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;
    }

}