I think this should be preferred over https://github.com/pydantic/pydantic/pull/6915, mostly because the implementation there involves duplicating the list of types in the union, and generally seems more fragile.

I've opened as draft until docs/tests are added, hoping @sydney-runkle can help get this across the line tomorrow.
Add CallableDiscriminator and Tag. I think this should be preferred over https://github.com/pydantic/pydantic/pull/6915, mostly because the implementation there involves duplicating the list of types in the union, and generally seems more fragile.

I've opened as draft until docs/tests are added, hoping @sydney-runkle can help get this across the line tomorrow.
"""Alias generators for converting between different capitalization conventions."""
import re

__all__ = ('to_pascal', 'to_camel', 'to_snake')


def to_pascal(snake: str) -> str:
    """Convert a snake_case string to PascalCase.

    Args:
        snake: The string to convert.

    Returns:
        The PascalCase string.
    """
    camel = snake.title()
    return re.sub('([0-9A-Za-z])_(?=[0-9A-Z])', lambda m: m.group(1), camel)


def to_camel(snake: str) -> str:
    """Convert a snake_case string to camelCase.

    Args:
        snake: The string to convert.

    Returns:
        The converted camelCase string.
    """
    camel = to_pascal(snake)
    return re.sub('(^_*[A-Z])', lambda m: m.group(1).lower(), camel)


def to_snake(camel: str) -> str:
    """Convert a PascalCase or camelCase string to snake_case.

    Args:
        camel: The string to convert.

    Returns:
        The converted string in snake_case.
    """
    snake = re.sub(r'([a-zA-Z])([0-9])', lambda m: f'{m.group(1)}_{m.group(2)}', camel)
    snake = re.sub(r'([a-z0-9])([A-Z])', lambda m: f'{m.group(1)}_{m.group(2)}', snake)
    return snake.lower()

"""Alias generators for converting between different capitalization conventions."""
import re

__all__ = ('to_pascal', 'to_camel', 'to_snake')


def to_pascal(snake: str) -> str:
    """Convert a snake_case string to PascalCase.

    Args:
        snake: The string to convert.

    Returns:
        The PascalCase string.
    """
    camel = snake.title()
    return re.sub('([0-9A-Za-z])_(?=[0-9A-Z])', lambda m: m.group(1), camel)


def to_camel(snake: str) -> str:
    """Convert a snake_case string to camelCase.

    Args:
        snake: The string to convert.

    Returns:
        The converted camelCase string.
    """
    camel = to_pascal(snake)
    return re.sub('(^_*[A-Z])', lambda m: m.group(1).lower(), camel)


def to_snake(camel: str) -> str:
    """Convert a PascalCase or camelCase string to snake_case.

    Args:
        camel: The string to convert.

    Returns:
        The converted string in snake_case.
    """
    snake = re.sub(r'([a-zA-Z])([0-9])', lambda m: f'{m.group(1)}_{m.group(2)}', camel)
    snake = re.sub(r'([a-z0-9])([A-Z])', lambda m: f'{m.group(1)}_{m.group(2)}', snake)
    return snake.lower()
