stubgen does not handle TypeAlias

[jpl-dhemberg]

Bug Report

When running stubgen on a file that uses TypeAlias, the stubbed type of the type alias is TypeAlias. This prevents the actual aliased type from being recorded in the stub file, and causes mypy to emit a [valid-type] error.

To Reproduce

Create a file tmp.py:

from typing import TypeAlias

Foo: TypeAlias = tuple[int, str]

Then run stubgen tmp.py.

Expected Behavior

I'm not exactly sure what the expected behavior is. I guess maybe it should behave similarly to Foo = tuple[int, str] (i.e. without the TypeAlias typehint), which stubgen includes verbatim in the stub file.

Actual Behavior

The stubbed type was only TypeAlias

$ cat out/tmp.pyi 
from typing import TypeAlias

Foo: TypeAlias

Then if this stub is used, mypy emits the following error:

Invalid type alias: expression is not a valid type  [valid-type]
Foo: TypeAlias
^

Your Environment

• Mypy version used: 1.15.0
• Mypy command-line flags: n/a
• Mypy configuration options from mypy.ini (and other config files): n/a
• Python version used: 3.10

[makridenko]

Hi! Can I work on this?

[sobolevn]

@makridenko sure, please go ahead!