[Serializer] Support multiple levels of discriminator mapping

[jeroennoten]

Q	A
Branch?	4.4
Bug fix?	yes
New feature?	no
Deprecations?	no
License	MIT

When using multiple levels of discriminator mapping for denormalizing to a multiple level class hierarchy, only the top level discriminator mapping is considered, resulting in an error: Cannot instantiate abstract class ...

Example:

/**
 * @DiscriminatorMap(typeProperty="type", mapping={"group"=GroupNode::class, "item"=ItemNode::class})
 */
abstract class Node {
    // ...
}

class GroupNode extends Node {
    // ...
}

/**
 * @DiscriminatorMap(typeProperty="item_type", mapping={"foo"=FooItemNode::class, "bar"=BarItemNode::class})
 */
abstract class ItemNode extends Node {
    // ...
}

class FooItemNode {
    // ...
}

class BarItemNode {
    // ...
}

$objectNormalizer = new ObjectNormalizer(new ClassMetadataFactory(new AnnotationLoader(new AnnotationReader())));
$node = $objectNormalizer->denormalize(['type' => 'item', 'item_type' => 'foo']);

This results in an error: Cannot instantiate abstract class ItemNode. Expected is that $node is of type FooItemNode after denormalization.

The solution is to recursively call AbstractObjectNormalizer::instantiateObject() when a mapping is found, instead of always calling parent::instantiateObject().

[fabpot]

Thank you @jeroennoten.