mypy does not support PEP 613 -- Explicit Type Aliases (python 3.10)

[rvaquerizor]

Bug Report

mypy does not support PEP 613 -- Explicit Type Aliases (python 3.10)

To Reproduce

1. Include an explicit type alias in your code, like the following:

TEMP: TypeAlias = tuple[str, str]
2. execute mypy on that file, and it will complain with the message pasted below.

Expected Behavior

Explicit Type aliases should be supported by mypy if python 3.10+ is used.

Actual Behavior

When I execute mypy on my file containing an explicit type alias, I get:

❯ mypy my_file.py
my_file.py:10: error: Variable "typing.TypeAlias" is not valid as a type
my_file.py:10: note: See https://mypy.readthedocs.io/en/latest/common_issues.html#variables-vs-type-aliases
my_file.py:10: error: Type application has too many types (1 expected)

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: 3.10
• Operating system and version: Ubuntu, 5.11.0-37-generic Refactor code into packages #41-Ubuntu SMP x86_64 x86_64 x86_64 GNU/Linux

[JelleZijlstra]

Already tracked in #9404.