Fix the non-creation of backup files in temporary-file directory on Windows.

 lisp/files.el (normal-backup-enable-predicate): On MS-Windows and
 MS-DOS compare truenames of temporary-file-directory and of the
 file, so that 8+3 aliases (usually found in $TEMP on Windows)
 don't fail comparison by compare-strings.  Also, compare file
 names case-insensitively on MS-Windows and MS-DOS.

2 files changed, 33 insertions, 17 deletions

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index 1af9905c7e3..8b249977e4e 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,11 @@
+2013-04-06  Eli Zaretskii  <eliz@gnu.org>
+
+        * files.el (normal-backup-enable-predicate): On MS-Windows and
+        MS-DOS compare truenames of temporary-file-directory and of the
+        file, so that 8+3 aliases (usually found in $TEMP on Windows)
+        don't fail comparison by compare-strings.  Also, compare file
+        names case-insensitively on MS-Windows and MS-DOS.
+
 2013-04-05  Stefan Monnier  <monnier@iro.umontreal.ca>
 
         * emacs-lisp/package.el (package-compute-transaction): Fix last fix.
diff --git a/lisp/files.el b/lisp/files.el
index 06958622d14..d098f0fcec7 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -4180,23 +4180,31 @@ ignored."
   "Default `backup-enable-predicate' function.
 Checks for files in `temporary-file-directory',
 `small-temporary-file-directory', and /tmp."
-  (not (or (let ((comp (compare-strings temporary-file-directory 0 nil
-                                        name 0 nil)))
-             ;; Directory is under temporary-file-directory.
-             (and (not (eq comp t))
-                  (< comp (- (length temporary-file-directory)))))
-           (let ((comp (compare-strings "/tmp" 0 nil
-                                        name 0 nil)))
-             ;; Directory is under /tmp.
-             (and (not (eq comp t))
-                  (< comp (- (length "/tmp")))))
-           (if small-temporary-file-directory
-               (let ((comp (compare-strings small-temporary-file-directory
-                                            0 nil
-                                            name 0 nil)))
-                 ;; Directory is under small-temporary-file-directory.
-                 (and (not (eq comp t))
-                      (< comp (- (length small-temporary-file-directory)))))))))
+  (let ((temporary-file-directory temporary-file-directory)
+        caseless)
+    ;; On MS-Windows, file-truename will convert short 8+3 alises to
+    ;; their long file-name equivalents, so compare-strings does TRT.
+    (if (memq system-type '(ms-dos windows-nt))
+        (setq temporary-file-directory (file-truename temporary-file-directory)
+              name (file-truename name)
+              caseless t))
+    (not (or (let ((comp (compare-strings temporary-file-directory 0 nil
+                                          name 0 nil caseless)))
+               ;; Directory is under temporary-file-directory.
+               (and (not (eq comp t))
+                    (< comp (- (length temporary-file-directory)))))
+             (let ((comp (compare-strings "/tmp" 0 nil
+                                          name 0 nil)))
+               ;; Directory is under /tmp.
+               (and (not (eq comp t))
+                    (< comp (- (length "/tmp")))))
+             (if small-temporary-file-directory
+                 (let ((comp (compare-strings small-temporary-file-directory
+                                              0 nil
+                                              name 0 nil caseless)))
+                   ;; Directory is under small-temporary-file-directory.
+                   (and (not (eq comp t))
+                        (< comp (- (length small-temporary-file-directory))))))))))
 
 (defun make-backup-file-name (file)
   "Create the non-numeric backup file name for FILE.