[LiveComponent] Incorrect handling of nullable enum types

[maartendekeizer]

I created a component with 2 writeable live props, both nullable and with a BackedEnumType.
When I changed a value a sync is happen as expected, but this will result in an error when one of the fields are empty

With request payload {"data":1,"newPriority":null,"newStatus":"new","_checksum":"***"} the following error occured
The data is neither an integer nor a string, you should pass an integer or a string that can be parsed as an enumeration case of type App\Enum\Priority.

And with request payload {"data":1,"newPriority":"high","newStatus":"","_checksum":"***"} the following error occured
"" is not a valid backing value for enum "App\Enum\Priority"

It think this is caused by the fact that the hydrator always try to denormalize and that empty strings are not converted to null values.

ux/src/LiveComponent/src/LiveComponentHydrator.php

Lines 170 to 175 in ebe425c

	if ($method = $liveProp->hydrateMethod()) {
	// TODO: Error checking
	$value = $component->$method($dehydratedValue);
	} elseif ($property->getType() instanceof \ReflectionNamedType && !$property->getType()->isBuiltin()) {
	$value = $this->normalizer->denormalize($value, $property->getType()->getName(), 'json', [self::LIVE_CONTEXT => true]);
	}

A suggestion for the fix

            if ($method = $liveProp->hydrateMethod()) {
                // TODO: Error checking
                $value = $component->$method($dehydratedValue);
            } elseif ($property->getType() instanceof \ReflectionNamedType && !$property->getType()->isBuiltin()) {
                if ($value === '' && $property->getType()->allowsNull() === true) {
                    // value is given as empty string, the property type is not a string (isBuiltin-method)
                    // so we can assume that value is meant to be empty
                    $value = null;
                }
                if ($value !== null || $property->getType()->allowsNull() === false) {
                    // if value is null but the property does not allow null run denormalization too
                    $value = $this->normalizer->denormalize($value, $property->getType()->getName(), 'json', [self::LIVE_CONTEXT => true]);
                }
            }

Component

<?php

declare(strict_types=1);

namespace App\Twig\Component;

use App\Enum\Priority;
use App\Enum\Status;
use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
use Symfony\UX\LiveComponent\Attribute\AsLiveComponent;
use Symfony\UX\LiveComponent\Attribute\LiveAction;
use Symfony\UX\LiveComponent\Attribute\LiveProp;


#[AsLiveComponent('prio', template: 'component/status.html.twig')]
class StatusComponent extends AbstractController
{
    #[LiveProp(writable: true)]
    public ?Priority $newPriority = null;

    #[LiveProp(writable: true)]
    public ?Status $newStatus = null;

    public function __invoke(): void
    {
    }
}

Template

    <div {{ attributes }}>
        Status: <input type="text" data-model="newStatus" value="{{ this.newStatus.value|default('') }}">
        Prio: <input type="text" data-model="newPriority" value="{{ this.newPriority.value|default('') }}">
        <br>
        {{ this.newStatus.value|default('') }} / {{ this.newPriority.value|default('') }}
    </div>

[kbond]

Thanks for the report @maartendekeizer, #416 should fix this.

[maartendekeizer]

@kbond Tried #416, it works for the situation where the payload value is null, but when a empty string is submitted I still got an error Expected argument of type "?App\Enum\MyEnum", "string" given at property path "myField".
I think an empty string is submitted when the user touched the input/select but did cleared the value afterwards.

[kbond]

Got it, I'll adjust my PR to account for this.

[kbond]

it works for the situation where the payload value is null, but when a empty string is submitted I still got an error

#416 should now account for this. @maartendekeizer, can you confirm?

[maartendekeizer]

@kbond yes, thanks a lot!