feature symfony#59828 [Serializer] Add defaultType to DiscriminatorMap (alanpoulain)

This PR was merged into the 7.3 branch.

Discussion
----------

[Serializer] Add `defaultType` to `DiscriminatorMap`

| Q             | A
| ------------- | ---
| Branch?       | 7.3
| Bug fix?      | no
| New feature?  | yes
| Deprecations? | no
| Issues        | N/A
| License       | MIT

I thought it would be nice to have a default type value for the discriminator map of the serializer.

For instance with this configuration:
```php
#[DiscriminatorMap(
    typeProperty: 'type',
    mapping: [
        'article' => Article::class,
        'video' => Video::class,
    ],
    defaultType: 'article'
)]
abstract class Element
{
    public string $product;
}

final class Article extends Element
{
    public string $title;
}

final class Video extends Element
{
    public int $duration;
}
```
It would deserialize to an `Article` with this data:
```json
{
    "product": "desk",
    "title": "PHP devs love Symfony"
}
```
And to a `Video` with this:
```json
{
    "product": "desk",
    "duration": 8765,
    "type": "video"
}
```

Commits
-------

9d089bd [Serializer] Add defaultType to DiscriminatorMap

Author: fabpot

src/Symfony/Component/Serializer/Attribute/DiscriminatorMap.php

@@ -22,12 +22,14 @@ class DiscriminatorMap
     /**
      * @param string                      $typeProperty The property holding the type discriminator
      * @param array<string, class-string> $mapping      The mapping between types and classes (i.e. ['admin_user' => AdminUser::class])
+     * @param ?string                     $defaultType  The fallback value if nothing specified by $typeProperty
      *
      * @throws InvalidArgumentException
      */
     public function __construct(
         private readonly string $typeProperty,
         private readonly array $mapping,
+        private readonly ?string $defaultType = null,
     ) {
         if (!$typeProperty) {
             throw new InvalidArgumentException(\sprintf('Parameter "typeProperty" given to "%s" cannot be empty.', static::class));
@@ -36,6 +38,10 @@ public function __construct(
         if (!$mapping) {
             throw new InvalidArgumentException(\sprintf('Parameter "mapping" given to "%s" cannot be empty.', static::class));
         }
+
+        if (null !== $this->defaultType && !\array_key_exists($this->defaultType, $this->mapping)) {
+            throw new InvalidArgumentException(\sprintf('Default type "%s" given to "%s" must be present in "mapping" types.', $this->defaultType, static::class));
+        }
     }
 
     public function getTypeProperty(): string
@@ -47,6 +53,11 @@ public function getMapping(): array
     {
         return $this->mapping;
     }
+
+    public function getDefaultType(): ?string
+    {
+        return $this->defaultType;
+    }
 }
 
 if (!class_exists(\Symfony\Component\Serializer\Annotation\DiscriminatorMap::class, false)) {

src/Symfony/Component/Serializer/CHANGELOG.md

@@ -7,6 +7,7 @@ CHANGELOG
  * Deprecate the `CompiledClassMetadataFactory` and `CompiledClassMetadataCacheWarmer` classes
  * Register `NormalizerInterface` and `DenormalizerInterface` aliases for named serializers
  * Add `NumberNormalizer` to normalize `BcMath\Number` and `GMP` as `string`
+ * Add `defaultType` to `DiscriminatorMap`
 
 7.2
 ---

src/Symfony/Component/Serializer/Mapping/ClassDiscriminatorMapping.php

@@ -22,6 +22,7 @@ class ClassDiscriminatorMapping
     public function __construct(
         private readonly string $typeProperty,
         private array $typesMapping = [],
+        private readonly ?string $defaultType = null,
     ) {
         uasort($this->typesMapping, static function (string $a, string $b): int {
             if (is_a($a, $b, true)) {
@@ -61,4 +62,9 @@ public function getTypesMapping(): array
     {
         return $this->typesMapping;
     }
+
+    public function getDefaultType(): ?string
+    {
+        return $this->defaultType;
+    }
 }

src/Symfony/Component/Serializer/Mapping/Factory/ClassMetadataFactoryCompiler.php

@@ -55,6 +55,7 @@ private function generateDeclaredClassMetadata(array $classMetadatas): string
             $classDiscriminatorMapping = $classMetadata->getClassDiscriminatorMapping() ? [
                 $classMetadata->getClassDiscriminatorMapping()->getTypeProperty(),
                 $classMetadata->getClassDiscriminatorMapping()->getTypesMapping(),
+                $classMetadata->getClassDiscriminatorMapping()->getDefaultType(),
             ] : null;
 
             $compiled .= \sprintf("\n'%s' => %s,", $classMetadata->getName(), VarExporter::export([

src/Symfony/Component/Serializer/Mapping/Loader/AttributeLoader.php

@@ -59,7 +59,7 @@ public function loadClassMetadata(ClassMetadataInterface $classMetadata): bool
 
         foreach ($this->loadAttributes($reflectionClass) as $attribute) {
             match (true) {
-                $attribute instanceof DiscriminatorMap => $classMetadata->setClassDiscriminatorMapping(new ClassDiscriminatorMapping($attribute->getTypeProperty(), $attribute->getMapping())),
+                $attribute instanceof DiscriminatorMap => $classMetadata->setClassDiscriminatorMapping(new ClassDiscriminatorMapping($attribute->getTypeProperty(), $attribute->getMapping(), $attribute->getDefaultType())),
                 $attribute instanceof Groups => $classGroups = $attribute->getGroups(),
                 $attribute instanceof Context => $classContextAttribute = $attribute,
                 default => null,

src/Symfony/Component/Serializer/Mapping/Loader/XmlFileLoader.php

@@ -107,7 +107,8 @@ public function loadClassMetadata(ClassMetadataInterface $classMetadata): bool
 
                 $classMetadata->setClassDiscriminatorMapping(new ClassDiscriminatorMapping(
                     (string) $xml->{'discriminator-map'}->attributes()->{'type-property'},
-                    $mapping
+                    $mapping,
+                    $xml->{'discriminator-map'}->attributes()->{'default-type'} ?? null
                 ));
             }
 

src/Symfony/Component/Serializer/Mapping/Loader/YamlFileLoader.php

@@ -133,7 +133,8 @@ public function loadClassMetadata(ClassMetadataInterface $classMetadata): bool
 
             $classMetadata->setClassDiscriminatorMapping(new ClassDiscriminatorMapping(
                 $yaml['discriminator_map']['type_property'],
-                $yaml['discriminator_map']['mapping']
+                $yaml['discriminator_map']['mapping'],
+                $yaml['discriminator_map']['default_type'] ?? null
             ));
         }
 

src/Symfony/Component/Serializer/Mapping/Loader/schema/dic/serializer-mapping/serializer-mapping-1.0.xsd

@@ -47,6 +47,7 @@
             <xsd:element name="mapping" type="discriminator-map-mapping" maxOccurs="unbounded" />
         </xsd:choice>
         <xsd:attribute name="type-property" type="xsd:string" use="required" />
+        <xsd:attribute name="default-type" type="xsd:string" />
     </xsd:complexType>
 
     <xsd:complexType name="discriminator-map-mapping">

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

@@ -1179,7 +1179,7 @@ private function getMappedClass(array $data, string $class, array $context): str
             return $class;
         }
 
-        if (null === $type = $data[$mapping->getTypeProperty()] ?? null) {
+        if (null === $type = $data[$mapping->getTypeProperty()] ?? $mapping->getDefaultType()) {
             throw NotNormalizableValueException::createForUnexpectedDataType(\sprintf('Type property "%s" not found for the abstract object "%s".', $mapping->getTypeProperty(), $class), null, ['string'], isset($context['deserialization_path']) ? $context['deserialization_path'].'.'.$mapping->getTypeProperty() : $mapping->getTypeProperty(), false);
         }
 

src/Symfony/Component/Serializer/Tests/Attribute/DiscriminatorMapTest.php

@@ -40,9 +40,16 @@ public function testExceptionWithEmptyTypeProperty()
         new DiscriminatorMap(typeProperty: '', mapping: ['foo' => 'FooClass']);
     }
 
-    public function testExceptionWitEmptyMappingProperty()
+    public function testExceptionWithEmptyMappingProperty()
     {
         $this->expectException(InvalidArgumentException::class);
         new DiscriminatorMap(typeProperty: 'type', mapping: []);
     }
+
+    public function testExceptionWithMissingDefaultTypeInMapping()
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage(sprintf('Default type "bar" given to "%s" must be present in "mapping" types.', DiscriminatorMap::class));
+        new DiscriminatorMap(typeProperty: 'type', mapping: ['foo' => 'FooClass'], defaultType: 'bar');
+    }
 }