[`flake8-type-checking`] False positives/negatives for TC001-004 for overlapping module imports

[Daverball]

Description

This bug was discovered in #15719

Given something like:

from __future__ import annotations

import importlib.abc
from typing import TYPE_CHECKING

if TYPE_CHECKING:
    import importlib.machinery

class Foo(importlib.abc.MetaPathFinder):
    def bar(self) -> importlib.machinery.ModuleSpec: ...

importlib.machinery will incorrectly be flagged with TC004, since importlib.abc.MetaPathFinder binds to the same binding as importlib.machinery.ModuleSpec, so since the former is used at runtime, it thinks that importlib.machinery needs to be moved outside the TYPE_CHECKING block.

Combining the two imports into a shared binding makes sense, since what will be looked up is importlib and not importlib.machinery or importlib.abc.

This means that when we're checking the import bindings we need to expand the single importlib binding to its two import statements importlib.abc and importlib.machinery and for each reference check which of the two imports will actually be relevant.

[coredumperror]

Could this possibly be why I'm getting TC004 from the following code?

from typing import TYPE_CHECKING
from django.urls import reverse_lazy

if TYPE_CHECKING:
    from django_stubs_ext import StrOrPromise


class ApplicationTable:

    #: The URL to submit form actions to
    form_url: StrOrPromise = reverse_lazy("operations:applications--actions")

https://play.ruff.rs/d3e8ee0f-a7ba-477c-964c-d59bda9c396d

It doesn't seem to make any sense that this would be triggering TC004.

[Daverball]

No, it makes perfect sense that this would emit TC004.

It's because your target version is Python 3.9 and you're not using from __future__ import annotations, so all annotations are evaluated at runtime, so this code will fail with a NameError at runtime if you run it with Python 3.9 - 3.13, it only works like this on Python 3.14.

Overlapping imports are only a concern if you import entire submodules from the same parent package.