[Serializer] Encode empty objects as objects, not arrays

Allows Normalizers to return a representation of an empty object that the encoder recognizes as such.

src/Symfony/Component/Serializer/Encoder/CsvEncoder.php

@@ -69,7 +69,7 @@ class CsvEncoder implements EncoderInterface, DecoderInterface
     {
         $handle = fopen('php://temp,', 'w+');
 
-        if (!\is_array($data)) {
+        if (!is_iterable($data)) {
             $data = [[$data]];
         } elseif (empty($data)) {
             $data = [[]];
@@ -210,10 +210,10 @@ class CsvEncoder implements EncoderInterface, DecoderInterface
     /**
      * Flattens an array and generates keys including the path.
      */
-    private function flatten(array $array, array &$result, string $keySeparator, string $parentKey = '', bool $escapeFormulas = false)
+    private function flatten(iterable $array, array &$result, string $keySeparator, string $parentKey = '', bool $escapeFormulas = false)
     {
         foreach ($array as $key => $value) {
-            if (\is_array($value)) {
+            if (is_iterable($value)) {
                 $this->flatten($value, $result, $keySeparator, $parentKey.$key.$keySeparator, $escapeFormulas);
             } else {
                 if ($escapeFormulas && \in_array(substr((string) $value, 0, 1), $this->formulasStartCharacters, true)) {
@@ -245,7 +245,7 @@ class CsvEncoder implements EncoderInterface, DecoderInterface
     /**
      * @return string[]
      */
-    private function extractHeaders(array $data): array
+    private function extractHeaders(iterable $data): array
     {
         $headers = [];
         $flippedHeaders = [];

src/Symfony/Component/Serializer/Encoder/YamlEncoder.php

@@ -14,6 +14,7 @@ namespace Symfony\Component\Serializer\Encoder;
 use Symfony\Component\Serializer\Exception\RuntimeException;
 use Symfony\Component\Yaml\Dumper;
 use Symfony\Component\Yaml\Parser;
+use Symfony\Component\Yaml\Yaml;
 
 /**
  * Encodes YAML data.
@@ -25,6 +26,8 @@ class YamlEncoder implements EncoderInterface, DecoderInterface
     const FORMAT = 'yaml';
     private const ALTERNATIVE_FORMAT = 'yml';
 
+    public const PRESERVE_EMPTY_OBJECTS = 'preserve_empty_objects';
+
     private $dumper;
     private $parser;
     private $defaultContext = ['yaml_inline' => 0, 'yaml_indent' => 0, 'yaml_flags' => 0];
@@ -47,6 +50,10 @@ class YamlEncoder implements EncoderInterface, DecoderInterface
     {
         $context = array_merge($this->defaultContext, $context);
 
+        if (isset($context[self::PRESERVE_EMPTY_OBJECTS])) {
+            $context['yaml_flags'] |= Yaml::DUMP_OBJECT_AS_MAP;
+        }
+
         return $this->dumper->dump($data, $context['yaml_inline'], $context['yaml_indent'], $context['yaml_flags']);
     }
 

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

@@ -88,6 +88,8 @@ abstract class AbstractObjectNormalizer extends AbstractNormalizer
      */
     public const DEEP_OBJECT_TO_POPULATE = 'deep_object_to_populate';
 
+    public const PRESERVE_EMPTY_OBJECTS = 'preserve_empty_objects';
+
     private $propertyTypeExtractor;
     private $typesCache = [];
     private $attributesCache = [];
@@ -206,6 +208,10 @@ abstract class AbstractObjectNormalizer extends AbstractNormalizer
             $data = $this->updateData($data, $attribute, $this->serializer->normalize($attributeValue, $format, $this->createChildContext($context, $attribute, $format)), $class, $format, $context);
         }
 
+        if (isset($context[self::PRESERVE_EMPTY_OBJECTS]) && !\count($data)) {
+            return new \ArrayObject();
+        }
+
         return $data;
     }
 

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

@@ -30,7 +30,7 @@ interface NormalizerInterface
      * @param string $format  Format the normalization result will be encoded as
      * @param array  $context Context options for the normalizer
      *
-     * @return array|string|int|float|bool
+     * @return array|string|int|float|bool|\ArrayObject \ArrayObject is used to make sure an empty object is encoded as an object not an array
      *
      * @throws InvalidArgumentException   Occurs when the object given is not an attempted type for the normalizer
      * @throws CircularReferenceException Occurs when the normalizer detects a circular reference when no circular

src/Symfony/Component/Serializer/Tests/Encoder/CsvEncoderTest.php

@@ -339,6 +339,43 @@ CSV
             ]));
     }
 
+    public function testEncodeArrayObject()
+    {
+        $value = new \ArrayObject(['foo' => 'hello', 'bar' => 'hey ho']);
+
+        $this->assertEquals(<<<'CSV'
+foo,bar
+hello,"hey ho"
+
+CSV
+            , $this->encoder->encode($value, 'csv'));
+
+        $value = new \ArrayObject();
+
+        $this->assertEquals("\n", $this->encoder->encode($value, 'csv'));
+    }
+
+    public function testEncodeNestedArrayObject()
+    {
+        $value = new \ArrayObject(['foo' => new \ArrayObject(['nested' => 'value']), 'bar' => new \ArrayObject(['another' => 'word'])]);
+
+        $this->assertEquals(<<<'CSV'
+foo.nested,bar.another
+value,word
+
+CSV
+            , $this->encoder->encode($value, 'csv'));
+    }
+
+    public function testEncodeEmptyArrayObject()
+    {
+        $value = new \ArrayObject();
+        $this->assertEquals("\n", $this->encoder->encode($value, 'csv'));
+
+        $value = ['foo' => new \ArrayObject()];
+        $this->assertEquals("\n\n", $this->encoder->encode($value, 'csv'));
+    }
+
     public function testSupportsDecoding()
     {
         $this->assertTrue($this->encoder->supportsDecoding('csv'));

src/Symfony/Component/Serializer/Tests/Encoder/JsonEncodeTest.php

@@ -46,6 +46,8 @@ class JsonEncodeTest extends TestCase
         return [
             [[], '[]', []],
             [[], '{}', ['json_encode_options' => JSON_FORCE_OBJECT]],
+            [new \ArrayObject(), '{}', []],
+            [new \ArrayObject(['foo' => 'bar']), '{"foo":"bar"}', []],
         ];
     }
 

src/Symfony/Component/Serializer/Tests/Encoder/XmlEncoderTest.php

@@ -48,6 +48,26 @@ class XmlEncoderTest extends TestCase
         $this->assertEquals($expected, $this->encoder->encode($obj, 'xml'));
     }
 
+    public function testEncodeArrayObject()
+    {
+        $obj = new \ArrayObject(['foo' => 'bar']);
+
+        $expected = '<?xml version="1.0"?>'."\n".
+            '<response><foo>bar</foo></response>'."\n";
+
+        $this->assertEquals($expected, $this->encoder->encode($obj, 'xml'));
+    }
+
+    public function testEncodeEmptyArrayObject()
+    {
+        $obj = new \ArrayObject();
+
+        $expected = '<?xml version="1.0"?>'."\n".
+            '<response/>'."\n";
+
+        $this->assertEquals($expected, $this->encoder->encode($obj, 'xml'));
+    }
+
     /**
      * @group legacy
      */

src/Symfony/Component/Serializer/Tests/Encoder/YamlEncoderTest.php

@@ -28,6 +28,8 @@ class YamlEncoderTest extends TestCase
 
         $this->assertEquals('foo', $encoder->encode('foo', 'yaml'));
         $this->assertEquals('{ foo: 1 }', $encoder->encode(['foo' => 1], 'yaml'));
+        $this->assertEquals('null', $encoder->encode(new \ArrayObject(['foo' => 1]), 'yaml'));
+        $this->assertEquals('{ foo: 1 }', $encoder->encode(new \ArrayObject(['foo' => 1]), 'yaml', ['preserve_empty_objects' => true]));
     }
 
     public function testSupportsEncoding()

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

@@ -198,12 +198,25 @@ class AbstractObjectNormalizerTest extends TestCase
             'allow_extra_attributes' => false,
         ]);
     }
+
+    public function testNormalizeEmptyObject()
+    {
+        $normalizer = new AbstractObjectNormalizerDummy();
+
+        // This results in objects turning into arrays in some encoders
+        $normalizedData = $normalizer->normalize(new EmptyDummy());
+        $this->assertEquals([], $normalizedData);
+
+        $normalizedData = $normalizer->normalize(new EmptyDummy(), 'any', ['preserve_empty_objects' => true]);
+        $this->assertEquals(new \ArrayObject(), $normalizedData);
+    }
 }
 
 class AbstractObjectNormalizerDummy extends AbstractObjectNormalizer
 {
     protected function extractAttributes($object, $format = null, array $context = [])
     {
+        return [];
     }
 
     protected function getAttributeValue($object, $attribute, $format = null, array $context = [])
@@ -233,6 +246,10 @@ class Dummy
     public $baz;
 }
 
+class EmptyDummy
+{
+}
+
 class AbstractObjectNormalizerWithMetadata extends AbstractObjectNormalizer
 {
     public function __construct()

src/Symfony/Component/Serializer/Tests/SerializerTest.php

@@ -194,6 +194,19 @@ class SerializerTest extends TestCase
         $this->assertEquals(json_encode($data), $result);
     }
 
+    public function testSerializeEmpty()
+    {
+        $serializer = new Serializer([new ObjectNormalizer()], ['json' => new JsonEncoder()]);
+        $data = ['foo' => new \stdClass()];
+
+        //Old buggy behaviour
+        $result = $serializer->serialize($data, 'json');
+        $this->assertEquals('{"foo":[]}', $result);
+
+        $result = $serializer->serialize($data, 'json', ['preserve_empty_objects' => true]);
+        $this->assertEquals('{"foo":{}}', $result);
+    }
+
     public function testSerializeNoEncoder()
     {
         $this->expectException('Symfony\Component\Serializer\Exception\UnexpectedValueException');