testing: replace all GOOS-specific path separators in TempDir

For GOOS=windows the path separator characters '\' and ':' also need be
replaced.

Updates #38465

Change-Id: If7c8cf93058c87d7df6cda140e82fd76578fe699
Reviewed-on: https://go-review.googlesource.com/c/go/+/229837
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/testing/testing.go

@@ -797,6 +797,11 @@ func (c *common) Cleanup(f func()) {
 	}
 }
 
+var (
+	rOnce sync.Once
+	r     *strings.Replacer
+)
+
 // TempDir returns a temporary directory for the test to use.
 // It is lazily created on first access, and calls t.Fatal if the directory
 // creation fails.
@@ -809,7 +814,10 @@ func (c *common) TempDir() string {
 
 		// ioutil.TempDir doesn't like path separators in its pattern,
 		// so mangle the name to accommodate subtests.
-		pattern := strings.ReplaceAll(c.Name(), "/", "_")
+		rOnce.Do(func() {
+			r = strings.NewReplacer("/", "_", "\\", "_", ":", "_")
+		})
+		pattern := r.Replace(c.Name())
 
 		c.tempDir, c.tempDirErr = ioutil.TempDir("", pattern)
 		if c.tempDirErr == nil {

src/testing/testing_test.go

@@ -21,6 +21,11 @@ func TestMain(m *testing.M) {
 func TestTempDir(t *testing.T) {
 	testTempDir(t)
 	t.Run("InSubtest", testTempDir)
+	t.Run("test/subtest", testTempDir)
+	t.Run("test\\subtest", testTempDir)
+	t.Run("test:subtest", testTempDir)
+	t.Run("test/..", testTempDir)
+	t.Run("../test", testTempDir)
 }
 
 func testTempDir(t *testing.T) {