[ticket/11943] Throw an exception if DEFINE is setup improperly

PHPBB3-11943

phpBB/phpbb/template/twig/tokenparser/defineparser.php

@@ -30,6 +30,13 @@ class defineparser extends \Twig_TokenParser
 			$stream->next();
 			$value = $this->parser->getExpressionParser()->parseExpression();
 
+			if ($value instanceof \Twig_Node_Expression_Name)
+			{
+				// This would happen if someone improperly formed their DEFINE syntax
+				// e.g. <!-- DEFINE $VAR = foo -->
+				throw new \Twig_Error_Syntax('Invalid DEFINE', $token->getLine(), $this->parser->getFilename());
+			}
+
 			$stream->expect(\Twig_Token::BLOCK_END_TYPE);
 		} else {
 			$capture = true;