bug#63470: [PATCH] Use faster option for running vc-hg status

[Spencer Baugh]

A fix to the patch: passing the correct configuration key as an
argument.  The old version did nothing... but fortunately it was setting
the configuration key to its default value, so it happened to work.
I've tested now that it works even when commands.status.relative=0 is
set by the user's hgrc.

>From ff6163fac51759945aa619ca6bf28413be4a53e0 Mon Sep 17 00:00:00 2001
From: Spencer Baugh <sbaugh@janestreet.com>
Date: Fri, 12 May 2023 15:28:06 -0400
Subject: [PATCH] Use faster option for running vc-hg status (Bug#63470)

In modern Mercurial, removing the "re:" "-I" "." options provides a
10x-20x speedup because it allows the Rust implementation of "hg
status" to be used.

* lisp/vc/vc-hg.el (vc-hg--program-version): Add.
(vc-hg-dir-status-files): Use --config commands.status.relative=1 to
make paths relative when available.
---
 lisp/vc/vc-hg.el | 25 ++++++++++++++++++-------
 1 file changed, 18 insertions(+), 7 deletions(-)

diff --git a/lisp/vc/vc-hg.el b/lisp/vc/vc-hg.el
index 78231a0c954..688fb6e0252 100644
--- a/lisp/vc/vc-hg.el
+++ b/lisp/vc/vc-hg.el
@@ -1377,17 +1377,28 @@ vc-hg-after-dir-status
 ;; Follows vc-exec-after.
 (declare-function vc-set-async-update "vc-dispatcher" (process-buffer))
 
+(defvar vc-hg--program-version nil)
+
+(defun vc-hg--program-version ()
+  (or vc-hg--program-version
+      (setq vc-hg--program-version
+            (with-temp-buffer
+              (condition-case _ (vc-hg-command t 0 nil "version")
+                (error "0")
+                (:success
+                 (goto-char (point-min))
+                 (re-search-forward "Mercurial Distributed SCM (version 
\\([0-9][0-9.]+\\)")
+                 (string-trim-right (match-string 1) "\\.")))))))
+
 (defun vc-hg-dir-status-files (dir files update-function)
   ;; XXX: We can't pass DIR directly to 'hg status' because that
   ;; returns all ignored files if FILES is non-nil (bug#22481).
   (let ((default-directory dir))
-    ;; TODO: Use "--config 'status.relative=1'" instead of "re:"
-    ;; when we're allowed to depend on Mercurial 4.2+
-    ;; (it's a bit faster).
-    (vc-hg-command (current-buffer) 'async files
-                   "status" "re:" "-I" "."
-                   (concat "-mardu" (if files "i"))
-                   "-C"))
+    (apply #'vc-hg-command (current-buffer) 'async files
+           "status" (concat "-mardu" (if files "i")) "-C"
+           (if (version<= "4.2" (vc-hg--program-version))
+               '("--config" "commands.status.relative=1")
+             '("re:" "-I" "."))))
   (vc-run-delayed
     (vc-hg-after-dir-status update-function)))
 
-- 
2.30.2