Improve dispatcher typing

[cdce8p]

Proposed change

An idea to improve the dispatcher typing, in particular async_dispatcher_connect and async_dispatcher_send.

def funct(data1: str, data2: int) -> None:
    ...

def other_funct(data1: str, data2: int, x: int) -> None:
    ...

async_dispatcher_connect(hass, "signal", funct)
async_dispatcher_connect(hass, "signal", other_funct)  # one more required argument
async_dispatcher_send(hass, "signal", "Hello")  # missing 'data2' arg

At the moment there is no automated check to see if either a compatible callable is passed to async_dispatcher_connect or async_dispatcher_send is called with the right arguments.

This PR adds a new generic type SignalType to enable mypy to find these issues and Pylance to provide better intellisense support.

SIGNAL: SignalType[str, int] = SignalType("signal")

async_dispatcher_connect(hass, SIGNAL, funct)
async_dispatcher_send(hass, SIGNAL, "Hello", 2)

async_dispatcher_connect(hass, SIGNAL, other_funct)  # mypy error
async_dispatcher_send(hass, SIGNAL, "Hello", 2, 2)  # type error; mypy can't detect that yet

With the updated typing the last two calls will result in type errors.
Pylance can already detect both whereas mypy seems have a bug with the second one, unfortunately.

--
My first idea was to make SignalType inherit from str to be able to use them interchangeably. Unfortunately, that meant the type checkers would revert back to the str overload if the arguments didn't match defeating the whole purpose of this change. I've added custom __hash__ and __eq__ methods for SignalType to be compatible with string dict keys.

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[MartinHjelmare]

The idea sounds ok, but we can't use it if mypy gives an error.

[cdce8p]

The idea sounds ok, but we can't use it if mypy gives an error.

The issue with mypy is that it can't detect error due to incorrect typing yet, i.e. a false-positive false-negative. We'll still get the intellisense support and type checking from Pylance / pyright.

Opened an issue for mypy: python/mypy#16739

--
The two type ignores are just to get the overload typing working.

[MartinHjelmare]

The issue with mypy is that it can't detect error due to incorrect typing yet, i.e. a false-positive.

Isn't that a false negative?

[cdce8p]

The issue with mypy is that it can't detect error due to incorrect typing yet, i.e. a false-positive.

Isn't that a false negative?

Yeah, I thought that I might have mixed them up 😅

[MartinHjelmare]

It's good that the mypy error isn't in the way although it'll give a somewhat false sense of comfort. I'm positive to the change. Let's hear what others think.

[cdce8p]

It's good that the mypy error isn't in the way although it'll give a somewhat false sense of comfort.

Opened a PR for Mypy. Hope it makes it in time for the next release. python/mypy#16759
With that, Mypy will output the same errors as pyright for an incorrect usage.

I'm positive to the change. Let's hear what others think.

👍🏻

[frenck]

With the issue/PR upstream in progress, I think it is fine for now.

Thanks, @cdce8p 👍

../Frenck