Fix phpstan/phpstan#14352: "Cannot re-assign $this." false-positive (#5281)

Author: phpstan-bot

Makefile

@@ -134,6 +134,7 @@ lint:
 		--exclude tests/PHPStan/Rules/EnumCases/data/bug-14252.php \
 		--exclude tests/PHPStan/Rules/Functions/data/bug-14241.php \
 		--exclude tests/PHPStan/Rules/Variables/data/bug-14349.php \
+		--exclude tests/PHPStan/Rules/Variables/data/bug-14352.php \
 		src tests
 
 install-paratest:

src/Rules/Variables/InvalidVariableAssignRule.php

@@ -2,6 +2,7 @@
 
 namespace PHPStan\Rules\Variables;
 
+use ArrayAccess;
 use PhpParser\Node;
 use PHPStan\Analyser\Scope;
 use PHPStan\DependencyInjection\RegisteredRule;
@@ -30,6 +31,14 @@ public function processNode(Node $node, Scope $scope): array
 		}
 
 		if ($variable->name === 'this') {
+			if ($scope->isInClass()) {
+				$classReflection = $scope->getClassReflection();
+
+				if ($classReflection->implementsInterface(ArrayAccess::class)) {
+					return [];
+				}
+			}
+
 			return [
 				RuleErrorBuilder::message('Cannot re-assign $this.')
 					->identifier('assign.this')

tests/PHPStan/Rules/Variables/InvalidVariableAssignRuleTest.php

@@ -4,6 +4,7 @@
 
 use PHPStan\Rules\Rule;
 use PHPStan\Testing\RuleTestCase;
+use PHPUnit\Framework\Attributes\RequiresPhp;
 
 /**
  * @extends RuleTestCase<InvalidVariableAssignRule>
@@ -50,6 +51,43 @@ public function testBug3585(): void
 		]);
 	}
 
+	#[RequiresPhp('>= 8.0')]
+	public function testBug14352(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-14352.php'], [
+			/*
+			[
+				'Cannot re-assign $this.',
+				13,
+			],
+			*/
+			[
+				'Cannot re-assign $this.',
+				37,
+			],
+			[
+				'Cannot re-assign $this.',
+				39,
+			],
+			[
+				'Cannot re-assign $this.',
+				47,
+			],
+			[
+				'Cannot re-assign $this.',
+				49,
+			],
+			[
+				'Cannot re-assign $this.',
+				57,
+			],
+			[
+				'Cannot re-assign $this.',
+				63,
+			],
+		]);
+	}
+
 	public function testBug14349(): void
 	{
 		$this->analyse([__DIR__ . '/data/bug-14349.php'], [

tests/PHPStan/Rules/Variables/data/bug-14352.php

@@ -0,0 +1,64 @@
+<?php declare(strict_types = 1);
+
+namespace Bug14352;
+
+use ArrayAccess;
+
+class TestArrayAccess implements ArrayAccess
+{
+	public function doFoo(string $key, string $value): void
+	{
+		$this[$key] = $value; // fine because ArrayAccess
+
+		$this = $value; // should still fail
+	}
+
+	public function offsetExists(mixed $offset): bool
+	{
+	}
+
+	public function offsetGet(mixed $offset): mixed
+	{
+	}
+
+	public function offsetSet(mixed $offset, mixed $value): void
+	{
+	}
+
+	public function offsetUnset(mixed $offset): void
+	{
+	}
+}
+
+final class FinalTestPlain
+{
+	public function doFoo(string $key, string $value): void
+	{
+		$this[$key] = $value;
+
+		$this = $value;
+	}
+}
+
+class TestPlain
+{
+	public function doFoo(string $key, string $value): void
+	{
+		$this[$key] = $value;
+
+		$this = $value;
+	}
+}
+
+class TestStatic
+{
+	static public function doFoo(string $value): void
+	{
+		$this = $value;
+	}
+}
+
+function doFoo(string $value): void
+{
+	$this = $value;
+}