class RouteProcessorCurrent

class RouteProcessorCurrent implements OutboundRouteProcessorInterface {
    
    /**
     * The current route match.
     *
     * @var \Drupal\Core\Routing\RouteMatchInterface
     */
    protected $routeMatch;
    
    /**
     * Constructs a new RouteProcessorCurrent.
     *
     * @param \Drupal\Core\Routing\RouteMatchInterface $route_match
     *   The current route match.
     */
    public function __construct(RouteMatchInterface $route_match) {
        $this->routeMatch = $route_match;
    }
    
    /**
     * {@inheritdoc}
     */
    public function processOutbound($route_name, Route $route, array &$parameters, ?BubbleableMetadata $bubbleable_metadata = NULL) {
        if ($route_name === '<current>') {
            if ($current_route = $this->routeMatch
                ->getRouteObject()) {
                $requirements = $current_route->getRequirements();
                // Setting _method and _schema is deprecated since 2.7. Using
                // setMethods() and setSchemes() are now the recommended ways.
                unset($requirements['_method']);
                unset($requirements['_schema']);
                $route->setRequirements($requirements);
                $route->setPath($current_route->getPath());
                $route->setSchemes($current_route->getSchemes());
                $route->setMethods($current_route->getMethods());
                $route->setOptions($current_route->getOptions());
                $route->setDefaults($current_route->getDefaults());
                $parameters = array_merge($parameters, $this->routeMatch
                    ->getRawParameters()
                    ->all());
                if ($bubbleable_metadata) {
                    $bubbleable_metadata->addCacheContexts([
                        'route',
                    ]);
                }
            }
            else {
                // If we have no current route match available, point to the frontpage.
                $route->setPath('/');
            }
        }
    }

}