Extend TYPE_CHECKING handling to classes and assignments

[bersbersbers]

Things to check first

• I have searched the existing issues and didn't find my bug already reported there

• I have checked that my bug is still present in the latest release

Typeguard version

4.2.1

Python version

3.12.3

What happened?

typechecked code tries to use a class that is hidden behind TYPE_CHECKING and should not be required at runtime.

How can we reproduce the bug?

bug.py

# python bug.py && mypy bug.py && pyright bug.py

from __future__ import annotations

from typing import TYPE_CHECKING, TypedDict

# from typeguard import typechecked

if TYPE_CHECKING:

    class Args(TypedDict):
        x: int
        y: int

# @typechecked
def bug() -> None:
    args: Args = {"x": 1, "y": 1}
    print(args)

bug()

python bug.py && mypy bug.py && pyright bug.py

{'x': 1, 'y': 1}
Success: no issues found in 1 source file
0 errors, 0 warnings, 0 informations 

Now add the @typechecked decorator, and run python bug.py again:

Traceback (most recent call last):
  File "C:\Code\project\bug.py", line 22, in <module>
    bug()
  File "C:\Code\project\bug.py", line 18, in bug
    args: Args = {"x": 1, "y": 1}
          ^^^^
NameError: name 'Args' is not defined. Did you mean: 'args'?

One workaround is to add bug2.py:

from typing import TypedDict

class Args(TypedDict):
    x: int
    y: int

and modify bug.py to

# python bug.py && mypy bug.py && pyright bug.py

from __future__ import annotations

from typing import TYPE_CHECKING

from typeguard import typechecked

if TYPE_CHECKING:
    from bug2 import Args

@typechecked
def bug() -> None:
    args: Args = {"x": 1, "y": 1}
    print(args)

bug()

But that feels kind of unnecessary, I think.