bug#65315: 30.0.50; vc-dir fails with Git < 2.7.0

[Bob Rogers]

   1.  On a system with a version of Git older than 2.7.0, navigate to a
git-controlled directory and invoke "emacs -Q".

   2.  With this as the default directory, invoke vc-dir.  This fails
with the error "vc-do-command: Failed (status 129): git --no-pager
remote get-url origin ."

   This is because the "get-url" subcommand of "git remote", used by
vc-git-repository-url, was added in 2.7.0 [1].  The attached patch
against master rev 1db7e8eba961e88181879213dd5374ad9e87ac76 uses "git
config" in a way that works in both old and new systems (tested with git
2.1.2 and git 2.35.3).

   Of course, supporting 7+-year-old versions of git is probably not a
high priority, so I won't be too disappointed if this fix is rejected.
On the other hand, it's a small change, and having vc-dir fail on any
system, especially when using Git, puts a big damper on being able to
use Emacs to hack on things in older systems, so I think it's worth
having.

                                        -- Bob Rogers
                                           http://www.rgrjr.com/

[1]  https://github.com/git/git/blob/master/Documentation/RelNotes/2.7.0.txt,
     line 13.

------------------------------------------------------------------------
In GNU Emacs 30.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version
 3.24.34, cairo version 1.16.0) of 2023-08-15 built on orion
Repository revision: 1db7e8eba961e88181879213dd5374ad9e87ac76
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12101004
System Description: openSUSE Leap 15.5

Configured using:
 'configure --with-dbus=no --with-gsettings=no --with-gif=ifavailable
 --with-tiff=no --with-gnutls=yes --with-gconf=no'

Configured features:
ACL CAIRO FREETYPE GIF GLIB GMP GNUTLS HARFBUZZ JPEG LIBSELINUX LIBXML2
MODULES NOTIFY INOTIFY PDUMPER PNG RSVG SECCOMP SOUND SQLITE3 THREADS
TOOLKIT_SCROLL_BARS X11 XDBE XIM XINPUT2 XPM GTK3 ZLIB

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

diff --git a/lisp/vc/vc-git.el b/lisp/vc/vc-git.el
index dfca944dc74..a7763360795 100644
--- a/lisp/vc/vc-git.el
+++ b/lisp/vc/vc-git.el
@@ -1342,8 +1342,10 @@ vc-git-conflicted-files
 (defun vc-git-repository-url (file-or-dir &optional remote-name)
   (let ((default-directory (vc-git-root file-or-dir)))
     (with-temp-buffer
-      (vc-git-command (current-buffer) 0 nil "remote" "get-url"
-                      (or remote-name "origin"))
+      ;; The "get-url" subcommand of "git remote" was new in git 2.7.0;
+      ;; "git config" also works in older versions.  -- rgr, 15-Aug-23.
+      (let ((opt-name (concat "remote." (or remote-name "origin") ".url")))
+       (vc-git-command (current-buffer) 0 (list "config" "--get" opt-name)))
       (buffer-substring-no-properties (point-min) (1- (point-max))))))
 
 ;; Everywhere but here, follows vc-git-command, which uses vc-do-command