Subject: bug#63949: 30.0.50; `vc-print-log´ does not erase buffer when called from *vc-change-log* buffer, at least for CVS logs

From: Jens Schmidt <[email-masked]>
Date: Wed, 7 Jun 2023 23:04:50 +0200

Start emacs -Q.  Visit a CVS-controlled file.  Then:

C-x v l
M->
C-x v l

Notice the CVS log added once more after current end of log buffer.

I tracked this down to the following snippet from `vc-do-command´:

     (save-current-buffer
       (unless (or (eq buffer t)
		  (and (stringp buffer)
		       (string= (buffer-name) buffer))
		  (eq buffer (current-buffer)))
         (vc-setup-buffer buffer))

That is, `vc-setup-buffer´ (which erases the buffer) is *not* called if 
the buffer where the VC command is to be executed in equals the current 
buffer.  I guess that logic has a reason, so it probably should be some 
upper layer which should erase *vc-log-buffer*...

For git, for example, function `vc-git-print-log´ calls 
`vc-setup-buffer´.  Probably the other VC backends should follow suit?

If this is the way to go, I could provide patches for VC backends CVS 
and RCS, pls let me know.

In GNU Emacs 30.0.50 (build 2, x86_64-pc-linux-gnu, GTK+ Version
  3.24.24, cairo version 1.16.0) of 2023-06-07 built on sappc2
Repository revision: a902156068ab071f93cc9bbd34cd320919b74064
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12011000
System Description: Debian GNU/Linux 11 (bullseye)

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

Important settings:
   value of $LC_COLLATE: POSIX
   value of $LC_TIME: POSIX
   value of $LANG: en_US.UTF-8
   value of $XMODIFIERS: @im=ibus
   locale-coding-system: utf-8-unix

Major mode: Git-Log-View

Minor modes in effect:
   tooltip-mode: t
   global-eldoc-mode: t
   show-paren-mode: t
   electric-indent-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
   buffer-read-only: t
   line-number-mode: t
   indent-tabs-mode: t
   transient-mark-mode: t
   auto-composition-mode: t
   auto-encryption-mode: t
   auto-compression-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message mailcap yank-media puny dired
dired-loaddefs rfc822 mml mml-sec password-cache epa derived epg rfc6068
epg-config gnus-util text-property-search mm-decode mm-bodies mm-encode
mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047
rfc2045 ietf-drums mm-util mail-prsvr mail-utils parse-time iso8601
time-date subr-x sh-script rx smie treesit cl-seq executable misearch
multi-isearch vc-hg vc-bzr vc-src vc-sccs vc-svn vc-cvs vc-rcs add-log
log-view pcvs-util cl-extra help-mode vc vc-git diff-mode easy-mmode
vc-dispatcher cl-loaddefs cl-lib rmc iso-transl tooltip cconv eldoc
paren electric uniquify ediff-hook vc-hooks lisp-float-type elisp-mode
mwheel term/x-win x-win term/common-win x-dnd tool-bar dnd fontset image
regexp-opt fringe tabulated-list replace newcomment text-mode lisp-mode
prog-mode register page tab-bar menu-bar rfn-eshadow isearch easymenu
timer select scroll-bar mouse jit-lock font-lock syntax font-core
term/tty-colors frame minibuffer nadvice seq simple cl-generic
indonesian philippine cham georgian utf-8-lang misc-lang vietnamese
tibetan thai tai-viet lao korean japanese eucjp-ms cp51932 hebrew greek
romanian slovak czech european ethiopic indian cyrillic chinese
composite emoji-zwj charscript charprop case-table epa-hook
jka-cmpr-hook help abbrev obarray oclosure cl-preloaded button loaddefs
theme-loaddefs faces cus-face macroexp files window text-properties
overlay sha1 md5 base64 format env code-pages mule custom widget keymap
hashtable-print-readable backquote threads dbusbind inotify lcms2
dynamic-setting system-font-setting font-render-setting cairo
move-toolbar gtk x-toolkit xinput2 x multi-tty make-network-process
emacs)

Memory information:
((conses 16 61575 13745)
  (symbols 48 7721 0)
  (strings 32 23157 2232)
  (string-bytes 1 634764)
  (vectors 16 14390)
  (vector-slots 8 207631 12167)
  (floats 8 35 32)
  (intervals 56 586 0)
  (buffers 976 13))