BubbleCachePreprocessor.php

<?php

namespace Drupal\module\Plugin\Preprocess;

use Drupal\Core\Cache\CacheableMetadata;
use Drupal\Core\Render\Element;
use Drupal\preprocess\PreprocessPluginBase;
use Symfony\Component\DependencyInjection\ContainerInterface;
use Drupal\Core\Plugin\ContainerFactoryPluginInterface;

/**
 * Base class for preprocess plugins.
 *
 * Define any helper functions needed in plugins within this class.
 */
class PreprocessBase extends PreprocessPluginBase implements ContainerFactoryPluginInterface {

  /**
   * Whether to bubble descendant cache metadata to the top level.
   *
   * @var bool
   */
  public $bubbleCache = FALSE;

  /**
   * Constructs a new PreprocessBase object.
   *
   * @param array $configuration
   *   A configuration array containing information about the plugin instance.
   * @param string $plugin_id
   *   The plugin_id for the plugin instance.
   * @param mixed $plugin_definition
   *   The plugin implementation definition.
   * @param \Symfony\Component\DependencyInjection\ContainerInterface $container
   *   The dependency injection container.
   */
  public function __construct(array $configuration, $plugin_id, $plugin_definition, ContainerInterface $container) {
    parent::__construct($configuration, $plugin_id, $plugin_definition);
  }

  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
    return new static(
      $configuration,
      $plugin_id,
      $plugin_definition,
      $container,
    );
  }

  /**
   * {@inheritdoc}
   */
  public function preprocess(array $variables): array {
    // Bubble cache metadata if configured to do so.
    if ($this->bubbleCache) {
      $cache = $this->bubbleCache($variables, CacheableMetadata::createFromRenderArray($variables));
      $cache->applyTo($variables);
    }
    return $variables;
  }

  /**
   * Ensures that all cache metadata for nested elements bubble to response.
   *
   * Some templates do not print the content render array choosing to instead
   * print variables created during preprocessing. When this happens, cache
   * metadata is lost causing improper cache behavior. This method does the work
   * of grabbing cache metadata from a render array regardless of the depth of
   * the #cache key in the array.
   *
   * @param array $variables
   *   Elements to pull cache metadata from.
   * @param \Drupal\Core\Cache\CacheableMetadata $cache
   *   Cache metadata for the current element.
   *
   * @return \Drupal\Core\Cache\CacheableMetadata
   *   Updated cache metadata.
   */
  public function bubbleCache(array $variables, CacheableMetadata $cache) {
    foreach (@Element::children($variables) as $key) {
      if (!empty($variables[$key])) {
        $cache = $this->bubbleCache($variables[$key], $cache);
      }
    }
    return $cache->merge(CacheableMetadata::createFromRenderArray($variables));
  }

}