Broken.php

<?php

namespace Drupal\Core\Entity\Plugin\EntityReferenceSelection;

use Drupal\Core\Entity\EntityReferenceSelection\SelectionPluginBase;
use Drupal\Core\Form\FormStateInterface;

/**
 * Defines a fallback plugin for missing entity_reference selection plugins.
 *
 * @EntityReferenceSelection(
 *   id = "broken",
 *   label = @Translation("Broken/Missing")
 * )
 */
class Broken extends SelectionPluginBase {
    
    /**
     * {@inheritdoc}
     */
    public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
        $form = parent::buildConfigurationForm($form, $form_state);
        $form['selection_handler'] = [
            '#markup' => $this->t('The selected selection handler is broken.'),
        ];
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getReferenceableEntities($match = NULL, $match_operator = 'CONTAINS', $limit = 0) {
        return [];
    }
    
    /**
     * {@inheritdoc}
     */
    public function countReferenceableEntities($match = NULL, $match_operator = 'CONTAINS') {
        return 0;
    }
    
    /**
     * {@inheritdoc}
     */
    public function validateReferenceableEntities(array $ids) {
        return [];
    }

}