New rule request: Local variable might be referenced before assignment

[Garrett-R]

It would be awesome if Ruff could catch an error (like PyCharm does) for code like this:

def func(x: bool) -> int:
    if x:
        y = 1
    return y

[charliermarsh]

Makes sense. It's not trivial to fix because it requires supporting full branch analysis, but it would be good to catch of course.

[Garrett-R]

Yeah, seems really complicated, as does all this linter magic haha

[inoa-jboliveira]

At least pycharm and possibly other IDEs static code analysis can catch this bug. I was also hoping to also find this rule in Ruff.
I thought F823 would catch this, but it doesn't.

[clemente0731]

SAME ISSUE FOR "Local variable might be referenced before assignment"

[clemente0731]

https://github.com/google/pytype can work well for this @charliermarsh