Date.php

<?php

namespace Drupal\Core\Render\Element;

use Drupal\Core\Render\Attribute\FormElement;
use Drupal\Core\Render\Element;

/**
 * Provides a form element for date selection.
 *
 * Properties:
 * - #default_value: A string for the default date in 'Y-m-d' format.
 * - #size: The size of the input element in characters.
 *
 * @code
 * $form['expiration'] = [
 *   '#type' => 'date',
 *   '#title' => $this->t('Content expiration'),
 *   '#default_value' => '2020-02-05',
 * ];
 * @endcode
 */

#[FormElement('date')]
class Date extends FormElementBase {

  /**
   * {@inheritdoc}
   */
  public function getInfo() {
    $class = static::class;
    return [
      '#input' => TRUE,
      '#theme' => 'input__date',
      '#process' => [
        [
          $class,
          'processAjaxForm',
        ],
      ],
      '#pre_render' => [
        [
          $class,
          'preRenderDate',
        ],
      ],
      '#theme_wrappers' => [
        'form_element',
      ],
      '#attributes' => [
        'type' => 'date',
      ],
      '#date_date_format' => 'Y-m-d',
    ];
  }

  /**
   * Adds form-specific attributes to a 'date' #type element.
   *
   * Supports HTML5 types of 'date', 'datetime', 'datetime-local', and 'time'.
   * Falls back to a plain textfield. Used as a sub-element by the datetime
   * element type.
   *
   * @param array $element
   *   An associative array containing the properties of the element.
   *   Properties used: #title, #value, #options, #description, #required,
   *   #attributes, #id, #name, #type, #min, #max, #step, #value, #size. The
   *   #name property will be sanitized before output. This is currently done by
   *   initializing Drupal\Core\Template\Attribute with all the attributes.
   *
   * @return array
   *   The $element with prepared variables ready for #theme 'input__date'.
   */
  public static function preRenderDate($element) {
    if (empty($element['#attributes']['type'])) {
      $element['#attributes']['type'] = 'date';
    }
    Element::setAttributes($element, [
      'id',
      'name',
      'type',
      'min',
      'max',
      'step',
      'value',
      'size',
    ]);
    static::setAttributes($element, [
      'form-' . $element['#attributes']['type'],
    ]);
    return $element;
  }

}