F821: false negatives when a file has from __future__ import annotations

[AlexWaygood]

Ruff currently emits no F821 errors on this .py file, but the lines marked with XXX all fail at runtime due to undefined names:

from __future__ import annotations

from typing import TypeAlias, Optional, Union

MaybeCStr: TypeAlias = Optional[CStr]  # XXX
MaybeCStr2: TypeAlias = Optional["CStr"]  # always okay
CStr: TypeAlias = Union[C, str]  # XXX
CStr2: TypeAlias = Union["C", str]  # always okay

class C: ...

class Leaf: ...
class Tree(list[Tree | Leaf]): ...  # XXX
class Tree2(list["Tree | Leaf"]): ...  # always okay

Note:

• Ruff correctly emits three errors on this file when from __future__ import annotations is not included
• Ruff correctly emits no errors on this file if it's a .pyi stub file.

[AlexWaygood]

The PR fixing this was reverted in #10513