Drupal 8 - Change the core's default path for `/contact` so that we can use it as an alias.

example.services.yml

services:
  example.route_subscriber:
    class: Drupal\example\Routing\RouteSubscriber
    tags:
      - { name: event_subscriber }

src-Routing-RouteSubscriber.php

<?php
// Save this file as `src/Routing/RouteSubscriber.php` in your module directory.

namespace Drupal\example\Routing;

use Drupal\Core\Routing\RouteSubscriberBase;
use Symfony\Component\Routing\RouteCollection;

/**
 * Listens to the dynamic route events.
 */
class RouteSubscriber extends RouteSubscriberBase {

  /**
   * {@inheritdoc}
   */
  public function alterRoutes(RouteCollection $collection) {
    // Change the core's default path for `/contact` so that we can use it as an alias.
    if ($route = $collection->get('contact.site_page')) {
      $route->setPath('/contactform');
    }
    if ($route = $collection->get('entity.contact_form.canonical')) {
      $route->setPath('/contactform/{contact_form}');
    }
  }

}