Allow mutations with iterator key

crates/ruff_linter/resources/test/fixtures/flake8_bugbear/B909.py

@@ -9,7 +9,7 @@
 some_other_list = [1, 2, 3]
 for elem in some_list:
     # errors
-    some_list.remove(elem)
+    some_list.remove(0)
     del some_list[2]
     some_list.append(elem)
     some_list.sort()
@@ -22,7 +22,7 @@
 
     # conditional break should error
     if elem == 2:
-        some_list.remove(elem)
+        some_list.remove(0)
         if elem == 3:
             break
 
@@ -81,7 +81,7 @@ def __init__(self, ls):
 a = A((1, 2, 3))
 # ensure member accesses are handled as errors
 for elem in a.some_list:
-    a.some_list.remove(elem)
+    a.some_list.remove(0)
     del a.some_list[2]
 
 
@@ -156,3 +156,5 @@ def __init__(self, ls):
 for elem in some_list:
     del some_list[elem]
     some_list[elem] = 1
+    some_list.remove(elem)
+    some_list.discard(elem)

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

@@ -7,8 +7,8 @@ use ruff_python_ast::comparable::ComparableExpr;
 use ruff_python_ast::name::UnqualifiedName;
 use ruff_python_ast::{
     visitor::{self, Visitor},
-    Expr, ExprAttribute, ExprCall, ExprSubscript, Stmt, StmtAssign, StmtAugAssign, StmtBreak,
-    StmtDelete, StmtFor, StmtIf,
+    Arguments, Expr, ExprAttribute, ExprCall, ExprSubscript, Stmt, StmtAssign, StmtAugAssign,
+    StmtBreak, StmtDelete, StmtFor, StmtIf,
 };
 use ruff_text_size::TextRange;
 
@@ -186,7 +186,7 @@ impl<'a> LoopMutationsVisitor<'a> {
     }
 
     /// Handle, e.g., `items.append(1)`.
-    fn handle_call(&mut self, func: &Expr) {
+    fn handle_call(&mut self, func: &Expr, arguments: &Arguments) {
         if let Expr::Attribute(ExprAttribute {
             range,
             value,
@@ -195,7 +195,17 @@ impl<'a> LoopMutationsVisitor<'a> {
         }) = func
         {
             if is_mutating_function(attr.as_str()) {
+                // Find, e.g., `items.remove(1)`.
                 if ComparableExpr::from(self.iter) == ComparableExpr::from(value) {
+                    // But allow, e.g., `for item in items: items.remove(item)`.
+                    if arguments.len() == 1 && matches!(attr.as_str(), "remove" | "discard") {
+                        if let [arg] = &*arguments.args {
+                            if ComparableExpr::from(self.target) == ComparableExpr::from(arg) {
+                                return;
+                            }
+                        }
+                    }
+
                     self.add_mutation(*range);
                 }
             }
@@ -271,8 +281,11 @@ impl<'a> Visitor<'a> for LoopMutationsVisitor<'a> {
 
     fn visit_expr(&mut self, expr: &'a Expr) {
         // Ex) `items.append(1)`
-        if let Expr::Call(ExprCall { func, .. }) = expr {
-            self.handle_call(func);
+        if let Expr::Call(ExprCall {
+            func, arguments, ..
+        }) = expr
+        {
+            self.handle_call(func, arguments);
         }
 
         visitor::walk_expr(self, expr);

crates/ruff_linter/src/rules/flake8_bugbear/snapshots/ruff_linter__rules__flake8_bugbear__tests__B909_B909.py.snap

@@ -5,7 +5,7 @@ B909.py:12:5: B909 Mutation to loop iterable `some_list` during iteration
    |
 10 | for elem in some_list:
 11 |     # errors
-12 |     some_list.remove(elem)
+12 |     some_list.remove(0)
    |     ^^^^^^^^^^^^^^^^ B909
 13 |     del some_list[2]
 14 |     some_list.append(elem)
@@ -14,7 +14,7 @@ B909.py:12:5: B909 Mutation to loop iterable `some_list` during iteration
 B909.py:13:5: B909 Mutation to loop iterable `some_list` during iteration
    |
 11 |     # errors
-12 |     some_list.remove(elem)
+12 |     some_list.remove(0)
 13 |     del some_list[2]
    |     ^^^^^^^^^^^^^^^^ B909
 14 |     some_list.append(elem)
@@ -23,7 +23,7 @@ B909.py:13:5: B909 Mutation to loop iterable `some_list` during iteration
 
 B909.py:14:5: B909 Mutation to loop iterable `some_list` during iteration
    |
-12 |     some_list.remove(elem)
+12 |     some_list.remove(0)
 13 |     del some_list[2]
 14 |     some_list.append(elem)
    |     ^^^^^^^^^^^^^^^^ B909
@@ -104,7 +104,7 @@ B909.py:25:9: B909 Mutation to loop iterable `some_list` during iteration
    |
 23 |     # conditional break should error
 24 |     if elem == 2:
-25 |         some_list.remove(elem)
+25 |         some_list.remove(0)
    |         ^^^^^^^^^^^^^^^^ B909
 26 |         if elem == 3:
 27 |             break
@@ -202,15 +202,15 @@ B909.py:84:5: B909 Mutation to loop iterable `a.some_list` during iteration
    |
 82 | # ensure member accesses are handled as errors
 83 | for elem in a.some_list:
-84 |     a.some_list.remove(elem)
+84 |     a.some_list.remove(0)
    |     ^^^^^^^^^^^^^^^^^^ B909
 85 |     del a.some_list[2]
    |
 
 B909.py:85:5: B909 Mutation to loop iterable `a.some_list` during iteration
    |
 83 | for elem in a.some_list:
-84 |     a.some_list.remove(elem)
+84 |     a.some_list.remove(0)
 85 |     del a.some_list[2]
    |     ^^^^^^^^^^^^^^^^^^ B909
    |