If you are here is because you have the Name source files using lowercase_with_underscores error in Flutter. How to solve it?

Easy. Click on the link you see in the error. That page tells that names like SliderMenu.dart, filesystem.dart or file-system.dart are bad. You should be using underscores, like slider_menu.dart or file_system.dart.

Once you change the name of the file, Flutter will be happy.