From 644e92394f744fdbea20344329403f8bc2c8522b Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Tue, 10 Mar 2026 14:19:24 +0000
Subject: [PATCH] Fix false positives for is_a() and instanceof checks on $this
 in traits

- When analyzing trait methods, $this is bound to each using class separately
- is_a($this, SomeClass::class) was reported as "always true" in SomeClass context
  and "always false" in SomeClass2 context, but both are false positives
- Added trait-aware check in ImpossibleCheckTypeHelper to treat $this as uncertain
  when inside a trait, since the same code is shared across multiple classes
- New regression test in tests/PHPStan/Rules/Comparison/data/bug-13023.php

Closes https://github.com/phpstan/phpstan/issues/13023
---
 .../Comparison/ImpossibleCheckTypeHelper.php  | 10 ++++++++
 ...mpossibleCheckTypeFunctionCallRuleTest.php |  6 +++++
 .../Rules/Comparison/data/bug-13023.php       | 25 +++++++++++++++++++
 3 files changed, 41 insertions(+)
 create mode 100644 tests/PHPStan/Rules/Comparison/data/bug-13023.php

diff --git a/src/Rules/Comparison/ImpossibleCheckTypeHelper.php b/src/Rules/Comparison/ImpossibleCheckTypeHelper.php
index 97a0179405..49429d1abb 100644
--- a/src/Rules/Comparison/ImpossibleCheckTypeHelper.php
+++ b/src/Rules/Comparison/ImpossibleCheckTypeHelper.php
@@ -310,6 +310,11 @@ public function findSpecifiedType(
 				continue;
 			}
 
+			if ($scope->isInTrait() && $sureType[0] instanceof Expr\Variable && $sureType[0]->name === 'this') {
+				$results[] = TrinaryLogic::createMaybe();
+				continue;
+			}
+
 			if ($this->treatPhpDocTypesAsCertain) {
 				$argumentType = $scope->getType($sureType[0]);
 			} else {
@@ -336,6 +341,11 @@ public function findSpecifiedType(
 				continue;
 			}
 
+			if ($scope->isInTrait() && $sureNotType[0] instanceof Expr\Variable && $sureNotType[0]->name === 'this') {
+				$results[] = TrinaryLogic::createMaybe();
+				continue;
+			}
+
 			if ($this->treatPhpDocTypesAsCertain) {
 				$argumentType = $scope->getType($sureNotType[0]);
 			} else {
diff --git a/tests/PHPStan/Rules/Comparison/ImpossibleCheckTypeFunctionCallRuleTest.php b/tests/PHPStan/Rules/Comparison/ImpossibleCheckTypeFunctionCallRuleTest.php
index 69e992139d..8f0f4843c2 100644
--- a/tests/PHPStan/Rules/Comparison/ImpossibleCheckTypeFunctionCallRuleTest.php
+++ b/tests/PHPStan/Rules/Comparison/ImpossibleCheckTypeFunctionCallRuleTest.php
@@ -1207,4 +1207,10 @@ public function testBug13799(): void
 		]);
 	}
 
+	public function testBug13023(): void
+	{
+		$this->treatPhpDocTypesAsCertain = true;
+		$this->analyse([__DIR__ . '/data/bug-13023.php'], []);
+	}
+
 }
diff --git a/tests/PHPStan/Rules/Comparison/data/bug-13023.php b/tests/PHPStan/Rules/Comparison/data/bug-13023.php
new file mode 100644
index 0000000000..cba8bf0226
--- /dev/null
+++ b/tests/PHPStan/Rules/Comparison/data/bug-13023.php
@@ -0,0 +1,25 @@
+<?php declare(strict_types = 1);
+
+namespace Bug13023;
+
+class SomeClass
+{
+	use MyTrait;
+}
+
+class SomeClass2
+{
+	use MyTrait;
+}
+
+trait MyTrait
+{
+	public function getRandom(): int
+	{
+		$value = random_int(1, 100);
+		if (is_a($this, SomeClass::class)) {
+			return $value * $value;
+		}
+		return $value;
+	}
+}