[`pyupgrade`] Avoid reporting `__future__` features as unnecessary when they are used (`UP010`) (#19769)
## Summary
Resolves #19561
Fixes the [unnecessary-future-import
(UP010)](https://docs.astral.sh/ruff/rules/unnecessary-future-import/)
rule to correctly identify when imported __future__ modules are actually
used in the code, preventing false positives.
I assume there is no way to check usage in `analyze::statements`,
because we don't have any usage bindings for imports. To determine
unused imports, we have to fully scan the file to create bindings and
then check usage, similar to [unused-import
(F401)](https://docs.astral.sh/ruff/rules/unused-import/#unused-import-f401).
So, `Rule::UnnecessaryFutureImport` was moved from the
`analyze::statements` to the `analyze::deferred_scopes` stage. This
caused the need to change the logic of future import handling to a
bindings-based approach.
Also, the diagnostic report was changed.
Before
```
|
1 | from __future__ import nested_scopes, generators
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ UP010
```
after
```
|
1 | from __future__ import nested_scopes, generators
| ^^^^^^^^^^^^^ UP010
```
I believe this is the correct way, because `generators` may be used, but
`nested_scopes` is not.
### Special case
I've found out about some specific case.
```python
from __future__ import nested_scopes
nested_scopes = 1
```
Here we can treat `nested_scopes` as an unused import because the
variable `nested_scopes` shadows it and we can safely remove the future
import (my fix does it).
But
[F401](https://docs.astral.sh/ruff/rules/unused-import/#unused-import-f401)
not triggered for such case
([sandbox](https://play.ruff.rs/296d9c7e-0f02-4659-b0c0-78cc21f3de76))
```
from foo import print_function
print_function = 1
```
In my mind, `print_function` here is an unused import and should be
deleted (my IDE highlight it). What do you think?
## Test Plan
Added test cases and snapshots:
- Split test file into separate _0 and _1 files for appropriate checks.
- Added test cases to verify fixes when future module are used.
---------
Co-authored-by: Igor Drokin <drokinii1017@gmail.com>
ruff
7b75aee2 - [`pyupgrade`] Avoid reporting `__future__` features as unnecessary when they are used (`UP010`) (#19769)
