InstallerRouteProviderLazyBuilder.php

<?php

namespace Drupal\Core\Installer;

use Drupal\Core\Routing\RouteProviderLazyBuilder;
use Symfony\Component\Routing\Route;

/**
 * A Route Provider front-end for use during the installer.
 */
class InstallerRouteProviderLazyBuilder extends RouteProviderLazyBuilder {
    
    /**
     * {@inheritdoc}
     */
    public function getRouteByName($name) {
        if ($name === '<none>' || $name === '<front>') {
            // During the installer template_preprocess_page() uses the routing system
            // to determine the front page. At this point building the router for this
            // is unnecessary work.
            return new Route('/');
        }
        return parent::getRouteByName($name);
    }

}