*** empty log message ***

1 files changed, 42 insertions, 15 deletions

diff --git a/lisp/diff.el b/lisp/diff.el
index 347bbb75d35..c317baf3281 100644
--- a/lisp/diff.el
+++ b/lisp/diff.el
@@ -166,21 +166,48 @@ With prefix arg, prompt for diff switches."
   (message "Comparing files %s %s..." new old)
   (setq new (expand-file-name new)
         old (expand-file-name old))
-  (let ((buf (compile-internal (mapconcat 'identity
-                                          (append '("diff")
-                                                  (if (consp diff-switches)
-                                                      diff-switches
-                                                    (list diff-switches))
-                                                  (list old)
-                                                  (list new))
-                                          " ")
-                               "No more differences" "Diff"
-                               'diff-parse-differences)))
-    (save-excursion
-      (set-buffer buf)
-      (set (make-local-variable 'diff-old-file) old)
-      (set (make-local-variable 'diff-new-file) new))
-    buf))
+  (let ((old-alt (diff-prepare old new))
+        (new-alt (diff-prepare new old))
+        buf)
+    (unwind-protect
+        (let ((command
+               (mapconcat 'identity
+                          (append '("diff")
+                                  (if (consp diff-switches)
+                                      diff-switches
+                                    (list diff-switches))
+                                  (if (or old-alt new-alt)
+                                      (list "-L" old "-L" new))
+                                  (list (or old-alt old))
+                                  (list (or new-alt new)))
+                          " ")))
+          (setq buf
+                (compile-internal command
+                                  "No more differences" "Diff"
+                                  'diff-parse-differences)))
+          (save-excursion
+            (set-buffer buf)
+            (set (make-local-variable 'diff-old-file) old)
+            (set (make-local-variable 'diff-new-file) new))
+          buf)
+      (if old-alt (delete-file old-alt))
+      (if new-alt (delete-file new-alt)))))
+
+;; Copy the file FILE into a temporary file if that is necessary
+;; for comparison.  (This is only necessary if the file name has a handler.)
+;; OTHER is the other file to be compared.
+(defun diff-prepare (file other)
+  (let (handler handlers)
+    (setq handlers file-name-handler-alist)
+    (while (and (consp handlers) (null handler))
+      (if (and (consp (car handlers))
+               (stringp (car (car handlers)))
+               (string-match (car (car handlers)) file))
+          (setq handler (cdr (car handlers))))
+      (setq handlers (cdr handlers)))
+    (if handler
+        (funcall handler 'diff-prepare file other)
+      nil)))
 
 ;;;###autoload
 (defun diff-backup (file &optional switches)