1 files changed, 26 insertions, 8 deletions

diff --git a/lisp/files.el b/lisp/files.el
index 1c97aaac71f..da2d9c1655b 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -296,21 +296,31 @@ Normally auto-save files are written under other names."
   `(("\\`/[^/]*:\\(.+/\\)*\\(.*\\)"
      ;; Don't put "\\2" inside expand-file-name, since it will be
      ;; transformed to "/2" on DOS/Windows.
-     ,(concat temporary-file-directory "\\2")))
+     ,(concat temporary-file-directory "\\2") t))
   "*Transforms to apply to buffer file name before making auto-save file name.
-Each transform is a list (REGEXP REPLACEMENT):
+Each transform is a list (REGEXP REPLACEMENT UNIQUIFY):
 REGEXP is a regular expression to match against the file name.
 If it matches, `replace-match' is used to replace the
 matching part with REPLACEMENT.
+If the optional element UNIQUIFY is non-nil, the auto-save file name is
+constructed by taking the directory part of the replaced file-name, 
+concatenated with the buffer file name with all directory separators
+changed to `!' to prevent clashes.  This will not work
+correctly if your filesystem truncates the resulting name.
+
 All the transforms in the list are tried, in the order they are listed.
 When one transform applies, its result is final;
 no further transforms are tried.
 
 The default value is set up to put the auto-save file into the
 temporary directory (see the variable `temporary-file-directory') for
-editing a remote file."
+editing a remote file.
+
+On MS-DOS filesystems without long names this variable is always
+ignored."
   :group 'auto-save
-  :type '(repeat (list (string :tag "Regexp") (string :tag "Replacement")))
+  :type '(repeat (list (string :tag "Regexp") (string :tag "Replacement")
+                                           (boolean :tag "Uniquify")))
   :version "21.1")
 
 (defcustom save-abbrevs t
@@ -3354,16 +3364,24 @@ See also `auto-save-file-name-p'."
   (if buffer-file-name
       (let ((list auto-save-file-name-transforms)
             (filename buffer-file-name)
-            result)
+            result uniq)
         ;; Apply user-specified translations
         ;; to the file name.
         (while (and list (not result))
           (if (string-match (car (car list)) filename)
               (setq result (replace-match (cadr (car list)) t nil
-                                          filename)))
+                                          filename)
+                                uniq (caddr (car list))))
           (setq list (cdr list)))
-        (if result (setq filename result))
-
+        (if result
+                (if uniq
+                        (setq filename (concat
+                                                        (file-name-directory result)
+                                                        (subst-char-in-string
+                                                         directory-sep-char ?!
+                                                         (replace-regexp-in-string "!" "!!"
+                                                                                                                 filename))))
+                  (setq filename result)))
         (setq result
               (if (and (eq system-type 'ms-dos)
                        (not (msdos-long-file-names)))