bug#38343: 27.0.50; vc git: Cannot edit outgoing log (like git commit --amend)

[Fredrik Nyqvist]

Hi,

I would like to use vc mode to edit an outgoing commit message.

Steps to reproduce:
1. emacs -Q /path/to/git/repo
2. Edit a file and then
3. Run vc-next-action to create a commit: C-x v v
4. Write a commit message and end with C-c C-c
5. Now Open the outgoing log (vc-log-outgoing) : C-x v O
6. Try to edit the commit message (log-view-modify-change-comment): e

This message is printed:

log-view-current-file: Unable to determine the current file


In GNU Emacs 27.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.5)
 of 2019-11-23 built on gnu
Repository revision: 6d4d00c63417e3479e978a373f252b9f2709ce39
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12004000
System Description: Debian GNU/Linux 10 (buster)

Recent messages:
Auto-saving...done
Specified image bit depth is not supported by XRender [2 times]

Configured features:
XPM JPEG TIFF GIF PNG SOUND DBUS GSETTINGS GLIB NOTIFY INOTIFY
LIBSELINUX GNUTLS FREETYPE HARFBUZZ XFT ZLIB TOOLKIT_SCROLL_BARS GTK3
X11 XDBE XIM MODULES THREADS PDUMPER GMP

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

Major mode: Dired by name

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

Load-path shadows:
None found.

Features:
(help-mode pp shadow sort mail-extr emacsbug message rmc puny
format-spec rfc822 mml easymenu mml-sec password-cache epa derived epg
epg-config gnus-util rmail rmail-loaddefs text-property-search time-date
subr-x seq byte-opt gv bytecomp byte-compile cconv 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
dired dired-loaddefs tooltip eldoc electric uniquify ediff-hook vc-hooks
lisp-float-type 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 elisp-mode lisp-mode prog-mode register page tab-bar menu-bar
rfn-eshadow isearch timer select scroll-bar mouse jit-lock font-lock
syntax facemenu font-core term/tty-colors frame minibuffer cl-generic
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 charscript charprop
case-table epa-hook jka-cmpr-hook help simple abbrev obarray
cl-preloaded nadvice loaddefs button faces cus-face macroexp files
text-properties overlay sha1 md5 base64 format env code-pages mule
custom widget hashtable-print-readable backquote threads dbusbind
inotify dynamic-setting system-font-setting font-render-setting
move-toolbar gtk x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 49936 10334)
 (symbols 48 6110 0)
 (strings 32 15815 1297)
 (string-bytes 1 516576)
 (vectors 16 10114)
 (vector-slots 8 132119 14836)
 (floats 8 23 70)
 (intervals 56 347 6)
 (buffers 1000 16))