NoReturn return type with singledispatch causing weird errors

[This was originally in a comment by @Dreamsorcerer]

...

This issue has mostly talked about the redefinition error. But, we should also have singledispatch typing working. e.g. With this example:

@singledispatch
def foo(data: object) -> NoReturn:
    raise ValueError(f"Unhandled type {type(data)}")
@foo.register
def _(data: str) -> str:
    return data
@foo.register
def _(data: int) -> str:
    return str(data)

a = foo(7)
reveal_type(a)

You also get errors due to not recognising the overloads:

src/service/transaction_status_service.py:72: error: Need type annotation for "a" [var-annotated]
src/service/transaction_status_service.py:73: note: Revealed type is "<nothing>"

It would be good for mypy to treat the @foo.register like an @overload.

I was also getting unreachable code errors after every call to the defined function. However, I was unable to reproduce it with a minimal example, so not sure exactly what is causing that.

Inizia con l'esempio di singledispatch nell'issue e esamina il commento originale collegato e la discussione sul comportamento esistente delle ridefinizioni. Riproduci gli errori segnalati, quindi verifica che le implementazioni registrate siano trattate come overloads, con il risultato della chiamata inferito come str e gli errori spuri relativi a codice irraggiungibile e annotazioni di variabili risolti.