From c273c15cb13bb86420dda1e5341a4e19517532b5 Mon Sep 17 00:00:00 2001 From: Eelco Dolstra Date: Mon, 26 May 2014 13:46:11 +0200 Subject: [PATCH] =?UTF-8?q?Add=20primop=20=E2=80=98scopedImport=E2=80=99?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit ‘scopedImport’ works like ‘import’, except that it takes a set of attributes to be added to the lexical scope of the expression, essentially extending or overriding the builtin variables. For instance, the expression scopedImport { x = 1; } ./foo.nix where foo.nix contains ‘x’, will evaluate to 1. This has a few applications: * It allows getting rid of function argument specifications in package expressions. For instance, a package expression like: { stdenv, fetchurl, libfoo }: stdenv.mkDerivation { ... buildInputs = [ libfoo ]; } can now we written as just stdenv.mkDerivation { ... buildInputs = [ libfoo ]; } and imported in all-packages.nix as: bar = scopedImport pkgs ./bar.nix; So whereas we once had dependencies listed in three places (buildInputs, the function, and the call site), they now only need to appear in one place. * It allows overriding builtin functions. For instance, to trace all calls to ‘map’: let overrides = { map = f: xs: builtins.trace "map called!" (map f xs); # Ensure that our override gets propagated by calls to # import/scopedImport. import = fn: scopedImport overrides fn; scopedImport = attrs: fn: scopedImport (overrides // attrs) fn; # Also update ‘builtins’. builtins = builtins // overrides; }; in scopedImport overrides ./bla.nix * Similarly, it allows extending the set of builtin functions. For instance, during Nixpkgs/NixOS evaluation, the Nixpkgs library functions could be added to the default scope. There is a downside: calls to scopedImport are not memoized, unlike import. So importing a file multiple times leads to multiple parsings / evaluations. It would be possible to construct the AST only once, but that would require careful handling of variables/environments. --- src/libexpr/eval.hh | 1 + src/libexpr/nixexpr.hh | 1 - src/libexpr/parser.y | 10 ++++++++-- src/libexpr/primops.cc | 25 +++++++++++++++++++++++++ tests/lang/eval-okay-import.exp | 1 + tests/lang/eval-okay-import.nix | 11 +++++++++++ tests/lang/imported.nix | 3 +++ tests/lang/imported2.nix | 1 + 8 files changed, 50 insertions(+), 3 deletions(-) create mode 100644 tests/lang/eval-okay-import.exp create mode 100644 tests/lang/eval-okay-import.nix create mode 100644 tests/lang/imported.nix create mode 100644 tests/lang/imported2.nix diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh index 6d4cb8ab..ad4c6a4b 100644 --- a/src/libexpr/eval.hh +++ b/src/libexpr/eval.hh @@ -124,6 +124,7 @@ public: /* Parse a Nix expression from the specified file. */ Expr * parseExprFromFile(const Path & path); + Expr * parseExprFromFile(const Path & path, StaticEnv & staticEnv); /* Parse a Nix expression from the specified string. */ Expr * parseExprFromString(const string & s, const Path & basePath, StaticEnv & staticEnv); diff --git a/src/libexpr/nixexpr.hh b/src/libexpr/nixexpr.hh index 813efbe2..fbd5bad8 100644 --- a/src/libexpr/nixexpr.hh +++ b/src/libexpr/nixexpr.hh @@ -336,5 +336,4 @@ struct StaticEnv }; - } diff --git a/src/libexpr/parser.y b/src/libexpr/parser.y index dbcffff9..06d6d643 100644 --- a/src/libexpr/parser.y +++ b/src/libexpr/parser.y @@ -592,7 +592,13 @@ Path resolveExprPath(Path path) Expr * EvalState::parseExprFromFile(const Path & path) { - return parse(readFile(path).c_str(), path, dirOf(path), staticBaseEnv); + return parseExprFromFile(path, staticBaseEnv); +} + + +Expr * EvalState::parseExprFromFile(const Path & path, StaticEnv & staticEnv) +{ + return parse(readFile(path).c_str(), path, dirOf(path), staticEnv); } @@ -608,7 +614,7 @@ Expr * EvalState::parseExprFromString(const string & s, const Path & basePath) } - void EvalState::addToSearchPath(const string & s, bool warn) +void EvalState::addToSearchPath(const string & s, bool warn) { size_t pos = s.find('='); string prefix; diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc index f402478d..533ae376 100644 --- a/src/libexpr/primops.cc +++ b/src/libexpr/primops.cc @@ -93,6 +93,30 @@ static void prim_import(EvalState & state, const Pos & pos, Value * * args, Valu } +static void prim_scopedImport(EvalState & state, const Pos & pos, Value * * args, Value & v) +{ + PathSet context; + state.forceAttrs(*args[0]); + Path path = resolveExprPath(state.coerceToPath(pos, *args[1], context)); + + Env * env = &state.allocEnv(args[0]->attrs->size()); + env->up = &state.baseEnv; + + StaticEnv staticEnv(false, &state.staticBaseEnv); + + unsigned int displ = 0; + for (auto & attr : *args[0]->attrs) { + staticEnv.vars[attr.name] = displ; + env->values[displ++] = attr.value; + } + + startNest(nest, lvlTalkative, format("evaluating file `%1%'") % path); + Expr * e = state.parseExprFromFile(path, staticEnv); + + e->eval(state, *env, v); +} + + /* Return a string representing the type of the expression. */ static void prim_typeOf(EvalState & state, const Pos & pos, Value * * args, Value & v) { @@ -1247,6 +1271,7 @@ void EvalState::createBaseEnv() // Miscellaneous addPrimOp("import", 1, prim_import); + addPrimOp("scopedImport", 2, prim_scopedImport); addPrimOp("__typeOf", 1, prim_typeOf); addPrimOp("isNull", 1, prim_isNull); addPrimOp("__isFunction", 1, prim_isFunction); diff --git a/tests/lang/eval-okay-import.exp b/tests/lang/eval-okay-import.exp new file mode 100644 index 00000000..c508125b --- /dev/null +++ b/tests/lang/eval-okay-import.exp @@ -0,0 +1 @@ +[ 1 2 3 4 5 6 7 8 9 10 ] diff --git a/tests/lang/eval-okay-import.nix b/tests/lang/eval-okay-import.nix new file mode 100644 index 00000000..0b18d941 --- /dev/null +++ b/tests/lang/eval-okay-import.nix @@ -0,0 +1,11 @@ +let + + overrides = { + import = fn: scopedImport overrides fn; + + scopedImport = attrs: fn: scopedImport (overrides // attrs) fn; + + builtins = builtins // overrides; + } // import ./lib.nix; + +in scopedImport overrides ./imported.nix diff --git a/tests/lang/imported.nix b/tests/lang/imported.nix new file mode 100644 index 00000000..fb39ee4e --- /dev/null +++ b/tests/lang/imported.nix @@ -0,0 +1,3 @@ +# The function ‘range’ comes from lib.nix and was added to the lexical +# scope by scopedImport. +range 1 5 ++ import ./imported2.nix diff --git a/tests/lang/imported2.nix b/tests/lang/imported2.nix new file mode 100644 index 00000000..6d0a2992 --- /dev/null +++ b/tests/lang/imported2.nix @@ -0,0 +1 @@ +range 6 10