Subject: bug#75709: Emacs fails to start with "List contains a loop" error

From: Thiago Jung Bauermann <[email-masked]>
Date: Mon, 20 Jan 2025 19:43:00 -0300

Since a recent "guix pull", Emacs (I tested with the emacs-pgtk package)
can't start up anymore:

$ emacs
List contains a loop: ("/home/user/.guix-profile/lib/emacs/native-site-lisp" "/gnu/store/k62mmzkbmivw2r3wwlpcxs3lp9vwjyac-emacs-lsp-mode-9.0.0/lib/emacs/native-site-lisp" "/home/user/.guix-profile/lib/emacs/native-site-lisp" "/home/user/.guix-profile/lib/emacs/native-site-lisp" "/gnu/store/k62mmzkbmivw2r3wwlpcxs3lp9vwjyac-emacs-lsp-mode-9.0.0/lib/emacs/native-site-lisp" . #2)
$ echo $?
255

The root cause of the problem is that I have duplicate path entries in
these environment variables:

$ env | grep EMACS
EMACSNATIVELOADPATH=/home/sademeo/.guix-profile/lib/emacs/native-site-lisp:/home/sademeo/.guix-profile/lib/emacs/native-site-lisp
EMACSLOADPATH=/home/sademeo/.guix-profile/share/emacs/site-lisp:/home/sademeo/.guix-profile/share/emacs/site-lisp

If I remove the duplicate entries, Emacs starts correctly again.

I suppose this is a common problem (it's surprisingly hard to ensure a
given shell initialization snippet will run only once), and also it's
hardly a fatal or unrecoverable error. IMHO it should warrant at most a
warning message (if that), not a complete abort of the program.

With that in mind, I bisected Guix and arrived at this commit:

e9b13294700de7082ee23aa6e1c17b4a8c8828ec is the first bad commit
commit e9b13294700de7082ee23aa6e1c17b4a8c8828ec

    profiles: emacs-subdirs: Also expand native-comp-eln-load-path.

To reproduce the problem, it's enough to install emacs-pgtk and
emacs-ccls in your profile. It might be necessary to remove them and
then install them again, not sure why.

Guix version:

$ guix describe
Generation 17   jan 20 2025 18:48:17    (current)
  guix e9b1329
    repository URL: https://git.savannah.gnu.org/git/guix.git
    commit: e9b13294700de7082ee23aa6e1c17b4a8c8828ec

It's probably irrelevant, but just for completeness: Guix is installed
on top of Ubuntu 24.10.

--
Thiago