test(api): add reproducer for DeserializeProvider enum validation bug

Reproduces the bug that will occur when upgrading to Symfony 8.1.
Symfony PR #62574 (commit 35b1aec) improves BackedEnumNormalizer error
messages, but API Platform's DeserializeProvider does not handle the
case where expectedTypes is null/empty, producing:
"This value should be of type ." (empty type).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: vincentchalamon

api/src/Serializer/BackedEnumNormalizerDecorator.php

@@ -0,0 +1,98 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Serializer;
+
+use Symfony\Component\DependencyInjection\Attribute\AsDecorator;
+use Symfony\Component\Serializer\Exception\NotNormalizableValueException;
+use Symfony\Component\Serializer\Normalizer\BackedEnumNormalizer;
+use Symfony\Component\Serializer\Normalizer\DenormalizerInterface;
+use Symfony\Component\Serializer\Normalizer\NormalizerInterface;
+
+/**
+ * Reproducer for https://github.com/api-platform/demo/issues/601.
+ *
+ * This decorator simulates the behavior introduced in symfony/serializer by
+ * Symfony PR #62574 (commit 35b1aec), which improves BackedEnumNormalizer
+ * error messages. That change was temporarily in v8.0.5 (then reverted) and
+ * will ship in Symfony 8.1.
+ *
+ * The improved normalizer distinguishes two error cases:
+ *   1. Type mismatch: data is not int/string → expectedTypes = [$backingType]
+ *   2. Invalid value: data is the right type but not a valid enum case
+ *      → expectedTypes = null, message lists valid values
+ *
+ * Case 2 exposes a bug in api-platform/state's DeserializeProvider which does
+ * not handle null/empty expectedTypes, producing: "This value should be of type ."
+ *
+ * @todo Remove this decorator once Symfony 8.1 is adopted and the upstream
+ *       API Platform bug is fixed.
+ */
+#[AsDecorator('serializer.normalizer.backed_enum')]
+final class BackedEnumNormalizerDecorator implements NormalizerInterface, DenormalizerInterface
+{
+    public function __construct(
+        private readonly BackedEnumNormalizer $inner,
+    ) {
+    }
+
+    public function normalize(mixed $data, ?string $format = null, array $context = []): int|string
+    {
+        return $this->inner->normalize($data, $format, $context);
+    }
+
+    public function supportsNormalization(mixed $data, ?string $format = null, array $context = []): bool
+    {
+        return $this->inner->supportsNormalization($data, $format, $context);
+    }
+
+    public function denormalize(mixed $data, string $type, ?string $format = null, array $context = []): mixed
+    {
+        if (!is_subclass_of($type, \BackedEnum::class)) {
+            return $this->inner->denormalize($data, $type, $format, $context);
+        }
+
+        $backingType = (new \ReflectionEnum($type))->getBackingType()?->getName();
+
+        // Case 1: Type mismatch — data is not the expected backing type
+        if (null === $data || ('int' === $backingType && !\is_int($data)) || ('string' === $backingType && !\is_string($data))) {
+            throw NotNormalizableValueException::createForUnexpectedDataType(
+                \sprintf('The data must be of type %s.', $backingType),
+                $data,
+                [$backingType],
+                $context['deserialization_path'] ?? null,
+                true,
+            );
+        }
+
+        // Case 2: Invalid value — right type but not a valid enum case
+        try {
+            return $type::from($data);
+        } catch (\ValueError|\TypeError $e) {
+            $validValues = array_map(
+                static fn (\BackedEnum $case): string => \is_string($case->value)
+                    ? \sprintf("'%s'", $case->value)
+                    : (string) $case->value,
+                $type::cases(),
+            );
+
+            throw new NotNormalizableValueException(
+                message: \sprintf('The data must be one of the following values: %s', implode(', ', $validValues)),
+                previous: $e,
+                path: $context['deserialization_path'] ?? null,
+                useMessageForUser: true,
+            );
+        }
+    }
+
+    public function supportsDenormalization(mixed $data, string $type, ?string $format = null, array $context = []): bool
+    {
+        return $this->inner->supportsDenormalization($data, $type, $format, $context);
+    }
+
+    public function getSupportedTypes(?string $format): array
+    {
+        return $this->inner->getSupportedTypes($format);
+    }
+}

api/tests/Api/Admin/BookTest.php

@@ -308,6 +308,7 @@ public static function getInvalidDataOnCreate(): iterable
 
     public static function getInvalidData(): iterable
     {
+        $validValuesHint = "The data must be one of the following values: 'https://schema.org/NewCondition', 'https://schema.org/RefurbishedCondition', 'https://schema.org/DamagedCondition', 'https://schema.org/UsedCondition'";
         yield 'empty data' => [
             [
                 'book' => '',
@@ -317,11 +318,11 @@ public static function getInvalidData(): iterable
             [
                 '@type' => 'ConstraintViolation',
                 'title' => 'An error occurred',
-                'description' => 'condition: This value should be of type int|string.',
+                'description' => 'condition: ' . $validValuesHint,
                 'violations' => [
                     [
                         'propertyPath' => 'condition',
-                        'hint' => 'The data must belong to a backed enumeration of type ' . BookCondition::class,
+                        'hint' => $validValuesHint,
                     ],
                 ],
             ],
@@ -335,11 +336,11 @@ public static function getInvalidData(): iterable
             [
                 '@type' => 'ConstraintViolation',
                 'title' => 'An error occurred',
-                'description' => 'condition: This value should be of type int|string.',
+                'description' => 'condition: ' . $validValuesHint,
                 'violations' => [
                     [
                         'propertyPath' => 'condition',
-                        'hint' => 'The data must belong to a backed enumeration of type ' . BookCondition::class,
+                        'hint' => $validValuesHint,
                     ],
                 ],
             ],