app\assets\AppAsset::init PHP Method

    public function init()
    {
        parent::init();
        // /!\ CSS/LESS development only setting /!\
        // Touch the asset folder with the highest mtime of all contained files
        // This will create a new folder in web/assets for every change and request
        // made to the app assets.
        if (getenv('APP_ASSET_FORCE_PUBLISH')) {
            $path = \Yii::getAlias($this->sourcePath);
            $files = FileHelper::findFiles($path);
            $mtimes = [];
            foreach ($files as $file) {
                $mtimes[] = filemtime($file);
            }
            touch($path, max($mtimes));
        }
    }