Add test for eval.TooManyArgError()

[tchssk]

Related to #3512

[raphael]

This is great! I left a couple of comments that might be good to address, thank you!

[raphael]

The value returned by this function might be used to do validations later on so the idea is to not return nil as the validation code assumes there's always an expression (which could be invalid). So we shouldn't return here - or return a zero result expression.

[tchssk]

There are already two lines that return nil in ResultType. Are these wrong?

goa/dsl/result_type.go

Lines 65 to 69 in 78b71ce

	func ResultType(identifier string, args ...any) *expr.ResultTypeExpr {
	if _, ok := eval.Current().(eval.TopExpr); !ok {
	eval.IncompatibleDSL()
	return nil
	}

goa/dsl/result_type.go

Lines 109 to 116 in 78b71ce

	for _, rt := range expr.Root.ResultTypes {
	if re := rt.(*expr.ResultTypeExpr); re.Identifier == canonicalID {
	eval.ReportError(
	"result type %#v with canonical identifier %#v is defined twice",
	identifier, canonicalID)
	return nil
	}
	}

[raphael]

Good point, looks like Type can also return nil so this case is probably safe.

[raphael]

same as above