Use GroupTree ancestors linear scopes

In this commit we're replacing the recursive ancestors scope in
the `GroupTree` concern, for their linear version.

Changelog: performance

app/controllers/concerns/group_tree.rb

@@ -38,8 +38,13 @@ module GroupTree
     #
     # Pagination needs to be applied before loading the ancestors to
     # make sure ancestors are not cut off by pagination.
-    Gitlab::ObjectHierarchy.new(Group.where(id: filtered_groups.select(:id)))
-      .base_and_ancestors
+    filtered_groups_relation = Group.where(id: filtered_groups.select(:id))
+
+    if Feature.enabled?(:linear_group_tree_ancestor_scopes, current_user, default_enabled: :yaml)
+      filtered_groups_relation.self_and_ancestors
+    else
+      Gitlab::ObjectHierarchy.new(filtered_groups_relation).base_and_ancestors
+    end
   end
   # rubocop: enable CodeReuse/ActiveRecord
 end

config/feature_flags/development/linear_group_tree_ancestor_scopes.yml

+---
+name: linear_group_tree_ancestor_scopes
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/70503
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/341117
+milestone: '14.4'
+type: development
+group: group::access
+default_enabled: false

spec/controllers/concerns/group_tree_spec.rb

@@ -21,82 +21,94 @@ RSpec.describe GroupTree do
   end
 
   describe 'GET #index' do
-    it 'filters groups' do
-      other_group = create(:group, name: 'filter')
-      other_group.add_owner(user)
+    shared_examples 'returns filtered groups' do
+      it 'filters groups' do
+        other_group = create(:group, name: 'filter')
+        other_group.add_owner(user)
 
-      get :index, params: { filter: 'filt' }, format: :json
+        get :index, params: { filter: 'filt' }, format: :json
 
-      expect(assigns(:groups)).to contain_exactly(other_group)
-    end
+        expect(assigns(:groups)).to contain_exactly(other_group)
+      end
 
-    context 'for subgroups' do
-      it 'only renders root groups when no parent was given' do
-        create(:group, :public, parent: group)
+      context 'for subgroups' do
+        it 'only renders root groups when no parent was given' do
+          create(:group, :public, parent: group)
 
-        get :index, format: :json
+          get :index, format: :json
 
-        expect(assigns(:groups)).to contain_exactly(group)
-      end
+          expect(assigns(:groups)).to contain_exactly(group)
+        end
 
-      it 'contains only the subgroup when a parent was given' do
-        subgroup = create(:group, :public, parent: group)
+        it 'contains only the subgroup when a parent was given' do
+          subgroup = create(:group, :public, parent: group)
 
-        get :index, params: { parent_id: group.id }, format: :json
+          get :index, params: { parent_id: group.id }, format: :json
 
-        expect(assigns(:groups)).to contain_exactly(subgroup)
-      end
+          expect(assigns(:groups)).to contain_exactly(subgroup)
+        end
 
-      it 'allows filtering for subgroups and includes the parents for rendering' do
-        subgroup = create(:group, :public, parent: group, name: 'filter')
+        it 'allows filtering for subgroups and includes the parents for rendering' do
+          subgroup = create(:group, :public, parent: group, name: 'filter')
 
-        get :index, params: { filter: 'filt' }, format: :json
+          get :index, params: { filter: 'filt' }, format: :json
 
-        expect(assigns(:groups)).to contain_exactly(group, subgroup)
-      end
+          expect(assigns(:groups)).to contain_exactly(group, subgroup)
+        end
 
-      it 'does not include groups the user does not have access to' do
-        parent = create(:group, :private)
-        subgroup = create(:group, :private, parent: parent, name: 'filter')
-        subgroup.add_developer(user)
-        _other_subgroup = create(:group, :private, parent: parent, name: 'filte')
+        it 'does not include groups the user does not have access to' do
+          parent = create(:group, :private)
+          subgroup = create(:group, :private, parent: parent, name: 'filter')
+          subgroup.add_developer(user)
+          _other_subgroup = create(:group, :private, parent: parent, name: 'filte')
 
-        get :index, params: { filter: 'filt' }, format: :json
+          get :index, params: { filter: 'filt' }, format: :json
 
-        expect(assigns(:groups)).to contain_exactly(parent, subgroup)
-      end
+          expect(assigns(:groups)).to contain_exactly(parent, subgroup)
+        end
 
-      it 'preloads parents regardless of pagination' do
-        allow(Kaminari.config).to receive(:default_per_page).and_return(1)
-        group = create(:group, :public)
-        subgroup = create(:group, :public, parent: group)
-        search_result = create(:group, :public, name: 'result', parent: subgroup)
+        it 'preloads parents regardless of pagination' do
+          allow(Kaminari.config).to receive(:default_per_page).and_return(1)
+          group = create(:group, :public)
+          subgroup = create(:group, :public, parent: group)
+          search_result = create(:group, :public, name: 'result', parent: subgroup)
 
-        get :index, params: { filter: 'resu' }, format: :json
+          get :index, params: { filter: 'resu' }, format: :json
 
-        expect(assigns(:groups)).to contain_exactly(group, subgroup, search_result)
+          expect(assigns(:groups)).to contain_exactly(group, subgroup, search_result)
+        end
       end
-    end
 
-    context 'json content' do
-      it 'shows groups as json' do
-        get :index, format: :json
+      context 'json content' do
+        it 'shows groups as json' do
+          get :index, format: :json
 
-        expect(json_response.first['id']).to eq(group.id)
-      end
+          expect(json_response.first['id']).to eq(group.id)
+        end
 
-      context 'nested groups' do
-        it 'expands the tree when filtering' do
-          subgroup = create(:group, :public, parent: group, name: 'filter')
+        context 'nested groups' do
+          it 'expands the tree when filtering' do
+            subgroup = create(:group, :public, parent: group, name: 'filter')
 
-          get :index, params: { filter: 'filt' }, format: :json
+            get :index, params: { filter: 'filt' }, format: :json
 
-          children_response = json_response.first['children']
+            children_response = json_response.first['children']
 
-          expect(json_response.first['id']).to eq(group.id)
-          expect(children_response.first['id']).to eq(subgroup.id)
+            expect(json_response.first['id']).to eq(group.id)
+            expect(children_response.first['id']).to eq(subgroup.id)
+          end
         end
       end
     end
+
+    it_behaves_like 'returns filtered groups'
+
+    context 'when feature flag :linear_group_tree_ancestor_scopes is disabled' do
+      before do
+        stub_feature_flags(linear_group_tree_ancestor_scopes: false)
+      end
+
+      it_behaves_like 'returns filtered groups'
+    end
   end
 end