Use dimFetch flag and check $this type with !->no() for ArrayAccess reassignment

Instead of checking the assigned expression type, use a dimFetch flag on
VariableAssignNode to distinguish $this[$key] = $value from $this = $value.
Check $this type with !->no() so non-final classes that might implement
ArrayAccess through subclasses are not falsely reported.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

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 $dimFetch = false,
 	)
 	{
 		parent::__construct($variable->getAttributes());
@@ -27,6 +28,11 @@ public function getAssignedExpr(): Expr
 		return $this->assignedExpr;
 	}
 
+	public function isDimFetch(): bool
+	{
+		return $this->dimFetch;
+	}
+
 	#[Override]
 	public function getType(): string
 	{

src/Rules/Variables/InvalidVariableAssignRule.php

@@ -32,10 +32,7 @@ public function processNode(Node $node, Scope $scope): array
 		}
 
 		if ($variable->name === 'this') {
-			$expr = $node->getAssignedExpr();
-			$type = $scope->getType($expr);
-
-			if ((new ObjectType(ArrayAccess::class))->isSuperTypeOf($type)->yes()) {
+			if ($node->isDimFetch() && !(new ObjectType(ArrayAccess::class))->isSuperTypeOf($scope->getType($variable))->no()) {
 				return [];
 			}
 

tests/PHPStan/Rules/Variables/InvalidVariableAssignRuleTest.php

@@ -63,6 +63,10 @@ public function testBug14352(): void
 				'Cannot re-assign $this.',
 				37,
 			],
+			[
+				'Cannot re-assign $this.',
+				61,
+			],
 		]);
 	}
 

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

@@ -30,6 +30,30 @@ public function offsetUnset(mixed $offset): void
 	}
 }
 
+class TestArrayAccessReassign implements ArrayAccess
+{
+	public function doFoo(self $other): void
+	{
+		$this = $other; // 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