Fix named routes modifying arguments

actionpack/lib/action_dispatch/routing/route_set.rb

@@ -165,13 +165,14 @@ def define_hash_access(route, name, kind, options)
               remove_possible_method :#{selector}
               def #{selector}(*args)
                 options = args.extract_options!
+                result = #{options.inspect}
 
                 if args.any?
-                  options[:_positional_args] = args
-                  options[:_positional_keys] = #{route.segment_keys.inspect}
+                  result[:_positional_args] = args
+                  result[:_positional_keys] = #{route.segment_keys.inspect}
                 end
 
-                options ? #{options.inspect}.merge(options) : #{options.inspect}
+                result.merge(options)
               end
               protected :#{selector}
             END_EVAL

actionpack/test/dispatch/routing_test.rb

@@ -863,6 +863,17 @@ def test_url_for_with_no_side_effects
     assert_equal original_options, options
   end
 
+  # tests the arguments modification free version of define_hash_access
+  def test_named_route_with_no_side_effects
+    original_options = { :host => 'test.host' }
+    options = original_options.dup
+
+    profile_customer_url("customer_model", options)
+
+    # verify that the options passed in have not changed from the original ones
+    assert_equal original_options, options
+  end
+
   def test_projects_status
     with_test_routes do
       assert_equal '/projects/status', url_for(:controller => 'projects', :action => 'status', :only_path => true)