FilesystemLoader.php

<?php

namespace Drupal\Core\Template\Loader;

use Drupal\Core\Extension\ModuleHandlerInterface;
use Drupal\Core\Extension\ThemeHandlerInterface;

/**
 * Loads templates from the filesystem.
 *
 * This loader adds module and theme template paths as namespaces to the Twig
 * filesystem loader so that templates can be referenced by namespace, like
 * @block/block.html.twig or @mytheme/page.html.twig.
 */
class FilesystemLoader extends \Twig_Loader_Filesystem {
    
    /**
     * 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 $theme_handler
     *   The theme handler service.
     */
    public function __construct($paths, ModuleHandlerInterface $module_handler, ThemeHandlerInterface $theme_handler) {
        parent::__construct($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);
        }
    }
    
    /**
     * 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, '/\\');
    }

}