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.
import warnings
from collections import ChainMap
from functools import partial, partialmethod, wraps
from itertools import chain
from types import FunctionType
from typing import TYPE_CHECKING, Any, Callable, Dict, Iterable, List, Optional, Set, Tuple, Type, Union, overload

from .errors import ConfigError
from .typing import AnyCallable
from .utils import ROOT_KEY, in_ipython

if TYPE_CHECKING:
    from .typing import AnyClassMethod


class Validator:
    __slots__ = 'func', 'pre', 'each_item', 'always', 'check_fields', 'skip_on_failure'

    def __init__(
        self,
        func: AnyCallable,
        pre: bool = False,
        each_item: bool = False,
        always: bool = False,
        check_fields: bool = False,
        skip_on_failure: bool = False,
    ):
        self.func = func
        self.pre = pre
        self.each_item = each_item
        self.always = always
        self.check_fields = check_fields
        self.skip_on_failure = skip_on_failure


if TYPE_CHECKING:
    from inspect import Signature

    from .config import BaseConfig
    from .fields import ModelField
    from .types import ModelOrDc

    ValidatorCallable = Callable[[Optional[ModelOrDc], Any, Dict[str, Any], ModelField, Type[BaseConfig]], Any]
    ValidatorsList = List[ValidatorCallable]
    ValidatorListDict = Dict[str, List[Validator]]

_FUNCS: Set[str] = set()
VALIDATOR_CONFIG_KEY = '__validator_config__'
ROOT_VALIDATOR_CONFIG_KEY = '__root_validator_config__'


def validator(
    *fields: str,
    pre: bool = False,
    each_item: bool = False,
    always: bool = False,
    check_fields: bool = True,
    whole: Optional[bool] = None,
    allow_reuse: bool = False,
) -> Callable[[AnyCallable], 'AnyClassMethod']:
    """
    Decorate methods on the class indicating that they should be used to validate fields
    :param fields: which field(s) the method should be called on
    :param pre: whether or not this validator should be called before the standard validators (else after)
    :param each_item: for complex objects (sets, lists etc.) whether to validate individual elements rather than the
      whole object
    :param always: whether this method and other validators should be called even if the value is missing
    :param check_fields: whether to check that the fields actually exist on the model
    :param allow_reuse: whether to track and raise an error if another validator refers to the decorated function
    """
    if not fields:
        raise ConfigError('validator with no fields specified')
    elif isinstance(fields[0], FunctionType):
        raise ConfigError(
            "validators should be used with fields and keyword arguments, not bare. "  # noqa: Q000
            "E.g. usage should be `@validator('<field_name>', ...)`"
        )
    elif not all(isinstance(field, str) for field in fields):
        raise ConfigError(
            "validator fields should be passed as separate string args. "  # noqa: Q000
            "E.g. usage should be `@validator('<field_name_1>', '<field_name_2>', ...)`"
        )

    if whole is not None:
        warnings.warn(
            'The "whole" keyword argument is deprecated, use "each_item" (inverse meaning, default False) instead',
            DeprecationWarning,
        )
        assert each_item is False, '"each_item" and "whole" conflict, remove "whole"'
        each_item = not whole

    def dec(f: AnyCallable) -> 'AnyClassMethod':
        f_cls = _prepare_validator(f, allow_reuse)
        setattr(
            f_cls,
            VALIDATOR_CONFIG_KEY,
            (
                fields,
                Validator(func=f_cls.__func__, pre=pre, each_item=each_item, always=always, check_fields=check_fields),
            ),
        )
        return f_cls

    return dec


@overload
def root_validator(_func: AnyCallable) -> 'AnyClassMethod':
    ...


@overload
def root_validator(
    *, pre: bool = False, allow_reuse: bool = False, skip_on_failure: bool = False
) -> Callable[[AnyCallable], 'AnyClassMethod']:
    ...


def root_validator(
    _func: Optional[AnyCallable] = None, *, pre: bool = False, allow_reuse: bool = False, skip_on_failure: bool = False
) -> Union['AnyClassMethod', Callable[[AnyCallable], 'AnyClassMethod']]:
    """
    Decorate methods on a model indicating that they should be used to validate (and perhaps modify) data either
    before or after standard model parsing/validation is performed.
    """
    if _func:
        f_cls = _prepare_validator(_func, allow_reuse)
        setattr(
            f_cls, ROOT_VALIDATOR_CONFIG_KEY, Validator(func=f_cls.__func__, pre=pre, skip_on_failure=skip_on_failure)
        )
        return f_cls

    def dec(f: AnyCallable) -> 'AnyClassMethod':
        f_cls = _prepare_validator(f, allow_reuse)
        setattr(
            f_cls, ROOT_VALIDATOR_CONFIG_KEY, Validator(func=f_cls.__func__, pre=pre, skip_on_failure=skip_on_failure)
        )
        return f_cls

    return dec


def _prepare_validator(function: AnyCallable, allow_reuse: bool) -> 'AnyClassMethod':
    """
    Avoid validators with duplicated names since without this, validators can be overwritten silently
    which generally isn't the intended behaviour, don't run in ipython (see #312) or if allow_reuse is False.
    """
    f_cls = function if isinstance(function, classmethod) else classmethod(function)
    if not in_ipython() and not allow_reuse:
        ref = (
            getattr(f_cls.__func__, '__module__', '<No __module__>')
            + '.'
            + getattr(f_cls.__func__, '__qualname__', f'<No __qualname__: id:{id(f_cls.__func__)}>')
        )
        if ref in _FUNCS:
            raise ConfigError(f'duplicate validator function "{ref}"; if this is intended, set `allow_reuse=True`')
        _FUNCS.add(ref)
    return f_cls


class ValidatorGroup:
    def __init__(self, validators: 'ValidatorListDict') -> None:
        self.validators = validators
        self.used_validators = {'*'}

    def get_validators(self, name: str) -> Optional[Dict[str, Validator]]:
        self.used_validators.add(name)
        validators = self.validators.get(name, [])
        if name != ROOT_KEY:
            validators += self.validators.get('*', [])
        if validators:
            return {getattr(v.func, '__name__', f'<No __name__: id:{id(v.func)}>'): v for v in validators}
        else:
            return None

    def check_for_unused(self) -> None:
        unused_validators = set(
            chain.from_iterable(
                (
                    getattr(v.func, '__name__', f'<No __name__: id:{id(v.func)}>')
                    for v in self.validators[f]
                    if v.check_fields
                )
                for f in (self.validators.keys() - self.used_validators)
            )
        )
        if unused_validators:
            fn = ', '.join(unused_validators)
            raise ConfigError(
                f"Validators defined with incorrect fields: {fn} "  # noqa: Q000
                f"(use check_fields=False if you're inheriting from the model and intended this)"
            )


def extract_validators(namespace: Dict[str, Any]) -> Dict[str, List[Validator]]:
    validators: Dict[str, List[Validator]] = {}
    for var_name, value in namespace.items():
        validator_config = getattr(value, VALIDATOR_CONFIG_KEY, None)
        if validator_config:
            fields, v = validator_config
            for field in fields:
                if field in validators:
                    validators[field].append(v)
                else:
                    validators[field] = [v]
    return validators


def extract_root_validators(namespace: Dict[str, Any]) -> Tuple[List[AnyCallable], List[Tuple[bool, AnyCallable]]]:
    from inspect import signature

    pre_validators: List[AnyCallable] = []
    post_validators: List[Tuple[bool, AnyCallable]] = []
    for name, value in namespace.items():
        validator_config: Optional[Validator] = getattr(value, ROOT_VALIDATOR_CONFIG_KEY, None)
        if validator_config:
            sig = signature(validator_config.func)
            args = list(sig.parameters.keys())
            if args[0] == 'self':
                raise ConfigError(
                    f'Invalid signature for root validator {name}: {sig}, "self" not permitted as first argument, '
                    f'should be: (cls, values).'
                )
            if len(args) != 2:
                raise ConfigError(f'Invalid signature for root validator {name}: {sig}, should be: (cls, values).')
            # check function signature
            if validator_config.pre:
                pre_validators.append(validator_config.func)
            else:
                post_validators.append((validator_config.skip_on_failure, validator_config.func))
    return pre_validators, post_validators


def inherit_validators(base_validators: 'ValidatorListDict', validators: 'ValidatorListDict') -> 'ValidatorListDict':
    for field, field_validators in base_validators.items():
        if field not in validators:
            validators[field] = []
        validators[field] += field_validators
    return validators


def make_generic_validator(validator: AnyCallable) -> 'ValidatorCallable':
    """
    Make a generic function which calls a validator with the right arguments.

    Unfortunately other approaches (eg. return a partial of a function that builds the arguments) is slow,
    hence this laborious way of doing things.

    It's done like this so validators don't all need **kwargs in their signature, eg. any combination of
    the arguments "values", "fields" and/or "config" are permitted.
    """
    from inspect import signature

    if not isinstance(validator, (partial, partialmethod)):
        # This should be the default case, so overhead is reduced
        sig = signature(validator)
        args = list(sig.parameters.keys())
    else:
        # Fix the generated argument lists of partial methods
        sig = signature(validator.func)
        args = [
            k
            for k in signature(validator.func).parameters.keys()
            if k not in validator.args | validator.keywords.keys()
        ]

    first_arg = args.pop(0)
    if first_arg == 'self':
        raise ConfigError(
            f'Invalid signature for validator {validator}: {sig}, "self" not permitted as first argument, '
            f'should be: (cls, value, values, config, field), "values", "config" and "field" are all optional.'
        )
    elif first_arg == 'cls':
        # assume the second argument is value
        return wraps(validator)(_generic_validator_cls(validator, sig, set(args[1:])))
    else:
        # assume the first argument was value which has already been removed
        return wraps(validator)(_generic_validator_basic(validator, sig, set(args)))


def prep_validators(v_funcs: Iterable[AnyCallable]) -> 'ValidatorsList':
    return [make_generic_validator(f) for f in v_funcs if f]


all_kwargs = {'values', 'field', 'config'}


def _generic_validator_cls(validator: AnyCallable, sig: 'Signature', args: Set[str]) -> 'ValidatorCallable':
    # assume the first argument is value
    has_kwargs = False
    if 'kwargs' in args:
        has_kwargs = True
        args -= {'kwargs'}

    if not args.issubset(all_kwargs):
        raise ConfigError(
            f'Invalid signature for validator {validator}: {sig}, should be: '
            f'(cls, value, values, config, field), "values", "config" and "field" are all optional.'
        )

    if has_kwargs:
        return lambda cls, v, values, field, config: validator(cls, v, values=values, field=field, config=config)
    elif args == set():
        return lambda cls, v, values, field, config: validator(cls, v)
    elif args == {'values'}:
        return lambda cls, v, values, field, config: validator(cls, v, values=values)
    elif args == {'field'}:
        return lambda cls, v, values, field, config: validator(cls, v, field=field)
    elif args == {'config'}:
        return lambda cls, v, values, field, config: validator(cls, v, config=config)
    elif args == {'values', 'field'}:
        return lambda cls, v, values, field, config: validator(cls, v, values=values, field=field)
    elif args == {'values', 'config'}:
        return lambda cls, v, values, field, config: validator(cls, v, values=values, config=config)
    elif args == {'field', 'config'}:
        return lambda cls, v, values, field, config: validator(cls, v, field=field, config=config)
    else:
        # args == {'values', 'field', 'config'}
        return lambda cls, v, values, field, config: validator(cls, v, values=values, field=field, config=config)


def _generic_validator_basic(validator: AnyCallable, sig: 'Signature', args: Set[str]) -> 'ValidatorCallable':
    has_kwargs = False
    if 'kwargs' in args:
        has_kwargs = True
        args -= {'kwargs'}

    if not args.issubset(all_kwargs):
        raise ConfigError(
            f'Invalid signature for validator {validator}: {sig}, should be: '
            f'(value, values, config, field), "values", "config" and "field" are all optional.'
        )

    if has_kwargs:
        return lambda cls, v, values, field, config: validator(v, values=values, field=field, config=config)
    elif args == set():
        return lambda cls, v, values, field, config: validator(v)
    elif args == {'values'}:
        return lambda cls, v, values, field, config: validator(v, values=values)
    elif args == {'field'}:
        return lambda cls, v, values, field, config: validator(v, field=field)
    elif args == {'config'}:
        return lambda cls, v, values, field, config: validator(v, config=config)
    elif args == {'values', 'field'}:
        return lambda cls, v, values, field, config: validator(v, values=values, field=field)
    elif args == {'values', 'config'}:
        return lambda cls, v, values, field, config: validator(v, values=values, config=config)
    elif args == {'field', 'config'}:
        return lambda cls, v, values, field, config: validator(v, field=field, config=config)
    else:
        # args == {'values', 'field', 'config'}
        return lambda cls, v, values, field, config: validator(v, values=values, field=field, config=config)


def gather_all_validators(type_: 'ModelOrDc') -> Dict[str, 'AnyClassMethod']:
    all_attributes = ChainMap(*[cls.__dict__ for cls in type_.__mro__])  # type: ignore[arg-type,var-annotated]
    return {
        k: v
        for k, v in all_attributes.items()
        if hasattr(v, VALIDATOR_CONFIG_KEY) or hasattr(v, ROOT_VALIDATOR_CONFIG_KEY)
    }

import warnings
from collections import ChainMap
from functools import partial, partialmethod, wraps
from itertools import chain
from types import FunctionType
from typing import TYPE_CHECKING, Any, Callable, Dict, Iterable, List, Optional, Set, Tuple, Type, Union, overload

from .errors import ConfigError
from .typing import AnyCallable
from .utils import ROOT_KEY, in_ipython

if TYPE_CHECKING:
    from .typing import AnyClassMethod


class Validator:
    __slots__ = 'func', 'pre', 'each_item', 'always', 'check_fields', 'skip_on_failure'

    def __init__(
        self,
        func: AnyCallable,
        pre: bool = False,
        each_item: bool = False,
        always: bool = False,
        check_fields: bool = False,
        skip_on_failure: bool = False,
    ):
        self.func = func
        self.pre = pre
        self.each_item = each_item
        self.always = always
        self.check_fields = check_fields
        self.skip_on_failure = skip_on_failure


if TYPE_CHECKING:
    from inspect import Signature

    from .config import BaseConfig
    from .fields import ModelField
    from .types import ModelOrDc

    ValidatorCallable = Callable[[Optional[ModelOrDc], Any, Dict[str, Any], ModelField, Type[BaseConfig]], Any]
    ValidatorsList = List[ValidatorCallable]
    ValidatorListDict = Dict[str, List[Validator]]

_FUNCS: Set[str] = set()
VALIDATOR_CONFIG_KEY = '__validator_config__'
ROOT_VALIDATOR_CONFIG_KEY = '__root_validator_config__'


def validator(
    *fields: str,
    pre: bool = False,
    each_item: bool = False,
    always: bool = False,
    check_fields: bool = True,
    whole: Optional[bool] = None,
    allow_reuse: bool = False,
) -> Callable[[AnyCallable], 'AnyClassMethod']:
    """
    Decorate methods on the class indicating that they should be used to validate fields
    :param fields: which field(s) the method should be called on
    :param pre: whether or not this validator should be called before the standard validators (else after)
    :param each_item: for complex objects (sets, lists etc.) whether to validate individual elements rather than the
      whole object
    :param always: whether this method and other validators should be called even if the value is missing
    :param check_fields: whether to check that the fields actually exist on the model
    :param allow_reuse: whether to track and raise an error if another validator refers to the decorated function
    """
    if not fields:
        raise ConfigError('validator with no fields specified')
    elif isinstance(fields[0], FunctionType):
        raise ConfigError(
            "validators should be used with fields and keyword arguments, not bare. "  # noqa: Q000
            "E.g. usage should be `@validator('<field_name>', ...)`"
        )
    elif not all(isinstance(field, str) for field in fields):
        raise ConfigError(
            "validator fields should be passed as separate string args. "  # noqa: Q000
            "E.g. usage should be `@validator('<field_name_1>', '<field_name_2>', ...)`"
        )

    if whole is not None:
        warnings.warn(
            'The "whole" keyword argument is deprecated, use "each_item" (inverse meaning, default False) instead',
            DeprecationWarning,
        )
        assert each_item is False, '"each_item" and "whole" conflict, remove "whole"'
        each_item = not whole

    def dec(f: AnyCallable) -> 'AnyClassMethod':
        f_cls = _prepare_validator(f, allow_reuse)
        setattr(
            f_cls,
            VALIDATOR_CONFIG_KEY,
            (
                fields,
                Validator(func=f_cls.__func__, pre=pre, each_item=each_item, always=always, check_fields=check_fields),
            ),
        )
        return f_cls

    return dec


@overload
def root_validator(_func: AnyCallable) -> 'AnyClassMethod':
    ...


@overload
def root_validator(
    *, pre: bool = False, allow_reuse: bool = False, skip_on_failure: bool = False
) -> Callable[[AnyCallable], 'AnyClassMethod']:
    ...


def root_validator(
    _func: Optional[AnyCallable] = None, *, pre: bool = False, allow_reuse: bool = False, skip_on_failure: bool = False
) -> Union['AnyClassMethod', Callable[[AnyCallable], 'AnyClassMethod']]:
    """
    Decorate methods on a model indicating that they should be used to validate (and perhaps modify) data either
    before or after standard model parsing/validation is performed.
    """
    if _func:
        f_cls = _prepare_validator(_func, allow_reuse)
        setattr(
            f_cls, ROOT_VALIDATOR_CONFIG_KEY, Validator(func=f_cls.__func__, pre=pre, skip_on_failure=skip_on_failure)
        )
        return f_cls

    def dec(f: AnyCallable) -> 'AnyClassMethod':
        f_cls = _prepare_validator(f, allow_reuse)
        setattr(
            f_cls, ROOT_VALIDATOR_CONFIG_KEY, Validator(func=f_cls.__func__, pre=pre, skip_on_failure=skip_on_failure)
        )
        return f_cls

    return dec


def _prepare_validator(function: AnyCallable, allow_reuse: bool) -> 'AnyClassMethod':
    """
    Avoid validators with duplicated names since without this, validators can be overwritten silently
    which generally isn't the intended behaviour, don't run in ipython (see #312) or if allow_reuse is False.
    """
    f_cls = function if isinstance(function, classmethod) else classmethod(function)
    if not in_ipython() and not allow_reuse:
        ref = (
            getattr(f_cls.__func__, '__module__', '<No __module__>')
            + '.'
            + getattr(f_cls.__func__, '__qualname__', f'<No __qualname__: id:{id(f_cls.__func__)}>')
        )
        if ref in _FUNCS:
            raise ConfigError(f'duplicate validator function "{ref}"; if this is intended, set `allow_reuse=True`')
        _FUNCS.add(ref)
    return f_cls


class ValidatorGroup:
    def __init__(self, validators: 'ValidatorListDict') -> None:
        self.validators = validators
        self.used_validators = {'*'}

    def get_validators(self, name: str) -> Optional[Dict[str, Validator]]:
        self.used_validators.add(name)
        validators = self.validators.get(name, [])
        if name != ROOT_KEY:
            validators += self.validators.get('*', [])
        if validators:
            return {getattr(v.func, '__name__', f'<No __name__: id:{id(v.func)}>'): v for v in validators}
        else:
            return None

    def check_for_unused(self) -> None:
        unused_validators = set(
            chain.from_iterable(
                (
                    getattr(v.func, '__name__', f'<No __name__: id:{id(v.func)}>')
                    for v in self.validators[f]
                    if v.check_fields
                )
                for f in (self.validators.keys() - self.used_validators)
            )
        )
        if unused_validators:
            fn = ', '.join(unused_validators)
            raise ConfigError(
                f"Validators defined with incorrect fields: {fn} "  # noqa: Q000
                f"(use check_fields=False if you're inheriting from the model and intended this)"
            )


def extract_validators(namespace: Dict[str, Any]) -> Dict[str, List[Validator]]:
    validators: Dict[str, List[Validator]] = {}
    for var_name, value in namespace.items():
        validator_config = getattr(value, VALIDATOR_CONFIG_KEY, None)
        if validator_config:
            fields, v = validator_config
            for field in fields:
                if field in validators:
                    validators[field].append(v)
                else:
                    validators[field] = [v]
    return validators


def extract_root_validators(namespace: Dict[str, Any]) -> Tuple[List[AnyCallable], List[Tuple[bool, AnyCallable]]]:
    from inspect import signature

    pre_validators: List[AnyCallable] = []
    post_validators: List[Tuple[bool, AnyCallable]] = []
    for name, value in namespace.items():
        validator_config: Optional[Validator] = getattr(value, ROOT_VALIDATOR_CONFIG_KEY, None)
        if validator_config:
            sig = signature(validator_config.func)
            args = list(sig.parameters.keys())
            if args[0] == 'self':
                raise ConfigError(
                    f'Invalid signature for root validator {name}: {sig}, "self" not permitted as first argument, '
                    f'should be: (cls, values).'
                )
            if len(args) != 2:
                raise ConfigError(f'Invalid signature for root validator {name}: {sig}, should be: (cls, values).')
            # check function signature
            if validator_config.pre:
                pre_validators.append(validator_config.func)
            else:
                post_validators.append((validator_config.skip_on_failure, validator_config.func))
    return pre_validators, post_validators


def inherit_validators(base_validators: 'ValidatorListDict', validators: 'ValidatorListDict') -> 'ValidatorListDict':
    for field, field_validators in base_validators.items():
        if field not in validators:
            validators[field] = []
        validators[field] += field_validators
    return validators


def make_generic_validator(validator: AnyCallable) -> 'ValidatorCallable':
    """
    Make a generic function which calls a validator with the right arguments.

    Unfortunately other approaches (eg. return a partial of a function that builds the arguments) is slow,
    hence this laborious way of doing things.

    It's done like this so validators don't all need **kwargs in their signature, eg. any combination of
    the arguments "values", "fields" and/or "config" are permitted.
    """
    from inspect import signature

    if not isinstance(validator, (partial, partialmethod)):
        # This should be the default case, so overhead is reduced
        sig = signature(validator)
        args = list(sig.parameters.keys())
    else:
        # Fix the generated argument lists of partial methods
        sig = signature(validator.func)
        args = [
            k
            for k in signature(validator.func).parameters.keys()
            if k not in validator.args | validator.keywords.keys()
        ]

    first_arg = args.pop(0)
    if first_arg == 'self':
        raise ConfigError(
            f'Invalid signature for validator {validator}: {sig}, "self" not permitted as first argument, '
            f'should be: (cls, value, values, config, field), "values", "config" and "field" are all optional.'
        )
    elif first_arg == 'cls':
        # assume the second argument is value
        return wraps(validator)(_generic_validator_cls(validator, sig, set(args[1:])))
    else:
        # assume the first argument was value which has already been removed
        return wraps(validator)(_generic_validator_basic(validator, sig, set(args)))


def prep_validators(v_funcs: Iterable[AnyCallable]) -> 'ValidatorsList':
    return [make_generic_validator(f) for f in v_funcs if f]


all_kwargs = {'values', 'field', 'config'}


def _generic_validator_cls(validator: AnyCallable, sig: 'Signature', args: Set[str]) -> 'ValidatorCallable':
    # assume the first argument is value
    has_kwargs = False
    if 'kwargs' in args:
        has_kwargs = True
        args -= {'kwargs'}

    if not args.issubset(all_kwargs):
        raise ConfigError(
            f'Invalid signature for validator {validator}: {sig}, should be: '
            f'(cls, value, values, config, field), "values", "config" and "field" are all optional.'
        )

    if has_kwargs:
        return lambda cls, v, values, field, config: validator(cls, v, values=values, field=field, config=config)
    elif args == set():
        return lambda cls, v, values, field, config: validator(cls, v)
    elif args == {'values'}:
        return lambda cls, v, values, field, config: validator(cls, v, values=values)
    elif args == {'field'}:
        return lambda cls, v, values, field, config: validator(cls, v, field=field)
    elif args == {'config'}:
        return lambda cls, v, values, field, config: validator(cls, v, config=config)
    elif args == {'values', 'field'}:
        return lambda cls, v, values, field, config: validator(cls, v, values=values, field=field)
    elif args == {'values', 'config'}:
        return lambda cls, v, values, field, config: validator(cls, v, values=values, config=config)
    elif args == {'field', 'config'}:
        return lambda cls, v, values, field, config: validator(cls, v, field=field, config=config)
    else:
        # args == {'values', 'field', 'config'}
        return lambda cls, v, values, field, config: validator(cls, v, values=values, field=field, config=config)


def _generic_validator_basic(validator: AnyCallable, sig: 'Signature', args: Set[str]) -> 'ValidatorCallable':
    has_kwargs = False
    if 'kwargs' in args:
        has_kwargs = True
        args -= {'kwargs'}

    if not args.issubset(all_kwargs):
        raise ConfigError(
            f'Invalid signature for validator {validator}: {sig}, should be: '
            f'(value, values, config, field), "values", "config" and "field" are all optional.'
        )

    if has_kwargs:
        return lambda cls, v, values, field, config: validator(v, values=values, field=field, config=config)
    elif args == set():
        return lambda cls, v, values, field, config: validator(v)
    elif args == {'values'}:
        return lambda cls, v, values, field, config: validator(v, values=values)
    elif args == {'field'}:
        return lambda cls, v, values, field, config: validator(v, field=field)
    elif args == {'config'}:
        return lambda cls, v, values, field, config: validator(v, config=config)
    elif args == {'values', 'field'}:
        return lambda cls, v, values, field, config: validator(v, values=values, field=field)
    elif args == {'values', 'config'}:
        return lambda cls, v, values, field, config: validator(v, values=values, config=config)
    elif args == {'field', 'config'}:
        return lambda cls, v, values, field, config: validator(v, field=field, config=config)
    else:
        # args == {'values', 'field', 'config'}
        return lambda cls, v, values, field, config: validator(v, values=values, field=field, config=config)


def gather_all_validators(type_: 'ModelOrDc') -> Dict[str, 'AnyClassMethod']:
    all_attributes = ChainMap(*[cls.__dict__ for cls in type_.__mro__])  # type: ignore[arg-type,var-annotated]
    return {
        k: v
        for k, v in all_attributes.items()
        if hasattr(v, VALIDATOR_CONFIG_KEY) or hasattr(v, ROOT_VALIDATOR_CONFIG_KEY)
    }
