,
+std::set<StorePath> toDerivations(ref<Store> store,
     std::vector<std::shared_ptr<Installable>> installables,
     bool useDeriver = false);
 
diff --git a/src/nix/copy.cc b/src/nix/copy.cc
index b1aceb15c..85c777d38 100644
--- a/src/nix/copy.cc
+++ b/src/nix/copy.cc
@@ -80,14 +80,14 @@ struct CmdCopy : StorePathsCommand
         return srcUri.empty() ? StoreCommand::createStore() : openStore(srcUri);
     }
 
-    void run(ref<Store> srcStore, Paths storePaths) override
+    void run(ref<Store> srcStore, StorePaths storePaths) override
     {
         if (srcUri.empty() && dstUri.empty())
             throw UsageError("you must pass '--from' and/or '--to'");
 
         ref<Store> dstStore = dstUri.empty() ? openStore() : openStore(dstUri);
 
-        copyPaths(srcStore, dstStore, PathSet(storePaths.begin(), storePaths.end()),
+        copyPaths(srcStore, dstStore, storePathsToSet(storePaths),
             NoRepair, checkSigs, substitute);
     }
 };
diff --git a/src/nix/dump-path.cc b/src/nix/dump-path.cc
index 90f1552d9..bb741b572 100644
--- a/src/nix/dump-path.cc
+++ b/src/nix/dump-path.cc
@@ -20,7 +20,7 @@ struct CmdDumpPath : StorePathCommand
         };
     }
 
-    void run(ref<Store> store, const Path & storePath) override
+    void run(ref<Store> store, const StorePath & storePath) override
     {
         FdSink sink(STDOUT_FILENO);
         store->narFromPath(storePath, sink);
diff --git a/src/nix/installables.cc b/src/nix/installables.cc
index 0e8bba39d..8ce6bd06e 100644
--- a/src/nix/installables.cc
+++ b/src/nix/installables.cc
@@ -89,15 +89,25 @@ Buildable Installable::toBuildable()
 
 struct InstallableStorePath : Installable
 {
-    Path storePath;
+    ref<Store> store;
+    StorePath storePath;
 
-    InstallableStorePath(const Path & storePath) : storePath(storePath) { }
+    InstallableStorePath(ref<Store> store, const Path & storePath)
+        : store(store), storePath(store->parseStorePath(storePath)) { }
 
-    std::string what() override { return storePath; }
+    std::string what() override { return store->printStorePath(storePath); }
 
     Buildables toBuildables() override
     {
-        return {{isDerivation(storePath) ? storePath : "", {{"out", storePath}}}};
+        std::map<std::string, StorePath> outputs;
+        outputs.insert_or_assign("out", storePath.clone());
+        Buildable b{
+            .drvPath = storePath.isDerivation() ? storePath.clone() : std::optional<StorePath>(),
+            .outputs = std::move(outputs)
+        };
+        Buildables bs;
+        bs.push_back(std::move(b));
+        return bs;
     }
 };
 
@@ -120,17 +130,17 @@ struct InstallableValue : Installable
 
         Buildables res;
 
-        PathSet drvPaths;
+        StorePathSet drvPaths;
 
         for (auto & drv : drvs) {
-            Buildable b{drv.queryDrvPath()};
-            drvPaths.insert(b.drvPath);
+            Buildable b{.drvPath = state->store->parseStorePath(drv.queryDrvPath())};
+            drvPaths.insert(b.drvPath->clone());
 
             auto outputName = drv.queryOutputName();
             if (outputName == "")
-                throw Error("derivation '%s' lacks an 'outputName' attribute", b.drvPath);
+                throw Error("derivation '%s' lacks an 'outputName' attribute", state->store->printStorePath(*b.drvPath));
 
-            b.outputs.emplace(outputName, drv.queryOutPath());
+            b.outputs.emplace(outputName, state->store->parseStorePath(drv.queryOutPath()));
 
             res.push_back(std::move(b));
         }
@@ -138,10 +148,13 @@ struct InstallableValue : Installable
         // Hack to recognize .all: if all drvs have the same drvPath,
         // merge the buildables.
         if (drvPaths.size() == 1) {
-            Buildable b{*drvPaths.begin()};
+            Buildable b{.drvPath = drvPaths.begin()->clone()};
             for (auto & b2 : res)
-                b.outputs.insert(b2.outputs.begin(), b2.outputs.end());
-            return {b};
+                for (auto & output : b2.outputs)
+                    b.outputs.insert_or_assign(output.first, output.second.clone());
+            Buildables bs;
+            bs.push_back(std::move(b));
+            return bs;
         } else
             return res;
     }
@@ -212,7 +225,7 @@ static std::vector<std::shared_ptr<Installable>> parseInstallables(
             auto path = store->toStorePath(store->followLinksToStore(s));
 
             if (store->isStorePath(path))
-                result.push_back(std::make_shared<InstallableStorePath>(path));
+                result.push_back(std::make_shared<InstallableStorePath>(store, path));
         }
 
         else if (s == "" || std::regex_match(s, attrPathRegex))
@@ -242,19 +255,18 @@ Buildables build(ref<Store> store, RealiseMode mode,
 
     Buildables buildables;
 
-    PathSet pathsToBuild;
+    std::vector<StorePathWithOutputs> pathsToBuild;
 
     for (auto & i : installables) {
         for (auto & b : i->toBuildables()) {
-            if (b.drvPath != "") {
+            if (b.drvPath) {
                 StringSet outputNames;
                 for (auto & output : b.outputs)
                     outputNames.insert(output.first);
-                pathsToBuild.insert(
-                    b.drvPath + "!" + concatStringsSep(",", outputNames));
+                pathsToBuild.push_back({*b.drvPath, outputNames});
             } else
                 for (auto & output : b.outputs)
-                    pathsToBuild.insert(output.second);
+                    pathsToBuild.push_back({output.second.clone()});
             buildables.push_back(std::move(b));
         }
     }
@@ -267,19 +279,19 @@ Buildables build(ref<Store> store, RealiseMode mode,
     return buildables;
 }
 
-PathSet toStorePaths(ref<Store> store, RealiseMode mode,
+StorePathSet toStorePaths(ref<Store> store, RealiseMode mode,
     std::vector<std::shared_ptr<Installable>> installables)
 {
-    PathSet outPaths;
+    StorePathSet outPaths;
 
     for (auto & b : build(store, mode, installables))
         for (auto & output : b.outputs)
-            outPaths.insert(output.second);
+            outPaths.insert(output.second.clone());
 
     return outPaths;
 }
 
-Path toStorePath(ref<Store> store, RealiseMode mode,
+StorePath toStorePath(ref<Store> store, RealiseMode mode,
     std::shared_ptr<Installable> installable)
 {
     auto paths = toStorePaths(store, mode, {installable});
@@ -287,17 +299,17 @@ Path toStorePath(ref<Store> store, RealiseMode mode,
     if (paths.size() != 1)
             throw Error("argument '%s' should evaluate to one store path", installable->what());
 
-    return *paths.begin();
+    return paths.begin()->clone();
 }
 
-PathSet toDerivations(ref<Store> store,
+StorePathSet toDerivations(ref<Store> store,
     std::vector<std::shared_ptr<Installable>> installables, bool useDeriver)
 {
-    PathSet drvPaths;
+    StorePathSet drvPaths;
 
     for (auto & i : installables)
         for (auto & b : i->toBuildables()) {
-            if (b.drvPath.empty()) {
+            if (!b.drvPath) {
                 if (!useDeriver)
                     throw Error("argument '%s' did not evaluate to a derivation", i->what());
                 for (auto & output : b.outputs) {
@@ -305,10 +317,10 @@ PathSet toDerivations(ref<Store> store,
                     if (derivers.empty())
                         throw Error("'%s' does not have a known deriver", i->what());
                     // FIXME: use all derivers?
-                    drvPaths.insert(*derivers.begin());
+                    drvPaths.insert(derivers.begin()->clone());
                 }
             } else
-                drvPaths.insert(b.drvPath);
+                drvPaths.insert(b.drvPath->clone());
         }
 
     return drvPaths;
diff --git a/src/nix/local.mk b/src/nix/local.mk
index c09efd1fc..a34cca9fd 100644
--- a/src/nix/local.mk
+++ b/src/nix/local.mk
@@ -15,7 +15,7 @@ nix_SOURCES := \
   $(wildcard src/nix-prefetch-url/*.cc) \
   $(wildcard src/nix-store/*.cc) \
 
-nix_LIBS = libexpr libmain libstore libutil
+nix_LIBS = libexpr libmain libstore libutil libnixrust
 
 nix_LDFLAGS = -pthread $(SODIUM_LIBS) $(EDITLINE_LIBS) $(BOOST_LDFLAGS) -lboost_context -lboost_thread -lboost_system
 
diff --git a/src/nix/log.cc b/src/nix/log.cc
index 122a3d690..795991cb7 100644
--- a/src/nix/log.cc
+++ b/src/nix/log.cc
@@ -43,7 +43,7 @@ struct CmdLog : InstallableCommand
 
         RunPager pager;
         for (auto & sub : subs) {
-            auto log = b.drvPath != "" ? sub->getBuildLog(b.drvPath) : nullptr;
+            auto log = b.drvPath ? sub->getBuildLog(*b.drvPath) : nullptr;
             for (auto & output : b.outputs) {
                 if (log) break;
                 log = sub->getBuildLog(output.second);
diff --git a/src/nix/ls.cc b/src/nix/ls.cc
index 9408cc9da..3ef1f2750 100644
--- a/src/nix/ls.cc
+++ b/src/nix/ls.cc
@@ -67,7 +67,7 @@ struct MixLs : virtual Args, MixJSON
         if (st.type == FSAccessor::Type::tMissing)
             throw Error(format("path '%1%' does not exist") % path);
         doPath(st, path,
-            st.type == FSAccessor::Type::tDirectory ? "." : baseNameOf(path),
+            st.type == FSAccessor::Type::tDirectory ? "." : std::string(baseNameOf(path)),
             showDirectory);
     }
 
diff --git a/src/nix/main.cc b/src/nix/main.cc
index 5454f4b34..41d44f431 100644
--- a/src/nix/main.cc
+++ b/src/nix/main.cc
@@ -135,7 +135,7 @@ void mainWrapped(int argc, char * * argv)
     initGC();
 
     programPath = argv[0];
-    string programName = baseNameOf(programPath);
+    auto programName = std::string(baseNameOf(programPath));
 
     {
         auto legacy = (*RegisterLegacyCommand::commands)[programName];
diff --git a/src/nix/make-content-addressable.cc b/src/nix/make-content-addressable.cc
index 5b99b5084..524d467c2 100644
--- a/src/nix/make-content-addressable.cc
+++ b/src/nix/make-content-addressable.cc
@@ -29,34 +29,36 @@ struct CmdMakeContentAddressable : StorePathsCommand
             },
         };
     }
-    void run(ref<Store> store, Paths storePaths) override
+    void run(ref<Store> store, StorePaths storePaths) override
     {
-        auto paths = store->topoSortPaths(PathSet(storePaths.begin(), storePaths.end()));
+        auto paths = store->topoSortPaths(storePathsToSet(storePaths));
 
-        paths.reverse();
+        std::reverse(paths.begin(), paths.end());
 
-        std::map<Path, Path> remappings;
+        std::map<StorePath, StorePath> remappings;
 
         for (auto & path : paths) {
+            auto pathS = store->printStorePath(path);
             auto oldInfo = store->queryPathInfo(path);
-            auto oldHashPart = storePathToHash(path);
-            auto name = storePathToName(path);
+            auto oldHashPart = storePathToHash(pathS);
 
             StringSink sink;
             store->narFromPath(path, sink);
 
             StringMap rewrites;
 
-            ValidPathInfo info;
+            StorePathSet references;
+            bool hasSelfReference = false;
             for (auto & ref : oldInfo->references) {
                 if (ref == path)
-                    info.references.insert("self");
+                    hasSelfReference = true;
                 else {
-                    auto replacement = get(remappings, ref, ref);
+                    auto i = remappings.find(ref);
+                    auto replacement = i != remappings.end() ? i->second.clone() : ref.clone();
                     // FIXME: warn about unremapped paths?
-                    info.references.insert(replacement);
                     if (replacement != ref)
-                        rewrites[storePathToHash(ref)] = storePathToHash(replacement);
+                        rewrites.insert_or_assign(store->printStorePath(ref), store->printStorePath(replacement));
+                    references.insert(std::move(replacement));
                 }
             }
 
@@ -65,24 +67,26 @@ struct CmdMakeContentAddressable : StorePathsCommand
             HashModuloSink hashModuloSink(htSHA256, oldHashPart);
             hashModuloSink((unsigned char *) sink.s->data(), sink.s->size());
 
-            info.narHash = hashModuloSink.finish().first;
+            auto narHash = hashModuloSink.finish().first;
+
+            ValidPathInfo info(store->makeFixedOutputPath(true, narHash, path.name(), references, hasSelfReference));
+            info.references = std::move(references);
+            if (hasSelfReference) info.references.insert(info.path.clone());
+            info.narHash = narHash;
             info.narSize = sink.s->size();
-            replaceInSet(info.references, path, std::string("self"));
-            info.path = store->makeFixedOutputPath(true, info.narHash, name, info.references);
-            replaceInSet(info.references, std::string("self"), info.path);
             info.ca = makeFixedOutputCA(true, info.narHash);
 
-            printError("rewrote '%s' to '%s'", path, info.path);
+            printError("rewrote '%s' to '%s'", pathS, store->printStorePath(info.path));
 
             auto source = sinkToSource([&](Sink & nextSink) {
-                RewritingSink rsink2(oldHashPart, storePathToHash(info.path), nextSink);
+                RewritingSink rsink2(oldHashPart, storePathToHash(store->printStorePath(info.path)), nextSink);
                 rsink2((unsigned char *) sink.s->data(), sink.s->size());
                 rsink2.flush();
             });
 
             store->addToStore(info, *source);
 
-            remappings[path] = info.path;
+            remappings.insert_or_assign(std::move(path), std::move(info.path));
         }
     }
 };
diff --git a/src/nix/path-info.cc b/src/nix/path-info.cc
index 2cb718f12..bffa7b356 100644
--- a/src/nix/path-info.cc
+++ b/src/nix/path-info.cc
@@ -78,36 +78,36 @@ struct CmdPathInfo : StorePathsCommand, MixJSON
         std::cout << fmt("\t%6.1f%c", res, idents.at(power));
     }
 
-    void run(ref<Store> store, Paths storePaths) override
+    void run(ref<Store> store, StorePaths storePaths) override
     {
         size_t pathLen = 0;
         for (auto & storePath : storePaths)
-            pathLen = std::max(pathLen, storePath.size());
+            pathLen = std::max(pathLen, store->printStorePath(storePath).size());
 
         if (json) {
             JSONPlaceholder jsonRoot(std::cout);
             store->pathInfoToJSON(jsonRoot,
                 // FIXME: preserve order?
-                PathSet(storePaths.begin(), storePaths.end()),
+                storePathsToSet(storePaths),
                 true, showClosureSize, AllowInvalid);
         }
 
         else {
 
-            for (auto storePath : storePaths) {
+            for (auto & storePath : storePaths) {
                 auto info = store->queryPathInfo(storePath);
-                storePath = info->path; // FIXME: screws up padding
+                auto storePathS = store->printStorePath(storePath);
 
-                std::cout << storePath;
+                std::cout << storePathS;
 
                 if (showSize || showClosureSize || showSigs)
-                    std::cout << std::string(std::max(0, (int) pathLen - (int) storePath.size()), ' ');
+                    std::cout << std::string(std::max(0, (int) pathLen - (int) storePathS.size()), ' ');
 
                 if (showSize)
                     printSize(info->narSize);
 
                 if (showClosureSize)
-                    printSize(store->getClosureSize(storePath).first);
+                    printSize(store->getClosureSize(info->path).first);
 
                 if (showSigs) {
                     std::cout << '\t';
diff --git a/src/nix/progress-bar.cc b/src/nix/progress-bar.cc
index 661966733..d20c09f26 100644
--- a/src/nix/progress-bar.cc
+++ b/src/nix/progress-bar.cc
@@ -24,6 +24,13 @@ static uint64_t getI(const std::vector<Logger::Field> & fields, size_t n)
     return fields[n].i;
 }
 
+static std::string_view storePathToName(std::string_view path)
+{
+    auto base = baseNameOf(path);
+    auto i = base.find('-');
+    return i == std::string::npos ? base.substr(0, 0) : base.substr(i + 1);
+}
+
 class ProgressBar : public Logger
 {
 private:
@@ -148,7 +155,7 @@ public:
         if (type == actBuild) {
             auto name = storePathToName(getS(fields, 0));
             if (hasSuffix(name, ".drv"))
-                name.resize(name.size() - 4);
+                name = name.substr(name.size() - 4);
             i->s = fmt("building " ANSI_BOLD "%s" ANSI_NORMAL, name);
             auto machineName = getS(fields, 1);
             if (machineName != "")
@@ -173,7 +180,7 @@ public:
         if (type == actPostBuildHook) {
             auto name = storePathToName(getS(fields, 0));
             if (hasSuffix(name, ".drv"))
-                name.resize(name.size() - 4);
+                name = name.substr(name.size() - 4);
             i->s = fmt("post-build " ANSI_BOLD "%s" ANSI_NORMAL, name);
             i->name = DrvName(name).name;
         }
diff --git a/src/nix/repl.cc b/src/nix/repl.cc
index c2b65b6ea..e6c811a7b 100644
--- a/src/nix/repl.cc
+++ b/src/nix/repl.cc
@@ -413,7 +413,7 @@ Path NixRepl::getDerivationPath(Value & v) {
     if (!drvInfo)
         throw Error("expression does not evaluate to a derivation, so I can't build it");
     Path drvPath = drvInfo->queryDrvPath();
-    if (drvPath == "" || !state.store->isValidPath(drvPath))
+    if (drvPath == "" || !state.store->isValidPath(state.store->parseStorePath(drvPath)))
         throw Error("expression did not evaluate to a valid derivation");
     return drvPath;
 }
@@ -521,10 +521,10 @@ bool NixRepl::processLine(string line)
                but doing it in a child makes it easier to recover from
                problems / SIGINT. */
             if (runProgram(settings.nixBinDir + "/nix", Strings{"build", "--no-link", drvPath}) == 0) {
-                Derivation drv = readDerivation(drvPath);
+                auto drv = readDerivation(*state.store, drvPath);
                 std::cout << std::endl << "this derivation produced the following outputs:" << std::endl;
                 for (auto & i : drv.outputs)
-                    std::cout << format("  %1% -> %2%") % i.first % i.second.path << std::endl;
+                    std::cout << fmt("  %s -> %s\n", i.first, state.store->printStorePath(i.second.path));
             }
         } else if (command == ":i") {
             runProgram(settings.nixBinDir + "/nix-env", Strings{"-i", drvPath});
diff --git a/src/nix/run.cc b/src/nix/run.cc
index ece4d3854..f885c5e49 100644
--- a/src/nix/run.cc
+++ b/src/nix/run.cc
@@ -119,24 +119,24 @@ struct CmdRun : InstallablesCommand
                 unsetenv(var.c_str());
         }
 
-        std::unordered_set<Path> done;
-        std::queue<Path> todo;
-        for (auto & path : outPaths) todo.push(path);
+        std::unordered_set<StorePath> done;
+        std::queue<StorePath> todo;
+        for (auto & path : outPaths) todo.push(path.clone());
 
         auto unixPath = tokenizeString<Strings>(getEnv("PATH").value_or(""), ":");
 
         while (!todo.empty()) {
-            Path path = todo.front();
+            auto path = todo.front().clone();
             todo.pop();
-            if (!done.insert(path).second) continue;
+            if (!done.insert(path.clone()).second) continue;
 
             if (true)
-                unixPath.push_front(path + "/bin");
+                unixPath.push_front(store->printStorePath(path) + "/bin");
 
-            auto propPath = path + "/nix-support/propagated-user-env-packages";
+            auto propPath = store->printStorePath(path) + "/nix-support/propagated-user-env-packages";
             if (accessor->stat(propPath).type == FSAccessor::tRegular) {
                 for (auto & p : tokenizeString<Paths>(readFile(propPath)))
-                    todo.push(p);
+                    todo.push(store->parseStorePath(p));
             }
         }
 
diff --git a/src/nix/show-derivation.cc b/src/nix/show-derivation.cc
index 6065adc4d..0ede7b468 100644
--- a/src/nix/show-derivation.cc
+++ b/src/nix/show-derivation.cc
@@ -46,9 +46,9 @@ struct CmdShowDerivation : InstallablesCommand
         auto drvPaths = toDerivations(store, installables, true);
 
         if (recursive) {
-            PathSet closure;
+            StorePathSet closure;
             store->computeFSClosure(drvPaths, closure);
-            drvPaths = closure;
+            drvPaths = std::move(closure);
         }
 
         {
@@ -56,17 +56,19 @@ struct CmdShowDerivation : InstallablesCommand
         JSONObject jsonRoot(std::cout, true);
 
         for (auto & drvPath : drvPaths) {
-            if (!isDerivation(drvPath)) continue;
+            if (!drvPath.isDerivation()) continue;
 
-            auto drvObj(jsonRoot.object(drvPath));
+            auto drvPathS = store->printStorePath(drvPath);
 
-            auto drv = readDerivation(drvPath);
+            auto drvObj(jsonRoot.object(drvPathS));
+
+            auto drv = readDerivation(*store, drvPathS);
 
             {
                 auto outputsObj(drvObj.object("outputs"));
                 for (auto & output : drv.outputs) {
                     auto outputObj(outputsObj.object(output.first));
-                    outputObj.attr("path", output.second.path);
+                    outputObj.attr("path", store->printStorePath(output.second.path));
                     if (output.second.hash != "") {
                         outputObj.attr("hashAlgo", output.second.hashAlgo);
                         outputObj.attr("hash", output.second.hash);
@@ -77,13 +79,13 @@ struct CmdShowDerivation : InstallablesCommand
             {
                 auto inputsList(drvObj.list("inputSrcs"));
                 for (auto & input : drv.inputSrcs)
-                    inputsList.elem(input);
+                    inputsList.elem(store->printStorePath(input));
             }
 
             {
                 auto inputDrvsObj(drvObj.object("inputDrvs"));
                 for (auto & input : drv.inputDrvs) {
-                    auto inputList(inputDrvsObj.list(input.first));
+                    auto inputList(inputDrvsObj.list(store->printStorePath(input.first)));
                     for (auto & outputId : input.second)
                         inputList.elem(outputId);
                 }
diff --git a/src/nix/sigs.cc b/src/nix/sigs.cc
index 23bc83ad0..5f07448e0 100644
--- a/src/nix/sigs.cc
+++ b/src/nix/sigs.cc
@@ -27,7 +27,7 @@ struct CmdCopySigs : StorePathsCommand
         return "copy path signatures from substituters (like binary caches)";
     }
 
-    void run(ref<Store> store, Paths storePaths) override
+    void run(ref<Store> store, StorePaths storePaths) override
     {
         if (substituterUris.empty())
             throw UsageError("you must specify at least one substituter using '-s'");
@@ -44,18 +44,20 @@ struct CmdCopySigs : StorePathsCommand
 
         //logger->setExpected(doneLabel, storePaths.size());
 
-        auto doPath = [&](const Path & storePath) {
+        auto doPath = [&](const Path & storePathS) {
             //Activity act(*logger, lvlInfo, format("getting signatures for '%s'") % storePath);
 
             checkInterrupt();
 
+            auto storePath = store->parseStorePath(storePathS);
+
             auto info = store->queryPathInfo(storePath);
 
             StringSet newSigs;
 
             for (auto & store2 : substituters) {
                 try {
-                    auto info2 = store2->queryPathInfo(storePath);
+                    auto info2 = store2->queryPathInfo(info->path);
 
                     /* Don't import signatures that don't match this
                        binary. */
@@ -80,11 +82,11 @@ struct CmdCopySigs : StorePathsCommand
         };
 
         for (auto & storePath : storePaths)
-            pool.enqueue(std::bind(doPath, storePath));
+            pool.enqueue(std::bind(doPath, store->printStorePath(storePath)));
 
         pool.process();
 
-        printInfo(format("imported %d signatures") % added);
+        printInfo("imported %d signatures", added);
     }
 };
 
@@ -109,7 +111,7 @@ struct CmdSignPaths : StorePathsCommand
         return "sign the specified paths";
     }
 
-    void run(ref<Store> store, Paths storePaths) override
+    void run(ref<Store> store, StorePaths storePaths) override
     {
         if (secretKeyFile.empty())
             throw UsageError("you must specify a secret key file using '-k'");
@@ -123,7 +125,7 @@ struct CmdSignPaths : StorePathsCommand
 
             auto info2(*info);
             info2.sigs.clear();
-            info2.sign(secretKey);
+            info2.sign(*store, secretKey);
             assert(!info2.sigs.empty());
 
             if (!info->sigs.count(*info2.sigs.begin())) {
@@ -132,7 +134,7 @@ struct CmdSignPaths : StorePathsCommand
             }
         }
 
-        printInfo(format("added %d signatures") % added);
+        printInfo("added %d signatures", added);
     }
 };
 
diff --git a/src/nix/upgrade-nix.cc b/src/nix/upgrade-nix.cc
index e6c369a7c..87f1f9d1b 100644
--- a/src/nix/upgrade-nix.cc
+++ b/src/nix/upgrade-nix.cc
@@ -58,13 +58,9 @@ struct CmdUpgradeNix : MixDryRun, StoreCommand
 
         printInfo("upgrading Nix in profile '%s'", profileDir);
 
-        Path storePath;
-        {
-            Activity act(*logger, lvlInfo, actUnknown, "querying latest Nix version");
-            storePath = getLatestNix(store);
-        }
+        auto storePath = getLatestNix(store);
 
-        auto version = DrvName(storePathToName(storePath)).version;
+        auto version = DrvName(storePath.name()).version;
 
         if (dryRun) {
             stopProgressBar();
@@ -73,13 +69,13 @@ struct CmdUpgradeNix : MixDryRun, StoreCommand
         }
 
         {
-            Activity act(*logger, lvlInfo, actUnknown, fmt("downloading '%s'...", storePath));
+            Activity act(*logger, lvlInfo, actUnknown, fmt("downloading '%s'...", store->printStorePath(storePath)));
             store->ensurePath(storePath);
         }
 
         {
-            Activity act(*logger, lvlInfo, actUnknown, fmt("verifying that '%s' works...", storePath));
-            auto program = storePath + "/bin/nix-env";
+            Activity act(*logger, lvlInfo, actUnknown, fmt("verifying that '%s' works...", store->printStorePath(storePath)));
+            auto program = store->printStorePath(storePath) + "/bin/nix-env";
             auto s = runProgram(program, false, {"--version"});
             if (s.find("Nix") == std::string::npos)
                 throw Error("could not verify that '%s' works", program);
@@ -88,9 +84,10 @@ struct CmdUpgradeNix : MixDryRun, StoreCommand
         stopProgressBar();
 
         {
-            Activity act(*logger, lvlInfo, actUnknown, fmt("installing '%s' into profile '%s'...", storePath, profileDir));
+            Activity act(*logger, lvlInfo, actUnknown,
+                fmt("installing '%s' into profile '%s'...", store->printStorePath(storePath), profileDir));
             runProgram(settings.nixBinDir + "/nix-env", false,
-                {"--profile", profileDir, "-i", storePath, "--no-sandbox"});
+                {"--profile", profileDir, "-i", store->printStorePath(storePath), "--no-sandbox"});
         }
 
         printError(ANSI_GREEN "upgrade to version %s done" ANSI_NORMAL, version);
@@ -129,15 +126,17 @@ struct CmdUpgradeNix : MixDryRun, StoreCommand
             !hasSuffix(userEnv, "user-environment"))
             throw Error("directory '%s' does not appear to be part of a Nix profile", where);
 
-        if (!store->isValidPath(userEnv))
+        if (!store->isValidPath(store->parseStorePath(userEnv)))
             throw Error("directory '%s' is not in the Nix store", userEnv);
 
         return profileDir;
     }
 
     /* Return the store path of the latest stable Nix. */
-    Path getLatestNix(ref<Store> store)
+    StorePath getLatestNix(ref<Store> store)
     {
+        Activity act(*logger, lvlInfo, actUnknown, "querying latest Nix version");
+
         // FIXME: use nixos.org?
         auto req = DownloadRequest(storePathsUrl);
         auto res = getDownloader()->download(req);
@@ -148,7 +147,7 @@ struct CmdUpgradeNix : MixDryRun, StoreCommand
         Bindings & bindings(*state->allocBindings(0));
         auto v2 = findAlongAttrPath(*state, settings.thisSystem, bindings, *v);
 
-        return state->forceString(*v2);
+        return store->parseStorePath(state->forceString(*v2));
     }
 };
 
diff --git a/src/nix/verify.cc b/src/nix/verify.cc
index fa1414196..9b0658803 100644
--- a/src/nix/verify.cc
+++ b/src/nix/verify.cc
@@ -49,7 +49,7 @@ struct CmdVerify : StorePathsCommand
         };
     }
 
-    void run(ref<Store> store, Paths storePaths) override
+    void run(ref<Store> store, StorePaths storePaths) override
     {
         std::vector<ref<Store>> substituters;
         for (auto & s : substituterUris)
@@ -80,7 +80,7 @@ struct CmdVerify : StorePathsCommand
                 MaintainCount<std::atomic<size_t>> mcActive(active);
                 update();
 
-                auto info = store->queryPathInfo(storePath);
+                auto info = store->queryPathInfo(store->parseStorePath(storePath));
 
                 if (!noContents) {
 
@@ -88,7 +88,7 @@ struct CmdVerify : StorePathsCommand
                     if (info->ca == "")
                         hashSink = std::make_unique<HashSink>(info->narHash.type);
                     else
-                        hashSink = std::make_unique<HashModuloSink>(info->narHash.type, storePathToHash(info->path));
+                        hashSink = std::make_unique<HashModuloSink>(info->narHash.type, storePathToHash(store->printStorePath(info->path)));
 
                     store->narFromPath(info->path, *hashSink);
 
@@ -96,10 +96,10 @@ struct CmdVerify : StorePathsCommand
 
                     if (hash.first != info->narHash) {
                         corrupted++;
-                        act2.result(resCorruptedPath, info->path);
+                        act2.result(resCorruptedPath, store->printStorePath(info->path));
                         printError(
-                            format("path '%s' was modified! expected hash '%s', got '%s'")
-                            % info->path % info->narHash.to_string() % hash.first.to_string());
+                            "path '%s' was modified! expected hash '%s', got '%s'",
+                            store->printStorePath(info->path), info->narHash.to_string(), hash.first.to_string());
                     }
 
                 }
@@ -120,7 +120,7 @@ struct CmdVerify : StorePathsCommand
                         auto doSigs = [&](StringSet sigs) {
                             for (auto sig : sigs) {
                                 if (!sigsSeen.insert(sig).second) continue;
-                                if (validSigs < ValidPathInfo::maxSigs && info->checkSignature(publicKeys, sig))
+                                if (validSigs < ValidPathInfo::maxSigs && info->checkSignature(*store, publicKeys, sig))
                                     validSigs++;
                             }
                         };
@@ -147,8 +147,8 @@ struct CmdVerify : StorePathsCommand
 
                     if (!good) {
                         untrusted++;
-                        act2.result(resUntrustedPath, info->path);
-                        printError(format("path '%s' is untrusted") % info->path);
+                        act2.result(resUntrustedPath, store->printStorePath(info->path));
+                        printError("path '%s' is untrusted", store->printStorePath(info->path));
                     }
 
                 }
@@ -164,7 +164,7 @@ struct CmdVerify : StorePathsCommand
         };
 
         for (auto & storePath : storePaths)
-            pool.enqueue(std::bind(doPath, storePath));
+            pool.enqueue(std::bind(doPath, store->printStorePath(storePath)));
 
         pool.process();
 
diff --git a/src/nix/why-depends.cc b/src/nix/why-depends.cc
index fa2a903a8..8566e5851 100644
--- a/src/nix/why-depends.cc
+++ b/src/nix/why-depends.cc
@@ -73,9 +73,9 @@ struct CmdWhyDepends : SourceExprCommand
         auto packagePath = toStorePath(store, Build, package);
         auto dependency = parseInstallable(*this, store, _dependency, false);
         auto dependencyPath = toStorePath(store, NoBuild, dependency);
-        auto dependencyPathHash = storePathToHash(dependencyPath);
+        auto dependencyPathHash = storePathToHash(store->printStorePath(dependencyPath));
 
-        PathSet closure;
+        StorePathSet closure;
         store->computeFSClosure({packagePath}, closure, false, false);
 
         if (!closure.count(dependencyPath)) {
@@ -91,28 +91,28 @@ struct CmdWhyDepends : SourceExprCommand
 
         struct Node
         {
-            Path path;
-            PathSet refs;
-            PathSet rrefs;
+            StorePath path;
+            StorePathSet refs;
+            StorePathSet rrefs;
             size_t dist = inf;
             Node * prev = nullptr;
             bool queued = false;
             bool visited = false;
         };
 
-        std::map<Path, Node> graph;
+        std::map<StorePath, Node> graph;
 
         for (auto & path : closure)
-            graph.emplace(path, Node{path, store->queryPathInfo(path)->references});
+            graph.emplace(path.clone(), Node{path.clone(), cloneStorePathSet(store->queryPathInfo(path)->references)});
 
         // Transpose the graph.
         for (auto & node : graph)
             for (auto & ref : node.second.refs)
-                graph[ref].rrefs.insert(node.first);
+                graph.find(ref)->second.rrefs.insert(node.first.clone());
 
         /* Run Dijkstra's shortest path algorithm to get the distance
            of every path in the closure to 'dependency'. */
-        graph[dependencyPath].dist = 0;
+        graph[dependencyPath.clone()].dist = 0;
 
         std::priority_queue<Node *> queue;
 
@@ -151,12 +151,14 @@ struct CmdWhyDepends : SourceExprCommand
         struct BailOut { };
 
         printNode = [&](Node & node, const string & firstPad, const string & tailPad) {
+            auto pathS = store->printStorePath(node.path);
+
             assert(node.dist != inf);
             std::cout << fmt("%s%s%s%s" ANSI_NORMAL "\n",
                 firstPad,
                 node.visited ? "\e[38;5;244m" : "",
                 firstPad != "" ? "=> " : "",
-                node.path);
+                pathS);
 
             if (node.path == dependencyPath && !all
                 && packagePath != dependencyPath)
@@ -175,7 +177,7 @@ struct CmdWhyDepends : SourceExprCommand
                 auto & node2 = graph.at(ref);
                 if (node2.dist == inf) continue;
                 refs.emplace(node2.dist, &node2);
-                hashes.insert(storePathToHash(node2.path));
+                hashes.insert(storePathToHash(store->printStorePath(node2.path)));
             }
 
             /* For each reference, find the files and symlinks that
@@ -187,7 +189,7 @@ struct CmdWhyDepends : SourceExprCommand
             visitPath = [&](const Path & p) {
                 auto st = accessor->stat(p);
 
-                auto p2 = p == node.path ? "/" : std::string(p, node.path.size() + 1);
+                auto p2 = p == pathS ? "/" : std::string(p, pathS.size() + 1);
 
                 auto getColour = [&](const std::string & hash) {
                     return hash == dependencyPathHash ? ANSI_GREEN : ANSI_BLUE;
@@ -231,11 +233,11 @@ struct CmdWhyDepends : SourceExprCommand
 
             // FIXME: should use scanForReferences().
 
-            visitPath(node.path);
+            visitPath(pathS);
 
             RunPager pager;
             for (auto & ref : refs) {
-                auto hash = storePathToHash(ref.second->path);
+                auto hash = storePathToHash(store->printStorePath(ref.second->path));
 
                 bool last = all ? ref == *refs.rbegin() : true;
 
diff --git a/src/resolve-system-dependencies/local.mk b/src/resolve-system-dependencies/local.mk
index f9db16268..bf65f7905 100644
--- a/src/resolve-system-dependencies/local.mk
+++ b/src/resolve-system-dependencies/local.mk
@@ -6,6 +6,6 @@ resolve-system-dependencies_DIR := $(d)
 
 resolve-system-dependencies_INSTALL_DIR := $(libexecdir)/nix
 
-resolve-system-dependencies_LIBS := libstore libmain libutil
+resolve-system-dependencies_LIBS := libstore libmain libutil libnixrust
 
 resolve-system-dependencies_SOURCES := $(d)/resolve-system-dependencies.cc
diff --git a/src/resolve-system-dependencies/resolve-system-dependencies.cc b/src/resolve-system-dependencies/resolve-system-dependencies.cc
index 45e8b6796..8f0c99c84 100644
--- a/src/resolve-system-dependencies/resolve-system-dependencies.cc
+++ b/src/resolve-system-dependencies/resolve-system-dependencies.cc
@@ -179,8 +179,8 @@ int main(int argc, char ** argv)
         if (std::string(argv[1]) == "--test")
             impurePaths.insert(argv[2]);
         else {
-            auto drv = store->derivationFromPath(Path(argv[1]));
-            impurePaths = tokenizeString<StringSet>(get(drv.env, "__impureHostDeps"));
+            auto drv = store->derivationFromPath(store->parseStorePath(argv[1]));
+            impurePaths = tokenizeString<StringSet>(get(drv.env, "__impureHostDeps").value_or(""));
             impurePaths.insert("/usr/lib/libSystem.dylib");
         }