Fix handling of typing.Optional in stubgen

[WesleyTheGeolien]

When running stubgen on my local repository I noticed a couple of errors occurring notably around the handling of typing.Union / typing.Optional when --inspect-mode was being used.

I am running Python 3.10.14 on Linux.

I put together a mre:

from typing import Optional

def func0(left: int, right: Optional[int]) -> int:
    """Add 2 numbers together"""
    if right:
        return left + right
    return left

def func1(left: int, right: Optional[int] = None) -> int:
    """Add 2 numbers together"""
    if right:
        return left + right
    return left

I put this in mre.py then ran:

stubgen ./mre.py --include-docstrings --inspect-mode

I would get:

TypeError: compile() arg 1 must be a string, bytes or AST object

calling get_annotations(arg) fixed this as the object being passed through was <class 'int'> and not the string version

return f"{t.args[0].accept(self)} | None"
IndexError: tuple index out of range

this was because Optional[int] was becoming typing.Optional and not typing.Optional[int] I updated handling to pass the [int] through (this may be incorrect though)

[WesleyTheGeolien]

I am sorry in advance, I have not created any tests as I am unsure how your test suite is setup.

[hamdanal]

Thank you for working on this.
Stubgen tests are in this file https://github.com/python/mypy/blob/master/test-data/unit/stubgen.test. You can look at existing test cases for inspiration. You can test stubgen in --inspect-mode by including # flags: --inspect-mode as the first line of the test case.

[hamdanal]

Is this related to the issue with Optional? I think this change (and the one below) are causing the CI failure.