Add engine draw_paths to app

railties/CHANGELOG.md

@@ -1,3 +1,8 @@
+*   Add engine's draw paths to application route set, so that the application
+    can draw route files defined in engine paths.
+
+    *Gannon McGibbon*
+
 *   Support `VISUAL` environment variable for commands which open an editor,
     and prefer it over `EDITOR`.
 

railties/lib/rails/engine.rb

@@ -586,6 +586,7 @@ def load_seed
       routing_paths = paths["config/routes.rb"].existent
       external_paths = self.paths["config/routes"].paths
       routes.draw_paths.concat(external_paths)
+      app.routes.draw_paths.concat(external_paths)
 
       if routes? || routing_paths.any?
         app.routes_reloader.paths.unshift(*routing_paths)

railties/test/railties/engine_test.rb

@@ -267,6 +267,34 @@ class AddFirstNameToUsers < ActiveRecord::Migration::Current
       assert_nothing_raised { BukkitController }
     end
 
+    test "can draw routes in app routes from engines" do
+      @plugin.write "config/routes/testing.rb", <<~RUBY
+        Rails.application.routes.draw do
+          get "/testing", to: "test#action", as: :testing
+        end
+      RUBY
+
+      @plugin.write "config/routes.rb", <<~RUBY
+        Rails.application.routes.draw do
+          draw(:testing)
+        end
+      RUBY
+
+      @plugin.write "app/controllers/testing_controller.rb", <<-RUBY
+        class TestingController < ActionController::Base
+          def index
+            render plain: "test"
+          end
+        end
+      RUBY
+
+      boot_rails
+
+      get("/testing")
+
+      assert_equal("test", last_response.body)
+    end
+
     test "adds its views to view paths" do
       @plugin.write "app/controllers/bukkit_controller.rb", <<-RUBY
         class BukkitController < ActionController::Base