git bisect points to 94076fe

Splitting up the typedef fixes the warning and the build failure, but this is
of course not possible/difficult to do when interfacing with other libraries.

package main

// typedef struct { int a; } S;
// typedef S *PTRS;
//
// void cfuncptr(PTRS s) {}
import "C"

func main() {
	var s C.S
	C.cfuncptr(C.PTRS(&s))
}

CC @randall77

Well this looks really painful.

@gopherbot please file this to be considered for backport to 1.11 and 1.10. This is a regression.

Backport issue(s) opened: #27395 (for 1.11), #27396 (for 1.10).

Remember to create the cherry-pick CL(s) as soon as the patch is submitted to master, according to https://golang.org/wiki/MinorReleases.

@randall77 Any ideas on this one?

The breaking change seems to have been https://golang.org/cl/122575 for #24161.

Before that change _cgo_gotypes.go has this:

type _Ctype_PTRS *_Ctype_struct___0

type _Ctype_S = _Ctype_struct___0

type _Ctype_struct___0 struct {
	a _Ctype_int
}

func _Cfunc_cfuncptr(p0 *_Ctype_struct___0) (r1 _Ctype_void) {

After that change the file has this:

type _Ctype_PTRS *_Ctype_struct___0

type _Ctype_S = _Ctype_struct___0

type _Ctype_struct___0 struct {
	a _Ctype_int
}

type _Ctype_struct___1 struct {
	a _Ctype_int
}

func _Cfunc_cfuncptr(p0 *_Ctype_struct___1) (r1 _Ctype_void) {

Either way the generated .cgo1.go file has this:

	var s _Ctype_struct___0
	(_Cfunc_cfuncptr)(_Ctype_PTRS(&s))

So the problem seems to be this introduced _Ctype_struct___1 type.

Change https://golang.org/cl/152762 mentions this issue: cmd/cgo: preserve type information across loadDWARF loop

Change https://golang.org/cl/154277 mentions this issue: [release-branch.go1.11] cmd/cgo: preserve type information across loadDWARF loop