False positive: `Protocol member cannot be final` in non-instance assignment in a method

[bzoracler]

Bug Report, reproduction, & actual behaviour

See mypy Playground:

import typing as t

class A(t.Protocol):
    def method(self) -> None:
        var: t.Final = 0  # mypy: Protocol member cannot be final  [misc]

Expected Behavior

No issues

Your Environment

• Mypy version used: 1.10
• Mypy command-line flags: None
• Mypy configuration options from mypy.ini (and other config files): None
• Python version used: 3.10, 3.12

[GiorgosPapoutsakis]

From my understanding, this behavior is a feature and not a bug. It is hard-coded and tested to ensure that protocol members cannot be marked as Final. Therefore, the expected behavior is correctly reported by mypy. Although this functionality can be restrictive in some use cases and maybe is worth considering a change. Should I try to make this modification?

[bzoracler]

This is a bug because var here is just a variable in the local function scope, not a protocol member. A protocol member would look like self.var inside the body of an instance method, or just var directly in the class body (not inside a method).

[GiorgosPapoutsakis]

Thank you for the clarification