lib/Twig/lib/Twig/Environment.php
public function isTemplateFresh($name, $time)
    {
        if (0 === $this->lastModifiedExtension) {
            foreach ($this->extensions as $extension) {
                $r = new ReflectionObject($extension);
                if (file_exists($r->getFileName()) && ($extensionTime = filemtime($r->getFileName())) > $this->lastModifiedExtension) {
                    $this->lastModifiedExtension = $extensionTime;
                }
            }
        }

        return $this->lastModifiedExtension <= $time && $this->getLoader()->isFresh($name, $time);
    }
public function isTemplateFresh($name, $time)
    {
        if (0 === $this->lastModifiedExtension) {
            foreach ($this->extensions as $extension) {
                $r = new ReflectionObject($extension);
                if (file_exists($r->getFileName()) && ($extensionTime = filemtime($r->getFileName())) > $this->lastModifiedExtension) {
                    $this->lastModifiedExtension = $extensionTime;
                }
            }
        }

        return $this->lastModifiedExtension <= $time && $this->getLoader()->isFresh($name, $time);
    }
Returns true if the template is still fresh.

Besides checking the loader for freshness information,
this method also checks if the enabled extensions have
not changed.

@param string $name The template name
@param int    $time The last modification time of the cached template

@return bool true if the template is fresh, false otherwise