From 13e1a546965122af5caf1fcbd4b5006c4aef42a0 Mon Sep 17 00:00:00 2001
From: Sander Muller <github@scode.nl>
Date: Mon, 9 Nov 2026 11:07:58 +0100
Subject: [PATCH] Use rtrim() semantics for chop() on constant strings

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 .../Php/TrimFunctionDynamicReturnTypeExtension.php  |  2 +-
 tests/PHPStan/Analyser/nsrt/bug-15684.php           | 13 +++++++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)
 create mode 100644 tests/PHPStan/Analyser/nsrt/bug-15684.php

diff --git a/src/Type/Php/TrimFunctionDynamicReturnTypeExtension.php b/src/Type/Php/TrimFunctionDynamicReturnTypeExtension.php
index 4a88a6616f0..f1d3e7fdf0b 100644
--- a/src/Type/Php/TrimFunctionDynamicReturnTypeExtension.php
+++ b/src/Type/Php/TrimFunctionDynamicReturnTypeExtension.php
@@ -71,7 +71,7 @@ public function getTypeFromFunctionCall(
 				if (count($stringConstantStrings) > 0) {
 					foreach ($stringConstantStrings as $stringConstantString) {
 						$result[] = new ConstantStringType(
-							$functionName === 'rtrim'
+							in_array($functionName, ['rtrim', 'chop'], true)
 								? rtrim($stringConstantString->getValue(), $trimConstantString->getValue())
 								: trim($stringConstantString->getValue(), $trimConstantString->getValue()),
 							true,
diff --git a/tests/PHPStan/Analyser/nsrt/bug-15684.php b/tests/PHPStan/Analyser/nsrt/bug-15684.php
new file mode 100644
index 00000000000..6ebb65d56f7
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/bug-15684.php
@@ -0,0 +1,13 @@
+<?php declare(strict_types = 1);
+
+namespace Bug15684;
+
+use function PHPStan\Testing\assertType;
+
+function doFoo(): void
+{
+	assertType("' a'", chop(' a ', ' '));
+	assertType("'yax'", chop('yax', 'y'));
+	assertType("' a'", rtrim(' a ', ' '));
+	assertType('true', chop(' a ', ' ') === ' a');
+}