GNU bug report logs - #60643
29.0.50; set-buffer-major-mode resets buffer local variables

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Joseph Turner <joseph <at> breatheoutbreathe.in>
Subject: bug#60643: closed (Re: bug#60643: 29.0.50; set-buffer-major-mode
 resets buffer local variables)
Date: Sun, 08 Jan 2023 10:29:02 +0000

[Message part 1 (text/plain, inline)]

Your bug report

#60643: 29.0.50; set-buffer-major-mode resets buffer local variables

which was filed against the emacs package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 60643 <at> debbugs.gnu.org.

-- 
60643: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=60643
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Joseph Turner <joseph <at> breatheoutbreathe.in>
To: Eli Zaretskii <eliz <at> gnu.org>, ruijie <at> netyu.xyz
Cc: 60643-done <at> debbugs.gnu.org
Subject: Re: bug#60643: 29.0.50; set-buffer-major-mode resets buffer local
 variables
Date: Sun, 08 Jan 2023 01:09:55 -0800

Hello!

Eli Zaretskii <eliz <at> gnu.org> writes:

> Changing the major mode kills all buffer-local variables. If you don't
> want some variable to be killed, give it the permanent-local property.

Ruijie Yu <ruijie <at> netyu.xyz> writes:

> There is another concept called "permanent local variables" which you
> might be thinking about when looking at "local variables", see info node
> `(elisp) Standard Properties' for more information.

Thank you both for your help!! This solves it:

(put 'test-var 'permanent-local t)

Joseph

[Message part 3 (message/rfc822, inline)]

From: Joseph Turner <joseph <at> breatheoutbreathe.in>
To: bug-gnu-emacs <at> gnu.org
Subject: 29.0.50; set-buffer-major-mode resets buffer local variables
Date: Sat, 07 Jan 2023 20:48:54 -0800

Hello!

It appears that set-buffer-major-mode resets buffer local variables.

To reproduce with `emacs -Q`:

(defvar-local test-var nil)
(setq test-var t)
(message "%s" test-var) ;; t
;; (set-auto-mode)
(set-buffer-major-mode (current-buffer))
(message "%s" test-var) ;; nil

Is this behavior expected?

Thank you!!

Joseph

In GNU Emacs 29.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version
3.24.30, cairo version 1.16.0)
Windowing system distributor 'The X.Org Foundation', version 11.0.12011000
System Description: Debian GNU/Linux 11 (bullseye)

Configured using:
 'configure
 CONFIG_SHELL=/gnu/store/4y5m9lb8k3qkb1y9m02sw9w9a6hacd16-bash-minimal-5.1.8/bin/bash
 SHELL=/gnu/store/4y5m9lb8k3qkb1y9m02sw9w9a6hacd16-bash-minimal-5.1.8/bin/bash
 --prefix=/gnu/store/4mnib031vflf88ms8w7kyfahcbv1k9vc-emacs-next-29.0.50-3.22e8a77
 --enable-fast-install --with-modules --with-cairo
 --with-native-compilation --disable-build-details'

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
JSON LCMS2 LIBOTF LIBSELINUX LIBSYSTEMD LIBXML2 M17N_FLT MODULES
NATIVE_COMP NOTIFY INOTIFY PDUMPER PNG RSVG SECCOMP SOUND SQLITE3
THREADS TIFF TOOLKIT_SCROLL_BARS X11 XDBE XIM XINPUT2 XPM GTK3 ZLIB

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