From 32f6952bbe46d5387769838541d98ebbc0b11a96 Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Fri, 27 Feb 2026 17:16:37 +0000
Subject: [PATCH] Fix false positives for is_a() and similar checks on $this
 inside traits

- In ImpossibleCheckTypeHelper::findSpecifiedType(), treat class-specific type
  checks on $this as uncertain when inside a trait, since $this is polymorphic
  across the different classes that use the trait
- Added isThis() helper method for detecting $this expression references
- New regression test in tests/PHPStan/Rules/Comparison/data/bug-13023.php

Closes https://github.com/phpstan/phpstan/issues/13023
---
 .../Comparison/ImpossibleCheckTypeHelper.php  | 16 ++++++++++++
 ...mpossibleCheckTypeFunctionCallRuleTest.php |  6 +++++
 .../Rules/Comparison/data/bug-13023.php       | 25 +++++++++++++++++++
 3 files changed, 47 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 1ebe569289..052a8feefb 100644
--- a/src/Rules/Comparison/ImpossibleCheckTypeHelper.php
+++ b/src/Rules/Comparison/ImpossibleCheckTypeHelper.php
@@ -299,6 +299,7 @@ public function findSpecifiedType(
 				}
 			}
 		}
+		$isInTrait = $scope->isInTrait();
 		foreach ($sureTypes as $sureType) {
 			if (self::isSpecified($typeSpecifierScope, $node, $sureType[0])) {
 				$results[] = TrinaryLogic::createMaybe();
@@ -322,6 +323,11 @@ public function findSpecifiedType(
 				$argumentType = $scope->getType($assignedInCallVar->expr);
 			}
 
+			if ($isInTrait && self::isThis($sureType[0]) && $resultType->getObjectClassNames() !== []) {
+				$results[] = TrinaryLogic::createMaybe();
+				continue;
+			}
+
 			$results[] = $resultType->isSuperTypeOf($argumentType)->result;
 		}
 
@@ -340,6 +346,11 @@ public function findSpecifiedType(
 			/** @var Type $resultType */
 			$resultType = $sureNotType[1];
 
+			if ($isInTrait && self::isThis($sureNotType[0]) && $resultType->getObjectClassNames() !== []) {
+				$results[] = TrinaryLogic::createMaybe();
+				continue;
+			}
+
 			$results[] = $resultType->isSuperTypeOf($argumentType)->negate()->result;
 		}
 
@@ -376,6 +387,11 @@ private static function isSpecified(Scope $scope, Expr $node, Expr $expr): bool
 		) && $scope->hasExpressionType($expr)->yes();
 	}
 
+	private static function isThis(Expr $expr): bool
+	{
+		return $expr instanceof Expr\Variable && $expr->name === 'this';
+	}
+
 	/**
 	 * @param Node\Arg[] $args
 	 */
diff --git a/tests/PHPStan/Rules/Comparison/ImpossibleCheckTypeFunctionCallRuleTest.php b/tests/PHPStan/Rules/Comparison/ImpossibleCheckTypeFunctionCallRuleTest.php
index 0a399fdc3c..535e7e945d 100644
--- a/tests/PHPStan/Rules/Comparison/ImpossibleCheckTypeFunctionCallRuleTest.php
+++ b/tests/PHPStan/Rules/Comparison/ImpossibleCheckTypeFunctionCallRuleTest.php
@@ -1179,4 +1179,10 @@ public function testBug14177(): void
 		$this->analyse([__DIR__ . '/data/bug-14177.php'], []);
 	}
 
+	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..dae307df47
--- /dev/null
+++ b/tests/PHPStan/Rules/Comparison/data/bug-13023.php
@@ -0,0 +1,25 @@
+<?php
+
+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;
+	}
+}