Re: [patch] text property `point-entered': function called to often

[Oliver Scholz]

"Stefan Monnier" <monnier+gnu/emacs/address@hidden> writes:

[...]
>> But Emacs calls this function _each_ time point moves.
>
> Actually, it doesn't.  It calls it when point hits the text-property
> and a second time when point leaves the non-text-propertized area,
> but it doesn't call it when moving inside the text.
> I.e. it calls it once when reaching the edge of the propertized
> text and a second time when reaching the inside of it.

[My apologies, I have confused two different bugs in my report. In
fact it does call the function each time point moves in _my_ setup,
but this does not happen with emacs -q. I have not yet investigated
the cause. I will do, of course, but not at once.]

> The problem is that text-properties apply to chars while point
> is always between two chars.  This is why there is a fromprev
> and toprev which hold the proplist before the from position
> and before the to position (as opposed to from and to which hold
> the proplist after the from and to positions).

My understanding is that the relevant text properties should be the
ones "at", that is _after_ point. This is IMO consistent with the
usage of other special properties like `keymap'. 

> Have you taken a look at the various users of those properties
> to see whether your patch would have an impact (beneficial maybe)
> on their code ?

Only cursory yet, as I have to admit. In gomoku.el it doesn't matter,
in table.el the impact would be rather benefial as the according
function is less often called unnecessarily (no big deal OTOH). I
realize that the `point-entered' text property seems to be used in
sgml-mode.el, but I have not yet looked in what way.

> I think the cleanest behavior would be to rely on the stickiness
> of the point-left (or point-entered) property to determine when
> the call the function (either when reaching the edge or when
> reaching the inside of the text).
[...]

Is that really worth the trouble? _My_ mental modell at least is
that "point has moved inside a text area specified with a text
property" means the same as "the character after point now has the
text property in question". 

    Oliver
-- 
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