cmd/cgo: build failed when any code have CFLAGS: -Werror=unused-vairable

[gopherbot]

by Snyh1010:

1. What is a short input program that triggers the error?
package main

//#cgo CFLAGS: -Werror=unused-variable
//void test(){}
import "C"

func main() {
        C.test()
}

2. What is the full compiler output?
snyh:shm$go build
# _/run/shm
./a.go: In function ‘_cgo_043ca501ac1f_Cfunc_test’:
./a.go:32:49: error: unused variable ‘a’ [-Werror=unused-variable]
cc1: some warnings being treated as errors

------------------------------------------
I have fixed this by  a CL https://golang.org/cl/118890044/  

The  CL(https://golang.org/cl/109640045)  had fix this problem under gcc. 
The first time I hasn't notice clang, so when the CL has been submitted, it broken
freebsd because clang.  And the CL has been undo.

The broken problem is not caused by my code, it's appeared upon the submission because
the CL contains the test code let the problem appeared. 

I have fixed the problem  both clang and gcc.  But it seems no one have confidence to
submit it this time, I have send the CL request. 

Anyway I want the problem be fixed, with or without my CL.

[ianlancetaylor]

Comment 1:

Labels changed: added repo-main, release-go1.4.

[mdempsky]

Comment 2:

At least since 2.95, GCC has supported the "unused" attribute to suppress warnings about
unused variables.  I've prepared https://golang.org/cl/121550043/ to make use
of this in cgo.
It also looks like -Werror=unused-variable has been supported since GCC 4.2, so it
should be available on OS X and BSD too.  Though even if we wanted to support an
old-timey platform using an older GCC, we could just add an appropriate "// +build
!openbsd,vax" line to issue8420.go.
snyh: Can you please confirm whether the above CL adequately addresses your needs?

[rsc]

Comment 3:

I'm not touching this for the 1.4 release. There is an easy fix. Do not say CFLAGS:
-Werror=unused-variable.

Labels changed: added release-none, removed release-go1.4.

Status changed to Accepted.

[ysmolski]

Compiling this program

package main

// #cgo CFLAGS: -Werror=unused-variable
// void test(){}
import "C"

func main() {
    C.test()
}

on mac gives me:

...go/src/tmp % go build
# tmp
./main.go:8:2: could not determine kind of name for C.test

@mdempsky should we fix this?

[ianlancetaylor]

It's fine if someone wants to fix this, but it's not an important bug to fix.

[mohamadpk]

disable c go on environment variable or CGO_ENABLED=0