Hello,

A colleague reported this weird “unbound variable” error message, which
is ignored in this case but can be fatal in other cases (see below):

--8<---------------cut here---------------start------------->8---
$ guix time-machine -C /tmp/channels.scm -- shell emacs-elementaryx-ox-publish-as-default bash-minimal -n
error: #{ %make-platform-procedure/abi-check}#: unbound variable
hint: Did you forget a `use-modules' form?

14.4 MB would be downloaded
$ cat /tmp/channels.scm 
(list (channel
        (name 'guix)
        (url "https://git.savannah.gnu.org/git/guix.git")
        (branch "master")
        (commit
          "5a95cf76e1d0f9fdff5b232b42337c657b76d1d4")
        (introduction
          (make-channel-introduction
            "9edb3f66fd807b096b48283debdcddccfea34bad"
            (openpgp-fingerprint
              "BBB0 2DDF 2CEA F6A8 0D1D  E643 A2A0 6DF2 A33A 54FA"))))
      (channel
        (name 'guix-hpc)
        (url "https://gitlab.inria.fr/guix-hpc/guix-hpc.git")
        (branch "master")
        (commit
          "b7608db6ecff32e2569ed8407d62ac1485e2856a")))
--8<---------------cut here---------------end--------------->8---

The crux of the problem is that ‘platforms’ happily browses any
‘guix/platforms’ it finds in the load path; in my case, after looking
for guix/platforms modules in this specific Guix instance, it goes on to
browse ~/.guix-home/profile/… and /run/current-system/profile/…, both of
which being on GUILE_LOAD_PATH.  The modules it finds there, in this
case, are not ABI-compatible with those of the Guix instance, hence the
error message.

Reduced case:

--8<---------------cut here---------------start------------->8---
$ guix time-machine -C /tmp/channels.scm -- repl -q
GNU Guile 3.0.9
Copyright (C) 1995-2023 Free Software Foundation, Inc.

Guile comes with ABSOLUTELY NO WARRANTY; for details type `,show w'.
This program is free software, and you are welcome to redistribute it
under certain conditions; type `,show c' for details.

Enter `,help' for help.
scheme@(guix-user)> ,use(guix platform)
scheme@(guix-user)> (platform-modules)
error: #{ %make-platform-procedure/abi-check}#: unbound variable
hint: Did you forget a `use-modules' form?

$1 = (#<interface (guix platforms arm) 7f2929e0c8c0> #<interface (guix platforms avr) 7f2929e0c640> #<interface (guix platforms mips) 7f2929e0c3c0> #<interface (guix platforms or1k) 7f2929e0c140> #<interface (guix platforms powerpc) 7f2929ebde60> #<interface (guix platforms riscv) 7f2929ebdbe0> #<interface (guix platforms x86) 7f2929ebd960> #<interface (guix platforms arm) 7f2929e0c8c0> #<interface (guix platforms avr) 7f2929e0c640> #<interface (guix platforms mips) 7f2929e0c3c0> #<interface (guix platforms or1k) 7f2929e0c140> #<interface (guix platforms powerpc) 7f2929ebde60> #<interface (guix platforms riscv) 7f2929ebdbe0> #<interface (guix platforms x86) 7f2929ebd960>)
scheme@(guix-user)> %load-path
$2 = ("/gnu/store/n9xy5r1a0njyn8ml33p4mm8rxfn93drb-guix-module-union/share/guile/site/3.0" "/gnu/store/1gd9nsy4cps8fnrd1avkc9l01l7ywiai-guile-3.0.9/share/guile/3.0" "/gnu/store/1gd9nsy4cps8fnrd1avkc9l01l7ywiai-guile-3.0.9/share/guile/3.0" "/gnu/store/1gd9nsy4cps8fnrd1avkc9l01l7ywiai-guile-3.0.9/share/guile/site/3.0" "/gnu/store/1gd9nsy4cps8fnrd1avkc9l01l7ywiai-guile-3.0.9/share/guile/site" "/gnu/store/1gd9nsy4cps8fnrd1avkc9l01l7ywiai-guile-3.0.9/share/guile" "/home/ludo/.guix-home/profile/share/guile/site/3.0" "/home/ludo/.guix-home/profile/share/guile/site/3.0" "/run/current-system/profile/share/guile/site/3.0")
--8<---------------cut here---------------end--------------->8---

The same problem exists in:

  • ‘image-modules’ in (gnu system images);

  • ‘build-system-modules’ in (guix import utils);

  • ‘importer-modules’ in (guix upstream);

  • ‘bootloader-modules’ in (gnu bootloader).

One radical way to fix it would be to not use anything outside the
module union: