Ignore `PLW2901` when using typing cast (#3891)

crates/ruff/resources/test/fixtures/pylint/redefined_loop_name.py

@@ -1,3 +1,6 @@
+import typing
+from typing import cast
+
 # For -> for, variable reused
 for i in []:
     for i in []:  # error
@@ -43,6 +46,9 @@ for i in []:
 
 # For -> assignment
 for i in []:
+    # ignore typing cast
+    i = cast(int, i)
+    i = typing.cast(int, i)
     i = 5  # error
 
 # For -> augmented assignment
@@ -53,6 +59,10 @@ for i in []:
 for i in []:
     i: int = 5  # error
 
+# For -> annotated assignment without value
+for i in []:
+    i: int  # no error
+
 # Async for -> for, variable reused
 async for i in []:
     for i in []:  # error

crates/ruff/src/rules/pylint/rules/redefined_loop_name.rs

@@ -10,6 +10,7 @@ use ruff_python_ast::helpers::unparse_expr;
 use ruff_python_ast::types::{Node, Range};
 use ruff_python_ast::visitor;
 use ruff_python_ast::visitor::Visitor;
+use ruff_python_semantic::context::Context;
 
 use crate::checkers::ast::Checker;
 
@@ -140,6 +141,7 @@ struct ExprWithInnerBindingKind<'a> {
 }
 
 struct InnerForWithAssignTargetsVisitor<'a> {
+    context: &'a Context<'a>,
     dummy_variable_rgx: &'a Regex,
     assignment_targets: Vec<ExprWithInnerBindingKind<'a>>,
 }
@@ -174,7 +176,14 @@ where
                 );
             }
             // Assignment, augmented assignment, and annotated assignment.
-            StmtKind::Assign { targets, .. } => {
+            StmtKind::Assign { targets, value, .. } => {
+                // Check for single-target assignments which are of the
+                // form `x = cast(..., x)`.
+                if targets.first().map_or(false, |target| {
+                    assignment_is_cast_expr(self.context, value, target)
+                }) {
+                    return;
+                }
                 self.assignment_targets.extend(
                     assignment_targets_from_assign_targets(targets, self.dummy_variable_rgx).map(
                         |expr| ExprWithInnerBindingKind {
@@ -184,7 +193,20 @@ where
                     ),
                 );
             }
-            StmtKind::AugAssign { target, .. } | StmtKind::AnnAssign { target, .. } => {
+            StmtKind::AugAssign { target, .. } => {
+                self.assignment_targets.extend(
+                    assignment_targets_from_expr(target, self.dummy_variable_rgx).map(|expr| {
+                        ExprWithInnerBindingKind {
+                            expr,
+                            binding_kind: InnerBindingKind::Assignment,
+                        }
+                    }),
+                );
+            }
+            StmtKind::AnnAssign { target, value, .. } => {
+                if value.is_none() {
+                    return;
+                }
                 self.assignment_targets.extend(
                     assignment_targets_from_expr(target, self.dummy_variable_rgx).map(|expr| {
                         ExprWithInnerBindingKind {
@@ -209,6 +231,34 @@ where
     }
 }
 
+/// Checks whether the given assignment value is a `typing.cast` expression
+/// and that the target name is the same as the argument name.
+///
+/// Example:
+/// ```python
+/// from typing import cast
+///
+/// x = cast(int, x)
+/// ```
+fn assignment_is_cast_expr(context: &Context, value: &Expr, target: &Expr) -> bool {
+    let ExprKind::Call { func, args, .. } = &value.node else {
+        return false;
+    };
+    let ExprKind::Name { id: target_id, .. } = &target.node else {
+        return false;
+    };
+    if args.len() != 2 {
+        return false;
+    }
+    let ExprKind::Name { id: arg_id, .. } = &args[1].node else {
+        return false;
+    };
+    if arg_id != target_id {
+        return false;
+    }
+    context.match_typing_expr(func, "cast")
+}
+
 fn assignment_targets_from_expr<'a, U>(
     expr: &'a Expr<U>,
     dummy_variable_rgx: &'a Regex,
@@ -299,6 +349,7 @@ pub fn redefined_loop_name<'a, 'b>(checker: &'a mut Checker<'b>, node: &Node<'b>
                         })
                         .collect();
                 let mut visitor = InnerForWithAssignTargetsVisitor {
+                    context: &checker.ctx,
                     dummy_variable_rgx: &checker.settings.dummy_variable_rgx,
                     assignment_targets: vec![],
                 };
@@ -317,6 +368,7 @@ pub fn redefined_loop_name<'a, 'b>(checker: &'a mut Checker<'b>, node: &Node<'b>
                         })
                         .collect();
                 let mut visitor = InnerForWithAssignTargetsVisitor {
+                    context: &checker.ctx,
                     dummy_variable_rgx: &checker.settings.dummy_variable_rgx,
                     assignment_targets: vec![],
                 };

crates/ruff/src/rules/pylint/snapshots/ruff__rules__pylint__tests__PLW2901_redefined_loop_name.py.snap

@@ -8,10 +8,10 @@ expression: diagnostics
     suggestion: ~
     fixable: false
   location:
-    row: 3
+    row: 6
     column: 8
   end_location:
-    row: 3
+    row: 6
     column: 9
   fix:
     edits: []
@@ -22,10 +22,10 @@ expression: diagnostics
     suggestion: ~
     fixable: false
   location:
-    row: 8
+    row: 11
     column: 8
   end_location:
-    row: 8
+    row: 11
     column: 9
   fix:
     edits: []
@@ -36,10 +36,10 @@ expression: diagnostics
     suggestion: ~
     fixable: false
   location:
-    row: 13
+    row: 16
     column: 17
   end_location:
-    row: 13
+    row: 16
     column: 18
   fix:
     edits: []
@@ -50,10 +50,10 @@ expression: diagnostics
     suggestion: ~
     fixable: false
   location:
-    row: 18
+    row: 21
     column: 17
   end_location:
-    row: 18
+    row: 21
     column: 18
   fix:
     edits: []
@@ -64,10 +64,10 @@ expression: diagnostics
     suggestion: ~
     fixable: false
   location:
-    row: 34
+    row: 37
     column: 12
   end_location:
-    row: 34
+    row: 37
     column: 13
   fix:
     edits: []
@@ -78,10 +78,10 @@ expression: diagnostics
     suggestion: ~
     fixable: false
   location:
-    row: 40
+    row: 43
     column: 12
   end_location:
-    row: 40
+    row: 43
     column: 13
   fix:
     edits: []
@@ -92,10 +92,10 @@ expression: diagnostics
     suggestion: ~
     fixable: false
   location:
-    row: 41
+    row: 44
     column: 16
   end_location:
-    row: 41
+    row: 44
     column: 17
   fix:
     edits: []
@@ -106,10 +106,10 @@ expression: diagnostics
     suggestion: ~
     fixable: false
   location:
-    row: 46
+    row: 52
     column: 4
   end_location:
-    row: 46
+    row: 52
     column: 5
   fix:
     edits: []
@@ -120,10 +120,10 @@ expression: diagnostics
     suggestion: ~
     fixable: false
   location:
-    row: 50
+    row: 56
     column: 4
   end_location:
-    row: 50
+    row: 56
     column: 5
   fix:
     edits: []
@@ -134,10 +134,10 @@ expression: diagnostics
     suggestion: ~
     fixable: false
   location:
-    row: 54
+    row: 60
     column: 4
   end_location:
-    row: 54
+    row: 60
     column: 5
   fix:
     edits: []
@@ -148,10 +148,10 @@ expression: diagnostics
     suggestion: ~
     fixable: false
   location:
-    row: 58
+    row: 68
     column: 8
   end_location:
-    row: 58
+    row: 68
     column: 9
   fix:
     edits: []
@@ -162,10 +162,10 @@ expression: diagnostics
     suggestion: ~
     fixable: false
   location:
-    row: 63
+    row: 73
     column: 14
   end_location:
-    row: 63
+    row: 73
     column: 15
   fix:
     edits: []
@@ -176,10 +176,10 @@ expression: diagnostics
     suggestion: ~
     fixable: false
   location:
-    row: 68
+    row: 78
     column: 8
   end_location:
-    row: 68
+    row: 78
     column: 9
   fix:
     edits: []
@@ -190,10 +190,10 @@ expression: diagnostics
     suggestion: ~
     fixable: false
   location:
-    row: 73
+    row: 83
     column: 8
   end_location:
-    row: 73
+    row: 83
     column: 9
   fix:
     edits: []
@@ -204,10 +204,10 @@ expression: diagnostics
     suggestion: ~
     fixable: false
   location:
-    row: 78
+    row: 88
     column: 8
   end_location:
-    row: 78
+    row: 88
     column: 9
   fix:
     edits: []
@@ -218,10 +218,10 @@ expression: diagnostics
     suggestion: ~
     fixable: false
   location:
-    row: 78
+    row: 88
     column: 11
   end_location:
-    row: 78
+    row: 88
     column: 12
   fix:
     edits: []
@@ -232,10 +232,10 @@ expression: diagnostics
     suggestion: ~
     fixable: false
   location:
-    row: 95
+    row: 105
     column: 8
   end_location:
-    row: 95
+    row: 105
     column: 9
   fix:
     edits: []
@@ -246,10 +246,10 @@ expression: diagnostics
     suggestion: ~
     fixable: false
   location:
-    row: 112
+    row: 122
     column: 12
   end_location:
-    row: 112
+    row: 122
     column: 13
   fix:
     edits: []
@@ -260,10 +260,10 @@ expression: diagnostics
     suggestion: ~
     fixable: false
   location:
-    row: 118
+    row: 128
     column: 16
   end_location:
-    row: 118
+    row: 128
     column: 17
   fix:
     edits: []
@@ -274,10 +274,10 @@ expression: diagnostics
     suggestion: ~
     fixable: false
   location:
-    row: 133
+    row: 143
     column: 4
   end_location:
-    row: 133
+    row: 143
     column: 8
   fix:
     edits: []
@@ -288,10 +288,10 @@ expression: diagnostics
     suggestion: ~
     fixable: false
   location:
-    row: 138
+    row: 148
     column: 4
   end_location:
-    row: 138
+    row: 148
     column: 10
   fix:
     edits: []
@@ -302,10 +302,10 @@ expression: diagnostics
     suggestion: ~
     fixable: false
   location:
-    row: 143
+    row: 153
     column: 4
   end_location:
-    row: 143
+    row: 153
     column: 7
   fix:
     edits: []
@@ -316,10 +316,10 @@ expression: diagnostics
     suggestion: ~
     fixable: false
   location:
-    row: 148
+    row: 158
     column: 4
   end_location:
-    row: 148
+    row: 158
     column: 9
   fix:
     edits: []
@@ -330,10 +330,10 @@ expression: diagnostics
     suggestion: ~
     fixable: false
   location:
-    row: 153
+    row: 163
     column: 4
   end_location:
-    row: 153
+    row: 163
     column: 8
   fix:
     edits: []
@@ -344,10 +344,10 @@ expression: diagnostics
     suggestion: ~
     fixable: false
   location:
-    row: 155
+    row: 165
     column: 4
   end_location:
-    row: 155
+    row: 165
     column: 7
   fix:
     edits: []