Subject: bug#1586: prefix arg when mouse clicking on header line

From: Stefan Monnier <[email-masked]>
Date: Mon, 04 Jul 2011 15:05:44 -0400

>> If a command takes a mouse event and an (optional) prefix arg as its
>> arguments, the interactive specifications are
>> (interactive "e\nP")
>> or
>> (interactive (list last-input-event current-prefix-arg))
>> 
>> This works fine inside the main part of a window. For a command
>> that does the same thing in the header line, these interactive
>> specifications do not work.

> Thanks for the bug report.  I've committed a fix.

Does this actually fix the problem?  If so, I don't understand why:
a down event that's not bound to anything should be dropped entirely by
read-key-sequence.

So my guess at the problem is that [header-line down-mouse-1] is not
left unbound but instead is bound to something
(e.g. `mouse-drag-header-line' or `ignore'), so your code won't be
executed at all in that case.

Now, I'm not sure if we should preserve the prefix arg even if the down
event is bound, or rather just change `mouse-drag-header-line' and/or
`ignore' to propagate the current-prefix-arg to the next event; but
unless I'm missing something your fix should have no effect.

        Stefan

>>>>> "Chong" == Chong Yidong <[email-masked]> writes:

> ------------------------------------------------------------
> revno: 104891
> committer: Chong Yidong <[email-masked]>
> branch nick: trunk
> timestamp: Sat 2011-07-02 19:40:04 -0400
> message:
>   Fix corner case in prefix-arg handling for mouse events (Bug#1586).
  
>   * src/keyboard.c (command_loop_1): If a down-mouse event is unbound,
>   leave any prefix arg for the up event.
> modified:
>   src/ChangeLog
>   src/keyboard.c

> === modified file 'src/ChangeLog'
> --- a/src/ChangeLog	2011-07-02 16:18:24 +0000
> +++ b/src/ChangeLog	2011-07-02 23:40:04 +0000
> @@ -1,3 +1,8 @@
> +2011-07-02  Chong Yidong  <[email-masked]>
> +
> +	* keyboard.c (command_loop_1): If a down-mouse event is unbound,
> +	leave any prefix arg for the up event (Bug#1586).
> +
>  2011-07-02  Lars Magne Ingebrigtsen  <[email-masked]>
 
>  	* lread.c (syms_of_lread): Mention single symbols defined by

> === modified file 'src/keyboard.c'
> --- a/src/keyboard.c	2011-07-02 04:27:41 +0000
> +++ b/src/keyboard.c	2011-07-02 23:40:04 +0000
> @@ -1539,7 +1539,18 @@
>  	  message_with_string ("%s is undefined", keys, 0);
>  	  KVAR (current_kboard, defining_kbd_macro) = Qnil;
>  	  update_mode_lines = 1;
> -	  KVAR (current_kboard, Vprefix_arg) = Qnil;
> +	  /* If this is a down-mouse event, don't reset prefix-arg;
> +	     pass it to the command run by the up event.  */
> +	  if (EVENT_HAS_PARAMETERS (last_command_event))
> +	    {
> +	      Lisp_Object breakdown
> +		= parse_modifiers (EVENT_HEAD (last_command_event));
> +	      int modifiers = XINT (XCAR (XCDR (breakdown)));
> +	      if (!(modifiers & down_modifier))
> +		KVAR (current_kboard, Vprefix_arg) = Qnil;
> +	    }
> +	  else
> +	    KVAR (current_kboard, Vprefix_arg) = Qnil;
>  	}
>        else
>  	{

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