Optimize issue search when sorting by weight

When searching for issues within a project or group, `IssuableFinder`
has an optimization that uses a CTE to filter the list of authorized
issues before searching within the list for text. This CTE optimization
fence is currently only used when the user specifies a simple sorting
parameter, such as `created_at`, and not popularity. These attributes
are generally stored directly with the model, so the CTE can easily do
an `ORDER BY` without joining another table (e.g. `award_emoji` for
popularity).

In EE, `weight` is another simple sorting parameter, and we should take
advantage of the CTE for that. This commit adds `weight` to
`Issue.simple_sorts`. When a user sorts by weight, this should help
speed up the search query and avoid a database statement timeout.

Improves https://gitlab.com/gitlab-org/gitlab/issues/34661

changelogs/unreleased/sh-add-weight-simple-sort.yml

+---
+title: Optimize issue search when sorting by weight
+merge_request: 24208
+author:
+type: performance

ee/app/models/ee/issue.rb

@@ -145,7 +145,20 @@ module EE
     end
 
     class_methods do
-      # override
+      extend ::Gitlab::Utils::Override
+
+      override :simple_sorts
+      def simple_sorts
+        super.merge(
+          {
+            'weight' => -> { order_weight_asc.with_order_id_desc },
+            'weight_asc' => -> { order_weight_asc.with_order_id_desc },
+            'weight_desc' => -> { order_weight_desc.with_order_id_desc }
+          }
+        )
+      end
+
+      override :sort_by_attribute
       def sort_by_attribute(method, excluded_labels: [])
         case method.to_s
         when 'weight', 'weight_asc' then order_weight_asc.with_order_id_desc

ee/spec/models/issue_spec.rb

@@ -210,6 +210,15 @@ describe Issue do
     end
   end
 
+  describe '.simple_sorts' do
+    it 'includes weight with other base keys' do
+      expect(Issue.simple_sorts.keys).to match_array(
+        %w(created_asc created_at_asc created_date created_desc created_at_desc
+           id_asc id_desc updated_desc updated_asc updated_at_asc updated_at_desc
+           weight weight_asc weight_desc))
+    end
+  end
+
   describe '#sort' do
     let(:project) { create(:project) }