I've tested this patch (on its own, applied to wip-ppc64le locally,
without the other two patches mentioned earlier in this thread), and it
successfully restores the "supported systems" for emacs (thus fixing the
tests/package.sh test failure), without changing rust's list of
supported systems, which remains hard-coded to x86_64-linux.

Eventually I think I will definitely need a change like the one Chris
proposed in order to actually troubleshoot build failures involving rust
on powerpc64le-linux, but I suppose when the time comes, I can do it in
a private branch and save the build farm some wasted cycles.  It's fine
with me if we don't make a change like that right now, since it isn't
blocking my porting work.

Mark H Weaver <mhw@netris.org> writes:

> Aside: I wish that Guix included a convenient tool to answer the
> question "Why does package X depend on package Y?", i.e. "What paths of
> dependencies lead from package X to package Y?", without having to view
> the entire dependency graph (which is often too complex to grasp
> visually).

Ricardo Wurmus <rekado@elephly.net> writes:

> (“guix graph” is of no help here, because it doesn’t show build system
> packages, so I looked through the derivations.)

The "--paths" option with "--type=bag" shows you this (results
below were, of course, taken before applying the patch above):

--8<---------------cut here---------------start------------->8---
marusich@suzaku:~/repos/guix$ ./pre-inst-env guix graph --type=bag --path gtk+ rust
gtk+@3.24.24
gdk-pixbuf+svg@2.42.2
librsvg@2.50.3
rust@1.49.0
--8<---------------cut here---------------end--------------->8---

Christopher Baines <mail@cbaines.net> writes:

> I've gone ahead and pushed the patch I proposed to master, I think it's
> a step forward.
>
> As you say, adapting the change for core-updates might be good as
> well. I want to check though if rust builds for i686-linux on
> core-updates, as the path is different to master, so it may well work.
>
> So yeah, once I've found out whether rust works on i686-linux on
> core-updates, I might make a change there too.

I don't have a strong personal opinion about this, since I'm building
everything from source anyway, and I want a patch like this eventually
on core-updates, too.  However, in light of Mark's comments, is it a
good idea to apply that patch right now?

-- 
Chris