fix(serializer): collection property in an output dto

src/Serializer/AbstractItemNormalizer.php

@@ -732,6 +732,10 @@ protected function getAttributeValue(object $object, string $attribute, ?string
             }
 
             if ('array' === $type->getBuiltinType()) {
+                if ($className = ($type->getCollectionValueTypes()[0] ?? null)?->getClassName()) {
+                    $context = $this->createOperationContext($context, $className);
+                }
+
                 $childContext = $this->createChildContext($context, $attribute, $format);
                 $childContext['output']['gen_id'] = $propertyMetadata->getGenId() ?? true;
 

tests/Fixtures/TestBundle/ApiResource/Issue6211/ArrayPropertyDtoOperation.php

@@ -0,0 +1,32 @@
+<?php
+
+/*
+ * This file is part of the API Platform project.
+ *
+ * (c) Kévin Dunglas <dunglas@gmail.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+declare(strict_types=1);
+
+namespace ApiPlatform\Tests\Fixtures\TestBundle\ApiResource\Issue6211;
+
+use ApiPlatform\Metadata\Get;
+use ApiPlatform\Tests\Fixtures\TestBundle\Dto\ArrayPropertyDto;
+
+#[Get(provider: [ArrayPropertyDtoOperation::class, 'provide'], output: ArrayPropertyDto::class)]
+class ArrayPropertyDtoOperation
+{
+    public static function provide(): ArrayPropertyDto
+    {
+        $d = new ArrayPropertyDto();
+        $d->name = 'test';
+        $c = new ArrayPropertyDto();
+        $c->name = 'test2';
+        $d->greetings = [$c];
+
+        return $d;
+    }
+}

tests/Fixtures/TestBundle/Dto/ArrayPropertyDto.php

@@ -0,0 +1,24 @@
+<?php
+
+/*
+ * This file is part of the API Platform project.
+ *
+ * (c) Kévin Dunglas <dunglas@gmail.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+declare(strict_types=1);
+
+namespace ApiPlatform\Tests\Fixtures\TestBundle\Dto;
+
+final class ArrayPropertyDto
+{
+    public string $name = '';
+
+    /**
+     * @var array<ArrayPropertyDto>
+     */
+    public array $greetings = [];
+}

tests/Functional/ArrayDtoTest.php

@@ -0,0 +1,25 @@
+<?php
+
+/*
+ * This file is part of the API Platform project.
+ *
+ * (c) Kévin Dunglas <dunglas@gmail.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+declare(strict_types=1);
+
+namespace ApiPlatform\Tests\Functional;
+
+use ApiPlatform\Symfony\Bundle\Test\ApiTestCase;
+
+final class ArrayDtoTest extends ApiTestCase
+{
+    public function testWithGroupFilter(): void
+    {
+        $response = self::createClient()->request('GET', '/array_property_dto_operations');
+        $this->assertArraySubset(['name' => 'test', 'greetings' => [['name' => 'test2']]], $response->toArray());
+    }
+}