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Support signal parameter/argument types #68

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@altendky

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So I don't know that this pans out but here's a very preliminary proof of concept that my initial thoughts were wrong and this is at least vaguely possible without a mypy plugin. It doesn't deal with the variadic nature of signal parameters nor does it make any attempt at #9. Anyways, I just wrote it up out of curiosity so figured I'd share it here. Though it may still require a mypy plugin to actually get it working right. Oh yeah, also doesn't cover connecting to a proper 'slot'.

Based on the signal classes in #56.

https://mypy-play.net/?mypy=latest&python=3.8&flags=strict&gist=fb8771c87a891edcfa30d522ae588638

import typing


TA = typing.TypeVar("TA")
TB = typing.TypeVar("TB")


class pyqtBoundSignal(typing.Generic[TA, TB]):
    signal: str = ""

    def emit(self, a: TA, b: TB) -> None: ...


class pyqtSignal(typing.Generic[TA, TB]):
    def __init__(self, a: typing.Type[TA], b: typing.Type[TB], *, name: str = ...) -> None: ...

    @typing.overload
    def __get__(self, instance: None, owner: object) -> "pyqtSignal": ...
    @typing.overload
    def __get__(self, instance: object, owner: object) -> pyqtBoundSignal[TA, TB]: ...
    
    def __get__(self, instance, owner):
        # mypy-play doesn't seem to offer a 'stub' option
        pass


class D:
    signal = pyqtSignal(int, str)


d = D()
d.signal.emit(1, "s")
d.signal.emit(1, 2)
main.py:33: error: Argument 2 to "emit" of "pyqtBoundSignal" has incompatible type "int"; expected "str"
Found 1 error in 1 file (checked 1 source file)

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