diff options
| -rw-r--r-- | src/libexpr/eval.cc | 47 |
1 files changed, 24 insertions, 23 deletions
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc index 0446376f3..2b697882b 100644 --- a/src/libexpr/eval.cc +++ b/src/libexpr/eval.cc @@ -1366,29 +1366,30 @@ void EvalState::autoCallFunction(Bindings & args, Value & fun, Value & res) actualArgs->attrs->push_back(*j); } else if (!i.def) { throwUndefinedVarError(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 with nix-build 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 { - ... - - See this nix pill for more information re callPackage format: - https://nixos.org/guides/nix-pills/callpackage-design-pattern.html)", i.name); + +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 with nix-build 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); } } } |