OptionalSuffixExtension.php

<?php

namespace App\Form\Extension;

use Symfony\Component\Form\AbstractTypeExtension;
use Symfony\Component\Form\Extension\Core\Type\FormType;
use Symfony\Component\Form\FormInterface;
use Symfony\Component\Form\FormView;
use Symfony\Component\Translation\TranslatorInterface;

/**
 * Append an (optional) prefix to any form field.
 */
class OptionalSuffixExtension extends AbstractTypeExtension
{
    /**
     * @var TranslatorInterface
     */
    private $translator;

    public function __construct(TranslatorInterface $translator)
    {
        $this->translator = $translator;
    }

    public function finishView(FormView $view, FormInterface $form, array $options)
    {
        unset($form);
        unset($options);

        if (!$view->vars['required']) {
            if ($view->parent !== null && $view->parent->vars['block_prefixes'][1] === 'choice') {
                // Do not add an optional to any element of an expanded choice tpye.
                return;
            }

            if (!empty($view->vars['label'])) {
                if ($view->vars['translation_domain'] !== false) {
                    // Translate the label
                    $view->vars['label'] = $this->translator->trans(
                        $view->vars['label'],
                        [],
                        $view->vars['translation_domain']
                    );
                }

                $view->vars['label'] .= sprintf(' (%s)', $this->translator->trans('optional'));
                $view->vars['translation_domain'] = false; // Prevent a second translation attempt
            }
        }
    }

    /**
     * Returns the name of the type being extended.
     *
     * @return string The name of the type being extended
     */
    public function getExtendedType()
    {
        return FormType::class;
    }
}