Avoid calculation of closes_issues.

We just need to get merge requests closes issues when 
we’re going to show them

CHANGELOG

@@ -34,6 +34,7 @@ v 8.10.0 (unreleased)
   - Bump Rinku to 2.0.0
   - Remove unused front-end variable -> default_issues_tracker
   - Better caching of git calls on ProjectsController#show.
+  - Avoid to retrieve MR closes_issues as much as possible.
   - Add API endpoint for a group issues !4520 (mahcsig)
   - Add Bugzilla integration !4930 (iamtjg)
   - Instrument Rinku usage

app/controllers/projects/merge_requests_controller.rb

@@ -9,7 +9,6 @@ class Projects::MergeRequestsController < Projects::ApplicationController
     :edit, :update, :show, :diffs, :commits, :builds, :merge, :merge_check,
     :ci_status, :toggle_subscription, :cancel_merge_when_build_succeeds, :remove_wip
   ]
-  before_action :closes_issues, only: [:edit, :update, :show, :diffs, :commits, :builds]
   before_action :validates_merge_request, only: [:show, :diffs, :commits, :builds]
   before_action :define_show_vars, only: [:show, :diffs, :commits, :builds]
   before_action :define_widget_vars, only: [:merge, :cancel_merge_when_build_succeeds, :merge_check]
@@ -308,10 +307,6 @@ class Projects::MergeRequestsController < Projects::ApplicationController
   alias_method :issuable, :merge_request
   alias_method :awardable, :merge_request
 
-  def closes_issues
-    @closes_issues ||= @merge_request.closes_issues
-  end
-
   def authorize_update_merge_request!
     return render_404 unless can?(current_user, :update_merge_request, @merge_request)
   end
@@ -377,7 +372,6 @@ class Projects::MergeRequestsController < Projects::ApplicationController
   def define_widget_vars
     @pipeline = @merge_request.pipeline
     @pipelines = [@pipeline].compact
-    closes_issues
   end
 
   def invalid_mr

app/helpers/merge_requests_helper.rb

@@ -55,6 +55,10 @@ module MergeRequestsHelper
     end.sort.to_sentence
   end
 
+  def mr_closes_issues
+    @mr_closes_issues ||= @merge_request.closes_issues
+  end
+
   def mr_change_branches_path(merge_request)
     new_namespace_project_merge_request_path(
       @project.namespace, @project,

app/views/projects/merge_requests/widget/_open.html.haml

@@ -22,10 +22,10 @@
     - elsif @merge_request.can_be_merged?
       = render 'projects/merge_requests/widget/open/accept'
 
-  - if @closes_issues.present?
+  - if mr_closes_issues.present?
     .mr-widget-footer
       %span
         %i.fa.fa-check
-        Accepting this merge request will close #{"issue".pluralize(@closes_issues.size)}
+        Accepting this merge request will close #{"issue".pluralize(mr_closes_issues.size)}
         = succeed '.' do
-          != markdown issues_sentence(@closes_issues), pipeline: :gfm, author: @merge_request.author
+          != markdown issues_sentence(mr_closes_issues), pipeline: :gfm, author: @merge_request.author