`Enum.value` typed as `Any` when using `functools.cache`

[kmurphy4]

Bug Report

If I define a method with @functools.cache on an Enum, then the type of that Enum's value attr becomes Any. Without the @functools.cache annotation, it gets typed correctly.

Also, this behavior does not occur if you use enum literals - i.e., Foo.BAR.value is typed correctly, but foo.value (for a foo: Foo) is wrong.

To Reproduce

https://mypy-play.net/?mypy=latest&python=3.12&gist=b2a218b8db8367b2ac62dcf583a8c4f7

Expected Behavior

The type assertion in frobnicate() should succeed.

Actual Behavior

The type assertion in frobnicate() fails 😿.

[sterliakov]

This is a deficiency in enum plugin. As a workaround you can be slightly more explicit and help mypy by marking that method as @nonmember (3.11+):

import enum
import functools
import typing as t


class Color(enum.Enum):
    RED = enum.auto()
    
    @enum.nonmember
    @functools.cache
    def lowercase_name(self) -> str:
        return self.name.lower()


t.assert_type(Color.RED.value, int)  # works


def frobnicate(color: Color) -> None:
    t.assert_type(color.value, int)

https://mypy-play.net/?mypy=latest&python=3.12&gist=eaf416f505bfebbba0c2f9c5c85fa93a

mypy/mypy/plugins/enums.py

Lines 186 to 202 in 7982761

	stnodes = (info.get(name) for name in info.names)
	# Enums _can_ have methods, instance attributes, and `nonmember`s.
	# Omit methods and attributes created by assigning to self.*
	# for our value inference.
	node_types = (
	get_proper_type(n.type) if n else None
	for n in stnodes
	if n is None or not n.implicit
	)
	proper_types = [
	_infer_value_type_with_auto_fallback(ctx, t)
	for t in node_types
	if t is None
	or (not isinstance(t, CallableType) and not is_named_instance(t, "enum.nonmember"))
	]