3 files changed, 48 insertions, 7 deletions
diff --git a/actionpack/lib/action_dispatch/routing/mapper.rb b/actionpack/lib/action_dispatch/routing/mapper.rb
index a2570cb877..f3aa09f4a7 100644
--- a/actionpack/lib/action_dispatch/routing/mapper.rb
+++ b/actionpack/lib/action_dispatch/routing/mapper.rb
@@ -261,7 +261,11 @@ module ActionDispatch
 
           raise "A rack application must be specified" unless path
 
+          options[:as] ||= app_name(app)
+
           match(path, options.merge(:to => app, :anchor => false, :format => false))
+
+          define_generate_prefix(app, options[:as])
           self
         end
 
@@ -269,6 +273,29 @@ module ActionDispatch
           @set.default_url_options = options
         end
         alias_method :default_url_options, :default_url_options=
+
+        private
+          def app_name(app)
+            return unless app.respond_to?(:routes)
+            class_name = app.class.is_a?(Class) ? app.name : app.class.name
+            ActiveSupport::Inflector.underscore(class_name).gsub("/", "_")
+          end
+
+          def define_generate_prefix(app, name)
+            return unless app.respond_to?(:routes)
+
+            _route = @set.named_routes.routes[name.to_sym]
+            _router = @set
+            app.routes.class_eval do
+              define_method :_generate_prefix do |options|
+                keys = _route.segment_keys + ActionDispatch::Routing::RouteSet::RESERVED_OPTIONS
+                prefix_options = options.reject { |k, v| !(keys).include?(k) }
+                # we must actually delete prefix segment keys to avoid passing them to next url_for
+                _route.segment_keys.each { |k| options.delete(k) }
+                _router.url_helpers.send("#{name}_path", prefix_options)
+              end
+            end
+          end
       end
 
       module HttpHelpers
diff --git a/actionpack/lib/action_dispatch/routing/route_set.rb b/actionpack/lib/action_dispatch/routing/route_set.rb
index b531cc1a8e..cb0373951f 100644
--- a/actionpack/lib/action_dispatch/routing/route_set.rb
+++ b/actionpack/lib/action_dispatch/routing/route_set.rb
@@ -303,10 +303,9 @@ module ActionDispatch
       end
 
       class Generator #:nodoc:
-        attr_reader :options, :recall, :set, :script_name, :named_route
+        attr_reader :options, :recall, :set, :named_route
 
         def initialize(options, recall, set, extras = false)
-          @script_name = options.delete(:script_name)
           @named_route = options.delete(:use_route)
           @options     = options.dup
           @recall      = recall.dup
@@ -401,7 +400,7 @@ module ActionDispatch
           return [path, params.keys] if @extras
 
           path << "?#{params.to_query}" if params.any?
-          "#{script_name}#{path}"
+          path
         rescue Rack::Mount::RoutingError
           raise_routing_error
         end
@@ -453,7 +452,11 @@ module ActionDispatch
         Generator.new(options, recall, self, extras).generate
       end
 
-      RESERVED_OPTIONS = [:anchor, :params, :only_path, :host, :protocol, :port, :trailing_slash]
+      RESERVED_OPTIONS = [:anchor, :params, :only_path, :host, :protocol, :port, :trailing_slash, :script_name, :skip_prefix, :routes]
+
+      def _generate_prefix(options = {})
+        nil
+      end
 
       def url_for(options)
         finalize!
@@ -464,7 +467,6 @@ module ActionDispatch
         rewritten_url = ""
 
         path_segments = options.delete(:_path_segments)
-
         unless options[:only_path]
           rewritten_url << (options[:protocol] || "http")
           rewritten_url << "://" unless rewritten_url.match("://")
@@ -476,9 +478,15 @@ module ActionDispatch
           rewritten_url << ":#{options.delete(:port)}" if options.key?(:port)
         end
 
+        path = [options.delete(:script_name)]
+        if !options.delete(:skip_prefix)
+          path << _generate_prefix(options)
+        end
+
         path_options = options.except(*RESERVED_OPTIONS)
         path_options = yield(path_options) if block_given?
-        path = generate(path_options, path_segments || {})
+        path << generate(path_options, path_segments || {})
+        path = path.compact.join ''
 
         # ROUTES TODO: This can be called directly, so script_name should probably be set in the routes
         rewritten_url << (options[:trailing_slash] ? path.sub(/\?|\z/) { "/" + $& } : path)
diff --git a/actionpack/lib/action_dispatch/routing/url_for.rb b/actionpack/lib/action_dispatch/routing/url_for.rb
index 28ec830fe8..f73067688c 100644
--- a/actionpack/lib/action_dispatch/routing/url_for.rb
+++ b/actionpack/lib/action_dispatch/routing/url_for.rb
@@ -128,7 +128,13 @@ module ActionDispatch
         when String
           options
         when nil, Hash
-          _routes.url_for((options || {}).reverse_merge!(url_options).symbolize_keys)
+          routes = (options ? options.delete(:routes) : nil) || _routes
+
+          if respond_to?(:env) && env && routes.equal?(env["action_dispatch.routes"])
+             options[:skip_prefix] = true
+          end
+
+          routes.url_for((options || {}).reverse_merge!(url_options).symbolize_keys)
         else
           polymorphic_url(options)
         end