cmd/compile: error positions are verbose in cgo-using files

[aclements]

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

go version devel +11c61eb6af Fri Jun 9 04:38:37 2017 +0000 linux/amd64

What did you do?

Build a file that imports "C" and has compile errors in it.

What did you expect to see?

Go 1.8 printed out succinct error messages that were the same whether or not the package imported "C". Eg.,

$ go build
./model.go:89: invalid operation: i < n (mismatched types int and C.uint)

What did you see instead?

At tip, the error positions are much more verbose and include a reference to a temporary path generated by the cgo tool that doesn't even exist after the go tool exits:

$ go build
./model.go:89[/tmp/go-build298567481/github.com/aclements/go-z3/z3/_test/_obj_test/model.cgo1.go:110:25]: invalid operation: i < n (mismatched types int and _Ctype_uint)

/cc @griesemer @mdempsky

[ALTree]

Introduced in 2a5cf48.

[odeke-em]

Repro for a test when fixing it:

package main

import "C"

func main() {
	n := C.uint(10)
	i := 1
	if i < n {
	}
}

[griesemer]

This may be due to a regex not matching anymore when the position information contains column info. It may be as easy as disabling the printing of column info when invoking the compiler.

[gopherbot]

CL https://golang.org/cl/45612 mentions this issue.