Allow Annotated to wrap Final and ClassVar

[GBeauregard]

Bug Report

The behavior of Annotated has been changed so that it is allowed at runtime to wrap ClassVar and Final. This change helps avoid friction with other users of annotations; see https://bugs.python.org/issue46491 for context. This change has landed in 3.11 and has been backported to 3.9, 3.10, and typing_extensions. mypy should follow suit in allowing the wrapping in order to allow the friction lifting to happen in practice.

To Reproduce

from typing import Annotated, ClassVar, Final

class C:
    classvar: Annotated[ClassVar[int], (2, 5)] = 4
    const: Annotated[Final[int], "metadata"] = 4

Expected Behavior

The above code should type check.

Actual Behavior

antest/antest.py:4: error: Invalid type: ClassVar nested inside other type
antest/antest.py:5: error: Final can be only used as an outermost qualifier in a variable annotation
Found 2 errors in 1 file (checked 1 source file)

Your Environment

• Mypy version used: 0.931
• Mypy command-line flags: none
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: 3.9.9
• Operating system and version: Gentoo Linux stable

Additional Context
Corresponding issue for dataclasses (incl InitVar) is at https://bugs.python.org/issue46511
pyright changed at microsoft/pyright@8ce7fa6
pytype issue at google/pytype#1110
pyre issue at facebook/pyre-check#577

[hmc-cs-mdrissi]

I'd like to take this task. I'm pretty happy my comment led to this change so I'm happy to cover the pr. I'll try to do it this weekend.

[JWCS]

@hmc-cs-mdrissi Is this resolved now with #116069?

[hmc-cs-mdrissi]

No. That is related (but little different) python typing runtime change, while this issue is for type checker change. I'd forgotten about this mypy issue.