Add squashing capability to the pull request merge function.

Fixes #324.
Fixes #353.

Change-Id: If176b98b951db7f2e45ad7578bb8eeac13ffdbc2

github/github.go

@@ -69,6 +69,9 @@ const (
 
 	// https://developer.github.com/changes/2016-05-12-reactions-api-preview/
 	mediaTypeReactionsPreview = "application/vnd.github.squirrel-girl-preview"
+
+	// https://developer.github.com/changes/2016-04-01-squash-api-preview/
+	mediaTypeSquashPreview = "application/vnd.github.polaris-preview+json"
 )
 
 // A Client manages communication with the GitHub API.

github/pulls.go

@@ -248,19 +248,30 @@ type PullRequestMergeResult struct {
 	Message *string `json:"message,omitempty"`
 }
 
+// PullRequestOptions lets you define how a pull request will be merged.
+type PullRequestOptions struct {
+	Squash bool
+}
+
 type pullRequestMergeRequest struct {
 	CommitMessage *string `json:"commit_message"`
+	Squash        *bool   `json:"squash,omitempty"`
 }
 
 // Merge a pull request (Merge Button™).
 //
 // GitHub API docs: https://developer.github.com/v3/pulls/#merge-a-pull-request-merge-buttontrade
-func (s *PullRequestsService) Merge(owner string, repo string, number int, commitMessage string) (*PullRequestMergeResult, *Response, error) {
+func (s *PullRequestsService) Merge(owner string, repo string, number int, commitMessage string, options *PullRequestOptions) (*PullRequestMergeResult, *Response, error) {
 	u := fmt.Sprintf("repos/%v/%v/pulls/%d/merge", owner, repo, number)
 
-	req, err := s.client.NewRequest("PUT", u, &pullRequestMergeRequest{
-		CommitMessage: &commitMessage,
-	})
+	pullRequestBody := &pullRequestMergeRequest{CommitMessage: &commitMessage}
+	if options != nil {
+		pullRequestBody.Squash = &options.Squash
+	}
+	req, err := s.client.NewRequest("PUT", u, pullRequestBody)
+
+	// TODO: This header will be unnecessary when the API is no longer in preview.
+	req.Header.Set("Accept", mediaTypeSquashPreview)
 
 	if err != nil {
 		return nil, nil, err

github/pulls_test.go

@@ -341,6 +341,7 @@ func TestPullRequestsService_Merge(t *testing.T) {
 
 	mux.HandleFunc("/repos/o/r/pulls/1/merge", func(w http.ResponseWriter, r *http.Request) {
 		testMethod(t, r, "PUT")
+		testHeader(t, r, "Accept", mediaTypeSquashPreview)
 		fmt.Fprint(w, `
 			{
 			  "sha": "6dcb09b5b57875f334f61aebed695e2e4193db5e",
@@ -349,7 +350,8 @@ func TestPullRequestsService_Merge(t *testing.T) {
 			}`)
 	})
 
-	merge, _, err := client.PullRequests.Merge("o", "r", 1, "merging pull request")
+	options := &PullRequestOptions{Squash: true}
+	merge, _, err := client.PullRequests.Merge("o", "r", 1, "merging pull request", options)
 	if err != nil {
 		t.Errorf("PullRequests.Merge returned error: %v", err)
 	}