bug#58270: 29.0.50; vc-tor/TRAMP issue

[Philip Kaludercic]

If connecting to a remote server and accessing a file under version
control, this error message appears if "torsocks" is not installed:

         env: ‘torsocks’: No such file or directory

I guess this patch would fix the issue:

diff --git a/lisp/vc/vc-dispatcher.el b/lisp/vc/vc-dispatcher.el
index dc3ed52650..4348e42722 100644
--- a/lisp/vc/vc-dispatcher.el
+++ b/lisp/vc/vc-dispatcher.el
@@ -346,7 +346,7 @@ vc-do-command
         (vc-setup-buffer buffer))
       (cl-destructuring-bind (command file-or-list flags)
           (funcall vc-filter-command-function command file-or-list flags)
-        (when vc-tor
+        (when (and vc-tor (executable-find "torsocks"))
           (push command flags)
           (setq command "torsocks"))
         (let* (;; FIXME: file-relative-name can return a bogus result

but then a user could be deceived into thinking that VC is using tor
even if it actually isn't the case.  Perhaps adding a warning would be
enough?  Or could vc-tor be given an option to only activate if
possible?

I also have the interesting case that I was accessing a file version
controlled under RCS, so no network communication was going to be
necessary in the first place.


In GNU Emacs 29.0.50 (build 8, x86_64-pc-linux-gnu, GTK+ Version
 3.24.34, cairo version 1.17.6) of 2022-09-30 built on rhea
Repository revision: 7c455f41186f1acbd8c68fec39fc4d3f5fa7bc60
Repository branch: local
System Description: Fedora Linux 36 (Workstation Edition)

Configured using:
 'configure --with-pgtk --with-imagemagick'

Configured features:
CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GSETTINGS HARFBUZZ IMAGEMAGICK
JPEG JSON LIBSELINUX LIBSYSTEMD LIBXML2 MODULES NOTIFY INOTIFY PDUMPER
PGTK PNG RSVG SECCOMP SOUND SQLITE3 THREADS TIFF TOOLKIT_SCROLL_BARS XIM
GTK3 ZLIB

Important settings:
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  value of $XMODIFIERS: @im=ibus
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Major mode: ELisp/l

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Load-path shadows:
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/home/philip/.config/emacs/elpa/inspector-0.8/inspector
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/home/philip/.config/emacs/elpa/inspector-0.8/inspector-tests
/home/philip/.config/emacs/site-lisp/rcirc-color/rcirc-color hides 
/home/philip/.config/emacs/elpa/rcirc-color-0.4.3/rcirc-color
/home/philip/.config/emacs/elpa/transient-0.3.7/transient hides 
/home/philip/Source/emacs/lisp/transient

Features:
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Memory information:
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