From 579d38f602071c3da20f28a598a087ce70beab7f Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Sat, 28 Feb 2026 14:50:56 +0000
Subject: [PATCH] Fix bogus write-only error when appending to ArrayAccess
 property

- In ClassStatementsGatherer, also record a PropertyRead when a PropertyAssignNode
  is for an ArrayAccess property via array dim fetch (e.g. $this->array[] = $s),
  because this is semantically $this->array->offsetSet() which reads the property
- New regression test in tests/PHPStan/Rules/DeadCode/data/bug-6777.php
- Updated existing WriteToCollection test expectations

Closes https://github.com/phpstan/phpstan/issues/6777
---
 src/Node/ClassStatementsGatherer.php          | 16 +++++++++++++++-
 .../UnusedPrivatePropertyRuleTest.php         | 19 +++++++++----------
 .../PHPStan/Rules/DeadCode/data/bug-6777.php  | 15 +++++++++++++++
 3 files changed, 39 insertions(+), 11 deletions(-)
 create mode 100644 tests/PHPStan/Rules/DeadCode/data/bug-6777.php

diff --git a/src/Node/ClassStatementsGatherer.php b/src/Node/ClassStatementsGatherer.php
index a2bb6889d5..663d8c4e0d 100644
--- a/src/Node/ClassStatementsGatherer.php
+++ b/src/Node/ClassStatementsGatherer.php
@@ -13,11 +13,14 @@
 use PhpParser\Node\Identifier;
 use PHPStan\Analyser\Scope;
 use PHPStan\Node\Constant\ClassConstantFetch;
+use PHPStan\Node\Expr\SetExistingOffsetValueTypeExpr;
+use PHPStan\Node\Expr\SetOffsetValueTypeExpr;
 use PHPStan\Node\Property\PropertyAssign;
 use PHPStan\Node\Property\PropertyRead;
 use PHPStan\Node\Property\PropertyWrite;
 use PHPStan\Reflection\ClassReflection;
 use PHPStan\ShouldNotHappenException;
+use PHPStan\Type\ObjectType;
 use PHPStan\Type\TypeUtils;
 use ReflectionProperty;
 use function count;
@@ -200,7 +203,18 @@ private function gatherNodes(Node $node, Scope $scope): void
 			return;
 		}
 		if ($node instanceof PropertyAssignNode) {
-			$this->propertyUsages[] = new PropertyWrite($node->getPropertyFetch(), $scope, false);
+			$propertyFetch = $node->getPropertyFetch();
+			$assignedExpr = $node->getAssignedExpr();
+			if ($assignedExpr instanceof SetOffsetValueTypeExpr || $assignedExpr instanceof SetExistingOffsetValueTypeExpr) {
+				$propertyType = $scope->getType($propertyFetch);
+				if (
+					!$propertyType->isArray()->yes()
+					&& (new ObjectType(\ArrayAccess::class))->isSuperTypeOf($propertyType)->yes()
+				) {
+					$this->propertyUsages[] = new PropertyRead($propertyFetch, $scope);
+				}
+			}
+			$this->propertyUsages[] = new PropertyWrite($propertyFetch, $scope, false);
 			$this->propertyAssigns[] = new PropertyAssign($node, $scope);
 			return;
 		}
diff --git a/tests/PHPStan/Rules/DeadCode/UnusedPrivatePropertyRuleTest.php b/tests/PHPStan/Rules/DeadCode/UnusedPrivatePropertyRuleTest.php
index 199e22d1a2..6cc5e5e230 100644
--- a/tests/PHPStan/Rules/DeadCode/UnusedPrivatePropertyRuleTest.php
+++ b/tests/PHPStan/Rules/DeadCode/UnusedPrivatePropertyRuleTest.php
@@ -130,16 +130,6 @@ public function testRule(): void
 				191,
 				$tip,
 			],
-			[
-				'Property UnusedPrivateProperty\WriteToCollection::$collection1 is never read, only written.',
-				221,
-				$tip,
-			],
-			[
-				'Property UnusedPrivateProperty\WriteToCollection::$collection2 is never read, only written.',
-				224,
-				$tip,
-			],
 		]);
 		$this->analyse([__DIR__ . '/data/TestExtension.php'], [
 			[
@@ -410,4 +400,13 @@ public function testBug9213(): void
 		$this->analyse([__DIR__ . '/data/bug-9213.php'], []);
 	}
 
+	#[RequiresPhp('>= 8.0')]
+	public function testBug6777(): void
+	{
+		$this->alwaysWrittenTags = [];
+		$this->alwaysReadTags = [];
+
+		$this->analyse([__DIR__ . '/data/bug-6777.php'], []);
+	}
+
 }
diff --git a/tests/PHPStan/Rules/DeadCode/data/bug-6777.php b/tests/PHPStan/Rules/DeadCode/data/bug-6777.php
new file mode 100644
index 0000000000..0e24d4eced
--- /dev/null
+++ b/tests/PHPStan/Rules/DeadCode/data/bug-6777.php
@@ -0,0 +1,15 @@
+<?php // lint >= 8.0
+
+declare(strict_types = 1);
+
+namespace Bug6777;
+
+class HelloWorld
+{
+	/** @param \ArrayObject<int, string> $array */
+	public function __construct(private \ArrayObject $array){}
+
+	public function send(string $s) : void{
+		$this->array[] = $s;
+	}
+}