`in` operator error with Generator

[grayjk]

Bug Report
https://mypy-play.net/?mypy=latest&python=3.12&gist=790ec23819f191c250a9574f2b123d8d

To Reproduce

1 in (i for i in (signal.SIGINT,))

Expected Behavior
No error

Actual Behavior
error: Unsupported operand types for in ("int" and "Generator[Signals, None, None]") [operator]

If the generator is changed to a list comprehension, there is no error

Your Environment

• Mypy version used: 2.1.0 and master branch
• Python version used: 3.12

[beanscg]

I checked the current membership-checking path. in comparisons are handled in visit_comparison_expr: for operator in, mypy gathers iterable item types and reports unsupported_operand_types("in", left_type, right_type) if the left type is not a subtype of the synthesized item union (mypy/checkexpr.py:3710-3806). mypy/operators.py:29 maps in to __contains__ for the normal operator path.

The repro is interesting because the generator expression over signal.SIGINT should expose item type Signals, and Signals is int-compatible at runtime. A focused regression can compare:

• 1 in (i for i in (signal.SIGINT,))
• 1 in [i for i in (signal.SIGINT,)]

and assert the generator path derives the same membership item compatibility as the list-comprehension path rather than treating the generator container itself as unsupported.