StopIteration is silently ignored inside database transactions

[MadLittleMods]

Spawning from #17512 (comment),

If you accidentally cause a StopIteration exception to be thrown inside a transaction (txn stuff), nothing will appear in the logs even though everything blew up. It never reaches our try/except block that normally handles logging the exceptions.

You can run easily run into this by using something like next(iter(my_map.keys())) (to grab the first key in the iterable) where my_map is just an empty dictionary. But this problem is easily reproduced by just doing raise StopIteration directly.

Dev notes

Seems related to https://peps.python.org/pep-0479/ but that makes it seem like with that change (since Python 3.7), StopIteration shouldn't be silently ignored like it is now.

I'm guessing this is a bad interaction between the with context managers at various points and make_deferred_yieldable(...) swallowing it.

There have been more recent related issues around this like python/cpython#112182