From af67d361f206e448fdbb46683b0efa7b2ad25892 Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Tue, 10 Mar 2026 14:25:47 +0000
Subject: [PATCH] Fix arrow functions inheriting property type narrowings from
 parent scope

- Arrow functions inherited all expression types from the parent scope, including property narrowings from assignments (e.g. $this->prop = [])
- Closures correctly reset property types by building a fresh scope, but arrow functions did not
- Filter out non-readonly PropertyFetch narrowings in enterArrowFunctionWithoutReflection, matching closure behavior
- Fix TemplateTypeTrait to capture $this->default in a local variable before passing to arrow function
- New regression test in tests/PHPStan/Analyser/nsrt/bug-13563.php
---
 src/Analyser/MutatingScope.php            | 30 ++++++++++++-
 src/Type/Generic/TemplateTypeTrait.php    |  3 +-
 tests/PHPStan/Analyser/nsrt/bug-13563.php | 55 +++++++++++++++++++++++
 3 files changed, 85 insertions(+), 3 deletions(-)
 create mode 100644 tests/PHPStan/Analyser/nsrt/bug-13563.php

diff --git a/src/Analyser/MutatingScope.php b/src/Analyser/MutatingScope.php
index f1dfb1f0da..608de72386 100644
--- a/src/Analyser/MutatingScope.php
+++ b/src/Analyser/MutatingScope.php
@@ -2321,13 +2321,39 @@ public function enterArrowFunctionWithoutReflection(Expr\ArrowFunction $arrowFun
 			$arrowFunctionScope = $arrowFunctionScope->invalidateExpression(new Variable('this'));
 		}
 
+		$filteredExpressionTypes = $this->invalidateStaticExpressions($arrowFunctionScope->expressionTypes);
+		$filteredNativeExpressionTypes = $arrowFunctionScope->nativeExpressionTypes;
+
+		if (!$arrowFunction->static && $this->hasVariableType('this')->yes()) {
+			foreach ($filteredExpressionTypes as $exprString => $typeHolder) {
+				$expr = $typeHolder->getExpr();
+				if (!$expr instanceof PropertyFetch) {
+					continue;
+				}
+				if ($this->isReadonlyPropertyFetch($expr, true)) {
+					continue;
+				}
+				unset($filteredExpressionTypes[$exprString]);
+			}
+			foreach ($filteredNativeExpressionTypes as $exprString => $typeHolder) {
+				$expr = $typeHolder->getExpr();
+				if (!$expr instanceof PropertyFetch) {
+					continue;
+				}
+				if ($this->isReadonlyPropertyFetch($expr, true)) {
+					continue;
+				}
+				unset($filteredNativeExpressionTypes[$exprString]);
+			}
+		}
+
 		return $this->scopeFactory->create(
 			$arrowFunctionScope->context,
 			$this->isDeclareStrictTypes(),
 			$arrowFunctionScope->getFunction(),
 			$arrowFunctionScope->getNamespace(),
-			$this->invalidateStaticExpressions($arrowFunctionScope->expressionTypes),
-			$arrowFunctionScope->nativeExpressionTypes,
+			$filteredExpressionTypes,
+			$filteredNativeExpressionTypes,
 			$arrowFunctionScope->conditionalExpressions,
 			$arrowFunctionScope->inClosureBindScopeClasses,
 			new ClosureType(),
diff --git a/src/Type/Generic/TemplateTypeTrait.php b/src/Type/Generic/TemplateTypeTrait.php
index d823f9b20d..afba955ad2 100644
--- a/src/Type/Generic/TemplateTypeTrait.php
+++ b/src/Type/Generic/TemplateTypeTrait.php
@@ -74,7 +74,8 @@ public function describe(VerbosityLevel $level): string
 			}
 			$defaultDescription = '';
 			if ($this->default !== null) {
-				$recursionGuard = RecursionGuard::runOnObjectIdentity($this->default, fn () => $this->default->describe($level));
+				$default = $this->default;
+				$recursionGuard = RecursionGuard::runOnObjectIdentity($default, static fn () => $default->describe($level));
 				if (!$recursionGuard instanceof ErrorType) {
 					$defaultDescription .= sprintf(' = %s', $recursionGuard);
 				}
diff --git a/tests/PHPStan/Analyser/nsrt/bug-13563.php b/tests/PHPStan/Analyser/nsrt/bug-13563.php
new file mode 100644
index 0000000000..cf6d850900
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/bug-13563.php
@@ -0,0 +1,55 @@
+<?php declare(strict_types = 1);
+
+namespace Bug13563;
+
+use DateTime;
+use function PHPStan\Testing\assertType;
+
+class Invoker
+{
+	/**
+	 * @var array<string, \Closure>
+	 */
+	private array $callbacks = [];
+
+	public function willReturnCallback(string $method, callable $callback): void
+	{
+		$this->callbacks[$method] = \Closure::fromCallable($callback);
+	}
+}
+
+class MyTest
+{
+	/**
+	 * @var array<int, DateTime>
+	 */
+	private array $dates = [];
+
+	/**
+	 * @var array<int, DateTime>
+	 */
+	private array $propNotCleared = [];
+
+	public function setUp(): void
+	{
+		$invoker = new Invoker();
+		$this->dates = [];
+
+		assertType('array{}', $this->dates);
+
+		// Arrow function should see the declared property type, not the narrowed array{} type
+		$invoker->willReturnCallback('get', fn (int $id) => assertType('array<int, DateTime>', $this->dates));
+
+		// Closure correctly sees the declared property type
+		$invoker->willReturnCallback('get', function (int $id) {
+			assertType('array<int, DateTime>', $this->dates);
+		});
+
+		// Property not cleared - both should see the declared type
+		assertType('array<int, DateTime>', $this->propNotCleared);
+		$invoker->willReturnCallback('get', fn (int $id) => assertType('array<int, DateTime>', $this->propNotCleared));
+		$invoker->willReturnCallback('get', function (int $id) {
+			assertType('array<int, DateTime>', $this->propNotCleared);
+		});
+	}
+}