Use common namespace ancestor queries

Changelog: performance

app/models/integration.rb

@@ -274,7 +274,7 @@ class Integration < ApplicationRecord
   end
 
   def self.closest_group_integration(type, scope)
-    group_ids = scope.ancestors.select(:id)
+    group_ids = scope.ancestors(hierarchy_order: :asc).select(:id)
     array = group_ids.to_sql.present? ? "array(#{group_ids.to_sql})" : 'ARRAY[]'
 
     where(type: type, group_id: group_ids, inherit_from_id: nil)

app/models/namespaces/traversal/linear.rb

@@ -177,6 +177,12 @@ module Namespaces
         if hierarchy_order
           depth_sql = "ABS(#{traversal_ids.count} - array_length(traversal_ids, 1))"
           skope = skope.select(skope.arel_table[Arel.star], "#{depth_sql} as depth")
+          # The SELECT includes an extra depth attribute. We wrap the SQL in a
+          # standard SELECT to avoid mismatched attribute errors when trying to
+          # chain future ActiveRelation commands, and retain the ordering.
+          skope = self.class
+            .without_sti_condition
+            .from(skope, self.class.table_name)
             .order(depth: hierarchy_order)
         end
 

app/models/project.rb

@@ -914,7 +914,13 @@ class Project < ApplicationRecord
       .base_and_ancestors(upto: top, hierarchy_order: hierarchy_order)
   end
 
-  alias_method :ancestors, :ancestors_upto
+  def ancestors(hierarchy_order: nil)
+    if Feature.enabled?(:linear_project_ancestors, self, default_enabled: :yaml)
+      group&.self_and_ancestors(hierarchy_order: hierarchy_order) || Group.none
+    else
+      ancestors_upto(hierarchy_order: hierarchy_order)
+    end
+  end
 
   def ancestors_upto_ids(...)
     ancestors_upto(...).pluck(:id)

config/feature_flags/development/linear_project_ancestors.yml

+---
+name: linear_project_ancestors
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/68072
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/338403
+milestone: '14.2'
+type: development
+group: group::access
+default_enabled: false

ee/spec/helpers/projects/project_members_helper_spec.rb

@@ -33,7 +33,7 @@ RSpec.describe Projects::ProjectMembersHelper do
 
       expect(project.members.count).to eq(3)
 
-      expect { call_project_members_app_data_json }.not_to exceed_query_limit(control_count).with_threshold(6) # existing n+1
+      expect { call_project_members_app_data_json }.not_to exceed_query_limit(control_count).with_threshold(7) # existing n+1
     end
   end
 

spec/models/project_spec.rb

@@ -6,6 +6,7 @@ RSpec.describe Project, factory_default: :keep do
   include ProjectForksHelper
   include GitHelpers
   include ExternalAuthorizationServiceHelpers
+  include ReloadHelpers
   using RSpec::Parameterized::TableSyntax
 
   let_it_be(:namespace) { create_default(:namespace).freeze }
@@ -3021,14 +3022,86 @@ RSpec.describe Project, factory_default: :keep do
     end
   end
 
+  shared_context 'project with group ancestry' do
+    let(:parent) { create(:group) }
+    let(:child) { create(:group, parent: parent) }
+    let(:child2) { create(:group, parent: child) }
+    let(:project) { create(:project, namespace: child2) }
+
+    before do
+      reload_models(parent, child, child2)
+    end
+  end
+
+  shared_context 'project with namespace ancestry' do
+    let(:namespace) { create :namespace }
+    let(:project) { create :project, namespace: namespace }
+  end
+
+  shared_examples 'project with group ancestors' do
+    it 'returns all ancestors' do
+      is_expected.to contain_exactly(child2, child, parent)
+    end
+  end
+
+  shared_examples 'project with ordered group ancestors' do
+    let(:hierarchy_order) { :desc }
+
+    it 'returns ancestors ordered by descending hierarchy' do
+      is_expected.to eq([parent, child, child2])
+    end
+  end
+
+  shared_examples '#ancestors' do
+    context 'group ancestory' do
+      include_context 'project with group ancestry'
+
+      it_behaves_like 'project with group ancestors' do
+        subject { project.ancestors }
+      end
+
+      it_behaves_like 'project with ordered group ancestors' do
+        subject { project.ancestors(hierarchy_order: hierarchy_order) }
+      end
+    end
+
+    context 'namespace ancestry' do
+      include_context 'project with namespace ancestry'
+
+      subject { project.ancestors }
+
+      it { is_expected.to be_empty }
+    end
+  end
+
+  describe '#ancestors' do
+    context 'with linear_project_ancestors feature flag enabled' do
+      before do
+        stub_feature_flags(linear_project_ancestors: true)
+      end
+
+      include_examples '#ancestors'
+    end
+
+    context 'with linear_project_ancestors feature flag disabled' do
+      before do
+        stub_feature_flags(linear_project_ancestors: false)
+      end
+
+      include_examples '#ancestors'
+    end
+  end
+
   describe '#ancestors_upto' do
-    let_it_be(:parent) { create(:group) }
-    let_it_be(:child) { create(:group, parent: parent) }
-    let_it_be(:child2) { create(:group, parent: child) }
-    let_it_be(:project) { create(:project, namespace: child2) }
+    context 'group ancestry' do
+      include_context 'project with group ancestry'
+
+      it_behaves_like 'project with group ancestors' do
+        subject { project.ancestors_upto }
+      end
 
-    it 'returns all ancestors when no namespace is given' do
-      expect(project.ancestors_upto).to contain_exactly(child2, child, parent)
+      it_behaves_like 'project with ordered group ancestors' do
+        subject { project.ancestors_upto(hierarchy_order: hierarchy_order) }
       end
 
       it 'includes ancestors upto but excluding the given ancestor' do
@@ -3036,16 +3109,21 @@ RSpec.describe Project, factory_default: :keep do
       end
 
       describe 'with hierarchy_order' do
-      it 'returns ancestors ordered by descending hierarchy' do
-        expect(project.ancestors_upto(hierarchy_order: :desc)).to eq([parent, child, child2])
-      end
-
         it 'can be used with upto option' do
           expect(project.ancestors_upto(parent, hierarchy_order: :desc)).to eq([child, child2])
         end
       end
     end
 
+    context 'namespace ancestry' do
+      include_context 'project with namespace ancestry'
+
+      subject { project.ancestors_upto }
+
+      it { is_expected.to be_empty }
+    end
+  end
+
   describe '#root_ancestor' do
     let(:project) { create(:project) }