Flarum\Asset\RevisionCompiler::putRevision PHP Method

    protected function putRevision($revision)
    {
        if (file_exists($file = $this->getRevisionFile())) {
            $manifest = json_decode(file_get_contents($file), true);
        } else {
            $manifest = [];
        }
        $manifest[$this->filename] = $revision;
        return file_put_contents($this->getRevisionFile(), json_encode($manifest));
    }