Resolve: Epic labels in system notes point to the epic itself

Fix label notes on epics with empty links

app/models/concerns/cache_markdown_field.rb

@@ -15,7 +15,7 @@ module CacheMarkdownField
 
   # Increment this number every time the renderer changes its output
   CACHE_COMMONMARK_VERSION_START  = 10
-  CACHE_COMMONMARK_VERSION        = 15
+  CACHE_COMMONMARK_VERSION        = 16
 
   # changes to these attributes cause the cache to be invalidates
   INVALIDATED_BY = %w[author project].freeze

ee/app/models/ee/resource_label_event.rb

@@ -19,5 +19,10 @@ module EE
     def issuable
       epic || super
     end
+
+    override :banzai_render_context
+    def banzai_render_context(field)
+      epic ? super.merge(label_url_method: :group_epics_url) : super
+    end
   end
 end

ee/changelogs/unreleased/issue_10439.yml

+---
+title: 'Resolve: Epic labels in system notes point to the epic itself'
+merge_request: 11234
+author:
+type: fixed

ee/spec/models/label_note_spec.rb

@@ -3,6 +3,8 @@
 require 'spec_helper'
 
 describe LabelNote do
+  include Gitlab::Routing.url_helpers
+
   set(:group)  { create(:group) }
   set(:user)   { create(:user) }
   set(:label) { create(:group_label, group: group) }
@@ -14,5 +16,14 @@ describe LabelNote do
     let(:project) { nil }
 
     it_behaves_like 'label note created from events'
+
+    it 'includes a link to the list of epics filtered by the label' do
+      resource_key = resource.class.name.underscore.to_s
+      events = [build(:resource_label_event, label: label, resource_key => resource)]
+
+      note = described_class.from_events(events)
+
+      expect(note.note_html).to include(group_epics_path(group, label_name: label.title))
+    end
   end
 end