$payment = EasyWeChat::payment();
try {
    $payment->handlePaidNotify(function ($message, $fail) {
        $fail('xxx');
    });
} catch (EasyWeChat\Kernel\Exceptions\Exception $e) {
    Log::warning('WeChatPay Notify Exception',
        ['code' => $e->getCode(), 'message' => $e->getMessage()]
    );
}

这里为啥$fail能这样用,追了下源码

namespace EasyWeChat\Payment\Notify;

use Closure;

class Paid extends Handler
{
    /**
     * @param \Closure $closure
     *
     * @return \Symfony\Component\HttpFoundation\Response
     *
     * @throws \EasyWeChat\Kernel\Exceptions\Exception
     */
    public function handle(Closure $closure)
    {
        $this->strict(
            \call_user_func($closure, $this->getMessage(), [$this, 'fail'])
        );

        return $this->toResponse();
    }
}
//toresponese
    public function toResponse(): Response
    {
        $base = [
            'return_code' => is_null($this->fail) ? static::SUCCESS : static::FAIL,
            'return_msg' => $this->fail,
        ];

        $attributes = array_merge($base, $this->attributes);

        if ($this->sign) {
            $attributes['sign'] = Support\generate_sign($attributes, $this->app->getKey());
        }

        return new Response(XML::build($attributes));
    }
    //strict
        protected function strict($result)
    {
        if (true !== $result && is_null($this->fail)) {
            $this->fail(strval($result));
        }
    }

上边来看$fail实际上传入的是[$this,'fail'],那为啥能$fail(‘’);
是我理解错文档了还是代码分析错了