Hello Guix!

As you may know, librsvg 2.50 on ‘core-updates-frozen’ depends on Rust.
However mrustc, which we use to build the first Rust compiler, currently
only works on x86_64.  This means that ~28% of the packages on
‘core-updates-frozen’ are x86_64-only (vs. ~15% on ‘master’).

Among these, the most problematic missing packages are desktop
environments: Xfce, GNOME, etc.  So far our “pledge”, encoded in
‘etc/release-manifest.scm’, was that all the desktop environments would
be available on x86_64 and i686, so that one could install Guix System
just the same way on both.  Currently this is no longer possible on
‘core-updates-frozen’, and I think that’s a problem.

The patch below does something unorthodox: it reintroduces librsvg 2.40
(written in C) and uses it selectively so we can have a desktop
environment with Xfce on i686.  It’s not enough to get GDM though;
there’s a couple of GNOME packages that depend on librsvg and I haven’t
checked whether they work with the old librsvg.

I think that’s the most realistic way to salvage desktops on i686 for
now.  In the future mrustc may well support i686¹, or perhaps GCC-Rust
will be mature enough to replace mrustc, but in both cases we’re talking
about a longer time frame.

What do people think?

Thanks,
Ludo’.

¹ https://github.com/thepowersgang/mrustc/issues/78