Type checker thinks `pendulum.travel_to()` does not implement `Traveller.__exit__`

[amotl]

Hi there,

we observed a false positive on type checking when using ty 0.0.52 on a downstream project. When using pendulum.travel_to() as a context manager, ty complains like this:

error[invalid-context-manager]: Object of type `pendulum.testing.traveller.Traveller @ traveller.py:64:15 | pendulum.testing.traveller.Traveller @ traveller.py:167:11`
cannot be used with `with` because it does not correctly implement `__exit__`

We've already reported it to the ty issue tracker:

• diagnostic for wrongly annotated __enter__ or __exit__ should be on implementation, not usage site astral-sh/ty#3832

With kind regards,
Andreas.

/cc @carljm

[carljm]

It would probably be useful to note that the reason ty complains about this context manager is that the parameters to __exit__ all need to accept None as a possible argument type, since that's how __exit__ is called at runtime if no exception occurred.

[amotl]

Thank you so much for investigating this. Indeed your suggestion sounds like an easy fix.

[ashb]

Yes, that is likely ty being "strictly correct", but we should fix our types on exit to allow nones.