Cloning an object breaks serialization recursion

[azuradara]

Description

Overview

Starting from 8.1.0 cloning recursive objects inline when calling serialize() breaks the serialization recursion. For example:

serialize(clone $obj);

However, assigning the clone to a variable and then passing it to the serialize() function will not break.

$clone = clone $obj;

serialize($clone);

Additionally, there is some undefined behavior related to defining an "instance" property on the object and assigning the object's instance to it within the __clone() magic method which somehow fixes everything. Not sure about this part, but this is the only way I got it to work consistently in my usecase.

Here's a 3v4l link: https://3v4l.org/6FKnp#v810

Reproduction

The following code:

Click to expand codeblock

<?php

class A {
    public B|C $x;
    
    public function __construct(B|C $x) {
        $this->x = $x;
    }
    
    public function __sleep()
    {
        return ['x'];
    }
}

class B {
    public A $a;
    
    public function __serialize()
    {
        return ['a' => new A($this)];
    }
}

class C {
    public A $a;
    private self $instance;
    
    public function __serialize()
    {
        return ['a' => new A($this)];
    }
    
    public function __clone() {
        $this->instance = $this;
    }
}

// instantiate
$b = new B();
$c = new C();

// clone and assign
$ib = clone $b;
$ic = clone $c;

// serialize
$sb = serialize($b);
$scb = serialize(clone $b);
$sib = serialize($ib);

$sc = serialize($c);
$scc = serialize(clone $c);
$sic = serialize($ic);

// unserialize
$ub = unserialize($sb);
$ucb = unserialize($scb);
$uib = unserialize($sib);

$uc = unserialize($sc);
$ucc = unserialize($scc);
$uic = unserialize($sic);


// expected behavior is b == b->a->x
printf("original ids:          b:%s, b->a:%s, b->a->x:%s \n", spl_object_id($ub), spl_object_id($ub->a), spl_object_id($ub->a->x));
printf("cloned ids:            b:%s, b->a:%s, b->a->x:%s \n", spl_object_id($ucb), spl_object_id($ucb->a), spl_object_id($ucb->a->x));
printf("cloned & assigned ids: b:%s, b->a:%s, b->a->x:%s \n", spl_object_id($uib), spl_object_id($uib->a), spl_object_id($uib->a->x));

printf(PHP_EOL);


// expected behavior is c == c->a->x
printf("original ids:          c:%s, c->a:%s, c->a->x:%s \n", spl_object_id($uc), spl_object_id($uc->a), spl_object_id($uc->a->x));
printf("cloned ids:            c:%s, c->a:%s, c->a->x:%s \n", spl_object_id($ucc), spl_object_id($ucc->a), spl_object_id($ucc->a->x));
printf("cloned & assigned ids: c:%s, c->a:%s, c->a->x:%s \n", spl_object_id($uic), spl_object_id($uic->a), spl_object_id($uic->a->x));

printf(PHP_EOL);

printf("serialized original:    %s\n", $sb);
printf("serialized clone   :    %s\n", $scb);

?>

Outputs this:

original ids:          b:6, b->a:7, b->a->x:6 
cloned ids:            b:8, b->a:9, b->a->x:10 
cloned & assigned ids: b:12, b->a:13, b->a->x:12 

original ids:          c:14, c->a:15, c->a->x:14 
cloned ids:            c:16, c->a:17, c->a->x:16 
cloned & assigned ids: c:18, c->a:19, c->a->x:18 

serialized original:    O:1:"B":1:{s:1:"a";O:1:"A":1:{s:1:"x";r:1;}}
serialized clone   :    O:1:"B":1:{s:1:"a";O:1:"A":1:{s:1:"x";O:1:"B":1:{s:1:"a";O:1:"A":1:{s:1:"x";r:3;}}}}

But I expected this output instead:

original ids:          b:6, b->a:7, b->a->x:6 
cloned ids:            b:8, b->a:9, b->a->x:8 
cloned & assigned ids: b:10, b->a:11, b->a->x:10 

original ids:          c:12, c->a:13, c->a->x:12 
cloned ids:            c:14, c->a:15, c->a->x:14 
cloned & assigned ids: c:16, c->a:17, c->a->x:16 

serialized original:    O:1:"B":1:{s:1:"a";O:1:"A":1:{s:1:"x";r:1;}}
serialized clone   :    O:1:"B":1:{s:1:"a";O:1:"A":1:{s:1:"x";r:1;}}

PHP Version

8.2.0

Operating System

Debian 12

[nielsdos]

Can confirm in 8.1+, broke in 6c5942f