Override of the default Filesystem loader for twig to be used on Google Appengine.

AppEngine.php

<?php

/**
 * Override of the default Filesystem loader for twig to be used on Google Appengine.
 * Appengine cannot write to the disk so all templates must be precompiled and the 
 * file id must stay the same.
 * 
 * See https://www.leonrenkema.nl/2015/07/05/php-on-app-engine/
 */
class Twig_Loader_AppEngine extends Twig_Loader_Filesystem
{
    /**
     * Checks if the template can be found.
     *
     * @param string $name The template name
     *
     * @return bool true if the template exists, false otherwise
     */
    protected function doFindTemplate($name)
    {
        $this->validateName($name);

        if (isset($this->cache[$name])) {
            return true;
        }

        if (isset($this->errorCache[$name])) {
            return false;
        }

        list($namespace, $shortname) = $this->parseName($name);

        if (!isset($this->paths[$namespace])) {
            $this->errorCache[$name] = sprintf('There are no registered paths for namespace "%s".', $namespace);

            return false;
        }

        foreach ($this->paths[$namespace] as $path) {
            if (is_file($path.'/'.$shortname)) {

                $this->cache[$name] = $path.'/'.$shortname;

                return true;
            }
        }

        $this->errorCache[$name] = sprintf('Unable to find template "%s" (looked into: %s).', $name, implode(', ', $this->paths[$namespace]));

        return false;
    }
}