GNU bug report logs - #75817
[PATCH] profiles: emacs-subdirs: Avoid building list with a loop

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Message #14 received at 75817 <at> debbugs.gnu.org (full text, mbox):

From: Thiago Jung Bauermann <bauermann <at> kolabnow.com>
To: 75817 <at> debbugs.gnu.org
Cc: Liliana Marie Prikler <liliana.prikler <at> gmail.com>,
 Thiago Jung Bauermann <bauermann <at> kolabnow.com>
Subject: [PATCH v2] profiles: emacs-subdirs: Avoid building list with a loop
Date: Sat, 25 Jan 2025 01:14:08 -0300

If the EMACSNATIVELOADPATH environment variable (by mistake) has duplicated
paths, Emacs fails to load with:

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

A git bisect in Guix to find when the problem was introduced arrived at
commit e9b13294700d ("profiles: emacs-subdirs: Also expand
native-comp-eln-load-path.").

Fix the problem by applying Liliana's suggestion of changing 'nconc' to
'append' in the Elisp code written to subdirs.el.

* guix/profiles.scm (emacs-subdirs): Use 'append' rather than 'nconc'.

Change-Id: If646b806f24666b5247850d30d2819c7482c130b
Fixes: Emacs "List contains a loop" error <https://issues.guix.gnu.org/75709>
Suggested-by: Liliana Marie Prikler <liliana.prikler <at> gmail.com>
---
 guix/profiles.scm | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

Changes since v1:
Made the following changes suggested by Liliana:
- Added comment to Elisp comment warning about destructive procedures
- Added short bug description to "Fixes" tag.

diff --git a/guix/profiles.scm b/guix/profiles.scm
index 87b9543ac01f..fb4dbc5bd079 100644
--- a/guix/profiles.scm
+++ b/guix/profiles.scm
@@ -1230,8 +1230,12 @@ (define build
                         (setq native-comp-eln-load-path
                               (mapcan (lambda (dir)
                                         (if (equal dir needle)
-                                            (nconc ',native-comp-dirs
-                                                   (list dir))
+                                            ;; Note: needle may be found
+                                            ;; multiple times, so don't use
+                                            ;; destructive procedures like
+                                            ;; nconc.
+                                            (append ',native-comp-dirs
+                                                    (list dir))
                                             (list dir)))
                                       native-comp-eln-load-path))))
                    port)

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