feature #24375 [Serializer] Serialize and deserialize from abstract classes (sroze)

This PR was squashed before being merged into the 4.1-dev branch (closes #24375).

Discussion
----------

[Serializer] Serialize and deserialize from abstract classes

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | ø
| License       | MIT
| Doc PR        | Not yet

This PR adds a feature in the Serializer: allow to serialize and de-serialize abstract classes. Such feature is especially useful when dealing with domain objects.

# Example

Let's take the example of the following objects:
- `CodeRepository` defines a set of properties like `name` and `url`
- `GitHubCodeRepository` and `BitBucketCodeRepository` extends from the abstract `CodeRepository` class and adds a few properties.
- `Project` has a relation with a `codeRepository`, which has a type `CodeRepository`.

At the moment, the serializer can't serialize/deserialize correctly this `Project` object has it doesn't know how to deal with this `CodeRepository` abstract object.

This feature allows the serializer to deal with such situation. The `ObjectNormalizer` has now access to a `ClassDiscriminatorResolver` that knows, for a given abstract class:
- Is the "type" property it needs to read/write to uniquely identify each sub-class
- What's the name of the "type" for each sub-class mapping

# Usage without Framework Bundle

```php
$discriminatorResolver = new ClassDiscriminatorResolver();
$discriminatorResolver->addClassMapping(CodeRepository::class, new ClassDiscriminatorMapping('type', [
    'github' => GitHubCodeRepository::class,
    'bitbucket' => BitBucketCodeRepository::class,
]));

$serializer = new Serializer(array(new ObjectNormalizer(null, null, null, null, $discriminatorResolver)), array('json' => new JsonEncoder()));

$serialized = $serializer->serialize(new GitHubCodeRepository());
// {"type": "github"}

$repository = $serializer->unserialize($serialized, CodeRepository::class, 'json');
// GitHubCodeRepository

```

# Usage with the Framework Bundle

```yaml
framework:
    serializer:
        discriminator_class_mapping:
            App\CodeRepository:
                 type_property: type
                 mapping:
                    github: App\GitHubCodeRepository
                    bitbucket: App\BitBucketCodeRepository
```

# Usage with Annotations/XML/YAML

```php
use Symfony\Component\Serializer\Annotation\DiscriminatorMap;

/**
 * @DiscriminatorMap(typeProperty="type", mapping={
 *    "first"="Symfony\Component\Serializer\Tests\Fixtures\AbstractDummyFirstChild",
 *    "second"="Symfony\Component\Serializer\Tests\Fixtures\AbstractDummySecondChild"
 * })
 */
abstract class AbstractDummy
{
    public $foo;

    public function __construct($foo = null)
    {
        $this->foo = $foo;
    }
}
```

# TODO

- [x] Working as standalone
- [x] Working with the framework bundle
- [x] Tests on mapping classes

Commits
-------

4c6e05b7ee [Serializer] Serialize and deserialize from abstract classes

Author: fabpot

DependencyInjection/FrameworkExtension.php

@@ -62,6 +62,7 @@
 use Symfony\Component\Security\Core\Security;
 use Symfony\Component\Serializer\Encoder\DecoderInterface;
 use Symfony\Component\Serializer\Encoder\EncoderInterface;
+use Symfony\Component\Serializer\Mapping\ClassDiscriminatorFromClassMetadata;
 use Symfony\Component\Serializer\Mapping\Factory\CacheClassMetadataFactory;
 use Symfony\Component\Serializer\Normalizer\DateIntervalNormalizer;
 use Symfony\Component\Serializer\Normalizer\DenormalizerInterface;
@@ -1153,6 +1154,11 @@ private function registerSerializerConfiguration(array $config, ContainerBuilder
             $container->removeDefinition('serializer.normalizer.dateinterval');
         }
 
+        if (!class_exists(ClassDiscriminatorFromClassMetadata::class)) {
+            $container->removeAlias('Symfony\Component\Serializer\Mapping\ClassDiscriminatorResolverInterface');
+            $container->removeDefinition('serializer.mapping.class_discriminator_resolver');
+        }
+
         $chainLoader = $container->getDefinition('serializer.mapping.chain_loader');
 
         if (!class_exists('Symfony\Component\PropertyAccess\PropertyAccessor')) {

Resources/config/serializer.xml

@@ -24,6 +24,12 @@
 
         <service id="serializer.property_accessor" alias="property_accessor" />
 
+        <!-- Discriminator Map -->
+        <service id="serializer.mapping.class_discriminator_resolver" class="Symfony\Component\Serializer\Mapping\ClassDiscriminatorFromClassMetadata">
+            <argument type="service" id="serializer.mapping.class_metadata_factory" />
+        </service>
+        <service id="Symfony\Component\Serializer\Mapping\ClassDiscriminatorResolverInterface" alias="serializer.mapping.class_discriminator_resolver" />
+
         <!-- Normalizer -->
         <service id="serializer.normalizer.dateinterval" class="Symfony\Component\Serializer\Normalizer\DateIntervalNormalizer">
             <!-- Run before serializer.normalizer.object -->
@@ -50,6 +56,7 @@
             <argument>null</argument> <!-- name converter -->
             <argument type="service" id="serializer.property_accessor" />
             <argument type="service" id="property_info" on-invalid="ignore" />
+            <argument type="service" id="serializer.mapping.class_discriminator_resolver" on-invalid="ignore" />
 
             <!-- Run after all custom normalizers -->
             <tag name="serializer.normalizer" priority="-1000" />