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Invalid await diagnostics

crates/ty_python_semantic/resources/mdtest/diagnostics/invalid_await.md

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Invalid await diagnostics

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Basic

This is a test showcasing a primitive case where an object is not awaitable.

py
async def main() -> None:
    await 1  # error: [invalid-await]

Custom type with missing __await__

This diagnostic also points to the class definition if available.

py
class MissingAwait:
    pass

async def main() -> None:
    await MissingAwait()  # error: [invalid-await]

Custom type with possibly missing __await__

This diagnostic also points to the method definition if available.

py
from datetime import datetime

class PossiblyUnbound:
    if datetime.today().weekday() == 0:
        def __await__(self):
            yield

async def main() -> None:
    await PossiblyUnbound()  # error: [invalid-await]

Union type where one member lacks __await__

py
class Awaitable:
    def __await__(self):
        yield

class NotAwaitable: ...

async def _(flag: bool) -> None:
    x = Awaitable() if flag else NotAwaitable()
    await x  # error: [invalid-await]

__await__ definition with extra arguments

Currently, the signature of __await__ isn't checked for conformity with the Awaitable protocol directly. Instead, individual anomalies are reported, such as the following. Here, the diagnostic reports that the object is not implicitly awaitable, while also pointing at the function parameters.

py
class InvalidAwaitArgs:
    def __await__(self, value: int):
        yield value

async def main() -> None:
    await InvalidAwaitArgs()  # error: [invalid-await]

Non-callable __await__

This diagnostic doesn't point to the attribute definition, but complains about it being possibly not awaitable.

py
class NonCallableAwait:
    __await__ = 42

async def main() -> None:
    await NonCallableAwait()  # error: [invalid-await]

__await__ definition with explicit invalid return type

__await__ must return a valid iterator. This diagnostic also points to the method definition if available.

py
class InvalidAwaitReturn:
    def __await__(self) -> int:
        return 5

async def main() -> None:
    await InvalidAwaitReturn()  # error: [invalid-await]

Invalid union return type

When multiple potential definitions of __await__ exist, all of them must be proper in order for an instance to be awaitable. In this specific case, no specific function definition is highlighted.

py
import typing
from datetime import datetime

class UnawaitableUnion:
    if datetime.today().weekday() == 6:
        def __await__(self) -> typing.Generator[typing.Any, None, None]:
            yield

    else:
        def __await__(self) -> int:
            return 5

async def main() -> None:
    await UnawaitableUnion()  # error: [invalid-await]