fix: properly format empty object with JSON normalizer

Objects that yield no value or have no property will now properly be
formatted into `{}` instead of `[]`.

src/Normalizer/ArrayNormalizer.php

@@ -4,6 +4,7 @@
 
 namespace CuyZ\Valinor\Normalizer;
 
+use CuyZ\Valinor\Normalizer\Transformer\EmptyObject;
 use CuyZ\Valinor\Normalizer\Transformer\RecursiveTransformer;
 
 use function array_map;
@@ -38,6 +39,8 @@ private function normalizeIterator(mixed $value): mixed
  }
 
  $value = array_map($this->normalizeIterator(...), $value);
+ } elseif ($value instanceof EmptyObject) {
+ return [];
  }
 
  return $value;

src/Normalizer/Formatter/JsonFormatter.php

@@ -5,6 +5,7 @@
 namespace CuyZ\Valinor\Normalizer\Formatter;
 
 use CuyZ\Valinor\Normalizer\Formatter\Exception\CannotFormatInvalidTypeToJson;
+use CuyZ\Valinor\Normalizer\Transformer\EmptyObject;
 use Generator;
 
 use function array_is_list;
@@ -41,6 +42,8 @@ public function format(mixed $value): void
  * tools understand that JSON_THROW_ON_ERROR is always set.
  */
  $this->write(json_encode($value, $this->jsonEncodingOptions));
+ } elseif ($value instanceof EmptyObject) {
+ $this->write('{}');
  } elseif (is_iterable($value)) {
  // Note: when a generator is formatted, it is considered as a list
  // if its first key is 0. This is done early because the first JSON

src/Normalizer/Transformer/EmptyObject.php

@@ -0,0 +1,13 @@
+<?php
+
+declare(strict_types=1);
+
+namespace CuyZ\Valinor\Normalizer\Transformer;
+
+use CuyZ\Valinor\Utility\IsSingleton;
+
+/** @internal */
+final class EmptyObject
+{
+ use IsSingleton;
+}

src/Normalizer/Transformer/RecursiveTransformer.php

@@ -24,6 +24,7 @@
 use function is_a;
 use function is_array;
 use function is_iterable;
+use function is_object;
 
 /** @internal */
 final class RecursiveTransformer
@@ -105,11 +106,17 @@ private function defaultTransformer(mixed $value, WeakMap $references): mixed
  );
  }
 
- return (function () use ($value, $references) {
+ $result = (function () use ($value, $references) {
  foreach ($value as $key => $item) {
  yield $key => $this->doTransform($item, $references);
  }
  })();
+
+ if (! $result->valid()) {
+ return EmptyObject::get();
+ }
+
+ return $result;
  }
 
  if (is_object($value) && ! $value instanceof Closure) {
@@ -126,9 +133,15 @@ private function defaultTransformer(mixed $value, WeakMap $references): mixed
  }
 
  if ($value::class === stdClass::class) {
+ $result = (array)$value;
+
+ if ($result === []) {
+ return EmptyObject::get();
+ }
+
  return array_map(
  fn (mixed $value) => $this->doTransform($value, $references),
- (array)$value
+ $result
  );
  }
 

tests/Integration/Normalizer/NormalizerTest.php

@@ -695,6 +695,32 @@ public function __construct(
  'transformerAttributes' => [],
  'jsonEncodingOptions' => JSON_HEX_AMP,
  ];
+
+ yield 'stdClass with no property' => [
+ 'input' => new stdClass(),
+ 'expected array' => [],
+ 'expected_json' => '{}',
+ ];
+
+ yield 'ArrayObject with no property' => [
+ 'input' => new ArrayObject(),
+ 'expected array' => [],
+ 'expected_json' => '{}',
+ ];
+
+ yield 'iterable class with no property' => [
+ 'input' => new class () implements IteratorAggregate {
+ public function getIterator(): Traversable
+ {
+ // @phpstan-ignore-next-line / Empty array is here on purpose
+ foreach ([] as $value) {
+ yield $value;
+ }
+ }
+ },
+ 'expected array' => [],
+ 'expected_json' => '{}',
+ ];
  }
 
  public function test_generator_of_scalar_yields_expected_array(): void