woo hoo - getting there with the cross-reference issue. Should fix the problem and updated spec

app/services/system_note_service.rb

@@ -280,6 +280,7 @@ class SystemNoteService
   # mentioner - Mentionable object
   #
   # Returns Boolean
+
   def self.cross_reference_exists?(noteable, mentioner)
     # Initial scope should be system notes of this noteable type
     notes = Note.system.where(noteable_type: noteable.class)
@@ -291,14 +292,20 @@ class SystemNoteService
       notes = notes.where(noteable_id: noteable.id)
     end
 
-    gfm_reference = mentioner.gfm_reference(nil)
-    notes = notes.where('note LIKE ?', "#{cross_reference_note_prefix}%#{gfm_reference}")
-
-    notes.count > 0
+    notes_for_mentioner(mentioner, noteable, notes).count > 0
   end
 
   private
 
+  def self.notes_for_mentioner(mentioner, noteable, notes)
+    if mentioner.is_a?(Commit)
+      notes.where('note LIKE ?', "#{cross_reference_note_prefix}%#{mentioner.to_reference(nil)}")
+    else
+      gfm_reference = mentioner.gfm_reference(noteable.project)
+      notes.where(note: cross_reference_note_content(gfm_reference))
+    end
+  end
+
   def self.create_note(args = {})
     Note.create(args.merge(system: true))
   end

spec/services/system_note_service_spec.rb

@@ -425,18 +425,20 @@ describe SystemNoteService, services: true do
       end
     end
 
-    context 'commit from fork' do
+    context 'commit with cross-reference from fork' do
       let(:author2) { create(:user) }
       let(:forked_project) { Projects::ForkService.new(project, author2).execute }
       let(:commit2) { forked_project.commit }
 
       before do
-        described_class.cross_reference(noteable, commit2, author2)
+        allow(commit0).to receive(:to_reference) { noteable.project.to_reference +
+            commit0.class.reference_prefix + commit0.id}
+        described_class.cross_reference(noteable, commit0, author2)
       end
 
-      it 'is falsey when is a fork mentioning an external issue' do
+      it 'is true when a fork mentions an external issue' do
         expect(described_class.cross_reference_exists?(noteable, commit2)).
-            to be_falsey
+            to be true
       end
     end
   end