Support NotRequired in TypedDict when __future__.annotations is enabled

[guacs]

Description

PEP 655 adds support for NotRequired and Required. Currently it seems msgspec doesn't support it, but it does support total=False when defining a TypedDict. Is this something that can be supported?

I actually encountered this when I was trying to create a typed dictionary for specifying the values that can be updated in a specific table in Postgres. That is, whichever values are provided would be updated. Initially I had something like this:

class UpdateRequest(TypedDict):

    id: str
    some_value: NotRequired[int]
    another_value: NotRequired[str]
    ...

This is what the body of the request from the client was going to be. I refactored this to make it work with msgpec by doing the following:

class UpdateEntity(TypedDict, total=False):

    some_value: int
    another_value: str
    ...

class UpdateRequest(TypedDict):

     id: str
     update_details: UpdateEntity

[jcrist]

Thanks for opening this issue. NotRequired/Required do work, but only if you don't use from __future__ import annotations. This is due to an upstream bug in CPython (see python/typing_extensions#55 and python/cpython#97727).

You can work around this issue for now by doing as you've done above, or avoiding the from __future__ import annotations import.

In the long run I think we'll move to parsing the Required/NotRequired types directly ourselves, rather than relying on the current buggy typing.TypedDict internals to do it for us.

[guacs]

Ohh I see. I guess I'll go with my workaround for now. Thank you very much, and thanks for a great library :)

[jcrist]

No problem! I'm going to keep this open for now to remind me to update our logic to manually handle Required/NotRequired rather than relying on TypedDict to do it for us.

[guacs]

Yeah sure that's a good idea.