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

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

[Joseph Turner via Bug reports for GNU Emacs, the Swiss army knife of text editors]

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

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

[Ruijie Yu via Bug reports for GNU Emacs, the Swiss army knife of text editors]

Joseph Turner via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org> writes:

> 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

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.

Best,


RY

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

[Eli Zaretskii]

> Date: Sat, 07 Jan 2023 20:48:54 -0800
> From:  Joseph Turner via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> 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?

Yes, I think so.  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.

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

[Joseph Turner via Bug reports for GNU Emacs, the Swiss army knife of text editors]

Hello!

Eli Zaretskii <eliz@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@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

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

[Joseph Turner via Bug reports for GNU Emacs, the Swiss army knife of text editors]

Hello!

Eli Zaretskii <eliz@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@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