From 1e4377c9c63c1fc52f9fd1c7240c607e430c8784 Mon Sep 17 00:00:00 2001
From: Vasco Schiavo <115561717+VascoSch92@users.noreply.github.com>
Date: Wed, 14 May 2025 17:07:11 +0200
Subject: [PATCH] [`ruff`] add fix safety section (`RUF007`) (#17755)

The PR add the `fix safety` section for rule `RUF007` (#15584 )

It seems that the fix was always marked as unsafe #14401

## Unsafety example

This first example is a little extreme. In fact, the class `Foo`
overrides the `__getitem__` method but in a very special, way. The
difference lies in the fact that `zip(letters, letters[1:])` call the
slice `letters[1:]` which is behaving weird in this case, while
`itertools.pairwise(letters)` call just `__getitem__(0), __getitem__(1),
...` and so on.

Note that the diagnostic is emitted: [playground](https://play.ruff.rs)

I don't know if we want to mention this problem, as there is a subtile
bug in the python implementation of `Foo` which make the rule unsafe.

```python
from dataclasses import dataclass
import itertools

@dataclass
class Foo:
    letters: str

    def __getitem__(self, index):
        return self.letters[index] + "_foo"


letters = Foo("ABCD")
zip_ = zip(letters, letters[1:])
for a, b in zip_:
    print(a, b) # A_foo B, B_foo C, C_foo D, D_foo _

pair = itertools.pairwise(letters)
for a, b in pair:
    print(a, b) # A_foo B_foo, B_foo C_foo, C_foo D_foo
```

This other example is much probable.
here, `itertools.pairwise` was shadowed by a costume function
[(playground)](https://play.ruff.rs)

```python
from dataclasses import dataclass
from itertools import pairwise

def pairwise(a):
    return []

letters = "ABCD"
zip_ = zip(letters, letters[1:])
print([(a, b) for a, b in zip_]) # [('A', 'B'), ('B', 'C'), ('C', 'D')]

pair = pairwise(letters)
print(pair) # []
```
---
 .../src/rules/ruff/rules/zip_instead_of_pairwise.rs       | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/crates/ruff_linter/src/rules/ruff/rules/zip_instead_of_pairwise.rs b/crates/ruff_linter/src/rules/ruff/rules/zip_instead_of_pairwise.rs
index 9a473eb32b..286560187a 100644
--- a/crates/ruff_linter/src/rules/ruff/rules/zip_instead_of_pairwise.rs
+++ b/crates/ruff_linter/src/rules/ruff/rules/zip_instead_of_pairwise.rs
@@ -29,6 +29,14 @@ use crate::{checkers::ast::Checker, importer::ImportRequest};
 /// pairwise(letters)  # ("A", "B"), ("B", "C"), ("C", "D")
 /// ```
 ///
+/// ## Fix safety
+///
+/// The fix is always marked unsafe because it assumes that slicing an object
+/// (e.g., `obj[1:]`) produces a value with the same type and iteration behavior
+/// as the original object, which is not guaranteed for user-defined types that
+/// override `__getitem__` without properly handling slices. Moreover, the fix
+/// could delete comments.
+///
 /// ## References
 /// - [Python documentation: `itertools.pairwise`](https://docs.python.org/3/library/itertools.html#itertools.pairwise)
 #[derive(ViolationMetadata)]