`unserialize` doesn't respect `class_alias` for properties

Description

The following code:

<?php // serialize.php

class Hello {
    public function __construct (
        private readonly int $answer
    ) {}
}

$x = serialize(new Hello(42));
file_put_contents('serialized.bin', $x);

<?php // unserialize.php
class HelloAlias {
    public function __construct (
       public readonly int $answer
    ) {}
}

class_alias(HelloAlias::class, 'Hello');

$x = file_get_contents('serialized.bin');
$z = unserialize($x);
var_dump($z->answer);

Resulted in this output:

PHP Deprecated:  Creation of dynamic property HelloAlias::$answer is deprecated in unserialize-bug/unserialize.php on line 12

Fatal error: Uncaught Error: Typed property HelloAlias::$answer must not be accessed before initialization in unserialize-bug/unserialize.php:13
Stack trace:
#0 {main}
  thrown in unserialize-bug/unserialize.php on line 13

But I expected this output instead:

int(42)

If I look at the serialized.bin file, I can see that for the variable "answer", there is {s:13:"�Hello�answer";i:42;} stored (containing the class without alias).

When I add debug for __unserialize

public function __unserialize (array $arr): void {
    var_dump($arr);
}

I will get this output. The Helloanswer is actually \0Hello\0answer

➜  unserialize-bug php unserialize.php
array(1) {
  ["Helloanswer"]=>
  int(42)
}

Using this naiive fix will work, but is really ugly:

public function __unserialize (array $arr): void {
    foreach ($arr as $k => $v) {
        $key = str_replace("\0Hello\0", '', $k);
        $this->$key = $v;
    }
}

PHP Version

➜  php -v
PHP 8.3.20 (cli) (built: Apr  8 2025 20:21:18) (NTS)
Copyright (c) The PHP Group
Zend Engine v4.3.20, Copyright (c) Zend Technologies
    with Zend OPcache v8.3.20, Copyright (c), by Zend Technologies

Operating System

No response

まず、提供されている serialize.php と unserialize.php スクリプトを PHP 8.3.20 で実行し、次に serialized.bin と __unserialize のデバッグ出力を調べて、エイリアスされたプロパティ名がどのように表現されているかを追跡します。再現ケースが動的プロパティを作成せず、型付きプロパティを未初期化のままにすることもなく、int(42) を返せば完了です。