Fix filtering epics when sorting by dates

- use cte optimisation for searching by start_date and due_date

changelogs/unreleased/230827-fix-epics-filter.yml

+---
+title: Fix filtering epics when sorting by dates
+merge_request: 42827
+author:
+type: fixed

ee/app/models/ee/epic.rb

@@ -144,6 +144,8 @@ module EE
     end
 
     class_methods do
+      extend ::Gitlab::Utils::Override
+
       # We support internal references (&epic_id) and cross-references (group.full_path&epic_id)
       #
       # Escaped versions with `&` will be extracted too
@@ -199,6 +201,18 @@ module EE
         end
       end
 
+      override :simple_sorts
+      def simple_sorts
+        super.merge(
+          {
+            'start_date_asc' => -> { order_start_date_asc.with_order_id_desc },
+            'start_date_desc' => -> { order_start_date_desc.with_order_id_desc },
+            'end_date_asc' => -> { order_end_date_asc.with_order_id_desc },
+            'end_date_desc' => -> { order_end_date_desc.with_order_id_desc }
+          }
+        )
+      end
+
       def parent_class
         ::Group
       end

ee/spec/finders/epics_finder_spec.rb

@@ -7,7 +7,7 @@ RSpec.describe EpicsFinder do
   let_it_be(:search_user) { create(:user) }
   let_it_be(:group) { create(:group, :private) }
   let_it_be(:another_group) { create(:group) }
-  let_it_be(:epic1) { create(:epic, :opened, group: group, title: 'This is awesome epic', created_at: 1.week.ago) }
+  let_it_be(:epic1) { create(:epic, :opened, group: group, title: 'This is awesome epic', created_at: 1.week.ago, end_date: 10.days.ago) }
   let_it_be(:epic2) { create(:epic, :opened, group: group, created_at: 4.days.ago, author: user, start_date: 2.days.ago, end_date: 3.days.from_now) }
   let_it_be(:epic3) { create(:epic, :closed, group: group, description: 'not so awesome', start_date: 5.days.ago, end_date: 3.days.ago) }
   let_it_be(:epic4) { create(:epic, :closed, group: another_group) }
@@ -471,6 +471,11 @@ RSpec.describe EpicsFinder do
 
               expect(filtered_epics).to contain_exactly(labeled_epic)
             end
+
+            it 'filters correctly by short expressions when sorting by due date' do
+              expect(epics(attempt_group_search_optimizations: true, search: 'aw', sort: 'end_date_desc'))
+                .to eq([epic3, epic1])
+            end
           end
         end