bug#74276: 30.0.90; undo does not account for overlays now that markers are not used

[Eli Zaretskii]

> Cc: karthikchikmagalur@gmail.com
> Date: Sat, 09 Nov 2024 12:11:50 +0530
> From:  James Thomas via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> - emacs -Q
> - Type: abcdef
> - C-a
> - M-: (overlay-put (make-overlay (point) (+ (point) 3)) 'face 'highlight)
> - Mark the text 'bcd' and delete it
> - M-x undo (does not restore overlay correctly)
> 
> (The solution seems to me to be for undo to also store the overlay,
> adjustment, and whether left, right or both boundaries are involved, and
> use it)

This didn't work with the old implementation of overlays, either.  I
just tested in Emacs 25 and I see the same results there.

Stefan, does undo restore overlays, and if so, how?  I don't see
anything pertinent in the Undo section of the ELisp manual except the
reference to markers (which overlays don't have anymore).  Did that
ever work, and if so, how?  And how should it work now?