Eager load more issue associations to reduce N+1 queries

In an attempt to address performance issues outlined here: https://gitlab.com/gitlab-org/gitlab/-/issues/214482

ee/changelogs/unreleased/ali-improve-issue-search-performance.yml

+---
+title: 'Advanced Search API: Eager load more issue associations to reduce N+1 queries'
+merge_request: 30233
+author:
+type: performance

ee/lib/gitlab/elastic/search_results.rb

@@ -29,7 +29,7 @@ module Gitlab
         when 'projects'
           eager_load(projects, page, eager: [:route, :namespace, :compliance_framework_setting])
         when 'issues'
-          eager_load(issues, page, eager: { project: [:route, :namespace] })
+          eager_load(issues, page, eager: { project: [:route, :namespace], labels: [], timelogs: [], assignees: [] })
         when 'merge_requests'
           eager_load(merge_requests, page, eager: { target_project: [:route, :namespace] })
         when 'milestones'

ee/spec/requests/api/search_spec.rb

@@ -100,6 +100,24 @@ describe API::Search do
         end
       end
     end
+
+    context 'for issues scope', :sidekiq_inline do
+      before do
+        create_list(:issue, 4, project: project)
+        ensure_elasticsearch_index!
+      end
+
+      it 'avoids N+1 queries' do
+        control = ActiveRecord::QueryRecorder.new { get api(endpoint, user), params: { scope: 'issues', search: '*' } }
+
+        new_issues = create_list(:issue, 4, project: project)
+
+        ensure_elasticsearch_index!
+
+        # Some N+1 queries still exist
+        expect { get api(endpoint, user), params: { scope: 'issues', search: '*' } }.not_to exceed_query_limit(control.count + new_issues.count * 4)
+      end
+    end
   end
 
   describe 'GET /search' do