Issue #2847611 by dawehner, webflo:...

Issue #2847611 by dawehner, webflo: \Drupal\Core\Template\TwigExtension::getLink overrides existing classes

core/lib/Drupal/Core/Template/TwigExtension.php

@@ -284,10 +284,7 @@ public function getLink($text, $url, $attributes = []) {
       if ($attributes instanceof Attribute) {
         $attributes = $attributes->toArray();
       }
-      if ($existing_attributes = $url->getOption('attributes')) {
-        $attributes = array_merge($existing_attributes, $attributes);
-      }
-      $url->setOption('attributes', $attributes);
+      $url->mergeOptions(['attributes' => $attributes]);
     }
     // The text has been processed by twig already, convert it to a safe object
     // for the render system.

core/tests/Drupal/Tests/Core/Template/TwigExtensionTest.php

@@ -8,6 +8,7 @@
 use Drupal\Core\Template\Loader\StringLoader;
 use Drupal\Core\Template\TwigEnvironment;
 use Drupal\Core\Template\TwigExtension;
+use Drupal\Core\Url;
 use Drupal\Tests\UnitTestCase;
 
 /**
@@ -345,6 +346,17 @@ public function testCreateAttribute() {
     $this->assertEquals($expected, $result);
   }
 
+  /**
+   * @covers ::getLink
+   */
+  public function testLinkWithOverriddenAttributes() {
+    $url = Url::fromRoute('<front>', [], ['attributes' => ['class' => ['foo']]]);
+
+    $build = $this->systemUnderTest->getLink('test', $url, ['class' => ['bar']]);
+
+    $this->assertEquals(['foo', 'bar'], $build['#url']->getOption('attributes')['class']);
+  }
+
 }
 
 class TwigExtensionTestString {