Add a system note and update relevant merge requests when a branch is deleted or re-added

If a branch is deleted with an open merge request, amended offline, and then pushed again,
GitLab doesn't bother to update the merge request even though the last commit ID and/or
code may have changed. This MR ensures that each push will update any relevant merge
requests and adds a system note if this happens as well.

Closes #2926

1 files changed, 19 insertions, 0 deletions

diff --git a/spec/services/merge_requests/refresh_service_spec.rb b/spec/services/merge_requests/refresh_service_spec.rb
index 9516e7936d8..edb9fd0b43c 100644
--- a/spec/services/merge_requests/refresh_service_spec.rb
+++ b/spec/services/merge_requests/refresh_service_spec.rb
@@ -106,6 +106,25 @@ describe MergeRequests::RefreshService do
       it { expect(@fork_merge_request.notes).to be_empty }
     end
 
+    context 'push new branch that exists in a merge request' do
+      let(:refresh_service) { service.new(@fork_project, @user) }
+      before do
+        allow(refresh_service).to receive(:execute_hooks)
+        refresh_service.execute(Gitlab::Git::BLANK_SHA, @newrev, 'refs/heads/master')
+        reload_mrs
+      end
+
+      it 'should execute hooks with update action' do
+        expect(refresh_service).to have_received(:execute_hooks).
+                                       with(@fork_merge_request, 'update')
+      end
+
+      it { expect(@merge_request.notes).to be_empty }
+      it { expect(@merge_request).to be_open }
+      it { expect(@fork_merge_request.notes.last.note).to include('Source branch `master` added') }
+      it { expect(@fork_merge_request).to be_open }
+    end
+
     def reload_mrs
       @merge_request.reload
       @fork_merge_request.reload