[syntax-errors] nonlocal declaration at module level (#17559)

## Summary

Part of #17412

Add a new compile-time syntax error for detecting `nonlocal`
declarations at a module level.

## Test Plan

- Added new inline tests for the syntax error
- Updated existing tests for `nonlocal` statement parsing to be inside a
function scope

Co-authored-by: Brent Westbrook <36778786+ntBre@users.noreply.github.com>

Author: abhijeetbodas2001

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

@@ -616,7 +616,8 @@ impl SemanticSyntaxContext for Checker<'_> {
             | SemanticSyntaxErrorKind::DuplicateMatchClassAttribute(_)
             | SemanticSyntaxErrorKind::InvalidStarExpression
             | SemanticSyntaxErrorKind::AsyncComprehensionInSyncComprehension(_)
-            | SemanticSyntaxErrorKind::DuplicateParameter(_) => {
+            | SemanticSyntaxErrorKind::DuplicateParameter(_)
+            | SemanticSyntaxErrorKind::NonlocalDeclarationAtModuleLevel => {
                 if self.settings.preview.is_enabled() {
                     self.semantic_errors.borrow_mut().push(error);
                 }

crates/ruff_python_parser/resources/inline/err/nonlocal_declaration_at_module_level.py

@@ -0,0 +1,2 @@
+nonlocal x
+nonlocal x, y

crates/ruff_python_parser/resources/inline/err/nonlocal_stmt_empty.py

@@ -1 +1,2 @@
-nonlocal
+def _():
+    nonlocal

crates/ruff_python_parser/resources/inline/err/nonlocal_stmt_expression.py

@@ -1 +1,2 @@
-nonlocal x + 1
+def _():
+    nonlocal x + 1

crates/ruff_python_parser/resources/inline/err/nonlocal_stmt_trailing_comma.py

@@ -1,3 +1,4 @@
-nonlocal ,
-nonlocal x,
-nonlocal x, y,
+def _():
+    nonlocal ,
+    nonlocal x,
+    nonlocal x, y,

crates/ruff_python_parser/resources/inline/ok/nonlocal_declaration_at_module_level.py

@@ -0,0 +1,2 @@
+def _():
+    nonlocal x

crates/ruff_python_parser/resources/inline/ok/nonlocal_stmt.py

@@ -1,2 +1,3 @@
-nonlocal x
-nonlocal x, y, z
+def _():
+    nonlocal x
+    nonlocal x, y, z

crates/ruff_python_parser/src/parser/statement.rs

@@ -897,29 +897,33 @@ impl<'src> Parser<'src> {
         self.bump(TokenKind::Nonlocal);
 
         // test_err nonlocal_stmt_trailing_comma
-        // nonlocal ,
-        // nonlocal x,
-        // nonlocal x, y,
+        // def _():
+        //     nonlocal ,
+        //     nonlocal x,
+        //     nonlocal x, y,
 
         // test_err nonlocal_stmt_expression
-        // nonlocal x + 1
+        // def _():
+        //     nonlocal x + 1
         let names = self.parse_comma_separated_list_into_vec(
             RecoveryContextKind::Identifiers,
             Parser::parse_identifier,
         );
 
         if names.is_empty() {
             // test_err nonlocal_stmt_empty
-            // nonlocal
+            // def _():
+            //     nonlocal
             self.add_error(
                 ParseErrorType::EmptyNonlocalNames,
                 self.current_token_range(),
             );
         }
 
         // test_ok nonlocal_stmt
-        // nonlocal x
-        // nonlocal x, y, z
+        // def _():
+        //     nonlocal x
+        //     nonlocal x, y, z
         ast::StmtNonlocal {
             range: self.node_range(start),
             names,

crates/ruff_python_parser/src/semantic_errors.rs

@@ -142,6 +142,22 @@ impl SemanticSyntaxChecker {
                     AwaitOutsideAsyncFunctionKind::AsyncWith,
                 );
             }
+            Stmt::Nonlocal(ast::StmtNonlocal { range, .. }) => {
+                // test_ok nonlocal_declaration_at_module_level
+                // def _():
+                //     nonlocal x
+
+                // test_err nonlocal_declaration_at_module_level
+                // nonlocal x
+                // nonlocal x, y
+                if ctx.in_module_scope() {
+                    Self::add_error(
+                        ctx,
+                        SemanticSyntaxErrorKind::NonlocalDeclarationAtModuleLevel,
+                        *range,
+                    );
+                }
+            }
             _ => {}
         }
 
@@ -933,6 +949,9 @@ impl Display for SemanticSyntaxError {
             SemanticSyntaxErrorKind::DuplicateParameter(name) => {
                 write!(f, r#"Duplicate parameter "{name}""#)
             }
+            SemanticSyntaxErrorKind::NonlocalDeclarationAtModuleLevel => {
+                write!(f, "nonlocal declaration not allowed at module level")
+            }
         }
     }
 }
@@ -1254,6 +1273,9 @@ pub enum SemanticSyntaxErrorKind {
     /// lambda x, x: ...
     /// ```
     DuplicateParameter(String),
+
+    /// Represents a nonlocal declaration at module level
+    NonlocalDeclarationAtModuleLevel,
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]

crates/ruff_python_parser/tests/fixtures.rs

@@ -538,7 +538,7 @@ impl SemanticSyntaxContext for SemanticSyntaxCheckerVisitor<'_> {
     }
 
     fn in_module_scope(&self) -> bool {
-        true
+        self.scopes.len() == 1
     }
 
     fn in_function_scope(&self) -> bool {