[Serializer] Add support for extending stdClass objects

[template-provider]

Symfony version(s) affected

6.4

Description

The serialize and unserialize for stdClass works because of this code in the class ObjectNormalizer + method extractAttributes

        if (\stdClass::class === $object::class) {
            return array_keys((array) $object);
        }

but this code does not check for classes, that are extending stdClass.

How to reproduce

<?php

declare(strict_types = 1);

use stdClass;

class Contact extends stdClass
{
    public string $email = '';
}

        $encoders = [new JsonEncoder()];

        $classMetadataFactory = new ClassMetadataFactory(new AttributeLoader());
        $metadataAwareNameConverter = new MetadataAwareNameConverter($classMetadataFactory);
        $extractor = new PropertyInfoExtractor([], [new PhpDocExtractor(), new ReflectionExtractor()]);

        $objectNormalizer =  new ObjectNormalizer(
            classMetadataFactory: $classMetadataFactory,
            nameConverter: $metadataAwareNameConverter,
            propertyTypeExtractor: $extractor,
            defaultContext: [
                AbstractObjectNormalizer::SKIP_UNINITIALIZED_VALUES => true,
                AbstractObjectNormalizer::SKIP_NULL_VALUES => true,
                AbstractObjectNormalizer::DISABLE_TYPE_ENFORCEMENT => true,
            ],
        );

        $normalizers = [
            $objectNormalizer,
        ];

        $serializer = new Serializer($normalizers, $encoders)

$contact = new Contact();
$contact->email = 'foo@example.com';
$contact->foo = 'bar';

$serializer->serialize($contact, 'json')

Possible Solution

Better would be some additional code like this:

        $classParents = class_parents($object::class);
        if (false !== $classParents && in_array(\stdClass::class, $classParents)) {
            return array_keys((array) $object);
        }

Additional Context

No response

[alexandre-daubois]

What about classes extending stdClass and also defining other properties, public or not, with getters/setters? Just casting the object with as it is done with stdClass wouldn't fully work, isn't it?

[template-provider]

I am not 100 percent sure what you mean. A getter/setter does not change anything for unknown properties during serialize/unserialize. The only possible solution would be magic getters/setters to set the unknown property.
But I have not tested it yet and do not even know if symfony serializer works with __get and __set.
Could you provide an example what you mean plz?

[template-provider]

And as described above the problem is in unserialize to. In this case the following lines:
https://github.com/symfony/property-access/blob/7.0/PropertyAccessor.php#L525

            } elseif ($object instanceof \stdClass && property_exists($object, $property)) {
                $object->$property = $value;
            } elseif (!$this->ignoreInvalidProperty) {

The property_exists might not be needed imho. "} elseif ($object instanceof \stdClass) {" works