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
 */
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;
    }

}