Add explicit type hint to BaseSettings.model_config

[Viicos]

Noticed this small issue when working inside settings_customise_sources. Before this PR (by using either cls or settings_cls):

After:

What's weird is that my IDE seems to infer the type correctly in other places, even without this improvement:

By the way, is the settings_cls argument necessary, as settings_customise_sources is already a class method and we have access to cls?

Selected Reviewer: @dmontagu

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (107e8de) 97.42% compared to head (434bca1) 97.42%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #97   +/-   ##
=======================================
  Coverage   97.42%   97.42%           
=======================================
  Files           5        5           
  Lines         311      311           
  Branches       68       68           
=======================================
  Hits          303      303           
  Misses          6        6           
  Partials        2        2           

Impacted Files	Coverage Δ
pydantic_settings/main.py	100.00% <100.00%> (ø)

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[Viicos]

I think the mypy issue comes from the fact that model_config is defined in two places on BaseModel:

    if typing.TYPE_CHECKING:
        # Here we provide annotations for the attributes of BaseModel.
        # Many of these are populated by the metaclass, which is why this section is in a `TYPE_CHECKING` block.
        # However, for the sake of easy review, we have included type annotations of all class and instance attributes
        # of `BaseModel` here:

        # Class attributes
        model_config: ClassVar[ConfigDict]

And later on:

    __slots__ = '__dict__', '__pydantic_fields_set__', '__pydantic_extra__', '__pydantic_private__'

    model_config = ConfigDict()
    __pydantic_complete__ = False
    __pydantic_root_model__ = False

Would it be safe to remove the first one in the if TYPE_CHECKING block, and modify the remaining one to model_config: ClassVar[ConfigDict] = ConfigDict()?

[hramezani]

Thanks @Viicos for this patch.

Yeah, seems the mypy error will be fixed by the change you mentioned on pydantic side.

You have to create a PR on pydantic and suggest the change. We(other people on the team and I) will review the PR. they may have different opinions on that.

[davidhewitt]

I noticed the lint is using pydantic 2.0b3 and since beta 3 we had pydantic/pydantic#6260 which added the type annotation to model_config which is proposed to be changed in pydantic/pydantic#6393

Perhaps there is no change needed in pydantic and the mypy issue will be resolved by updating the linting requirements to 2.0? We could merge #99 and then rebase this PR to confirm.

[Viicos]

@davidhewitt Good catch, I will rebase once #99 gets merged. It seems to work with a MRE:

https://mypy-play.net/?mypy=latest&python=3.11&gist=ba7caebef09f0b3aa5397d05dfef4541

(the error appears if you remove the if TYPE_CHECKING block).

[hramezani]

@Viicos As #99 has been merged, Could you please rebase this PR on top of main?

[Viicos]

Rebasing fixed it.

Please review

[hramezani]

Thanks @Viicos