Add epic support to UrlBuilder

This assures that epic and epic note URLs are built correctly
with UrlBuilder.

changelogs/unreleased/9801-epic-copy-link.yml

+---
+title: Added 'copy link' in epic comment dropdown.
+merge_request: 17224
+author:
+type: added

ee/lib/ee/gitlab/url_builder.rb

@@ -7,10 +7,23 @@ module EE
 
       override :url
       def url
-        return project_design_url(object.project, object) if object.is_a?(DesignManagement::Design)
-
+        case object
+        when DesignManagement::Design
+          project_design_url(object.project, object)
+        when Epic
+          group_epic_url(object.group, object)
+        else
           super
         end
       end
+
+      override :note_url
+      def note_url
+        return super unless object.for_epic?
+
+        epic = object.noteable
+        group_epic_url(epic.group, epic, anchor: dom_id(object))
+      end
+    end
   end
 end

ee/spec/lib/ee/gitlab/url_builder_spec.rb

@@ -13,5 +13,26 @@ describe Gitlab::UrlBuilder do
         expect(url).to eq "#{Settings.gitlab['url']}/#{design.project.full_path}/-/designs/#{design.id}"
       end
     end
+
+    context 'when passing an epic' do
+      it 'returns a proper URL' do
+        epic = build_stubbed(:epic, iid: 42)
+
+        url = described_class.build(epic)
+
+        expect(url).to eq "#{Settings.gitlab['url']}/groups/#{epic.group.full_path}/-/epics/#{epic.iid}"
+      end
+    end
+
+    context 'when passing an epic note' do
+      it 'returns a proper URL' do
+        epic = create(:epic)
+        note = build_stubbed(:note_on_epic, noteable: epic)
+
+        url = described_class.build(note)
+
+        expect(url).to eq "#{Settings.gitlab['url']}/groups/#{epic.group.full_path}/-/epics/#{epic.iid}#note_#{note.id}"
+      end
+    end
   end
 end