missing argument error

src/libexpr/eval.cc

@@ -660,6 +660,14 @@ LocalNoInlineNoReturn(void throwUndefinedVarError(const Pos & pos, const char *
  });
 }
 
+LocalNoInlineNoReturn(void throwMissingArgumentError(const Pos & pos, const char * s, const string & s1))
+{
+ throw MissingArgumentError({
+ .hint = hintfmt(s, s1),
+ .errPos = pos
+ });
+}
+
 LocalNoInline(void addErrorTrace(Error & e, const char * s, const string & s2))
 {
  e.addTrace(std::nullopt, s, s2);
@@ -1365,15 +1373,15 @@ void EvalState::autoCallFunction(Bindings & args, Value & fun, Value & res)
  if (j != args.end()) {
  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%')
+ 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 with nix-build that expects
+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.

src/libexpr/nixexpr.hh

@@ -17,6 +17,7 @@ MakeError(ThrownError, AssertionError);
 MakeError(Abort, EvalError);
 MakeError(TypeError, EvalError);
 MakeError(UndefinedVarError, Error);
+MakeError(MissingArgumentError, Error);
 MakeError(RestrictedPathError, Error);