GNU bug report logs - #14191
24.3.50; (buffer-list) returns list with non-current buffer as its first element

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Joost Kremers <joostkremers <at> fastmail.fm>
Subject: bug#14191: closed (Re: bug#14191: 24.3.50; (buffer-list) returns
 list with non-current buffer as its first element)
Date: Fri, 12 Apr 2013 17:37:02 +0000

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

Your bug report

#14191: 24.3.50; (buffer-list) returns list with non-current buffer as its first element

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 14191 <at> debbugs.gnu.org.

-- 
14191: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=14191
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

[Message part 2 (message/rfc822, inline)]

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: Joost Kremers <joostkremers <at> fastmail.fm>
Cc: 14191-done <at> debbugs.gnu.org
Subject: Re: bug#14191: 24.3.50;
	(buffer-list) returns list with non-current buffer as its first
	element
Date: Fri, 12 Apr 2013 13:32:58 -0400

> - start Emacs with `emacs -Q'
> - M-x ielm RET
> - at the prompt, type (buffer-list)
[...]
> Although the *ielm* buffer is current, the first buffer in the list is
> the *scratch* buffer.

I've installed the patch below which should restore the old behavior.
Thanks for the nice test case.


        Stefan


=== modified file 'src/window.c'
--- src/window.c	2013-04-11 16:06:47 +0000
+++ src/window.c	2013-04-12 17:30:35 +0000
@@ -489,7 +489,10 @@
   Fset_buffer (w->contents);
 
   if (EQ (window, selected_window) && !inhibit_point_swap)
-    return window;
+    /* `switch-to-buffer' uses (select-window (selected-window)) as a "clever"
+       way to call record_buffer from Elisp, so it's important that we call
+       record_buffer before returning here.  */
+    goto record_and_return;
 
   sf = SELECTED_FRAME ();
   if (XFRAME (WINDOW_FRAME (w)) != sf)
@@ -508,7 +511,10 @@
     fset_selected_window (sf, window);
 
   select_window_1 (window, inhibit_point_swap);
+  bset_last_selected_window (XBUFFER (w->contents), window);
+  windows_or_buffers_changed++;
 
+ record_and_return:
   /* record_buffer can run QUIT, so make sure it is run only after we have
      re-established the invariant between selected_window and selected_frame,
      otherwise the temporary broken invariant might "escape" (bug#14161).  */
@@ -518,8 +524,6 @@
       record_buffer (w->contents);
     }
 
-  bset_last_selected_window (XBUFFER (w->contents), window);
-  windows_or_buffers_changed++;
   return window;
 }
 

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

From: Joost Kremers <joostkremers <at> fastmail.fm>
To: bug-gnu-emacs <at> gnu.org
Subject: 24.3.50;
	(buffer-list) returns list with non-current buffer as its first
	element
Date: Fri, 12 Apr 2013 14:34:05 +0200

(buffer-list) returns a list of buffers, but the first buffer in the
list is not the current buffer.

Recipe to reproduce:

- start Emacs with `emacs -Q'

- M-x ielm RET

- at the prompt, type (buffer-list)

Output (list of buffers wrapped for better readability):

,----
| *** Welcome to IELM ***  Type (describe-mode) for help.
| ELISP> (buffer-list)
| (#<buffer *scratch*> #<buffer  *Minibuf-1*> #<buffer  *Minibuf-0*>
|  #<buffer *Messages*> #<buffer  *code-conversion-work*> 
|  #<buffer  *Echo Area 0*> #<buffer  *Echo Area 1*> #<buffer *ielm*>)
`----

Although the *ielm* buffer is current, the first buffer in the list is
the *scratch* buffer.

Doing the same thing in an Emacs Debian (Ubuntu) snapshot from a few
weeks ago:

,----
| *** Welcome to IELM ***  Type (describe-mode) for help.
| ELISP> (buffer-list)
| (#<buffer *ielm*> #<buffer *scratch*> #<buffer  *Minibuf-1*>
|  #<buffer  *Minibuf-0*> #<buffer *Messages*>
|  #<buffer  *code-conversion-work*> #<buffer  *Echo Area 0*>
|  #<buffer  *Echo Area 1*>)
|
| ELISP> (emacs-version)
| "GNU Emacs 24.3.50.1 (i686-pc-linux-gnu)\n of 2013-03-19 on gold, modified by Debian"
`----

Here, the output of buffer-list has the *ielm* buffer as its first
element. (Note, I've included the output of (emacs-version) here: this
is obviously *not* the version in which the bug occurs. That version is
given below.)

Note that I'm just using the *ielm* buffer to show the output of
(buffer-list). It has nothing to do with the bug itself. Using `M-x eval
RET (buffer-list) RET' gives the same result, as does using
(buffer-list) in Elisp. (Which is how I ran into the bug: swbuff.el from
http://emhacks.sourceforge.net/ stopped working properly. I traced the
problem to this changed behaviour of buffer-list.)

HTH

Joost Kremers







In GNU Emacs 24.3.50.1 (i686-pc-linux-gnu, GTK+ Version 3.6.0)
 of 2013-04-11 on fermium, modified by Debian
 (emacs-snapshot package, version 2:20130410-1~ppa1~quantal1)
Windowing system distributor `The X.Org Foundation', version 11.0.11300000
System Description:	Ubuntu 12.10

Configured using:
 `configure --build i686-linux-gnu --host i686-linux-gnu --prefix=/usr
 --sharedstatedir=/var/lib --libexecdir=/usr/lib --localstatedir=/var
 --infodir=/usr/share/info --mandir=/usr/share/man --with-pop=yes
 --enable-locallisppath=/etc/emacs-snapshot:/etc/emacs:/usr/local/share/emacs/24.3.50/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/24.3.50/site-lisp:/usr/share/emacs/site-lisp
 --without-compress-info --with-crt-dir=/usr/lib/i386-linux-gnu/
 --with-x=yes --with-x-toolkit=gtk3 --with-imagemagick=yes
 CFLAGS='-DDEBIAN -DSITELOAD_PURESIZE_EXTRA=5000 -g -O2'
 CPPFLAGS='-D_FORTIFY_SOURCE=2' LDFLAGS='-g -Wl,--as-needed
 -znocombreloc''

Important settings:
  value of $LC_MONETARY: en_US.UTF-8
  value of $LC_NUMERIC: en_US.UTF-8
  value of $LC_TIME: en_US.UTF-8
  value of $LANG: en_GB.UTF-8
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t

Major mode: IELM

Minor modes in effect:
  tooltip-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
M-x i e l m <return> ( b u f f e r - l i s t ) <return> 
<help-echo> <help-echo> <help-echo> <up> <up> <up> 
<up> C-a a <backspace> <up> <left> <left> <left> <left> 
<left> <left> <left> C-SPC <down> <down> <down> <down> 
<down> <down> M-w ( e m a c s - v e r s i o n ) <return> 
<help-echo> <help-echo> <up> <up> <up> <right> C-SPC 
<down> <down> M-w C-x C-g M-x e m a c <tab> b u <tab> 
<M-backspace> <M-backspace> r e p <tab> o r <tab> 
<return>

Recent messages:
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-- 
Joost Kremers
Life has its moments

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