[Serializer] Add a MaxDepth handler

Author: dunglas

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
 -----

Normalizer/AbstractObjectNormalizer.php

@@ -41,6 +41,11 @@ abstract class AbstractObjectNormalizer extends AbstractNormalizer
     private $attributesCache = array();
     private $cache = array();
 
+    /**
+     * @var callable|null
+     */
+    private $maxDepthHandler;
+
     /**
      * @var ClassDiscriminatorResolverInterface|null
      */
@@ -86,11 +91,15 @@ public function normalize($object, $format = null, array $context = array())
         $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], $attributeValue);
@@ -204,6 +213,14 @@ abstract protected function extractAttributes($object, $format = null, array $co
      */
     abstract protected function getAttributeValue($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}
      */

Tests/Normalizer/ObjectNormalizerTest.php

@@ -613,6 +613,27 @@ public function testMaxDepth()
         );
 
         $this->assertEquals($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);
     }
 
     /**