Move pipelines from widget.json to cached_widget.json

Since we already have expiration mechanism for pipelines
What about moving them into cached_widget.json

app/serializers/merge_request_poll_cached_widget_entity.rb

@@ -46,6 +46,12 @@ class MergeRequestPollCachedWidgetEntity < IssuableEntity
     end
   end
 
+  expose :actual_head_pipeline, as: :pipeline, if: -> (mr, _) {
+    Feature.enabled?(:merge_request_cached_pipeline_serializer, mr.project) && presenter(mr).can_read_pipeline?
+  } do |merge_request, options|
+    MergeRequests::PipelineEntity.represent(merge_request.actual_head_pipeline, options)
+  end
+
   # Paths
   #
   expose :target_branch_commits_path do |merge_request|

app/serializers/merge_request_poll_widget_entity.rb

@@ -19,7 +19,9 @@ class MergeRequestPollWidgetEntity < Grape::Entity
   # User entities
   expose :merge_user, using: UserEntity
 
-  expose :actual_head_pipeline, as: :pipeline, if: -> (mr, _) { presenter(mr).can_read_pipeline? } do |merge_request, options|
+  expose :actual_head_pipeline, as: :pipeline, if: -> (mr, _) {
+    Feature.disabled?(:merge_request_cached_pipeline_serializer, mr.project) && presenter(mr).can_read_pipeline?
+  } do |merge_request, options|
     MergeRequests::PipelineEntity.represent(merge_request.actual_head_pipeline, options)
   end
 

app/services/ci/expire_pipeline_cache_service.rb

@@ -32,11 +32,18 @@ module Ci
       Gitlab::Routing.url_helpers.project_new_merge_request_path(project, format: :json)
     end
 
+    def pipelines_project_merge_request_path(merge_request)
+      Gitlab::Routing.url_helpers.pipelines_project_merge_request_path(merge_request.target_project, merge_request, format: :json)
+    end
+
+    def merge_request_widget_path(merge_request)
+      Gitlab::Routing.url_helpers.cached_widget_project_json_merge_request_path(merge_request.project, merge_request, format: :json)
+    end
+
     def each_pipelines_merge_request_path(pipeline)
       pipeline.all_merge_requests.each do |merge_request|
-        path = Gitlab::Routing.url_helpers.pipelines_project_merge_request_path(merge_request.target_project, merge_request, format: :json)
-
-        yield(path)
+        yield(pipelines_project_merge_request_path(merge_request))
+        yield(merge_request_widget_path(merge_request))
       end
     end
 

config/feature_flags/development/merge_request_cached_pipeline_serializer.yml

+---
+name: merge_request_cached_pipeline_serializer
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/38273
+rollout_issue_url:
+type: development
+group: group::source code
+default_enabled: false

spec/serializers/merge_request_poll_cached_widget_entity_spec.rb

@@ -213,4 +213,55 @@ RSpec.describe MergeRequestPollCachedWidgetEntity do
       end
     end
   end
+
+  describe 'pipeline' do
+    let_it_be(:pipeline) { create(:ci_empty_pipeline, project: project, ref: resource.source_branch, sha: resource.source_branch_sha, head_pipeline_of: resource) }
+
+    before do
+      allow_any_instance_of(MergeRequestPresenter).to receive(:can?).and_call_original
+      allow_any_instance_of(MergeRequestPresenter).to receive(:can?).with(user, :read_pipeline, anything).and_return(can_access)
+    end
+
+    context 'when user has access to pipelines' do
+      let(:can_access) { true }
+
+      context 'when is up to date' do
+        let(:req) { double('request', current_user: user, project: project) }
+
+        it 'returns pipeline' do
+          pipeline_payload =
+            MergeRequests::PipelineEntity
+              .represent(pipeline, request: req)
+              .as_json
+
+          expect(subject[:pipeline]).to eq(pipeline_payload)
+        end
+
+        context 'when merge_request_cached_pipeline_serializer is disabled' do
+          it 'does not return pipeline' do
+            stub_feature_flags(merge_request_cached_pipeline_serializer: false)
+
+            expect(subject[:pipeline]).to be_nil
+          end
+        end
+      end
+
+      context 'when user does not have access to pipelines' do
+        let(:can_access) { false }
+        let(:req) { double('request', current_user: user, project: project) }
+
+        it 'does not have pipeline' do
+          expect(subject[:pipeline]).to eq(nil)
+        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 eq(nil)
+        end
+      end
+    end
+  end
 end

spec/serializers/merge_request_poll_widget_entity_spec.rb

@@ -222,13 +222,21 @@ RSpec.describe MergeRequestPollWidgetEntity do
       context 'when is up to date' do
         let(:req) { double('request', current_user: user, project: project) }
 
-        it 'returns pipeline' do
-          pipeline_payload =
-            MergeRequests::PipelineEntity
-              .represent(pipeline, request: req)
-              .as_json
+        it 'does not return pipeline' do
+          expect(subject[:pipeline]).to be_nil
+        end
+
+        context 'when merge_request_cached_pipeline_serializer is disabled' do
+          it 'returns detailed info about pipeline' do
+            stub_feature_flags(merge_request_cached_pipeline_serializer: false)
+
+            pipeline_payload =
+              MergeRequests::PipelineEntity
+                .represent(pipeline, request: req)
+                .as_json
 
-          expect(subject[:pipeline]).to eq(pipeline_payload)
+            expect(subject[:pipeline]).to eq(pipeline_payload)
+          end
         end
 
         it 'returns ci_status' do
@@ -249,10 +257,6 @@ RSpec.describe MergeRequestPollWidgetEntity do
       let(:result) { false }
       let(:req) { double('request', current_user: user, project: project) }
 
-      it 'does not have pipeline' do
-        expect(subject[:pipeline]).to eq(nil)
-      end
-
       it 'does not return ci_status' do
         expect(subject[:ci_status]).to eq(nil)
       end

spec/services/ci/expire_pipeline_cache_service_spec.rb

@@ -26,9 +26,11 @@ RSpec.describe Ci::ExpirePipelineCacheService do
       project = merge_request.target_project
 
       merge_request_pipelines_path = "/#{project.full_path}/-/merge_requests/#{merge_request.iid}/pipelines.json"
+      merge_request_widget_path = "/#{project.full_path}/-/merge_requests/#{merge_request.iid}/cached_widget.json"
 
       allow_any_instance_of(Gitlab::EtagCaching::Store).to receive(:touch)
       expect_any_instance_of(Gitlab::EtagCaching::Store).to receive(:touch).with(merge_request_pipelines_path)
+      expect_any_instance_of(Gitlab::EtagCaching::Store).to receive(:touch).with(merge_request_widget_path)
 
       subject.execute(merge_request.all_pipelines.last)
     end