TextareaWidget.php

<?php

namespace Drupal\text\Plugin\Field\FieldWidget;

use Drupal\Core\Field\FieldItemListInterface;
use Drupal\Core\Field\Plugin\Field\FieldWidget\StringTextareaWidget;
use Drupal\Core\Form\FormStateInterface;
use Symfony\Component\Validator\ConstraintViolationInterface;

/**
 * Plugin implementation of the 'text_textarea' widget.
 *
 * @FieldWidget(
 *   id = "text_textarea",
 *   label = @Translation("Text area (multiple rows)"),
 *   field_types = {
 *     "text_long"
 *   }
 * )
 */
class TextareaWidget extends StringTextareaWidget {
    
    /**
     * {@inheritdoc}
     */
    public function settingsForm(array $form, FormStateInterface $form_state) {
        $element = parent::settingsForm($form, $form_state);
        $element['rows']['#description'] = $this->t('Text editors (like CKEditor) may override this setting.');
        return $element;
    }
    
    /**
     * {@inheritdoc}
     */
    public function formElement(FieldItemListInterface $items, $delta, array $element, array &$form, FormStateInterface $form_state) {
        $main_widget = parent::formElement($items, $delta, $element, $form, $form_state);
        $element = $main_widget['value'];
        $element['#type'] = 'text_format';
        $element['#format'] = $items[$delta]->format;
        $element['#base_type'] = $main_widget['value']['#type'];
        return $element;
    }
    
    /**
     * {@inheritdoc}
     */
    public function errorElement(array $element, ConstraintViolationInterface $violation, array $form, FormStateInterface $form_state) {
        if (isset($element['format']['#access']) && !$element['format']['#access'] && preg_match('/^[0-9]*\\.format$/', $violation->getPropertyPath())) {
            // Ignore validation errors for formats if formats may not be changed,
            // such as when existing formats become invalid.
            // See \Drupal\filter\Element\TextFormat::processFormat().
            return FALSE;
        }
        return $element;
    }

}