Throw a SyntaxError instead of a PHP fatal error when a macro argument is defined twice

CHANGELOG

@@ -1,6 +1,6 @@
 # 3.28.1 (2026-XX-XX)
 
- * n/a
+ * Fix duplicated macro argument names triggering a PHP fatal error instead of a `SyntaxError`
 
 # 3.28.0 (2026-07-03)
 

src/Node/Expression/TempNameExpression.php

@@ -18,6 +18,10 @@ class TempNameExpression extends AbstractExpression
 {
     public const RESERVED_NAMES = ['varargs', 'context', 'macros', 'blocks', 'this'];
 
+    // Prefix applied to reserved names so their compiled PHP variables cannot clash
+    // with the internal ones ($varargs, $context, $macros, $blocks, $this)
+    public const RESERVED_NAME_PREFIX = "\u{035C}";
+
     public function __construct(string|int|null $name, int $lineno)
     {
         // All names supported by ExpressionParser::parsePrimaryExpression() should be excluded
@@ -32,7 +36,7 @@ class TempNameExpression extends AbstractExpression
         if (null !== $name && (\is_int($name) || ctype_digit($name))) {
             $name = (int) $name;
         } elseif (\in_array($name, self::RESERVED_NAMES, true)) {
-            $name = "\u{035C}".$name;
+            $name = self::RESERVED_NAME_PREFIX.$name;
         }
 
         parent::__construct([], ['name' => $name], $lineno);

src/Node/MacroNode.php

@@ -15,6 +15,7 @@ use Twig\Attribute\YieldReady;
 use Twig\Compiler;
 use Twig\Error\SyntaxError;
 use Twig\Node\Expression\ArrayExpression;
+use Twig\Node\Expression\TempNameExpression;
 use Twig\Node\Expression\Variable\LocalVariable;
 
 /**
@@ -47,10 +48,16 @@ class MacroNode extends Node
             $arguments = $args;
         }
 
+        $seen = [];
         foreach ($arguments->getKeyValuePairs() as $pair) {
-            if ("\u{035C}".self::VARARGS_NAME === $pair['key']->getAttribute('name')) {
+            $argName = $pair['key']->getAttribute('name');
+            if (TempNameExpression::RESERVED_NAME_PREFIX.self::VARARGS_NAME === $argName) {
                 throw new SyntaxError(\sprintf('The argument "%s" in macro "%s" cannot be defined because the variable "%s" is reserved for arbitrary arguments.', self::VARARGS_NAME, $name, self::VARARGS_NAME), $pair['value']->getTemplateLine(), $pair['value']->getSourceContext());
             }
+            if (isset($seen[$argName])) {
+                throw new SyntaxError(\sprintf('Argument "%s" is defined twice for macro "%s".', $this->stripReservedPrefix($argName), $name), $pair['value']->getTemplateLine(), $pair['value']->getSourceContext());
+            }
+            $seen[$argName] = true;
         }
 
         parent::__construct(['body' => $body, 'arguments' => $arguments], ['name' => $name], $lineno);
@@ -88,10 +95,7 @@ class MacroNode extends Node
 
         foreach ($arguments->getKeyValuePairs() as $pair) {
             $name = $pair['key'];
-            $var = $name->getAttribute('name');
-            if (str_starts_with($var, "\u{035C}")) {
-                $var = substr($var, \strlen("\u{035C}"));
-            }
+            $var = $this->stripReservedPrefix($name->getAttribute('name'));
             $compiler
                 ->write('')
                 ->string($var)
@@ -118,4 +122,9 @@ class MacroNode extends Node
             ->write("}\n\n")
         ;
     }
+
+    private function stripReservedPrefix(string $name): string
+    {
+        return str_starts_with($name, TempNameExpression::RESERVED_NAME_PREFIX) ? substr($name, \strlen(TempNameExpression::RESERVED_NAME_PREFIX)) : $name;
+    }
 }

tests/Fixtures/macros/duplicate_argument.test

@@ -0,0 +1,8 @@
+--TEST--
+macro with a duplicated argument name
+--TEMPLATE--
+{% macro test(a, b, a) %}{% endmacro %}
+--DATA--
+return []
+--EXCEPTION--
+Twig\Error\SyntaxError: Argument "a" is defined twice for macro "test" in "index.twig" at line 2.

tests/Fixtures/macros/duplicate_reserved_argument.test

@@ -0,0 +1,8 @@
+--TEST--
+macro with a duplicated argument name matching a reserved variable name
+--TEMPLATE--
+{% macro test(context, context) %}{% endmacro %}
+--DATA--
+return []
+--EXCEPTION--
+Twig\Error\SyntaxError: Argument "context" is defined twice for macro "test" in "index.twig" at line 2.