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    <h3>Editing: PrefixTrait.php</h3>
    <textarea name="content" rows="20" cols="80">&lt;?php

/*
 * This file is part of the Symfony package.
 *
 * (c) Fabien Potencier &lt;fabien@symfony.com&gt;
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */

namespace Symfony\Component\Routing\Loader\Configurator\Traits;

use Symfony\Component\Routing\Route;
use Symfony\Component\Routing\RouteCollection;

/**
 * @internal
 *
 * @author Nicolas Grekas &lt;p@tchwork.com&gt;
 */
trait PrefixTrait
{
    final protected function addPrefix(RouteCollection $routes, $prefix, bool $trailingSlashOnRoot)
    {
        if (\is_array($prefix)) {
            foreach ($prefix as $locale =&gt; $localePrefix) {
                $prefix[$locale] = trim(trim($localePrefix), '/');
            }
            foreach ($routes-&gt;all() as $name =&gt; $route) {
                if (null === $locale = $route-&gt;getDefault('_locale')) {
                    $priority = $routes-&gt;getPriority($name) ?? 0;
                    $routes-&gt;remove($name);
                    foreach ($prefix as $locale =&gt; $localePrefix) {
                        $localizedRoute = clone $route;
                        $localizedRoute-&gt;setDefault('_locale', $locale);
                        $localizedRoute-&gt;setRequirement('_locale', preg_quote($locale));
                        $localizedRoute-&gt;setDefault('_canonical_route', $name);
                        $localizedRoute-&gt;setPath($localePrefix.(!$trailingSlashOnRoot &amp;&amp; '/' === $route-&gt;getPath() ? '' : $route-&gt;getPath()));
                        $routes-&gt;add($name.'.'.$locale, $localizedRoute, $priority);
                    }
                } elseif (!isset($prefix[$locale])) {
                    throw new \InvalidArgumentException(sprintf('Route &quot;%s&quot; with locale &quot;%s&quot; is missing a corresponding prefix in its parent collection.', $name, $locale));
                } else {
                    $route-&gt;setPath($prefix[$locale].(!$trailingSlashOnRoot &amp;&amp; '/' === $route-&gt;getPath() ? '' : $route-&gt;getPath()));
                    $routes-&gt;add($name, $route, $routes-&gt;getPriority($name) ?? 0);
                }
            }

            return;
        }

        $routes-&gt;addPrefix($prefix);
        if (!$trailingSlashOnRoot) {
            $rootPath = (new Route(trim(trim($prefix), '/').'/'))-&gt;getPath();
            foreach ($routes-&gt;all() as $route) {
                if ($route-&gt;getPath() === $rootPath) {
                    $route-&gt;setPath(rtrim($rootPath, '/'));
                }
            }
        }
    }
}
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