It reads:

--8<---------------cut here---------------start------------->8---
$ ./pre-inst-env guix time-machine -q -C channels.scm -- help

;;; (file "channels.scm")

;;; (try-canonicalize-path "channels.scm")

;;; (load-file #<unspecified>)

;;; (load-channels #<unspecified>)
guix time-machine: error: 'channels.scm' did not return a list of channels
--8<---------------cut here---------------end--------------->8---

In other words, instead of raising an error, it returns #<unspecified>
and thus because ’load-channels’ tests against ’list?’ which
#<unspecified> is obviously not then bang!

Bah the easy fix is to check with ’unspecified?’ directly in
’load-channels’.  But that does not really fix the issue, IMHO.

The issue is that because a file named channels.scm is around in
load-path.  For instance, let say the non-existent file is named
’packages.scm’:

--8<---------------cut here---------------start------------->8---
$ ls packages.scm
ls: cannot access 'packages.scm': No such file or directory

$ guix time-machine -q -C packages.scm -- help
guix time-machine: error: 'packages.scm' did not return a list of channels
--8<---------------cut here---------------end--------------->8---

In other words, is the comment accurate

               ;; Give 'load' an absolute file name so that it doesn't try to
               ;; search for FILE in %LOAD-PATH.

?

Well, since I am not sure to get the use case of
’try-canonicalize-path’, then I don’t know what could be the best fix.
But I guess ’canonicalize-path’ is not doing what we expect, right?

Cheers,
simon