feat: add labels to a github issue

internal/github/github.go

@@ -135,8 +135,15 @@ func (c *Client) CreatePullRequest(ctx context.Context, repo *Repository, remote
 	return pullRequestMetadata, nil
 }
 
+// AddLabelsToIssue adds labels to an existing issue in a GitHub repository.
+func (c *Client) AddLabelsToIssue(ctx context.Context, repo *Repository, number int, labels []string) error {
+	slog.Info("Labels added to issue", "number", number, "labels", labels)
+	_, _, err := c.Issues.AddLabelsToIssue(ctx, repo.Owner, repo.Name, number, labels)
+	return err
+}
+
 // FetchGitHubRepoFromRemote parses the GitHub repo name from the remote for this repository.
-// There must be a remote named 'origin' with a Github URL (as the first URL), in order to
+// There must be a remote named 'origin' with a GitHub URL (as the first URL), in order to
 // provide an unambiguous result.
 // Remotes without any URLs, or where the first URL does not start with https://github.com/ are ignored.
 func FetchGitHubRepoFromRemote(repo gitrepo.Repository) (*Repository, error) {

internal/github/github_test.go

@@ -400,3 +400,74 @@ func TestCreatePullRequest(t *testing.T) {
 		})
 	}
 }
+
+func TestAddLabelsToIssue(t *testing.T) {
+	t.Parallel()
+	for _, test := range []struct {
+		name          string
+		handler       http.HandlerFunc
+		issueNum      int
+		labels        []string
+		wantErr       bool
+		wantErrSubstr string
+	}{
+		{
+			name: "add labels to an issue",
+			handler: func(w http.ResponseWriter, r *http.Request) {
+				if r.Method != http.MethodPost {
+					t.Errorf("unexpected method: got %s, want %s", r.Method, http.MethodPost)
+				}
+				wantPath := "/repos/owner/repo/issues/7/labels"
+				if r.URL.Path != wantPath {
+					t.Errorf("unexpected path: got %s, want %s", r.URL.Path, wantPath)
+				}
+				var labels []string
+				if err := json.NewDecoder(r.Body).Decode(&labels); err != nil {
+					t.Fatalf("failed to decode request body: %v", err)
+				}
+				expectedBody := []string{"new-label", "another-label"}
+				if strings.Join(labels, ",") != strings.Join(expectedBody, ",") {
+					t.Errorf("unexpected body: got %q, want %q", labels, expectedBody)
+				}
+			},
+			issueNum: 7,
+			labels:   []string{"new-label", "another-label"},
+		},
+		{
+			name:          "GitHub API error",
+			handler:       func(w http.ResponseWriter, r *http.Request) { w.WriteHeader(http.StatusInternalServerError) },
+			wantErr:       true,
+			wantErrSubstr: "500",
+		},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			t.Parallel()
+			server := httptest.NewServer(test.handler)
+			defer server.Close()
+
+			repo := &Repository{Owner: "owner", Name: "repo"}
+			client, err := newClientWithHTTP("fake-token", repo, server.Client())
+			if err != nil {
+				t.Fatalf("newClientWithHTTP() error = %v", err)
+			}
+			client.BaseURL, _ = url.Parse(server.URL + "/")
+
+			err = client.AddLabelsToIssue(context.Background(), repo, test.issueNum, test.labels)
+
+			if test.wantErr {
+				if err == nil {
+					t.Errorf("AddLabelsToIssue() should return an error")
+				}
+				if !strings.Contains(err.Error(), test.wantErrSubstr) {
+					t.Errorf("AddLabelsToIssue() err = %v, want error containing %q", err, test.wantErrSubstr)
+				}
+
+				return
+			}
+
+			if err != nil {
+				t.Errorf("AddLabelsToIssue() err = %v, want nil", err)
+			}
+		})
+	}
+}

internal/librarian/librarian.go

@@ -79,6 +79,7 @@ func Run(ctx context.Context, arg ...string) error {
 type GitHubClient interface {
 	GetRawContent(ctx context.Context, path, ref string) ([]byte, error)
 	CreatePullRequest(ctx context.Context, repo *github.Repository, remoteBranch, title, body string) (*github.PullRequestMetadata, error)
+	AddLabelsToIssue(ctx context.Context, repo *github.Repository, number int, labels []string) error
 }
 
 // ContainerClient is an abstraction over the Docker client.

internal/librarian/mocks_test.go

@@ -33,7 +33,9 @@ type mockGitHubClient struct {
 	rawContent             []byte
 	rawErr                 error
 	createPullRequestCalls int
+	addLabelsToIssuesCalls int
 	createPullRequestErr   error
+	addLabelsToIssuesErr   error
 	createdPR              *github.PullRequestMetadata
 }
 
@@ -49,6 +51,11 @@ func (m *mockGitHubClient) CreatePullRequest(ctx context.Context, repo *github.R
 	return m.createdPR, nil
 }
 
+func (m *mockGitHubClient) AddLabelsToIssue(ctx context.Context, repo *github.Repository, number int, labels []string) error {
+	m.addLabelsToIssuesCalls++
+	return m.addLabelsToIssuesErr
+}
+
 // mockContainerClient is a mock implementation of the ContainerClient interface for testing.
 type mockContainerClient struct {
 	ContainerClient