Eager load Issues/MRs project for Milestone.

With this change we avoid doing N+1 queries when viewing Milestone's
Issues/MRs from a Group context.

app/models/global_milestone.rb

@@ -76,11 +76,11 @@ class GlobalMilestone
   end
 
   def issues
-    @issues ||= Issue.of_milestones(milestones.map(&:id))
+    @issues ||= Issue.of_milestones(milestones.map(&:id)).includes(:project)
   end
 
   def merge_requests
-    @merge_requests ||= MergeRequest.of_milestones(milestones.map(&:id))
+    @merge_requests ||= MergeRequest.of_milestones(milestones.map(&:id)).includes(:target_project)
   end
 
   def participants

app/views/groups/milestones/show.html.haml

@@ -73,7 +73,7 @@
     = render 'shared/milestones/issues_tab', unassigned: @milestone.opened_issues.unassigned, assigned: @milestone.opened_issues.assigned, closed: @milestone.closed_issues
 
   .tab-pane#tab-merge-requests
-    = render 'shared/milestones/merge_requests_tab', unassigned: @milestone.opened_merge_requests.unassigned, assigned: @milestone.opened_merge_requests.assigned, closed: @milestone.closed_merge_requests, merged: @milestone.merge_requests.merged
+    = render 'shared/milestones/merge_requests_tab', unassigned: @milestone.opened_merge_requests.unassigned, assigned: @milestone.opened_merge_requests.assigned, closed: @milestone.merge_requests.closed, merged: @milestone.merge_requests.merged
 
   .tab-pane#tab-participants
     .gray-content-block.middle-block

app/views/shared/milestones/_issue.html.haml

-- project = issue.project
+-# @project is present when viewing Project's milestone
+- project = @project || issue.project
+
 %li{ id: dom_id(issue, 'sortable'), class: 'issue-row', 'data-iid' => issue.iid, 'data-url' => issue_path(issue) }
   %span
     = link_to_gfm issue.title, [project.namespace.becomes(Namespace), project, issue], title: issue.title

app/views/shared/milestones/_merge_request.html.haml

+-# @project is present when viewing Project's milestone
 - project = @project || merge_request.project
 
 %li{ id: dom_id(merge_request, 'sortable'),  class: 'mr-row', 'data-iid' => merge_request.iid, 'data-url' => merge_request_path(merge_request) }