Ubuntu 18.04 on Dell Alienware m15 Nvidia GTX 1070 : stuck after login

Once Ubuntu 18.04 is installed, I got stuck after the graphical login.

It appears this is a known bug (Password accepted but login fails (blank purple screen and mouse pointer only)), and people have already brought a workaround on AskUbuntu: Ubuntu 18.04 and nVidia. Stuck after boot.

So for short:

• Edit your Grub linux line to add nouveau.modeset=0 (you’ll be able to correctly log in)
• Then install proprietary drivers

TODO: find a way to make this usable with FLOSS drivers (called nouveau)