bug#36785: Impossible to pull on foreign distro

[Julien Lepiller]

Hi guix,

I gave a small tutorial to someone today, where we installed guix on top of a 
foreign distro. We used the script and everything went smoothly, and after 
finding out that we were going to build php (we were trying to define a VM that 
would serve one of their services), we tried to run guix pull:

sudo guix pull —commit=…

However the command failed immediately with:

Migrating profile generations to '/var/guix/profiles/per-user/root'...
Guix pull: error: symlink: File exists: 
"/var/guix/profiles/per-user/root/current-guix"

Indeed, the file exists and everything looks good. Why does guix try to migrate 
a profile that's already good?

I was able to work around that situation, but it's not great for our users.