TypedDict diamond inheritance fails with `Overwriting TypedDict field "x" while merging`

[EvanKrall]

This file:

from mypy_extensions import TypedDict


class Grandparent(TypedDict):
 a: str


class ParentB(Grandparent):
 b: str


class ParentC(Grandparent):
 c: str


class Child(ParentB, ParentC):
 pass

Produces the error test.py:16: error: Overwriting TypedDict field "a" while merging

I expected this to not error - in some sense, we aren't overwriting field a -- it's ultimately coming from the same place through both branches of the inheritance graph.

Maybe more generally, it should not be an error to overwrite a TypedDict field with the exact same type?

[JukkaL]

Yeah, if the type is always the same, this message doesn't seem useful.

[GPHemsley]

Looks like this is related (though it predates TypedDict): #4354

[vnmabus]

It is also useful to allow redefining attributes with the same type, in the case that one wants to inherit from a total=False TypedDict but make some attributes required.