Drupal text field widget to set custom maxlength

TextfieldWithMaxlengthWidget

<?php

namespace Drupal\mymodule\Plugin\Field\FieldWidget;

use Drupal\Core\Field\FieldItemListInterface;
use Drupal\Core\Field\Plugin\Field\FieldWidget\StringTextfieldWidget;
use Drupal\Core\Form\FormStateInterface;

/**
 * Plugin implementation of the 'textfield_with_maxlength' widget.
 *
 * @FieldWidget(
 *   id = "textfield_with_maxlength",
 *   label = @Translation("Textfield with maxlength"),
 *   field_types = {
 *     "text",
 *     "string"
 *   }
 * )
 */
class TextfieldWithMaxlengthWidget extends StringTextfieldWidget {

  /**
   * {@inheritdoc}
   */
  public static function defaultSettings() {
    return [
      'custom_maxlength' => NULL,
    ] + parent::defaultSettings();
  }

  /**
   * {@inheritdoc}
   */
  public function settingsForm(array $form, FormStateInterface $form_state) {
    $elements = parent::settingsForm($form, $form_state);

    $elements['custom_maxlength'] = [
      '#type' => 'number',
      '#title' => t('Maxlength of textfield'),
      '#default_value' => $this->getCustomMaxLength(),
      '#description' => t('Set a custom maxlength. Leave it empty to use field default value (@size).', ['@size' => $this->getFieldSetting('max_length')]),
      '#min' => 1,
      '#max' => $this->getFieldSetting('max_length'),
    ];

    return $elements;
  }

  /**
   * {@inheritdoc}
   */
  public function settingsSummary() {
    $summary = parent::settingsSummary();

    $summary[] = t('Maxlength: @size', ['@size' => $this->getCustomMaxLength()]);

    return $summary;
  }

  /**
   * {@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['#maxlength'] = $this->getCustomMaxLength();

    return $element;
  }

  /**
   * Return custom maxlength.
   *
   * This method returns the custom maxlength if is set, otherwise defaults to
   * the field max_length setting.
   *
   * @return int
   *   The maxlength size.
   */
  protected function getCustomMaxLength() {
    return $this->getSetting('custom_maxlength') ?: $this->getFieldSetting('max_length');
  }

}