New Enum validation doesn't work for custom __new__ methods

[aikow]

Initial Checks

• I confirm that I'm using Pydantic V2

Description

The newly release improvements to the Enum class break enums with a custom __new__ implementation.

I don't think this is an official intended use case of the Enum class, so I don't have an issue with this if this doesn't get fixed.

A super easy work-around is to use a PlainValidator to just call the constructor in python, not rust.

print(
    TypeAdapter(Annotated[Animal, PlainValidator(lambda s: Animal(s))]).validate_python(
        "meow"
    )
)

Example Code

from enum import Enum
from pydantic import TypeAdapter


class Animal(Enum):
    CAT = "cat", "meow"
    DOG = "dog", "woof"

    def __new__(cls, species: str, sound: str):
        obj = object.__new__(cls)

        obj._value_ = species
        obj._all_values = (species, sound)

        obj.species = species
        obj.sound = sound

        cls._value2member_map_[sound] = obj

        return obj


print(Animal("cat"))
print(Animal("meow"))
print(TypeAdapter(Animal).validate_python("meow"))

Python, Pydantic & OS Version

pydantic version: 2.7.0
        pydantic-core version: 2.18.1
          pydantic-core build: profile=release pgo=false
                 install path: /Users/aikow/.miniconda3/envs/py310-pydantic/lib/python3.10/site-packages/pydantic
               python version: 3.10.14 | packaged by conda-forge | (main, Mar 20 2024, 12:53:34) [Clang 16.0.6 ]
                     platform: macOS-14.4.1-x86_64-i386-64bit
             related packages: typing_extensions-4.11.0
                       commit: unknown

[samuelcolvin]

Makes sense, happy to accept a pr to pydantic-core to detect custom __new__ methods and call them if that's possible.

Btw, we already support the __missing__ if that helps?