Sync approvals_required count setting to rules

When project/MR's approvals_before_merge is changed,
update its rule's approvals_required.

ee/app/services/ee/merge_requests/update_service.rb

@@ -25,6 +25,8 @@ module EE
           cleanup_approvers(merge_request, reload: true)
         end
 
+        sync_approval_rules(merge_request)
+
         merge_request
       end
 
@@ -42,6 +44,14 @@ module EE
 
         merge_request.approvals.delete_all if target_project.reset_approvals_on_push
       end
+
+      # TODO remove after #1979 is closed
+      def sync_approval_rules(merge_request)
+        return if merge_request.merged?
+        return unless merge_request.previous_changes.include?(:approvals_before_merge)
+
+        merge_request.approval_rules.regular.update_all(approvals_required: merge_request.approvals_before_merge)
+      end
     end
   end
 end

ee/app/services/ee/projects/update_service.rb

@@ -37,6 +37,8 @@ module EE
 
           sync_wiki_on_enable if !wiki_was_enabled && project.wiki_enabled?
           project.import_state.force_import_job! if params[:mirror].present? && project.mirror?
+
+          sync_approval_rules
         end
 
         result
@@ -67,6 +69,13 @@ module EE
       def sync_wiki_on_enable
         ::Geo::RepositoryUpdatedService.new(project.wiki.repository).execute
       end
+
+      # TODO remove after #1979 is closed
+      def sync_approval_rules
+        return unless project.previous_changes.include?(:approvals_before_merge)
+
+        project.approval_rules.update_all(approvals_required: project.approvals_before_merge)
+      end
     end
   end
 end

ee/spec/services/merge_requests/update_service_spec.rb

@@ -56,5 +56,17 @@ describe MergeRequests::UpdateService, :mailer do
         end.not_to change { ActionMailer::Base.deliveries.count }
       end
     end
+
+    context 'when approvals_before_merge changes' do
+      it "updates approval_rules' approvals_required" do
+        rule = create(:approval_merge_request_rule, merge_request: merge_request)
+        code_owner_rule = create(:approval_merge_request_rule, merge_request: merge_request, code_owner: true)
+
+        update_merge_request(approvals_before_merge: 42)
+
+        expect(rule.reload.approvals_required).to eq(42)
+        expect(code_owner_rule.reload.approvals_required).to eq(0)
+      end
+    end
   end
 end

ee/spec/services/projects/update_service_spec.rb

@@ -215,6 +215,16 @@ describe Projects::UpdateService, '#execute' do
     end
   end
 
+  context 'with approval_rules' do
+    it "updates approval_rules' approvals_required" do
+      rule = create(:approval_project_rule, project: project)
+
+      update_project(project, user, approvals_before_merge: 42)
+
+      expect(rule.reload.approvals_required).to eq(42)
+    end
+  end
+
   def update_project(project, user, opts)
     Projects::UpdateService.new(project, user, opts).execute
   end