Enum types are incorrectly inferred

[ivany4]

Bug Report

mypy does not infer enum values correctly. E.g. It would be reasonable to expect that IntEnum subclasses have their raw values as ints. Instead, mypy detects it as a literal of whatever it sees. This is especially a problem for *.pyi stubs, where options are assigned ellipsis.

In addition, Python documentation allows specifying special _value_ attribute, that type-checkers should use to infer the raw value type. E.g. they even have a snippet:

class ColumnType(Enum):
    _value_: int
    DORIC = ...
    IONIC = ...
    CORINTHIAN = ...

reveal_type(ColumnType.DORIC.value)  # Revealed type is int (or object or Any)

To Reproduce

import enum
import typing

class Simple(enum.IntEnum):
    OPTION = ...

class WithValue(enum.IntEnum):
    _value_: int
    OPTION = ...

class WithDirectValue(enum.IntEnum):
    _value_: int
    OPTION = 2

class NonInt(enum.Enum):
    _value_: str
    OPTION = "str"

typing.reveal_type(Simple.OPTION)
typing.reveal_type(Simple.OPTION.value)
typing.reveal_type(WithValue.OPTION)
typing.reveal_type(WithValue.OPTION.value)
typing.reveal_type(WithDirectValue.OPTION)
typing.reveal_type(WithDirectValue.OPTION.value)
typing.reveal_type(NonInt.OPTION)
typing.reveal_type(NonInt.OPTION.value)

GIST: https://gist.github.com/mypy-play/18540009e25f31525cd1b872ca2a252c

Expected Behavior

The output is:

note: Revealed type is "Literal[Simple.OPTION]?"
note: Revealed type is "int"
note: Revealed type is "Literal[WithValue.OPTION]?"
note: Revealed type is "int"
note: Revealed type is "Literal[WithDirectValue.OPTION]?"
note: Revealed type is "int"
note: Revealed type is "Literal[NonInt.OPTION]?"
note: Revealed type is "str"

Actual Behavior

The output is:

note: Revealed type is "Literal[Simple.OPTION]?"
note: Revealed type is "types.EllipsisType"
note: Revealed type is "Literal[WithValue.OPTION]?"
note: Revealed type is "types.EllipsisType"
note: Revealed type is "Literal[WithDirectValue.OPTION]?"
note: Revealed type is "Literal[2]?"
note: Revealed type is "Literal[NonInt.OPTION]?"
note: Revealed type is "Literal['str']?"

Your Environment

• Mypy version used: 1.16.1
• Mypy command-line flags: mypy file.py
• Python version used: 3.11.11 (but Gist is also at Python 3.12)

[sterliakov]

WithDirectValue.OPTION and NonInt.OPTION should both still be inferred as literals, only omitted attributes (as ellipsis) should fall back to _value_ type. From spec:

If the literal values for enum members are not supplied, as they sometimes are not within a type stub file, a type checker can use the type of the value attribute:

It shouldn't override regular literal inference unless it's impossible.