Fix double execution of COUNT query on group pages

Calling `finder.execute.count` twice will perform two queries, but these are all
in the same file, so it's easy to just reuse them.

app/views/layouts/nav/sidebar/_group.html.haml

-- issues = IssuesFinder.new(current_user, group_id: @group.id, state: 'opened').execute
-- merge_requests = MergeRequestsFinder.new(current_user, group_id: @group.id, state: 'opened', non_archived: true).execute
+- issues_count = IssuesFinder.new(current_user, group_id: @group.id, state: 'opened').execute.count
+- merge_requests_count = MergeRequestsFinder.new(current_user, group_id: @group.id, state: 'opened', non_archived: true).execute.count
 .nav-sidebar{ class: ("sidebar-collapsed-desktop" if collapsed_sidebar?) }
   .nav-sidebar-inner-scroll
@@ -39,14 +39,14 @@
             = sprite_icon('issues')
           %span.nav-item-name
             Issues
-          %span.badge.count= number_with_delimiter(issues.count)
+          %span.badge.count= number_with_delimiter(issues_count)
         %ul.sidebar-sub-level-items
           = nav_link(path: ['groups#issues', 'labels#index', 'milestones#index'], html_options: { class: "fly-out-top-item" } ) do
             = link_to issues_group_path(@group) do
               %strong.fly-out-top-item-name
                 #{ _('Issues') }
-              %span.badge.count.issue_counter.fly-out-badge= number_with_delimiter(issues.count)
+              %span.badge.count.issue_counter.fly-out-badge= number_with_delimiter(issues_count)
           %li.divider.fly-out-top-item
           = nav_link(path: 'groups#issues', html_options: { class: 'home' }) do
             = link_to issues_group_path(@group), title: 'List' do
@@ -69,13 +69,13 @@
             = sprite_icon('git-merge')
           %span.nav-item-name
             Merge Requests
-          %span.badge.count= number_with_delimiter(merge_requests.count)
+          %span.badge.count= number_with_delimiter(merge_requests_count)
         %ul.sidebar-sub-level-items.is-fly-out-only
           = nav_link(path: 'groups#merge_requests', html_options: { class: "fly-out-top-item" } ) do
             = link_to merge_requests_group_path(@group) do
               %strong.fly-out-top-item-name
                 #{ _('Merge Requests') }
-              %span.badge.count.merge_counter.js-merge-counter.fly-out-badge= number_with_delimiter(merge_requests.count)
+              %span.badge.count.merge_counter.js-merge-counter.fly-out-badge= number_with_delimiter(merge_requests_count)
       = nav_link(path: 'group_members#index') do
         = link_to group_group_members_path(@group) do
           .nav-icon-container

changelogs/unreleased/41546-count-query-for-issues-and-mrs-runs-twice-on-group-index.yml

+---
+title: Fix double query execution on groups page
+merge_request: 16314
+author:
+type: performance