fix(jsonschema): fallback the schema for mixed properties to string|null instead of null

src/JsonSchema/Metadata/Property/Factory/SchemaPropertyMetadataFactory.php

@@ -280,6 +280,7 @@ private function getJsonSchemaFromType(Type $type, ?bool $readableLink = null):
                 TypeIdentifier::OBJECT => ['type' => 'object'],
                 TypeIdentifier::RESOURCE => ['type' => 'string'],
                 TypeIdentifier::CALLABLE => ['type' => 'string'],
+                TypeIdentifier::MIXED => ['type' => 'string'],
                 default => ['type' => 'null'],
             };
 

src/JsonSchema/Tests/Fixtures/DummyWithMixed.php

@@ -0,0 +1,23 @@
+<?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\JsonSchema\Tests\Fixtures;
+
+use ApiPlatform\Metadata\ApiResource;
+
+#[ApiResource]
+class DummyWithMixed
+{
+    public mixed $mixedProperty;
+    public array $mixedArrayProperty;
+}

src/JsonSchema/Tests/Metadata/Property/Factory/SchemaPropertyMetadataFactoryTest.php

@@ -16,6 +16,7 @@
 use ApiPlatform\JsonSchema\Metadata\Property\Factory\SchemaPropertyMetadataFactory;
 use ApiPlatform\JsonSchema\Tests\Fixtures\DummyWithCustomOpenApiContext;
 use ApiPlatform\JsonSchema\Tests\Fixtures\DummyWithEnum;
+use ApiPlatform\JsonSchema\Tests\Fixtures\DummyWithMixed;
 use ApiPlatform\JsonSchema\Tests\Fixtures\DummyWithUnionTypeProperty;
 use ApiPlatform\JsonSchema\Tests\Fixtures\Enum\IntEnumAsIdentifier;
 use ApiPlatform\Metadata\ApiProperty;
@@ -167,4 +168,37 @@ public function testUnionTypeAnyOfIsArray(): void
 
         $this->assertEquals($expectedSchema, $apiProperty->getSchema());
     }
+
+    public function testMixed(): void
+    {
+        if (!method_exists(PropertyInfoExtractor::class, 'getType')) { // @phpstan-ignore-line symfony/property-info 6.4 is still allowed and this may be true
+            $this->markTestSkipped('This test only supports type-info component');
+        }
+
+        $resourceClassResolver = $this->createMock(ResourceClassResolverInterface::class);
+        $apiProperty = new ApiProperty(nativeType: Type::mixed());
+        $decorated = $this->createMock(PropertyMetadataFactoryInterface::class);
+        $decorated->expects($this->once())->method('create')->with(DummyWithMixed::class, 'mixedProperty')->willReturn($apiProperty);
+
+        $schemaPropertyMetadataFactory = new SchemaPropertyMetadataFactory($resourceClassResolver, $decorated);
+        $apiProperty = $schemaPropertyMetadataFactory->create(DummyWithMixed::class, 'mixedProperty');
+
+        $this->assertEquals([
+            'type' => ['string', 'null'],
+        ], $apiProperty->getSchema());
+
+        $apiProperty = new ApiProperty(nativeType: Type::array(Type::mixed()));
+        $decorated = $this->createMock(PropertyMetadataFactoryInterface::class);
+        $decorated->expects($this->once())->method('create')->with(DummyWithMixed::class, 'mixedArrayProperty')->willReturn($apiProperty);
+
+        $schemaPropertyMetadataFactory = new SchemaPropertyMetadataFactory($resourceClassResolver, $decorated);
+        $apiProperty = $schemaPropertyMetadataFactory->create(DummyWithMixed::class, 'mixedArrayProperty');
+
+        $this->assertEquals([
+            'type' => 'array',
+            'items' => [
+                'type' => ['string', 'null'],
+            ],
+        ], $apiProperty->getSchema());
+    }
 }