BigPipeMessagesHooks.php

<?php

declare (strict_types=1);
namespace Drupal\big_pipe_messages_test\Hook;

use Drupal\Core\Hook\Attribute\Hook;
use Drupal\Core\Security\Attribute\TrustedCallback;

/**
 * Hook implementations for big_pipe_test.
 */
class BigPipeMessagesHooks {
  
  /**
   * Implements hook_element_info_alter().
   */
  public function elementInfoAlter(array &$info) : void {
    $info['status_messages']['#pre_render'][] = static::class . '::preRenderMessages';
  }
  
  /**
   * Pre render callback.
   *
   * Removes #placeholder_strategy from the messages element to force the
   * messages placeholder to go via the big pipe strategy for testing purposes.
   */
  public static function preRenderMessages(array $element) : array {
    if (isset($element['#attached']['placeholders'])) {
      $key = key($element['#attached']['placeholders']);
      unset($element['#attached']['placeholders'][$key]['#placeholder_strategy_denylist']);
    }
    if (isset($element['messages']['#attached']['placeholders'])) {
      $key = key($element['messages']['#attached']['placeholders']);
      unset($element['messages']['#attached']['placeholders'][$key]['#placeholder_strategy_denylist']);
    }
    return $element;
  }

}