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)

1 files changed, 35 insertions, 19 deletions

diff --git a/lisp/files.el b/lisp/files.el
index 8021e1bbed5..9a79b2a0c73 100644
--- 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))))))