cmd/go: avoid setting variables for '/' and ':' in TestScript subprocess environments

Also simplify platform-dependent handling of the PATH variable,
to make it more like the existing platform-dependent handling for
HOME and TMPDIR.

Fixes #53671.

Change-Id: Ica2665d3f61988c66fb6982b9feb61ca48eced79
Reviewed-on: https://go-review.googlesource.com/c/go/+/416554
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/cmd/go/go_test.go

@@ -1363,6 +1363,15 @@ func tempEnvName() string {
 	}
 }
 
+func pathEnvName() string {
+	switch runtime.GOOS {
+	case "plan9":
+		return "path"
+	default:
+		return "PATH"
+	}
+}
+
 func TestDefaultGOPATH(t *testing.T) {
 	tg := testgo(t)
 	defer tg.cleanup()

src/cmd/go/script_test.go

@@ -163,7 +163,7 @@ func (ts *testScript) setup() {
 	ts.cd = filepath.Join(ts.workdir, "gopath/src")
 	ts.env = []string{
 		"WORK=" + ts.workdir, // must be first for ts.abbrev
-		"PATH=" + testBin + string(filepath.ListSeparator) + os.Getenv("PATH"),
+		pathEnvName() + "=" + testBin + string(filepath.ListSeparator) + os.Getenv(pathEnvName()),
 		homeEnvName() + "=/no-home",
 		"CCACHE_DISABLE=1", // ccache breaks with non-existent HOME
 		"GOARCH=" + runtime.GOARCH,
@@ -187,8 +187,6 @@ func (ts *testScript) setup() {
 		tempEnvName() + "=" + filepath.Join(ts.workdir, "tmp"),
 		"devnull=" + os.DevNull,
 		"goversion=" + goVersion(ts),
-		":=" + string(os.PathListSeparator),
-		"/=" + string(os.PathSeparator),
 		"CMDGO_TEST_RUN_MAIN=true",
 	}
 	if testenv.Builder() != "" || os.Getenv("GIT_TRACE_CURL") == "1" {
@@ -203,10 +201,6 @@ func (ts *testScript) setup() {
 		ts.env = append(ts.env, "TESTGONETWORK=panic", "TESTGOVCS=panic")
 	}
 
-	if runtime.GOOS == "plan9" {
-		ts.env = append(ts.env, "path="+testBin+string(filepath.ListSeparator)+os.Getenv("path"))
-	}
-
 	for _, key := range extraEnvKeys {
 		if val := os.Getenv(key); val != "" {
 			ts.env = append(ts.env, key+"="+val)
@@ -219,6 +213,10 @@ func (ts *testScript) setup() {
 			ts.envMap[kv[:i]] = kv[i+1:]
 		}
 	}
+	// Add entries for ${:} and ${/} to make it easier to write platform-independent
+	// environment variables.
+	ts.envMap["/"] = string(os.PathSeparator)
+	ts.envMap[":"] = string(os.PathListSeparator)
 
 	fmt.Fprintf(&ts.log, "# (%s)\n", time.Now().UTC().Format(time.RFC3339))
 	ts.mark = ts.log.Len()
@@ -1264,12 +1262,7 @@ func (ts *testScript) lookPath(command string) (string, error) {
 		}
 	}
 
-	pathName := "PATH"
+	for _, dir := range strings.Split(ts.envMap[pathEnvName()], string(filepath.ListSeparator)) {
-	if runtime.GOOS == "plan9" {
-		pathName = "path"
-	}
-
-	for _, dir := range strings.Split(ts.envMap[pathName], string(filepath.ListSeparator)) {
 		if searchExt {
 			ents, err := os.ReadDir(dir)
 			if err != nil {

src/cmd/go/testdata/script/README

@@ -41,12 +41,19 @@ Scripts also have access to these other environment variables:
 	GODEBUG=<actual GODEBUG>
 	devnull=<value of os.DevNull>
 	goversion=<current Go version; for example, 1.12>
-	:=<OS-specific path list separator>
 
-The scripts' supporting files are unpacked relative to $GOPATH/src (aka $WORK/gopath/src)
+On Plan 9, the variables $path and $home are set instead of $PATH and $HOME.
-and then the script begins execution in that directory as well. Thus the example above runs
+On Windows, the variables $USERPROFILE and $TMP are set instead of
-in $WORK/gopath/src with GOPATH=$WORK/gopath and $WORK/gopath/src/hello.go
+$HOME and $TMPDIR.
-containing the listed contents.
+
+In addition, variables named ':' and '/' are expanded within script arguments
+(expanding to the value of os.PathListSeparator and os.PathSeparator
+respectively) but are not inherited in subprocess environments.
+
+The scripts' supporting files are unpacked relative to $GOPATH/src
+(aka $WORK/gopath/src) and then the script begins execution in that directory as
+well. Thus the example above runs in $WORK/gopath/src with GOPATH=$WORK/gopath
+and $WORK/gopath/src/hello.go containing the listed contents.
 
 The lines at the top of the script are a sequence of commands to be executed
 by a tiny script engine in ../../script_test.go (not the system shell).