[pylint] redefined-loop-name (W2901) (#3022)

Slightly broadens W2901 to cover `with` statements too.

Closes #2972.

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

@@ -0,0 +1,155 @@
+# For -> for, variable reused
+for i in []:
+    for i in []:  # error
+        pass
+
+# With -> for, variable reused
+with None as i:
+    for i in []:  # error
+        pass
+
+# For -> with, variable reused
+for i in []:
+    with None as i:  # error
+        pass
+
+# With -> with, variable reused
+with None as i:
+    with None as i:  # error
+        pass
+
+# For -> for, different variable
+for i in []:
+    for j in []:  # ok
+        pass
+
+# With -> with, different variable
+with None as i:
+    with None as j:  # ok
+        pass
+
+# For -> for -> for, doubly nested variable reuse
+for i in []:
+    for j in []:
+        for i in []:  # error
+            pass
+
+# For -> for -> for -> for, doubly nested variable reuse x2
+for i in []:
+    for j in []:
+        for i in []:  # error
+            for j in []:  # error
+                pass
+
+# For -> assignment
+for i in []:
+    i = 5  # error
+
+# For -> augmented assignment
+for i in []:
+    i += 5  # error
+
+# For -> annotated assignment
+for i in []:
+    i: int = 5  # error
+
+# Async for -> for, variable reused
+async for i in []:
+    for i in []:  # error
+        pass
+
+# For -> async for, variable reused
+for i in []:
+    async for i in []:  # error
+        pass
+
+# For -> for, outer loop unpacks tuple
+for i, j in enumerate([]):
+    for i in []:  # error
+        pass
+
+# For -> for, inner loop unpacks tuple
+for i in []:
+    for i, j in enumerate([]):  # error
+        pass
+
+# For -> for, both loops unpack tuple
+for (i, (j, k)) in []:
+    for i, j in enumerate([]):  # two errors
+        pass
+
+# For else -> for, variable reused in else
+for i in []:
+    pass
+else:
+    for i in []:  # no error
+        pass
+
+# For -> for, ignore dummy variables
+for _ in []:
+    for _ in []:  # no error
+        pass
+
+# For -> for, outer loop unpacks with asterisk
+for i, *j in []:
+    for j in []:  # error
+        pass
+
+# For -> function definition
+for i in []:
+    def f():
+        i = 2  # no error
+
+# For -> class definition
+for i in []:
+    class A:
+        i = 2  # no error
+
+# For -> function definition -> for -> assignment
+for i in []:
+    def f():
+        for i in []:  # no error
+            i = 2  # error
+
+# For -> class definition -> for -> for
+for i in []:
+    class A:
+        for i in []:  # no error
+            for i in []:  # error
+                pass
+
+# For -> use in assignment target without actual assignment; subscript
+for i in []:
+    a[i] = 2  # no error
+    i[a] = 2  # no error
+
+# For -> use in assignment target without actual assignment; attribute
+for i in []:
+    a.i = 2  # no error
+    i.a = 2  # no error
+
+# For target with subscript -> assignment
+for a[0] in []:
+    a[0] = 2  # error
+    a[1] = 2  # no error
+
+# For target with subscript -> assignment
+for a['i'] in []:
+    a['i'] = 2  # error
+    a['j'] = 2  # no error
+
+# For target with attribute -> assignment
+for a.i in []:
+    a.i = 2  # error
+    a.j = 2  # no error
+
+# For target with double nested attribute -> assignment
+for a.i.j in []:
+    a.i.j = 2  # error
+    a.j.i = 2  # no error
+
+# For target with attribute -> assignment with different spacing
+for a.i in []:
+    a. i = 2  # error
+for a. i in []:
+    a.i = 2  # error

crates/ruff/src/ast/helpers.rs

@@ -928,7 +928,10 @@ pub fn binding_range(binding: &Binding, locator: &Locator) -> Range {
 }
 
 // Return the ranges of `Name` tokens within a specified node.
-pub fn find_names<T>(located: &Located<T>, locator: &Locator) -> Vec<Range> {
+pub fn find_names<'a, T, U>(
+    located: &'a Located<T, U>,
+    locator: &'a Locator,
+) -> impl Iterator<Item = Range> + 'a {
     let contents = locator.slice(&Range::from_located(located));
     lexer::make_tokenizer_located(contents, located.location)
         .flatten()
@@ -937,7 +940,6 @@ pub fn find_names<T>(located: &Located<T>, locator: &Locator) -> Vec<Range> {
             location: start,
             end_location: end,
         })
-        .collect()
 }
 
 /// Return the `Range` of `name` in `Excepthandler`.

crates/ruff/src/ast/types.rs

@@ -29,7 +29,7 @@ impl Range {
         }
     }
 
-    pub fn from_located<T>(located: &Located<T>) -> Self {
+    pub fn from_located<T, U>(located: &Located<T, U>) -> Self {
         Range::new(located.location, located.end_location.unwrap())
     }
 

crates/ruff/src/checkers/ast.rs

@@ -342,7 +342,7 @@ where
         match &stmt.node {
             StmtKind::Global { names } => {
                 let scope_index = *self.scope_stack.last().expect("No current scope found");
-                let ranges = helpers::find_names(stmt, self.locator);
+                let ranges: Vec<Range> = helpers::find_names(stmt, self.locator).collect();
                 if scope_index != GLOBAL_SCOPE_INDEX {
                     // Add the binding to the current scope.
                     let context = self.execution_context();
@@ -372,7 +372,7 @@ where
             }
             StmtKind::Nonlocal { names } => {
                 let scope_index = *self.scope_stack.last().expect("No current scope found");
-                let ranges = helpers::find_names(stmt, self.locator);
+                let ranges: Vec<Range> = helpers::find_names(stmt, self.locator).collect();
                 if scope_index != GLOBAL_SCOPE_INDEX {
                     let context = self.execution_context();
                     let scope = &mut self.scopes[scope_index];
@@ -1651,6 +1651,9 @@ where
                         self.current_stmt_parent().map(Into::into),
                     );
                 }
+                if self.settings.rules.enabled(&Rule::RedefinedLoopName) {
+                    pylint::rules::redefined_loop_name(self, &Node::Stmt(stmt));
+                }
             }
             StmtKind::While { body, orelse, .. } => {
                 if self.settings.rules.enabled(&Rule::FunctionUsesLoopVariable) {
@@ -1695,6 +1698,9 @@ where
                 if self.settings.rules.enabled(&Rule::UselessElseOnLoop) {
                     pylint::rules::useless_else_on_loop(self, stmt, body, orelse);
                 }
+                if self.settings.rules.enabled(&Rule::RedefinedLoopName) {
+                    pylint::rules::redefined_loop_name(self, &Node::Stmt(stmt));
+                }
                 if matches!(stmt.node, StmtKind::For { .. }) {
                     if self.settings.rules.enabled(&Rule::ReimplementedBuiltin) {
                         flake8_simplify::rules::convert_for_loop_to_any_all(

crates/ruff/src/codes.rs

@@ -146,6 +146,7 @@ pub fn code_to_rule(linter: Linter, code: &str) -> Option<Rule> {
         (Pylint, "R0913") => Rule::TooManyArguments,
         (Pylint, "R0912") => Rule::TooManyBranches,
         (Pylint, "R0915") => Rule::TooManyStatements,
+        (Pylint, "W2901") => Rule::RedefinedLoopName,
 
         // flake8-builtins
         (Flake8Builtins, "001") => Rule::BuiltinVariableShadowing,

crates/ruff/src/registry.rs

@@ -149,6 +149,7 @@ ruff_macros::register_rules!(
     rules::pylint::rules::TooManyArguments,
     rules::pylint::rules::TooManyBranches,
     rules::pylint::rules::TooManyStatements,
+    rules::pylint::rules::RedefinedLoopName,
     // flake8-builtins
     rules::flake8_builtins::rules::BuiltinVariableShadowing,
     rules::flake8_builtins::rules::BuiltinArgumentShadowing,

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

@@ -47,6 +47,7 @@ mod tests {
     #[test_case(Rule::BidirectionalUnicode, Path::new("bidirectional_unicode.py"); "PLE2502")]
     #[test_case(Rule::BadStrStripCall, Path::new("bad_str_strip_call.py"); "PLE01310")]
     #[test_case(Rule::YieldInInit, Path::new("yield_in_init.py"); "PLE0100")]
+    #[test_case(Rule::RedefinedLoopName, Path::new("redefined_loop_name.py"); "PLW2901")]
     fn rules(rule_code: Rule, path: &Path) -> Result<()> {
         let snapshot = format!("{}_{}", rule_code.noqa_code(), path.to_string_lossy());
         let diagnostics = test_path(

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

@@ -11,6 +11,7 @@ pub use magic_value_comparison::{magic_value_comparison, MagicValueComparison};
 pub use merge_isinstance::{merge_isinstance, ConsiderMergingIsinstance};
 pub use nonlocal_without_binding::NonlocalWithoutBinding;
 pub use property_with_parameters::{property_with_parameters, PropertyWithParameters};
+pub use redefined_loop_name::{redefined_loop_name, RedefinedLoopName};
 pub use return_in_init::{return_in_init, ReturnInInit};
 pub use too_many_arguments::{too_many_arguments, TooManyArguments};
 pub use too_many_branches::{too_many_branches, TooManyBranches};
@@ -40,6 +41,7 @@ mod magic_value_comparison;
 mod merge_isinstance;
 mod nonlocal_without_binding;
 mod property_with_parameters;
+mod redefined_loop_name;
 mod return_in_init;
 mod too_many_arguments;
 mod too_many_branches;