Make unused variable pattern configurable (#265)

resources/test/fixtures/F841.py

@@ -10,13 +10,13 @@ except ValueError as e:
     print(e)
 
 
-def f():
+def f1():
     x = 1
     y = 2
     z = x + y
 
 
-def g():
+def f2():
     foo = (1, 2)
     (a, b) = (1, 2)
 
@@ -26,6 +26,12 @@ def g():
     (x, y) = baz = bar
 
 
-def h():
+def f3():
     locals()
     x = 1
+
+
+def f4():
+    _ = 1
+    __ = 1
+    _discarded = 1

src/ast/checks.rs

@@ -1,6 +1,7 @@
 use std::collections::BTreeSet;
 
 use itertools::izip;
+use regex::Regex;
 use rustpython_parser::ast::{
     Arg, Arguments, Cmpop, Constant, Excepthandler, ExcepthandlerKind, Expr, ExprKind, Keyword,
     Location, Stmt, StmtKind, Unaryop,
@@ -71,7 +72,11 @@ pub fn check_not_tests(
 }
 
 /// Check UnusedVariable compliance.
-pub fn check_unused_variables(scope: &Scope, locator: &dyn CheckLocator) -> Vec<Check> {
+pub fn check_unused_variables(
+    scope: &Scope,
+    locator: &dyn CheckLocator,
+    dummy_variable_rgx: &Regex,
+) -> Vec<Check> {
     let mut checks: Vec<Check> = vec![];
 
     if matches!(
@@ -82,13 +87,12 @@ pub fn check_unused_variables(scope: &Scope, locator: &dyn CheckLocator) -> Vec<
     }
 
     for (name, binding) in scope.values.iter() {
-        // TODO(charlie): Ignore if using `locals`.
         if binding.used.is_none()
-            && name != "_"
+            && matches!(binding.kind, BindingKind::Assignment)
+            && !dummy_variable_rgx.is_match(name)
             && name != "__tracebackhide__"
             && name != "__traceback_info__"
             && name != "__traceback_supplement__"
-            && matches!(binding.kind, BindingKind::Assignment)
         {
             checks.push(Check::new(
                 CheckKind::UnusedVariable(name.to_string()),

src/check_ast.rs

@@ -1415,8 +1415,11 @@ impl<'a> Checker<'a> {
     fn check_deferred_assignments(&mut self) {
         if self.settings.select.contains(&CheckCode::F841) {
             while let Some(index) = self.deferred_assignments.pop() {
-                self.checks
+                self.checks.extend(checks::check_unused_variables(
-                    .extend(checks::check_unused_variables(&self.scopes[index], self));
+                    &self.scopes[index],
+                    self,
+                    &self.settings.dummy_variable_rgx,
+                ));
             }
         }
     }

src/check_lines.rs

@@ -182,6 +182,8 @@ pub fn check_lines(
 mod tests {
     use std::collections::BTreeSet;
 
+    use regex::Regex;
+
     use super::check_lines;
     use super::*;
 
@@ -198,6 +200,7 @@ mod tests {
                 exclude: vec![],
                 extend_exclude: vec![],
                 select: BTreeSet::from_iter(vec![CheckCode::E501]),
+                dummy_variable_rgx: Regex::new(r"^_+").unwrap(),
             };
             check_lines(
                 &mut checks,

src/linter.rs

@@ -119,6 +119,7 @@ mod tests {
     use std::path::Path;
 
     use anyhow::Result;
+    use regex::Regex;
     use rustpython_parser::lexer;
     use rustpython_parser::lexer::LexResult;
 
@@ -596,6 +597,21 @@ mod tests {
         Ok(())
     }
 
+    #[test]
+    fn f841_dummy_variable_rgx() -> Result<()> {
+        let mut checks = check_path(
+            Path::new("./resources/test/fixtures/F841.py"),
+            &settings::Settings {
+                dummy_variable_rgx: Regex::new(r"^z$").unwrap(),
+                ..settings::Settings::for_rule(CheckCode::F841)
+            },
+            &fixer::Mode::Generate,
+        )?;
+        checks.sort_by_key(|check| check.location);
+        insta::assert_yaml_snapshot!(checks);
+        Ok(())
+    }
+
     #[test]
     fn f901() -> Result<()> {
         let mut checks = check_path(

src/main.rs

@@ -1,5 +1,6 @@
 extern crate core;
 
+use regex::Regex;
 use std::io;
 use std::path::{Path, PathBuf};
 use std::process::ExitCode;
@@ -85,6 +86,9 @@ struct Cli {
     /// Enable automatic additions of noqa directives to failing lines.
     #[clap(long, action)]
     add_noqa: bool,
+    /// Regular expression matching the name of dummy variables.
+    #[clap(long)]
+    dummy_variable_rgx: Option<Regex>,
 }
 
 #[cfg(feature = "update-informer")]
@@ -265,6 +269,9 @@ fn inner_main() -> Result<ExitCode> {
     if !cli.extend_ignore.is_empty() {
         settings.ignore(&cli.extend_ignore);
     }
+    if let Some(dummy_variable_rgx) = cli.dummy_variable_rgx {
+        settings.dummy_variable_rgx = dummy_variable_rgx;
+    }
 
     if cli.show_settings && cli.show_files {
         eprintln!("Error: specify --show-settings or show-files (not both).");

src/pyproject.rs

@@ -30,6 +30,7 @@ pub struct Config {
     pub extend_exclude: Option<Vec<String>>,
     pub select: Option<Vec<CheckCode>>,
     pub ignore: Option<Vec<CheckCode>>,
+    pub dummy_variable_rgx: Option<String>,
 }
 
 #[derive(Debug, PartialEq, Eq, Deserialize)]
@@ -130,6 +131,7 @@ mod tests {
                     extend_exclude: None,
                     select: None,
                     ignore: None,
+                    dummy_variable_rgx: None,
                 })
             })
         );
@@ -150,6 +152,7 @@ line-length = 79
                     extend_exclude: None,
                     select: None,
                     ignore: None,
+                    dummy_variable_rgx: None,
                 })
             })
         );
@@ -170,6 +173,7 @@ exclude = ["foo.py"]
                     extend_exclude: None,
                     select: None,
                     ignore: None,
+                    dummy_variable_rgx: None,
                 })
             })
         );
@@ -190,6 +194,7 @@ select = ["E501"]
                     extend_exclude: None,
                     select: Some(vec![CheckCode::E501]),
                     ignore: None,
+                    dummy_variable_rgx: None,
                 })
             })
         );
@@ -210,6 +215,7 @@ ignore = ["E501"]
                     extend_exclude: None,
                     select: None,
                     ignore: Some(vec![CheckCode::E501]),
+                    dummy_variable_rgx: None,
                 })
             })
         );
@@ -274,6 +280,7 @@ other-attribute = 1
                 ]),
                 select: None,
                 ignore: None,
+                dummy_variable_rgx: None,
             }
         );
 

src/settings.rs

@@ -2,9 +2,10 @@ use std::collections::BTreeSet;
 use std::hash::{Hash, Hasher};
 use std::path::{Path, PathBuf};
 
-use anyhow::Result;
+use anyhow::{anyhow, Result};
 use glob::Pattern;
 use once_cell::sync::Lazy;
+use regex::Regex;
 
 use crate::checks::{CheckCode, DEFAULT_CHECK_CODES};
 use crate::fs;
@@ -43,6 +44,7 @@ pub struct Settings {
     pub exclude: Vec<FilePattern>,
     pub extend_exclude: Vec<FilePattern>,
     pub select: BTreeSet<CheckCode>,
+    pub dummy_variable_rgx: Regex,
 }
 
 impl Settings {
@@ -54,6 +56,7 @@ impl Settings {
             exclude: vec![],
             extend_exclude: vec![],
             select: BTreeSet::from([check_code]),
+            dummy_variable_rgx: DEFAULT_DUMMY_VARIABLE_RGX.clone(),
         }
     }
 
@@ -65,6 +68,7 @@ impl Settings {
             exclude: vec![],
             extend_exclude: vec![],
             select: BTreeSet::from_iter(check_codes),
+            dummy_variable_rgx: DEFAULT_DUMMY_VARIABLE_RGX.clone(),
         }
     }
 }
@@ -72,6 +76,7 @@ impl Settings {
 impl Hash for Settings {
     fn hash<H: Hasher>(&self, state: &mut H) {
         self.line_length.hash(state);
+        self.dummy_variable_rgx.as_str().hash(state);
         for value in self.select.iter() {
             value.hash(state);
         }
@@ -102,6 +107,9 @@ static DEFAULT_EXCLUDE: Lazy<Vec<FilePattern>> = Lazy::new(|| {
     ]
 });
 
+static DEFAULT_DUMMY_VARIABLE_RGX: Lazy<Regex> =
+    Lazy::new(|| Regex::new("^(_+|(_+[a-zA-Z0-9_]*[a-zA-Z0-9]+?))$").unwrap());
+
 impl Settings {
     pub fn from_pyproject(
         pyproject: Option<PathBuf>,
@@ -133,6 +141,11 @@ impl Settings {
             } else {
                 BTreeSet::from_iter(DEFAULT_CHECK_CODES)
             },
+            dummy_variable_rgx: match config.dummy_variable_rgx {
+                Some(pattern) => Regex::new(&pattern)
+                    .map_err(|e| anyhow!("Invalid dummy-variable-rgx value: {e}"))?,
+                None => DEFAULT_DUMMY_VARIABLE_RGX.clone(),
+            },
             pyproject,
             project_root,
         };

src/snapshots/ruff__linter__tests__f841_dummy_variable_rgx.snap

@@ -0,0 +1,47 @@
+---
+source: src/linter.rs
+expression: checks
+---
+- kind:
+    UnusedVariable: e
+  location:
+    row: 3
+    column: 1
+  fix: ~
+- kind:
+    UnusedVariable: foo
+  location:
+    row: 20
+    column: 5
+  fix: ~
+- kind:
+    UnusedVariable: a
+  location:
+    row: 21
+    column: 6
+  fix: ~
+- kind:
+    UnusedVariable: b
+  location:
+    row: 21
+    column: 9
+  fix: ~
+- kind:
+    UnusedVariable: _
+  location:
+    row: 35
+    column: 5
+  fix: ~
+- kind:
+    UnusedVariable: __
+  location:
+    row: 36
+    column: 5
+  fix: ~
+- kind:
+    UnusedVariable: _discarded
+  location:
+    row: 37
+    column: 5
+  fix: ~
+