cmd/gopherbot, maintner: add the author of the change to the notification on github

When a new change is pushed, the bot posts a message on Github following this new format:
Change https://golang.org/cl/NNNN by AUTHOR mentions this issue

A new method to the CL's API in the maintner package is added
to provide the related absolute url.

Fixes #26816

Author: Ivan Palladino

cmd/gopherbot/gopherbot.go

@@ -899,7 +899,7 @@ func (b *gopherbot) closeStaleWaitingForInfo(ctx context.Context) error {
 
 }
 
-// cl2issue writes "Change https://golang.org/cl/NNNN mentions this issue"
+// cl2issue writes "Change https://golang.org/cl/NNNN by AUTHOR mentions this issue"
 // and the change summary on GitHub when a new Gerrit change references a GitHub issue.
 func (b *gopherbot) cl2issue(ctx context.Context) error {
 	monthAgo := time.Now().Add(-30 * 24 * time.Hour)
@@ -915,6 +915,7 @@ func (b *gopherbot) cl2issue(ctx context.Context) error {
 				// already processed this issue.
 				return nil
 			}
+			prefix := fmt.Sprintf("Change %s", cl.URL().String())
 			for _, ref := range cl.GitHubIssueRefs {
 				if id := ref.Repo.ID(); id.Owner != "golang" || id.Repo != "go" {
 					continue
@@ -924,17 +925,17 @@ func (b *gopherbot) cl2issue(ctx context.Context) error {
 					continue
 				}
 				hasComment := false
-				substr := fmt.Sprintf("%d mentions this issue", cl.Number)
 				gi.ForeachComment(func(c *maintner.GitHubComment) error {
-					if strings.Contains(c.Body, substr) {
+					if strings.HasPrefix(c.Body, prefix) {
 						hasComment = true
 						return errStopIteration
 					}
 					return nil
 				})
 				if !hasComment {
 					printIssue("cl2issue", gi)
-					msg := fmt.Sprintf("Change https://golang.org/cl/%d mentions this issue: `%s`", cl.Number, cl.Commit.Summary())
+					author := cl.Owner().Name()
+					msg := fmt.Sprintf("%s by %s mentions this issue: `%s`", prefix, author, cl.Commit.Summary())
 					if err := b.addGitHubComment(ctx, "golang", "go", gi.Number, msg); err != nil {
 						return err
 					}

maintner/gerrit.go

@@ -509,6 +509,16 @@ func (cl *GerritCL) CommitAtVersion(version int32) *GitCommit {
 	return cl.Project.commit[hash]
 }
 
+// URL returns the absolute url of the CL.
+func (cl *GerritCL) URL() *url.URL {
+	s := fmt.Sprintf("https://golang.org/cl/%d", cl.Number)
+	u, err := url.Parse(s)
+	if err != nil {
+		return &url.URL{}
+	}
+	return u
+}
+
 func (cl *GerritCL) updateGithubIssueRefs() {
 	gp := cl.Project
 	gerrit := gp.gerrit

maintner/gerrit_test.go

@@ -559,3 +559,20 @@ func TestGerritHashtagsLen(t *testing.T) {
 		}
 	}
 }
+
+func TestGerritURL(t *testing.T) {
+	tests := []struct {
+		set  int32
+		want string
+	}{
+		{0, "https://golang.org/cl/0"},
+		{1238812784, "https://golang.org/cl/1238812784"},
+	}
+	for _, tt := range tests {
+		cl := &GerritCL{Number: tt.set}
+		got := cl.URL().String()
+		if got != tt.want {
+			t.Errorf("For set %d, url = %#v; want %v", tt.set, got, tt.want)
+		}
+	}
+}