[ruff] Implemented used-dummy-variable (RUF052) (#14611)

Co-authored-by: Alex Waygood <[email protected]>

crates/ruff_linter/resources/test/fixtures/ruff/RUF052.py

@@ -0,0 +1,106 @@
+# Correct
+
+for _ in range(5):
+    pass
+
+_valid_type = int
+
+_valid_var_1: _valid_type
+
+_valid_var_1 = 1
+
+_valid_var_2 = 2
+
+_valid_var_3 = _valid_var_1 + _valid_var_2
+
+def _valid_fun():
+    pass    
+
+_valid_fun()
+
+def fun(arg):
+    _valid_unused_var = arg
+    pass
+
+_x = "global"
+
+def fun():
+    global _x
+    return _x
+
+def fun():
+    __dunder__ = "dunder variable"
+    return __dunder__
+
+def fun():
+    global _x
+    _x = "reassigned global"
+    return _x  
+
+class _ValidClass:
+    pass
+
+_ValidClass()
+
+class ClassOk:
+    _valid_private_cls_attr = 1
+
+    print(_valid_private_cls_attr)
+
+    def __init__(self):
+        self._valid_private_ins_attr = 2
+        print(self._valid_private_ins_attr)
+
+    def _valid_method(self):
+        return self._valid_private_ins_attr
+
+    def method(arg):
+        _valid_unused_var = arg
+        return 
+
+def fun(x):
+    _ = 1
+    __ = 2
+    ___ = 3
+    if x == 1:
+        return _
+    if x == 2:
+        return __
+    if x == 3:
+        return ___
+    return x
+
+# Incorrect
+
+class Class_:
+    def fun(self):
+        _var = "method variable" # [RUF052]
+        return _var
+
+def fun(_var): # [RUF052]
+    return _var
+
+def fun():
+    _list = "built-in" # [RUF052]
+    return _list
+
+x = "global"
+
+def fun():
+    global x
+    _x = "shadows global" # [RUF052]
+    return _x
+
+def foo():
+  x = "outer"
+  def bar():
+    nonlocal x
+    _x = "shadows nonlocal" # [RUF052]
+    return _x
+  bar()
+  return x
+
+def fun():
+    x = "local"
+    _x = "shadows local" # [RUF052]
+    return _x

crates/ruff_linter/src/checkers/ast/analyze/bindings.rs

@@ -10,6 +10,7 @@ use crate::rules::{
 /// Run lint rules over the [`Binding`]s.
 pub(crate) fn bindings(checker: &mut Checker) {
     if !checker.any_enabled(&[
+        Rule::AssignmentInAssert,
         Rule::InvalidAllFormat,
         Rule::InvalidAllObject,
         Rule::NonAsciiName,
@@ -18,7 +19,7 @@ pub(crate) fn bindings(checker: &mut Checker) {
         Rule::UnsortedDunderSlots,
         Rule::UnusedVariable,
         Rule::UnquotedTypeAlias,
-        Rule::AssignmentInAssert,
+        Rule::UsedDummyVariable,
     ]) {
         return;
     }
@@ -88,6 +89,11 @@ pub(crate) fn bindings(checker: &mut Checker) {
                 checker.diagnostics.push(diagnostic);
             }
         }
+        if checker.enabled(Rule::UsedDummyVariable) {
+            if let Some(diagnostic) = ruff::rules::used_dummy_variable(checker, binding) {
+                checker.diagnostics.push(diagnostic);
+            }
+        }
         if checker.enabled(Rule::AssignmentInAssert) {
             if let Some(diagnostic) = ruff::rules::assignment_in_assert(checker, binding) {
                 checker.diagnostics.push(diagnostic);

crates/ruff_linter/src/codes.rs

@@ -984,6 +984,7 @@ pub fn code_to_rule(linter: Linter, code: &str) -> Option<(RuleGroup, Rule)> {
         (Ruff, "040") => (RuleGroup::Preview, rules::ruff::rules::InvalidAssertMessageLiteralArgument),
         (Ruff, "041") => (RuleGroup::Preview, rules::ruff::rules::UnnecessaryNestedLiteral),
         (Ruff, "048") => (RuleGroup::Preview, rules::ruff::rules::MapIntVersionParsing),
+        (Ruff, "052") => (RuleGroup::Preview, rules::ruff::rules::UsedDummyVariable),
         (Ruff, "055") => (RuleGroup::Preview, rules::ruff::rules::UnnecessaryRegularExpression),
         (Ruff, "100") => (RuleGroup::Stable, rules::ruff::rules::UnusedNOQA),
         (Ruff, "101") => (RuleGroup::Stable, rules::ruff::rules::RedirectedNOQA),

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

@@ -10,6 +10,7 @@ mod tests {
     use std::path::Path;
 
     use anyhow::Result;
+    use regex::Regex;
     use rustc_hash::FxHashSet;
     use test_case::test_case;
 
@@ -70,6 +71,7 @@ mod tests {
     #[test_case(Rule::InvalidAssertMessageLiteralArgument, Path::new("RUF040.py"))]
     #[test_case(Rule::UnnecessaryNestedLiteral, Path::new("RUF041.py"))]
     #[test_case(Rule::UnnecessaryNestedLiteral, Path::new("RUF041.pyi"))]
+    #[test_case(Rule::UsedDummyVariable, Path::new("RUF052.py"))]
     fn rules(rule_code: Rule, path: &Path) -> Result<()> {
         let snapshot = format!("{}_{}", rule_code.noqa_code(), path.to_string_lossy());
         let diagnostics = test_path(
@@ -449,4 +451,32 @@ mod tests {
         assert_messages!(snapshot, diagnostics);
         Ok(())
     }
+
+    #[test_case(Rule::UsedDummyVariable, Path::new("RUF052.py"), r"^_+", 1)]
+    #[test_case(Rule::UsedDummyVariable, Path::new("RUF052.py"), r"", 2)]
+    fn custom_regexp_preset(
+        rule_code: Rule,
+        path: &Path,
+        regex_pattern: &str,
+        id: u8,
+    ) -> Result<()> {
+        // Compile the regex from the pattern string
+        let regex = Regex::new(regex_pattern).unwrap();
+
+        let snapshot = format!(
+            "custom_dummy_var_regexp_preset__{}_{}_{}",
+            rule_code.noqa_code(),
+            path.to_string_lossy(),
+            id,
+        );
+        let diagnostics = test_path(
+            Path::new("ruff").join(path).as_path(),
+            &settings::LinterSettings {
+                dummy_variable_rgx: regex,
+                ..settings::LinterSettings::for_rule(rule_code)
+            },
+        )?;
+        assert_messages!(snapshot, diagnostics);
+        Ok(())
+    }
 }

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

@@ -38,6 +38,7 @@ pub(crate) use unraw_re_pattern::*;
 pub(crate) use unsafe_markup_use::*;
 pub(crate) use unused_async::*;
 pub(crate) use unused_noqa::*;
+pub(crate) use used_dummy_variable::*;
 pub(crate) use useless_if_else::*;
 pub(crate) use zip_instead_of_pairwise::*;
 
@@ -85,6 +86,7 @@ mod unraw_re_pattern;
 mod unsafe_markup_use;
 mod unused_async;
 mod unused_noqa;
+mod used_dummy_variable;
 mod useless_if_else;
 mod zip_instead_of_pairwise;