Do not load epics on epics index page

* epics index page now loads epics asynchronously, we don't have to load
  them
* JSON format is still needed because it's used when filtering issues by
  epic dropdown

ee/app/controllers/groups/epics_controller.rb

@@ -11,7 +11,6 @@ class Groups::EpicsController < Groups::ApplicationController
 
   before_action :check_epics_available!
   before_action :epic, except: [:index, :create, :new, :bulk_update]
-  before_action :set_issuables_index, only: :index
   before_action :authorize_update_issuable!, only: :update
   before_action :authorize_create_epic!, only: [:create, :new]
   before_action :verify_group_bulk_edit_enabled!, only: [:bulk_update]
@@ -33,12 +32,12 @@ class Groups::EpicsController < Groups::ApplicationController
   end
 
   def index
-    @epics = @issuables
-
     respond_to do |format|
       format.html
       format.json do
-        render json: serializer.represent(@epics)
+        set_issuables_index
+
+        render json: serializer.represent(@issuables)
       end
     end
   end

ee/spec/controllers/groups/epics_controller_spec.rb

@@ -65,94 +65,6 @@ RSpec.describe Groups::EpicsController do
         expect(response).to have_gitlab_http_status(:ok)
       end
 
-      context 'when there is no logged in user' do
-        it 'stores sorting param in a cookie' do
-          group.update!(visibility_level: Gitlab::VisibilityLevel::PUBLIC)
-          sign_out(user)
-
-          get :index, params: { group_id: group, sort: 'start_date_asc' }
-
-          expect(cookies['epic_sort']).to eq('start_date_asc')
-          expect(response).to have_gitlab_http_status(:ok)
-        end
-      end
-
-      context 'when there is a logged in user' do
-        context 'when epics_sort is nil' do
-          it 'stores sorting param in user preferences' do
-            get :index, params: { group_id: group, sort: 'start_date_asc' }
-
-            expect(user.user_preference.epics_sort).to eq('start_date_asc')
-            expect(response).to have_gitlab_http_status(:ok)
-          end
-        end
-
-        context 'when epics_sort is present' do
-          it 'update epics_sort with current value' do
-            user.user_preference.update!(epics_sort: 'created_desc')
-
-            get :index, params: { group_id: group, sort: 'start_date_asc' }
-
-            expect(user.reload.user_preference.epics_sort).to eq('start_date_asc')
-            expect(response).to have_gitlab_http_status(:ok)
-          end
-        end
-
-        it_behaves_like 'issuable list with anonymous search disabled' do
-          let(:params) { { group_id: group } }
-
-          before do
-            sign_out(user)
-            group.update!(visibility_level: Gitlab::VisibilityLevel::PUBLIC)
-          end
-        end
-      end
-
-      context 'with page param' do
-        let(:last_page) { group.epics.page.total_pages }
-
-        before do
-          allow(Kaminari.config).to receive(:default_per_page).and_return(1)
-        end
-
-        it 'redirects to last_page if page number is larger than number of pages' do
-          get :index, params: { group_id: group, page: (last_page + 1).to_param }
-
-          expect(response).to redirect_to(group_epics_path(page: last_page, state: controller.params[:state], scope: controller.params[:scope]))
-        end
-
-        it 'renders the specified page' do
-          get :index, params: { group_id: group, page: last_page.to_param }
-
-          expect(assigns(:epics).current_page).to eq(last_page)
-          expect(response).to have_gitlab_http_status(:ok)
-        end
-
-        it_behaves_like 'disabled when using an external authorization service' do
-          subject { get :index, params: { group_id: group } }
-        end
-      end
-
-      context "when epic has multiple labels" do
-        render_views
-
-        let(:label) { create(:label) }
-        let!(:labeled_epic) { create(:labeled_epic, group: group, labels: [label]) }
-
-        it 'does not cause N+1 queries' do
-          get :index, params: { group_id: group }
-
-          control_count = ActiveRecord::QueryRecorder.new do
-            get :index, params: { group_id: group }
-          end
-
-          label = create(:label)
-          create(:labeled_epic, group: group, labels: [label])
-
-          expect { get :index, params: { group_id: group } }.not_to exceed_query_limit(control_count)
-        end
-      end
-
       context 'when format is JSON' do
         before do
           allow(Kaminari.config).to receive(:default_per_page).and_return(1)