cmd/go: ignore C files when CGO_ENABLED=0

Before, those C files might have been intended for the Plan 9 C compiler,
but that option was removed in Go 1.5. We can simplify the maintenance
of cgo packages now if we assume C files (and C++ and M and SWIG files)
should only be considered when cgo is enabled.

Also remove newly unnecessary build tags in runtime/cgo's C files.

Fixes #14123

Change-Id: Ia5a7fe62b9469965aa7c3547fe43c6c9292b8205
Reviewed-on: https://go-review.googlesource.com/19613
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/go/build.go

@@ -1419,6 +1419,8 @@ func (b *builder) build(a *action) (err error) {
 		// cgo and non-cgo worlds, so it necessarily has files in both.
 		// In that case gcc only gets the gcc_* files.
 		var gccfiles []string
+		gccfiles = append(gccfiles, cfiles...)
+		cfiles = nil
 		if a.p.Standard && a.p.ImportPath == "runtime/cgo" {
 			filter := func(files, nongcc, gcc []string) ([]string, []string) {
 				for _, f := range files {
@@ -1430,11 +1432,9 @@ func (b *builder) build(a *action) (err error) {
 				}
 				return nongcc, gcc
 			}
-			cfiles, gccfiles = filter(cfiles, cfiles[:0], gccfiles)
 			sfiles, gccfiles = filter(sfiles, sfiles[:0], gccfiles)
 		} else {
-			gccfiles = append(cfiles, sfiles...)
-			cfiles = nil
+			gccfiles = append(gccfiles, sfiles...)
 			sfiles = nil
 		}
 

src/cmd/go/go_test.go

@@ -1226,14 +1226,6 @@ func TestGetGitDefaultBranch(t *testing.T) {
 	tg.grepStdout(`\* another-branch`, "not on correct default branch")
 }
 
-func TestDisallowedCSourceFiles(t *testing.T) {
-	tg := testgo(t)
-	defer tg.cleanup()
-	tg.setenv("GOPATH", filepath.Join(tg.pwd(), "testdata"))
-	tg.runFail("build", "badc")
-	tg.grepStderr("C source files not allowed", "go test did not say C source files not allowed")
-}
-
 func TestErrorMessageForSyntaxErrorInTestGoFileSaysFAIL(t *testing.T) {
 	tg := testgo(t)
 	defer tg.cleanup()

src/cmd/go/pkg.go

@@ -1012,6 +1012,19 @@ func (p *Package) load(stk *importStack, bp *build.Package, err error) *Package
 	}
 	p.Target = p.target
 
+	// If cgo is not enabled, ignore cgo supporting sources
+	// just as we ignore go files containing import "C".
+	if !buildContext.CgoEnabled {
+		p.CFiles = nil
+		p.CXXFiles = nil
+		p.MFiles = nil
+		p.SwigFiles = nil
+		p.SwigCXXFiles = nil
+		p.SysoFiles = nil
+		// Note that SFiles are okay (they go to the Go assembler)
+		// and HFiles are okay (they might be used by the SFiles).
+	}
+
 	// The gc toolchain only permits C source files with cgo.
 	if len(p.CFiles) > 0 && !p.usesCgo() && !p.usesSwig() && buildContext.Compiler == "gc" {
 		p.Error = &PackageError{

src/runtime/cgo/gcc_android.c

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build cgo
-
 #include <stdarg.h>
 #include <android/log.h>
 #include "libcgo.h"

src/runtime/cgo/gcc_android_386.c

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build cgo
-
 #include <string.h> /* for strerror */
 #include <pthread.h>
 #include <signal.h>

src/runtime/cgo/gcc_android_amd64.c

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build cgo
-
 #include <string.h> /* for strerror */
 #include <pthread.h>
 #include <signal.h>

src/runtime/cgo/gcc_android_arm.c

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build cgo
-
 #include <pthread.h>
 #include <signal.h>
 #include <stdio.h>

src/runtime/cgo/gcc_android_arm64.c

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build cgo
-
 #include <pthread.h>
 #include <signal.h>
 #include <stdio.h>

src/runtime/cgo/gcc_darwin_386.c

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build cgo
-
 #include <string.h> /* for strerror */
 #include <pthread.h>
 #include <signal.h>

src/runtime/cgo/gcc_darwin_amd64.c

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build cgo
-
 #include <string.h> /* for strerror */
 #include <pthread.h>
 #include <signal.h>

src/runtime/cgo/gcc_darwin_arm.c

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build cgo
-
 #include <limits.h>
 #include <pthread.h>
 #include <signal.h>

src/runtime/cgo/gcc_darwin_arm64.c

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build cgo
-
 #include <limits.h>
 #include <pthread.h>
 #include <signal.h>

src/runtime/cgo/gcc_dragonfly_amd64.c

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build cgo
-
 #include <sys/types.h>
 #include <sys/signalvar.h>
 #include <pthread.h>

src/runtime/cgo/gcc_fatalf.c

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build cgo
-
 // +build !android,linux
 
 #include <stdarg.h>

src/runtime/cgo/gcc_freebsd_386.c

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build cgo
-
 #include <sys/types.h>
 #include <sys/signalvar.h>
 #include <pthread.h>

src/runtime/cgo/gcc_freebsd_amd64.c

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build cgo
-
 #include <sys/types.h>
 #include <sys/signalvar.h>
 #include <pthread.h>

src/runtime/cgo/gcc_freebsd_arm.c

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build cgo
-
 #include <sys/types.h>
 #include <machine/sysarch.h>
 #include <sys/signalvar.h>

src/runtime/cgo/gcc_libinit_linux_ppc64x.c

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build cgo
-
 // TODO: see issue #10410
 // +build linux
 // +build ppc64 ppc64le

src/runtime/cgo/gcc_libinit_openbsd.c

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build cgo
-
 #include <stdio.h>
 #include <stdlib.h>
 

src/runtime/cgo/gcc_libinit_windows.c

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build cgo
-
 #include <stdio.h>
 #include <stdlib.h>
 

src/runtime/cgo/gcc_linux_386.c

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build cgo
-
 #include <pthread.h>
 #include <string.h>
 #include <signal.h>

src/runtime/cgo/gcc_linux_amd64.c

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build cgo
-
 #include <pthread.h>
 #include <errno.h>
 #include <string.h> // strerror

src/runtime/cgo/gcc_linux_arm.c

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build cgo
-
 #include <pthread.h>
 #include <string.h>
 #include <signal.h>

src/runtime/cgo/gcc_linux_arm64.c

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build cgo
-
 #include <pthread.h>
 #include <string.h>
 #include <signal.h>

src/runtime/cgo/gcc_linux_ppc64x.c

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build cgo
-
 // +build ppc64 ppc64le
 
 #include <pthread.h>

src/runtime/cgo/gcc_mmap.c

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build cgo
-
 // +build linux,amd64
 
 #include <errno.h>

src/runtime/cgo/gcc_netbsd_386.c

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build cgo
-
 #include <sys/types.h>
 #include <pthread.h>
 #include <signal.h>

src/runtime/cgo/gcc_netbsd_amd64.c

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build cgo
-
 #include <sys/types.h>
 #include <pthread.h>
 #include <signal.h>

src/runtime/cgo/gcc_netbsd_arm.c

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build cgo
-
 #include <sys/types.h>
 #include <pthread.h>
 #include <signal.h>

src/runtime/cgo/gcc_openbsd_386.c

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build cgo
-
 #include <sys/types.h>
 #include <dlfcn.h>
 #include <errno.h>

src/runtime/cgo/gcc_openbsd_amd64.c

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build cgo
-
 #include <sys/types.h>
 #include <dlfcn.h>
 #include <errno.h>

src/runtime/cgo/gcc_signal_darwin_armx.c

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build cgo
-
 // Emulation of the Unix signal SIGSEGV.
 //
 // On iOS, Go tests and apps under development are run by lldb.

src/runtime/cgo/gcc_signal_darwin_lldb.c

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build cgo
-
 // +build !lldb
 // +build darwin
 // +build arm arm64

src/runtime/cgo/gcc_solaris_amd64.c

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build cgo
-
 #include <pthread.h>
 #include <string.h>
 #include <signal.h>

src/runtime/cgo/gcc_util.c

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build cgo
-
 #include "libcgo.h"
 
 /* Stub for calling malloc from Go */

src/runtime/cgo/gcc_windows_386.c

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build cgo
-
 #define WIN32_LEAN_AND_MEAN
 #include <windows.h>
 #include <process.h>

src/runtime/cgo/gcc_windows_amd64.c

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build cgo
-
 #define WIN64_LEAN_AND_MEAN
 #include <windows.h>
 #include <process.h>