Fix crash with "go test -v -cpu=1,1 ./cmd/camput/"

Don't double-register the help flag. Only affects tests run twice, like above.

Change-Id: Ia235f2e2aa4a70e3b5a5c6fe21d8add90069664f

cmd/camput/camput_test.go

@@ -89,6 +89,23 @@ func TestUsageOnNoargs(t *testing.T) {
 	}
 }
 
+// TestCommandUsage tests that we output a command-specific usage message and return
+// with a non-zero exit status.
+func TestCommandUsage(t *testing.T) {
+	var e env
+	out, err, code := e.Run("attr")
+	if code != 1 {
+		t.Errorf("exit code = %d; want 1", code)
+	}
+	if len(out) != 0 {
+		t.Errorf("wanted nothing on stdout; got:\n%s", out)
+	}
+	sub := "Attr takes 3 args: <permanode> <attr> <value>"
+	if !bytes.Contains(err, []byte(sub)) {
+		t.Errorf("stderr doesn't contain substring %q. Got:\n%s", sub, err)
+	}
+}
+
 func TestUploadingChangingDirectory(t *testing.T) {
 	// TODO(bradfitz):
 	//    $ mkdir /tmp/somedir

pkg/cmdmain/cmdmain.go

@@ -61,6 +61,7 @@ var (
 	// mode name to actual subcommand mapping
 	modeCommand = make(map[string]CommandRunner)
 	modeFlags   = make(map[string]*flag.FlagSet)
+	wantHelp    = make(map[string]*bool)
 
 	// Indirections for replacement by tests
 	Stderr io.Writer = os.Stderr
@@ -100,6 +101,10 @@ func RegisterCommand(mode string, makeCmd func(Flags *flag.FlagSet) CommandRunne
 	}
 	flags := flag.NewFlagSet(mode+" options", flag.ContinueOnError)
 	flags.Usage = func() {}
+
+	var cmdHelp bool
+	flags.BoolVar(&cmdHelp, "help", false, "Help for this mode.")
+	wantHelp[mode] = &cmdHelp
 	modeFlags[mode] = flags
 	modeCommand[mode] = makeCmd(flags)
 }
@@ -249,13 +254,11 @@ func Main() {
 
 	cmdFlags := modeFlags[mode]
 	cmdFlags.SetOutput(Stderr)
-	var cmdHelp bool
-	cmdFlags.BoolVar(&cmdHelp, "help", false, "Help for this mode.")
 	err := cmdFlags.Parse(args[1:])
 	if err != nil {
 		err = ErrUsage
 	} else {
-		if cmdHelp {
+		if *wantHelp[mode] {
 			help(mode)
 			return
 		}