cmd/go: pass an unmodified environment to a go run program

Fixes #11709.
Fixed #11449.

Change-Id: If8fdb27d3dc25fb7017226d143a29cbebc1374c5
Reviewed-on: https://go-review.googlesource.com/12483
Reviewed-by: David Crawshaw <crawshaw@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/go/generate.go

@@ -402,7 +402,7 @@ func (g *Generator) exec(words []string) {
 		"GOFILE=" + g.file,
 		"GOPACKAGE=" + g.pkg,
 	}
-	cmd.Env = mergeEnvLists(env, os.Environ())
+	cmd.Env = mergeEnvLists(env, origEnv)
 	err := cmd.Run()
 	if err != nil {
 		g.errorf("running %q: %s", words[0], err)

src/cmd/go/go_test.go

@@ -2229,3 +2229,18 @@ func TestGoInstallShadowedGOPATH(t *testing.T) {
 	tg.runFail("install")
 	tg.grepStderr("no install location for.*gopath2.src.test: hidden by .*gopath1.src.test", "missing error")
 }
+
+func TestIssue11709(t *testing.T) {
+	tg := testgo(t)
+	defer tg.cleanup()
+	tg.tempFile("run.go", `
+		package main
+		import "os"
+		func main() {
+			if os.Getenv("TERM") != "" {
+				os.Exit(1)
+			}
+		}`)
+	tg.unsetenv("TERM")
+	tg.run("run", tg.path("run.go"))
+}

src/cmd/go/main.go

@@ -112,6 +112,8 @@ func setExitStatus(n int) {
 	exitMu.Unlock()
 }
 
+var origEnv []string
+
 func main() {
 	_ = go11tag
 	flag.Usage = usage
@@ -159,6 +161,7 @@ func main() {
 	// the same default computation of these as we do,
 	// but in practice there might be skew
 	// This makes sure we all agree.
+	origEnv = os.Environ()
 	for _, env := range mkEnv() {
 		if os.Getenv(env.name) != env.value {
 			os.Setenv(env.name, env.value)

src/cmd/go/run.go

@@ -137,6 +137,7 @@ func runStdin(cmdline []string) {
 	cmd.Stdin = os.Stdin
 	cmd.Stdout = os.Stdout
 	cmd.Stderr = os.Stderr
+	cmd.Env = origEnv
 	startSigHandlers()
 	if err := cmd.Run(); err != nil {
 		errorf("%v", err)