diff options
| -rw-r--r-- | src/libexpr/eval.cc | 32 |
1 files changed, 7 insertions, 25 deletions
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc index cf9f6c543..540bfcf7b 100644 --- a/src/libexpr/eval.cc +++ b/src/libexpr/eval.cc @@ -1373,31 +1373,13 @@ void EvalState::autoCallFunction(Bindings & args, Value & fun, Value & res) if (j != args.end()) { actualArgs->attrs->push_back(*j); } else if (!i.def) { - throwMissingArgumentError(i.pos, R"(cannot auto-call a function that has an argument without a default value ('%1%') - -An 'auto-call' is when a nix expression is evaluated without any external arguments. -If that nix expression is a function, and that function's arguments all have default -values, then all is well. - -But if the function arguments don't have default values, evaluation fails. - -The classic case for this error is evaluating a nix file that expects -to be evaluated by callPackage. - # in 'callPackage' format: expression is a function that takes an argument 'stdenv'. - # callPackage would implicitly pull 'stdenv' from nixpkgs, then call this function. - { stdenv }: - stdenv.mkDerivation { - ... - - # in 'auto-call' format: nixpkgs is imported explicitly, and used directly. - let - nixpkgs = import <nixpkgs> {}; - in - nixpkgs.stdenv.mkDerivation { - ... - -More about callPackage: -https://nixos.org/guides/nix-pills/callpackage-design-pattern.html)", i.name); + throwMissingArgumentError(i.pos, R"(cannot evaluate a function that has an argument without a value ('%1%') + +Nix attempted to evaluate a function as a top level expression; in this case it must have all its +arguments supplied either by default values, or passed explicitly with --arg or --argstr. + +https://nixos.org/manual/nix/stable/#ss-functions)", i.name); + } } } |