options could be of any kind of Hash (Hash, HashWithIndifferentAccess or OrderedHash) this way we keep the properties of the options passed as an argument

actionpack/lib/action_dispatch/routing/route_set.rb

@@ -454,7 +454,7 @@ module ActionDispatch
 
       def url_for(options)
         finalize!
-        options = default_url_options.merge(options || {})
+        options = (options || {}).reverse_merge!(default_url_options)
 
         handle_positional_args(options)
 

actionpack/lib/action_dispatch/routing/url_for.rb

@@ -129,7 +129,7 @@ module ActionDispatch
         when String
           options
         when nil, Hash
-          _routes.url_for(url_options.merge((options || {}).symbolize_keys))
+          _routes.url_for((options || {}).reverse_merge!(url_options).symbolize_keys)
         else
           polymorphic_url(options)
         end

actionpack/lib/action_view/helpers/url_helper.rb

@@ -95,7 +95,7 @@ module ActionView
         when String
           options
         when Hash
-          options = { :only_path => options[:host].nil? }.update(options.symbolize_keys)
+          options = options.symbolize_keys.reverse_merge!(:only_path => options[:host].nil?)
           super
         when :back
           controller.request.env["HTTP_REFERER"] || 'javascript:history.back()'