Cache url_helpers separately for mailers

The commit 3b63780 re-introduced url helper caching but we need to
cache a separate module for Action Mailer without paths.

actionpack/lib/action_dispatch/routing/route_set.rb

@@ -410,63 +410,69 @@ def #{name}
       end
 
       def url_helpers(supports_path = true)
-        @url_helpers ||= begin
-          routes = self
+        if supports_path
+          @url_helpers_with_paths ||= generate_url_helpers(supports_path)
+        else
+          @url_helpers_without_paths ||= generate_url_helpers(supports_path)
+        end
+      end
 
-          Module.new do
-            extend ActiveSupport::Concern
-            include UrlFor
+      def generate_url_helpers(supports_path)
+        routes = self
 
-            # Define url_for in the singleton level so one can do:
-            # Rails.application.routes.url_helpers.url_for(args)
-            @_routes = routes
-            class << self
-              def url_for(options)
-                @_routes.url_for(options)
-              end
+        Module.new do
+          extend ActiveSupport::Concern
+          include UrlFor
 
-              def optimize_routes_generation?
-                @_routes.optimize_routes_generation?
-              end
-
-              attr_reader :_routes
-              def url_options; {}; end
+          # Define url_for in the singleton level so one can do:
+          # Rails.application.routes.url_helpers.url_for(args)
+          @_routes = routes
+          class << self
+            def url_for(options)
+              @_routes.url_for(options)
             end
 
-            url_helpers = routes.named_routes.url_helpers_module
-
-            # Make named_routes available in the module singleton
-            # as well, so one can do:
-            # Rails.application.routes.url_helpers.posts_path
-            extend url_helpers
-
-            # Any class that includes this module will get all
-            # named routes...
-            include url_helpers
-
-            if supports_path
-              path_helpers = routes.named_routes.path_helpers_module
-
-              include path_helpers
-              extend path_helpers
+            def optimize_routes_generation?
+              @_routes.optimize_routes_generation?
             end
 
-            # plus a singleton class method called _routes ...
-            included do
-              singleton_class.send(:redefine_method, :_routes) { routes }
-            end
-
-            # And an instance method _routes. Note that
-            # UrlFor (included in this module) add extra
-            # conveniences for working with @_routes.
-            define_method(:_routes) { @_routes || routes }
-
-            define_method(:_generate_paths_by_default) do
-              supports_path
-            end
-
-            private :_generate_paths_by_default
+            attr_reader :_routes
+            def url_options; {}; end
           end
+
+          url_helpers = routes.named_routes.url_helpers_module
+
+          # Make named_routes available in the module singleton
+          # as well, so one can do:
+          # Rails.application.routes.url_helpers.posts_path
+          extend url_helpers
+
+          # Any class that includes this module will get all
+          # named routes...
+          include url_helpers
+
+          if supports_path
+            path_helpers = routes.named_routes.path_helpers_module
+
+            include path_helpers
+            extend path_helpers
+          end
+
+          # plus a singleton class method called _routes ...
+          included do
+            singleton_class.send(:redefine_method, :_routes) { routes }
+          end
+
+          # And an instance method _routes. Note that
+          # UrlFor (included in this module) add extra
+          # conveniences for working with @_routes.
+          define_method(:_routes) { @_routes || routes }
+
+          define_method(:_generate_paths_by_default) do
+            supports_path
+          end
+
+          private :_generate_paths_by_default
         end
       end