fix(mapper): serialize nested objects

packages/mapper/src/Mappers/ObjectToArrayMapper.php

@@ -69,7 +69,9 @@ private function resolvePropertyValue(PropertyReflector $property, object $objec
                     continue;
                 }
 
-                $propertyValue[$key] = map($value)->toArray();
+                $propertyValue[$key] = map($value)
+                    ->in($this->context)
+                    ->toArray();
             }
 
             return $propertyValue;
@@ -79,6 +81,12 @@ private function resolvePropertyValue(PropertyReflector $property, object $objec
             return $serializer->serialize($propertyValue);
         }
 
+        if ($propertyValue !== null && is_object($propertyValue)) {
+            return map($propertyValue)
+                ->in($this->context)
+                ->toArray();
+        }
+
         return $propertyValue;
     }
 

tests/Integration/Mapper/Fixtures/NestedObjectWithDate.php

@@ -0,0 +1,17 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Tempest\Integration\Mapper\Fixtures;
+
+use Tempest\DateTime\DateTime;
+use Tempest\DateTime\FormatPattern;
+use Tempest\Validation\Rules\HasDateTimeFormat;
+
+final readonly class NestedObjectWithDate
+{
+    public function __construct(
+        #[HasDateTimeFormat(FormatPattern::ISO8601)]
+        public DateTime $createdAt,
+    ) {}
+}

tests/Integration/Mapper/Fixtures/ObjectWithNestedObjectAndDate.php

@@ -0,0 +1,20 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Tempest\Integration\Mapper\Fixtures;
+
+use Tempest\DateTime\DateTime;
+use Tempest\DateTime\FormatPattern;
+use Tempest\Validation\Rules\HasDateTimeFormat;
+
+final readonly class ObjectWithNestedObjectAndDate
+{
+    public function __construct(
+        #[HasDateTimeFormat(FormatPattern::ISO8601)]
+        public DateTime $createdAt,
+        public NestedObjectWithDate $child,
+        /** @var \Tests\Tempest\Integration\Mapper\Fixtures\NestedObjectWithDate[] */
+        public array $children,
+    ) {}
+}

tests/Integration/Mapper/Mappers/ObjectToArrayMapperTest.php

@@ -4,12 +4,21 @@
 
 namespace Tests\Tempest\Integration\Mapper\Mappers;
 
+use PHPUnit\Framework\Attributes\RequiresPhpExtension;
 use PHPUnit\Framework\Attributes\Test;
+use RuntimeException;
+use Tempest\DateTime\DateTime;
+use Tempest\Mapper\Mapper;
+use Tempest\Mapper\MapperConfig;
+use Tempest\Support\Json\Exception\JsonCouldNotBeEncoded;
 use Tests\Tempest\Integration\FrameworkIntegrationTestCase;
+use Tests\Tempest\Integration\Mapper\Fixtures\NestedObjectWithDate;
 use Tests\Tempest\Integration\Mapper\Fixtures\ObjectA;
 use Tests\Tempest\Integration\Mapper\Fixtures\ObjectWithJsonSerialize;
+use Tests\Tempest\Integration\Mapper\Fixtures\ObjectWithNestedObjectAndDate;
 use Tests\Tempest\Integration\Mapper\Fixtures\ObjectWithNullableProperties;
 use Tests\Tempest\Integration\Mapper\Fixtures\ObjectWithScalarValues;
+use Tests\Tempest\Integration\Mapper\Fixtures\ParentObject;
 
 use function Tempest\Mapper\map;
 
@@ -69,4 +78,110 @@
             $array,
         );
     }
+
+    #[Test]
+    public function object_with_single_nested_object_to_array(): void
+    {
+        $date = DateTime::parse('2026-08-19T12:34:56+00:00');
+
+        $array = map(new ObjectWithNestedObjectAndDate(
+            createdAt: $date,
+            child: new NestedObjectWithDate($date),
+            children: [new NestedObjectWithDate($date)],
+        ))->toArray();
+
+        $this->assertSame(
+            [
+                'createdAt' => '2026-08-19T12:34:56.000Z',
+                'child' => [
+                    'createdAt' => '2026-08-19T12:34:56.000Z',
+                ],
+                'children' => [
+                    ['createdAt' => '2026-08-19T12:34:56.000Z'],
+                ],
+            ],
+            $array,
+        );
+    }
+
+    #[Test]
+    #[RequiresPhpExtension('pcntl')]
+    public function cyclic_nested_objects_fail_instead_of_hanging(): void
+    {
+        $parent = map([
+            'name' => 'parent',
+            'child' => ['name' => 'child'],
+        ])->to(ParentObject::class);
+        $this->assertInstanceOf(ParentObject::class, $parent);
+
+        pcntl_async_signals(true);
+        pcntl_signal(SIGALRM, static function (): never {
+            throw new RuntimeException('Serialization did not terminate');
+        });
+        pcntl_alarm(2);
+
+        try {
+            $this->expectException(JsonCouldNotBeEncoded::class);
+
+            map($parent)->toJson();
+        } finally {
+            pcntl_alarm(0);
+            pcntl_signal(SIGALRM, SIG_DFL);
+        }
+    }
+
+    #[Test]
+    public function nested_objects_do_not_resolve_unused_mappers(): void
+    {
+        map(new ObjectA('a', 'b'))->toArray();
+
+        $this->container
+            ->get(MapperConfig::class)
+            ->addMapper(MapperResolutionProbe::class);
+
+        MapperResolutionProbe::$constructions = 0;
+
+        map(new ObjectWithMapperResolutionChildren([
+            new MapperResolutionChild('a'),
+            new MapperResolutionChild('b'),
+            new MapperResolutionChild('c'),
+        ]))->toArray();
+
+        $this->assertSame(0, MapperResolutionProbe::$constructions);
+    }
+}
+
+final readonly class ObjectWithMapperResolutionChildren
+{
+    public function __construct(
+        /** @var \Tests\Tempest\Integration\Mapper\Mappers\MapperResolutionChild[] */
+        public array $children,
+    ) {}
+}
+
+final readonly class MapperResolutionChild
+{
+    public function __construct(
+        public string $name,
+    ) {}
+}
+
+final class MapperResolutionProbe implements Mapper
+{
+    public static int $constructions = 0;
+
+    public function __construct()
+    {
+        self::$constructions++;
+    }
+
+    public function canMap(mixed $from, mixed $to): bool
+    {
+        return false;
+    }
+
+    public function map(mixed $from, mixed $to): mixed
+    {
+        return $from;
+    }
 }

tests/Integration/Mapper/Mappers/ObjectToJsonMapperTest.php

@@ -5,8 +5,11 @@
 namespace Tests\Tempest\Integration\Mapper\Mappers;
 
 use PHPUnit\Framework\Attributes\Test;
+use Tempest\DateTime\DateTime;
 use Tests\Tempest\Integration\FrameworkIntegrationTestCase;
+use Tests\Tempest\Integration\Mapper\Fixtures\NestedObjectWithDate;
 use Tests\Tempest\Integration\Mapper\Fixtures\ObjectA;
+use Tests\Tempest\Integration\Mapper\Fixtures\ObjectWithNestedObjectAndDate;
 use Tests\Tempest\Integration\Mapper\Fixtures\ObjectWithScalarValues;
 
 use function Tempest\Mapper\map;
@@ -42,4 +45,29 @@ public function object_with_scalar_values_to_json(): void
             json_decode($json, associative: true, flags: JSON_THROW_ON_ERROR),
         );
     }
+
+    #[Test]
+    public function object_with_single_nested_object_to_json(): void
+    {
+        $date = DateTime::parse('2026-08-19T12:34:56+00:00');
+
+        $json = map(new ObjectWithNestedObjectAndDate(
+            createdAt: $date,
+            child: new NestedObjectWithDate($date),
+            children: [new NestedObjectWithDate($date)],
+        ))->toJson();
+
+        $this->assertSame(
+            [
+                'createdAt' => '2026-08-19T12:34:56.000Z',
+                'child' => [
+                    'createdAt' => '2026-08-19T12:34:56.000Z',
+                ],
+                'children' => [
+                    ['createdAt' => '2026-08-19T12:34:56.000Z'],
+                ],
+            ],
+            json_decode($json, associative: true, flags: JSON_THROW_ON_ERROR),
+        );
+    }
 }

tests/Integration/Mapper/Serializers/ArrayOfObjectsSerializerTest.php

@@ -3,9 +3,16 @@
 namespace Tests\Tempest\Integration\Mapper\Serializers;
 
 use PHPUnit\Framework\Attributes\Test;
+use Tempest\Mapper\DynamicSerializer;
 use Tempest\Mapper\Exceptions\ValueCouldNotBeSerialized;
+use Tempest\Mapper\MappingContext;
+use Tempest\Mapper\Serializer;
+use Tempest\Mapper\SerializerFactory;
 use Tempest\Mapper\Serializers\ArrayOfObjectsSerializer;
 use Tempest\Mapper\Serializers\EnumSerializer;
+use Tempest\Reflection\PropertyReflector;
+use Tempest\Reflection\TypeReflector;
+use Tempest\Support\Priority;
 use Tests\Tempest\Integration\FrameworkIntegrationTestCase;
 use Tests\Tempest\Integration\Mapper\Fixtures\ObjectWithSerializerProperties;
 
@@ -51,4 +58,52 @@
 
         new EnumSerializer()->serialize('foo');
     }
+
+    #[Test]
+    public function uses_mapping_context_for_nested_objects(): void
+    {
+        $context = MappingContext::from('api');
+
+        $this->container
+            ->get(SerializerFactory::class)
+            ->addSerializer(
+                ContextStringSerializer::class,
+                priority: Priority::HIGHEST,
+                context: $context,
+            );
+
+        $serializer = $this->container->get(
+            ArrayOfObjectsSerializer::class,
+            context: $context,
+        );
+
+        $this->assertSame(
+            [['name' => 'api:a']],
+            $serializer->serialize([new ContextObject('a')]),
+        );
+    }
+}
+
+final readonly class ContextObject
+{
+    public function __construct(
+        public string $name,
+    ) {}
+}
+
+final class ContextStringSerializer implements Serializer, DynamicSerializer
+{
+    public static function accepts(PropertyReflector|TypeReflector $input): bool
+    {
+        $type = $input instanceof PropertyReflector
+            ? $input->getType()
+            : $input;
+
+        return $type->getName() === 'string';
+    }
+
+    public function serialize(mixed $input): string
+    {
+        return 'api:' . $input;
+    }
 }