> Ah. I did install patched guix into the system (and that's how
> https://debbugs.gnu.org/cgi/bugreport.cgi?bug=50090).
> 
> I still don't quite understand if channel we pull from also should be patched.
> Let's assume it should:
> 
>   $ LANG=C ./pre-inst-env guix pull --url=. --commit=e9029ed5eae45ee8f53f055ee66f9bce353cac84 --root=guix0
>   guix pull: error: root=guix0: unrecognized option
> 
> I'm not sure what --root= does. Is it a user name? Or a profile name?

I forgot the exact option, it should have been "--profile=guix0".
From (guix)Submitting patches:

  15. Make sure your changes do not break Guix and simulate a ‘guix
     pull’ with:
          guix pull --url=/path/to/your/checkout --profile=/tmp/guix.master

Greetings,
Maxime.