forked from lix-project/lix
Add primop ‘scopedImport’
‘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.
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f0fdbd0897
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c273c15cb1
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@ -124,6 +124,7 @@ public:
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/* Parse a Nix expression from the specified file. */
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/* Parse a Nix expression from the specified file. */
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Expr * parseExprFromFile(const Path & path);
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Expr * parseExprFromFile(const Path & path);
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Expr * parseExprFromFile(const Path & path, StaticEnv & staticEnv);
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/* Parse a Nix expression from the specified string. */
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/* Parse a Nix expression from the specified string. */
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Expr * parseExprFromString(const string & s, const Path & basePath, StaticEnv & staticEnv);
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Expr * parseExprFromString(const string & s, const Path & basePath, StaticEnv & staticEnv);
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@ -336,5 +336,4 @@ struct StaticEnv
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};
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};
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}
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}
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@ -592,7 +592,13 @@ Path resolveExprPath(Path path)
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Expr * EvalState::parseExprFromFile(const Path & path)
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Expr * EvalState::parseExprFromFile(const Path & path)
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{
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{
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return parse(readFile(path).c_str(), path, dirOf(path), staticBaseEnv);
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return parseExprFromFile(path, staticBaseEnv);
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}
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Expr * EvalState::parseExprFromFile(const Path & path, StaticEnv & staticEnv)
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{
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return parse(readFile(path).c_str(), path, dirOf(path), staticEnv);
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}
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}
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@ -608,7 +614,7 @@ Expr * EvalState::parseExprFromString(const string & s, const Path & basePath)
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}
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}
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void EvalState::addToSearchPath(const string & s, bool warn)
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void EvalState::addToSearchPath(const string & s, bool warn)
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{
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{
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size_t pos = s.find('=');
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size_t pos = s.find('=');
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string prefix;
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string prefix;
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@ -93,6 +93,30 @@ static void prim_import(EvalState & state, const Pos & pos, Value * * args, Valu
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}
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}
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static void prim_scopedImport(EvalState & state, const Pos & pos, Value * * args, Value & v)
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{
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PathSet context;
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state.forceAttrs(*args[0]);
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Path path = resolveExprPath(state.coerceToPath(pos, *args[1], context));
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Env * env = &state.allocEnv(args[0]->attrs->size());
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env->up = &state.baseEnv;
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StaticEnv staticEnv(false, &state.staticBaseEnv);
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unsigned int displ = 0;
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for (auto & attr : *args[0]->attrs) {
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staticEnv.vars[attr.name] = displ;
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env->values[displ++] = attr.value;
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}
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startNest(nest, lvlTalkative, format("evaluating file `%1%'") % path);
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Expr * e = state.parseExprFromFile(path, staticEnv);
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e->eval(state, *env, v);
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}
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/* Return a string representing the type of the expression. */
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/* Return a string representing the type of the expression. */
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static void prim_typeOf(EvalState & state, const Pos & pos, Value * * args, Value & v)
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static void prim_typeOf(EvalState & state, const Pos & pos, Value * * args, Value & v)
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{
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{
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@ -1247,6 +1271,7 @@ void EvalState::createBaseEnv()
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// Miscellaneous
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// Miscellaneous
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addPrimOp("import", 1, prim_import);
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addPrimOp("import", 1, prim_import);
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addPrimOp("scopedImport", 2, prim_scopedImport);
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addPrimOp("__typeOf", 1, prim_typeOf);
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addPrimOp("__typeOf", 1, prim_typeOf);
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addPrimOp("isNull", 1, prim_isNull);
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addPrimOp("isNull", 1, prim_isNull);
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addPrimOp("__isFunction", 1, prim_isFunction);
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addPrimOp("__isFunction", 1, prim_isFunction);
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1
tests/lang/eval-okay-import.exp
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1
tests/lang/eval-okay-import.exp
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@ -0,0 +1 @@
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[ 1 2 3 4 5 6 7 8 9 10 ]
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11
tests/lang/eval-okay-import.nix
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11
tests/lang/eval-okay-import.nix
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@ -0,0 +1,11 @@
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let
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overrides = {
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import = fn: scopedImport overrides fn;
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scopedImport = attrs: fn: scopedImport (overrides // attrs) fn;
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builtins = builtins // overrides;
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} // import ./lib.nix;
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in scopedImport overrides ./imported.nix
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3
tests/lang/imported.nix
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3
tests/lang/imported.nix
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@ -0,0 +1,3 @@
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# The function ‘range’ comes from lib.nix and was added to the lexical
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# scope by scopedImport.
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range 1 5 ++ import ./imported2.nix
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1
tests/lang/imported2.nix
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1
tests/lang/imported2.nix
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@ -0,0 +1 @@
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range 6 10
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