Cgo function produces "warning: assignment from incompatible pointer type"

[gopherbot]

by kballard:

Building launchpad.net/goyaml produces a series of warnings:

decode.go: In function ‘_cgo_27a928056cbd_Cfunc_event_alias’:
decode.go:34:7: warning: assignment from incompatible pointer type [enabled by default]
decode.go: In function ‘_cgo_27a928056cbd_Cfunc_event_mapping_start’:
decode.go:44:7: warning: assignment from incompatible pointer type [enabled by default]
decode.go: In function ‘_cgo_27a928056cbd_Cfunc_event_scalar’:
decode.go:54:7: warning: assignment from incompatible pointer type [enabled by default]
decode.go: In function ‘_cgo_27a928056cbd_Cfunc_event_sequence_start’:
decode.go:64:7: warning: assignment from incompatible pointer type [enabled by default]

The Cgo-generated function for the first warning looks like

void
_cgo_27a928056cbd_Cfunc_event_mapping_start(void *v)
{
    struct {
        yaml_event_t* p0;
        const struct {yaml_char_t* anchor; yaml_char_t* tag; int implicit; yaml_mapping_style_t style; }* r;
    } __attribute__((__packed__)) *a = v;
    a->r = (const struct {yaml_char_t* anchor; yaml_char_t* tag; int implicit; yaml_mapping_style_t style; }*) event_mapping_start((void*)a->p0);
}

The warning is on the `a->r = ...` line.

If I ask Clang to build this file, the warning is a bit more verbose:

decode.go:34:7: warning: incompatible pointer types assigning to 'const struct
<anonymous struct at decode.go:32:9> *' from 'const struct <anonymous struct at
      decode.go:34:16> *' [-Wincompatible-pointer-types]
        a->r = (const struct {yaml_char_t* anchor; }*) event_alias((void*)a->p0);
             ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


What steps will reproduce the problem?
1. Build launchpad.net/goyaml

What is the expected output?
No warnings

What do you see instead?
The warnings listed above

Which compiler are you using (5g, 6g, 8g, gccgo)?
8g

Which operating system are you using?
Ubuntu 12.04

Which version are you using?  (run 'go version')
go version go1.1 linux/386

[ianlancetaylor]

Comment 1:

Status changed to Duplicate.

Merged into issue #4857.