cmd/compile: panic.Fatalf should not report "use of builtin panic not in function call" but instead "panic.Fatalf undefined (builtin panic has no field or method Fatalf)"

[odeke-em]

What version of Go are you using (go version)?

At pre-Go1.16 on tip 55b5801

Does this issue reproduce with the latest release?

Yes

What did you do?

, running this code https://play.golang.org/p/akRcEUKPrTA or inlined below

package main

func main() {
	panic.Fatalf("foo")
}

What did you expect to see?

panic.Fatalf undefined (builtin panic has no field or method Fatalf)

What did you see instead?

use of builtin panic not in function call

which would be similar to panic being present on a line but without any invocation https://play.golang.org/p/35T1E3Xttpp or

package main

func main() {
	panic
}

./prog.go:4:2: use of builtin panic not in function call

[choleraehyq]

How to figure out whether an error message is wrong? There is no specification about it. IMHO the current error message is not confusing.

[cagedmantis]

/cc @randall77 @griesemer

[mdempsky]

I think either error message is fine here. However, go/types reports the requested error message, so this will likely change once we adopt types2 anyway.