Pyright: Bug with generic functions taking generic callbacks

Created on 3 Dec 2020 · 3Comments · Source: microsoft/pyright

Environment data

Language Server version: Pylance language server 2020.12.1-pre.1 (pyright ea581b3f)
OS and version: Mac OS X 11.0.1
Python version (& distribution if applicable, e.g. Anaconda): Python 3.9 (brew)

Expected behaviour

Pylance should be able to assign a function that takes e.g an int as arg to a generic function that returns a TSource expects a function that takes a TSource as arg, and then returns a TSource. The current version of Pylance is unable to see that TSource is int. It's a bit complex so please look at the self-contained code snippet below.

Actual behaviour

Screenshot 2020-12-03 at 09 41 23

Logs

[Info  - 7:43:16 AM] Pylance language server 2020.12.1-pre.1 (pyright ea581b3f) starting
[Info  - 7:43:16 AM] Server root directory: /Users/dbrattli/.vscode/extensions/ms-python.vscode-pylance-2020.12.1-pre.1/dist
[Error - 7:43:16 AM] stubPath /Users/dbrattli/Developer/Github/Expression/typings is not a valid directory.
[Info  - 9:27:27 AM] No configuration file found.
[Info  - 9:27:27 AM] Setting pythonPath for service "Expression": "/usr/local/opt/[email protected]/bin/python3"
...
Nothing special here

Code Snippet / Additional information

import asyncio
from asyncio import Future
from typing import Awaitable, Callable, TypeVar

TSource = TypeVar("TSource")

Continuation = Callable[[TSource], None]
#Callback = Callable[[Continuation[TSource]], None]


def from_continuation(callback: Callable[[Continuation[TSource]], None]) -> Awaitable[TSource]:
    future: Future[TSource] = asyncio.Future()

    def done(value: TSource) -> None:
        future.set_result(value)

    callback(done)
    return asyncio.ensure_future(future)


async def test() -> int:
    def callback(done: Continuation[int]) -> None:
        done(42)

    return await from_continuation(callback)

Making a type alias for the callback (code below) does not help either but also gives an additional error:

Screenshot 2020-12-03 at 09 44 01

import asyncio
from asyncio import Future
from typing import Awaitable, Callable, TypeVar

TSource = TypeVar("TSource")

Continuation = Callable[[TSource], None]
Callback = Callable[[Continuation[TSource]], None]


def from_continuation(callback: Callback[TSource]) -> Awaitable[TSource]:
    future: Future[TSource] = asyncio.Future()

    def done(value: TSource) -> None:
        future.set_result(value)

    callback(done)
    return asyncio.ensure_future(future)


async def test() -> int:
    def callback(done: Continuation[int]) -> None:
        done(42)

    return await from_continuation(callback)

Example of real usage (a bit more complex):

addressed in next version bug

Source

dbrattli

All 3 comments

Thanks for the bug report. There were two separate bugs here. The first had to do with nested Callable types (i.e. a Callable that included a Callable parameter). The second had to do with generic type aliases that included Callable types. Both of these bugs will be fixed in the next release.