class ContestType extends AbstractType {
public function buildForm(FormBuilderInterface $builder, array $options)
{
    $builder
        ->add('tournament', EntityType::class, [
            'class' => Tournament::class,
            'choice_label' => 'name',
            'required' => false,
        ])
        ->add('player', EntityType::class, [
            'class' => Player::class,
            'choice_label' => 'pseudo',
            'required' => false,
            ])
        ->add('loser', EntityType::class, [
            'class' => Player::class,
            'choice_label' => 'pseudo',
            'required' => false,
        ])
        ->add('game', EntityType::class, [
            'class' => Game::class,
            'choice_label' => 'name',
        ]);

    $builder->get('tournament')->addEventListener(
        FormEvents::POST_SUBMIT,
        function (FormEvent $event) {
            $form = $event->getForm();

            $this->addPlayerField($form->getParent(), $form->getData());
        }
    );

}

private function addPlayerField(FormInterface $form, ?Tournament $tournament)
{
    $builder = $form->getConfig()->getFormFactory()->createNamedBuilder(
        'player',
        EntityType::class,
        null,
        [
            'class' => Player::class,
            'choices' => $tournament->getPlayers(),
            'auto_initialize' => false,
            'choice_label' => 'pseudo',
            'required' => false,

        ] );


    $builder->addEventListener(
        FormEvents::POST_SUBMIT,
        function (FormEvent $event) {
            $form = $event->getForm();

            $this->addLoserField($form->getParent(), $form->getData());

        }
    );

    $form->add($builder->getForm());
}


private function addLoserField(FormInterface $form, ?Player $player)
{
    $form->add( 'loser', EntityType::class, [
        'class' => Player::class,
        'choice_label' => 'pseudo',
        'choices' => $player->getTeam()->getPlayers(),
        'required' => false,
        ]);
}


public function configureOptions(OptionsResolver $resolver)
{
    $resolver->setDefaults([
        'data_class' => Contest::class,
    ]);
}}