[php-src] Issue #11205: Serialization issue with parent class and missing __serialize() method

Issue: https://github.com/php/php-src/issues/11205 Author: SoftCreatR ### Description This issue likely is both a bug report and a feature request, because it appears to be an oversight: For a class extending an abstract class that is not under my control I needed to control the serialization format to “flush” a “cache property” either when serializing or unserializing the class. I wanted to implement this using the recommended __serialize() and __unserialize() hooks. Unfortunately the abstract parent class does not implement these methods and it also contains important private properties that need to be preserved. As these properties are private, I cannot access those in my child class and neither should I need to know about their existence. However by implementing __serialize() and __unserialize() those private properties will not be preserved and reset to their default value. An example is showcased in https://3v4l.org/Qdkcs and also included below: ```php <?php class P { private int $someProp = 0; public function setProp(int $value): void { $this->someProp = $value; } } class C extends P { private array $cache = []; private int $someOtherProp; public function __construct(int $value) { $this->someOtherProp = $value; } public function fillCache(): void { $this->cache[] = 'value'; } public function __serialize(): array { return [ 'someOtherProp' => $this->someOtherProp ]; } public function __unserialize(array $data): void { $this->someOtherProp = $data['someOtherProp']; $this->cache = []; } } $c = new C(7); $c->setProp(5); $c->fillCache(); var_dump($c); var_dump($s = serialize($c)); var_dump(unserialize($s)); ?> ``` Should private properties of parent classes be implicitly preserved or a default implementation of __serialize() be generated that I can call in my child class? ### PHP Version 8.1.18 ### Operating System Ubuntu 22.04