cmd/cgo: -Wunused-variable warning when calling a C function of type: void (*func)(void) #76861
Description
Go version
go version go1.25.4 darwin/arm64
Output of go env in your module/workspace:
AR='ar'
CC='clang'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='clang++'
GCCGO='gccgo'
GO111MODULE=''
GOARCH='arm64'
GOARM64='v8.0'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/Users/joerichey/Library/Caches/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/Users/joerichey/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/5m/z1mvvbh96w1bzx49721xsh_h00cpn8/T/go-build2277445497=/tmp/go-build -gno-record-gcc-switches -fno-common'
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMOD='/Users/joerichey/dev/test/tmp/go.mod'
GOMODCACHE='/Users/joerichey/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/joerichey/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/Users/joerichey/Library/Application Support/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.25.4'
GOWORK=''
PKG_CONFIG='pkg-config'What did you do?
When using CGO to call C code, if the called function looks like:
void foo(void) {}a -Wunused-variable warning will be emitted.
Full example:
// #cgo CFLAGS: -Wall
// void foo(void) {}
import "C"
func main() {
C.foo()
}Note that if:
- A function is not called
- A function takes in any argument
- A function returns a value
then no warning will be emitted. This example compiles fine:
// #cgo CFLAGS: -Wall
// int bar(void) { return 5; }
// void baz(int x) {}
import "C"
func main() {
C.bar()
C.baz(7)
}What did you see happen?
Running:
go build .outputs:
# example.com/example
cgo-gcc-prolog:49:33: warning: unused variable '_cgo_a' [-Wunused-variable]
What did you expect to see?
CGO binding could should not create unused variables by default.