API: Reference MRs cross-project wise

lib/api/issues.rb

@@ -311,7 +311,7 @@ module API
 
         merge_requests =
           if merge_request_iids.present?
-            MergeRequestsFinder.new(current_user, project_id: user_project.id, iids: merge_request_iids).execute
+            MergeRequest.all.where(iid: merge_request_iids)
           else
             MergeRequest.none
           end

spec/requests/api/issues_spec.rb

@@ -1792,7 +1792,7 @@ describe API::Issues do
         description: "See #{issue.to_reference}"
       }
       create(:merge_request, attributes).tap do |merge_request|
-        create(:note, :system, project: project, noteable: issue, author: user, note: merge_request.to_reference(full: true))
+        create(:note, :system, project: issue.project, noteable: issue, author: user, note: merge_request.to_reference(full: true))
       end
     end
 
@@ -1829,6 +1829,15 @@ describe API::Issues do
       expect_paginated_array_response(related_mr.id)
     end
 
+    it 'returns merge requests cross-project wide' do
+      project2 = create(:project, :public, creator_id: user.id, namespace: user.namespace)
+      merge_request = create_referencing_mr(user, project2, issue)
+
+      get_related_merge_requests(project.id, issue.iid, user)
+
+      expect_paginated_array_response(merge_request.id)
+    end
+
     context 'no merge request mentioned a issue' do
       it 'returns empty array' do
         get_related_merge_requests(project.id, closed_issue.iid, user)