From bbc26b2f1101d69a1f374ca1822b337fcb8bfd4c Mon Sep 17 00:00:00 2001
From: GiGaGon <107241144+MeGaGiGaGon@users.noreply.github.com>
Date: Mon, 23 Jun 2025 06:22:36 -0700
Subject: [PATCH] [`pyupgrade`] Add fix safety section to `UP004` (#18853)

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## Summary

<!-- What's the purpose of the change? What does it do, and why? -->

Part of #15584

This adds a `Fix safety` section to [useless-object-inheritance
(UP004)](https://docs.astral.sh/ruff/rules/useless-object-inheritance/#useless-object-inheritance-up004)

I could not track down the original PR as this rule is so old it has
gone through several large ruff refactors.
No reasoning is given on the unsafety in the PR/code.
The unsafety is determined here:

https://github.com/astral-sh/ruff/blob/f24e650dfd9d20c3d01c2615da3f4778da3cf036/crates/ruff_linter/src/rules/pyupgrade/rules/useless_class_metaclass_type.rs#L76-L80

Unsafe fix demonstration:
[playground](https://play.ruff.rs/12b24eb4-d7a5-4ae0-93bb-492d64967ae3)
```py
class A(  # will be deleted
    object
):
    ...
```

## Test Plan

<!-- How was it tested? -->

N/A, no tests/functionality affected
---
 .../src/rules/pyupgrade/rules/useless_object_inheritance.rs    | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/crates/ruff_linter/src/rules/pyupgrade/rules/useless_object_inheritance.rs b/crates/ruff_linter/src/rules/pyupgrade/rules/useless_object_inheritance.rs
index 3d8e1cd766..cb1fe0152e 100644
--- a/crates/ruff_linter/src/rules/pyupgrade/rules/useless_object_inheritance.rs
+++ b/crates/ruff_linter/src/rules/pyupgrade/rules/useless_object_inheritance.rs
@@ -26,6 +26,9 @@ use crate::{AlwaysFixableViolation, Fix};
 /// class Foo: ...
 /// ```
 ///
+/// ## Fix safety
+/// This fix is unsafe if it would cause comments to be deleted.
+///
 /// ## References
 /// - [PEP 3115 – Metaclasses in Python 3000](https://peps.python.org/pep-3115/)
 #[derive(ViolationMetadata)]