Silex 2.3.0搭配Symfony4.4报错：Call to a member function has() on null

我们有一个基于Silex 2.2.5分支与Symfony 3.4的大型旧应用，计划迁移出Silex，但目前仍在多工程师协作开发中。为在PHP7.4于2022年11月停止支持前升级到PHP8.1，我们将依赖升级至Silex 2.3.0与Symfony4.4，过程无问题，但页面加载时出现致命错误：
PHP Fatal error: Uncaught Error: Call to a member function has() on null in /var/task/vendor/symfony/http-kernel/EventListener/SessionListener.php:41

该错误来自Symfony4.4新增的onKernelRequest方法，调试发现$this->container为null，且SessionListener的构造函数未被调用。临时移除该方法后站点可正常运行，但这并非可行方案。我们查阅Silex文档未找到适配Symfony4.4的额外要求，搜索得知可能需通过services.yml注入容器依赖，但项目无此文件，现寻求解决思路，是否有成功运行Silex2.3.0与Symfony4.4的案例？

完整错误栈信息 #

result = {array} [9]
 0 = {array} [7]
  file = "/var/task/vendor/symfony/event-dispatcher/EventDispatcher.php"
  line = {int} 264
  function = "onKernelRequest"
  class = "Symfony\Component\HttpKernel\EventListener\SessionListener"
  object = {OurCompany\Session\SessionListener} [3]
  type = "->"
  args = {array} [3]
 1 = {array} [7]
  file = "/var/task/vendor/symfony/event-dispatcher/EventDispatcher.php"
  line = {int} 239
  function = "doDispatch"
  class = "Symfony\Component\EventDispatcher\EventDispatcher"
  object = {Symfony\Component\EventDispatcher\EventDispatcher} [3]
  type = "->"
  args = {array} [3]
 2 = {array} [7]
  file = "/var/task/vendor/symfony/event-dispatcher/EventDispatcher.php"
  line = {int} 73
  function = "callListeners"
  class = "Symfony\Component\EventDispatcher\EventDispatcher"
  object = {Symfony\Component\EventDispatcher\EventDispatcher} [3]
  type = "->"
  args = {array} [3]
 3 = {array} [7]
  file = "/var/task/vendor/symfony/http-kernel/HttpKernel.php"
  line = {int} 135
  function = "dispatch"
  class = "Symfony\Component\EventDispatcher\EventDispatcher"
  object = {Symfony\Component\EventDispatcher\EventDispatcher} [3]
  type = "->"
  args = {array} [2]
 4 = {array} [7]
  file = "/var/task/vendor/symfony/http-kernel/HttpKernel.php"
  line = {int} 81
  function = "handleRaw"
  class = "Symfony\Component\HttpKernel\HttpKernel"
  object = {Symfony\Component\HttpKernel\HttpKernel} [4]
  type = "->"
  args = {array} [2]
 5 = {array} [7]
  file = "/var/task/vendor/silex/silex/src/Silex/Application.php"
  line = {int} 496
  function = "handle"
  class = "Symfony\Component\HttpKernel\HttpKernel"
  object = {Symfony\Component\HttpKernel\HttpKernel} [4]
  type = "->"
  args = {array} [3]
 6 = {array} [7]
  file = "/var/task/vendor/silex/silex/src/Silex/Application.php"
  line = {int} 477
  function = "handle"
  class = "Silex\Application"
  object = {OurCompany\Application} [9]
  type = "->"
  args = {array} [1]
 7 = {array} [7]
  file = "/var/task/lib/Application.php"
  line = {int} 37
  function = "run"
  class = "Silex\Application"
  object = {OurCompany\Application} [9]
  type = "->"
  args = {array} [1]
 8 = {array} [7]
  file = "/var/task/web/index.php"
  line = {int} 43
  function = "run"
  class = "OurCompany\Application"
  object = {OurCompany\Application} [9]
  type = "->"
  args = {array} [1]

解决思路 #

1. 修正自定义SessionListener的注册与依赖注入 #

从错误栈可见，实际执行的是OurCompany\Session\SessionListener而非Symfony原生类，说明你们自定义了SessionListener。Symfony4.4的原生SessionListener构造函数要求注入ContainerInterface，如果自定义类继承了它，必须确保：

• 自定义类的构造函数正确接收并传递容器参数给父类
• 在Silex中注册该服务时注入容器实例

示例注册代码：

$app['session.listener'] = function ($app) {
    return new OurCompany\Session\SessionListener($app);
};

2. 兼容Symfony4.4的SessionListener逻辑改动 #

若自定义Listener不需要Symfony4.4新增的onKernelRequest逻辑，可以直接重写该方法，避免调用容器相关代码；若需要保留新逻辑，必须保证容器被正确注入。

3. 手动配置服务（无需services.yml） #

Silex支持纯代码配置服务，无需依赖services.yml。在应用初始化阶段，确保SessionListener服务被正确定义：

use OurCompany\Session\SessionListener;
use Symfony\Component\DependencyInjection\ContainerInterface;

$app->register(new Silex\Provider\SessionServiceProvider());

// 覆盖默认的session listener服务
$app['session.listener'] = function (ContainerInterface $container) {
    return new SessionListener($container);
};

4. 排查服务冲突 #

检查项目中其他自定义服务、事件订阅者的注册方式，确保它们符合Symfony4.4的依赖注入规范，避免出现容器未正确传递的情况。

关于兼容性案例 #

确实有团队成功运行Silex 2.3.0 + Symfony4.4，核心是确保所有依赖容器的服务（如事件监听器）在注册时都正确注入容器实例，适配Symfony4.4的组件改动。

内容的提问来源于stack exchange，提问作者Aaryn