cmd/compile: bad error message for argument missing type

[prattmic]

Go version

1.23

Output of go env in your module/workspace:

N/A

What did you do?

https://go.dev/play/p/hgKdYn08tsY

I forgot to add the type to the last argument of a function definition:

func f(a int, b) {
}

This should have some type name after b.

What did you see happen?

./prog.go:7:15: syntax error: mixed named and unnamed parameters

What did you expect to see?

All parameters are named here, the actual problem is the missing type, so I expected something like: "syntax error: parameter 'b' missing type"

[prattmic]

cc @golang/compiler

[gabyhelp]

Related Issues and Documentation

• cmd/gc: Improve error message when no types in function signature #10762 (closed)
• cmd/compile/internal/syntax: unclear error message for function type have type parameters #48382 (closed)
• cmd/gc: incorrect error message #10671 (closed)
• cmd/compile: confusing (but accurate) error message for function with variadic arguments if argument is not the last #28450 (closed)
• cmd/compile: no need to complain about missing type arguments after type inference error #50588 (closed)
• cmd/compile: generic error does not identify relevant type #64276 (closed)
• cmd/compile: misleading error message when struct lacks expected type parameters #49541 (closed)

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[prattmic]

Thanks @gabyhelp. #10762 points out that this could be ambiguous. If b is a type, then the error message would be accurate.

Still, as a user I know b is not a type, so the error message is not very helpful.

[adonovan]

This error comes from the parser, so it can't use knowledge of what kind of symbol b is. I suppose the type checker could emit a second error:

./prog.go:7:15: syntax error: mixed named and unnamed parameters
./prog.go:7:15: type error: parameter b has no type