bug#56545: guix time-machine/shell throws "unsupported manifest format" error

[Maxim Cournoyer]

Hi Guix,

I recently tried re-entering an older environment via:

$ guix describe
Generation 128  Jul 06 2022 14:50:39    (current)
  guix 17892c5
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: master
    commit: 17892c5f9c5c5c93325884834a58cc2a4fafa51f
  sfl-packages 6385881
    repository URL: https://gitlab.com/Apteryks/sfl-guix-channel
    branch: master
    commit: 6385881124429016f750b0f562b70e07f592275e
    
$ guix time-machine -C channels.scm -- shell

with in the current directory the project manifest file:

--8<---------------cut here---------------start------------->8---
(packages->manifest
 (map specification->package
      (list
       ;; General utilities.
       "bash"
       "coreutils"
       "cpio"
       "cqfd"
       "findutils"
       "gawk"
       "git"
       "grep"
       "gzip"
       "info-reader"                   ;to generate the info dir entry
       "less"                          ;for a better git experience
       "make"
       "man-db"                     ;to generate the manpages database
       "pandoc"
       "pict"
       "sed"
       "openssh"                        ;for the SSH client used by git
       "tar"
       "tree"
       "wget"

       ;; Python and libraries.
       "python-matplotlib"
       "python-paramiko"
       "python-robotframework"
       "python-robotframework-datadriver"
       "python-robotframework-sshlibrary"
       "python-robotframework-stacktrace"
       "python-scp"
       "python-selenium"
       "python-tenacity"
       "python-wrapper"

       ;; Drivers
       "python-labjack"

       ;; Development tools.
       "python-flake8"
       "python-flake8-isort"
       "python-ipython"
       "python-ipython-documentation"
       ;; To use ipdb with Python's breakpoint():
       ;; 'export PYTHONBREAKPOINT=ipdb.sset_trace'
       ;; then set 'breakpoint()' in Python sources or
       ;; 'Evaluate breakpoint()' in RobotFramework sources.
       "python-ipdb"
       "python-isort"
       "python-pdbpp"                   ;for the 'sticky' mode
       "python-pylint"
       "python-robotframework-lint"

       ;; Browsers.
       "icecat"
       "ungoogled-chromium")))
--8<---------------cut here---------------end--------------->8---

and the channels.scm file:

--8<---------------cut here---------------start------------->8---
(list (channel
       (inherit %default-guix-channel)
       (commit
        "ceeb2bfcaeb4380e01d26c8425e28b94ac13558a"))) ;2022-06-07
--8<---------------cut here---------------end--------------->8---

and was surprised to be greeted with the following error:


--8<---------------cut here---------------start------------->8---
(repl-version 0 1 1)
(exception %exception (non-self-quoting 140737300283024 "#<&message message: 
\"unsupported manifest format\">"))
/var/log/guix/drvs/j8/0wjfx7s7nxhcn0wjxfysnnv2knx0c1-guix-package-cache.drv 
(END)
--8<---------------cut here---------------end--------------->8---

What does it mean?  Which manifest is it referring to?

Thanks,

Maxim