fix: Add label for PRs on release init (#1911)

Fixes: #1888

Changes: Each command can configure a list of labels to add. The
configured labels are added at the end of `commitAndPush` step.

Note: Not sure if there is a way to test that the Github UI has a label
added. I can add a create a potential dry-run of the `librarian release
init` command with screenshots.

Successful PR generation:
#1935
<img width="2566" height="920" alt="image"
src="https://github.com/user-attachments/assets/c12241c4-31ab-4aee-9c01-0a34bca26602"
/>

Logs:
<img width="2038" height="258" alt="image"
src="https://github.com/user-attachments/assets/e9e91eab-c7b6-4e1d-9327-2809c472f19a"
/>

---------

Signed-off-by: Lawrence Qiu <[email protected]>

Author: lqiu96

internal/librarian/command.go

@@ -48,14 +48,15 @@ type GitHubClientFactory func(token string, repo *github.Repository) (GitHubClie
 type ContainerClientFactory func(workRoot, image, userUID, userGID string) (ContainerClient, error)
 
 type commitInfo struct {
-	cfg             *config.Config
-	state           *config.LibrarianState
-	repo            gitrepo.Repository
-	ghClient        GitHubClient
-	idToCommits     map[string]string
-	failedLibraries []string
-	commitMessage   string
-	prType          string
+	cfg               *config.Config
+	state             *config.LibrarianState
+	repo              gitrepo.Repository
+	ghClient          GitHubClient
+	idToCommits       map[string]string
+	failedLibraries   []string
+	commitMessage     string
+	prType            string
+	pullRequestLabels []string
 }
 
 type commandRunner struct {
@@ -328,8 +329,7 @@ func copyLibrary(dst, src string, library *config.LibraryState) error {
 	return nil
 }
 
-// commitAndPush creates a commit and push request to GitHub for the generated
-// changes.
+// commitAndPush creates a commit and push request to GitHub for the generated changes.
 // It uses the GitHub client to create a PR with the specified branch, title, and
 // description to the repository.
 func commitAndPush(ctx context.Context, info *commitInfo) error {
@@ -380,10 +380,28 @@ func commitAndPush(ctx context.Context, info *commitInfo) error {
 		return fmt.Errorf("failed to create pull request body: %w", err)
 	}
 
-	if _, err = info.ghClient.CreatePullRequest(ctx, gitHubRepo, branch, cfg.Branch, title, prBody); err != nil {
+	pullRequestMetadata, err := info.ghClient.CreatePullRequest(ctx, gitHubRepo, branch, cfg.Branch, title, prBody)
+	if err != nil {
 		return fmt.Errorf("failed to create pull request: %w", err)
 	}
 
+	return addLabelsToPullRequest(ctx, info.ghClient, info.pullRequestLabels, pullRequestMetadata)
+}
+
+// addLabelsToPullRequest adds a list of labels to a single pull request (specified by the id number).
+// Should only be called on a valid Github pull request.
+// Passing in `nil` for labels will no-op and an empty list for labels will clear all labels on the PR.
+// TODO: Consolidate the params to a potential PullRequestInfo struct.
+func addLabelsToPullRequest(ctx context.Context, ghClient GitHubClient, pullRequestLabels []string, prMetadata *github.PullRequestMetadata) error {
+	// Do not update if there are aren't labels provided
+	if pullRequestLabels == nil {
+		return nil
+	}
+	// Github API treats Issues and Pull Request the same
+	// https://docs.github.com/en/rest/issues/labels#add-labels-to-an-issue
+	if err := ghClient.AddLabelsToIssue(ctx, prMetadata.Repo, prMetadata.Number, pullRequestLabels); err != nil {
+		return fmt.Errorf("failed to add labels to pull request: %w", err)
+	}
 	return nil
 }
 

internal/librarian/command_test.go

@@ -1403,6 +1403,69 @@ func TestCommitAndPush(t *testing.T) {
 	}
 }
 
+func TestAddLabelsToPullRequest(t *testing.T) {
+	for _, test := range []struct {
+		name                  string
+		setupMockRepo         func(t *testing.T) gitrepo.Repository
+		mockGithubClient      *mockGitHubClient
+		prMetadata            github.PullRequestMetadata
+		wantPullRequestLabels []string
+		wantErr               bool
+		expectedErrMsg        string
+	}{
+		{
+			name: "Add All Labels",
+			setupMockRepo: func(t *testing.T) gitrepo.Repository {
+				return &MockRepository{}
+			},
+			mockGithubClient: &mockGitHubClient{},
+			prMetadata: github.PullRequestMetadata{
+				Repo:   &github.Repository{Owner: "test-owner", Name: "test-repo"},
+				Number: 7,
+			},
+			wantPullRequestLabels: []string{"release:pending", "1234", "label1234"},
+		},
+		{
+			name: "Failed to add labels",
+			setupMockRepo: func(t *testing.T) gitrepo.Repository {
+				return &MockRepository{}
+			},
+			mockGithubClient: &mockGitHubClient{
+				addLabelsToIssuesErr: errors.New("Can't add labels"),
+			},
+			prMetadata: github.PullRequestMetadata{
+				Repo:   &github.Repository{Owner: "test-owner", Name: "test-repo"},
+				Number: 7,
+			},
+			wantPullRequestLabels: []string{"release:pending", "1234", "label1234"},
+			wantErr:               true,
+			expectedErrMsg:        "failed to add labels to pull request",
+		},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			client := test.mockGithubClient
+			prMetadata := test.prMetadata
+			err := addLabelsToPullRequest(context.Background(), client, test.wantPullRequestLabels, &prMetadata)
+
+			if test.wantErr {
+				if err == nil {
+					t.Errorf("addLabelsToPullRequest() expected error, got nil")
+				}
+				if test.expectedErrMsg != "" && !strings.Contains(err.Error(), test.expectedErrMsg) {
+					t.Errorf("addLabelsToPullRequest() error = %v, expected to contain: %q", err, test.expectedErrMsg)
+				}
+				return
+			}
+			if err != nil {
+				t.Errorf("%s: addLabelsToPullRequest() returned unexpected error: %v", test.name, err)
+			}
+			if diff := cmp.Diff(test.wantPullRequestLabels, test.mockGithubClient.labels); diff != "" {
+				t.Errorf("addLabelsToPullRequest() mismatch (-want +got):\n%s", diff)
+			}
+		})
+	}
+}
+
 func TestCopyLibraryFiles(t *testing.T) {
 	t.Parallel()
 	setup := func(src string, files []string) {

internal/librarian/mocks_test.go

@@ -68,6 +68,7 @@ func (m *mockGitHubClient) CreatePullRequest(ctx context.Context, repo *github.R
 
 func (m *mockGitHubClient) AddLabelsToIssue(ctx context.Context, repo *github.Repository, number int, labels []string) error {
 	m.addLabelsToIssuesCalls++
+	m.labels = append(m.labels, labels...)
 	return m.addLabelsToIssuesErr
 }
 

internal/librarian/release_init.go

@@ -112,6 +112,9 @@ func (r *initRunner) run(ctx context.Context) error {
 		ghClient:      r.ghClient,
 		commitMessage: "chore: create a release",
 		prType:        release,
+		// Newly created PRs from the `release init` command should have a
+		// `release:pending` Github tab to be tracked for release.
+		pullRequestLabels: []string{"release:pending"},
 	}
 	if err := commitAndPush(ctx, commitInfo); err != nil {
 		return fmt.Errorf("failed to commit and push: %w", err)