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.

1 files changed, 48 insertions, 7 deletions

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