GNU bug report logs - #10114
24.0.91; (not (eq (current-buffer) (window-buffer (selected-window))))

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Richard Copley <rcopley <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 24.0.91; (not (eq (current-buffer) (window-buffer (selected-window))))
Date: Tue, 22 Nov 2011 23:11:31 +0000

When you remove the current buffer from the selected window,
the buffer that gets displayed in the selected window isn't always
the same as the buffer that gets made the new current buffer.
The command M-x test (see below) manifests the problem
for me from runemacs -Q.

Output on Emacs 23.3:
Current: *Test*<2>; Selected: *Test*<2>; [...]
Current: *Test*<1>; Selected: *Test*<1>; [...]

Output on Emacs bzr trunk:
Current: *Test*<2>; Selected: *Test*<2>; [...]
Current: *Test*<1>; Selected: *scratch*; [...]

(defun test ()
  (interactive)
  (progn
    ;; This seems to sow enough confusion.
    (switch-to-buffer-other-window "*Test*<1>")
    (switch-to-buffer-other-window "*Test*<2>")
    (delete-other-windows))
  (while
      (progn
        (message
         "Current: %s; Selected: %s; \
type k to kill current buffer, \
any other key to quit"
         (current-buffer)
         (window-buffer (selected-window)))
        (and (eq (read-event) ?k)
	     (kill-buffer))))
  (clear-this-command-keys t))

In GNU Emacs 24.0.91.1 (i386-mingw-nt6.1.7601)
 of 2011-11-20 on MACHINE
Windowing system distributor `Microsoft Corp.', version 6.1.7601
configured using `configure --with-gcc (4.6)'

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: ENG
  value of $XMODIFIERS: nil
  locale-coding-system: cp1252
  default enable-multibyte-characters: t

Major mode: Lisp Interaction

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 r e p o r t - e m a c s - b u g <return>

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.

Load-path shadows:
None found.

Features:
(shadow sort gnus-util mail-extr message format-spec rfc822 mml easymenu
mml-sec mm-decode mm-bodies mm-encode mail-parse rfc2231 rfc2047 rfc2045
ietf-drums mm-util mail-prsvr mailabbrev mail-utils gmm-utils mailheader
emacsbug time-date tooltip ediff-hook vc-hooks lisp-float-type mwheel
dos-w32 disp-table ls-lisp w32-win w32-vars tool-bar dnd fontset image
fringe lisp-mode register page menu-bar rfn-eshadow timer select
scroll-bar mouse jit-lock font-lock syntax facemenu font-core frame cham
georgian utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao
korean japanese hebrew greek romanian slovak czech european ethiopic
indian cyrillic chinese case-table epa-hook jka-cmpr-hook help simple
abbrev minibuffer button faces cus-face files text-properties overlay
sha1 md5 base64 format env code-pages mule custom widget
hashtable-print-readable backquote make-network-process multi-tty emacs)

Message #10 received at 10114-done <at> debbugs.gnu.org (full text, mbox):

From: martin rudalics <rudalics <at> gmx.at>
To: 10114-done <at> debbugs.gnu.org
Cc: Richard Copley <rcopley <at> gmail.com>
Subject: Re: bug#10114: 24.0.91;	(not (eq (current-buffer) (window-buffer
	(selected-window))))
Date: Wed, 23 Nov 2011 11:06:44 +0100

> When you remove the current buffer from the selected window,
> the buffer that gets displayed in the selected window isn't always
> the same as the buffer that gets made the new current buffer.
> The command M-x test (see below) manifests the problem
> for me from runemacs -Q.
>
> Output on Emacs 23.3:
> Current: *Test*<2>; Selected: *Test*<2>; [...]
> Current: *Test*<1>; Selected: *Test*<1>; [...]
>
> Output on Emacs bzr trunk:
> Current: *Test*<2>; Selected: *Test*<2>; [...]
> Current: *Test*<1>; Selected: *scratch*; [...]

The output on Emacs bzr trunk should be

Current: *Test*<2>; Selected: *Test*<2>; [...]
Current: *scratch*; Selected: *scratch*; [...]

because *scratch* was the buffer shown before *Test*<2>*.

> (defun test ()
>   (interactive)
>   (progn
>     ;; This seems to sow enough confusion.
>     (switch-to-buffer-other-window "*Test*<1>")
>     (switch-to-buffer-other-window "*Test*<2>")
>     (delete-other-windows))
>   (while
>       (progn
>         (message
>          "Current: %s; Selected: %s; \
> type k to kill current buffer, \
> any other key to quit"
>          (current-buffer)
>          (window-buffer (selected-window)))
>         (and (eq (read-event) ?k)
> 	     (kill-buffer))))
>   (clear-this-command-keys t))
>
> In GNU Emacs 24.0.91.1 (i386-mingw-nt6.1.7601)
>  of 2011-11-20 on MACHINE
> Windowing system distributor `Microsoft Corp.', version 6.1.7601
> configured using `configure --with-gcc (4.6)'

The problems happens because `kill-buffer' makes another buffer current
when killing the current buffer and calls `replace-buffer-in-windows'
which ends up calling `switch-to-prev-buffer' for the selected window.
The latter refuses to change the current buffer because the selected
window's buffer is _not_ the current buffer (a behavior needed to make
`switch-to-prev-buffer' work within buffer excursions).

So the solution is to have `kill-buffer' call `replace-buffer-in-windows'
_before_ making another buffer current.

Thanks for the excellent report, martin

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