bug#53514: Guix should not set global variables that may affect host

[Liliana Marie Prikler <liliana.prikler@ist.tugraz.at>]

Hi,

Am Montag, dem 24.01.2022 um 17:24 -0500 schrieb Maxim Cournoyer:
> Hello!
> 
> There are multiple reports about the negative effects of Guix setting
> variables such as XDG_DATA_DIRS on foreign distributions, that may
> cause problems a severe as locking users out of their graphical
> session [0].
> 
> In my opinion, we should pursue patching every application/library to
> use a Guix-specific variant, e.g. GUIX_XDG_DATA_DIRS instead of
> XDG_DATA_DIRS, to avoid interfering with the host system, as was done
> for GUIX_PYTHONPATH.
> 
> This is a big task in itself; we can open more focused/actionable
> tasks for each environment variable, starting with those causing the
> most serious issues.
> 
> Any takers?
I'm not convinced that patching XDG_DATA_DIRS is a good solution here.
Even if we go forward and implement this for each and every
library/application, (it would be reasonably simple to do so for glib
and qt at least, but there's many more consumers, including Guix
itself), we'd just force users on foreign distros to set up their
XDG_DATA_DIRS for us if they e.g. want to have desktop icons available,
so they'd quickly encounter the same issue on their own.

I see two ways forward for this:  First, "ignore it" and just document
the behaviour.  This isn't just a bug Guix is suffering from, it also
affects other third-party package installers like Flatpak and Snap. 
Since distros increasingly become aware of them, this will soon no
longer be an issue for most our users.  Second, extend search-paths
with a way of enforcing a default value when none is set.  This way,
Guix will still override XDG_DATA_DIRS, but since
$HOME/.local/share:/usr/share is set as the default as per spec, it
will do what the distro expected.

WDYT?