Support default values for `CliPositionalArg` when parsing from the CLI

[jploskey]

Currently, there doesn't appear to be a way to have an optional positional argument when parsing settings from the CLI. This is a blocker for me, trying to migrate over from typer.

Running the following will result in this error: pydantic_settings.sources.SettingsError: positional argument BaseMainCommand.value has a default value

from pydantic_settings import BaseSettings, CliPositionalArg, SettingsConfigDict


class Main(BaseSettings):
    model_config = SettingsConfigDict(
        cli_parse_args=True,
        cli_enforce_required=True,
    )

    value: CliPositionalArg[int | None] = None


parsed = Main() # Error is raised here.
print(parsed.value)

[hramezani]

@kschwab can you take a look?

[kschwab]

@jploskey @hramezani opened #519 for resolution 👍🏾

[hramezani]

Thanks @kschwab for the PR. @jploskey could you confirm the fix?

[jploskey]

@hramezani @kschwab I can confirm the fix works! Thank you so much.