Refactor Merge Requests tab into a custom partial

* Add Labels tab to Groups
* Add decorator for label so it's aware of Milestones.

app/decorators/label_with_milestone.rb

+class LabelWithMilestone
+  attr_reader :milestone
+
+  def initialize(label, milestone)
+    @label, @milestone = label, milestone
+  end
+
+  def method_missing(meth, *args)
+    if @label.respond_to?(meth)
+      @label.send(meth, *args)
+    else
+      super
+    end
+  end
+
+  def respond_to?(meth)
+    @label.respond_to?(meth)
+  end
+end

app/models/global_milestone.rb

@@ -87,6 +87,12 @@ class GlobalMilestone
     @participants ||= milestones.map(&:participants).flatten.compact.uniq
   end
 
+  def labels
+    @labels ||= milestones.map do |ms|
+                  ms.labels.map { |label| LabelWithMilestone.new(label, ms) }
+                end.flatten.sort_by!(&:title)
+  end
+
   def opened_issues
     issues.opened
   end

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

@@ -67,13 +67,17 @@
     = link_to '#tab-participants', 'data-toggle' => 'tab' do
       Participants
       %span.badge= @milestone.participants.count
+  %li
+    = link_to '#tab-labels', 'data-toggle' => 'tab', 'data-show' => '.tab-issues-buttons' do
+      Labels
+      %span.badge= @milestone.labels.count
 
 .tab-content.milestone-content
   .tab-pane.active#tab-issues
     = 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.merge_requests.closed, merged: @milestone.merge_requests.merged
-
   .tab-pane#tab-participants
     = render 'shared/milestones/participants_tab', users: @milestone.participants
+  .tab-pane#tab-labels
+    = render 'shared/milestones/labels_tab', labels: @milestone.labels

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

@@ -100,16 +100,4 @@
   .tab-pane#tab-participants
     = render 'shared/milestones/participants_tab', users: @users
   .tab-pane#tab-labels
-    %ul.bordered-list.manage-labels-list
-      - @labels.each do |label|
-        %li
-          = render_colored_label(label)
-          - args = [@milestone.project.namespace, @milestone.project, milestone_title: @milestone.title, label_name: label.title]
-          - options = args.extract_options!
-
-          %span.issues-count
-            = link_to namespace_project_issues_path(*args, options.merge(state: 'opened')) do
-              = pluralize label.open_issues_count, 'open issue'
-          %span.issues-count
-            = link_to namespace_project_issues_path(*args, options.merge(state: 'closed')) do
-              = pluralize label.closed_issues_count, 'closed issue'
+    = render 'shared/milestones/labels_tab', labels: @labels

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

+%ul.bordered-list.manage-labels-list
+  - labels.each do |label|
+    - milestone = @milestone.is_a?(Milestone) ? @milestone : label.milestone
+
+    %li
+      = render_colored_label(label)
+      - args = [milestone.project.namespace, milestone.project, milestone_title: milestone.title, label_name: label.title]
+      - options = args.extract_options!
+
+      %span.issues-count
+        = link_to namespace_project_issues_path(*args, options.merge(state: 'opened')) do
+          = pluralize label.open_issues_count, 'open issue'
+      %span.issues-count
+        = link_to namespace_project_issues_path(*args, options.merge(state: 'closed')) do
+          = pluralize label.closed_issues_count, 'closed issue'

config/application.rb

@@ -15,6 +15,7 @@ module Gitlab
 
     # Custom directories with classes and modules you want to be autoloadable.
     config.autoload_paths.push(*%W(#{config.root}/lib
+                                   #{config.root}/app/decorators
                                    #{config.root}/app/models/hooks
                                    #{config.root}/app/models/concerns
                                    #{config.root}/app/models/project_services