Fix url generation for mounted Engine

I added integration tests for generating urls in Engine and application
and tweaked Engines to fully cooparate with new router's behavior:
* Rails.application now sets ORIGINAL_SCRIPT_NAME
* Rails.application also sets its routes as env['action_dispatch.parent_routes']
* Engine implements responds_to? class method to respond to all the
  instance methods, like #routes

railties/lib/rails/application.rb

@@ -121,14 +121,20 @@ def load_console(sandbox=false)
     alias :build_middleware_stack :app
 
     def call(env)
+      if Rails.application == self
+        env["ORIGINAL_SCRIPT_NAME"] = env["SCRIPT_NAME"]
+        env["action_dispatch.parent_routes"] = routes
+      end
+
+      env["action_dispatch.routes"] = routes
       app.call(env.reverse_merge!(env_defaults))
     end
 
     def env_defaults
-      @env_defaults ||= super.merge({
+      @env_defaults ||= {
         "action_dispatch.parameter_filter" => config.filter_parameters,
         "action_dispatch.secret_token" => config.secret_token
-      })
+      }
     end
 
     def initializers

railties/lib/rails/engine.rb

@@ -159,13 +159,8 @@ def endpoint
     end
 
     def call(env)
-      app.call(env.reverse_merge!(env_defaults))
-    end
-
-    def env_defaults
-      @env_defaults ||= {
-        "action_dispatch.routes" => routes
-      }
+      env["action_dispatch.routes"] = routes
+      app.call(env)
     end
 
     def routes

railties/test/railties/mounted_engine_routes_test.rb

+require 'isolation/abstract_unit'
+
+module ApplicationTests
+  class ApplicationRoutingTest < Test::Unit::TestCase
+     require 'rack/test'
+     include Rack::Test::Methods
+     include ActiveSupport::Testing::Isolation
+
+    def setup
+      build_app
+
+      add_to_config("config.action_dispatch.show_exceptions = false")
+
+      @plugin = engine "blog"
+
+      app_file 'config/routes.rb', <<-RUBY
+        AppTemplate::Application.routes.draw do |map|
+          match "/engine_route" => "application_generating#engine_route"
+          match "/url_for_engine_route" => "application_generating#url_for_engine_route"
+          scope "/:user", :user => "anonymous" do
+            mount Blog::Engine => "/blog"
+          end
+          root :to => 'main#index'
+        end
+      RUBY
+
+      @plugin.write "lib/blog.rb", <<-RUBY
+        module Blog
+          class Engine < ::Rails::Engine
+          end
+        end
+      RUBY
+
+      app_file "config/initializers/bla.rb", <<-RUBY
+        Blog::Engine.eager_load!
+      RUBY
+
+      @plugin.write "config/routes.rb", <<-RUBY
+        Blog::Engine.routes.draw do
+          resources :posts do
+            get :generate_application_route
+          end
+        end
+      RUBY
+
+      @plugin.write "app/controllers/posts_controller.rb", <<-RUBY
+        class PostsController < ActionController::Base
+          include Blog::Engine.routes.url_helpers
+
+          def index
+            render :text => post_path(1)
+          end
+
+          def generate_application_route
+            path = url_for( :routes => Rails.application.routes,
+                            :controller => "main",
+                            :action => "index",
+                            :only_path => true)
+            render :text => path
+          end
+        end
+      RUBY
+
+      app_file "app/controllers/application_generating_controller.rb", <<-RUBY
+        class ApplicationGeneratingController < ActionController::Base
+          include Blog::Engine.routes.url_helpers
+
+          def engine_route
+            render :text => posts_path
+          end
+
+          def url_for_engine_route
+            render :text => url_for(:controller => "posts", :action => "index", :user => "john", :only_path => true)
+          end
+        end
+      RUBY
+
+      boot_rails
+    end
+
+    def app
+      @app ||= begin
+        require "#{app_path}/config/environment"
+        Rails.application
+      end
+    end
+
+    test "routes generation in engine and application" do
+      # test generating engine's route from engine
+      get "/john/blog/posts"
+      assert_equal "/john/blog/posts/1", last_response.body
+
+      # test generating engine's route from application
+      get "/engine_route"
+      assert_equal "/anonymous/blog/posts", last_response.body
+      get "/url_for_engine_route"
+      assert_equal "/john/blog/posts", last_response.body
+
+      # test generating application's route from engine
+      get "/someone/blog/generate_application_route"
+      assert_equal "/", last_response.body
+      get "/someone/blog/generate_application_route", {}, "SCRIPT_NAME" => "/foo"
+      assert_equal "/foo/", last_response.body
+    end
+  end
+end
+