Faulty type inference for Enum attributes

Bug Report

Accessing an instance of an enum though another instance leads to the wrong type being inferred for the instance.

To Reproduce

See: https://mypy-play.net/?mypy=master&python=3.12&flags=disallow-any-unimported&gist=26f57e606e831442885c45110b8d8650

import enum

class Color(enum.Enum):
    RED = "RED"
    GREEN = "GREEN"
    BLUE = "BLUE"

c = Color.RED

# error: Incompatible types in assignment (expression has type "str", variable has type "Color")  [assignment]
c = c.GREEN

Expected Behavior

I expect mypy to understand that c.GREEN is also of type Color.

Actual Behavior

Mypy thinks c.GREEN is of type str.

main.py:11: error: Incompatible types in assignment (expression has type "str", variable has type "Color")  [assignment]
Found 1 error in 1 file (checked 1 source file)

Your Environment

Mypy version used: master (post 1.3.0 at time of writing)
Mypy command-line flags: n/a
Mypy configuration options from mypy.ini (and other config files): n/a
Python version used: 3.12

This is affecting me as well, but triggering a "Statement is unreachable" error when warn_unreachable = True is in my mypy.ini. Consider the following (using the previous color enum):

import enum

class Color(enum.Enum):
    RED = "RED"
    GREEN = "GREEN"
    BLUE = "BLUE"

def test(c:Color) -> str:
    if c == c.RED:
        return "it's red"
    if c == c.GREEN:
        return "it's green"
    if c == c.BLUE:
        return "it's blue"

    return "unknown color"

MyPy 1.3.0 doesn't complain about this code, but MyPy 1.4.0 gives "Statement is unreachable" errors for each of the three conditional returns.

Support attribute access on enum members correctly (python#19422)

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Faulty type inference for `Enum` attributes #15454

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Faulty type inference for Enum attributes #15454

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blbelew commented on Jun 26, 2023

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Faulty type inference for `Enum` attributes #15454