fallbackaction.php

См. документацию.

<?php
 
namespace Bitrix\Main\Engine;
 
final class FallbackAction extends Action
{
    public const ACTION_NAME   = 'fallback';
    public const ACTION_METHOD = 'fallbackAction';

    private $originalActionName;
 
    public function __construct($name, Controller $controller, $config = [])
    {
        $this->originalActionName = $name;
        parent::__construct(self::ACTION_NAME, $controller, $config);
    }
 
    protected function buildBinder()
    {
        if ($this->binder === null)
        {
            $controller = $this->getController();
            $this->binder = AutoWire\ControllerBinder::buildForMethod($controller, self::ACTION_METHOD)
                ->setController($controller)
                ->setSourcesParametersToMap([
                    ['actionName' => $this->originalActionName]
                ])
            ;
        }
 
        return $this;
    }
}