Re: A bug, I think, in key-binding

[David Kastrup <dak@gnu.org>]

Richard Stallman <rms@gnu.org> writes:

>     `read-key-sequence', although the DOC string does not mention it, will
>     also substitute any mouse-activated maps for the buffer-local maps, if
>     they are present and a click event is used.
>
> What do you mean by "mouse-activated maps"?  Do you mean keymaps that
> come from properties that apply to the character that was clicked
> on?

Keymaps on display properties, before-string properties and
after-string properties.

> The way we describe that feature is that the location of the click
> overrides point for choosing the character whose properties should
> be used.

I was not able to glean that from the DOC string.

>     But if we take a look at `key-binding':
>
>     we will find that the same expression "current keymaps" suddenly fails
>     to include mouse-activated maps even for click events.
>
> That is true.  But I think key-binding MUST do what it now does.
> That is an essential primitive for accessing keymaps.

So it is quite lamentable that its current implementation does not do
the trick.  The command loop could not get implemented using it.
Instead, read-key-sequence stashes the looked-up command away in a
secret internal variable where the command loop retrieves it.  While
it is efficient to avoid the double lookup (read-key-sequence has to
know how to combine primitive events to a sequence, and that requires
the maps), it also makes key-binding pretty much a sham: it is neither
used nor usable for its central purpose in the command loop.

> Perhaps we should have a function to do lookup on a key sequence
> just the same way the command loop does.  That can be written in
> Lisp; it just has to see if the first event is a mouse even, and
> move point there inside save-excursion.
>
> What do you think of this solution?

It is not sufficient to relocate point temporarily (I believe this
might actually already be done), since the maps of mouse clicks depent
on the actual screen position, not just the point position, of a mouse
click.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum