Stubgen applies Generator type to function with nested generator

[ska-kialo]

Bug Report

When stubgen encounters a function with a nested generator-function, that generator type is used for the return type of the function, even if the function itself does not return a generator.

To Reproduce

1. Create a file generator.py:

   def some_function():
       def generator():
           yield "a"
   
       return 5

2. Run stubgen generator.py.

Expected Behavior
The function in the generated type stub has a "regular" return type.

from collections.abc import Generator
from typing import Any

def some_function() -> Any: ...  # or int

Actual Behavior
The stub function has a Generator[None, None, Any] type.

from collections.abc import Generator
from typing import Any

def some_function() -> Generator[None, None, Any]: ...

Your Environment

• Mypy version used: 0.930
• Mypy command-line flags: stubgen generator.py
• Mypy configuration options from mypy.ini (and other config files): -
• Python version used: 3.9.9
• Operating system and version: macOS 12.1