Incorrect type of enum in "if" clause

[dimastbk]

Bug Report

mypy incorrectly calculates the type of emun if its value is checked with tuple().__contains__ in "if" clause.

To Reproduce

https://gist.github.com/mypy-play/e316d3d5b495cb113cacc9c55136dea7

Expected Behavior

main.py:10: note: Revealed type is "Literal[__main__.Op.A]"
main.py:13: note: Revealed type is "Literal[__main__.Op.B]"

Actual Behavior

main.py:10: note: Revealed type is "__main__.Op"
main.py:13: note: Revealed type is "Literal[__main__.Op.B]"
main.py:16: error: Argument 1 to "assert_never" has incompatible type "Literal[Op.A]"; expected "Never"  [arg-type]

Pyright works fine with it - https://pyright-play.net/?code=JYWwDg9gTgLgBAUwHYFcQChSVnGBPMYJAc3XQGMAbAQwGda4B5MACmTQDoBRVEASgBc6OCLgBBOAF44AImozhogEJTZAIwXoAJggBmcKCiQsIYAUzCDFI4PtNwicFsw5iANFdFfcBIsQ5QCABuCNSUAPr4YAgmltbegTAoUEjxCJS2cPaS0i5KQt6iUX4BwaERUTGmfPFeicmpXum0CAWFPoQkHHQtsOFIZVCxNUA.

Your Environment

• Mypy version used: 1.18.2
• Mypy command-line flags:
• Mypy configuration options from mypy.ini (and other config files):
• Python version used: 3.12

[sherlock2215]

Heyy, @dimastbk can I be assigned to this issue?
I'm ready to set up the development environment and start investigating the type narrowing logic.

[A5rocks]

Feel free to try, no assignment necessary.