yii\base\Controller::findLayoutFile PHP Method

    public function findLayoutFile($view)
    {
        $module = $this->module;
        if (is_string($this->layout)) {
            $layout = $this->layout;
        } elseif ($this->layout === null) {
            while ($module !== null && $module->layout === null) {
                $module = $module->module;
            }
            if ($module !== null && is_string($module->layout)) {
                $layout = $module->layout;
            }
        }
        if (!isset($layout)) {
            return false;
        }
        if (strncmp($layout, '@', 1) === 0) {
            $file = Yii::getAlias($layout);
        } elseif (strncmp($layout, '/', 1) === 0) {
            $file = Yii::$app->getLayoutPath() . DIRECTORY_SEPARATOR . substr($layout, 1);
        } else {
            $file = $module->getLayoutPath() . DIRECTORY_SEPARATOR . $layout;
        }
        if (pathinfo($file, PATHINFO_EXTENSION) !== '') {
            return $file;
        }
        $path = $file . '.' . $view->defaultExtension;
        if ($view->defaultExtension !== 'php' && !is_file($path)) {
            $path = $file . '.php';
        }
        return $path;
    }