Put EE routes in EE files under EE directories

.rubocop.yml

@@ -76,6 +76,7 @@ Naming/FileName:
     - 'qa/qa/specs/**/*'
     - 'qa/bin/*'
     - 'config/**/*'
+    - 'ee/config/**/*'
     - 'lib/generators/**/*'
     - 'locale/unfound_translations.rb'
     - 'ee/locale/unfound_translations.rb'

config/initializers/routing_draw.rb

 # Adds draw method into Rails routing
-# It allows us to keep routing splitted into files
-class ActionDispatch::Routing::Mapper
-  def draw(routes_name)
-    instance_eval(File.read(Rails.root.join("config/routes/#{routes_name}.rb")))
-  end
-end
+# It allows us to keep routing split into files
+ActionDispatch::Routing::Mapper.prepend Gitlab::Patch::DrawRoute

config/routes/admin.rb

@@ -71,6 +71,7 @@ namespace :admin do
   resource :logs, only: [:show]
   resource :health_check, controller: 'health_check', only: [:show]
   resource :background_jobs, controller: 'background_jobs', only: [:show]
+
   resource :system_info, controller: 'system_info', only: [:show]
   resources :requests_profiles, only: [:index, :show], param: :name, constraints: { name: /.+\.html/ }
 
@@ -104,6 +105,7 @@ namespace :admin do
 
   resource :application_settings, only: [:show, :update] do
     resources :services, only: [:index, :edit, :update]
+
     get :usage_data
     put :reset_registration_token
     put :reset_health_check_token

config/routes/group.rb

+# frozen_string_literal: true
+
 resources :groups, only: [:index, :new, :create] do
   post :preview_markdown
 end
@@ -63,7 +65,6 @@ constraints(::Constraints::GroupUrlConstrainer.new) do
       end
     end
 
-    # On CE only index and show actions are needed
     resources :boards, only: [:index, :show]
 
     resources :runners, only: [:index, :edit, :update, :destroy, :show] do

doc/development/ee_features.md

@@ -332,6 +332,15 @@ full implementation details.
 [ce-mr-full-private]: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/12373
 [ee-mr-full-private]: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/2199
 
+### Code in `config/routes`
+
+When we add `draw :admin` in `config/routes.rb`, the application will also
+load the file located in `config/routes/admin.rb`, and also
+`ee/config/routes/admin.rb` if the file exists.
+
+So if we want to extend a particular route file, just add the same file
+located in `ee/config/routes`.
+
 ### Code in `app/controllers/`
 
 In controllers, the most common type of conflict is with `before_action` that

lib/gitlab/patch/draw_route.rb

+# frozen_string_literal: true
+
+# We're patching `ActionDispatch::Routing::Mapper` in
+# config/initializers/routing_draw.rb
+module Gitlab
+  module Patch
+    module DrawRoute
+      def draw(routes_name)
+        instance_eval(File.read(Rails.root.join("config/routes/#{routes_name}.rb")))
+
+        draw_ee(routes_name)
+      end
+
+      def draw_ee(routes_name)
+        path = Rails.root.join("ee/config/routes/#{routes_name}.rb")
+
+        instance_eval(File.read(path)) if File.exist?(path)
+      end
+    end
+  end
+end