bug#47496: Very slow `guix environment -l nyxt/build-scripts/guix.scm

[Pierre Neidhardt]

Nyxt provides a "guix.scm" to build Nyxt locally:

https://github.com/atlas-engineer/nyxt/blob/3239b10d816861d329dce10863cb84f9d0bd76ed/build-scripts/guix.scm

A few weeks ago (not sure exactly when and why), `guix environment -l
guix.scm` started being extremely slow.

By this, I mean that

--8<---------------cut here---------------start------------->8---
$ guix environment -v 99 --pure --load=build-scripts/guix.scm 
--8<---------------cut here---------------end--------------->8---

hangs for minutes, maybe hours before it proceeds.
It does not display anything, not even with "-v 99".

In one occurrence, it even hung completely after downloading a few substitutes:

--8<---------------cut here---------------start------------->8---
$ guix environment -v 99 --pure --load=build-scripts/guix.scm 
13.0 MB will be downloaded
downloading from 
https://ci.guix.gnu.org/nar/lzip/c3755727p11afak5azj52xv4hv9jy0wj-libselinux-3.0-python
 ...
 libselinux-3.0-python  141KiB                      1.1MiB/s 00:00 
[##################] 100.0%

downloading from 
https://ci.guix.gnu.org/nar/lzip/qlyzqdx6i50d3rfz6hapf53gpjc43n7c-python-3.8.2-tk
 ...
 python-3.8.2-tk  30KiB                             7.4MiB/s 00:00 
[##################] 100.0%

15.3 MB will be downloaded
downloading from 
https://ci.guix.gnu.org/nar/lzip/v2kdcv8d5dxsbb7s73nj020jry78mcvw-glib-2.62.6 
...
 glib-2.62.6  2.4MiB                                1.7MiB/s 00:01 
[##################] 100.0%

downloading from 
https://ci.guix.gnu.org/nar/lzip/s5dlqhxqa36vax72mx341lhlrz7b1mpz-python2-2.7.17
 ...
 python2-2.7.17  9.5MiB                             4.6MiB/s 00:02 
[##################] 100.0%

downloading from 
https://ci.guix.gnu.org/nar/gzip/d1n7p65d3k8ddj0pmydgrsbk26xv5808-glib-2.62.6-bin
 ...
 glib-2.62.6-bin  149KiB                            2.5MiB/s 00:00 
[##################] 100.0%

downloading from 
https://ci.guix.gnu.org/nar/lzip/wk4k3cnygif6is42iq5wgp1yihr5abv5-python2-2.7.17-tk
 ...
 python2-2.7.17-tk  28KiB                           5.9MiB/s 00:00 
[##################] 100.0%

downloading from 
https://ci.guix.gnu.org/nar/lzip/rhwgqqg43jhwb4hzpzljp4b1ax9i0786-serf-1.3.9 ...
 serf-1.3.9  78KiB                                  5.5MiB/s 00:00 
[##################] 100.0%

downloading from 
https://ci.guix.gnu.org/nar/lzip/9y6v4zy10pcanivd05chfryc2nsxnian-subversion-1.14.1
 ...
 subversion-1.14.1  2.5MiB                          8.3MiB/s 00:00 
[##################] 100.0%
--8<---------------cut here---------------end--------------->8---

(That's the full output, it hung there.)

Something must be wrong, because I found a workaround that's fishy: if I
comment out some inputs from the guix.scm and build the environment,
then it works.  Then I uncomment the commented inputs and this time the
environment builds in a few seconds.

Any idea?

-- 
Pierre Neidhardt
https://ambrevar.xyz/

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