bug#5185: 23.1; Elusive *cvs* buffer.

[Sergei Organov <osv@javad.com>]

This bug is not in fact 23.1-specific. It is there, say, in 22.2.1 as
well.

The cvs-update command from PCL-CVS somehow manages to create and show
*cvs* buffer that is not recorded in the buffer-list frame
parameter. I.e., the buffer *cvs*, when first created and made current
by cvs-update, becomes current in the only visible window in the only
frame, yet it is not there in the frame parameter 'buffer-list. This
does not happen when there are multiple windows visible in the frame. As
cvs-update doesn't seem to touch 'buffer-list directly, there should be
a bug in core emacs functions somewhere, I believe.

To reproduce the bug one can invoke `cvs-update' over some
CVS-controlled directory when single window is visible, then open
another frame, switch to *scratch* there, and evaluate

  (frame-parameter (next-frame) 'buffer-list) 

The result won't contain *cvs* buffer visible in the original frame.
Switching back to original frame and then once again to the new frame
will put *cvs* buffer into the list (evaluate the above once again to
see it). You can see this in the automatically recorded "Recent
messages:" at the end of this bug-report:

(#<buffer frame-parameter.el> #<buffer  *Minibuf-1*> #<buffer *scratch*>)
(#<buffer *cvs*> #<buffer frame-parameter.el> #<buffer  *Minibuf-1*> #<buffer *scratch*>)

are these two consecutive results of evaluation with switching back and
force between those two frames in-between.

Even switching to mini-buffer will record *cvs* buffer into 'buffer-list
parameter, so one can't even use "M-x eval-expression" to see the
problem.

This bug, for example, breaks the following function that is intended
to always switch between two recent buffers:

  (defun switch-to-previous-buffer ()
    "Switch to the previous buffer."
    (interactive)
    (switch-to-buffer (other-buffer (current-buffer))))

When this function is assigned to a key, e.g.:

  (global-set-key [(control meta ?l)] 'switch-to-previous-buffer)

then pressing this key twice will restore the original buffer, except
in case of such elusive *cvs* buffer, as first invocation of this
function makes *cvs* the last buffer in the list of buffers, and the
next invocation doesn't select it back.


In GNU Emacs 23.1.1 (i486-pc-linux-gnu, GTK+ Version 2.12.12)
 of 2009-10-19 on debian-build.int-office-er.priv, modified by Debian
Windowing system distributor `The X.Org Foundation', version 11.0.10402000
configured using `configure  '--build=i486-linux-gnu' '--host=i486-linux-gnu' '--prefix=/usr' '--sharedstatedir=/var/lib' '--libexecdir=/usr/lib' '--localstatedir=/var/lib' '--infodir=/usr/share/info' '--mandir=/usr/share/man' '--with-pop=yes' '--enable-locallisppath=/etc/emacs23:/etc/emacs:/usr/local/share/emacs/23.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/23.1/site-lisp:/usr/share/emacs/site-lisp:/usr/share/emacs/23.1/leim' '--with-x=yes' '--with-x-toolkit=gtk' '--with-toolkit-scroll-bars' 'build_alias=i486-linux-gnu' 'host_alias=i486-linux-gnu' 'CFLAGS=-DDEBIAN -g -O2' 'LDFLAGS=-g' 'CPPFLAGS=''

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: en_US.UTF-8
  value of $XMODIFIERS: nil
  locale-coding-system: utf-8-unix
  default-enable-multibyte-characters: t

Major mode: CVS

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

Recent input:
<help-echo> <help-echo> <help-echo> <help-echo> <help-echo> 
<menu-bar> <file> <make-frame> <help-echo> <help-echo> 
<help-echo> <help-echo> <help-echo> <help-echo> <help-echo> 
<help-echo> <help-echo> <help-echo> <help-echo> <help-echo> 
<help-echo> <help-echo> <help-echo> <help-echo> <help-echo> 
<help-echo> <help-echo> <menu-bar> <file> <make-frame> 
<switch-frame> <help-echo> <backspace> <f2> <switch-frame> 
M-x M-x c v s C-g C-x s y C-x C-e <switch-frame> C-x 
C-e C-x C-b <C-tab> C-x o C-n C-n C-p d C-n d x C-x 
k <return> <C-tab> C-x o C-x 1 C-x C-e <switch-frame> 
M-x <up> c v s - u p d a t e <return> <backspace> <backspace> 
<backspace> <backspace> . . / l d r p p c <return> 
<switch-frame> C-x C-e <switch-frame> <switch-frame> 
C-x C-e C-x b m e <backspace> <backspace> M <backspace> 
* M e s <tab> <return> <up> <up> <up> <up> <up> <up> 
<up> <up> <up> <up> <up> <up> <up> <up> <up> <up> <up> 
<up> <up> <up> <up> <up> <up> <up> <up> <up> <up> <up> 
<up> <up> <up> <up> C-SPC <down> <down> <down> <down> 
<down> <down> <down> <down> <down> <down> <down> <down> 
<down> <down> <down> <down> <down> <down> <down> <down> 
<down> <down> <up> <up> <up> <up> <up> <up> <up> <up> 
<up> <up> <up> <up> <up> <down> <down> <down> <down> 
<down> <down> <down> <down> <down> <down> <down> <down> 
<down> <down> <down> <down> <down> <down> <down> <down> 
<down> <down> <up> <up> <up> <up> <up> <up> <up> <up> 
<up> <up> <up> <up> <up> <up> <up> <up> <up> <up> <up> 
<up> <up> <up> <up> <down> <down> <down> <down> <down> 
C-g <down> <down> <down> <down> <up> <up> <up> <up> 
<up> <up> <up> <up> <down> <down> <down> <down> <down> 
<down> <up> <switch-frame> M-x e m a c s - b <backspace> 
r e p o <tab> <backspace> <backspace> <backspace> <backspace> 
b u <tab> <backspace> <backspace> <backspace> <backspace> 
<backspace> <backspace> <backspace> <backspace> r e 
p o <tab> r t - e m <tab> <return>

Recent messages:
(#<buffer frame-parameter.el> #<buffer  *Minibuf-1*> #<buffer *scratch*>)
goto-history-element: Beginning of history; no preceding item
(No files need saving)
Running cvs update ...
CVS process has completed in *cvs*
(#<buffer frame-parameter.el> #<buffer  *Minibuf-1*> #<buffer *scratch*>)
(#<buffer *cvs*> #<buffer frame-parameter.el> #<buffer  *Minibuf-1*> #<buffer *scratch*>)
Mark set
Quit
Making completion list...