Fix resolve WIP clearing merge request area

When we split the merge request widget into cached and non-cached
serializers in
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/15045, some merge
request endpoints (e.g. `/remove_wip`, `/cancel_auto_merge`) weren't
adapted to ensure that all the data was returned. As a result, the
frontend would set its merge request state to the partial data it did
have, but then it would clear out data that it didn't have (e.g. CI
pipeline).

When a user clicked on the `Resolve WIP Status` or `Cancel automatic
merge` button, this would cause certain elements (e.g. CI pipeline
status, merge area) to disappear until the next refresh occurred.

We worked around the problem in the MWPS refresh case on the frontend in
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/26232 by forcing a
refresh, but that didn't fix the "Resolve Work in Progress" case. This
fix combines both the cached and non-cached data to ensure the response
data contains all the information necessary for the frontend.

Closes https://gitlab.com/gitlab-org/gitlab/-/issues/214750

app/controllers/projects/merge_requests_controller.rb

@@ -340,11 +340,13 @@ class Projects::MergeRequestsController < Projects::MergeRequests::ApplicationCo
   end
 
   def serialize_widget(merge_request)
-    serializer.represent(merge_request, serializer: 'widget')
+    cached_data = serializer.represent(merge_request, serializer: 'poll_cached_widget')
+    widget_data = serializer.represent(merge_request, serializer: 'poll_widget')
+    cached_data.merge!(widget_data)
   end
 
   def serializer
-    MergeRequestSerializer.new(current_user: current_user, project: merge_request.project)
+    @serializer ||= MergeRequestSerializer.new(current_user: current_user, project: merge_request.project)
   end
 
   def define_edit_vars

app/serializers/merge_request_serializer.rb

@@ -15,6 +15,10 @@ class MergeRequestSerializer < BaseSerializer
         MergeRequestBasicEntity
       when 'noteable'
         MergeRequestNoteableEntity
+      when 'poll_cached_widget'
+        MergeRequestPollCachedWidgetEntity
+      when 'poll_widget'
+        MergeRequestPollWidgetEntity
       else
         # fallback to widget for old poll requests without `serializer` set
         MergeRequestWidgetEntity

changelogs/unreleased/sh-fix-wip-resolve-merge-request.yml

+---
+title: Fix resolve WIP clearing merge request area
+merge_request: 29757
+author:
+type: fixed

spec/controllers/projects/merge_requests_controller_spec.rb

@@ -1245,7 +1245,7 @@ describe Projects::MergeRequestsController do
     end
 
     it 'renders MergeRequest as JSON' do
-      expect(json_response.keys).to include('id', 'iid')
+      expect(json_response.keys).to include('id', 'iid', 'title', 'has_ci', 'merge_status', 'can_be_merged', 'current_user')
     end
   end
 
@@ -1279,7 +1279,7 @@ describe Projects::MergeRequestsController do
     it 'renders MergeRequest as JSON' do
       subject
 
-      expect(json_response.keys).to include('id', 'iid')
+      expect(json_response.keys).to include('id', 'iid', 'title', 'has_ci', 'merge_status', 'can_be_merged', 'current_user')
     end
   end
 

spec/features/merge_request/user_resolves_wip_mr_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe 'Merge request > User resolves Work in Progress', :js do
+  let(:project) { create(:project, :public, :repository) }
+  let(:user) { project.creator }
+  let(:merge_request) do
+    create(:merge_request_with_diffs, source_project: project,
+                                      author: user,
+                                      title: 'WIP: Bug NS-04',
+                                      merge_params: { force_remove_source_branch: '1' })
+  end
+  let(:pipeline) do
+    create(:ci_pipeline, project: project,
+                         sha: merge_request.diff_head_sha,
+                         ref: merge_request.source_branch,
+                         head_pipeline_of: merge_request)
+  end
+
+  before do
+    project.add_maintainer(user)
+  end
+
+  context 'when there is active pipeline for merge request' do
+    before do
+      create(:ci_build, pipeline: pipeline)
+      sign_in(user)
+      visit project_merge_request_path(project, merge_request)
+      wait_for_requests
+    end
+
+    it 'retains merge request data after clicking Resolve WIP status' do
+      expect(page.find('.ci-widget-content')).to have_content("Pipeline ##{pipeline.id}")
+      expect(page).to have_content "This is a Work in Progress"
+
+      click_button('Resolve WIP status')
+
+      wait_for_requests
+
+      # If we don't disable the wait here, the test will wait until the
+      # merge request widget refreshes, which masks missing elements
+      # that should already be present.
+      expect(page.find('.ci-widget-content', wait: 0)).to have_content("Pipeline ##{pipeline.id}")
+      expect(page).not_to have_content('This is a Work in Progress')
+    end
+  end
+end

spec/serializers/merge_request_serializer_spec.rb

@@ -69,6 +69,22 @@ describe MergeRequestSerializer do
     end
   end
 
+  context 'poll cached widget merge request serialization' do
+    let(:serializer) { 'poll_cached_widget' }
+
+    it 'matches basic merge request json schema' do
+      expect(json_entity).to match_schema('entities/merge_request_poll_cached_widget')
+    end
+  end
+
+  context 'poll widget merge request serialization' do
+    let(:serializer) { 'poll_widget' }
+
+    it 'matches basic merge request json schema' do
+      expect(json_entity).to match_schema('entities/merge_request_poll_widget')
+    end
+  end
+
   context 'no serializer' do
     let(:serializer) { nil }