[flake8-bugbear] Ignore non-NFKC attribute names in B009 and B010 (B009, B010)

crates/ruff_linter/resources/test/fixtures/flake8_bugbear/B009_B010.py

@@ -70,3 +70,12 @@
 
 # Regression test for: https://github.com/astral-sh/ruff/issues/18353
 setattr(foo, "__debug__", 0)
+
+# Regression test for: https://github.com/astral-sh/ruff/issues/21126
+# Non-NFKC attribute names should be ignored. Python normalizes identifiers in
+# attribute access (obj.attr) using NFKC, but does not normalize string
+# arguments passed to getattr/setattr. Rewriting `getattr(ns, "ſ")` to
+# `ns.ſ` would be interpreted as `ns.s` at runtime, changing behavior.
+# Example: the long s character "ſ" normalizes to "s" under NFKC.
+getattr(foo, "ſ")
+setattr(foo, "ſ", 1)

crates/ruff_linter/src/rules/flake8_bugbear/rules/getattr_with_constant.rs

@@ -3,6 +3,7 @@ use ruff_python_ast::{self as ast, Expr};
 use ruff_python_stdlib::identifiers::{is_identifier, is_mangled_private};
 use ruff_source_file::LineRanges;
 use ruff_text_size::Ranged;
+use unicode_normalization::UnicodeNormalization;
 
 use crate::checkers::ast::Checker;
 use crate::fix::edits::pad;
@@ -69,6 +70,14 @@ pub(crate) fn getattr_with_constant(checker: &Checker, expr: &Expr, func: &Expr,
         return;
     }
 
+    // Ignore non-NFKC attribute names. Python normalizes identifiers using NFKC, so using
+    // attribute syntax (e.g., `obj.attr`) would normalize the name and potentially change
+    // program behavior.
+    let attr_name = value.to_str();
+    if attr_name.nfkc().collect::<String>() != attr_name {
+        return;
+    }
+
     let mut diagnostic = checker.report_diagnostic(GetAttrWithConstant, expr.range());
     diagnostic.set_fix(Fix::safe_edit(Edit::range_replacement(
         pad(

crates/ruff_linter/src/rules/flake8_bugbear/rules/setattr_with_constant.rs

@@ -4,6 +4,7 @@ use ruff_text_size::{Ranged, TextRange};
 use ruff_macros::{ViolationMetadata, derive_message_formats};
 use ruff_python_codegen::Generator;
 use ruff_python_stdlib::identifiers::{is_identifier, is_mangled_private};
+use unicode_normalization::UnicodeNormalization;
 
 use crate::checkers::ast::Checker;
 use crate::{AlwaysFixableViolation, Edit, Fix};
@@ -89,6 +90,14 @@ pub(crate) fn setattr_with_constant(checker: &Checker, expr: &Expr, func: &Expr,
         return;
     }
 
+    // Ignore non-NFKC attribute names. Python normalizes identifiers using NFKC, so using
+    // attribute syntax (e.g., `obj.attr = value`) would normalize the name and potentially change
+    // program behavior.
+    let attr_name = name.to_str();
+    if attr_name.nfkc().collect::<String>() != attr_name {
+        return;
+    }
+
     // We can only replace a `setattr` call (which is an `Expr`) with an assignment
     // (which is a `Stmt`) if the `Expr` is already being used as a `Stmt`
     // (i.e., it's directly within an `Stmt::Expr`).