(vc-switch-backend): Try to be more careful with unwanted

side-effect due to mixing various backends's file properties.

2 files changed, 29 insertions, 19 deletions

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index 0999e794216..44439658b56 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,5 +1,8 @@
 2006-10-20  Stefan Monnier  <monnier@iro.umontreal.ca>
 
+        * vc.el (vc-switch-backend): Try to be more careful with unwanted
+        side-effect due to mixing various backends's file properties.
+
         * vc-svn.el (vc-svn-parse-status): Remove unused arg `localp'.
         Add arg `filename' instead.  Don't set vc-backend if `filename' is set.
         Return `filename's status if applicable.  Update callers.
diff --git a/lisp/vc.el b/lisp/vc.el
index d72ee4c7e4e..afeba8d2409 100644
--- a/lisp/vc.el
+++ b/lisp/vc.el
@@ -2682,25 +2682,32 @@ To get a prompt, use a prefix argument."
         (error "There is no version-controlled file in this buffer"))
     (let ((backend (vc-backend buffer-file-name))
           (backends nil))
-      (unless backend
-        (error "File %s is not under version control" buffer-file-name))
-      ;; Find the registered backends.
-      (dolist (backend vc-handled-backends)
-        (when (vc-call-backend backend 'registered buffer-file-name)
-          (push backend backends)))
-      ;; Find the next backend.
-      (let ((def (car (delq backend (append (memq backend backends) backends))))
-            (others (delete backend backends)))
-        (cond
-         ((null others) (error "No other backend to switch to"))
-         (current-prefix-arg
-          (intern
-           (upcase
-            (completing-read
-             (format "Switch to backend [%s]: " def)
-             (mapcar (lambda (b) (list (downcase (symbol-name b)))) backends)
-             nil t nil nil (downcase (symbol-name def))))))
-       (t def))))))
+      (unwind-protect
+          (progn
+            (unless backend
+              (error "File %s is not under version control" buffer-file-name))
+            ;; Find the registered backends.
+            (dolist (backend vc-handled-backends)
+              (when (vc-call-backend backend 'registered buffer-file-name)
+                (push backend backends)))
+            ;; Find the next backend.
+            (let ((def (car (delq backend
+                                  (append (memq backend backends) backends))))
+                  (others (delete backend backends)))
+              (cond
+               ((null others) (error "No other backend to switch to"))
+               (current-prefix-arg
+                (intern
+                 (upcase
+                  (completing-read
+                   (format "Switch to backend [%s]: " def)
+                   (mapcar (lambda (b) (list (downcase (symbol-name b)))) backends)
+                   nil t nil nil (downcase (symbol-name def))))))
+               (t def))))
+        ;; Calling the `registered' method can mess up the file
+        ;; properties, so we want to revert them to what they were.
+        (if (and backend (delete backend backends))
+            (vc-call-backend backend 'registered buffer-file-name))))))
   (unless (eq backend (vc-backend file))
     (vc-file-clearprops file)
     (vc-file-setprop file 'vc-backend backend)