[Serializer] Add a MaxDepth handler

src/Symfony/Bundle/FrameworkBundle/DependencyInjection/Configuration.php

@@ -731,6 +731,7 @@ class Configuration implements ConfigurationInterface
                         ->booleanNode('enable_annotations')->{!class_exists(FullStack::class) && class_exists(Annotation::class) ? 'defaultTrue' : 'defaultFalse'}()->end()
                         ->scalarNode('name_converter')->end()
                         ->scalarNode('circular_reference_handler')->end()
+                        ->scalarNode('max_depth_handler')->end()
                         ->arrayNode('mapping')
                             ->addDefaultsIfNotSet()
                             ->fixXmlConfig('path')

src/Symfony/Bundle/FrameworkBundle/DependencyInjection/FrameworkExtension.php

@@ -1273,6 +1273,10 @@ class FrameworkExtension extends Extension
         if (isset($config['circular_reference_handler']) && $config['circular_reference_handler']) {
             $container->getDefinition('serializer.normalizer.object')->addMethodCall('setCircularReferenceHandler', array(new Reference($config['circular_reference_handler'])));
         }
+
+        if ($config['max_depth_handler'] ?? false) {
+            $container->getDefinition('serializer.normalizer.object')->addMethodCall('setMaxDepthHandler', array(new Reference($config['max_depth_handler'])));
+        }
     }
 
     private function registerPropertyInfoConfiguration(array $config, ContainerBuilder $container, XmlFileLoader $loader)

src/Symfony/Bundle/FrameworkBundle/Resources/config/schema/symfony-1.0.xsd

@@ -239,6 +239,7 @@
         <xsd:attribute name="cache" type="xsd:string" />
         <xsd:attribute name="enable-annotations" type="xsd:boolean" />
         <xsd:attribute name="name-converter" type="xsd:string" />
+        <xsd:attribute name="max-depth-handler" type="xsd:string" />
     </xsd:complexType>
 
     <xsd:complexType name="property_info">

src/Symfony/Bundle/FrameworkBundle/Tests/DependencyInjection/Fixtures/php/full.php

@@ -68,6 +68,7 @@ $container->loadFromExtension('framework', array(
         'enabled' => true,
         'enable_annotations' => true,
         'name_converter' => 'serializer.name_converter.camel_case_to_snake_case',
+        'max_depth_handler' => 'my.max.depth.handler',
     ),
     'property_info' => true,
     'ide' => 'file%%link%%format',

src/Symfony/Bundle/FrameworkBundle/Tests/DependencyInjection/Fixtures/xml/full.xml

@@ -41,7 +41,7 @@
         </framework:translator>
         <framework:validation enabled="true" />
         <framework:annotations cache="file" debug="true" file-cache-dir="%kernel.cache_dir%/annotations" />
-        <framework:serializer enabled="true" enable-annotations="true" name-converter="serializer.name_converter.camel_case_to_snake_case" />
+        <framework:serializer enabled="true" enable-annotations="true" name-converter="serializer.name_converter.camel_case_to_snake_case" max-depth-handler="my.max.depth.handler" />
         <framework:property-info />
     </framework:config>
 </container>

src/Symfony/Bundle/FrameworkBundle/Tests/DependencyInjection/Fixtures/yml/full.yml

@@ -54,6 +54,7 @@ framework:
          enabled:        true
          enable_annotations: true
          name_converter: serializer.name_converter.camel_case_to_snake_case
+         max_depth_handler: my.max.depth.handler
     property_info: ~
     ide: file%%link%%format
     request:

src/Symfony/Bundle/FrameworkBundle/Tests/DependencyInjection/FrameworkExtensionTest.php

@@ -804,6 +804,7 @@ abstract class FrameworkExtensionTest extends TestCase
         $this->assertNull($container->getDefinition('serializer.mapping.class_metadata_factory')->getArgument(1));
         $this->assertEquals(new Reference('serializer.name_converter.camel_case_to_snake_case'), $container->getDefinition('serializer.normalizer.object')->getArgument(1));
         $this->assertEquals(new Reference('property_info', ContainerBuilder::IGNORE_ON_INVALID_REFERENCE), $container->getDefinition('serializer.normalizer.object')->getArgument(3));
+        $this->assertEquals(array('setMaxDepthHandler', array(new Reference('my.max.depth.handler'))), $container->getDefinition('serializer.normalizer.object')->getMethodCalls()[0]);
     }
 
     public function testRegisterSerializerExtractor()

src/Symfony/Component/Serializer/CHANGELOG.md

@@ -9,6 +9,8 @@ CHANGELOG
 * added an optional `default_constructor_arguments` option of context to specify a default data in
   case the object is not initializable by its constructor because of data missing
 * added optional `bool $escapeFormulas = false` argument to `CsvEncoder::__construct`
+* added `AbstractObjectNormalizer::setMaxDepthHandler` to set a handler to call when the configured
+  maximum depth is reached
 
 4.0.0
 -----

src/Symfony/Component/Serializer/Normalizer/AbstractObjectNormalizer.php

@@ -41,6 +41,11 @@ abstract class AbstractObjectNormalizer extends AbstractNormalizer
     private $attributesCache = array();
     private $cache = array();
 
+    /**
+     * @var callable|null
+     */
+    private $maxDepthHandler;
+
     /**
      * @var ClassDiscriminatorResolverInterface|null
      */
@@ -86,11 +91,15 @@ abstract class AbstractObjectNormalizer extends AbstractNormalizer
         $attributesMetadata = $this->classMetadataFactory ? $this->classMetadataFactory->getMetadataFor($class)->getAttributesMetadata() : null;
 
         foreach ($attributes as $attribute) {
-            if (null !== $attributesMetadata && $this->isMaxDepthReached($attributesMetadata, $class, $attribute, $context)) {
+            $maxDepthReached = false;
+            if (null !== $attributesMetadata && ($maxDepthReached = $this->isMaxDepthReached($attributesMetadata, $class, $attribute, $context)) && !$this->maxDepthHandler) {
                 continue;
             }
 
             $attributeValue = $this->getAttributeValue($object, $attribute, $format, $context);
+            if ($maxDepthReached) {
+                $attributeValue = \call_user_func($this->maxDepthHandler, $attributeValue);
+            }
 
             if (isset($this->callbacks[$attribute])) {
                 $attributeValue = call_user_func($this->callbacks[$attribute], $attributeValue);
@@ -204,6 +213,14 @@ abstract class AbstractObjectNormalizer extends AbstractNormalizer
      */
     abstract protected function getAttributeValue($object, $attribute, $format = null, array $context = array());
 
+    /**
+     * Sets an handler function that will be called when the max depth is reached.
+     */
+    public function setMaxDepthHandler(?callable $handler): void
+    {
+        $this->maxDepthHandler = $handler;
+    }
+
     /**
      * {@inheritdoc}
      */

src/Symfony/Component/Serializer/Tests/Normalizer/ObjectNormalizerTest.php

@@ -613,6 +613,27 @@ class ObjectNormalizerTest extends TestCase
         );
 
         $this->assertEquals($expected, $result);
+
+        $expected = array(
+            'bar' => null,
+            'foo' => 'level1',
+            'child' => array(
+                'bar' => null,
+                'foo' => 'level2',
+                'child' => array(
+                    'bar' => null,
+                    'child' => null,
+                    'foo' => 'handler',
+                ),
+            ),
+        );
+
+        $this->normalizer->setMaxDepthHandler(function ($obj) {
+            return 'handler';
+        });
+
+        $result = $serializer->normalize($level1, null, array(ObjectNormalizer::ENABLE_MAX_DEPTH => true));
+        $this->assertEquals($expected, $result);
     }
 
     /**