cmd/go: prefer $GOTMPDIR over operating system tmp dir for temp files

We build and run executables in the work directory,
and some users have $TMPDIR set noexec.

Fixes #8451.

Change-Id: I76bf2ddec84e9cb37ad9a6feb53a1a84b47aa263
Reviewed-on: https://go-review.googlesource.com/75475
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>

src/cmd/dist/util.go

@@ -326,7 +326,7 @@ func xreaddirfiles(dir string) []string {
 // xworkdir creates a new temporary directory to hold object files
 // and returns the name of that directory.
 func xworkdir() string {
-	name, err := ioutil.TempDir("", "go-tool-dist-")
+	name, err := ioutil.TempDir(os.Getenv("GOTMPDIR"), "go-tool-dist-")
 	if err != nil {
 		fatalf("%v", err)
 	}

src/cmd/go/alldocs.go

@@ -331,6 +331,8 @@
 // The -json flag prints the environment in JSON format
 // instead of as a shell script.
 //
+// For more about environment variables, see 'go help environment'.
+//
 //
 // Start a bug report
 //
@@ -1103,6 +1105,12 @@
 // 		See https://golang.org/doc/articles/race_detector.html.
 // 	GOROOT
 // 		The root of the go tree.
+// 	GOTMPDIR
+// 		The directory where the go command will write
+// 		temporary source files, packages, and binaries.
+// 	GOCACHE
+// 		The directory where the go command will store
+// 		cached information for reuse in future builds.
 //
 // Environment variables for use with cgo:
 //

src/cmd/go/go_test.go

@@ -4690,6 +4690,20 @@ func TestUpxCompression(t *testing.T) {
 	}
 }
 
+func TestGOTMPDIR(t *testing.T) {
+	tg := testgo(t)
+	defer tg.cleanup()
+	tg.parallel()
+	tg.setenv("GOPATH", filepath.Join(tg.pwd(), "testdata"))
+	tg.makeTempdir()
+	tg.setenv("GOTMPDIR", tg.tempdir)
+	tg.setenv("GOCACHE", "off")
+
+	// complex/x is a trivial non-main package.
+	tg.run("build", "-work", "-x", "complex/w")
+	tg.grepStderr("WORK="+regexp.QuoteMeta(tg.tempdir), "did not work in $GOTMPDIR")
+}
+
 func TestBuildCache(t *testing.T) {
 	if strings.Contains(os.Getenv("GODEBUG"), "gocacheverify") {
 		t.Skip("GODEBUG gocacheverify")

src/cmd/go/internal/envcmd/env.go

@@ -32,6 +32,8 @@ each named variable on its own line.
 
 The -json flag prints the environment in JSON format
 instead of as a shell script.
+
+For more about environment variables, see 'go help environment'.
 	`,
 }
 
@@ -48,6 +50,7 @@ func MkEnv() []cfg.EnvVar {
 	env := []cfg.EnvVar{
 		{Name: "GOARCH", Value: cfg.Goarch},
 		{Name: "GOBIN", Value: cfg.GOBIN},
+		{Name: "GOCACHE", Value: cache.DefaultDir()},
 		{Name: "GOEXE", Value: cfg.ExeSuffix},
 		{Name: "GOHOSTARCH", Value: runtime.GOARCH},
 		{Name: "GOHOSTOS", Value: runtime.GOOS},
@@ -55,8 +58,8 @@ func MkEnv() []cfg.EnvVar {
 		{Name: "GOPATH", Value: cfg.BuildContext.GOPATH},
 		{Name: "GORACE", Value: os.Getenv("GORACE")},
 		{Name: "GOROOT", Value: cfg.GOROOT},
+		{Name: "GOTMPDIR", Value: os.Getenv("GOTMPDIR")},
 		{Name: "GOTOOLDIR", Value: base.ToolDir},
-		{Name: "GOCACHE", Value: cache.DefaultDir()},
 
 		// disable escape codes in clang errors
 		{Name: "TERM", Value: "dumb"},

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

@@ -471,6 +471,12 @@ General-purpose environment variables:
 		See https://golang.org/doc/articles/race_detector.html.
 	GOROOT
 		The root of the go tree.
+	GOTMPDIR
+		The directory where the go command will write
+		temporary source files, packages, and binaries.
+	GOCACHE
+		The directory where the go command will store
+		cached information for reuse in future builds.
 
 Environment variables for use with cgo:
 

src/cmd/go/internal/work/action.go

@@ -200,7 +200,7 @@ func (b *Builder) Init() {
 	if cfg.BuildN {
 		b.WorkDir = "$WORK"
 	} else {
-		b.WorkDir, err = ioutil.TempDir("", "go-build")
+		b.WorkDir, err = ioutil.TempDir(os.Getenv("GOTMPDIR"), "go-build")
 		if err != nil {
 			base.Fatalf("%s", err)
 		}