Issue #2698141 by TravisCarden, ChuChuNaKu, effulgentsia: Empty Twig {% trans %} tag causes unhelpful fatal exception

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

@@ -169,6 +169,9 @@ class TwigNodeTrans extends \Twig_Node {
         }
       }
     }
+    elseif (!$body->hasAttribute('data')) {
+      throw new \Twig_Error_Syntax('{% trans %} tag cannot be empty');
+    }
     else {
       $text = $body->getAttribute('data');
     }

core/modules/system/src/Tests/Theme/TwigTransTest.php

@@ -91,6 +91,30 @@ class TwigTransTest extends WebTestBase {
     $this->assertTwigTransTags();
   }
 
+  /**
+   * Test empty Twig "trans" tags.
+   */
+  public function testEmptyTwigTransTags() {
+    $elements = [
+      '#type' => 'inline_template',
+      '#template' => '{% trans %}{% endtrans %}',
+    ];
+    /** @var \Drupal\Core\Render\RendererInterface $renderer */
+    $renderer = \Drupal::service('renderer');
+
+    try {
+      $renderer->renderPlain($elements);
+
+      $this->fail('{% trans %}{% endtrans %} did not throw an exception.');
+    }
+    catch (\Twig_Error_Syntax $e) {
+      $this->assertTrue(strstr($e->getMessage(), '{% trans %} tag cannot be empty'), '{% trans %}{% endtrans %} threw the expected exception.');
+    }
+    catch (\Exception $e) {
+      $this->fail('{% trans %}{% endtrans %} threw an unexpected exception.');
+    }
+  }
+
   /**
    * Asserts Twig trans tags.
    */