3 files changed, 20 insertions, 10 deletions
diff --git a/actionpack/lib/action_dispatch/routing/mapper.rb b/actionpack/lib/action_dispatch/routing/mapper.rb
index d1c5b5a7ff..a2ba4e26ea 100644
--- a/actionpack/lib/action_dispatch/routing/mapper.rb
+++ b/actionpack/lib/action_dispatch/routing/mapper.rb
@@ -652,18 +652,25 @@ module ActionDispatch
           def define_generate_prefix(app, name)
             _route = @set.named_routes.get name
             _routes = @set
-            app.routes.define_mounted_helper(name)
+
+            script_namer = ->(options) do
+              prefix_options = options.slice(*_route.segment_keys)
+              prefix_options[:relative_url_root] = "".freeze
+              # We must actually delete prefix segment keys to avoid passing them to next url_for.
+              _route.segment_keys.each { |k| options.delete(k) }
+              _routes.url_helpers.send("#{name}_path", prefix_options)
+            end
+
+            app.routes.define_mounted_helper(name, script_namer)
+
             app.routes.extend Module.new {
               def optimize_routes_generation?; false; end
+
               define_method :find_script_name do |options|
                 if options.key? :script_name
                   super(options)
                 else
-                  prefix_options = options.slice(*_route.segment_keys)
-                  prefix_options[:relative_url_root] = "".freeze
-                  # We must actually delete prefix segment keys to avoid passing them to next url_for.
-                  _route.segment_keys.each { |k| options.delete(k) }
-                  _routes.url_helpers.send("#{name}_path", prefix_options)
+                  script_namer.call(options)
                 end
               end
             }
diff --git a/actionpack/lib/action_dispatch/routing/route_set.rb b/actionpack/lib/action_dispatch/routing/route_set.rb
index ebe809f64e..a146d1fb1a 100644
--- a/actionpack/lib/action_dispatch/routing/route_set.rb
+++ b/actionpack/lib/action_dispatch/routing/route_set.rb
@@ -449,7 +449,7 @@ module ActionDispatch
         MountedHelpers
       end
 
-      def define_mounted_helper(name)
+      def define_mounted_helper(name, script_namer = nil)
         return if MountedHelpers.method_defined?(name)
 
         routes = self
@@ -457,7 +457,7 @@ module ActionDispatch
 
         MountedHelpers.class_eval do
           define_method "_#{name}" do
-            RoutesProxy.new(routes, _routes_context, helpers)
+            RoutesProxy.new(routes, _routes_context, helpers, script_namer)
           end
         end
 
diff --git a/actionpack/lib/action_dispatch/routing/routes_proxy.rb b/actionpack/lib/action_dispatch/routing/routes_proxy.rb
index c1423f770f..7a6c2e95d8 100644
--- a/actionpack/lib/action_dispatch/routing/routes_proxy.rb
+++ b/actionpack/lib/action_dispatch/routing/routes_proxy.rb
@@ -8,9 +8,10 @@ module ActionDispatch
       attr_accessor :scope, :routes
       alias :_routes :routes
 
-      def initialize(routes, scope, helpers)
+      def initialize(routes, scope, helpers, script_namer = nil)
         @routes, @scope = routes, scope
         @helpers = helpers
+        @script_namer = script_namer
       end
 
       def url_options
@@ -29,7 +30,9 @@ module ActionDispatch
           self.class.class_eval <<-RUBY, __FILE__, __LINE__ + 1
             def #{method}(*args)
               options = args.extract_options!
-              args << url_options.merge((options || {}).symbolize_keys)
+              options = url_options.merge((options || {}).symbolize_keys)
+              options.reverse_merge!(script_name: @script_namer.call(options)) if @script_namer
+              args << options
               @helpers.#{method}(*args)
             end
           RUBY