`builtins.filter` support for PEP 647 `TypeGuard`

[Jasha10]

Is your feature request related to a problem? Please describe.
Currently it seems that pyright does not support passing a type guard function as the first argument to the builtin filter function.
Here is an example:

# tmp.py
from typing import Iterable, Optional, TypeGuard


def is_not_none(x: Optional[int]) -> TypeGuard[int]:
    return x is not None

generate_optional: Iterable[Optional[int]] = (x if x % 2 == 0 else None for x in range(100))
list_optional: list[Optional[int]] = [0, None, 1, None, 2]
generate_ints: Iterable[int] = filter(is_not_none, list_optional)

$ pyright tmp.py
...
  /home/jasha10/tmp.py:9:32 - error: Expression of type "filter[int | None]" cannot be assigned to declared type "Iterable[int]"
    TypeVar "_T_co@Iterable" is covariant
      Type "int | None" cannot be assigned to type "int"
        Type "None" cannot be assigned to type "int" (reportGeneralTypeIssues)
1 error, 0 warnings, 0 infos

Describe the solution you'd like
It would be nice if type guard functions could be used with functional programming primitives such as filter.

[erictraut]

This isn't a missing feature in pyright. It's a missing overload in the builtins.pyi type stub for the filter class.

If you add the following overload signature to the filter class, your example will type check fine.

    @overload
    def __init__(
        self, __function: Callable[[_S], TypeGuard[_T]], __iterable: Iterable[_S]
    ) -> None: ...

You can submit a feature request — or better yet, a PR — in the typeshed github repo. Pyright picks up new versions of typeshed stubs frequently.

[Jasha10]

Excellent, thanks.

[layday]

Another PR to add this to the typeshed was closed last week because it confused mypy, see python/typeshed#6140.