Merge branch 'feature/improve-mrwbs-and-todos-for-pipelines' into 'master'

Trigger Merge When Pipeline Succeeds on pipeline event

## What does this MR do?

This MR is meant to improve merge when build succeeds triggers, which has an impact on performance.

- [x] Move Merge When Build Succeeds trigger from commit status to pipeline event
- [x] Drop support for triggering event for branches that include commit status submitted without branch (no longer relevant)
- [x] Perform Merge When Pipeline Succeeds asynchronously to improve performance and avoid race conditions
- [x] Add missing feature test that verifies if MWBS feature actually works and merges merge requests
- [x] Update the documentation to reflect change in the behavior

Moved to separate merge request:

- [ ] Rename Merge When Build Succeeds to Merge When Pipeline Succeeds
- [ ] Update documentation to reflect name change for this feature

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing

See merge request !6675

1 files changed, 43 insertions, 50 deletions

diff --git a/spec/services/merge_requests/merge_when_build_succeeds_service_spec.rb b/spec/services/merge_requests/merge_when_build_succeeds_service_spec.rb
index 9a29e400654..b80cfd8f450 100644
--- a/spec/services/merge_requests/merge_when_build_succeeds_service_spec.rb
+++ b/spec/services/merge_requests/merge_when_build_succeeds_service_spec.rb
@@ -58,57 +58,67 @@ describe MergeRequests::MergeWhenBuildSucceedsService do
   end
 
   describe "#trigger" do
-    context 'build with ref' do
-      let(:build)     { create(:ci_build, ref: mr_merge_if_green_enabled.source_branch, status: "success") }
+    let(:merge_request_ref) { mr_merge_if_green_enabled.source_branch }
+    let(:merge_request_head) do
+      project.commit(mr_merge_if_green_enabled.source_branch).id
+    end
 
-      it "merges all merge requests with merge when build succeeds enabled" do
-        allow_any_instance_of(MergeRequest).to receive(:pipeline).and_return(pipeline)
-        allow(pipeline).to receive(:success?).and_return(true)
+    context 'when triggered by pipeline with valid ref and sha' do
+      let(:triggering_pipeline) do
+        create(:ci_pipeline, project: project, ref: merge_request_ref,
+                             sha: merge_request_head, status: 'success')
+      end
 
+      it "merges all merge requests with merge when build succeeds enabled" do
         expect(MergeWorker).to receive(:perform_async)
-        service.trigger(build)
+        service.trigger(triggering_pipeline)
       end
     end
 
-    context 'triggered by an old build' do
-      let(:old_build) { create(:ci_build, ref: mr_merge_if_green_enabled.source_branch, status: "success") }
-      let(:build)     { create(:ci_build, ref: mr_merge_if_green_enabled.source_branch, status: "success") }
-
-      it "merges all merge requests with merge when build succeeds enabled" do
-        allow_any_instance_of(MergeRequest).to receive(:pipeline).and_return(pipeline)
-        allow(pipeline).to receive(:success?).and_return(true)
-        allow(old_build).to receive(:sha).and_return('1234abcdef')
+    context 'when triggered by an old pipeline' do
+      let(:old_pipeline) do
+        create(:ci_pipeline, project: project, ref: merge_request_ref,
+                             sha: '1234abcdef', status: 'success')
+      end
 
+      it 'it does not merge merge request' do
         expect(MergeWorker).not_to receive(:perform_async)
-        service.trigger(old_build)
+        service.trigger(old_pipeline)
       end
     end
 
-    context 'commit status without ref' do
-      let(:commit_status) { create(:generic_commit_status, status: 'success') }
-
-      before { mr_merge_if_green_enabled }
-
-      it "doesn't merge a requests for status on other branch" do
-        allow(project.repository).to receive(:branch_names_contains).with(commit_status.sha).and_return([])
+    context 'when triggered by pipeline from a different branch' do
+      let(:unrelated_pipeline) do
+        create(:ci_pipeline, project: project, ref: 'feature',
+                             sha: merge_request_head, status: 'success')
+      end
 
+      it 'does not merge request' do
         expect(MergeWorker).not_to receive(:perform_async)
-        service.trigger(commit_status)
+        service.trigger(unrelated_pipeline)
       end
+    end
+  end
 
-      it 'discovers branches and merges all merge requests when status is success' do
-        allow(project.repository).to receive(:branch_names_contains).
-          with(commit_status.sha).and_return([mr_merge_if_green_enabled.source_branch])
-        allow(pipeline).to receive(:success?).and_return(true)
-        allow_any_instance_of(MergeRequest).to receive(:pipeline).and_return(pipeline)
-        allow(pipeline).to receive(:success?).and_return(true)
+  describe "#cancel" do
+    before do
+      service.cancel(mr_merge_if_green_enabled)
+    end
 
-        expect(MergeWorker).to receive(:perform_async)
-        service.trigger(commit_status)
-      end
+    it "resets all the merge_when_build_succeeds params" do
+      expect(mr_merge_if_green_enabled.merge_when_build_succeeds).to be_falsey
+      expect(mr_merge_if_green_enabled.merge_params).to eq({})
+      expect(mr_merge_if_green_enabled.merge_user).to be nil
+    end
+
+    it 'Posts a system note' do
+      note = mr_merge_if_green_enabled.notes.last
+      expect(note.note).to include 'Canceled the automatic merge'
     end
+  end
 
-    context 'properly handles multiple stages' do
+  describe 'pipeline integration' do
+    context 'when there are multiple stages in the pipeline' do
       let(:ref) { mr_merge_if_green_enabled.source_branch }
       let(:sha) { project.commit(ref).id }
 
@@ -148,21 +158,4 @@ describe MergeRequests::MergeWhenBuildSucceedsService do
       end
     end
   end
-
-  describe "#cancel" do
-    before do
-      service.cancel(mr_merge_if_green_enabled)
-    end
-
-    it "resets all the merge_when_build_succeeds params" do
-      expect(mr_merge_if_green_enabled.merge_when_build_succeeds).to be_falsey
-      expect(mr_merge_if_green_enabled.merge_params).to eq({})
-      expect(mr_merge_if_green_enabled.merge_user).to be nil
-    end
-
-    it 'Posts a system note' do
-      note = mr_merge_if_green_enabled.notes.last
-      expect(note.note).to include 'Canceled the automatic merge'
-    end
-  end
 end