is there way to make both --opt-with-dash and environment variable work at the same time?

[braindevices]

test using #468

import os
import traceback
from pydantic import AliasChoices, AliasGenerator, BaseModel
from pydantic_settings import BaseSettings, SettingsConfigDict, version
import sys
import pydantic.version

class SubModel(BaseModel):
    v1: str = "default"
    v2: bytes = b"hello"
    v3: int


class Settings(BaseSettings):
    model_config = SettingsConfigDict(
        env_prefix="MYTEST_",
        env_nested_delimiter="__",
        cli_parse_args=True,
        nested_model_default_partial_update=True,
        alias_generator=AliasGenerator(lambda s: s.replace('_', '-'))
    )

    v0: str = "ok"
    sub_model: SubModel = SubModel(v1="top default", v3=33)


class Settings1(BaseSettings):
    model_config = SettingsConfigDict(
        env_prefix="MYTEST_",
        env_nested_delimiter="__",
        cli_parse_args=True,
        nested_model_default_partial_update=True
    )

    v0: str = "ok"
    sub_model: SubModel = SubModel(v1="top default", v3=33)


class Settings2(BaseSettings):
    model_config = SettingsConfigDict(
        env_prefix="MYTEST_",
        env_nested_delimiter="__",
        cli_parse_args=True,
        extra="ignore",
        nested_model_default_partial_update=True,
        alias_generator=AliasGenerator(validation_alias=lambda field_name: AliasChoices(field_name, field_name.replace("_", "-")))
    )

    v0: str = "ok"
    sub_model: SubModel = SubModel(v1="top default", v3=33)


def help(cls: BaseSettings):
    sys.argv = [
        cls.__name__,
        "-h"
    ]
    try:
        cls()
    except SystemExit:
        print("sys.exit() was called and handled.")
    print("After exit")

def test_cli(cls: BaseSettings, dash: bool, disable_cli: bool = False):
    sys.argv = [
        'setting',
        *(["--sub-model.v1=cli" if dash else "--sub_model.v1=cli"] if not disable_cli else [])
    ]
    print("argv:", sys.argv)
    # for k, v in os.environ.items():
    #     if k.startswith("MYTEST_"):
    #         print(k, v)
    try:
        a = cls()
        print(f"in test cli: {cls.__name__}()=", a)
    except Exception:
        traceback.print_exc()

def main():
    print("pydnatic version:", pydantic.version.VERSION)
    print("pydantic_settings version:", version.VERSION)

    help(Settings)
    help(Settings1)
    help(Settings2)

    # test_cli(Settings, dash=True)
    os.environ["V0"] = "env no prefix"
    os.environ["SUB_MODEL_V1"] = "env no prefix"
    os.environ["SUB_MODEL_V2"] = "env no prefix"
    os.environ["SUB_MODEL__V1"] = "env__no__prefix"
    os.environ["SUB_MODEL__V2"] = "env__no__prefix"
    os.environ["MYTEST_V0"] = "env with prefix"
    os.environ["MYTEST_SUB_MODEL__V1"] = "env with prefix"
    os.environ["MYTEST_SUB_MODEL__V2"] = "env with prefix"
    test_cli(Settings1, dash=False)
    test_cli(Settings, dash=True)
    test_cli(Settings2, dash=False)
    test_cli(Settings2, dash=True)
    test_cli(Settings2, dash=False, disable_cli=True)


if __name__ == "__main__":
    main()

output:

pydnatic version: 2.9.2
pydantic_settings version: 2.6.1
usage: Settings [-h] [--v0 str] [--sub-model JSON] [--sub-model.v1 str] [--sub-model.v2 bytes] [--sub-model.v3 int]

options:
  -h, --help            show this help message and exit
  --v0 str              (default: ok)

sub-model options:
  --sub-model JSON      set sub-model from JSON string
  --sub-model.v1 str    (default: top default)
  --sub-model.v2 bytes  (default: b'hello')
  --sub-model.v3 int    (default: 33)
sys.exit() was called and handled.
After exit
usage: Settings1 [-h] [--v0 str] [--sub_model JSON] [--sub_model.v1 str] [--sub_model.v2 bytes] [--sub_model.v3 int]

options:
  -h, --help            show this help message and exit
  --v0 str              (default: ok)

sub_model options:
  --sub_model JSON      set sub_model from JSON string
  --sub_model.v1 str    (default: top default)
  --sub_model.v2 bytes  (default: b'hello')
  --sub_model.v3 int    (default: 33)
sys.exit() was called and handled.
After exit
usage: Settings2 [-h] [--v0 str] [--sub_model JSON] [--sub_model.v1 str] [--sub_model.v2 bytes] [--sub_model.v3 int]

options:
  -h, --help            show this help message and exit
  --v0 str              (default: ok)

sub_model options:
  --sub_model JSON, --sub-model JSON
                        set sub_model from JSON string
  --sub_model.v1 str, --sub-model.v1 str
                        (default: top default)
  --sub_model.v2 bytes, --sub-model.v2 bytes
                        (default: b'hello')
  --sub_model.v3 int, --sub-model.v3 int
                        (default: 33)

argv: ['setting', '--sub_model.v1=cli']
in test cli: Settings1()= v0='env with prefix' sub_model=SubModel(v1='cli', v2=b'env with prefix', v3=33)
argv: ['setting', '--sub-model.v1=cli']
in test cli: Settings()= v0='env no prefix' sub_model=SubModel(v1='cli', v2=b'hello', v3=33)
argv: ['setting', '--sub_model.v1=cli']
in test cli: Settings2()= v0='env no prefix' sub_model=SubModel(v1='top default', v2=b'hello', v3=33)
argv: ['setting', '--sub-model.v1=cli']
in test cli: Settings2()= v0='env no prefix' sub_model=SubModel(v1='top default', v2=b'hello', v3=33)
argv: ['setting']
in test cli: Settings2()= v0='env no prefix' sub_model=SubModel(v1='top default', v2=b'hello', v3=33)

So the Settings, use alias_generator=AliasGenerator(lambda s: s.replace('_', '-')) which cause the env_prefix has no effect, the sub_model become sub-model so it won't find any sub_model in env.

Settings1, doe not have the alias generator, so the env options works normally.

Settings2, attempt to use alias_generator=AliasGenerator(validation_alias=lambda field_name: AliasChoices(field_name, field_name.replace("_", "-"))) to allow both --sub-model and env_* options to work. But it raise error without extra="ignore":

pydantic_core._pydantic_core.ValidationError: 1 validation error for Settings2
sub-model
  Extra inputs are not permitted [type=extra_forbidden, input_value={'v1': 'env__no__prefix', 'v2': 'env__no__prefix'}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.9/v/extra_forbidden

with extra="ignore", both '--sub_model.v1=cli' and '--sub-model.v1=cli' has no effect.