fixed scoping issue for nonlocals - now also indirect outer scopes are supported

Author: TheAnyKey

Lib/test/test_named_expression.py

@@ -166,7 +166,7 @@ def test_named_expression_invalid_rebinding_comprehension_inner_loop(self):
                 with self.assertRaisesRegex(SyntaxError, msg):
                     exec(f"lambda: {code}", {}) # Function scope
 
-    @unittest.expectedFailure # TODO RustPython
+    @unittest.expectedFailure # TODO RustPythonskip
     def test_named_expression_invalid_comprehension_iterable_expression(self):
         cases = [
             ("Top level", "[i for i in (i := range(5))]"),
@@ -394,21 +394,21 @@ def test_named_expression_scope_10(self):
         self.assertEqual(b, [1, 1])
         self.assertEqual(a, 1)
 
-    # the following test is not from CPyrgon and just as refernce for a common scoping problem of RustPython
-    @unittest.skip # needs skipping due to weired behaviour
+    # the following test is not from CPython and just as refernce for a common scoping problem of RustPython
     def test_named_expression_scop_10_rp_scope_prob(self):
         def foo():
-            rr=0
+            rr=36
             def foo0():
                 nonlocal rr
                 def foo1():
                     nonlocal rr
+                    self.assertEqual(rr,36)
                     rr+=42
                 foo1()
             foo0()
             return rr
 
-        self.assertEqual(foo(), 42)
+        self.assertEqual(foo(), 78)
 
 
     def test_named_expression_scope_11(self):
@@ -550,7 +550,6 @@ def f():
         f()
         self.assertEqual(GLOBAL_VAR, None)
 
-    @unittest.expectedFailure # TODO RustPython
     def test_named_expression_nonlocal_scope(self):
         sentinel = object()
         def f():

compiler/src/symboltable.rs

@@ -221,11 +221,19 @@ impl<'a> SymbolTableAnalyzer<'a> {
         } else {
             match symbol.scope {
                 SymbolScope::Nonlocal => {
-                    // check if name is defined in parent table!
-                    let parent_symbol_table = self.tables.last();
-                    if let Some((symbols, _)) = parent_symbol_table {
-                        let scope_depth = self.tables.len();
-                        if !symbols.contains_key(&symbol.name) || scope_depth < 2 {
+                    let scope_depth = self.tables.len();
+                    if scope_depth > 0 {
+                        // check if the name is already defined in any outer scope
+                        // therefore
+                        if scope_depth < 2
+                            || !self
+                                .tables
+                                .iter()
+                                .skip(1) // omit the global scope as it is not non-local
+                                .rev() // revert the order for better performance
+                                .any(|t| t.0.contains_key(&symbol.name))
+                        // true when any of symbol tables contains the name -> then negate
+                        {
                             return Err(SymbolTableError {
                                 error: format!("no binding for nonlocal '{}' found", symbol.name),
                                 location: Default::default(),

vm/src/scope.rs

@@ -113,11 +113,29 @@ impl NameProtocol for Scope {
     }
 
     fn store_cell(&self, vm: &VirtualMachine, name: &str, value: PyObjectRef) {
-        self.locals
-            .get(1)
-            .expect("no outer scope for non-local")
-            .set_item(name, value, vm)
-            .unwrap();
+        // find the innermost outer scope that contains the symbol name
+        if let Some(locals) = self
+            .locals
+            .iter()
+            .rev()
+            .filter(|l| l.contains_key(name, vm))
+            .nth(0)
+        {
+            // add to the symbol
+            locals.set_item(name, value, vm).unwrap();
+        } else {
+            // somewhat limited solution -> fallback to the old rustpython strategy
+            // and store the next outer scope
+            // This case is usually considered as a failure case, but kept for the moment
+            // to support the scope propagation for named expression assignments to so far
+            // unknown names in comprehensions. We need to consider here more context
+            // information for correct handling.
+            self.locals
+                .get(1)
+                .expect("no outer scope for non-local")
+                .set_item(name, value, vm)
+                .unwrap();
+        }
     }
 
     fn store_name(&self, vm: &VirtualMachine, key: &str, value: PyObjectRef) {