disallow untyped defs

[graingert]

disallow untyped defs and fix runtime problems discovered by typing all defs:

• TextStream.extra_attributes no longer crashes with an attribute error
• await maybe_async(current_task()) no longer returns None
• fix warning message to refer to anyio.maybe_async
• pickle.dumps(get_current_task()) now correctly raises a TypeError (or similar on pypy) rather than pickling to None
• task names are converted to str on the asyncio back-end

also type level errors:

• various types, such as anyio.Lock() that were missing a constructor type now have one, see Function is missing type annotation for __init__(self) python/mypy#5943 (comment)
• anyio._backend._asyncio.run takes a coroutine factory and returns the coroutine result - rather than any callable
• await anyio.Event().wait() returns None at runtime, rather than bool. Updated type annotations to reflect this
• anyio.lowlevel.RunVar().get type annotation was updated to return either the default value or the contained type

[uSpike]

Should there be a new wrapper function for asyncio current_task() which always returns a task? This would avoid all of the casting and # type: ignore statements.

[agronholm]

Some question, some change suggestions.

[agronholm]

Almost there! Just a suggestion regarding the type of extra_attributes, and some minor changes.

[agronholm]

Since the cancel_scope member is never accessed unless the cancel scope is active, perhaps this should be declared just with its type and no default value on the class? Without setting it to None in the initializer?

[graingert]

I think that's pretty much equivalent to a # type: ignore[assignment], but means you're assigning to attributes outside the constructor. I think the real fix is to use a TaskGroup/TaskGroupManager pattern like trio:

class TaskGroup(abc.TaskGroup):
    def __init__(self, nursery: trio.Nursery):
        self._active = True
        self._nursery = nursery
        self._cancel_scope = CancelScope(nursery.cancel_scope)

class TaskGroupManager(abc.TaskGroupManager):
    def __init__(self):
        self._nursery_manager = trio.open_nursery()

    async def __aenter____(self):
        return TaskGroup(await self._nursery_manager.__aenter__())

    async def __aexit__(self, *args, **kwargs):
        return await self._nursery_manager.__aexit__()

[agronholm]

Thank you for your hard work on this!