laravel8路由错误Target class [App\Http\Controllers\RosaController] does not exist.需要添加命名空间。
解决方法1

use Illuminate\Support\Facades\Route;
use App\Http\Controllers\Web\RosaController;

Route::get('/',[RosaController::class,'index']);

解决方法2

namespace App\Http\Controllers;
use Illuminate\Support\Facades\Route;

Route::get('/',[Web\RosaController::class,'index']);