Implement F821

resources/test/src/F821.py

@@ -0,0 +1,14 @@
+def get_name():
+    return self.name
+
+
+def get_name():
+    return (self.name,)
+
+
+def get_name():
+    del self.name
+
+
+def get_name(self):
+    return self.name

resources/test/src/pyproject.toml

@@ -8,6 +8,7 @@ select = [
     "F541",
     "F634",
     "F706",
+    "F821",
     "F831",
     "F832",
     "F901",

src/check_ast.rs

@@ -299,7 +299,7 @@ impl Visitor for Checker<'_> {
             ExprKind::Name { ctx, .. } => match ctx {
                 ExprContext::Load => self.handle_node_load(expr),
                 ExprContext::Store => self.handle_node_store(expr),
-                ExprContext::Del => {}
+                ExprContext::Del => self.handle_node_delete(expr),
             },
             ExprKind::GeneratorExp { .. }
             | ExprKind::ListComp { .. }
@@ -439,8 +439,16 @@ impl Checker<'_> {
                 }
                 if let Some(binding) = scope.values.get_mut(id) {
                     binding.used = Some(scope_id);
+                    return;
                 }
             }
+
+            if self.settings.select.contains(&CheckCode::F821) {
+                self.checks.push(Check {
+                    kind: CheckKind::UndefinedName(id.clone()),
+                    location: expr.location,
+                })
+            }
         }
     }
 
@@ -480,6 +488,20 @@ impl Checker<'_> {
         }
     }
 
+    fn handle_node_delete(&mut self, expr: &Expr) {
+        if let ExprKind::Name { id, .. } = &expr.node {
+            let current = self.scopes.last_mut().expect("No current scope found.");
+            if current.values.remove(id).is_none()
+                && self.settings.select.contains(&CheckCode::F821)
+            {
+                self.checks.push(Check {
+                    kind: CheckKind::UndefinedName(id.clone()),
+                    location: expr.location,
+                })
+            }
+        }
+    }
+
     fn check_deferred(&mut self, path: &str) {
         for value in self.deferred.clone() {
             if let Ok(expr) = &parser::parse_expression(&value, path) {

src/checks.rs

@@ -13,6 +13,7 @@ pub enum CheckCode {
     F541,
     F634,
     F706,
+    F821,
     F831,
     F832,
     F901,
@@ -29,6 +30,7 @@ impl FromStr for CheckCode {
             "F541" => Ok(CheckCode::F541),
             "F634" => Ok(CheckCode::F634),
             "F706" => Ok(CheckCode::F706),
+            "F821" => Ok(CheckCode::F821),
             "F831" => Ok(CheckCode::F831),
             "F832" => Ok(CheckCode::F832),
             "F901" => Ok(CheckCode::F901),
@@ -46,6 +48,7 @@ impl CheckCode {
             CheckCode::F541 => "F541",
             CheckCode::F634 => "F634",
             CheckCode::F706 => "F706",
+            CheckCode::F821 => "F821",
             CheckCode::F831 => "F831",
             CheckCode::F832 => "F832",
             CheckCode::F901 => "F901",
@@ -61,6 +64,7 @@ impl CheckCode {
             CheckCode::F541 => &LintSource::AST,
             CheckCode::F634 => &LintSource::AST,
             CheckCode::F706 => &LintSource::AST,
+            CheckCode::F821 => &LintSource::AST,
             CheckCode::F831 => &LintSource::AST,
             CheckCode::F832 => &LintSource::AST,
             CheckCode::F901 => &LintSource::AST,
@@ -83,6 +87,7 @@ pub enum CheckKind {
     LineTooLong,
     RaiseNotImplemented,
     ReturnOutsideFunction,
+    UndefinedName(String),
     UndefinedLocal(String),
     UnusedImport(String),
 }
@@ -98,6 +103,7 @@ impl CheckKind {
             CheckKind::LineTooLong => &CheckCode::E501,
             CheckKind::RaiseNotImplemented => &CheckCode::F901,
             CheckKind::ReturnOutsideFunction => &CheckCode::F706,
+            CheckKind::UndefinedName(_) => &CheckCode::F821,
             CheckKind::UndefinedLocal(_) => &CheckCode::F832,
             CheckKind::UnusedImport(_) => &CheckCode::F401,
         }
@@ -123,6 +129,9 @@ impl CheckKind {
             CheckKind::ReturnOutsideFunction => {
                 "a `return` statement outside of a function/method".to_string()
             }
+            CheckKind::UndefinedName(name) => {
+                format!("Undefined name `{name}`")
+            }
             CheckKind::UndefinedLocal(name) => {
                 format!("Local variable `{name}` referenced before assignment")
             }

src/linter.rs

@@ -248,6 +248,42 @@ mod tests {
         Ok(())
     }
 
+    #[test]
+    fn f821() -> Result<()> {
+        let actual = check_path(
+            &Path::new("./resources/test/src/F821.py"),
+            &settings::Settings {
+                line_length: 88,
+                exclude: vec![],
+                select: BTreeSet::from([CheckCode::F821]),
+            },
+            &cache::Mode::None,
+        )?;
+        let expected = vec![
+            Message {
+                kind: CheckKind::UndefinedName("self".to_string()),
+                location: Location::new(2, 12),
+                filename: "./resources/test/src/F821.py".to_string(),
+            },
+            Message {
+                kind: CheckKind::UndefinedName("self".to_string()),
+                location: Location::new(6, 13),
+                filename: "./resources/test/src/F821.py".to_string(),
+            },
+            Message {
+                kind: CheckKind::UndefinedName("self".to_string()),
+                location: Location::new(10, 9),
+                filename: "./resources/test/src/F821.py".to_string(),
+            },
+        ];
+        assert_eq!(actual.len(), expected.len());
+        for i in 0..actual.len() {
+            assert_eq!(actual[i], expected[i]);
+        }
+
+        Ok(())
+    }
+
     #[test]
     fn f831() -> Result<()> {
         let actual = check_path(

src/pyproject.rs

@@ -233,6 +233,7 @@ other-attribute = 1
                     CheckCode::F541,
                     CheckCode::F634,
                     CheckCode::F706,
+                    CheckCode::F821,
                     CheckCode::F831,
                     CheckCode::F832,
                     CheckCode::F901,

src/settings.rs

@@ -48,6 +48,7 @@ impl Settings {
                     CheckCode::F541,
                     CheckCode::F634,
                     CheckCode::F706,
+                    CheckCode::F821,
                     CheckCode::F831,
                     CheckCode::F832,
                     CheckCode::F901,