EntityReferenceAutocompleteTagsWidget.php

<?php

namespace Drupal\Core\Field\Plugin\Field\FieldWidget;

use Drupal\Core\Field\Attribute\FieldWidget;
use Drupal\Core\Field\FieldItemListInterface;
use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\StringTranslation\TranslatableMarkup;

/**
 * Plugin implementation of the 'entity_reference_autocomplete_tags' widget.
 */
class EntityReferenceAutocompleteTagsWidget extends EntityReferenceAutocompleteWidget {
    
    /**
     * {@inheritdoc}
     */
    public function formElement(FieldItemListInterface $items, $delta, array $element, array &$form, FormStateInterface $form_state) {
        $element = parent::formElement($items, $delta, $element, $form, $form_state);
        $element['target_id']['#tags'] = TRUE;
        $element['target_id']['#default_value'] = $items->referencedEntities();
        return $element;
    }
    
    /**
     * {@inheritdoc}
     */
    public function massageFormValues(array $values, array $form, FormStateInterface $form_state) {
        return $values['target_id'];
    }

}