From c9c3b23a77ca033c2e1203645298d152f6c04902 Mon Sep 17 00:00:00 2001
From: Pascal CESCON - Amoifr <pascal.cescon@gmail.com>
Date: Wed, 19 Aug 2026 17:35:38 +0200
Subject: [PATCH] Fix the empty comment "{##}" being lexed as a documentation
 comment opening

---
 src/Lexer.php        |  6 +++++-
 tests/ParserTest.php | 15 ++++++++++++++-
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/src/Lexer.php b/src/Lexer.php
index c2e9f31ba..25b9f2143 100644
--- a/src/Lexer.php
+++ b/src/Lexer.php
@@ -95,6 +95,10 @@ class Lexer
             return;
         }
 
+        // when the comment closing tag starts with "#" (as "#}" does), the empty comment ("{##}")
+        // starts like a documentation comment ("{##"); make sure it keeps lexing as a comment
+        $emptyCommentLookahead = str_starts_with($this->options['tag_comment'][1], '#') ? '(?!'.preg_quote(substr($this->options['tag_comment'][1], 1), '#').')' : '';
+
         // when PHP 7.3 is the min version, we will be able to remove the '#' part in preg_quote as it's part of the default
         $this->regexes = [
             // }}
@@ -187,7 +191,7 @@ class Lexer
                     '|'.
                     preg_quote($this->options['tag_block'][0], '#'). // {%
                     '|'.
-                    preg_quote($this->options['tag_comment'][0].'#', '#'). // {##
+                    preg_quote($this->options['tag_comment'][0].'#', '#').$emptyCommentLookahead. // {## (but not the empty comment {##})
                     '|'.
                     preg_quote($this->options['tag_comment'][0], '#'). // {#
                 ')('.
diff --git a/tests/ParserTest.php b/tests/ParserTest.php
index bff1fa34d..f90fa46c5 100644
--- a/tests/ParserTest.php
+++ b/tests/ParserTest.php
@@ -349,6 +349,19 @@ TWIG, 'index')));
         $this->assertNull($body->getNode('4')->getDocumentation());
     }
 
+    public function testEmptyCommentIsNotLexedAsDocumentation(): void
+    {
+        $twig = new Environment(new ArrayLoader(), ['autoescape' => false]);
+        $module = $twig->parse($twig->tokenize(new Source(<<<'TWIG'
+{##}{{ answer }}
+{% block a %}x{##}{% endblock %}{% block b %}y{% endblock %}
+TWIG, 'index')));
+        $body = $module->getNode('body')->getNode('0');
+
+        $this->assertInstanceOf(PrintNode::class, $body->getNode('0'));
+        $this->assertNull($body->getNode('0')->getDocumentation());
+    }
+
     public function testInlineDocumentationBeforeATagNameIsIgnored(): void
     {
         $twig = new Environment(new ArrayLoader(), ['autoescape' => false]);
@@ -440,7 +453,7 @@ TWIG, 'index')));
     {
         $twig = new Environment(new ArrayLoader());
 
-        $this->expectDeprecation('Since twig/twig 3.29: Defining the macro "input" more than once in "index" is deprecated and will throw a SyntaxError in Twig 4.0 (first definition at line 1, second at line 1).');
+        $this->expectDeprecation('Since twig/twig 3.29: Defining the macro "input" more than once in "index" is deprecated and will throw a SyntaxError in Twig 4.0 (first definition at line 1, second at line 1). The last definition is used in Twig 3.');
 
         $module = $twig->parse($twig->tokenize(new Source('{## First #}{% macro input() %}{% endmacro %}{## Second #}{% macro input() %}{% endmacro %}', 'index')));