bug#7541: 24.0.50; define-key error message for non-prefix M-[char]

[Don March <don@ohspite.net>]

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Typing and evaluating the following code in the scratch
buffer results in an (appropriate) error, but with an incorrect
message:

(setq new-kmap (make-sparse-keymap))
(define-key new-kmap [?a 27] 'command)
(define-key new-kmap [?a ?\M-x] 'command)
;; Debugger entered--Lisp error:
;;   (error "Key sequence a M-x starts with non-prefix key a")
;; (should be:
;;          "Key sequence a M-x starts with non-prefix key a ESC")

The code in keymap.c loops over the characters in the key sequence and
says to report everything before the current character as the
non-prefix key.  But that misses the case when M-x is converted into
[27 ?x] and it's the `27' part that causes the error.

Please see the attached patch.

A few other cases that show the problem:

(setq a (make-sparse-keymap))
(define-key a [27] 'command)
(define-key a [?\M-x] 'command)
;; Debugger entered--Lisp error:
;;   (error "Key sequence M-x starts with non-prefix key ")
;; (should be:
;;          "Key sequence M-x starts with non-prefix key ESC")

(setq new-kmap (make-sparse-keymap))
(define-key new-kmap [?a 27] 'command)
(define-key new-kmap [?a 27 ?x] 'command)
;; Debugger entered--Lisp error:
;;   (error "Key sequence a M-x starts with non-prefix key a ESC")
;; (error text is correct)

(setq new-kmap (make-sparse-keymap))
(define-key new-kmap [?a] 'command)
(define-key new-kmap [?a ?\M-x] 'command)
;; Debugger entered--Lisp error:
;;    (error "Key sequence a M-x starts with non-prefix key a")
;; (error text is correct)

In GNU Emacs 24.0.50.1 (i686-pc-linux-gnu, GTK+ Version 2.22.0)
 of 2010-12-03 on lappy
Windowing system distributor `The X.Org Foundation', version 11.0.10900000

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=== modified file 'src/ChangeLog'
*** src/ChangeLog	2010-12-02 09:33:57 +0000
--- src/ChangeLog	2010-12-03 16:15:41 +0000
***************
*** 1,3 ****
--- 1,8 ----
+ 2010-12-03  Don March  <don@ohspite.net>
+ 
+ 	* keymap.c (Fdefine_key): Fix non-prefix key error message when
+ 	last character M-[char] is translated to ESC [char].
+ 
  2010-12-02  Jan Djärv  <jan.h.d@swipnet.se>
  
  	* nsmenu.m (update_frame_tool_bar): Remove NSLog on invalid image.

=== modified file 'src/keymap.c'
*** src/keymap.c	2010-08-09 09:35:21 +0000
--- src/keymap.c	2010-12-03 08:05:11 +0000
*************** binding KEY to DEF is added at the front
*** 1234,1246 ****
  
        keymap = get_keymap (cmd, 0, 1);
        if (!CONSP (keymap))
! 	/* We must use Fkey_description rather than just passing key to
! 	   error; key might be a vector, not a string.  */
! 	error ("Key sequence %s starts with non-prefix key %s",
! 	       SDATA (Fkey_description (key, Qnil)),
! 	       SDATA (Fkey_description (Fsubstring (key, make_number (0),
! 						    make_number (idx)),
! 					Qnil)));
      }
  }
  
--- 1234,1260 ----
  
        keymap = get_keymap (cmd, 0, 1);
        if (!CONSP (keymap))
! 	{
! 	  char trailing_esc[5];
! 	  if (c == meta_prefix_char && metized)
! 	    {
! 	      if (idx == 0)
! 		strcpy(trailing_esc, "ESC");
! 	      else
! 		strcpy(trailing_esc, " ESC");
! 	    }
! 	  else
! 	      strcpy(trailing_esc, ""); 
! 
! 	  /* We must use Fkey_description rather than just passing key to
! 	     error; key might be a vector, not a string.  */
! 	  error ("Key sequence %s starts with non-prefix key %s%s",
! 		 SDATA (Fkey_description (key, Qnil)),
! 		 SDATA (Fkey_description (Fsubstring (key, make_number (0),
! 						      make_number (idx)),
! 					  Qnil)),
! 		 trailing_esc);		 
! 	}
      }
  }