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

- Added `isDimFetchAssign` property to VariableAssignNode to distinguish
  direct variable assignments from array dimension fetch assignments
- Set the flag to true in AssignHandler when processing ArrayDimFetch chains
- Updated InvalidVariableAssignRule to skip $this check for dim-fetch assigns
- New regression test in tests/PHPStan/Rules/Variables/data/bug-14352.php

Author: phpstan-bot

src/Analyser/ExprHandler/AssignHandler.php

@@ -463,7 +463,7 @@ public function processAssignVar(
 
 			if ($varType->isArray()->yes() || !(new ObjectType(ArrayAccess::class))->isSuperTypeOf($varType)->yes()) {
 				if ($var instanceof Variable && is_string($var->name)) {
-					$nodeScopeResolver->callNodeCallback($nodeCallback, new VariableAssignNode($var, new TypeExpr($valueToWrite)), $scopeBeforeAssignEval, $storage);
+					$nodeScopeResolver->callNodeCallback($nodeCallback, new VariableAssignNode($var, new TypeExpr($valueToWrite), true), $scopeBeforeAssignEval, $storage);
 					$scope = $scope->assignVariable($var->name, $valueToWrite, $nativeValueToWrite, TrinaryLogic::createYes());
 				} else {
 					if ($var instanceof PropertyFetch || $var instanceof StaticPropertyFetch) {
@@ -480,7 +480,7 @@ public function processAssignVar(
 				}
 			} else {
 				if ($var instanceof Variable) {
-					$nodeScopeResolver->callNodeCallback($nodeCallback, new VariableAssignNode($var, $assignedPropertyExpr), $scopeBeforeAssignEval, $storage);
+					$nodeScopeResolver->callNodeCallback($nodeCallback, new VariableAssignNode($var, $assignedPropertyExpr, true), $scopeBeforeAssignEval, $storage);
 				} elseif ($var instanceof PropertyFetch || $var instanceof StaticPropertyFetch) {
 					$nodeScopeResolver->callNodeCallback($nodeCallback, new PropertyAssignNode($var, $assignedPropertyExpr, $isAssignOp), $scopeBeforeAssignEval, $storage);
 					if ($var instanceof PropertyFetch && $var->name instanceof Node\Identifier && !$isAssignOp) {
@@ -799,7 +799,7 @@ public function processAssignVar(
 			}
 
 			if ($var instanceof Variable && is_string($var->name)) {
-				$nodeScopeResolver->callNodeCallback($nodeCallback, new VariableAssignNode($var, $assignedPropertyExpr), $scope, $storage);
+				$nodeScopeResolver->callNodeCallback($nodeCallback, new VariableAssignNode($var, $assignedPropertyExpr, true), $scope, $storage);
 				$scope = $scope->assignVariable($var->name, $valueToWrite, $nativeValueToWrite, TrinaryLogic::createYes());
 			} else {
 				if ($var instanceof PropertyFetch || $var instanceof StaticPropertyFetch) {

src/Node/VariableAssignNode.php

@@ -12,6 +12,7 @@ final class VariableAssignNode extends NodeAbstract implements VirtualNode
 	public function __construct(
 		private Expr\Variable $variable,
 		private Expr $assignedExpr,
+		private bool $isDimFetchAssign = false,
 	)
 	{
 		parent::__construct($variable->getAttributes());
@@ -27,6 +28,11 @@ public function getAssignedExpr(): Expr
 		return $this->assignedExpr;
 	}
 
+	public function isDimFetchAssign(): bool
+	{
+		return $this->isDimFetchAssign;
+	}
+
 	#[Override]
 	public function getType(): string
 	{

src/Rules/Variables/InvalidVariableAssignRule.php

@@ -29,7 +29,7 @@ public function processNode(Node $node, Scope $scope): array
 			return [];
 		}
 
-		if ($variable->name === 'this') {
+		if ($variable->name === 'this' && !$node->isDimFetchAssign()) {
 			return [
 				RuleErrorBuilder::message('Cannot re-assign $this.')
 					->identifier('assign.this')

tests/PHPStan/Rules/Variables/InvalidVariableAssignRuleTest.php

@@ -50,6 +50,11 @@ public function testBug3585(): void
 		]);
 	}
 
+	public function testBug14352(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-14352.php'], []);
+	}
+
 	public function testBug14349(): void
 	{
 		$this->analyse([__DIR__ . '/data/bug-14349.php'], [

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

@@ -0,0 +1,11 @@
+<?php declare(strict_types = 1);
+
+namespace Bug14352;
+
+class Test
+{
+	public function doFoo(string $key, string $value): void
+	{
+		$this[$key] = $value;
+	}
+}