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Old CUA and new keyboard.c (was: Problem with latest CVS version of keyb

From: Stefan Monnier
Subject: Old CUA and new keyboard.c (was: Problem with latest CVS version of keyboard.c (solved) )
Date: Wed, 12 Jun 2002 11:19:27 -0400

> >Hmm... I don't see it here.  I suspect that it's due to my change
> >(Richard's seems unrelated), but could you try to revert only one
> >of the two changes, just to make sure which of the two is posing
> >problems ?
> >
> >Does it happen with `-q --no-site-file' ?
> No it doesn't.
> I think I found the problem:  I used an old version of cua-mode (cua.el
> Version: 2.10) which seems to have been broken by recent changes made in
> keyboard.c.  After removing this file and using new cua code in the
> distribution all worked fine :-)

It's good to see that this problem is solved, but it's important
to try and figure out why things happened that way.  It may very
well be a bug introduced by my change (the code in read_key_sequence
is really intricate)....

...hmm.... it turns out it's a nasty problem:

cua-2.10 puts a CUA-prefix-handler function on C-x in key-translation-map.
This function will remap C-x to something else or to the same
thing depending on the situation.  Problem is, this function
is used for C-c as well (and maybe other keys), so it needs to be
told what was the key that triggered it.
It figures this out by using last-input-char (it also uses this-command-keys
although I'm not quite sure why and what it does with it).

So the problem is that key-translation-map used to be applied immediately
and thus CUA-prefix-handler was called as soon as the user hit C-x, whereas
the new code waits to see whether this C-x starts a function-key
sequence (in which case key-translation-map should not be applied yet)
and thus CUA-prefix-handler is only called once the user hits the next key.

Let's say she wants to do C-x C-f so with the new keyboard.c code,
when CUA-prefix-handler is called last-input-char is not C-x but C-f,
so CUA gets all confused and we end up with C-f C-f whereas
CUA thought it wasn't changing anything.

Not knowing exactly what the semantics of last-input-char are supposed
to be and how/if functions in key-translation-map should be allowed
to use it or should use some other way to figure out what key sequence
triggered them, I'm wondering if my fix introduced a "significant"
incompatibility or not.
Also if it should be fixed, I'm not sure how to go about it.

Any idea ?  Kim ?


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