Update participant_approvers for efficiency

ee/app/models/ee/merge_request.rb

@@ -57,11 +57,16 @@ module EE
       strong_memoize(:participant_approvers) do
         next [] unless approval_needed?
 
-        approvers = []
-        approvers.concat(overall_approvers(exclude_code_owners: true))
-        approvers.concat(approvers_from_groups)
-
-        ::User.where(id: approvers.map(&:id)).where.not(id: approved_by_users.select(:id))
+        if ::Feature.enabled?(:approval_rule)
+          approval_state.filtered_approvers(code_owner: false, unactioned: true)
+        else
+          approvers = [
+            *overall_approvers(exclude_code_owners: true),
+            *approvers_from_groups
+          ]
+
+          ::User.where(id: approvers.map(&:id)).where.not(id: approved_by_users.select(:id))
+        end
       end
     end
 

ee/spec/models/merge_request_spec.rb

@@ -17,10 +17,37 @@ describe MergeRequest do
   end
 
   describe '#participant_approvers' do
+    let(:approvers) { create_list(:user, 2) }
+    let(:code_owners) { create_list(:user, 2) }
+
+    let!(:regular_rule) { create(:approval_merge_request_rule, merge_request: merge_request, users: approvers) }
+    let!(:code_owner_rule) { create(:approval_merge_request_rule, merge_request: merge_request, users: code_owners, code_owner: true) }
+
+    let!(:approval) { create(:approval, merge_request: merge_request, user: approvers.last) }
+
+    before do
+      allow(subject).to receive(:code_owners).and_return(code_owners)
+    end
+
+    it 'returns empty array if approval not needed' do
+      allow(subject).to receive(:approval_needed?).and_return(false)
+
+      expect(subject.participant_approvers).to be_empty
+    end
+
+    it 'returns approvers if approval is needed, excluding code owners' do
+      allow(subject).to receive(:approval_needed?).and_return(true)
+
+      expect(subject.participant_approvers).to contain_exactly(approvers.first)
+    end
+  end
+
+  describe '#participant_approvers with approval_rules disabled' do
     let!(:approver) { create(:approver, target: project) }
     let(:code_owners) { [double(:code_owner)] }
 
     before do
+      stub_feature_flags(approval_rules: false)
       allow(subject).to receive(:code_owners).and_return(code_owners)
     end