From 1252f55e2be703019cf4e0a6901a2318dfb0baf5 Mon Sep 17 00:00:00 2001
From: David Grudl <david@grudl.com>
Date: Sat, 24 Jan 2026 08:14:25 +0100
Subject: [PATCH] fixed escaped hash in regex extended mode

\# was incorrectly treated as comment start in /x mode
---
 src/Type/Regex/RegexGroupParser.php               |  3 ++-
 tests/PHPStan/Analyser/nsrt/preg_match_shapes.php | 15 +++++++++++++++
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/src/Type/Regex/RegexGroupParser.php b/src/Type/Regex/RegexGroupParser.php
index 6259e7e87d..d78ebaaa8f 100644
--- a/src/Type/Regex/RegexGroupParser.php
+++ b/src/Type/Regex/RegexGroupParser.php
@@ -85,7 +85,8 @@ public function parseGroups(string $regex): ?RegexAstWalkResult
 
 			if (str_contains($modifiers, 'x')) {
 				// in freespacing mode the # character starts a comment and runs until the end of the line
-				$regex = preg_replace('/(?<!\?)#.*/', '', $regex) ?? '';
+				// but \# is an escaped literal hash, and (?#...) is an inline comment - neither starts a line comment
+				$regex = preg_replace('/(?<!\\\\)(?<!\(\?)#.*/', '', $regex) ?? '';
 			}
 
 			$rawRegex = $this->regexExpressionHelper->removeDelimitersAndModifiers($regex);
diff --git a/tests/PHPStan/Analyser/nsrt/preg_match_shapes.php b/tests/PHPStan/Analyser/nsrt/preg_match_shapes.php
index 545fd191f1..0a4cc7f6e1 100644
--- a/tests/PHPStan/Analyser/nsrt/preg_match_shapes.php
+++ b/tests/PHPStan/Analyser/nsrt/preg_match_shapes.php
@@ -1073,3 +1073,18 @@ function bug12792(string $string): void {
 		assertType('array{string, non-empty-string}', $match); // could be array{'acd'|'ayd'|'bd', 'c'|'xb'|'y'}
 	}
 }
+
+function testExtendedSyntaxEscapedHash(string $string): void {
+	// \# in extended mode should be treated as literal hash, not comment
+	if (preg_match('/^ ([\#.]) $/x', $string, $matches)) {
+		assertType("array{non-falsy-string, '#'|'.'}", $matches);
+	}
+
+	// Real comment vs escaped hash
+	if (preg_match('/
+		(\d+)      # this is a comment
+		([\#ab]+)  # hash in character class (escaped)
+	/x', $string, $matches)) {
+		assertType('array{non-falsy-string, numeric-string, non-empty-string}', $matches);
+	}
+}