Recursive symfony/configuration

Configuration.php

<?php

use Symfony\Component\Config\Definition\Builder\ArrayNodeDefinition;
use Symfony\Component\Config\Definition\Builder\TreeBuilder;
use Symfony\Component\Config\Definition\ConfigurationInterface;

/**
 * Helper function to create recursive nodes
 */
function recursiveNode(string $name, callable $callback)
{
    $builder = new TreeBuilder();
    $root = $builder->root($name, 'variable');

    $root->defaultValue([]);

    $root
        ->beforeNormalization()
        ->ifTrue(function ($v) { return !is_array($v); })
        ->thenInvalid("The {$name} element must be an array.")
    ;

    $root
        ->beforeNormalization()
        ->always(function (iterable $children) use ($builder, $callback) {
            $config = [];
            foreach ($children as $name => $child) {
                $node = $builder->root($name);
                $callback($node, $callback);
                $config[$name] = $node->getNode(true)->finalize($child);
            }
            return $config;
        })
    ;

    return $root;
}

/**
 * Usage of recursiveNode
 * This allows for configuration like:
 *
 * routing_bundle:
 *    routes:
 *        - name: route_1
 *          url: url_1
 *          children:
 *              - name: route_2
 *                url: url_2
 *              - name: route_3
 *                url: url_3
 *                children:
 *                    - name: route_4
 *                    - url: url_4
 *        - name: route_5
 *          url: url_5
 */
class Configuration implements ConfigurationInterface
{
    public function getConfigTreeBuilder()
    {
        $tree = new TreeBuilder();
        $root = $tree->root('my_routing_bundle');

        $root
            ->children()
                ->append(
                    recursiveNode('routes', function ($node, $recursive) {
                        return $this->routes($node, $recursive);
                    })
                )
            ->end()
        ;

        return $tree;
    }

    private function routes(ArrayNodeDefinition $node, callable $recursive)
    {
        $node
            ->addDefaultsIfNotSet()
            ->children()
                ->scalarNode('description')->end()
                ->scalarNode('name')
                    ->isRequired()
                    ->cannotBeEmpty()
                ->end()
                ->scalarNode('url')
                    ->defaultNull()
                ->end()
                ->append(recursiveNode('children', $recursive))
        ;
    }
}