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## Summary - Add support for the return types of `async` functions - Add type inference for `await` expressions - Add support for `async with` / async context managers - Add support for `yield from` expressions This PR is generally lacking proper error handling in some cases (e.g. illegal `__await__` attributes). I'm planning to work on this in a follow-up. part of https://github.com/astral-sh/ty/issues/151 closes https://github.com/astral-sh/ty/issues/736 ## Ecosystem There are a lot of true positives on `prefect` which look similar to: ```diff prefect (https://github.com/PrefectHQ/prefect) + src/integrations/prefect-aws/tests/workers/test_ecs_worker.py:406:12: error[unresolved-attribute] Type `str` has no attribute `status_code` ``` This is due to a wrong return type annotation [here](e926b8c4c1/src/integrations/prefect-aws/tests/workers/test_ecs_worker.py (L355-L391)). ```diff mitmproxy (https://github.com/mitmproxy/mitmproxy) + test/mitmproxy/addons/test_clientplayback.py:18:1: error[invalid-argument-type] Argument to function `asynccontextmanager` is incorrect: Expected `(...) -> AsyncIterator[Unknown]`, found `def tcp_server(handle_conn, **server_args) -> Unknown | tuple[str, int]` ``` [This](a4d794c59a/test/mitmproxy/addons/test_clientplayback.py (L18-L19)) is a true positive. That function should return `AsyncIterator[Address]`, not `Address`. I looked through almost all of the other new diagnostics and they all look like known problems or true positives. ## Typing conformance The typing conformance diff looks good. ## Test Plan New Markdown tests
123 lines
2.3 KiB
Markdown
123 lines
2.3 KiB
Markdown
# `async` / `await`
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## Basic
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```py
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async def retrieve() -> int:
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return 42
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async def main():
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result = await retrieve()
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reveal_type(result) # revealed: int
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```
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## Generic `async` functions
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```py
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from typing import TypeVar
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T = TypeVar("T")
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async def persist(x: T) -> T:
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return x
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async def f(x: int):
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result = await persist(x)
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reveal_type(result) # revealed: int
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```
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## Use cases
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### `Future`
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```py
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import asyncio
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import concurrent.futures
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def blocking_function() -> int:
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return 42
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async def main():
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loop = asyncio.get_event_loop()
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with concurrent.futures.ThreadPoolExecutor() as pool:
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result = await loop.run_in_executor(pool, blocking_function)
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# TODO: should be `int`
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reveal_type(result) # revealed: Unknown
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```
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### `asyncio.Task`
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```py
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import asyncio
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async def f() -> int:
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return 1
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async def main():
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task = asyncio.create_task(f())
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result = await task
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# TODO: this should be `int`
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reveal_type(result) # revealed: Unknown
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```
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### `asyncio.gather`
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```py
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import asyncio
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async def task(name: str) -> int:
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return len(name)
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async def main():
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(a, b) = await asyncio.gather(
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task("A"),
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task("B"),
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)
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# TODO: these should be `int`
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reveal_type(a) # revealed: Unknown
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reveal_type(b) # revealed: Unknown
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```
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## Under the hood
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```toml
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[environment]
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python-version = "3.12" # Use 3.12 to be able to use PEP 695 generics
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```
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Let's look at the example from the beginning again:
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```py
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async def retrieve() -> int:
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return 42
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```
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When we look at the signature of this function, we see that it actually returns a `CoroutineType`:
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```py
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reveal_type(retrieve) # revealed: def retrieve() -> CoroutineType[Any, Any, int]
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```
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The expression `await retrieve()` desugars into a call to the `__await__` dunder method on the
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`CoroutineType` object, followed by a `yield from`. Let's first see the return type of `__await__`:
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```py
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reveal_type(retrieve().__await__()) # revealed: Generator[Any, None, int]
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```
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We can see that this returns a `Generator` that yields `Any`, and eventually returns `int`. For the
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final type of the `await` expression, we retrieve that third argument of the `Generator` type:
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```py
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from typing import Generator
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def _():
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result = yield from retrieve().__await__()
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reveal_type(result) # revealed: int
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```
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