Re: Moving point around empty overlays with 'after-text

[Eli Zaretskii]

> Date: Sun, 09 Apr 2023 20:21:09 -0700
> From: Ash <ext0l@catgirl.ai>
> 
> When point is on a position with an inlay, the new variable 
> point-is-after-inlay (name subject to bikeshedding) controls where point 
> renders (before if nil, after if t). When inserting text, the inlay moves 
> forward if point-is-after-inlay is nil, and doesn't move if it's t; this 
> means characters appear where you'd expect.

How is this different from the front-advance and rear-advance
arguments you can specify when creating the overlay.

> We add a new (forward-char-respecting-inlay) function that sets 
> point-is-after-inlay to t if point is at the start of an inlay *and* 
> point-is-after-inlay is nil, or increments point if not (and the same for 
> backwards). Possibly add an 'always-respect-inlay' mode that makes 
> forward-char act like this, with the caveat that things might break in 
> strange ways.
> 
> Each inlay has a 'bias' of 'before or 'after that indicates what 
> point-is-before-inlay should be set to when navigating to it 'from afar' or 
> other cases where there's no good heuristic for where to put it; in general, 
> this should correspond to where the text is the inlay is semantically 
> annotating.
> 
> There's probably all kinds of edge cases I haven't thought about, of course. 
> Conversely, an even more general approach that would support multiple inlays 
> in a row would be to have point-is-after-inlay be an *index* (and rename it 
> 'point-inlay-index' or some such). Not sure what a concrete use case for that 
> would be.

I think before we invent some new complicated feature we should
explore the ones already there.

Did you look at how set-minibuffer-message succeeds in setting the
cursor? did you try using the same technique?

Did you try both before-string and after-string overlays?

Did you try non-"empty" overlays, i.e. those whose start and end are
not the same buffer position?  They can have before-string and
after-string properties as well.

And that is even before considering whether overlays are the best
infrastructure for implementing this stuff in Emacs.