<!-- Thank you for your contribution! -->
<!-- Unless your change is trivial, please create an issue to discuss the change before creating a PR -->

## Change Summary

I noticed similar or identical logic in several places and extracted a couple of methods to reduce duplication.

The two commits are fairly independent and it may be easier to view their diffs separately to understand the changes. The first is probably a bit more compelling.

Note that the original code replaced by `clean_schema` wasn't always exactly the same, but the differences didn't really strike me as intentional, and either way it seemed good to draw attention to those differences and consider discussing them or adding comments to clarify.

## Related issue number

There's no issue because this isn't fixing/adding anything notable, it's just refactoring. I thought it made more sense to discuss the changes here rather than in a separate issue.

## Checklist

* [x] The pull request title is a good summary of the changes - it will be used in the changelog
* [x] Unit tests for the changes exist
* [x] Tests pass on CI
* [x] Documentation reflects the changes where applicable
* [x] My PR is ready to review, **please add a comment including the phrase "please review" to assign reviewers**


Selected Reviewer: @adriangb
Refactoring schema-related code. <!-- Thank you for your contribution! -->
<!-- Unless your change is trivial, please create an issue to discuss the change before creating a PR -->

## Change Summary

I noticed similar or identical logic in several places and extracted a couple of methods to reduce duplication.

The two commits are fairly independent and it may be easier to view their diffs separately to understand the changes. The first is probably a bit more compelling.

Note that the original code replaced by `clean_schema` wasn't always exactly the same, but the differences didn't really strike me as intentional, and either way it seemed good to draw attention to those differences and consider discussing them or adding comments to clarify.

## Related issue number

There's no issue because this isn't fixing/adding anything notable, it's just refactoring. I thought it made more sense to discuss the changes here rather than in a separate issue.

## Checklist

* [x] The pull request title is a good summary of the changes - it will be used in the changelog
* [x] Unit tests for the changes exist
* [x] Tests pass on CI
* [x] Documentation reflects the changes where applicable
* [x] My PR is ready to review, **please add a comment including the phrase "please review" to assign reviewers**


Selected Reviewer: @adriangb
from __future__ import annotations as _annotations

import warnings
from typing import TYPE_CHECKING, Any

from typing_extensions import Literal, deprecated

from .._internal import _config
from ..warnings import PydanticDeprecatedSince20

if not TYPE_CHECKING:
    # See PyCharm issues https://youtrack.jetbrains.com/issue/PY-21915
    # and https://youtrack.jetbrains.com/issue/PY-51428
    DeprecationWarning = PydanticDeprecatedSince20

__all__ = 'BaseConfig', 'Extra'


class _ConfigMetaclass(type):
    def __getattr__(self, item: str) -> Any:
        warnings.warn(_config.DEPRECATION_MESSAGE, DeprecationWarning)

        try:
            return _config.config_defaults[item]
        except KeyError as exc:
            raise AttributeError(f"type object '{self.__name__}' has no attribute {exc}") from exc


@deprecated('BaseConfig is deprecated. Use the `pydantic.ConfigDict` instead.', category=PydanticDeprecatedSince20)
class BaseConfig(metaclass=_ConfigMetaclass):
    """This class is only retained for backwards compatibility.

    !!! Warning "Deprecated"
        BaseConfig is deprecated. Use the [`pydantic.ConfigDict`][pydantic.ConfigDict] instead.
    """

    def __getattr__(self, item: str) -> Any:
        warnings.warn(_config.DEPRECATION_MESSAGE, DeprecationWarning)
        try:
            return super().__getattribute__(item)
        except AttributeError as exc:
            try:
                return getattr(type(self), item)
            except AttributeError:
                # re-raising changes the displayed text to reflect that `self` is not a type
                raise AttributeError(str(exc)) from exc

    def __init_subclass__(cls, **kwargs: Any) -> None:
        warnings.warn(_config.DEPRECATION_MESSAGE, DeprecationWarning)
        return super().__init_subclass__(**kwargs)


class _ExtraMeta(type):
    def __getattribute__(self, __name: str) -> Any:
        # The @deprecated decorator accesses other attributes, so we only emit a warning for the expected ones
        if __name in {'allow', 'ignore', 'forbid'}:
            warnings.warn(
                "`pydantic.config.Extra` is deprecated, use literal values instead (e.g. `extra='allow'`)",
                DeprecationWarning,
                stacklevel=2,
            )
        return super().__getattribute__(__name)


@deprecated(
    "Extra is deprecated. Use literal values instead (e.g. `extra='allow'`)", category=PydanticDeprecatedSince20
)
class Extra(metaclass=_ExtraMeta):
    allow: Literal['allow'] = 'allow'
    ignore: Literal['ignore'] = 'ignore'
    forbid: Literal['forbid'] = 'forbid'

from __future__ import annotations as _annotations

import warnings
from typing import TYPE_CHECKING, Any

from typing_extensions import Literal, deprecated

from .._internal import _config
from ..warnings import PydanticDeprecatedSince20

if not TYPE_CHECKING:
    # See PyCharm issues https://youtrack.jetbrains.com/issue/PY-21915
    # and https://youtrack.jetbrains.com/issue/PY-51428
    DeprecationWarning = PydanticDeprecatedSince20

__all__ = 'BaseConfig', 'Extra'


class _ConfigMetaclass(type):
    def __getattr__(self, item: str) -> Any:
        warnings.warn(_config.DEPRECATION_MESSAGE, DeprecationWarning)

        try:
            return _config.config_defaults[item]
        except KeyError as exc:
            raise AttributeError(f"type object '{self.__name__}' has no attribute {exc}") from exc


@deprecated('BaseConfig is deprecated. Use the `pydantic.ConfigDict` instead.', category=PydanticDeprecatedSince20)
class BaseConfig(metaclass=_ConfigMetaclass):
    """This class is only retained for backwards compatibility.

    !!! Warning "Deprecated"
        BaseConfig is deprecated. Use the [`pydantic.ConfigDict`][pydantic.ConfigDict] instead.
    """

    def __getattr__(self, item: str) -> Any:
        warnings.warn(_config.DEPRECATION_MESSAGE, DeprecationWarning)
        try:
            return super().__getattribute__(item)
        except AttributeError as exc:
            try:
                return getattr(type(self), item)
            except AttributeError:
                # re-raising changes the displayed text to reflect that `self` is not a type
                raise AttributeError(str(exc)) from exc

    def __init_subclass__(cls, **kwargs: Any) -> None:
        warnings.warn(_config.DEPRECATION_MESSAGE, DeprecationWarning)
        return super().__init_subclass__(**kwargs)


class _ExtraMeta(type):
    def __getattribute__(self, __name: str) -> Any:
        # The @deprecated decorator accesses other attributes, so we only emit a warning for the expected ones
        if __name in {'allow', 'ignore', 'forbid'}:
            warnings.warn(
                "`pydantic.config.Extra` is deprecated, use literal values instead (e.g. `extra='allow'`)",
                DeprecationWarning,
                stacklevel=2,
            )
        return super().__getattribute__(__name)


@deprecated(
    "Extra is deprecated. Use literal values instead (e.g. `extra='allow'`)", category=PydanticDeprecatedSince20
)
class Extra(metaclass=_ExtraMeta):
    allow: Literal['allow'] = 'allow'
    ignore: Literal['ignore'] = 'ignore'
    forbid: Literal['forbid'] = 'forbid'
