An unusual but possible situation is when two objects have boolean modifiers with each other as a target.

This is a dependency cycle, and it quickly creates messy geometry and slows down Blender a lot.

This patch prevents the creation of this specific dependency cycle. There shouldn't be any actual usecase negatively affected.

I would understand the argument that trying to prevent this sort of situation is a slippery slope and that it shouldn't be a goal to babysit users, but this is a quick fix without much of a downside IMO.

I didn't find any instances of WM_report in rna_*.c files, but a report in the console defeats the purpose here.

D4730 would also display this information, but it wouldn't prevent the cycle.