PHP composer autoload 一直报错 class not found

Question

很久没使用composer了，今天试了一下，结果autoload一直都是报错

Fatal error: Uncaught Error: Class 'helper\Router' not found

文件结构：

Folder PATH listing for volume 新加卷
Volume serial number is 000C-8DEE
F:.
│   cmd.php
│   composer.json
├───helper
│       functions.php
│       Router.php
│
└───vendor
    │   autoload.php
    │
    └───composer
            autoload_classmap.php
            autoload_files.php
            autoload_namespaces.php
            autoload_psr4.php
            autoload_real.php
            autoload_static.php
            ClassLoader.php
            installed.json
            LICENSE

文件cmd.php 源码

<?php
require 'vendor/autoload.php';
$r = new helperRouter();

文件helper/Router.php 源码

<?php
namespace helper;
class Router {
}

文件composer.json 源码

{
  "name": "tool/import",
  "description": "create test data for test",
  "authors": [
    {
      "name": "author",
      "email": "[e-mail]"
 }
  ],
  "require": {},
  "autoload": {
  }
}

执行 php cmd.php 报错提示如下：

F:\test\demo003>php cmd.php
PHP Fatal error:  Uncaught Error: Class 'helper\Router' not found in F:\test\demo003\cmd.php:5
Stack trace:
#0 {main}
  thrown in F:\test\demo003\cmd.php on line 5

Fatal error: Uncaught Error: Class 'helper\Router' not found in F:\test\demo003\cmd.php:5
Stack trace:
#0 {main}
  thrown in F:\test\demo003\cmd.php on line 5

很多年没试过composer，现在autoload 不起作用了。试过这样写composer.json

"autoload": {
  "psr-4": {
    "\\": "/"
 },    
  "files": [
 ]
}

更新 composer dump-autoload 之后，依旧是提示那个错误。

Answer 1

 "psr-4": {
    "helper\\": "helper/"
 },