Difference with mypy when using manual overloads for TypeVarTuple *args

Discussed in https://github.com/microsoft/pyright/discussions/10602

^{Originally posted by jonaslb June 13, 2025}
I have the following example:

from collections.abc import Callable
from typing import overload


class X[CT]:
    @overload
    def method[T1, Out](
        self, x: "X[T1]", /, *, combine: Callable[[CT, T1], Out]
    ) -> Out: ...
    @overload
    def method[T1, T2, Out](
        self, x: "X[T1]", y: "X[T2]", /, *, combine: Callable[[CT, T1, T2], Out]
    ) -> Out: ...
    def method[*P, Out](
        self, *args: "X[object]", combine: Callable[[CT, *P], Out]
    ) -> Out:
        raise NotImplementedError()

Mypy has no issue with it.

Pylance says, on the method implementation, the following:

Overloaded implementation is not consistent with signature of overload 2
  Type "(self: Self@X[CT@X], *args: X[object], combine: (CT@X, *P@method) -> Out@method) -> Out@method" is not assignable to type "(self: Self@X[CT@X], x: X[T1@method], y: X[T2@method], /, *, combine: (CT@X, T1@method, T2@method) -> Out@method) -> Out@method"
    Keyword parameter "combine" of type "(CT@X, T1@method, T2@method) -> Out@method" is incompatible with type "(CT@X, *P@method) -> Out@method"
      Type "(CT@X, T1@method, T2@method) -> Out@method" is not assignable to type "(CT@X, *P@method) -> Out@method"
        Position-only parameter mismatch; expected 3 but received 2Pylance[reportInconsistentOverload](https://github.com/microsoft/pylance-release/blob/main/docs/diagnostics/reportInconsistentOverload.md)

It seems to me that (CT@X, T1@method, T2@method) should be assignable to (CT@X, *P@method), but I'm not sure if I'm missing something?

Start with the minimal Python example in the issue and reproduce the differing results between mypy and Pyright/Pylance. Review the reportInconsistentOverload diagnostic and the linked discussion for context; the issue is done when the behavior is resolved consistently with the intended overload compatibility and covered by an appropriate regression check.