From 0791a547c070b6c6504553c30d93c59b99fa4cdb Mon Sep 17 00:00:00 2001
From: "Aaron L. Zeng" <azeng@janestreet.com>
Date: Fri, 4 Sep 2026 16:27:10 -0400
Subject: [PATCH] Prevent vc-set-async-update error in process sentinel

* lisp/vc/vc-dir.el (vc-dir-refresh): New OK-IF-ALREADY-RUNNING
argument.
(vc-dir): Use it so that we do not error if already refreshing
(bug#81798).
* lisp/vc/vc-dispatcher.el (vc-set-async-update): Use it such
that if VC-Dir is already refreshing, we restart the refresh.
---
 lisp/vc/vc-dir.el        | 26 ++++++++++++++++++++------
 lisp/vc/vc-dispatcher.el |  4 ++--
 2 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/lisp/vc/vc-dir.el b/lisp/vc/vc-dir.el
index b3d2dbb677a..1d732ab6d3c 100644
--- a/lisp/vc/vc-dir.el
+++ b/lisp/vc/vc-dir.el
@@ -1813,12 +1813,26 @@ Called by VC backend `dir-status-files' implementations."
     (with-current-buffer vc-parent-buffer
       (vc-dir-show-more-button text))))
 
-(defun vc-dir-refresh ()
+(defun vc-dir-refresh (&optional ok-if-already-running)
   "Refresh the contents of the *VC-Dir* buffer.
-Throw an error if another update process is in progress."
+
+Signal an error if another update process is in progress, unless
+OK-IF-ALREADY-RUNNING is non-nil.
+
+If OK-IF-ALREADY-RUNNING is `restart' and another update process is in
+progress, kill it and start a new one."
   (interactive)
-  (if (vc-dir-busy)
-      (error "Another update process is in progress, cannot run two at a time")
+  (cond*
+   ((bind* (proc (and (buffer-live-p vc-dir-process-buffer)
+                      (get-buffer-process vc-dir-process-buffer)))))
+   ((and proc (not ok-if-already-running))
+    (error "Another update process is in progress, cannot run two at a time"))
+   ((and proc (not (eq ok-if-already-running 'restart)))) ;do nothing
+   (proc
+    ;; OK-IF-ALREADY-RUNNING is `restart'.
+    (delete-process proc)
+    :non-exit)
+   (t
     (let ((def-dir default-directory)
 	  (backend vc-dir-backend))
       (when (and vc-dir-save-some-buffers-on-revert (not non-essential))
@@ -1860,7 +1874,7 @@ Throw an error if another update process is in progress."
                      (vc-dir-refresh-files (mapcar #'vc-dir-fileinfo->name
                                                    remaining))
                    (setq mode-line-process nil)
-                   (run-hooks 'vc-dir-refresh-hook)))))))))))
+                   (run-hooks 'vc-dir-refresh-hook))))))))))))
 
 (defun vc-dir--refresh-headers (directory)
   "Refresh the headers for any VC-Dir buffers within DIRECTORY."
@@ -2047,7 +2061,7 @@ These are the commands available for use in the file status buffer:
   (let (pop-up-windows)		      ; based on cvs-examine; bug#6204
     (pop-to-buffer (vc-dir-prepare-status-buffer "*vc-dir*" dir backend)))
   (if (derived-mode-p 'vc-dir-mode)
-      (vc-dir-refresh)
+      (vc-dir-refresh t)
     ;; FIXME: find a better way to pass the backend to `vc-dir-mode'.
     (let ((use-vc-backend backend))
       (vc-dir-mode)
diff --git a/lisp/vc/vc-dispatcher.el b/lisp/vc/vc-dispatcher.el
index bc025b177a6..a125abbc655 100644
--- a/lisp/vc/vc-dispatcher.el
+++ b/lisp/vc/vc-dispatcher.el
@@ -682,7 +682,7 @@ Sets `compilation-error-regexp-alist' in accordance with the VC backend."
                   error-regexp-alist)))
   (run-mode-hooks 'vc-compilation-mode-hook))
 
-(declare-function vc-dir-refresh "vc-dir" ())
+(declare-function vc-dir-refresh "vc-dir" (&optional ok-if-already-running))
 
 (defun vc-set-async-update (process-buffer)
   "Set a `vc-exec-after' action appropriate to the current buffer.
@@ -706,7 +706,7 @@ If the current buffer visits a file, call `vc-refresh-state'."
               ;; Avoid interrupting the user with prompts to save
               ;; buffers.
               (let ((non-essential t))
-                (vc-dir-refresh))))
+                (vc-dir-refresh 'restart))))
             ((derived-mode-p 'dired-mode)
              (run-delayed
               (when (= (buffer-modified-tick buf) tick)