* src/keyboard.c (command_loop_1): If command is nil, call `undefined'.

* lisp/subr.el (undefined): Add missing behavior from the C code for
unbound keys.

2 files changed, 12 insertions, 1 deletions

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index 988047c9bc0..f15ba16da11 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,5 +1,8 @@
 2013-10-29  Stefan Monnier  <monnier@iro.umontreal.ca>
 
+        * subr.el (undefined): Add missing behavior from the C code for
+        unbound keys.
+
         * rect.el: Use lexical-binding.  Add new rectangular region support.
         (rectangle-mark): New command.
         (rectangle--region): New var.
diff --git a/lisp/subr.el b/lisp/subr.el
index ae1db6652db..0267366f1a8 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -586,7 +586,15 @@ saving keyboard macros (see `edmacro-mode')."
 (defun undefined ()
   "Beep to tell the user this binding is undefined."
   (interactive)
-  (ding))
+  (ding)
+  (message "%s is undefined" (key-description (this-single-command-keys)))
+  (setq defining-kbd-macro nil)
+  (force-mode-line-update)
+  ;; If this is a down-mouse event, don't reset prefix-arg;
+  ;; pass it to the command run by the up event.
+  (setq prefix-arg
+        (when (memq 'down (event-modifiers last-command-event))
+          current-prefix-arg)))
 
 ;; Prevent the \{...} documentation construct
 ;; from mentioning keys that run this command.