var_dump() may leak dumped value #19801

Description

The following code:

$a = [
    new class {
        function __debugInfo() {
            global $b;
            $b->a = null;
            gc_collect_cycles();
            return [];
        }
    },
];

$b = new stdClass;
$b->a = &$a;

var_dump($b);

Leaks $a here:

That's because GC_DELREF() decrements its refcount to zero without freeing it. When the array is in GC roots it may still end up being freed, but in this case GC roots are empty.

If GC_DELREF() decremented its refcount to a non-zero value, this would miss a potential garbage cycle as well.

Possibly, debug_zval_dump() and var_export() have the same issue.

PHP Version

master

Operating System

No response