Use actual head pipeline on merge request serializer

app/controllers/projects/merge_requests_controller.rb

@@ -283,15 +283,15 @@ class Projects::MergeRequestsController < Projects::MergeRequests::ApplicationCo
     @merge_request.update(merge_error: nil)
 
     if params[:merge_when_pipeline_succeeds].present?
-      return :failed unless @merge_request.current_head_pipeline
+      return :failed unless @merge_request.actual_head_pipeline
 
-      if @merge_request.current_head_pipeline.active?
+      if @merge_request.actual_head_pipeline.active?
         ::MergeRequests::MergeWhenPipelineSucceedsService
           .new(@project, current_user, merge_params)
           .execute(@merge_request)
 
         :merge_when_pipeline_succeeds
-      elsif @merge_request.current_head_pipeline.success?
+      elsif @merge_request.actual_head_pipeline.success?
         # This can be triggered when a user clicks the auto merge button while
         # the tests finish at about the same time
         @merge_request.merge_async(current_user.id, params)

app/models/merge_request.rb

@@ -148,7 +148,7 @@ class MergeRequest < ActiveRecord::Base
   # Use this method whenever you need to make sure the head_pipeline is synced with the
   # branch head commit, for example checking if a merge request can be merged.
   # For more information check: https://gitlab.com/gitlab-org/gitlab-ce/issues/40004
-  def current_head_pipeline
+  def actual_head_pipeline
     head_pipeline&.sha == diff_head_sha ? head_pipeline : nil
   end
 
@@ -831,7 +831,7 @@ class MergeRequest < ActiveRecord::Base
     return true unless project.only_allow_merge_if_pipeline_succeeds?
     return true unless head_pipeline
 
-    current_head_pipeline&.success? || current_head_pipeline&.skipped?
+    actual_head_pipeline&.success? || actual_head_pipeline&.skipped?
   end
 
   def environments_for(current_user)
@@ -1005,7 +1005,7 @@ class MergeRequest < ActiveRecord::Base
     return true if autocomplete_precheck
 
     return false unless mergeable?(skip_ci_check: true)
-    return false if current_head_pipeline && !(current_head_pipeline.success? || current_head_pipeline.active?)
+    return false if actual_head_pipeline && !(actual_head_pipeline.success? || actual_head_pipeline.active?)
     return false if last_diff_sha != diff_head_sha
 
     true

app/presenters/merge_request_presenter.rb

@@ -163,7 +163,7 @@ class MergeRequestPresenter < Gitlab::View::Presenter::Delegated
   end
 
   def pipeline
-    @pipeline ||= head_pipeline
+    @pipeline ||= actual_head_pipeline
   end
 
   def issues_sentence(project, issues)

app/serializers/merge_request_entity.rb

@@ -33,7 +33,7 @@ class MergeRequestEntity < IssuableEntity
   end
 
   expose :merge_commit_message
-  expose :head_pipeline, with: PipelineDetailsEntity, as: :pipeline
+  expose :actual_head_pipeline, with: PipelineDetailsEntity, as: :pipeline
 
   # Booleans
   expose :merge_ongoing?, as: :merge_ongoing

spec/models/merge_request_spec.rb

@@ -840,20 +840,20 @@ describe MergeRequest do
       end
     end
 
-    describe '#current_head_pipeline' do
+    describe '#actual_head_pipeline' do
       it 'returns nil for MR with old pipeline' do
         pipeline = create(:ci_empty_pipeline, sha: 'notlatestsha')
         subject.update_attribute(:head_pipeline_id, pipeline.id)
 
-        expect(subject.current_head_pipeline).to be_nil
+        expect(subject.actual_head_pipeline).to be_nil
       end
 
       it 'returns the pipeline for MR with recent pipeline' do
         pipeline = create(:ci_empty_pipeline, sha: 'lastsha')
         subject.update_attribute(:head_pipeline_id, pipeline.id)
 
-        expect(subject.current_head_pipeline).to eq(subject.head_pipeline)
-        expect(subject.current_head_pipeline).to eq(pipeline)
+        expect(subject.actual_head_pipeline).to eq(subject.head_pipeline)
+        expect(subject.actual_head_pipeline).to eq(pipeline)
       end
     end
   end

spec/serializers/merge_request_entity_spec.rb

@@ -5,23 +5,35 @@ describe MergeRequestEntity do
   let(:resource) { create(:merge_request, source_project: project, target_project: project) }
   let(:user)     { create(:user) }
 
-  let(:request) { double('request', current_user: user) }
+  let(:request) { double('request', current_user: user, project: project) }
 
   subject do
     described_class.new(resource, request: request).as_json
   end
 
-  it 'includes pipeline' do
-    req = double('request', current_user: user)
-    pipeline = build_stubbed(:ci_pipeline)
-    allow(resource).to receive(:head_pipeline).and_return(pipeline)
+  describe 'pipeline' do
+    let(:pipeline) { create(:ci_empty_pipeline, project: project, ref: resource.source_branch, sha: resource.source_branch_sha, head_pipeline_of: resource) }
 
+    context 'when is up to date' do
+      let(:req) { double('request', current_user: user, project: project) }
+
+      it 'returns pipeline' do
         pipeline_payload = PipelineDetailsEntity
           .represent(pipeline, request: req)
           .as_json
 
         expect(subject[:pipeline]).to eq(pipeline_payload)
       end
+    end
+
+    context 'when is not up to date' do
+      it 'returns nil' do
+        pipeline.update(sha: "not up to date")
+
+        expect(subject[:pipeline]).to be_nil
+      end
+    end
+  end
 
   it 'includes issues_links' do
     issues_links = subject[:issues_links]