RouteSet should be in charge of constructing the dispather

Now we can override how requests are dispatched in the routeset object

actionpack/lib/action_dispatch/routing/mapper.rb

@@ -66,7 +66,7 @@ module ActionDispatch
         attr_reader :requirements, :conditions, :defaults
         attr_reader :to, :default_controller, :default_action, :as, :anchor
 
-        def self.build(scope, path, options)
+        def self.build(scope, set, path, options)
           options = scope[:options].merge(options) if scope[:options]
 
           options.delete :only
@@ -77,12 +77,13 @@ module ActionDispatch
 
           defaults = (scope[:defaults] || {}).merge options.delete(:defaults) || {}
 
-          new scope, path, defaults, options
+          new scope, set, path, defaults, options
         end
 
-        def initialize(scope, path, defaults, options)
+        def initialize(scope, set, path, defaults, options)
           @requirements, @conditions = {}, {}
           @defaults = defaults
+          @set = set
 
           @to                 = options.delete :to
           @default_controller = options.delete(:controller) || scope[:controller]
@@ -249,9 +250,9 @@ module ActionDispatch
               Constraints.new(to, blocks, false)
             else
               if blocks.any?
-                Constraints.new(dispatcher, blocks, true)
+                Constraints.new(dispatcher(defaults), blocks, true)
               else
-                dispatcher
+                dispatcher(defaults)
               end
             end
           end
@@ -348,8 +349,8 @@ module ActionDispatch
             parser.parse path
           end
 
-          def dispatcher
-            Routing::RouteSet::Dispatcher.new(defaults)
+          def dispatcher(defaults)
+            @set.dispatcher defaults
           end
       end
 
@@ -1551,7 +1552,7 @@ module ActionDispatch
             options[:as] = name_for_action(options[:as], action)
           end
 
-          mapping = Mapping.build(@scope, URI.parser.escape(path), options)
+          mapping = Mapping.build(@scope, @set, URI.parser.escape(path), options)
           app, conditions, requirements, defaults, as, anchor = mapping.to_route
           @set.add_route(app, conditions, requirements, defaults, as, anchor)
         end

actionpack/lib/action_dispatch/routing/route_set.rb

@@ -334,6 +334,10 @@ module ActionDispatch
         @prepend.each { |blk| eval_block(blk) }
       end
 
+      def dispatcher(defaults)
+        Routing::RouteSet::Dispatcher.new(defaults)
+      end
+
       module MountedHelpers #:nodoc:
         extend ActiveSupport::Concern
         include UrlFor

actionpack/test/dispatch/mapper_test.rb

@@ -3,7 +3,7 @@ require 'abstract_unit'
 module ActionDispatch
   module Routing
     class MapperTest < ActiveSupport::TestCase
-      class FakeSet
+      class FakeSet < ActionDispatch::Routing::RouteSet
         attr_reader :routes
         alias :set :routes
 
@@ -38,7 +38,7 @@ module ActionDispatch
 
       def test_mapping_requirements
         options = { :controller => 'foo', :action => 'bar', :via => :get }
-        m = Mapper::Mapping.build({}, '/store/:name(*rest)', options)
+        m = Mapper::Mapping.build({}, FakeSet.new, '/store/:name(*rest)', options)
         _, _, requirements, _ = m.to_route
         assert_equal(/.+?/, requirements[:rest])
       end