Exhaustiveness checking false positives when using `match self` or `match self.value` inside an Enum

[rouge8]

Bug Report

When using match self or match self.value inside a method or property on an Enum, mypy reports an error on assert_never(). This works as expected in pyright.

To Reproduce

https://mypy-play.net/?mypy=latest&python=3.11&gist=6f0acfbf4f32fd48e7d6284b15368919

Actual Behavior

main.py:17: error: Argument 1 to "assert_never" has incompatible type "MyEnum"; expected "NoReturn"  [arg-type]
main.py:27: error: Argument 1 to "assert_never" has incompatible type "Union[str, str]"; expected "NoReturn"  [arg-type]
Found 2 errors in 1 file (checked 1 source file)

Your Environment

• Mypy version used: mypy 1.2.0 (compiled: yes)
• Mypy command-line flags: --show-error-codes
• Mypy configuration options from mypy.ini (and other config files): n/a
• Python version used: Python 3.11.1

[frou]

In the first method, it seems to be case self.a / case self.b that Mypy is choking on, not match self. Because it works when changing them to case MyEnum.a / case MyEnum.b

[frou]

Possibly related issue: #12107

[MestreLion]

Most likely a duplicate of #10910