<?php

$loader = require __DIR__.'/vendor/autoload.php';

use Doctrine\Common\Annotations\AnnotationReader;
use Doctrine\Common\Annotations\AnnotationRegistry;
use Symfony\Component\Serializer\Annotation\MaxDepth;
use Symfony\Component\Serializer\Normalizer\ObjectNormalizer;
use Symfony\Component\Serializer\Serializer;
use Symfony\Component\Serializer\Mapping\Loader\AnnotationLoader;
use Symfony\Component\Serializer\Mapping\Factory\ClassMetadataFactory;

AnnotationRegistry::registerLoader([$loader, 'loadClass']);

class MyObj
{
    public $foo;

    /**
     * @var self
     *
     * @MaxDepth(2)
     */
    public $child;
}

$classMetadataFactory = new ClassMetadataFactory(new AnnotationLoader(new AnnotationReader()));
$normalizer = new ObjectNormalizer($classMetadataFactory);
$serializer = new Serializer(array($normalizer));

$level1 = new MyObj();
$level1->foo = 'level1';

$level2 = new MyObj();
$level2->foo = 'level2';
$level1->child = $level2;

$level3 = new MyObj();
$level3->foo = 'level3';
$level2->child = $level3;

$level4 = new MyObj();
$level4->foo = 'level4';
$level3->child = $level4;

$level5 = new MyObj();
$level5->foo = 'level5';
$level4->child = $level5;

$result = $serializer->normalize($level1, null, array(ObjectNormalizer::ENABLE_MAX_DEPTH => true));

dump($result);

array:2 [
  "foo" => "level1"
  "child" => array:2 [
    "foo" => "level2"
    "child" => array:1 [
      "foo" => "level3"
    ]
  ]
]