Illuminate\Routing\RouteRegistrar

routes.php

<?php

/*
 * use Illuminate\Routing\RouteRegistrar@group instead of Illuminate\Routing\Router@group
 */
Route::domain('')
    ->middleware('')
    ->namespace('Product')
    ->prefix('products')
    ->as('products.')
->group(base_path('routes/groups/products.php'));

/*
 * Not like that
 */
Route::group([
    'domain' => '',
    'middleware' => '',
    'namespace' => 'Product',
    'prefix' => 'products',
    'as' => 'products.',
], base_path('routes/groups/products.php'));