operations: Implement UserMergeToRef

This commit ports the operations.UserMergeToRef RPC from Ruby to Go. The
Go implementation is as-of now hidden behind a new feature flag
"gitaly_go_user_merge_to_ref".

4 files changed, 86 insertions, 9 deletions

diff --git a/changelogs/unreleased/pks-go-user-merge-to-ref.yml b/changelogs/unreleased/pks-go-user-merge-to-ref.yml
new file mode 100644
index 000000000..4a206a734
--- /dev/null
+++ b/changelogs/unreleased/pks-go-user-merge-to-ref.yml
@@ -0,0 +1,5 @@
+---
+title: Port operations.UserMergeToRef to Go
+merge_request: 2580
+author:
+type: performance
diff --git a/internal/gitaly/service/operations/merge.go b/internal/gitaly/service/operations/merge.go
index 2a19c9171..c6a94f3c1 100644
--- a/internal/gitaly/service/operations/merge.go
+++ b/internal/gitaly/service/operations/merge.go
@@ -318,11 +318,77 @@ func validateUserMergeToRefRequest(in *gitalypb.UserMergeToRefRequest) error {
 	return nil
 }
 
+// userMergeToRef overwrites the given TargetRef to point to either Branch or
+// FirstParentRef. Afterwards, it performs a merge of SourceSHA with either
+// Branch or FirstParentRef and updates TargetRef to the merge commit.
+func (s *server) userMergeToRef(ctx context.Context, request *gitalypb.UserMergeToRefRequest) (*gitalypb.UserMergeToRefResponse, error) {
+	repoPath, err := s.locator.GetPath(request.Repository)
+	if err != nil {
+		return nil, err
+	}
+
+	repo := git.NewRepository(request.Repository)
+
+	refName := string(request.Branch)
+	if request.FirstParentRef != nil {
+		refName = string(request.FirstParentRef)
+	}
+
+	ref, err := repo.ResolveRefish(ctx, refName)
+	if err != nil {
+		//nolint:stylecheck
+		return nil, helper.ErrInvalidArgument(errors.New("Invalid merge source"))
+	}
+
+	sourceRef, err := repo.ResolveRefish(ctx, request.SourceSha)
+	if err != nil {
+		//nolint:stylecheck
+		return nil, helper.ErrInvalidArgument(errors.New("Invalid merge source"))
+	}
+
+	// First, overwrite the reference with the target reference.
+	if err := repo.UpdateRef(ctx, string(request.TargetRef), ref, ""); err != nil {
+		return nil, updateRefError{reference: string(request.TargetRef)}
+	}
+
+	// Now, we create the merge commit...
+	merge, err := git2go.MergeCommand{
+		Repository: repoPath,
+		AuthorName: string(request.User.Name),
+		AuthorMail: string(request.User.Email),
+		Message:    string(request.Message),
+		Ours:       ref,
+		Theirs:     sourceRef,
+	}.Run(ctx, s.cfg)
+	if err != nil {
+		if errors.Is(err, git2go.ErrInvalidArgument) {
+			return nil, helper.ErrInvalidArgument(err)
+		}
+		//nolint:stylecheck
+		return nil, fmt.Errorf("Failed to create merge commit for source_sha %s and target_sha %s at %s", sourceRef, string(request.TargetRef), refName)
+	}
+
+	// ... and move branch from target ref to the merge commit. The Ruby
+	// implementation doesn't invoke hooks, so we don't either.
+	if err := repo.UpdateRef(ctx, string(request.TargetRef), merge.CommitID, ref); err != nil {
+		//nolint:stylecheck
+		return nil, helper.ErrPreconditionFailed(fmt.Errorf("Could not update %s. Please refresh and try again", string(request.TargetRef)))
+	}
+
+	return &gitalypb.UserMergeToRefResponse{
+		CommitId: merge.CommitID,
+	}, nil
+}
+
 func (s *server) UserMergeToRef(ctx context.Context, in *gitalypb.UserMergeToRefRequest) (*gitalypb.UserMergeToRefResponse, error) {
 	if err := validateUserMergeToRefRequest(in); err != nil {
 		return nil, helper.ErrInvalidArgument(err)
 	}
 
+	if featureflag.IsEnabled(ctx, featureflag.GoUserMergeBranch) {
+		return s.userMergeToRef(ctx, in)
+	}
+
 	client, err := s.ruby.OperationServiceClient(ctx)
 	if err != nil {
 		return nil, helper.ErrInternal(err)
diff --git a/internal/gitaly/service/operations/merge_test.go b/internal/gitaly/service/operations/merge_test.go
index dd4a56fe6..3b4ef9e12 100644
--- a/internal/gitaly/service/operations/merge_test.go
+++ b/internal/gitaly/service/operations/merge_test.go
@@ -475,6 +475,10 @@ func TestFailedUserFFBranchDueToHooks(t *testing.T) {
 }
 
 func TestSuccessfulUserMergeToRefRequest(t *testing.T) {
+	testWithFeature(t, featureflag.GoUserMergeToRef, testSuccessfulUserMergeToRefRequest)
+}
+
+func testSuccessfulUserMergeToRefRequest(t *testing.T, ctx context.Context) {
 	serverSocketPath, stop := runOperationServiceServer(t)
 	defer stop()
 
@@ -536,9 +540,6 @@ func TestSuccessfulUserMergeToRefRequest(t *testing.T) {
 
 	for _, testCase := range testCases {
 		t.Run(testCase.desc, func(t *testing.T) {
-			ctx, cancel := testhelper.Context()
-			defer cancel()
-
 			request := &gitalypb.UserMergeToRefRequest{
 				Repository:     testRepo,
 				User:           testCase.user,
@@ -584,6 +585,10 @@ func TestSuccessfulUserMergeToRefRequest(t *testing.T) {
 }
 
 func TestFailedUserMergeToRefRequest(t *testing.T) {
+	testWithFeature(t, featureflag.GoUserMergeToRef, testFailedUserMergeToRefRequest)
+}
+
+func testFailedUserMergeToRefRequest(t *testing.T, ctx context.Context) {
 	serverSocketPath, stop := runOperationServiceServer(t)
 	defer stop()
 
@@ -669,9 +674,6 @@ func TestFailedUserMergeToRefRequest(t *testing.T) {
 
 	for _, testCase := range testCases {
 		t.Run(testCase.desc, func(t *testing.T) {
-			ctx, cancel := testhelper.Context()
-			defer cancel()
-
 			request := &gitalypb.UserMergeToRefRequest{
 				Repository: testCase.repo,
 				User:       testCase.user,
@@ -686,6 +688,10 @@ func TestFailedUserMergeToRefRequest(t *testing.T) {
 }
 
 func TestUserMergeToRefIgnoreHooksRequest(t *testing.T) {
+	testWithFeature(t, featureflag.GoUserMergeToRef, testUserMergeToRefIgnoreHooksRequest)
+}
+
+func testUserMergeToRefIgnoreHooksRequest(t *testing.T, ctx context.Context) {
 	serverSocketPath, stop := runOperationServiceServer(t)
 	defer stop()
 
@@ -717,9 +723,6 @@ func TestUserMergeToRefIgnoreHooksRequest(t *testing.T) {
 			require.NoError(t, err)
 			defer remove()
 
-			ctx, cancel := testhelper.Context()
-			defer cancel()
-
 			resp, err := client.UserMergeToRef(ctx, request)
 			require.NoError(t, err)
 			require.Empty(t, resp.PreReceiveError)
diff --git a/internal/metadata/featureflag/feature_flags.go b/internal/metadata/featureflag/feature_flags.go
index 836db2201..43b34c8a4 100644
--- a/internal/metadata/featureflag/feature_flags.go
+++ b/internal/metadata/featureflag/feature_flags.go
@@ -36,6 +36,8 @@ var (
 	LogCommandStats = FeatureFlag{Name: "log_command_stats", OnByDefault: false}
 	// GoUserMergeBranch enables the Go implementation of UserMergeBranch
 	GoUserMergeBranch = FeatureFlag{Name: "go_user_merge_branch", OnByDefault: false}
+	// GoUserMergeToRef enable the Go implementation of UserMergeToRef
+	GoUserMergeToRef = FeatureFlag{Name: "go_user_merge_to_ref", OnByDefault: false}
 )
 
 // All includes all feature flags.
@@ -51,6 +53,7 @@ var All = []FeatureFlag{
 	ReferenceTransactionHook,
 	RubyReferenceTransactionHook,
 	GoUserMergeBranch,
+	GoUserMergeToRef,
 }
 
 const (