From 14c42a8ddf377c8c79e43970a87b80af01258b5a Mon Sep 17 00:00:00 2001
From: Robsdedude <dev@rouvenbauer.de>
Date: Tue, 3 Jun 2025 00:51:09 +0000
Subject: [PATCH] [`refurb`] Mark `FURB180` fix unsafe when class has bases
 (#18149)

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## Summary

Mark `FURB180`'s fix as unsafe if the class already has base classes.
This is because the base classes might validate the other base classes
(like `typing.Protocol` does) or otherwise alter runtime behavior if
more base classes are added.

## Test Plan

The existing snapshot test covers this case already.

## References

Partially addresses https://github.com/astral-sh/ruff/issues/13307 (left
out way to permit certain exceptions)

---------

Co-authored-by: Brent Westbrook <36778786+ntBre@users.noreply.github.com>
Co-authored-by: Brent Westbrook <brentrwestbrook@gmail.com>
---
 .../src/rules/refurb/rules/metaclass_abcmeta.rs | 17 +++++++++++++++--
 ...ules__refurb__tests__FURB180_FURB180.py.snap |  4 ++--
 2 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/crates/ruff_linter/src/rules/refurb/rules/metaclass_abcmeta.rs b/crates/ruff_linter/src/rules/refurb/rules/metaclass_abcmeta.rs
index e079bd93d8..96016b0351 100644
--- a/crates/ruff_linter/src/rules/refurb/rules/metaclass_abcmeta.rs
+++ b/crates/ruff_linter/src/rules/refurb/rules/metaclass_abcmeta.rs
@@ -1,5 +1,6 @@
 use itertools::Itertools;
 
+use ruff_diagnostics::Applicability;
 use ruff_macros::{ViolationMetadata, derive_message_formats};
 use ruff_python_ast::StmtClassDef;
 use ruff_text_size::{Ranged, TextRange};
@@ -31,6 +32,11 @@ use crate::{AlwaysFixableViolation, Edit, Fix};
 ///     pass
 /// ```
 ///
+/// ## Fix safety
+/// The rule's fix is unsafe if the class has base classes. This is because the base classes might
+/// be validating the class's other base classes (e.g., `typing.Protocol` does this) or otherwise
+/// alter runtime behavior if more base classes are added.
+///
 /// ## References
 /// - [Python documentation: `abc.ABC`](https://docs.python.org/3/library/abc.html#abc.ABC)
 /// - [Python documentation: `abc.ABCMeta`](https://docs.python.org/3/library/abc.html#abc.ABCMeta)
@@ -69,6 +75,11 @@ pub(crate) fn metaclass_abcmeta(checker: &Checker, class_def: &StmtClassDef) {
         return;
     }
 
+    let applicability = if class_def.bases().is_empty() {
+        Applicability::Safe
+    } else {
+        Applicability::Unsafe
+    };
     let mut diagnostic = checker.report_diagnostic(MetaClassABCMeta, keyword.range);
 
     diagnostic.try_set_fix(|| {
@@ -80,7 +91,7 @@ pub(crate) fn metaclass_abcmeta(checker: &Checker, class_def: &StmtClassDef) {
         Ok(if position > 0 {
             // When the `abc.ABCMeta` is not the first keyword, put `abc.ABC` before the first
             // keyword.
-            Fix::safe_edits(
+            Fix::applicable_edits(
                 // Delete from the previous argument, to the end of the `metaclass` argument.
                 Edit::range_deletion(TextRange::new(
                     class_def.keywords()[position - 1].end(),
@@ -91,11 +102,13 @@ pub(crate) fn metaclass_abcmeta(checker: &Checker, class_def: &StmtClassDef) {
                     Edit::insertion(format!("{binding}, "), class_def.keywords()[0].start()),
                     import_edit,
                 ],
+                applicability,
             )
         } else {
-            Fix::safe_edits(
+            Fix::applicable_edits(
                 Edit::range_replacement(binding, keyword.range),
                 [import_edit],
+                applicability,
             )
         })
     });
diff --git a/crates/ruff_linter/src/rules/refurb/snapshots/ruff_linter__rules__refurb__tests__FURB180_FURB180.py.snap b/crates/ruff_linter/src/rules/refurb/snapshots/ruff_linter__rules__refurb__tests__FURB180_FURB180.py.snap
index 45df8c8e53..d351d92f93 100644
--- a/crates/ruff_linter/src/rules/refurb/snapshots/ruff_linter__rules__refurb__tests__FURB180_FURB180.py.snap
+++ b/crates/ruff_linter/src/rules/refurb/snapshots/ruff_linter__rules__refurb__tests__FURB180_FURB180.py.snap
@@ -50,7 +50,7 @@ FURB180.py:26:18: FURB180 [*] Use of `metaclass=abc.ABCMeta` to define abstract
    |
    = help: Replace with `abc.ABC`
 
-ℹ Safe fix
+ℹ Unsafe fix
 23 23 |     pass
 24 24 | 
 25 25 | 
@@ -68,7 +68,7 @@ FURB180.py:31:34: FURB180 [*] Use of `metaclass=abc.ABCMeta` to define abstract
    |
    = help: Replace with `abc.ABC`
 
-ℹ Safe fix
+ℹ Unsafe fix
 28 28 |     def foo(self): pass
 29 29 | 
 30 30 |