From 414397759a5390b54cee12c6834e6106bea12f5f Mon Sep 17 00:00:00 2001
From: Daiderd Jordan <daiderd@gmail.com>
Date: Sat, 25 Aug 2018 20:25:43 +0200
Subject: [PATCH 1/2] upgrade-nix: add --dry-run

---
 src/nix/upgrade-nix.cc | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/src/nix/upgrade-nix.cc b/src/nix/upgrade-nix.cc
index e23ae792..3417adb6 100644
--- a/src/nix/upgrade-nix.cc
+++ b/src/nix/upgrade-nix.cc
@@ -1,4 +1,5 @@
 #include "command.hh"
+#include "common-args.hh"
 #include "store-api.hh"
 #include "download.hh"
 #include "eval.hh"
@@ -6,7 +7,7 @@
 
 using namespace nix;
 
-struct CmdUpgradeNix : StoreCommand
+struct CmdUpgradeNix : MixDryRun, StoreCommand
 {
     Path profileDir;
 
@@ -61,21 +62,25 @@ struct CmdUpgradeNix : StoreCommand
 
         {
             Activity act(*logger, lvlInfo, actUnknown, fmt("downloading '%s'...", storePath));
-            store->ensurePath(storePath);
+            if (!dryRun)
+                store->ensurePath(storePath);
         }
 
         {
             Activity act(*logger, lvlInfo, actUnknown, fmt("verifying that '%s' works...", storePath));
-            auto program = 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);
+            if (!dryRun) {
+                auto program = 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);
+            }
         }
 
         {
             Activity act(*logger, lvlInfo, actUnknown, fmt("installing '%s' into profile '%s'...", storePath, profileDir));
-            runProgram(settings.nixBinDir + "/nix-env", false,
-                {"--profile", profileDir, "-i", storePath, "--no-sandbox"});
+            if (!dryRun)
+                runProgram(settings.nixBinDir + "/nix-env", false,
+                    {"--profile", profileDir, "-i", storePath, "--no-sandbox"});
         }
     }
 

From d85bb4814f4fa2ed6046bba6e8c6394adf9e5666 Mon Sep 17 00:00:00 2001
From: Daiderd Jordan <daiderd@gmail.com>
Date: Sat, 25 Aug 2018 20:33:01 +0200
Subject: [PATCH 2/2] upgrade-nix: resolve profile symlinks

The profile present in PATH is not necessarily the actual profile
location. User profiles are generally added as $HOME/.nix-profile
in which case the indirect profile link needs to be resolved first.

/home/user/.nix-profile -> /nix/var/nix/profiles/per-user/user/profile
/nix/var/nix/profiles/per-user/user/profile -> profile-15-link
/nix/var/nix/profiles/per-user/user/profile-14-link -> /nix/store/hyi4kkjh3bwi2z3wfljrkfymz9904h62-user-environment
/nix/var/nix/profiles/per-user/user/profile-15-link -> /nix/store/6njpl3qvihz46vj911pwx7hfcvwhifl9-user-environment

To upgrade nix here we want /nix/var/nix/profiles/per-user/user/profile-16-link
instead of /home/user/.nix-profile-1-link. The latter is not a gcroot
and would be garbage collected, resulting in a broken profile.

Fixes #2175
---
 src/nix/upgrade-nix.cc | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/src/nix/upgrade-nix.cc b/src/nix/upgrade-nix.cc
index 3417adb6..72b29828 100644
--- a/src/nix/upgrade-nix.cc
+++ b/src/nix/upgrade-nix.cc
@@ -103,11 +103,18 @@ struct CmdUpgradeNix : MixDryRun, StoreCommand
         if (hasPrefix(where, "/run/current-system"))
             throw Error("Nix on NixOS must be upgraded via 'nixos-rebuild'");
 
-        Path profileDir;
-        Path userEnv;
+        Path profileDir = dirOf(where);
+
+        // Resolve profile to /nix/var/nix/profiles/<name> link.
+        while (baseNameOf(dirOf(canonPath(profileDir))) != "profiles")
+            profileDir = readLink(profileDir);
+
+        printInfo("found profile '%s'", profileDir);
+
+        Path userEnv = canonPath(profileDir, true);
 
         if (baseNameOf(where) != "bin" ||
-            !hasSuffix(userEnv = canonPath(profileDir = dirOf(where), true), "user-environment"))
+            !hasSuffix(userEnv, "user-environment"))
             throw Error("directory '%s' does not appear to be part of a Nix profile", where);
 
         if (!store->isValidPath(userEnv))