Pattern matching is not exhaustive in a weird edge case with an enum member subject

[injust]

Bug Report

1. Access an enum member by name, but the name cannot be inline (e.g. you can access it from a variable)
2. Directly use the enum member as the subject in a match statement

If you do this, mypy does not think the match statement is exhaustive.

To Reproduce

https://mypy-play.net/?mypy=latest&python=3.13&flags=strict&gist=0d11136907ace743b0f2412ad0f26bb1

from enum import Enum, auto
from typing import reveal_type


class Thing(Enum):
    ONE = auto()
    TWO = auto()


two = "TWO"


def good() -> int:
    version = Thing[two]
    match version:
        case Thing.ONE:
            return 1
        case Thing.TWO:
            return 2


def bad() -> int:
    match Thing[two]:
        case Thing.ONE:
            return 1
        case Thing.TWO:
            return 2
        case _ as thing:
            reveal_type(thing)

If you replace Thing[two] with Thing["TWO"], the problem also goes away.

Expected Behavior

Both match statements are exhaustive, so there is a return statement for all cases.

Actual Behavior

main.py:22: error: Missing return statement  [return]
main.py:29: note: Revealed type is "__main__.Thing"
Found 1 error in 1 file (checked 1 source file)

Your Environment

• Mypy version used: 1.15.0
• Mypy command-line flags: --strict
• Python version used: 3.13

[sterliakov]

Given that your good version works, is it the same as #18440? Currently we do not narrow types of complex expressions in match statement other than function calls.

[injust]

Given that your good version works, is it the same as #18440? Currently we do not narrow types of complex expressions in match statement other than function calls.

Yes, it seems like the same issue. In the repro for #18440, if you change the function b from

match d[k]:

to

foo = d[k]
match foo:

Then it type checks. This is the same behaviour that I'm seeing here.