class UpdateRoot

class UpdateRoot {
    
    /**
     * The Drupal kernel.
     *
     * @var \Drupal\Core\DrupalKernelInterface
     */
    protected $drupalKernel;
    
    /**
     * The request stack.
     *
     * @var \Symfony\Component\HttpFoundation\RequestStack
     */
    protected $requestStack;
    
    /**
     * The update root.
     *
     * @var string
     */
    protected $updateRoot;
    
    /**
     * Constructs an UpdateRootFactory instance.
     *
     * @param \Drupal\Core\DrupalKernelInterface $drupal_kernel
     *   The Drupal kernel.
     * @param \Symfony\Component\HttpFoundation\RequestStack $request_stack
     *   The request stack.
     */
    public function __construct(DrupalKernelInterface $drupal_kernel, RequestStack $request_stack) {
        $this->drupalKernel = $drupal_kernel;
        $this->requestStack = $request_stack;
    }
    
    /**
     * Sets the root path under which projects are installed or updated.
     *
     * @param string $update_root
     *   The update root.
     */
    public function set(string $update_root) : void {
        $this->updateRoot = $update_root;
    }
    
    /**
     * Gets the root path under which projects are installed or updated.
     *
     * The Update Manager will ensure that project files can only be copied to
     * specific subdirectories of this root path.
     *
     * @return string
     */
    public function __toString() : string {
        // Return the $updateRoot when it is set.
        if (isset($this->updateRoot)) {
            return $this->updateRoot;
        }
        // Normally the Update Manager's root path is the same as the app root (the
        // directory in which the Drupal site is installed).
        $root_path = $this->drupalKernel
            ->getAppRoot();
        // When running in a test site, change the root path to be the testing site
        // directory. This ensures that it will always be writable by the webserver
        // (thereby allowing the actual extraction and installation of projects by
        // the Update Manager to be tested) and also ensures that new project files
        // added there won't be visible to the parent site and will be properly
        // cleaned up once the test finishes running. This is done here (rather
        // than having the tests enable a module which overrides the update root
        // factory service) to ensure that the parent site is automatically kept
        // clean without relying on test authors to take any explicit steps. See
        // also \Drupal\update\Tests\Functional\UpdateTestBase::setUp().
        if (DRUPAL_TEST_IN_CHILD_SITE) {
            $kernel = $this->drupalKernel;
            $request = $this->requestStack
                ->getCurrentRequest();
            $root_path .= '/' . $kernel::findSitePath($request);
        }
        return $root_path;
    }

}