From e07adf40d3fedeb5e410a1085d7abdf7d9275204 Mon Sep 17 00:00:00 2001
From: =?utf8?q?Andr=C3=A9=20Spiegel?= <spiegel@gnu.org>
Date: Fri, 22 Sep 2000 07:49:19 +0000
Subject: [PATCH] (vc-switch-backend): Signal an error if the file is not
 registered under the new backend.

---
 lisp/vc.el | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/lisp/vc.el b/lisp/vc.el
index b298831cb1b..4dba0fea2ae 100644
--- a/lisp/vc.el
+++ b/lisp/vc.el
@@ -2190,6 +2190,8 @@ VC's perspective on FILE, it does not register or unregister it."
    (list
     buffer-file-name
     (intern (upcase (read-string "Switch to backend: ")))))
+  (unless (vc-call-backend backend 'registered file)
+    (error "%s is not registered in %s" file backend))
   (vc-file-clearprops file)
   (vc-file-setprop file 'vc-backend backend)
   (vc-resynch-buffer file t t))
-- 
2.39.2