False negative: Tuple index out of range

[goodspark]

Bug Report

Getting a false negative on tuple indices and lengths.

To Reproduce

from typing import Tuple, Union

def zxc(x: Union[Tuple[str], Tuple[str, int]]) -> None:
    if len(x) == 1:
        print(x[0])
    elif len(x) == 2:
        print(x[0], x[1])  # line 7

mypy mypytest.py

Expected Behavior

Expected mypy to pass. As far as I can tell, the types are correct.

Actual Behavior

Mypy fails with:

mypytest.py:7: error: Tuple index out of range
Found 1 error in 1 file (checked 1 source file)

Your Environment

• Mypy version used: 0.812
• Mypy command-line flags: None
• Mypy configuration options from mypy.ini (and other config files): None
• Python version used: 3.8.5
• Operating system and version: Ubuntu 20.04

[hauntsaninja]

Duplicate of #9171 , #1178 and others (also this is a false positive :-) )