New Pattern update event

A new update event (patternkit.pattern_update) is fired for event subscribers when the Pattern entity referenced by a block is updated. The new event is intended to allow developers and pattern library maintainers to alter existing content within a site to match new schema structures applied during the update process.

An example scenario where the property name "text" in the "@patternkit/atoms/example/src/example" pattern is to be changed to "title" might be addressed with an event subscriber as shown below:

my_module.services.yml

services:
  my_module.example_update_subscriber:
    class: Drupal\my_module\EventSubscriber\ExampleUpdateSubscriber
    tags:
      - { name: event_subscriber }

my_module/src/EventSubscriber/ExampleUpdateSubscriber

namespace Drupal\my_module\EventSubscriber;

use Drupal\patternkit\Event\PatternUpdateEvent;
use Drupal\patternkit\PatternkitEvents;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;

/**
 * An event subscriber for the patternkit pattern update process.
 *
 * @see \Drupal\patternkit\PatternkitEvents
 * @see \Drupal\patternkit\Event\PatternUpdateEvent
 */
class ExampleUpdateSubscriber implements EventSubscriberInterface {

  /**
   * {@inheritdoc}
   */
  public static function getSubscribedEvents() {
    $events[PatternkitEvents::PATTERN_UPDATE] = ['onPatternUpdate', 200];

    return $events;
  }

  /**
   * React to the pattern update process and alter content if necessary.
   *
   * @param \Drupal\patternkit\Event\PatternUpdateEvent $event
   *   The pattern update event containing all update information.
   */
  public function onPatternUpdate(PatternUpdateEvent $event): void {
    $original_pattern = $event->getOriginalPattern();

    // Abort here if this isn't an applicable pattern.
    if ($original_pattern->getAssetId() !== '@patternkit/atoms/example/src/example') {
      return;
    }

    $content = $event->getContent();

    // Rename the text field if it exists in the content.
    if (isset($content['text'])) {
      $content['title'] = $content['text'];
      unset($content['text']);
      $event->setContent($content);
    }
  }

}