bug#42076: SSL_CERT_* variables and GVFS (and probably more) are not initialized if you don't use GDM

[raingloom <raingloom@riseup.net>]

Hi all!

As the subject says, the initialization of the all important
environment variables that Guix is built around are rather lacking.
I had a lot of SSL related errors for weeks until I figured out that it
was caused by SSL_CERT_{DIR,FILE} not being set. I consider this rather
serious as it makes it difficult to use git, download things, or even
access the web to find help in debugging the issue.

The other thing that is not set up is GVFS. This used to be an issue on
the default GDM based setups as well, but has been fixed a few months
ago. However, it was evidently not fixed universally, as seemingly
every other way of logging in does not start GVFS.

If users are expected to set this up for themselves, then we need
proper documentation on where it should be done, but ideally these
services should be working even in a plain console login.

I hope we can actually fix this properly this time.

My particular setup is SDDM+Sway+Zsh, but I've tested others as well
and they all failed.
My other machine uses GDM+i3 and that has no issues.