cmd/go, go/build: add support for gccgo tooldir

The gccgo toolchain does not put tools (cgo, vet, etc.) in
$GOROOT/pkg/tool, but instead in a directory available at
runtime.GCCGOTOOLDIR.

Update the go/build package and the cmd/go tool to use this tool
directory when using gccgo.

Change-Id: Ib827336ff53601208300aceb77f76c2e1b069859
Reviewed-on: https://go-review.googlesource.com/111097
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/go/alldocs.go

@@ -1100,6 +1100,9 @@
 //
 // Special-purpose environment variables:
 //
+// 	GCCGOTOOLDIR
+// 		If set, where to find gccgo tools, such as cgo.
+// 		The default is based on how gccgo was configured.
 // 	GOROOT_FINAL
 // 		The root of the installed Go tree, when it is
 // 		installed in a location other than where it is built.

src/cmd/go/internal/cfg/cfg.go

@@ -93,11 +93,14 @@ var (
 // Update build context to use our computed GOROOT.
 func init() {
 	BuildContext.GOROOT = GOROOT
+	if runtime.Compiler != "gccgo" {
 		// Note that we must use runtime.GOOS and runtime.GOARCH here,
-	// as the tool directory does not move based on environment variables.
-	// This matches the initialization of ToolDir in go/build,
-	// except for using GOROOT rather than runtime.GOROOT().
+		// as the tool directory does not move based on environment
+		// variables. This matches the initialization of ToolDir in
+		// go/build, except for using GOROOT rather than
+		// runtime.GOROOT.
 		build.ToolDir = filepath.Join(GOROOT, "pkg/tool/"+runtime.GOOS+"_"+runtime.GOARCH)
+	}
 }
 
 func findGOROOT() string {
@@ -105,6 +108,11 @@ func findGOROOT() string {
 		return filepath.Clean(env)
 	}
 	def := filepath.Clean(runtime.GOROOT())
+	if runtime.Compiler == "gccgo" {
+		// gccgo has no real GOROOT, and it certainly doesn't
+		// depend on the executable's location.
+		return def
+	}
 	exe, err := os.Executable()
 	if err == nil {
 		exe, err = filepath.Abs(exe)

src/cmd/go/internal/help/helpdoc.go

@@ -533,6 +533,9 @@ Architecture-specific environment variables:
 
 Special-purpose environment variables:
 
+	GCCGOTOOLDIR
+		If set, where to find gccgo tools, such as cgo.
+		The default is based on how gccgo was configured.
 	GOROOT_FINAL
 		The root of the installed Go tree, when it is
 		installed in a location other than where it is built.

src/cmd/go/internal/load/pkg.go

@@ -975,8 +975,12 @@ func (p *Package) load(stk *ImportStack, bp *build.Package, err error) {
 		if InstallTargetDir(p) == ToTool {
 			// This is for 'go tool'.
 			// Override all the usual logic and force it into the tool directory.
+			if cfg.BuildToolchainName == "gccgo" {
+				p.Target = filepath.Join(base.ToolDir, elem)
+			} else {
 				p.Target = filepath.Join(cfg.GOROOTpkg, "tool", full)
 			}
+		}
 		if p.Target != "" && cfg.BuildContext.GOOS == "windows" {
 			p.Target += ".exe"
 		}

src/cmd/go/internal/tool/tool.go

@@ -33,6 +33,17 @@ For more about each tool command, see 'go doc cmd/<command>'.
 
 var toolN bool
 
+// Return whether tool can be expected in the gccgo tool directory.
+// Other binaries could be in the same directory so don't
+// show those with the 'go tool' command.
+func isGccgoTool(tool string) bool {
+	switch tool {
+	case "cgo", "fix", "cover", "godoc", "vet":
+		return true
+	}
+	return false
+}
+
 func init() {
 	CmdTool.Flag.BoolVar(&toolN, "n", false, "")
 }
@@ -114,6 +125,11 @@ func listTools() {
 		if base.ToolIsWindows && strings.HasSuffix(name, base.ToolWindowsExtension) {
 			name = name[:len(name)-len(base.ToolWindowsExtension)]
 		}
+		// The tool directory used by gccgo will have other binaries
+		// in addition to go tools. Only display go tools here.
+		if cfg.BuildToolchainName == "gccgo" && !isGccgoTool(name) {
+			continue
+		}
 		fmt.Println(name)
 	}
 }

src/go/build/build.go

@@ -1595,7 +1595,7 @@ func init() {
 }
 
 // ToolDir is the directory containing build tools.
-var ToolDir = filepath.Join(runtime.GOROOT(), "pkg/tool/"+runtime.GOOS+"_"+runtime.GOARCH)
+var ToolDir = getToolDir()
 
 // IsLocalImport reports whether the import path is
 // a local import path, like ".", "..", "./foo", or "../foo".

src/go/build/gc.go

+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build gc
+
+package build
+
+import (
+	"path/filepath"
+	"runtime"
+)
+
+// getToolDir returns the default value of ToolDir.
+func getToolDir() string {
+	return filepath.Join(runtime.GOROOT(), "pkg/tool/"+runtime.GOOS+"_"+runtime.GOARCH)
+}

src/go/build/gccgo.go

+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build gccgo
+
+package build
+
+import "runtime"
+
+// getToolDir returns the default value of ToolDir.
+func getToolDir() string {
+	return envOr("GCCGOTOOLDIR", runtime.GCCGOTOOLDIR)
+}