carefully and quickly merge url_for options

actionpack/lib/action_dispatch/routing/url_for.rb

@@ -147,7 +147,7 @@ module ActionDispatch
         when String
           options
         when nil, Hash
-          _routes.url_for((options || {}).symbolize_keys.reverse_merge!(url_options))
+          _routes.url_for(_merge_url_for_options(options, url_options))
         else
           polymorphic_url(options)
         end
@@ -155,6 +155,22 @@ module ActionDispatch
 
       protected
 
+      def _merge_url_for_options(h1, h2)
+        opts = {}
+
+        h1.keys.each do |k|
+          s = k.to_sym
+          opts[s] = h1[k] unless opts.has_key?(s)
+        end if h1
+
+        h2.keys.each do |k|
+          s = k.to_sym
+          opts[s] = h2[k] unless opts.has_key?(s)
+        end if h2
+
+        opts
+      end
+
       def optimize_routes_generation?
         return @_optimized_routes if defined?(@_optimized_routes)
         @_optimized_routes = _routes.optimize_routes_generation? && default_url_options.empty?

actionpack/test/controller/url_for_test.rb

@@ -356,6 +356,15 @@ module AbstractController
         assert_equal("/c/a", W.new.url_for(HashWithIndifferentAccess.new('controller' => 'c', 'action' => 'a', 'only_path' => true)))
       end
 
+      def test_with_stringified_default_url_options
+        W.default_url_options['controller'] = 'd'
+        W.default_url_options['only_path']  = false
+        assert_equal("/c", W.new.url_for(:controller => 'c', :only_path => true))
+
+        W.default_url_options['action'] = 'b'
+        assert_equal("/c/a", W.new.url_for(:controller => 'c', :action => 'a', :only_path => true))
+      end
+
       def test_url_params_with_nil_to_param_are_not_in_url
         assert_equal("/c/a", W.new.url_for(:only_path => true, :controller => 'c', :action => 'a', :id => Struct.new(:to_param).new(nil)))
       end