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Unused awaitable

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

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Unused awaitable

Basic coroutine not awaited

Calling an async def function produces a coroutine that must be awaited.

py
async def fetch() -> int:
    return 42

async def fetch_complex(x) -> int:
    return 42

async def main():
    fetch()  # error: [unused-awaitable]
    fetch_complex(lambda: None)  # error: [unused-awaitable]

Awaited coroutine is fine

py
async def fetch() -> int:
    return 42

async def main():
    await fetch()

Assigned coroutine is fine

py
async def fetch() -> int:
    return 42

async def main():
    # TODO: ty should eventually warn about unused coroutines assigned to variables
    coro = fetch()

Coroutine passed to a function

When a coroutine is passed as an argument rather than used as an expression statement, no diagnostic should be emitted.

py
async def fetch() -> int:
    return 42

async def main():
    print(fetch())

Top-level coroutine call

The lint fires even outside of async def, since the coroutine is still discarded.

py
async def fetch() -> int:
    return 42

fetch()  # error: [unused-awaitable]

Union of awaitables

When every element of a union is awaitable, the lint should fire.

py
from types import CoroutineType
from typing import Any

def get_coroutine() -> CoroutineType[Any, Any, int] | CoroutineType[Any, Any, str]:
    raise NotImplementedError

async def main():
    get_coroutine()  # error: [unused-awaitable]

Union with non-awaitable

When a union contains a non-awaitable element, the lint should not fire.

py
from types import CoroutineType
from typing import Any

def get_maybe_coroutine() -> CoroutineType[Any, Any, int] | int:
    raise NotImplementedError

async def main():
    get_maybe_coroutine()

Intersection with awaitable

When an intersection type contains an awaitable element, the lint should fire.

py
from collections.abc import Coroutine
from types import CoroutineType
from ty_extensions import Intersection

class Foo: ...
class Bar: ...

def get_coroutine() -> Intersection[Coroutine[Foo, Foo, Foo], CoroutineType[Bar, Bar, Bar]]:
    raise NotImplementedError

async def main():
    get_coroutine()  # error: [unused-awaitable]

reveal_type and assert_type are not flagged

Calls to reveal_type and assert_type should not trigger this lint, even when their argument is an awaitable.

py
from typing_extensions import assert_type
from types import CoroutineType
from typing import Any

async def fetch() -> int:
    return 42

async def main():
    reveal_type(fetch())  # revealed: CoroutineType[Any, Any, int]
    assert_type(fetch(), CoroutineType[Any, Any, int])

Non-awaitable expression statement

Regular non-awaitable expression statements should not trigger this lint.

py
def compute() -> int:
    return 42

def main():
    compute()

Dynamic type

Any and Unknown types should not trigger the lint.

py
from typing import Any

def get_any() -> Any:
    return None

async def main():
    get_any()