1 files changed, 66 insertions, 0 deletions

diff --git a/app/services/issues/referenced_merge_requests_service.rb b/app/services/issues/referenced_merge_requests_service.rb
new file mode 100644
index 00000000000..40d78502697
--- /dev/null
+++ b/app/services/issues/referenced_merge_requests_service.rb
@@ -0,0 +1,66 @@
+# frozen_string_literal: true
+
+module Issues
+  class ReferencedMergeRequestsService < Issues::BaseService
+    def execute(issue)
+      referenced = referenced_merge_requests(issue)
+      closed_by = closed_by_merge_requests(issue)
+      preloader = ActiveRecord::Associations::Preloader.new
+
+      preloader.preload(referenced + closed_by,
+                        head_pipeline: { project: [:route, { namespace: :route }] })
+
+      [sort_by_iid(referenced), sort_by_iid(closed_by)]
+    end
+
+    def referenced_merge_requests(issue)
+      merge_requests = extract_merge_requests(issue)
+
+      cross_project_filter = -> (merge_requests) do
+        merge_requests.select { |mr| mr.target_project == project }
+      end
+
+      Ability.merge_requests_readable_by_user(
+        merge_requests,
+        current_user,
+        filters: {
+          read_cross_project: cross_project_filter
+        }
+      )
+    end
+
+    def closed_by_merge_requests(issue)
+      return [] unless issue.open?
+
+      merge_requests = extract_merge_requests(issue, filter: :system).select(&:open?)
+
+      return [] if merge_requests.empty?
+
+      ids = MergeRequestsClosingIssues.where(merge_request_id: merge_requests.map(&:id), issue_id: issue.id).pluck(:merge_request_id)
+      merge_requests.select { |mr| mr.id.in?(ids) }
+    end
+
+    private
+
+    def extract_merge_requests(issue, filter: nil)
+      ext = issue.all_references(current_user)
+      notes = issue_notes(issue)
+      notes = notes.select(&filter) if filter
+
+      notes.each do |note|
+        note.all_references(current_user, extractor: ext)
+      end
+
+      ext.merge_requests
+    end
+
+    def issue_notes(issue)
+      @issue_notes ||= {}
+      @issue_notes[issue] ||= issue.notes.includes(:author)
+    end
+
+    def sort_by_iid(merge_requests)
+      Gitlab::IssuableSorter.sort(project, merge_requests) { |mr| mr.iid.to_s }
+    end
+  end
+end