Give execute and maybeDeferred correct type annotations

[exarkun]

Currently maybeDeferred is annotated:

def maybeDeferred(
    f: Callable[..., _T], *args: object, **kwargs: object
) -> "Deferred[_T]":

The handling of the parameters of f and of args and kwargs is overly general. The handling of _T is incomplete and incorrect with respect to Deferred and coroutine.

execute is in roughly the same situation.

[arnimarj]

For what it's worth, I've been using this for a while now:

_P = ParamSpec('_P')
...
def maybeDeferred(f: Union[Callable[_P, _T], Awaitable[_T]], *args: _P.args, **kwargs: _P.kwargs) -> Deferred[_T]:
	...

[exarkun]

Thanks. I think the Union there is slightly wrong in a couple ways:

• f is not an Awaitable itself but a function that returns a value, possibly in some kind of async container.
• If the Union moves inside like Callable[_P, Union[Awaitable[_T], _T]] then the return type expresses nothing more than Callable[_P, _T] because _T includes all of Awaitable[_T] (ie, _T might be Awaitable[_S]).

So unfortunately the best type I can figure out for f is Callable[_P, _T] even though this clearly fails to capture a lot of interesting stuff about the type.