Reject an autoescape strategy that is neither a string nor false at compile time

CHANGELOG

@@ -1,5 +1,6 @@
 # 4.0.0 (2026-XX-XX)
 
+ * Reject an `autoescape` tag strategy that is neither a string nor `false` at compile time instead of failing at runtime
  * Remove support for cloning `Twig\Environment`; create a new environment instead
  * Remove support for calling `TemplateWrapper::unwrap()` without an environment argument
  * Stop detecting `echo` and `print` in compiled nodes; `yield` is the only supported mode and 3.x deprecates the alternative

src/Node/AutoEscapeNode.php

@@ -18,8 +18,6 @@ use Twig\Compiler;
  *
  * The value is the escaping strategy (can be html, js, ...)
  *
- * The true value is equivalent to html.
- *
  * If autoescaping is disabled, then the value is false.
  *
  * @author Fabien Potencier <fabien@symfony.com>

src/TokenParser/AutoEscapeTokenParser.php

@@ -33,10 +33,9 @@ final class AutoEscapeTokenParser extends AbstractTokenParser
             $value = 'html';
         } else {
             $expr = $this->parser->parseExpression();
-            if (!$expr instanceof ConstantExpression) {
-                throw new SyntaxError('An escaping strategy must be a string or false.', $stream->getCurrent()->getLine(), $stream->getSourceContext());
+            if (!$expr instanceof ConstantExpression || (!\is_string($value = $expr->getAttribute('value')) && false !== $value)) {
+                throw new SyntaxError('An escaping strategy must be a string or false.', $expr->getTemplateLine(), $stream->getSourceContext());
             }
-            $value = $expr->getAttribute('value');
         }
 
         $stream->expect(Token::BLOCK_END_TYPE);

tests/Fixtures/filters/force_escape.test

@@ -7,7 +7,7 @@
 
 {{ foo|e('html') -}}
 {{ foo|e('js') }}
-{% autoescape true %}
+{% autoescape 'html' %}
     {{ foo }}
 {% endautoescape %}
 --DATA--

tests/Fixtures/tags/autoescape/invalid_strategy.test

@@ -0,0 +1,8 @@
+--TEST--
+"autoescape" tag rejects a strategy that is neither a string nor false
+--TEMPLATE--
+{% autoescape true %}
+{{ var }}
+{% endautoescape %}
+--EXCEPTION--
+Twig\Error\SyntaxError: An escaping strategy must be a string or false in "index.twig" at line 2.