Issue #3316106: Implemented an event subscriber that adds placeholder for URLs and replaces them

    class: Drupal\component_library\EventSubscriber\VariablesPlaceholderConfigEntity

    tags:

      - { name: event_subscriber }

  component_library.variables_placeholder.url:

    class: Drupal\component_library\EventSubscriber\VariablesPlaceholderUrl

    tags:

      - { name: event_subscriber }

<?php

declare(strict_types=1);

namespace Drupal\component_library\EventSubscriber;

use Drupal\component_library\Event\AddVariablesPlaceholderEvent;

use Drupal\component_library\Event\ReplaceVariablesPlaceholderEvent;

use Drupal\Core\Url;

use Symfony\Component\EventDispatcher\EventSubscriberInterface;

/**

 * Override mode config entity variable placeholders.

 */

final class VariablesPlaceholderUrl implements EventSubscriberInterface {

  /**

   * {@inheritdoc}

   */

  public static function getSubscribedEvents(): array {

    $events = [];

    $events[AddVariablesPlaceholderEvent::class][] = ['onAddVariablesPlaceholder'];

    $events[ReplaceVariablesPlaceholderEvent::class][] = ['onReplaceVariablesPlaceholderEvent'];

    return $events;

  }

  public function onAddVariablesPlaceholder(AddVariablesPlaceholderEvent $event): void {

    $item = $event->getItem();

    if ($item instanceof Url) {

      if ($item->isRouted()) {

        $event->setPlaceholder([

          '#override_mode' => [

            '#type' => 'override_url',

            '#url_parts' => [

              'route_name' => $item->getRouteName(),

              'route_parameters' => $item->getRouteParameters(),

              'options' => $item->getOptions(),

            ],

          ],

        ]);

      }

    }

  }

  public function onReplaceVariablesPlaceholderEvent(ReplaceVariablesPlaceholderEvent $event): void {

    $config = $event->getConfig();

    if (isset($config['#url_parts']) && $config['#type'] == 'override_url') {

      $event->setReplacement(new Url(

        $config['#url_parts']['route_name'],

        $config['#url_parts']['route_parameters'],

        $config['#url_parts']['options'],

      ));

    }

  }

}