Added update branch API (#1187)

Fixes #1183.

github/github.go

@@ -137,6 +137,9 @@ const (
 
 	// https://developer.github.com/changes/2019-04-24-vulnerability-alerts/
 	mediaTypeRequiredVulnerabilityAlertsPreview = "application/vnd.github.dorian-preview+json"
+
+	// https://developer.github.com/changes/2019-05-29-update-branch-api/
+	mediaTypeUpdatePullRequestBranchPreview = "application/vnd.github.lydian-preview+json"
 )
 
 // A Client manages communication with the GitHub API.

github/pulls.go

@@ -242,6 +242,49 @@ func (s *PullRequestsService) Create(ctx context.Context, owner string, repo str
 	return p, resp, nil
 }
 
+// PullReqestBranchUpdateOptions specifies the optional parameters to the
+// PullRequestsService.UpdateBranch method.
+type PullReqestBranchUpdateOptions struct {
+	// ExpectedHeadSHA specifies the most recent commit on the pull request's branch.
+	// Default value is the SHA of the pull request's current HEAD ref.
+	ExpectedHeadSHA *string `json:"expected_head_sha,omitempty"`
+}
+
+// PullRequestBranchUpdateResponse specifies the response of pull request branch update.
+type PullRequestBranchUpdateResponse struct {
+	Message *string `json:"message,omitempty"`
+	URL     *string `json:"url,omitempty"`
+}
+
+// UpdateBranch updates the pull request branch with latest upstream changes.
+//
+// This method might return an AcceptedError and a status code of
+// 202. This is because this is the status that GitHub returns to signify that
+// it has now scheduled the update of the pull request branch in a background task.
+// A follow up request, after a delay of a second or so, should result
+// in a successful request.
+//
+// GitHub API docs: https://developer.github.com/v3/pulls/#update-a-pull-request-branch
+func (s *PullRequestsService) UpdateBranch(ctx context.Context, owner, repo string, number int, opts *PullReqestBranchUpdateOptions) (*PullRequestBranchUpdateResponse, *Response, error) {
+	u := fmt.Sprintf("repos/%v/%v/pulls/%d/update-branch", owner, repo, number)
+
+	req, err := s.client.NewRequest("PUT", u, opts)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	// TODO: remove custom Accept header when this API fully launches.
+	req.Header.Set("Accept", mediaTypeUpdatePullRequestBranchPreview)
+
+	p := new(PullRequestBranchUpdateResponse)
+	resp, err := s.client.Do(ctx, req, p)
+	if err != nil {
+		return nil, resp, err
+	}
+
+	return p, resp, nil
+}
+
 type pullRequestUpdate struct {
 	Title               *string `json:"title,omitempty"`
 	Body                *string `json:"body,omitempty"`

github/pulls_test.go

@@ -303,6 +303,39 @@ func TestPullRequestsService_Create_invalidOwner(t *testing.T) {
 	testURLParseError(t, err)
 }
 
+func TestPullRequestsService_UpdateBranch(t *testing.T) {
+	client, mux, _, teardown := setup()
+	defer teardown()
+
+	mux.HandleFunc("/repos/o/r/pulls/1/update-branch", func(w http.ResponseWriter, r *http.Request) {
+		testMethod(t, r, "PUT")
+		testHeader(t, r, "Accept", mediaTypeUpdatePullRequestBranchPreview)
+		fmt.Fprint(w, `
+			{
+			  "message": "Updating pull request branch.",
+			  "url": "https://github.com/repos/o/r/pulls/1"
+			}`)
+	})
+
+	opts := &PullReqestBranchUpdateOptions{
+		ExpectedHeadSHA: String("s"),
+	}
+
+	pull, _, err := client.PullRequests.UpdateBranch(context.Background(), "o", "r", 1, opts)
+	if err != nil {
+		t.Errorf("PullRequests.UpdateBranch returned error: %v", err)
+	}
+
+	want := &PullRequestBranchUpdateResponse{
+		Message: String("Updating pull request branch."),
+		URL:     String("https://github.com/repos/o/r/pulls/1"),
+	}
+
+	if !reflect.DeepEqual(pull, want) {
+		t.Errorf("PullRequests.UpdateBranch returned %+v, want %+v", pull, want)
+	}
+}
+
 func TestPullRequestsService_Edit(t *testing.T) {
 	client, mux, _, teardown := setup()
 	defer teardown()