diff -u b/core/modules/system/src/Tests/Theme/EngineTwigTest.php b/core/modules/system/src/Tests/Theme/EngineTwigTest.php
--- b/core/modules/system/src/Tests/Theme/EngineTwigTest.php
+++ b/core/modules/system/src/Tests/Theme/EngineTwigTest.php
@@ -76,6 +76,8 @@
     $expected = [
       'link via the linkgenerator: ' . $link_generator->generate('register', new Url('user.register')),
       'link via the linkgenerator: ' . $link_generator->generate('register', new Url('user.register', [], ['attributes' => ['foo' => 'bar']])),
+      'link via the linkgenerator: ' . $link_generator->generate('register', new Url('user.register', []), ['id' => 'kitten', 'foo' => 'bar']),
+      'link via the linkgenerator: ' . $link_generator->generate('register', new Url('user.register', [], ['id' => 'kitten'])),
     ];
 
     $content = $this->getRawContent();
diff -u b/core/modules/system/tests/modules/twig_theme_test/templates/twig_theme_test.link_generator.html.twig b/core/modules/system/tests/modules/twig_theme_test/templates/twig_theme_test.link_generator.html.twig
--- b/core/modules/system/tests/modules/twig_theme_test/templates/twig_theme_test.link_generator.html.twig
+++ b/core/modules/system/tests/modules/twig_theme_test/templates/twig_theme_test.link_generator.html.twig
@@ -2,0 +3,3 @@
+<div>link via the linkgenerator: {{ link("register", test_url_attribute, { 'id' : 'kitten' }) }}</div>
+<div>link via the linkgenerator: {{ link("register", path('user.register'), { 'id' : 'kitten' }) }}</div>
+
only in patch2:
unchanged:
--- a/core/modules/system/tests/modules/twig_theme_test/src/TwigThemeTestController.php
+++ b/core/modules/system/tests/modules/twig_theme_test/src/TwigThemeTestController.php
@@ -46,6 +46,7 @@ public function linkGeneratorRender() {
     return array(
       '#theme' => 'twig_theme_test_link_generator',
       '#test_url' => new Url('user.register'),
+      '#test_url_attribute' => new Url('user.register', [], ['attributes' => ['foo' => 'bar']]),
     );
   }
 
only in patch2:
unchanged:
--- a/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.module
+++ b/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.module
@@ -30,7 +30,7 @@ function twig_theme_test_theme($existing, $type, $theme, $path) {
     'template' => 'twig_theme_test.url_generator',
   );
   $items['twig_theme_test_link_generator'] = array(
-    'variables' => array('test_url' => NULL),
+    'variables' => array('test_url' => NULL, 'test_url_attribute' => NULL),
     'template' => 'twig_theme_test.link_generator',
   );
   return $items;