pre-release v0.920 incorrectly identifies enum as final

[terencehonles]

Bug Report

Mypy incorrectly identifies an enum as final. This appears related to / caused by #11247.

To Reproduce

1. create an enum with uninitialized annotated variables and a __new__ method
2. extend the enum with the actual values for the enum

Expected Behavior

Mypy would not complain about the enum.

Actual Behavior

error: Cannot inherit from final class "TestEnum" [misc]

Your Environment

• Mypy version used: https://github.com/mypyc/mypy_mypyc-wheels/releases/tag/v0.920%2Bdev.89bb94a636790fc969979a47d8cb88e33a22c17e
• Mypy command-line flags:
• Mypy configuration options from mypy.ini (and other config files):

  [mypy]                                                                         
  allow_redefinition = true                                                      
  disable_error_code =                                                           
      override,                                                                  
      var-annotated                                                              
  mypy_path = types/                                                             
  plugins =                                                                      
      mypy_django_plugin.main                                            
      numpy.typing.mypy_plugin,                                                  
      mypy_drf_plugin.main                                                       
  pretty = true                                                                  
  show_error_codes = true                                                        
  show_error_context = true                                                      
  warn_redundant_casts = true                                                    
  warn_unused_ignores = true                                                     
  warn_unreachable = true
  

• Python version used: 3.10.0
• Operating system and version: N/A

[terencehonles]

@sobolevn not sure if checking for initialized values would be trival to follow up with on your PR, but figured I'd ask you before looking into it myself.

[sobolevn]

__new__ is not required for the repro.

This example raises:

from enum import Enum

class A(Enum):
    x: int
    y: int

class B(A):
    x = 1
    y = 2

print(B.x, B.y)  # Runtime print: B.x, B.y

Output:

out/ex.py:12: error: Cannot inherit from final class "A"
out/ex.py:13: error: Cannot override writable attribute "x" with a final one
out/ex.py:14: error: Cannot override writable attribute "y" with a final one

So, this is a bug I guess. I will try to solve this right now.

[sobolevn]

The first one is quite easy to solve. But, I am not sure what to do with the 2nd and 3rd 🤔
Ideas?

[terencehonles]

__new__ is not required for the repro.

Thanks for checking, I figured it didn't, but I wanted to make sure the example matched my particular code.

[achimnol]

I'd like to reopen this issue, as mypy 0.930 release still gives me this error when inheriting a subclass (a custom StringSetFlag) of enum.Flag to define actual flags, which works fine in runtime.

[sobolevn]

@achimnol please, open a new one with a repro example. I would be happy to fix it 🙂