bug#57442: 29.0.50; diff file name deduction fails for VC backend SRC

[Wolfgang Scherer]

Steps to reproduce:

 * invoke emacs 29.0.50 (or any earlier version) with -Q,
 * open a file under versino control with SRC backend,
 * perform some modifications
 * produce a diff with |C-x v =|

|--- update-emacs-init.sh (r4) +++ update-emacs-init.sh (workfile) @@ -414,10 
+414,41 @@ REMOVED_DIST_LOCAL_SITE_LISP=' +csharpmode.el +dvc +tex-site-000.el 
tex-site.el -tex-site-000.el |

The file names are annotated with the revsions in parentheses. Pressing
RETURN on any line prompts for the file to be used:

   Use file /…/update-emacs-init.sh (workfile):
   /…/update-emacs-init.sh (workfile)

However, the expected behavior is for |diff-find-file-name| to correctly deduce 
the
file name.

Here is a sample advice, which solves the problem. It is just a hint as
to why the filename recognition fails:

|(defcustom vcx-diff-filename-remove-src-revison-always nil "If nil, only remove parenthesized revision from diff file 
names, if VC backend is SRC." :type 'boolean :group 'vc) (defun vcx-diff-filename-remove-src-revision (file) "Remove 
parenthesized revision from diff file name. Depending on `vcx-diff-filename-remove-src-revison-always', this is done only if the 
VC backend is SRC, or unconditionally." (or (and file (or vcx-diff-filename-remove-src-revison-always (eq 'SRC (or 
diff-vc-backend (vc-responsible-backend ".")))) (save-match-data (let ((pos (string-match "\\( ([^)]*)\\)\\'" 
file ))) (if pos (substring file 0 pos))))) file)) (defadvice diff-filename-drop-dir (around vcx-diff-fn-rm-src-rev activate) 
"Also remove parenthesized revision from diff file names. Calls `vcx-diff-filename-remove-src-revision' with the result of 
`diff-filename-drop-dir' or the original argument." (let ((file (ad-get-arg 0))) ad-do-it (setq ad-return-value 
(vcx-diff-filename-remove-src-revision
(or ad-return-value file))))) |

In GNU Emacs 29.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version

3.24.33, cairo version 1.16.0) of 2022-08-27 built on franke
Repository revision: c1442f96db64d545007f25995596b399f638e399
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12101003
System Description: Ubuntu 22.04.1 LTS

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 SQLITE3 THREADS TIFF
TOOLKIT_SCROLL_BARS WEBP X11 XDBE XIM XINPUT2 XPM GTK3 ZLIB

Important settings:
value of $LANG: de_DE.UTF-8
locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
tooltip-mode: t
global-eldoc-mode: t
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
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 time-date subr-x mm-decode
mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader
cl-loaddefs cl-lib sendmail rfc2047 rfc2045 ietf-drums mm-util
mail-prsvr mail-utils rmc iso-transl tooltip 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
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 44930 7772)
(symbols 48 6825 0)
(strings 32 15965 1116)
(string-bytes 1 425965)
(vectors 16 9347)
(vector-slots 8 154336 14252)
(floats 8 22 22)
(intervals 56 530 0)
(buffers 1000 11))
​