Extend MergeToRefService for creating merge ref from the other ref

Currently, MergeToRefService is specifically designed for
createing merge commits from source branch and target branch of
merge reqeusts. We extend this behavior to source branch and any
target ref paths.

4 files changed, 57 insertions, 14 deletions

diff --git a/spec/lib/gitlab/git/repository_spec.rb b/spec/lib/gitlab/git/repository_spec.rb
index cceeae8afe6..a28b95e5bff 100644
--- a/spec/lib/gitlab/git/repository_spec.rb
+++ b/spec/lib/gitlab/git/repository_spec.rb
@@ -1694,14 +1694,15 @@ describe Gitlab::Git::Repository, :seed_helper do
     let(:branch_head) { '6d394385cf567f80a8fd85055db1ab4c5295806f' }
     let(:left_sha) { 'cfe32cf61b73a0d5e9f13e774abde7ff789b1660' }
     let(:right_branch) { 'test-master' }
+    let(:first_parent_ref) { 'refs/heads/test-master' }
     let(:target_ref) { 'refs/merge-requests/999/merge' }
 
     before do
-      repository.create_branch(right_branch, branch_head) unless repository.branch_exists?(right_branch)
+      repository.create_branch(right_branch, branch_head) unless repository.ref_exists?(first_parent_ref)
     end
 
     def merge_to_ref
-      repository.merge_to_ref(user, left_sha, right_branch, target_ref, 'Merge message')
+      repository.merge_to_ref(user, left_sha, right_branch, target_ref, 'Merge message', first_parent_ref)
     end
 
     it 'generates a commit in the target_ref' do
@@ -1716,7 +1717,7 @@ describe Gitlab::Git::Repository, :seed_helper do
     end
 
     it 'does not change the right branch HEAD' do
-      expect { merge_to_ref }.not_to change { repository.find_branch(right_branch).target }
+      expect { merge_to_ref }.not_to change { repository.commit(first_parent_ref).sha }
     end
   end
 
diff --git a/spec/lib/gitlab/gitaly_client/operation_service_spec.rb b/spec/lib/gitlab/gitaly_client/operation_service_spec.rb
index 18663a72fcd..f38b8d31237 100644
--- a/spec/lib/gitlab/gitaly_client/operation_service_spec.rb
+++ b/spec/lib/gitlab/gitaly_client/operation_service_spec.rb
@@ -79,13 +79,13 @@ describe Gitlab::GitalyClient::OperationService do
     end
 
     describe '#user_merge_to_ref' do
-      let(:branch) { 'my-branch' }
+      let(:first_parent_ref) { 'refs/heads/my-branch' }
       let(:source_sha) { 'cfe32cf61b73a0d5e9f13e774abde7ff789b1660' }
       let(:ref) { 'refs/merge-requests/x/merge' }
       let(:message) { 'validación' }
       let(:response) { Gitaly::UserMergeToRefResponse.new(commit_id: 'new-commit-id') }
 
-      subject { client.user_merge_to_ref(user, source_sha, branch, ref, message) }
+      subject { client.user_merge_to_ref(user, source_sha, nil, ref, message, first_parent_ref) }
 
       it 'sends a user_merge_to_ref message' do
         expect_any_instance_of(Gitaly::OperationService::Stub)
diff --git a/spec/models/repository_spec.rb b/spec/models/repository_spec.rb
index 13da7bd7407..3d967aa4ab8 100644
--- a/spec/models/repository_spec.rb
+++ b/spec/models/repository_spec.rb
@@ -1420,12 +1420,13 @@ describe Repository do
                              source_project: project)
     end
 
-    it 'writes merge of source and target to MR merge_ref_path' do
+    it 'writes merge of source SHA and first parent ref to MR merge_ref_path' do
       merge_commit_id = repository.merge_to_ref(user,
                                                 merge_request.diff_head_sha,
                                                 merge_request,
                                                 merge_request.merge_ref_path,
-                                                'Custom message')
+                                                'Custom message',
+                                                merge_request.target_branch_ref)
 
       merge_commit = repository.commit(merge_commit_id)
 
diff --git a/spec/services/merge_requests/merge_to_ref_service_spec.rb b/spec/services/merge_requests/merge_to_ref_service_spec.rb
index 61f99f82a76..e2f201677fa 100644
--- a/spec/services/merge_requests/merge_to_ref_service_spec.rb
+++ b/spec/services/merge_requests/merge_to_ref_service_spec.rb
@@ -22,7 +22,6 @@ describe MergeRequests::MergeToRefService do
   shared_examples_for 'successfully merges to ref with merge method' do
     it 'writes commit to merge ref' do
       repository = project.repository
-      target_ref = merge_request.merge_ref_path
 
       expect(repository.ref_exists?(target_ref)).to be(false)
 
@@ -33,7 +32,7 @@ describe MergeRequests::MergeToRefService do
       expect(result[:status]).to eq(:success)
       expect(result[:commit_id]).to be_present
       expect(result[:source_id]).to eq(merge_request.source_branch_sha)
-      expect(result[:target_id]).to eq(merge_request.target_branch_sha)
+      expect(result[:target_id]).to eq(repository.commit(first_parent_ref).sha)
       expect(repository.ref_exists?(target_ref)).to be(true)
       expect(ref_head.id).to eq(result[:commit_id])
     end
@@ -74,17 +73,22 @@ describe MergeRequests::MergeToRefService do
 
   describe '#execute' do
     let(:service) do
-      described_class.new(project, user, commit_message: 'Awesome message',
-                                         should_remove_source_branch: true)
+      described_class.new(project, user, **params)
     end
 
+    let(:params) { { commit_message: 'Awesome message', should_remove_source_branch: true } }
+
     def process_merge_to_ref
       perform_enqueued_jobs do
         service.execute(merge_request)
       end
     end
 
-    it_behaves_like 'successfully merges to ref with merge method'
+    it_behaves_like 'successfully merges to ref with merge method' do
+      let(:first_parent_ref) { 'refs/heads/master' }
+      let(:target_ref) { merge_request.merge_ref_path }
+    end
+
     it_behaves_like 'successfully evaluates pre-condition checks'
 
     context 'commit history comparison with regular MergeService' do
@@ -129,14 +133,22 @@ describe MergeRequests::MergeToRefService do
       context 'when semi-linear merge method' do
         let(:merge_method) { :rebase_merge }
 
-        it_behaves_like 'successfully merges to ref with merge method'
+        it_behaves_like 'successfully merges to ref with merge method' do
+          let(:first_parent_ref) { 'refs/heads/master' }
+          let(:target_ref) { merge_request.merge_ref_path }
+        end
+
         it_behaves_like 'successfully evaluates pre-condition checks'
       end
 
       context 'when fast-forward merge method' do
         let(:merge_method) { :ff }
 
-        it_behaves_like 'successfully merges to ref with merge method'
+        it_behaves_like 'successfully merges to ref with merge method' do
+          let(:first_parent_ref) { 'refs/heads/master' }
+          let(:target_ref) { merge_request.merge_ref_path }
+        end
+
         it_behaves_like 'successfully evaluates pre-condition checks'
       end
 
@@ -178,5 +190,34 @@ describe MergeRequests::MergeToRefService do
 
       it { expect(todo).not_to be_done }
     end
+
+    describe 'cascading merge refs' do
+      set(:project) { create(:project, :repository) }
+      let(:params) { { commit_message: 'Cascading merge', first_parent_ref: first_parent_ref, target_ref: target_ref } }
+
+      context 'when first merge happens' do
+        let(:merge_request) do
+          create(:merge_request, source_project: project, source_branch: 'feature',
+                                 target_project: project, target_branch: 'master')
+        end
+
+        it_behaves_like 'successfully merges to ref with merge method' do
+          let(:first_parent_ref) { 'refs/heads/master' }
+          let(:target_ref) { 'refs/merge-requests/1/train' }
+        end
+
+        context 'when second merge happens' do
+          let(:merge_request) do
+            create(:merge_request, source_project: project, source_branch: 'improve/awesome',
+                                   target_project: project, target_branch: 'master')
+          end
+
+          it_behaves_like 'successfully merges to ref with merge method' do
+            let(:first_parent_ref) { 'refs/merge-requests/1/train' }
+            let(:target_ref) { 'refs/merge-requests/2/train' }
+          end
+        end
+      end
+    end
   end
 end