cmd/gc: Improve error message when no types in function signature

[btracey]

If one leaves out the types in a function signature (as in http://play.golang.org/p/dxiOWN_NS4)

func Foo(x, y, z) {}

The error is

/tmp/sandbox961476762/main.go:5: undefined: x
/tmp/sandbox961476762/main.go:5: undefined: y
/tmp/sandbox961476762/main.go:5: undefined: z

It would be nice if these said something along the lines of "no type provided in function signature" rather than undefined. This would be closer to the case where the final type is omitted (http://play.golang.org/p/TvhumXNd3Z)

/tmp/sandbox992442913/main.go:5: final function parameter must have type

[minux]

The error message is correct. From the compiler's standpoint, you have defined a function that takes three arguments, whose types are x, y, and z. But x, y, z are not defined, thus it gives the undefined message. It's hard to give intuitive error messages for Go's declarations, because it's too flexible.

[ianlancetaylor]

Closing this. Feel free to reopen if you have a suggestion for what the compiler can reasonably do. Note that this is not a syntax error, and that the compiler can't know that the names are undefined until parsing is complete.

[btracey]

Minux's reply makes sense, and I agree with the closure.