TypeGuard typechecking on `filter` is too strict

Bug Report

NB: This may be more properly an issue in Typeshed, or require changes in that project to fix, but our team encountered it via MyPy.

The type annotations on builtins.filter cause correct and idiomatic usages to fail to typecheck:

To Reproduce

# filter-mypy.py
path_parts: List[Optional[str]] = ["foo", None, "bar"]

"/".join(filter(None, path_parts))
"/".join(filter(bool, path_parts))
"/".join(filter(lambda s: isinstance(s, str), path_parts))

Expected:

$> mypy filter-mypy.py
Success: no issues found in 1 source file

Actual result:

$> mypy filter-mypy.py
filter-mypy.py:6: error: Argument 1 to "filter" has incompatible type "Type[bool]"; expected "Callable[[Optional[str]], TypeGuard[str]]"
filter-mypy.py:7: error: Argument 1 to "filter" has incompatible type "Callable[[Any], bool]"; expected "Callable[[Optional[str]], TypeGuard[str]]"
Found 2 errors in 1 file (checked 1 source file)

Your Environment

• Mypy version used:

$> mypy --version
mypy 0.950 (compiled: yes)

• Python version used:

$> python --version
Python 3.10.4

• Operating system and version: Ubuntu 20.04

The following is what my editor (VSCode) pulls up when I investigate the type hints for filter, though I doubt this is the same file that MyPy itself is consulting:

class filter(Iterator[_T], Generic[_T]):
    @overload
    def __init__(self, __function: None, __iterable: Iterable[_T | None]) -> None: ...
    @overload
    def __init__(self, __function: Callable[[_S], TypeGuard[_T]], __iterable: Iterable[_S]) -> None: ...
    @overload
    def __init__(self, __function: Callable[[_T], Any], __iterable: Iterable[_T]) -> None: ...

Note that both offending lines conform to the third type signature, but fail the second.

Reproduziere den Bericht mit dem bereitgestellten filter-mypy.py-Beispiel und untersuche die im Issue gezeigten builtins.filter-Overloads. Bestimme anschließend, ob der Fix in mypy oder typeshed vorgenommen werden sollte. Als erledigt gilt die Aufgabe, wenn die Verwendungen von None, bool und isinstance wie erwartet typgeprüft werden, ohne die Prüfung anderer filter-Aufrufe abzuschwächen.