__slots__ xor __dict__ , name mangling (#6392)

* __slots__ xor __dict__

* mangle_name for `__` prefixed members

Lib/test/datetimetester.py

@@ -5455,8 +5455,6 @@ class Oddballs(unittest.TestCase):
         self.assertEqual(as_datetime, datetime_sc)
         self.assertEqual(datetime_sc, as_datetime)
 
-    # TODO: RUSTPYTHON
-    @unittest.expectedFailure
     def test_extra_attributes(self):
         with self.assertWarns(DeprecationWarning):
             utcnow = datetime.utcnow()

Lib/test/test_contextlib.py

@@ -24,8 +24,6 @@ class TestAbstractContextManager(unittest.TestCase):
         manager = DefaultEnter()
         self.assertIs(manager.__enter__(), manager)
 
-    # TODO: RUSTPYTHON
-    @unittest.expectedFailure
     def test_slots(self):
         class DefaultContextManager(AbstractContextManager):
             __slots__ = ()

Lib/test/test_contextlib_async.py

@@ -27,8 +27,6 @@ class TestAbstractAsyncContextManager(unittest.IsolatedAsyncioTestCase):
         async with manager as context:
             self.assertIs(manager, context)
 
-    # TODO: RUSTPYTHON
-    @unittest.expectedFailure
     async def test_slots(self):
         class DefaultAsyncContextManager(AbstractAsyncContextManager):
             __slots__ = ()

Lib/test/test_dataclasses.py

@@ -2776,8 +2776,6 @@ class TestFrozen(unittest.TestCase):
 
 
 class TestSlots(unittest.TestCase):
-    # TODO: RUSTPYTHON
-    @unittest.expectedFailure
     def test_simple(self):
         @dataclass
         class C:
@@ -2819,8 +2817,6 @@ class TestSlots(unittest.TestCase):
         # We can add a new field to the derived instance.
         d.z = 10
 
-    # TODO: RUSTPYTHON
-    @unittest.expectedFailure
     def test_generated_slots(self):
         @dataclass(slots=True)
         class C:

Lib/test/test_decimal.py

@@ -2923,10 +2923,6 @@ class CPythonAPItests(PythonAPItests, unittest.TestCase):
 class PyPythonAPItests(PythonAPItests, unittest.TestCase):
     decimal = P
 
-    # TODO: RUSTPYTHON
-    @unittest.expectedFailure
-    def test_complex(self): # TODO(RUSTPYTHON): Remove this test when it pass
-        return super().test_complex()
 
 class ContextAPItests:
 

Lib/test/test_fractions.py

@@ -1137,8 +1137,6 @@ class FractionTest(unittest.TestCase):
         self.assertTypedEquals(dr, copy(dr))
         self.assertTypedEquals(dr, deepcopy(dr))
 
-    # TODO: RUSTPYTHON
-    @unittest.expectedFailure
     def test_slots(self):
         # Issue 4998
         r = F(13, 7)

Lib/test/test_functools.py

@@ -3278,7 +3278,6 @@ class TestCachedProperty(unittest.TestCase):
         self.assertEqual(item.get_cost(), 4)
         self.assertEqual(item.cached_cost, 3)
 
-    @unittest.expectedFailure # TODO: RUSTPYTHON
     def test_object_with_slots(self):
         item = CachedCostItemWithSlots()
         with self.assertRaisesRegex(

Lib/test/test_os.py

@@ -5332,7 +5332,6 @@ class TestPEP519(unittest.TestCase):
     def test_pathlike_class_getitem(self):
         self.assertIsInstance(os.PathLike[bytes], types.GenericAlias)
 
-    @unittest.expectedFailure # TODO: RUSTPYTHON
     def test_pathlike_subclass_slots(self):
         class A(os.PathLike):
             __slots__ = ()

Lib/test/test_statistics.py

@@ -2889,8 +2889,6 @@ class TestNormalDist:
     # inaccurate.  There isn't much we can do about this short of
     # implementing our own implementations from scratch.
 
-    # TODO: RUSTPYTHON
-    @unittest.expectedFailure
     def test_slots(self):
         nd = self.module.NormalDist(300, 23)
         with self.assertRaises(TypeError):

Lib/test/test_typing.py

@@ -5269,7 +5269,6 @@ class GenericTests(BaseTestCase):
         for t in things:
             self.assertEqual(weakref.ref(t)(), t)
 
-    @unittest.expectedFailure  # TODO: RUSTPYTHON - __slots__ with Generic doesn't prevent new attributes
     def test_parameterized_slots(self):
         T = TypeVar('T')
         class C(Generic[T]):
@@ -5289,7 +5288,6 @@ class GenericTests(BaseTestCase):
         self.assertEqual(get_type_hints(foo, globals(), locals())['x'], C[C])
         self.assertEqual(copy(C[int]), deepcopy(C[int]))
 
-    @unittest.expectedFailure  # TODO: RUSTPYTHON - __slots__ with Generic doesn't prevent new attributes
     def test_parameterized_slots_dict(self):
         T = TypeVar('T')
         class D(Generic[T]):

crates/vm/src/builtins/object.rs

@@ -66,10 +66,16 @@ impl Constructor for PyBaseObject {
         }
 
         // more or less __new__ operator
-        let dict = if cls.is(vm.ctx.types.object_type) {
-            None
-        } else {
+        // Only create dict if the class has HAS_DICT flag (i.e., __slots__ was not defined
+        // or __dict__ is in __slots__)
+        let dict = if cls
+            .slots
+            .flags
+            .has_feature(crate::types::PyTypeFlags::HAS_DICT)
+        {
             Some(vm.ctx.new_dict())
+        } else {
+            None
         };
 
         // Ensure that all abstract methods are implemented before instantiating instance.

crates/vm/src/builtins/type.rs

@@ -307,7 +307,12 @@ impl PyType {
     ) -> Result<PyRef<Self>, String> {
         let mro = Self::resolve_mro(&bases)?;
 
-        if base.slots.flags.has_feature(PyTypeFlags::HAS_DICT) {
+        // Inherit HAS_DICT from any base in MRO that has it
+        // (not just the first base, as any base with __dict__ means subclass needs it too)
+        if mro
+            .iter()
+            .any(|b| b.slots.flags.has_feature(PyTypeFlags::HAS_DICT))
+        {
             slots.flags |= PyTypeFlags::HAS_DICT
         }
 
@@ -1180,25 +1185,27 @@ impl Constructor for PyType {
 
         if let Some(ref slots) = heaptype_slots {
             let mut offset = base_member_count;
+            let class_name = typ.name().to_string();
             for member in slots.as_slice() {
+                // Apply name mangling for private attributes (__x -> _ClassName__x)
+                let mangled_name = mangle_name(&class_name, member.as_str());
                 let member_def = PyMemberDef {
-                    name: member.to_string(),
+                    name: mangled_name.clone(),
                     kind: MemberKind::ObjectEx,
                     getter: MemberGetter::Offset(offset),
                     setter: MemberSetter::Offset(offset),
                     doc: None,
                 };
+                let attr_name = vm.ctx.intern_str(mangled_name.as_str());
                 let member_descriptor: PyRef<PyMemberDescriptor> =
                     vm.ctx.new_pyref(PyMemberDescriptor {
                         common: PyDescriptorOwned {
                             typ: typ.clone(),
-                            name: vm.ctx.intern_str(member.as_str()),
+                            name: attr_name,
                             qualname: PyRwLock::new(None),
                         },
                         member: member_def,
                     });
-
-                let attr_name = vm.ctx.intern_str(member.as_str());
                 // __slots__ attributes always get a member descriptor
                 // (this overrides any inherited attribute from MRO)
                 typ.set_attr(attr_name, member_descriptor.into());
@@ -1223,7 +1230,10 @@ impl Constructor for PyType {
         // since they inherit it from type
 
         // Add __dict__ descriptor after type creation to ensure correct __objclass__
-        if !base_is_type {
+        // Only add if:
+        // 1. base is not type (type subclasses inherit __dict__ from type)
+        // 2. the class has HAS_DICT flag (i.e., __slots__ was not defined or __dict__ is in __slots__)
+        if !base_is_type && typ.slots.flags.has_feature(PyTypeFlags::HAS_DICT) {
             let __dict__ = identifier!(vm, __dict__);
             if !typ.attributes.read().contains_key(&__dict__) {
                 unsafe {
@@ -1785,6 +1795,18 @@ fn best_base<'a>(bases: &'a [PyTypeRef], vm: &VirtualMachine) -> PyResult<&'a Py
     Ok(base.unwrap())
 }
 
+/// Apply Python name mangling for private attributes.
+/// `__x` becomes `_ClassName__x` if inside a class.
+fn mangle_name(class_name: &str, name: &str) -> String {
+    // Only mangle names starting with __ and not ending with __
+    if !name.starts_with("__") || name.ends_with("__") || name.contains('.') {
+        return name.to_string();
+    }
+    // Strip leading underscores from class name
+    let class_name = class_name.trim_start_matches('_');
+    format!("_{}{}", class_name, name)
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

crates/vm/src/stdlib/typevar.rs

@@ -1,6 +1,6 @@
 // spell-checker:ignore typevarobject funcobj
 use crate::{
-    AsObject, PyObject, PyObjectRef, PyPayload, PyRef, PyResult, VirtualMachine,
+    AsObject, Context, PyObject, PyObjectRef, PyPayload, PyRef, PyResult, VirtualMachine,
     builtins::{PyTupleRef, PyTypeRef, pystr::AsPyStr},
     common::lock::PyMutex,
     function::{FuncArgs, IntoFuncArgs, PyComparisonValue},
@@ -972,6 +972,11 @@ pub struct Generic {}
 
 #[pyclass(flags(BASETYPE))]
 impl Generic {
+    #[pyattr]
+    fn __slots__(ctx: &Context) -> PyTupleRef {
+        ctx.empty_tuple.clone()
+    }
+
     #[pyclassmethod]
     fn __class_getitem__(cls: PyTypeRef, args: FuncArgs, vm: &VirtualMachine) -> PyResult {
         call_typing_args_kwargs("_generic_class_getitem", cls, args, vm)