bug#58158: 29.0.50; [overlay] Interval tree iteration considered harmful

[Eli Zaretskii]

> From: Gerd Möllmann <gerd.moellmann@gmail.com>
> Cc: Stefan Monnier <monnier@iro.umontreal.ca>,  58158@debbugs.gnu.org
> Date: Thu, 29 Sep 2022 11:09:17 +0200
> 
> I think it simply can't be that what is basically walking a binary tree
> requires such restrictions.  And if it does because of some quirk of the
> interval tree in itree.c, something is seriously wrong with the design.
> 
> That's a bit harsh, but I mean it :-).

Fair enough.

Can you propose a fix?

I guess the begin_iteration/end_iteration dance is because the tree
could be in inconsistent state in-between?  If so, what would it take
to avoid the inconsistency?