Exclude UPPER_CASE constants

crates/ruff_linter/resources/test/fixtures/flake8_bugbear/B006_10.py

@@ -3,7 +3,7 @@ MY_SET = {"ABC", "DEF"}  # plain set
 MY_LIST = [1, 2, 3]  # plain list
 MY_DICT = {"key": "value"}  # plain dict
 
-# NOT triggering B006 (should trigger)
+# NOT triggering B006 (correct - UPPER_CASE constants are excluded per PEP 8)
 def func_A(s: set[str] = MY_SET):
     return s
 
@@ -11,11 +11,11 @@ def func_A(s: set[str] = MY_SET):
 def func_B(s: set[str] = {"ABC", "DEF"}):
     return s
 
-# Should trigger B006
+# NOT triggering B006 (correct - UPPER_CASE constants are excluded per PEP 8)
 def func_C(items: list[int] = MY_LIST):
     return items
 
-# Should trigger B006
+# NOT triggering B006 (correct - UPPER_CASE constants are excluded per PEP 8)
 def func_D(data: dict[str, str] = MY_DICT):
     return data
 

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

@@ -10,6 +10,7 @@ use ruff_python_semantic::analyze::function_type::is_stub;
 use ruff_python_semantic::analyze::typing::{
     find_binding_value, is_immutable_annotation, is_mutable_expr,
 };
+use ruff_python_stdlib::str;
 use ruff_python_trivia::{indentation_at_offset, textwrap};
 use ruff_source_file::LineRanges;
 use ruff_text_size::Ranged;
@@ -145,6 +146,10 @@ fn is_guaranteed_mutable_expr(expr: &Expr, semantic: &SemanticModel) -> bool {
         }
         Expr::Named(ast::ExprNamed { value, .. }) => is_guaranteed_mutable_expr(value, semantic),
         Expr::Name(name) => {
+            // Exclude UPPER_CASE constants (PEP 8 convention - meant to be read-only)
+            if str::is_cased_uppercase(&name.id) {
+                return false;
+            }
             // Resolve module-level constants that are bound to mutable objects
             let Some(binding_id) = semantic.only_binding(name) else {
                 return false;

crates/ruff_linter/src/rules/flake8_bugbear/snapshots/ruff_linter__rules__flake8_bugbear__tests__B006_B006_10.py.snap

@@ -19,5 +19,5 @@ help: Replace with `None`; initialize within function
 13 +         s = {"ABC", "DEF"}
 14 |     return s
 15 | 
-16 | # Should trigger B006
+16 | # NOT triggering B006 (correct - UPPER_CASE constants are excluded per PEP 8)
 note: This is an unsafe fix and may change runtime behavior

crates/ruff_linter/src/rules/flake8_bugbear/snapshots/ruff_linter__rules__flake8_bugbear__tests__preview__B006_B006_10.py.snap

@@ -1,27 +1,6 @@
 ---
 source: crates/ruff_linter/src/rules/flake8_bugbear/mod.rs
 ---
-B006 [*] Do not use mutable data structures for argument defaults
- --> B006_10.py:7:26
-  |
-6 | # NOT triggering B006 (should trigger)
-7 | def func_A(s: set[str] = MY_SET):
-  |                          ^^^^^^
-8 |     return s
-  |
-help: Replace with `None`; initialize within function
-4  | MY_DICT = {"key": "value"}  # plain dict
-5  | 
-6  | # NOT triggering B006 (should trigger)
-   - def func_A(s: set[str] = MY_SET):
-7  + def func_A(s: set[str] = None):
-8  +     if s is None:
-9  +         s = MY_SET
-10 |     return s
-11 | 
-12 | # Triggering B006 (correct)
-note: This is an unsafe fix and may change runtime behavior
-
 B006 [*] Do not use mutable data structures for argument defaults
   --> B006_10.py:11:26
    |
@@ -40,46 +19,5 @@ help: Replace with `None`; initialize within function
 13 +         s = {"ABC", "DEF"}
 14 |     return s
 15 | 
-16 | # Should trigger B006
+16 | # NOT triggering B006 (correct - UPPER_CASE constants are excluded per PEP 8)
-note: This is an unsafe fix and may change runtime behavior
-
-B006 [*] Do not use mutable data structures for argument defaults
-  --> B006_10.py:15:31
-   |
-14 | # Should trigger B006
-15 | def func_C(items: list[int] = MY_LIST):
-   |                               ^^^^^^^
-16 |     return items
-   |
-help: Replace with `None`; initialize within function
-12 |     return s
-13 | 
-14 | # Should trigger B006
-   - def func_C(items: list[int] = MY_LIST):
-15 + def func_C(items: list[int] = None):
-16 +     if items is None:
-17 +         items = MY_LIST
-18 |     return items
-19 | 
-20 | # Should trigger B006
-note: This is an unsafe fix and may change runtime behavior
-
-B006 [*] Do not use mutable data structures for argument defaults
-  --> B006_10.py:19:35
-   |
-18 | # Should trigger B006
-19 | def func_D(data: dict[str, str] = MY_DICT):
-   |                                   ^^^^^^^
-20 |     return data
-   |
-help: Replace with `None`; initialize within function
-16 |     return items
-17 | 
-18 | # Should trigger B006
-   - def func_D(data: dict[str, str] = MY_DICT):
-19 + def func_D(data: dict[str, str] = None):
-20 +     if data is None:
-21 +         data = MY_DICT
-22 |     return data
-23 | 
 note: This is an unsafe fix and may change runtime behavior