[syntax-errors] return outside function (#17300)

Summary
--

This PR reimplements [return-outside-function
(F706)](https://docs.astral.sh/ruff/rules/return-outside-function/) as a
semantic syntax error.

These changes are very similar to those in
https://github.com/astral-sh/ruff/pull/17298.

Test Plan
--

New linter tests, plus existing F706 tests.

crates/ruff_linter/resources/test/fixtures/syntax_errors/return_outside_function.py

@@ -0,0 +1,23 @@
+def f():
+    return 1  # okay
+
+
+def f():
+    return  # okay
+
+
+async def f():
+    return  # okay
+
+
+return 1  # error
+return  # error
+
+
+class C:
+    return 1  # error
+
+
+def f():
+    class C:
+        return 1  # error

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

@@ -380,9 +380,6 @@ pub(crate) fn statement(stmt: &Stmt, checker: &mut Checker) {
             }
         }
         Stmt::Return(_) => {
-            if checker.enabled(Rule::ReturnOutsideFunction) {
-                pyflakes::rules::return_outside_function(checker, stmt);
-            }
             if checker.enabled(Rule::ReturnInInit) {
                 pylint::rules::return_in_init(checker, stmt);
             }

crates/ruff_linter/src/checkers/ast/mod.rs

@@ -66,7 +66,9 @@ use crate::importer::{ImportRequest, Importer, ResolutionError};
 use crate::noqa::NoqaMapping;
 use crate::package::PackageRoot;
 use crate::registry::Rule;
-use crate::rules::pyflakes::rules::{LateFutureImport, YieldOutsideFunction};
+use crate::rules::pyflakes::rules::{
+    LateFutureImport, ReturnOutsideFunction, YieldOutsideFunction,
+};
 use crate::rules::pylint::rules::LoadBeforeGlobalDeclaration;
 use crate::rules::{flake8_pyi, flake8_type_checking, pyflakes, pyupgrade};
 use crate::settings::{flags, LinterSettings};
@@ -597,6 +599,11 @@ impl SemanticSyntaxContext for Checker<'_> {
                     ));
                 }
             }
+            SemanticSyntaxErrorKind::ReturnOutsideFunction => {
+                if self.settings.rules.enabled(Rule::ReturnOutsideFunction) {
+                    self.report_diagnostic(Diagnostic::new(ReturnOutsideFunction, error.range));
+                }
+            }
             SemanticSyntaxErrorKind::ReboundComprehensionVariable
             | SemanticSyntaxErrorKind::DuplicateTypeParameter
             | SemanticSyntaxErrorKind::MultipleCaseAssignment(_)

crates/ruff_linter/src/linter.rs

@@ -1061,14 +1061,15 @@ mod tests {
         Ok(())
     }
 
-    #[test_case(Path::new("yield_scope.py"); "yield_scope")]
-    fn test_yield_scope(path: &Path) -> Result<()> {
+    #[test_case(Rule::YieldOutsideFunction, Path::new("yield_scope.py"))]
+    #[test_case(Rule::ReturnOutsideFunction, Path::new("return_outside_function.py"))]
+    fn test_syntax_errors(rule: Rule, path: &Path) -> Result<()> {
         let snapshot = path.to_string_lossy().to_string();
         let path = Path::new("resources/test/fixtures/syntax_errors").join(path);
         let messages = test_contents_syntax_errors(
             &SourceKind::Python(std::fs::read_to_string(&path)?),
             &path,
-            &settings::LinterSettings::for_rule(Rule::YieldOutsideFunction),
+            &settings::LinterSettings::for_rule(rule),
         );
         insta::with_settings!({filters => vec![(r"\\", "/")]}, {
             assert_messages!(snapshot, messages);

crates/ruff_linter/src/rules/pyflakes/rules/return_outside_function.rs

@@ -1,11 +1,5 @@
-use ruff_python_ast::Stmt;
-
-use ruff_diagnostics::{Diagnostic, Violation};
+use ruff_diagnostics::Violation;
 use ruff_macros::{derive_message_formats, ViolationMetadata};
-use ruff_python_semantic::ScopeKind;
-use ruff_text_size::Ranged;
-
-use crate::checkers::ast::Checker;
 
 /// ## What it does
 /// Checks for `return` statements outside of functions.
@@ -31,12 +25,3 @@ impl Violation for ReturnOutsideFunction {
         "`return` statement outside of a function/method".to_string()
     }
 }
-
-pub(crate) fn return_outside_function(checker: &Checker, stmt: &Stmt) {
-    if matches!(
-        checker.semantic().current_scope().kind,
-        ScopeKind::Class(_) | ScopeKind::Module
-    ) {
-        checker.report_diagnostic(Diagnostic::new(ReturnOutsideFunction, stmt.range()));
-    }
-}

crates/ruff_linter/src/snapshots/ruff_linter__linter__tests__return_outside_function.py.snap

@@ -0,0 +1,31 @@
+---
+source: crates/ruff_linter/src/linter.rs
+---
+resources/test/fixtures/syntax_errors/return_outside_function.py:13:1: F706 `return` statement outside of a function/method
+   |
+13 | return 1  # error
+   | ^^^^^^^^ F706
+14 | return  # error
+   |
+
+resources/test/fixtures/syntax_errors/return_outside_function.py:14:1: F706 `return` statement outside of a function/method
+   |
+13 | return 1  # error
+14 | return  # error
+   | ^^^^^^ F706
+   |
+
+resources/test/fixtures/syntax_errors/return_outside_function.py:18:5: F706 `return` statement outside of a function/method
+   |
+17 | class C:
+18 |     return 1  # error
+   |     ^^^^^^^^ F706
+   |
+
+resources/test/fixtures/syntax_errors/return_outside_function.py:23:9: F706 `return` statement outside of a function/method
+   |
+21 | def f():
+22 |     class C:
+23 |         return 1  # error
+   |         ^^^^^^^^ F706
+   |

crates/ruff_python_parser/src/semantic_errors.rs

@@ -93,12 +93,15 @@ impl SemanticSyntaxChecker {
                     );
                 }
             }
-            Stmt::Return(ast::StmtReturn {
-                value: Some(value), ..
-            }) => {
-                // test_err single_star_return
-                // def f(): return *x
-                Self::invalid_star_expression(value, ctx);
+            Stmt::Return(ast::StmtReturn { value, range }) => {
+                if let Some(value) = value {
+                    // test_err single_star_return
+                    // def f(): return *x
+                    Self::invalid_star_expression(value, ctx);
+                }
+                if !ctx.in_function_scope() {
+                    Self::add_error(ctx, SemanticSyntaxErrorKind::ReturnOutsideFunction, *range);
+                }
             }
             Stmt::For(ast::StmtFor { target, iter, .. }) => {
                 // test_err single_star_for
@@ -797,6 +800,9 @@ impl Display for SemanticSyntaxError {
             SemanticSyntaxErrorKind::YieldOutsideFunction(kind) => {
                 write!(f, "`{kind}` statement outside of a function")
             }
+            SemanticSyntaxErrorKind::ReturnOutsideFunction => {
+                f.write_str("`return` statement outside of a function")
+            }
         }
     }
 }
@@ -1092,6 +1098,9 @@ pub enum SemanticSyntaxErrorKind {
     /// [PEP 492]: https://peps.python.org/pep-0492/
     /// [PEP 530]: https://peps.python.org/pep-0530/
     YieldOutsideFunction(YieldOutsideFunctionKind),
+
+    /// Represents the use of `return` outside of a function scope.
+    ReturnOutsideFunction,
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]