Expand left sidebar when viewing group iteration report

`Issues` on the left sidebar did not expand to highlight
`Iterations`

ee/app/helpers/ee/nav_helper.rb

@@ -25,10 +25,14 @@ module EE
       controllers = %w(issues_analytics#show)
 
       if @group&.feature_available?(:iterations)
-        controllers = %w(iterations#index)
+        controllers = iterations_sub_menu_controllers
       end
 
       super.concat(controllers)
     end
+
+    def iterations_sub_menu_controllers
+      ['iterations#index', 'iterations#show']
+    end
   end
 end

ee/app/views/layouts/nav/sidebar/_group_iterations_link.html.haml

 - if group_sidebar_link?(:iterations)
-  = nav_link(path: 'iterations#index') do
+  = nav_link(path: iterations_sub_menu_controllers) do
     = link_to group_iterations_path(@group), data: { qa_selector: 'group_iterations_link' } do
       %span
         = _('Iterations')

ee/changelogs/unreleased/322019-iteration-group-report-view-missing-left-sidebar-status.yml

+---
+title: Expand left sidebar when viewing group iteration report
+merge_request: 56358
+author:
+type: fixed

ee/spec/features/groups/iterations/user_views_iteration_spec.rb

@@ -33,6 +33,12 @@ RSpec.describe 'User views iteration' do
       end
 
       it 'shows iteration info' do
+        aggregate_failures 'expect Iterations highlighted on left sidebar' do
+          page.within '.qa-group-sidebar' do
+            expect(page).to have_css('li.active > a', text: 'Iterations')
+          end
+        end
+
         aggregate_failures 'expect title, description, and dates' do
           expect(page).to have_content(iteration.title)
           expect(page).to have_content(iteration.description)