Allow TypeVarTuple as type argument for subclasses of generic TypedDict

Bug Report

I have a TypedDict class which has TypeVarTuple type argument(s), and that works as I would expect. However, when I try to make a class derived from that base class, I get unexpected errors from mypy. Different errors, actually, depending on whether I use Unpack or the new "star" unpacking syntax.

This all ought to work, though, right?

To Reproduce

# typeddict_typevartuple_310.py

from collections.abc import Callable
from typing import Generic, Tuple, TypedDict, TypeVar
from typing_extensions import TypeVarTuple, Unpack

ATs = TypeVarTuple('ATs')
RT = TypeVar('RT')


class BaseDict(TypedDict, Generic[Unpack[ATs], RT]):
    callback: Callable[[Unpack[ATs]], RT]
    arguments: Tuple[Unpack[ATs]]


class DerivedDict(BaseDict[Unpack[ATs], RT]):  # E: Unpack is only valid in a variadic position
    returned: RT

# typeddict_typevartuple_311.py

from collections.abc import Callable
from typing import Generic, TypedDict, TypeVar, TypeVarTuple

ATs = TypeVarTuple('ATs')
RT = TypeVar('RT')


class BaseDict(TypedDict, Generic[*ATs, RT]):
    callback: Callable[[*ATs], RT]
    arguments: tuple[*ATs]


class DerivedDict(BaseDict[*ATs, RT]):  # E: Invalid TypedDict type argument
    returned: RT

Expected Behavior

I would have expected mypy to accept both these versions as correct...

Actual Behavior

... But it fails both of them, with distinct messages (see inline comments).

Your Environment

• Mypy version used: mypy 1.10.0+dev.3c87af272cbf7c49699b7508c7f51365da139c05 (compiled: no)
• Mypy command-line flags: n/a
• Mypy configuration options from mypy.ini (and other config files): n/a
• Python version used: 3.10 and 3.11

Inizia eseguendo le due riproduzioni, typeddict_typevartuple_310.py e typeddict_typevartuple_311.py, con il comportamento di mypy segnalato. Traccia la validazione degli argomenti di tipo generici di TypedDict raggiunta da questi esempi, quindi aggiungi una copertura mirata sia per le forme con Unpack sia per le forme di spacchettamento con asterisco. Il lavoro è completato quando mypy accetta entrambe le definizioni TypedDict derivate senza gli errori segnalati.