Add mounted_helpers to routes

mounted_helpers are a bit similar to url_helpers. They're automatically
included in controllers for Rails.application and each of mounted
Engines. Mounted helper allows to call url_for and named helpers for
given application.

Given Blog::Engine mounted as blog_engine, there are 2 helpers defined:
app and blog_engine. You can call routes for app and engine using those
helpers:

app.root_url
app.url_for(:controller => "foo")
blog_engine.posts_path
blog_engine.url_for(@post)

1 files changed, 59 insertions, 0 deletions

diff --git a/actionpack/lib/action_dispatch/routing/route_set.rb b/actionpack/lib/action_dispatch/routing/route_set.rb
index b3945a4963..0f8bb5c504 100644
--- a/actionpack/lib/action_dispatch/routing/route_set.rb
+++ b/actionpack/lib/action_dispatch/routing/route_set.rb
@@ -261,6 +261,65 @@ module ActionDispatch
         named_routes.install(destinations, regenerate_code)
       end
 
+      class RoutesProxy
+        include ActionDispatch::Routing::UrlFor
+
+        %w(url_options polymorphic_url polymorphic_path).each do |method|
+          self.class_eval <<-RUBY, __FILE__, __LINE__ +1
+            def #{method}(*args)
+              scope.send(:_with_routes, routes) do
+                scope.#{method}(*args)
+              end
+            end
+          RUBY
+        end
+
+        attr_accessor :scope, :routes
+        alias :_routes :routes
+
+        def initialize(routes, scope)
+          @routes, @scope = routes, scope
+        end
+
+        def method_missing(method, *args)
+          if routes.url_helpers.respond_to?(method)
+            self.class.class_eval <<-RUBY, __FILE__, __LINE__ + 1
+              def #{method}(*args)
+                options = args.extract_options!
+                args << url_options.merge((options || {}).symbolize_keys)
+                routes.url_helpers.#{method}(*args)
+              end
+            RUBY
+            send(method, *args)
+          else
+            super
+          end
+        end
+      end
+
+      module MountedHelpers
+      end
+
+      def mounted_helpers(name = nil)
+        define_mounted_helper(name) if name
+        MountedHelpers
+      end
+
+      def define_mounted_helper(name, helpers = nil)
+        routes = self
+        MountedHelpers.class_eval do
+          define_method "_#{name}" do
+            RoutesProxy.new(routes, self)
+          end
+        end
+
+        MountedHelpers.class_eval <<-RUBY
+          def #{name}
+            @#{name} ||= _#{name}
+          end
+        RUBY
+      end
+
       def url_helpers
         @url_helpers ||= begin
           routes = self