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

[Gerd Möllmann]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

>> Info for Stefan: I've now removed the per-tree null node, and make check
>> shows no unexpected results.
>
> Thanks.  It's an improvement, but I still don't understand how it
> works :-(

Is it still null->parent?

If so, maybe it helps to picture that null is a child of many parents
:-).  Every node having null on the left or right is a parent in that
sense.  Therefore, if some code uses null->parent to do something it can
not be right.