bug#40820: 28.0.50; vc: vc-push requires ssh-askpass to enter key password

[Fredrik Nyqvist]

0. To get the error message at step 6, make sure that ssh-askpass is
not installed on the system.
1. Start Emacs emacs -Q
2. Edit a version controlled file (in this case git is used)
3. Do vc-next-action (C-x v v)
4. Enter a commit message and then press: C-c C-c
5. Try to push the file: C-x v P
6. Emacs now tries to launch ssh-askpass to enter the password. An error
message will be shown if ssh-askpass is not installed on the system:

ssh_askpass: exec(/usr/bin/ssh-askpass): No such file or directory

Should ssh-askpass really be needed by vc? When pushing a commit from a
shell or eshell buffer it is possible to enter the password without the
use of ssh-askpass, instead the password is entered from the
minibuffer.

Can the same be used by VC?


In GNU Emacs 28.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.5, cairo 
version 1.16.0)
 of 2020-04-19 built on gnu
Repository revision: 65990f47ccd6f1a3558910d71701a6f029c35433
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12004000
System Description: Debian GNU/Linux 10 (buster)

Configured using:
 'configure --with-gconf --with-xml2'

Configured features:
XPM JPEG TIFF GIF PNG CAIRO SOUND DBUS GSETTINGS GLIB NOTIFY INOTIFY
LIBSELINUX GNUTLS LIBXML2 FREETYPE HARFBUZZ 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