Fix backing up remote files in local directories on MS-Windows

* lisp/files.el (make-backup-file-name-1): Support remote file
names correctly when they are backed up into a local directory on
MS-Windows and MS-DOS.  (Bug#29440)

diff --git a/lisp/files.el b/lisp/files.el
index 8021e1bbed5aa2955d5b2975ba686d28a9a7d11d..9a79b2a0c734d0b776e58499ab3b4ed28f68e5fc 100644 (file)
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -4653,25 +4653,41 @@ The function `find-backup-file-name' also uses this."
              ;; "/drive_x".
              (or (file-name-absolute-p file)
                  (setq file (expand-file-name file))) ; make defaults explicit
-             ;; Replace any invalid file-name characters (for the
-             ;; case of backing up remote files).
-             (setq file (expand-file-name (convert-standard-filename file)))
-             (if (eq (aref file 1) ?:)
-                 (setq file (concat "/"
-                                    "drive_"
-                                    (char-to-string (downcase (aref file 0)))
-                                    (if (eq (aref file 2) ?/)
-                                        ""
-                                      "/")
-                                    (substring file 2)))))
-           ;; Make the name unique by substituting directory
-           ;; separators.  It may not really be worth bothering about
-           ;; doubling `!'s in the original name...
-           (expand-file-name
-            (subst-char-in-string
-             ?/ ?!
-             (replace-regexp-in-string "!" "!!" file))
-            backup-directory))
+              (cond
+               ((file-remote-p file)
+                ;; Remove the leading slash, if any, to prevent
+                ;; expand-file-name from adding a drive letter.
+                (and (memq (aref file 0) '(?/ ?\\))
+                     (setq file (substring file 1)))
+               ;; Replace any invalid file-name characters.
+                (setq file (convert-standard-filename file))
+                ;; Replace slashes to make the file name unique, and
+                ;; prepend backup-directory.
+                (expand-file-name
+                (subst-char-in-string
+                 ?/ ?!
+                 (replace-regexp-in-string "!" "!!"
+                                            (concat "/" file)))
+                backup-directory))
+               (t
+               ;; Replace any invalid file-name characters.
+               (setq file (expand-file-name (convert-standard-filename file)))
+               (if (eq (aref file 1) ?:)
+                   (setq file (concat "/"
+                                      "drive_"
+                                      (char-to-string (downcase (aref file 0)))
+                                      (if (eq (aref file 2) ?/)
+                                          ""
+                                        "/")
+                                      (substring file 2))))
+               ;; Make the name unique by substituting directory
+               ;; separators.  It may not really be worth bothering about
+               ;; doubling `!'s in the original name...
+               (expand-file-name
+                (subst-char-in-string
+                 ?/ ?!
+                 (replace-regexp-in-string "!" "!!" file))
+                backup-directory)))))
        (expand-file-name (file-name-nondirectory file)
                          (file-name-as-directory abs-backup-directory))))))