Currently the TCH (flake8-type-checking) rules require annotations to be stored as strings (i.e. not evaluated). Annotations are stored a strings if:

• The annotations are string literals (i.e. are quoted)
• The annotations are in a module with from __future__ import annotations (which causes evaluation of all annotations in the module to be skipped)
• The annotations are of local variables (the Python interpreter does not evaluate local variable annotations)

One approach to getting TCH autofix working is to inject from __future__ import annotations into all your source modules (using I002). This is not ideal because string annotations unavoidably break code that meets these conditions:

1. annotations are being created in a local scope
2. an annotation references a symbol only available in that local scope
3. the annotation must be operated on at runtime

Here is an example of code meeting these conditions:

def make_bar():
    class Bar:
        ...

    def bar(x: "Bar"):
        ...
    return bar

bar = make_bar()

# `bar` has a string annotation-- if we want to operate on it, we need to evaluate it. This requires
# calling `get_type_hints`, but this fails because "Bar" can't be dereferenced since referent `Bar`
# vanished with local scope
get_type_hints(bar)  # => NameError: name 'Bar' is not defined.

We have plenty of code meeting these conditions in Dagster (mostly in tests), so my experiment in injecting from __future__ import annotations to enable TCH autofix has failed. Other projects that use runtime type annotation introspection are likely to encounter the same issues.

Therefore, a significant enhancement to TCH autofix would be to detect where annotations could be stored as strings, and perform a targeted conversion for you using quoting. Example:

from threading import Lock

def foo(lock: Lock):
    ...

After applying TCH autofix:

from typing import TYPE_CHECKING

if TYPE_CHECKING:
    from threading import Lock

def foo(lock: "Lock"):
    ...

This would make TCH autofix a lot more useful for us and probably many other projects.