Cached merge request title partial

app/views/projects/merge_requests/_mr_title.html.haml

@@ -2,14 +2,16 @@
 - can_update_merge_request = can?(current_user, :update_merge_request, @merge_request)
 - can_reopen_merge_request = can?(current_user, :reopen_merge_request, @merge_request)
 - are_close_and_open_buttons_hidden = merge_request_button_hidden?(@merge_request, true) && merge_request_button_hidden?(@merge_request, false)
+- cache_key = [@project, @merge_request, can_update_merge_request, can_reopen_merge_request, are_close_and_open_buttons_hidden]
 
-- if @merge_request.closed_or_merged_without_fork?
+= cache_if(Feature.enabled?(:cached_mr_title, @project), cache_key, expires_in: 1.day) do
+  - if @merge_request.closed_or_merged_without_fork?
     .gl-alert.gl-alert-danger.gl-mb-5
       = sprite_icon('error', size: 16, css_class: 'gl-icon gl-alert-icon gl-alert-icon-no-title')
       .gl-alert-body
         The source project of this merge request has been removed.
 
-.detail-page-header.border-bottom-0.pt-0.pb-0
+  .detail-page-header.border-bottom-0.pt-0.pb-0
     .detail-page-header-body
       = render "shared/issuable/status_box", issuable: @merge_request
 

config/feature_flags/development/cached_mr_title.yml

+---
+name: cached_mr_title
+introduced_by_url: 
+rollout_issue_url: 
+milestone: '13.12'
+type: development
+group: group::source code
+default_enabled: false