cmd/internal/testdir: support -godebug

Similar with what we are doing for -goexperiment.

For #65778

Change-Id: I7dda69512a3ffb491e3de31941ae1c3d34fececf
Reviewed-on: https://go-review.googlesource.com/c/go/+/568156
Auto-Submit: Cuong Manh Le <cuong.manhle.vn@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>

src/cmd/internal/testdir/testdir_test.go

@@ -62,6 +62,7 @@ var (
  goarch string // Target GOARCH
  cgoEnabled bool
  goExperiment string
+ goDebug string
 
  // dirs are the directories to look for *.go files in.
  // TODO(bradfitz): just use all directories?
@@ -100,6 +101,7 @@ func Test(t *testing.T) {
  GOOS string
  GOARCH string
  GOEXPERIMENT string
+ GODEBUG string
  CGO_ENABLED string
  }
  if err := json.NewDecoder(stdout).Decode(&env); err != nil {
@@ -112,6 +114,7 @@ func Test(t *testing.T) {
  goarch = env.GOARCH
  cgoEnabled, _ = strconv.ParseBool(env.CGO_ENABLED)
  goExperiment = env.GOEXPERIMENT
+ goDebug = env.GODEBUG
 
  common := testCommon{
  gorootTestDir: filepath.Join(testenv.GOROOT(t), "test"),
@@ -537,6 +540,7 @@ func (t test) run() error {
  }
 
  goexp := goExperiment
+ godebug := goDebug
 
  // collect flags
  for len(args) > 0 && strings.HasPrefix(args[0], "-") {
@@ -569,6 +573,14 @@ func (t test) run() error {
  goexp += args[0]
  runenv = append(runenv, "GOEXPERIMENT="+goexp)
 
+ case "-godebug": // set GODEBUG environment
+ args = args[1:]
+ if godebug != "" {
+ godebug += ","
+ }
+ godebug += args[0]
+ runenv = append(runenv, "GODEBUG="+godebug)
+
  default:
  flags = append(flags, args[0])
  }
@@ -1014,7 +1026,7 @@ func (t test) run() error {
  runInDir = ""
  var out []byte
  var err error
- if len(flags)+len(args) == 0 && t.goGcflagsIsEmpty() && !*linkshared && goarch == runtime.GOARCH && goos == runtime.GOOS && goexp == goExperiment {
+ if len(flags)+len(args) == 0 && t.goGcflagsIsEmpty() && !*linkshared && goarch == runtime.GOARCH && goos == runtime.GOOS && goexp == goExperiment && godebug == goDebug {
  // If we're not using special go command flags,
  // skip all the go command machinery.
  // This avoids any time the go command would