<?php

namespace App\Service;


use Doctrine\ORM\QueryBuilder;
use Doctrine\Persistence\ObjectManager;
use Symfony\Bridge\Doctrine\Form\Type\EntityType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\Form\FormInterface;
use Symfony\Component\Form\FormTypeExtensionInterface;
use Symfony\Component\Form\FormView;
use Symfony\Component\OptionsResolver\OptionsResolver;


class EntityTypeExtension extends EntityType implements FormTypeExtensionInterface
{
    /**
     * {@inheritdoc}
     */
    public function configureOptions(OptionsResolver $resolver)
    {
        // This is a nasty way to get the choiceLoader callable defined by
        // the EntityType.        
        $myResolver = new class extends OptionsResolver {
            private $choiceLoader;

            public function setDefault($option, $value)
            {
                if ($option === 'choice_loader'){
                    $this->choiceLoader = $value;
                }

                parent::setDefault($option, $value);
            }

            public function getChoiceLoader()
            {
                return $this->choiceLoader;
            }
        };

        // Please be warned that the options are now configured twice, here and by Symfony.
        parent::configureOptions($myResolver);

        // This is magic: now the callable is bound to EntityTypeExtension
        // context instead of the EntityType context so we can override 
        // the getLoader() method-below
        $choiceLoader = $myResolver->getChoiceLoader();
        $resolver->setDefault('choice_loader', $choiceLoader);
    }

    /**
     * Return the default loader object.
     *
     * @param QueryBuilder $queryBuilder
     * @param string       $class
     *
     * @return ORMQueryBuilderLoader
     */
    public function getLoader(ObjectManager $manager, $queryBuilder, $class)
    {
        if (!$queryBuilder instanceof QueryBuilder) {
            throw new \TypeError(sprintf('Expected an instance of %s, but got %s.', QueryBuilder::class, \is_object($queryBuilder) ? \get_class($queryBuilder) : \gettype($queryBuilder)));
        }

        return new MyORMQueryBuilderLoader($queryBuilder);
    }

    public static function getExtendedTypes()
    {
        return [EntityType::class];
    }

    /**
     * @inheritDoc
     */
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
    }

    /**
     * @inheritDoc
     */
    public function buildView(
        FormView $view,
        FormInterface $form,
        array $options
    ) {
    }

    /**
     * @inheritDoc
     */
    public function finishView(
        FormView $view,
        FormInterface $form,
        array $options
    ) {
    }

    /**
     * @inheritDoc
     */
    public function getExtendedType()
    {
        return [EntityType::class];
    }
}

<?php

namespace App\Service;

use Doctrine\ORM\QueryBuilder;
use Doctrine\Persistence\ObjectManager;
use Symfony\Bridge\Doctrine\Form\Type\EntityType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\Form\FormInterface;
use Symfony\Component\Form\FormTypeExtensionInterface;
use Symfony\Component\Form\FormView;
use Symfony\Component\OptionsResolver\OptionsResolver;

class EntityTypeExtension extends EntityType implements FormTypeExtensionInterface
{
    /**
     * {@inheritdoc}
     */
    public function configureOptions(OptionsResolver $resolver)
    {
        $resolver->setDefault('choice_loader', function (Options $options, $choiceLoader) {
            return $choiceLoader instanceof \Closure ? \Closure::bind($choiceLoader, $this) : $choiceLoader;
        });
    }
    // ...
}