Set proper engine's asset directories when assets are served from engine.

When using stylesheet_link_tag(:all) or javascript_include_tag(:all),
assets directories are searched for css or js files. When
config.serve_static_assets is set to true, those files can be
served directly from engine's directories. That's why assets paths
should be set individually for controllers inside engine
if we want to serve static assets with ActionDispatch::Static

actionpack/lib/action_controller/railties/paths.rb

@@ -16,6 +16,14 @@ def self.with(app)
             if klass.superclass == ActionController::Base && ActionController::Base.include_all_helpers
               klass.helper :all
             end
+
+            if app.config.serve_static_assets && namespace
+              paths = namespace._railtie.config.paths
+
+              klass.config.assets_dir      = paths["public"].first
+              klass.config.javascripts_dir = paths["public/javascripts"].first
+              klass.config.stylesheets_dir = paths["public/stylesheets"].first
+            end
           end
         end
       end

railties/test/railties/engine_test.rb

@@ -721,5 +721,69 @@ class Engine < ::Rails::Engine
       engine_path = File.join(@plugin.path, '..', engine_dir)
       assert_equal Bukkits::Engine.instance, Rails::Engine.find(engine_path)
     end
+
+    test "ensure that engine properly sets assets directories" do
+      add_to_config("config.action_dispatch.show_exceptions = false")
+      add_to_config("config.serve_static_assets = true")
+
+      @plugin.write "lib/bukkits.rb", <<-RUBY
+        module Bukkits
+          class Engine < ::Rails::Engine
+            isolate_namespace Bukkits
+          end
+        end
+      RUBY
+
+      @plugin.write "public/stylesheets/foo.css", ""
+      @plugin.write "public/javascripts/foo.js", ""
+
+      @plugin.write "app/views/layouts/bukkits/application.html.erb", <<-RUBY
+        <%= stylesheet_link_tag :all %>
+        <%= javascript_include_tag :all %>
+        <%= yield %>
+      RUBY
+
+      @plugin.write "app/controllers/bukkits/home_controller.rb", <<-RUBY
+        module Bukkits
+          class HomeController < ActionController::Base
+            def index
+              render :text => "Good morning!", :layout => "bukkits/application"
+            end
+          end
+        end
+      RUBY
+
+      @plugin.write "config/routes.rb", <<-RUBY
+        Bukkits::Engine.routes.draw do
+          match "/home" => "home#index"
+        end
+      RUBY
+
+      app_file "config/routes.rb", <<-RUBY
+        Rails.application.routes.draw do
+          mount Bukkits::Engine => "/bukkits"
+        end
+      RUBY
+
+      require 'rack/test'
+      extend Rack::Test::Methods
+
+      boot_rails
+
+      require "#{rails_root}/config/environment"
+
+      assert_equal File.join(@plugin.path, "public"),             Bukkits::HomeController.assets_dir
+      assert_equal File.join(@plugin.path, "public/stylesheets"), Bukkits::HomeController.stylesheets_dir
+      assert_equal File.join(@plugin.path, "public/javascripts"), Bukkits::HomeController.javascripts_dir
+
+      assert_equal File.join(app_path, "public"),             ActionController::Base.assets_dir
+      assert_equal File.join(app_path, "public/stylesheets"), ActionController::Base.stylesheets_dir
+      assert_equal File.join(app_path, "public/javascripts"), ActionController::Base.javascripts_dir
+
+      get "/bukkits/home"
+
+      assert_match %r{bukkits/stylesheets/foo.css}, last_response.body
+      assert_match %r{bukkits/javascripts/foo.js}, last_response.body
+    end
   end
 end