Fix that optimized named routes should also work as singleton methods on the url_helpers module

actionpack/lib/action_dispatch/routing/route_set.rb

@@ -188,7 +188,8 @@ module ActionDispatch
               remove_possible_method :#{selector}
               def #{selector}(*args)
                 if #{optimize_helper?(route)} && args.size == #{route.required_parts.size} && !args.last.is_a?(Hash) && optimize_routes_generation?
-                  options = #{options.inspect}.merge!(url_options)
+                  options = #{options.inspect}
+                  options.merge!(url_options) if respond_to?(:url_options)
                   options[:path] = "#{optimized_helper(route)}"
                   ActionDispatch::Http::URL.url_for(options)
                 else

actionpack/test/dispatch/routing_test.rb

@@ -2538,3 +2538,27 @@ class TestConstraintsAccessingParameters < ActionDispatch::IntegrationTest
     assert_equal "bar", @request.params[:bar]
   end
 end
+
+class TestOptimizedNamedRoutes < ActionDispatch::IntegrationTest
+  Routes = ActionDispatch::Routing::RouteSet.new.tap do |app|
+    app.draw do
+      ok = lambda { |env| [200, { 'Content-Type' => 'text/plain' }, []] }
+      get '/foo' => ok, as: :foo
+    end
+  end
+
+  include Routes.url_helpers
+  def app; Routes end
+
+  test 'enabled when not mounted and default_url_options is empty' do
+    assert Routes.url_helpers.optimize_routes_generation?
+  end
+
+  test 'named route called as singleton method' do
+    assert_equal '/foo', Routes.url_helpers.foo_path
+  end
+
+  test 'named route called on included module' do
+    assert_equal '/foo', foo_path
+  end
+end