type inference inside of conditionally defined functions appears incorrect

[mikeshardmind]

Summary

Callable[..., Any] & ~None becomes Callable[..., Any] | None inside a function defined within the branch that narrowed to include ~None

Minimal repro:

https://play.ty.dev/ba37c54e-a0ea-4382-87fb-e2f4945868bf

real world code:

https://github.com/mikeshardmind/async-utils/blob/7bf094f063a727901539598811d3fd907ccf5342/src/async_utils/task_cache.py#L153-L158

relevant errors on that real world code with reveal types added:

info: revealed-type: Revealed type
   --> src\async_utils\task_cache.py:243:9
    |
241 |     else:
242 |         from typing import reveal_type
243 |         reveal_type(cache_transform)
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `((...) -> tuple[@Todo, dict[str, Any]]) & ~None`
244 |         def key_func(args: tuple[t.Any, ...], kwds: dict[t.Any, t.Any], /) -> Hashable:
245 |             reveal_type(cache_transform)
    |

info: revealed-type: Revealed type
   --> src\async_utils\task_cache.py:245:13
    |
243 |         reveal_type(cache_transform)
244 |         def key_func(args: tuple[t.Any, ...], kwds: dict[t.Any, t.Any], /) -> Hashable:
245 |             reveal_type(cache_transform)
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `((...) -> tuple[@Todo, dict[str, Any]]) | None`
246 |             return make_key(*cache_transform(args, kwds))
    |

error: lint:call-non-callable: Object of type `None` is not callable
   --> src\async_utils\task_cache.py:246:30
    |
244 |         def key_func(args: tuple[t.Any, ...], kwds: dict[t.Any, t.Any], /) -> Hashable:
245 |             reveal_type(cache_transform)
246 |             return make_key(*cache_transform(args, kwds))
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^
247 |
248 |     def wrapper[**P, R](coro: TaskCoroFunc[P, R], /) -> TaskFunc[P, R]:
    |
info: `lint:call-non-callable` is enabled by default

Version

0.0.0-alpha.7

[carljm]

Thanks for the report! Yeah, narrowing of nonlocal references inside nested functions is an area where we know we need to improve. It's tricky to find the right balance of useful vs sound, since functions are delayed-execution and the name could potentially be reassigned later in the scope (though of course in this case it isn't, and we should be able to see that)

[sharkdp]

Just adding a cross-reference to #210, which is a related issue (in a non-narrowing setting)