class FilesystemLoader

class FilesystemLoader extends TwigFilesystemLoader {
    
    /**
     * Allowed file extensions.
     *
     * @var string[]
     */
    protected $allowedFileExtensions = [
        'css',
        'html',
        'js',
        'svg',
        'twig',
    ];
    
    /**
     * Constructs a new FilesystemLoader object.
     *
     * @param string|array $paths
     *   A path or an array of paths to check for templates.
     * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
     *   The module handler service.
     * @param \Drupal\Core\Extension\ThemeHandlerInterface $theme_handler
     *   The theme handler service.
     * @param mixed[] $twig_config
     *   Twig configuration from the service container.
     */
    public function __construct($paths, ModuleHandlerInterface $module_handler, ThemeHandlerInterface $theme_handler, array $twig_config = []) {
        parent::__construct($paths);
        // Add namespaced paths for modules and themes.
        $namespaces = [];
        foreach ($module_handler->getModuleList() as $name => $extension) {
            $namespaces[$name] = $extension->getPath();
        }
        foreach ($theme_handler->listInfo() as $name => $extension) {
            $namespaces[$name] = $extension->getPath();
        }
        foreach ($namespaces as $name => $path) {
            $this->addPath($path . '/templates', $name);
            // Allow accessing the root of an extension by using the namespace without
            // using directory traversal from the `/templates` directory.
            $this->addPath($path, $name);
        }
        if (!empty($twig_config['allowed_file_extensions'])) {
            // Provide a safe fallback for sites that have not updated their
            // services.yml file or rebuilt the container, as well as for child
            // classes.
            $this->allowedFileExtensions = $twig_config['allowed_file_extensions'];
        }
    }
    
    /**
     * Adds a path where templates are stored.
     *
     * @param string $path
     *   A path where to look for templates.
     * @param string $namespace
     *   (optional) A path name.
     */
    public function addPath($path, $namespace = self::MAIN_NAMESPACE) {
        // Invalidate the cache.
        $this->cache = [];
        $this->paths[$namespace][] = rtrim($path, '/\\');
    }
    
    /**
     * {@inheritdoc}
     */
    protected function findTemplate($name, $throw = TRUE) {
        $extension = pathinfo($name, PATHINFO_EXTENSION);
        if (!in_array($extension, $this->allowedFileExtensions, TRUE)) {
            if (!$throw) {
                return NULL;
            }
            // Customize the list of extensions if no file extension is allowed.
            $extensions = $this->allowedFileExtensions;
            $no_extension = array_search('', $extensions, TRUE);
            if (is_int($no_extension)) {
                unset($extensions[$no_extension]);
                $extensions[] = 'or no file extension';
            }
            if (empty($extension)) {
                $extension = 'no file extension';
            }
            throw new LoaderError(sprintf("Template %s has an invalid file extension (%s). Only templates ending in one of %s are allowed. Set the twig.config.allowed_file_extensions container parameter to customize the allowed file extensions", $name, $extension, implode(', ', $extensions)));
        }
        // Previously it was possible to access files in the parent directory of a
        // namespace. This was removed in Twig 2.15.3. In order to support backwards
        // compatibility, we are adding path directory as a namespace, and therefore
        // we can remove the directory traversal from the name.
        // @todo deprecate this functionality for removal in Drupal 11.
        if (preg_match('/(^\\@[^\\/]+\\/)\\.\\.\\/(.*)/', $name, $matches)) {
            $name = $matches[1] . $matches[2];
        }
        return parent::findTemplate($name, $throw);
    }

}