bug#459: Zero-length overlays, overlay keymaps, and `overlays-at'

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: t.s.cubitt.98@cantab.net,  459@debbugs.gnu.org
> Date: Mon, 19 Jul 2021 18:37:07 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> > a) Modify (overlays-at pos) to return zero-length overlays that start
> >> > at pos (it already returns all other overlays that start at
> >> > pos). Again, this seems unlikely to have significant impact on other
> >> > parts of Emacs, since zero-length overlays are rarely used.
> >> >
> >> > b) Modify (overlays-at pos) to return zero-length overlays that start
> >> > at pos, and have a null front-advance and non-nil rear-advance
> >> > property. (The logic for this is the same as in option b) for the
> >> > overlay keymaps issue.)
> >> >
> >> > c) Leave `overlays-at' unchanged, and define a new function
> >> > `overlays-at-point' that implements either a) or b).
> 
> [...]
> 
> > We could add a new optional argument to overlays-at, to make it return
> > such overlays.  That would avoid the risk of breaking unsuspecting
> > callers.
> 
> Yeah, that's true.  Do you have any opinion on whether a) or b) would
> make the most sense if given this optional argument?  I'm leaning
> towards b)...

b) is fine by me, but let's hear from Stefan as well.