devapp,maintner: use ID instead of text for HelpWanted label

Add *GitHubIssue.HasLabelID method to maintner API.

Since the text will change to “help wanted”, adjust the logic to
make it a bit more future-proof.

Updates golang/go#22329

Change-Id: I22e9f06d6e2aca8ae4da31532f9cde2317a709ff
Reviewed-on: https://go-review.googlesource.com/83297
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

devapp/server.go

@@ -122,7 +122,7 @@ func (s *server) corpusUpdateLoop(ctx context.Context) {
 const (
 	issuesURLBase = "https://golang.org/issue/"
 
-	labelHelpWanted = "HelpWanted"
+	labelHelpWantedID = 150880243
 )
 
 func (s *server) updateHelpWantedIssues() {
@@ -134,7 +134,7 @@ func (s *server) updateHelpWantedIssues() {
 		if i.Closed {
 			return nil
 		}
-		if i.HasLabel(labelHelpWanted) {
+		if i.HasLabelID(labelHelpWantedID) {
 			ids = append(ids, i.Number)
 		}
 		return nil

maintner/github.go

@@ -333,6 +333,12 @@ func (gi *GitHubIssue) HasLabel(label string) bool {
 	return false
 }
 
+// HasLabelID returns whether the issue has a label with the given ID.
+func (gi *GitHubIssue) HasLabelID(id int64) bool {
+	_, ok := gi.Labels[id]
+	return ok
+}
+
 func (gi *GitHubIssue) getCreatedAt() time.Time {
 	if gi == nil {
 		return time.Time{}