flag: DISALLOW_INSTANTIATION (#6445)

* Set tp_new slot when build heap/static type

* Improve type tp_call impl to check tp_new existence and error if not exist

* Set DISALLOW_INSTANTIATION flag on several types according to cpython impl

* Allow #[pyslot] for function pointer

* Fix DISALLOW_INSTANTIATION

---------

Signed-off-by: snowapril <sinjihng@gmail.com>
Co-authored-by: snowapril <sinjihng@gmail.com>

Lib/test/test_descr.py

@@ -1788,7 +1788,6 @@ class ClassPropertiesAndMethods(unittest.TestCase, ExtraAssertions):
         self.assertEqual(b.foo, 3)
         self.assertEqual(b.__class__, D)
 
-    @unittest.expectedFailure
     def test_bad_new(self):
         self.assertRaises(TypeError, object.__new__)
         self.assertRaises(TypeError, object.__new__, '')

crates/derive-impl/src/pyclass.rs

@@ -954,7 +954,10 @@ where
         } else if let Ok(f) = args.item.function_or_method() {
             (&f.sig().ident, f.span())
         } else {
-            return Err(self.new_syn_error(args.item.span(), "can only be on a method"));
+            return Err(self.new_syn_error(
+                args.item.span(),
+                "can only be on a method or const function pointer",
+            ));
         };
 
         let item_attr = args.attrs.remove(self.index());
@@ -1496,7 +1499,9 @@ impl SlotItemMeta {
             }
         } else {
             let ident_str = self.inner().item_name();
-            let name = if let Some(stripped) = ident_str.strip_prefix("slot_") {
+            // Convert to lowercase to handle both SLOT_NEW and slot_new
+            let ident_lower = ident_str.to_lowercase();
+            let name = if let Some(stripped) = ident_lower.strip_prefix("slot_") {
                 proc_macro2::Ident::new(stripped, inner.item_ident.span())
             } else {
                 inner.item_ident.clone()
@@ -1609,7 +1614,6 @@ fn extract_impl_attrs(attr: PunctuatedNestedMeta, item: &Ident) -> Result<Extrac
     }];
     let mut payload = None;
 
-    let mut has_constructor = false;
     for attr in attr {
         match attr {
             NestedMeta::Meta(Meta::List(MetaList { path, nested, .. })) => {
@@ -1634,9 +1638,6 @@ fn extract_impl_attrs(attr: PunctuatedNestedMeta, item: &Ident) -> Result<Extrac
                                     "Try `#[pyclass(with(Constructor, ...))]` instead of `#[pyclass(with(DefaultConstructor, ...))]`. DefaultConstructor implicitly implements Constructor."
                                 )
                             }
-                            if path.is_ident("Constructor") || path.is_ident("Unconstructible") {
-                                has_constructor = true;
-                            }
                             (
                                 quote!(<Self as #path>::__extend_py_class),
                                 quote!(<Self as #path>::__OWN_METHOD_DEFS),
@@ -1689,11 +1690,6 @@ fn extract_impl_attrs(attr: PunctuatedNestedMeta, item: &Ident) -> Result<Extrac
             attr => bail_span!(attr, "Unknown pyimpl attribute"),
         }
     }
-    // TODO: DISALLOW_INSTANTIATION check is required
-    let _ = has_constructor;
-    // if !withs.is_empty() && !has_constructor {
-    //     bail_span!(item, "#[pyclass(with(...))] does not have a Constructor. Either #[pyclass(with(Constructor, ...))] or #[pyclass(with(Unconstructible, ...))] is mandatory. Consider to add `impl DefaultConstructor for T {{}}` or `impl Unconstructible for T {{}}`.")
-    // }
 
     Ok(ExtractedImplAttrs {
         payload,

crates/stdlib/src/array.rs

@@ -1399,7 +1399,7 @@ mod array {
         internal: PyMutex<PositionIterInternal<PyArrayRef>>,
     }
 
-    #[pyclass(with(IterNext, Iterable), flags(HAS_DICT))]
+    #[pyclass(with(IterNext, Iterable), flags(HAS_DICT, DISALLOW_INSTANTIATION))]
     impl PyArrayIter {
         #[pymethod]
         fn __setstate__(&self, state: PyObjectRef, vm: &VirtualMachine) -> PyResult<()> {

crates/stdlib/src/csv.rs

@@ -908,7 +908,7 @@ mod _csv {
         }
     }
 
-    #[pyclass(with(IterNext, Iterable))]
+    #[pyclass(with(IterNext, Iterable), flags(DISALLOW_INSTANTIATION))]
     impl Reader {
         #[pygetset]
         fn line_num(&self) -> u64 {
@@ -1059,7 +1059,7 @@ mod _csv {
         }
     }
 
-    #[pyclass]
+    #[pyclass(flags(DISALLOW_INSTANTIATION))]
     impl Writer {
         #[pygetset(name = "dialect")]
         const fn get_dialect(&self, _vm: &VirtualMachine) -> PyDialect {

crates/stdlib/src/pystruct.rs

@@ -16,7 +16,7 @@ pub(crate) mod _struct {
         function::{ArgBytesLike, ArgMemoryBuffer, PosArgs},
         match_class,
         protocol::PyIterReturn,
-        types::{Constructor, IterNext, Iterable, Representable, SelfIter, Unconstructible},
+        types::{Constructor, IterNext, Iterable, Representable, SelfIter},
     };
     use crossbeam_utils::atomic::AtomicCell;
 
@@ -189,7 +189,7 @@ pub(crate) mod _struct {
         }
     }
 
-    #[pyclass(with(Unconstructible, IterNext, Iterable))]
+    #[pyclass(with(IterNext, Iterable), flags(DISALLOW_INSTANTIATION))]
     impl UnpackIterator {
         #[pymethod]
         fn __length_hint__(&self) -> usize {
@@ -197,7 +197,7 @@ pub(crate) mod _struct {
         }
     }
     impl SelfIter for UnpackIterator {}
-    impl Unconstructible for UnpackIterator {}
+
     impl IterNext for UnpackIterator {
         fn next(zelf: &Py<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
             let size = zelf.format_spec.size;

crates/stdlib/src/sqlite.rs

@@ -75,7 +75,7 @@ mod _sqlite {
         sliceable::{SaturatedSliceIter, SliceableSequenceOp},
         types::{
             AsMapping, AsNumber, AsSequence, Callable, Comparable, Constructor, Hashable,
-            Initializer, IterNext, Iterable, PyComparisonOp, SelfIter, Unconstructible,
+            Initializer, IterNext, Iterable, PyComparisonOp, SelfIter,
         },
         utils::ToCString,
     };
@@ -2197,8 +2197,6 @@ mod _sqlite {
         inner: PyMutex<Option<BlobInner>>,
     }
 
-    impl Unconstructible for Blob {}
-
     #[derive(Debug)]
     struct BlobInner {
         blob: SqliteBlob,
@@ -2211,7 +2209,7 @@ mod _sqlite {
         }
     }
 
-    #[pyclass(with(AsMapping, Unconstructible, AsNumber, AsSequence))]
+    #[pyclass(flags(DISALLOW_INSTANTIATION), with(AsMapping, AsNumber, AsSequence))]
     impl Blob {
         #[pymethod]
         fn close(&self) {
@@ -2592,9 +2590,7 @@ mod _sqlite {
         }
     }
 
-    impl Unconstructible for Statement {}
-
-    #[pyclass(with(Unconstructible))]
+    #[pyclass(flags(DISALLOW_INSTANTIATION))]
     impl Statement {
         fn new(
             connection: &Connection,

crates/stdlib/src/unicodedata.rs

@@ -105,7 +105,7 @@ mod unicodedata {
         }
     }
 
-    #[pyclass]
+    #[pyclass(flags(DISALLOW_INSTANTIATION))]
     impl Ucd {
         #[pymethod]
         fn category(&self, character: PyStrRef, vm: &VirtualMachine) -> PyResult<String> {

crates/stdlib/src/zlib.rs

@@ -225,7 +225,7 @@ mod zlib {
         inner: PyMutex<PyDecompressInner>,
     }
 
-    #[pyclass]
+    #[pyclass(flags(DISALLOW_INSTANTIATION))]
     impl PyDecompress {
         #[pygetset]
         fn eof(&self) -> bool {
@@ -383,7 +383,7 @@ mod zlib {
         inner: PyMutex<CompressState<CompressInner>>,
     }
 
-    #[pyclass]
+    #[pyclass(flags(DISALLOW_INSTANTIATION))]
     impl PyCompress {
         #[pymethod]
         fn compress(&self, data: ArgBytesLike, vm: &VirtualMachine) -> PyResult<Vec<u8>> {

crates/vm/src/builtins/asyncgenerator.rs

@@ -8,7 +8,7 @@ use crate::{
     frame::FrameRef,
     function::OptionalArg,
     protocol::PyIterReturn,
-    types::{IterNext, Iterable, Representable, SelfIter, Unconstructible},
+    types::{IterNext, Iterable, Representable, SelfIter},
 };
 
 use crossbeam_utils::atomic::AtomicCell;
@@ -32,7 +32,7 @@ impl PyPayload for PyAsyncGen {
     }
 }
 
-#[pyclass(with(PyRef, Unconstructible, Representable))]
+#[pyclass(flags(DISALLOW_INSTANTIATION), with(PyRef, Representable))]
 impl PyAsyncGen {
     pub const fn as_coro(&self) -> &Coro {
         &self.inner
@@ -201,8 +201,6 @@ impl Representable for PyAsyncGen {
     }
 }
 
-impl Unconstructible for PyAsyncGen {}
-
 #[pyclass(module = false, name = "async_generator_wrapped_value")]
 #[derive(Debug)]
 pub(crate) struct PyAsyncGenWrappedValue(pub PyObjectRef);

crates/vm/src/builtins/builtin_func.rs

@@ -5,7 +5,7 @@ use crate::{
     common::wtf8::Wtf8,
     convert::TryFromObject,
     function::{FuncArgs, PyComparisonValue, PyMethodDef, PyMethodFlags, PyNativeFn},
-    types::{Callable, Comparable, PyComparisonOp, Representable, Unconstructible},
+    types::{Callable, Comparable, PyComparisonOp, Representable},
 };
 use std::fmt;
 
@@ -74,7 +74,7 @@ impl Callable for PyNativeFunction {
     }
 }
 
-#[pyclass(with(Callable, Unconstructible), flags(HAS_DICT))]
+#[pyclass(with(Callable), flags(HAS_DICT, DISALLOW_INSTANTIATION))]
 impl PyNativeFunction {
     #[pygetset]
     fn __module__(zelf: NativeFunctionOrMethod) -> Option<&'static PyStrInterned> {
@@ -145,8 +145,6 @@ impl Representable for PyNativeFunction {
     }
 }
 
-impl Unconstructible for PyNativeFunction {}
-
 // `PyCMethodObject` in CPython
 #[pyclass(name = "builtin_method", module = false, base = PyNativeFunction, ctx = "builtin_method_type")]
 pub struct PyNativeMethod {
@@ -155,8 +153,8 @@ pub struct PyNativeMethod {
 }
 
 #[pyclass(
-    with(Unconstructible, Callable, Comparable, Representable),
-    flags(HAS_DICT)
+    with(Callable, Comparable, Representable),
+    flags(HAS_DICT, DISALLOW_INSTANTIATION)
 )]
 impl PyNativeMethod {
     #[pygetset]
@@ -246,8 +244,6 @@ impl Representable for PyNativeMethod {
     }
 }
 
-impl Unconstructible for PyNativeMethod {}
-
 pub fn init(context: &Context) {
     PyNativeFunction::extend_class(context, context.types.builtin_function_or_method_type);
     PyNativeMethod::extend_class(context, context.types.builtin_method_type);

crates/vm/src/builtins/bytearray.rs

@@ -33,7 +33,7 @@ use crate::{
     types::{
         AsBuffer, AsMapping, AsNumber, AsSequence, Callable, Comparable, Constructor,
         DefaultConstructor, Initializer, IterNext, Iterable, PyComparisonOp, Representable,
-        SelfIter, Unconstructible,
+        SelfIter,
     },
 };
 use bstr::ByteSlice;
@@ -865,7 +865,7 @@ impl PyPayload for PyByteArrayIterator {
     }
 }
 
-#[pyclass(with(Unconstructible, IterNext, Iterable))]
+#[pyclass(flags(DISALLOW_INSTANTIATION), with(IterNext, Iterable))]
 impl PyByteArrayIterator {
     #[pymethod]
     fn __length_hint__(&self) -> usize {
@@ -886,8 +886,6 @@ impl PyByteArrayIterator {
     }
 }
 
-impl Unconstructible for PyByteArrayIterator {}
-
 impl SelfIter for PyByteArrayIterator {}
 impl IterNext for PyByteArrayIterator {
     fn next(zelf: &Py<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {

crates/vm/src/builtins/bytes.rs

@@ -25,7 +25,7 @@ use crate::{
     sliceable::{SequenceIndex, SliceableSequenceOp},
     types::{
         AsBuffer, AsMapping, AsNumber, AsSequence, Callable, Comparable, Constructor, Hashable,
-        IterNext, Iterable, PyComparisonOp, Representable, SelfIter, Unconstructible,
+        IterNext, Iterable, PyComparisonOp, Representable, SelfIter,
     },
 };
 use bstr::ByteSlice;
@@ -749,7 +749,7 @@ impl PyPayload for PyBytesIterator {
     }
 }
 
-#[pyclass(with(Unconstructible, IterNext, Iterable))]
+#[pyclass(flags(DISALLOW_INSTANTIATION), with(IterNext, Iterable))]
 impl PyBytesIterator {
     #[pymethod]
     fn __length_hint__(&self) -> usize {
@@ -770,7 +770,6 @@ impl PyBytesIterator {
             .set_state(state, |obj, pos| pos.min(obj.len()), vm)
     }
 }
-impl Unconstructible for PyBytesIterator {}
 
 impl SelfIter for PyBytesIterator {}
 impl IterNext for PyBytesIterator {

crates/vm/src/builtins/coroutine.rs

@@ -6,7 +6,7 @@ use crate::{
     frame::FrameRef,
     function::OptionalArg,
     protocol::PyIterReturn,
-    types::{IterNext, Iterable, Representable, SelfIter, Unconstructible},
+    types::{IterNext, Iterable, Representable, SelfIter},
 };
 use crossbeam_utils::atomic::AtomicCell;
 
@@ -24,7 +24,7 @@ impl PyPayload for PyCoroutine {
     }
 }
 
-#[pyclass(with(Py, Unconstructible, IterNext, Representable))]
+#[pyclass(flags(DISALLOW_INSTANTIATION), with(Py, IterNext, Representable))]
 impl PyCoroutine {
     pub const fn as_coro(&self) -> &Coro {
         &self.inner
@@ -123,8 +123,6 @@ impl Py<PyCoroutine> {
     }
 }
 
-impl Unconstructible for PyCoroutine {}
-
 impl Representable for PyCoroutine {
     #[inline]
     fn repr_str(zelf: &Py<Self>, vm: &VirtualMachine) -> PyResult<String> {

crates/vm/src/builtins/descriptor.rs

@@ -4,7 +4,7 @@ use crate::{
     builtins::{PyTypeRef, builtin_func::PyNativeMethod, type_},
     class::PyClassImpl,
     function::{FuncArgs, PyMethodDef, PyMethodFlags, PySetterValue},
-    types::{Callable, GetDescriptor, Representable, Unconstructible},
+    types::{Callable, GetDescriptor, Representable},
 };
 use rustpython_common::lock::PyRwLock;
 
@@ -105,8 +105,8 @@ impl PyMethodDescriptor {
 }
 
 #[pyclass(
-    with(GetDescriptor, Callable, Unconstructible, Representable),
-    flags(METHOD_DESCRIPTOR)
+    with(GetDescriptor, Callable, Representable),
+    flags(METHOD_DESCRIPTOR, DISALLOW_INSTANTIATION)
 )]
 impl PyMethodDescriptor {
     #[pygetset]
@@ -159,8 +159,6 @@ impl Representable for PyMethodDescriptor {
     }
 }
 
-impl Unconstructible for PyMethodDescriptor {}
-
 #[derive(Debug)]
 pub enum MemberKind {
     Bool = 14,
@@ -246,7 +244,10 @@ fn calculate_qualname(descr: &PyDescriptorOwned, vm: &VirtualMachine) -> PyResul
     }
 }
 
-#[pyclass(with(GetDescriptor, Unconstructible, Representable), flags(BASETYPE))]
+#[pyclass(
+    with(GetDescriptor, Representable),
+    flags(BASETYPE, DISALLOW_INSTANTIATION)
+)]
 impl PyMemberDescriptor {
     #[pygetset]
     fn __doc__(&self) -> Option<String> {
@@ -339,8 +340,6 @@ fn set_slot_at_object(
     Ok(())
 }
 
-impl Unconstructible for PyMemberDescriptor {}
-
 impl Representable for PyMemberDescriptor {
     #[inline]
     fn repr_str(zelf: &Py<Self>, _vm: &VirtualMachine) -> PyResult<String> {

crates/vm/src/builtins/dict.rs

@@ -19,7 +19,7 @@ use crate::{
     recursion::ReprGuard,
     types::{
         AsMapping, AsNumber, AsSequence, Callable, Comparable, Constructor, DefaultConstructor,
-        Initializer, IterNext, Iterable, PyComparisonOp, Representable, SelfIter, Unconstructible,
+        Initializer, IterNext, Iterable, PyComparisonOp, Representable, SelfIter,
     },
     vm::VirtualMachine,
 };
@@ -848,7 +848,7 @@ macro_rules! dict_view {
             }
         }
 
-        #[pyclass(with(Unconstructible, IterNext, Iterable))]
+        #[pyclass(flags(DISALLOW_INSTANTIATION), with(IterNext, Iterable))]
         impl $iter_name {
             fn new(dict: PyDictRef) -> Self {
                 $iter_name {
@@ -878,8 +878,6 @@ macro_rules! dict_view {
             }
         }
 
-        impl Unconstructible for $iter_name {}
-
         impl SelfIter for $iter_name {}
         impl IterNext for $iter_name {
             #[allow(clippy::redundant_closure_call)]
@@ -923,7 +921,7 @@ macro_rules! dict_view {
             }
         }
 
-        #[pyclass(with(Unconstructible, IterNext, Iterable))]
+        #[pyclass(flags(DISALLOW_INSTANTIATION), with(IterNext, Iterable))]
         impl $reverse_iter_name {
             fn new(dict: PyDictRef) -> Self {
                 let size = dict.size();
@@ -957,8 +955,6 @@ macro_rules! dict_view {
                     .rev_length_hint(|_| self.size.entries_size)
             }
         }
-        impl Unconstructible for $reverse_iter_name {}
-
         impl SelfIter for $reverse_iter_name {}
         impl IterNext for $reverse_iter_name {
             #[allow(clippy::redundant_closure_call)]
@@ -1126,16 +1122,18 @@ trait ViewSetOps: DictView {
 }
 
 impl ViewSetOps for PyDictKeys {}
-#[pyclass(with(
-    DictView,
-    Unconstructible,
-    Comparable,
-    Iterable,
-    ViewSetOps,
-    AsSequence,
-    AsNumber,
-    Representable
-))]
+#[pyclass(
+    flags(DISALLOW_INSTANTIATION),
+    with(
+        DictView,
+        Comparable,
+        Iterable,
+        ViewSetOps,
+        AsSequence,
+        AsNumber,
+        Representable
+    )
+)]
 impl PyDictKeys {
     #[pymethod]
     fn __contains__(zelf: PyObjectRef, key: PyObjectRef, vm: &VirtualMachine) -> PyResult<bool> {
@@ -1147,7 +1145,6 @@ impl PyDictKeys {
         PyMappingProxy::from(zelf.dict().clone())
     }
 }
-impl Unconstructible for PyDictKeys {}
 
 impl Comparable for PyDictKeys {
     fn cmp(
@@ -1190,16 +1187,18 @@ impl AsNumber for PyDictKeys {
 }
 
 impl ViewSetOps for PyDictItems {}
-#[pyclass(with(
-    DictView,
-    Unconstructible,
-    Comparable,
-    Iterable,
-    ViewSetOps,
-    AsSequence,
-    AsNumber,
-    Representable
-))]
+#[pyclass(
+    flags(DISALLOW_INSTANTIATION),
+    with(
+        DictView,
+        Comparable,
+        Iterable,
+        ViewSetOps,
+        AsSequence,
+        AsNumber,
+        Representable
+    )
+)]
 impl PyDictItems {
     #[pymethod]
     fn __contains__(zelf: PyObjectRef, needle: PyObjectRef, vm: &VirtualMachine) -> PyResult<bool> {
@@ -1210,7 +1209,6 @@ impl PyDictItems {
         PyMappingProxy::from(zelf.dict().clone())
     }
 }
-impl Unconstructible for PyDictItems {}
 
 impl Comparable for PyDictItems {
     fn cmp(
@@ -1264,14 +1262,16 @@ impl AsNumber for PyDictItems {
     }
 }
 
-#[pyclass(with(DictView, Unconstructible, Iterable, AsSequence, Representable))]
+#[pyclass(
+    flags(DISALLOW_INSTANTIATION),
+    with(DictView, Iterable, AsSequence, Representable)
+)]
 impl PyDictValues {
     #[pygetset]
     fn mapping(zelf: PyRef<Self>) -> PyMappingProxy {
         PyMappingProxy::from(zelf.dict().clone())
     }
 }
-impl Unconstructible for PyDictValues {}
 
 impl AsSequence for PyDictValues {
     fn as_sequence() -> &'static PySequenceMethods {

crates/vm/src/builtins/frame.rs

@@ -8,7 +8,7 @@ use crate::{
     class::PyClassImpl,
     frame::{Frame, FrameRef},
     function::PySetterValue,
-    types::{Representable, Unconstructible},
+    types::Representable,
 };
 use num_traits::Zero;
 
@@ -16,8 +16,6 @@ pub fn init(context: &Context) {
     Frame::extend_class(context, context.types.frame_type);
 }
 
-impl Unconstructible for Frame {}
-
 impl Representable for Frame {
     #[inline]
     fn repr(_zelf: &Py<Self>, vm: &VirtualMachine) -> PyResult<PyStrRef> {
@@ -31,7 +29,7 @@ impl Representable for Frame {
     }
 }
 
-#[pyclass(with(Unconstructible, Py))]
+#[pyclass(flags(DISALLOW_INSTANTIATION), with(Py))]
 impl Frame {
     #[pymethod]
     const fn clear(&self) {

crates/vm/src/builtins/generator.rs

@@ -10,7 +10,7 @@ use crate::{
     frame::FrameRef,
     function::OptionalArg,
     protocol::PyIterReturn,
-    types::{IterNext, Iterable, Representable, SelfIter, Unconstructible},
+    types::{IterNext, Iterable, Representable, SelfIter},
 };
 
 #[pyclass(module = false, name = "generator")]
@@ -26,7 +26,7 @@ impl PyPayload for PyGenerator {
     }
 }
 
-#[pyclass(with(Py, Unconstructible, IterNext, Iterable))]
+#[pyclass(flags(DISALLOW_INSTANTIATION), with(Py, IterNext, Iterable))]
 impl PyGenerator {
     pub const fn as_coro(&self) -> &Coro {
         &self.inner
@@ -114,8 +114,6 @@ impl Py<PyGenerator> {
     }
 }
 
-impl Unconstructible for PyGenerator {}
-
 impl Representable for PyGenerator {
     #[inline]
     fn repr_str(zelf: &Py<Self>, vm: &VirtualMachine) -> PyResult<String> {

crates/vm/src/builtins/getset.rs

@@ -7,7 +7,7 @@ use crate::{
     builtins::type_::PointerSlot,
     class::PyClassImpl,
     function::{IntoPyGetterFunc, IntoPySetterFunc, PyGetterFunc, PySetterFunc, PySetterValue},
-    types::{GetDescriptor, Unconstructible},
+    types::GetDescriptor,
 };
 
 #[pyclass(module = false, name = "getset_descriptor")]
@@ -96,7 +96,7 @@ impl PyGetSet {
     }
 }
 
-#[pyclass(with(GetDescriptor, Unconstructible))]
+#[pyclass(flags(DISALLOW_INSTANTIATION), with(GetDescriptor))]
 impl PyGetSet {
     // Descriptor methods
 
@@ -152,7 +152,6 @@ impl PyGetSet {
         Ok(unsafe { zelf.class.borrow_static() }.to_owned().into())
     }
 }
-impl Unconstructible for PyGetSet {}
 
 pub(crate) fn init(context: &Context) {
     PyGetSet::extend_class(context, context.types.getset_type);

crates/vm/src/builtins/list.rs

@@ -15,7 +15,7 @@ use crate::{
     sliceable::{SequenceIndex, SliceableSequenceMutOp, SliceableSequenceOp},
     types::{
         AsMapping, AsSequence, Comparable, Constructor, Initializer, IterNext, Iterable,
-        PyComparisonOp, Representable, SelfIter, Unconstructible,
+        PyComparisonOp, Representable, SelfIter,
     },
     utils::collection_repr,
     vm::VirtualMachine,
@@ -544,7 +544,7 @@ impl PyPayload for PyListIterator {
     }
 }
 
-#[pyclass(with(Unconstructible, IterNext, Iterable))]
+#[pyclass(flags(DISALLOW_INSTANTIATION), with(IterNext, Iterable))]
 impl PyListIterator {
     #[pymethod]
     fn __length_hint__(&self) -> usize {
@@ -565,7 +565,6 @@ impl PyListIterator {
             .builtins_iter_reduce(|x| x.clone().into(), vm)
     }
 }
-impl Unconstructible for PyListIterator {}
 
 impl SelfIter for PyListIterator {}
 impl IterNext for PyListIterator {
@@ -590,7 +589,7 @@ impl PyPayload for PyListReverseIterator {
     }
 }
 
-#[pyclass(with(Unconstructible, IterNext, Iterable))]
+#[pyclass(flags(DISALLOW_INSTANTIATION), with(IterNext, Iterable))]
 impl PyListReverseIterator {
     #[pymethod]
     fn __length_hint__(&self) -> usize {
@@ -611,7 +610,6 @@ impl PyListReverseIterator {
             .builtins_reversed_reduce(|x| x.clone().into(), vm)
     }
 }
-impl Unconstructible for PyListReverseIterator {}
 
 impl SelfIter for PyListReverseIterator {}
 impl IterNext for PyListReverseIterator {

crates/vm/src/builtins/memory.rs

@@ -23,7 +23,7 @@ use crate::{
     sliceable::SequenceIndexOp,
     types::{
         AsBuffer, AsMapping, AsSequence, Comparable, Constructor, Hashable, IterNext, Iterable,
-        PyComparisonOp, Representable, SelfIter, Unconstructible,
+        PyComparisonOp, Representable, SelfIter,
     },
 };
 use crossbeam_utils::atomic::AtomicCell;
@@ -1132,7 +1132,7 @@ impl PyPayload for PyMemoryViewIterator {
     }
 }
 
-#[pyclass(with(Unconstructible, IterNext, Iterable))]
+#[pyclass(flags(DISALLOW_INSTANTIATION), with(IterNext, Iterable))]
 impl PyMemoryViewIterator {
     #[pymethod]
     fn __reduce__(&self, vm: &VirtualMachine) -> PyTupleRef {
@@ -1141,7 +1141,6 @@ impl PyMemoryViewIterator {
             .builtins_iter_reduce(|x| x.clone().into(), vm)
     }
 }
-impl Unconstructible for PyMemoryViewIterator {}
 
 impl SelfIter for PyMemoryViewIterator {}
 impl IterNext for PyMemoryViewIterator {

crates/vm/src/builtins/range.rs

@@ -11,7 +11,7 @@ use crate::{
     protocol::{PyIterReturn, PyMappingMethods, PySequenceMethods},
     types::{
         AsMapping, AsSequence, Comparable, Hashable, IterNext, Iterable, PyComparisonOp,
-        Representable, SelfIter, Unconstructible,
+        Representable, SelfIter,
     },
 };
 use crossbeam_utils::atomic::AtomicCell;
@@ -548,7 +548,7 @@ impl PyPayload for PyLongRangeIterator {
     }
 }
 
-#[pyclass(with(Unconstructible, IterNext, Iterable))]
+#[pyclass(flags(DISALLOW_INSTANTIATION), with(IterNext, Iterable))]
 impl PyLongRangeIterator {
     #[pymethod]
     fn __length_hint__(&self) -> BigInt {
@@ -577,7 +577,6 @@ impl PyLongRangeIterator {
         )
     }
 }
-impl Unconstructible for PyLongRangeIterator {}
 
 impl SelfIter for PyLongRangeIterator {}
 impl IterNext for PyLongRangeIterator {
@@ -614,7 +613,7 @@ impl PyPayload for PyRangeIterator {
     }
 }
 
-#[pyclass(with(Unconstructible, IterNext, Iterable))]
+#[pyclass(flags(DISALLOW_INSTANTIATION), with(IterNext, Iterable))]
 impl PyRangeIterator {
     #[pymethod]
     fn __length_hint__(&self) -> usize {
@@ -640,7 +639,6 @@ impl PyRangeIterator {
         )
     }
 }
-impl Unconstructible for PyRangeIterator {}
 
 impl SelfIter for PyRangeIterator {}
 impl IterNext for PyRangeIterator {

crates/vm/src/builtins/set.rs

@@ -18,7 +18,7 @@ use crate::{
     types::AsNumber,
     types::{
         AsSequence, Comparable, Constructor, DefaultConstructor, Hashable, Initializer, IterNext,
-        Iterable, PyComparisonOp, Representable, SelfIter, Unconstructible,
+        Iterable, PyComparisonOp, Representable, SelfIter,
     },
     utils::collection_repr,
     vm::VirtualMachine,
@@ -1304,7 +1304,7 @@ impl PyPayload for PySetIterator {
     }
 }
 
-#[pyclass(with(Unconstructible, IterNext, Iterable))]
+#[pyclass(flags(DISALLOW_INSTANTIATION), with(IterNext, Iterable))]
 impl PySetIterator {
     #[pymethod]
     fn __length_hint__(&self) -> usize {
@@ -1330,7 +1330,6 @@ impl PySetIterator {
         ))
     }
 }
-impl Unconstructible for PySetIterator {}
 
 impl SelfIter for PySetIterator {}
 impl IterNext for PySetIterator {

crates/vm/src/builtins/str.rs

@@ -21,7 +21,7 @@ use crate::{
     sliceable::{SequenceIndex, SliceableSequenceOp},
     types::{
         AsMapping, AsNumber, AsSequence, Comparable, Constructor, Hashable, IterNext, Iterable,
-        PyComparisonOp, Representable, SelfIter, Unconstructible,
+        PyComparisonOp, Representable, SelfIter,
     },
 };
 use ascii::{AsciiChar, AsciiStr, AsciiString};
@@ -282,7 +282,7 @@ impl PyPayload for PyStrIterator {
     }
 }
 
-#[pyclass(with(Unconstructible, IterNext, Iterable))]
+#[pyclass(flags(DISALLOW_INSTANTIATION), with(IterNext, Iterable))]
 impl PyStrIterator {
     #[pymethod]
     fn __length_hint__(&self) -> usize {
@@ -307,8 +307,6 @@ impl PyStrIterator {
     }
 }
 
-impl Unconstructible for PyStrIterator {}
-
 impl SelfIter for PyStrIterator {}
 
 impl IterNext for PyStrIterator {

crates/vm/src/builtins/tuple.rs

@@ -16,7 +16,7 @@ use crate::{
     sliceable::{SequenceIndex, SliceableSequenceOp},
     types::{
         AsMapping, AsSequence, Comparable, Constructor, Hashable, IterNext, Iterable,
-        PyComparisonOp, Representable, SelfIter, Unconstructible,
+        PyComparisonOp, Representable, SelfIter,
     },
     utils::collection_repr,
     vm::VirtualMachine,
@@ -533,7 +533,7 @@ impl PyPayload for PyTupleIterator {
     }
 }
 
-#[pyclass(with(Unconstructible, IterNext, Iterable))]
+#[pyclass(flags(DISALLOW_INSTANTIATION), with(IterNext, Iterable))]
 impl PyTupleIterator {
     #[pymethod]
     fn __length_hint__(&self) -> usize {
@@ -554,7 +554,6 @@ impl PyTupleIterator {
             .builtins_iter_reduce(|x| x.clone().into(), vm)
     }
 }
-impl Unconstructible for PyTupleIterator {}
 
 impl SelfIter for PyTupleIterator {}
 impl IterNext for PyTupleIterator {

crates/vm/src/builtins/type.rs

@@ -191,13 +191,16 @@ impl PyType {
         name: &str,
         bases: Vec<PyRef<Self>>,
         attrs: PyAttributes,
-        slots: PyTypeSlots,
+        mut slots: PyTypeSlots,
         metaclass: PyRef<Self>,
         ctx: &Context,
     ) -> Result<PyRef<Self>, String> {
         // TODO: ensure clean slot name
         // assert_eq!(slots.name.borrow(), "");
 
+        // Set HEAPTYPE flag for heap-allocated types
+        slots.flags |= PyTypeFlags::HEAPTYPE;
+
         let name = ctx.new_str(name);
         let heaptype_ext = HeapTypeExt {
             name: PyRwLock::new(name.clone()),
@@ -401,6 +404,8 @@ impl PyType {
             None,
         );
 
+        Self::set_new(&new_type.slots, &new_type.base);
+
         let weakref_type = super::PyWeak::static_type();
         for base in new_type.bases.read().iter() {
             base.subclasses.write().push(
@@ -420,9 +425,6 @@ impl PyType {
 
         for cls in self.mro.read().iter() {
             for &name in cls.attributes.read().keys() {
-                if name == identifier!(ctx, __new__) {
-                    continue;
-                }
                 if name.as_bytes().starts_with(b"__") && name.as_bytes().ends_with(b"__") {
                     slot_name_set.insert(name);
                 }
@@ -436,6 +438,20 @@ impl PyType {
         for attr_name in slot_name_set {
             self.update_slot::<true>(attr_name, ctx);
         }
+
+        Self::set_new(&self.slots, &self.base);
+    }
+
+    fn set_new(slots: &PyTypeSlots, base: &Option<PyTypeRef>) {
+        if slots.flags.contains(PyTypeFlags::DISALLOW_INSTANTIATION) {
+            slots.new.store(None)
+        } else if slots.new.load().is_none() {
+            slots.new.store(
+                base.as_ref()
+                    .map(|base| base.slots.new.load())
+                    .unwrap_or(None),
+            )
+        }
     }
 
     // This is used for class initialization where the vm is not yet available.
@@ -1563,15 +1579,28 @@ impl Callable for PyType {
     type Args = FuncArgs;
     fn call(zelf: &Py<Self>, args: FuncArgs, vm: &VirtualMachine) -> PyResult {
         vm_trace!("type_call: {:?}", zelf);
-        let obj = call_slot_new(zelf.to_owned(), zelf.to_owned(), args.clone(), vm)?;
 
-        if (zelf.is(vm.ctx.types.type_type) && args.kwargs.is_empty()) || !obj.fast_isinstance(zelf)
-        {
+        if zelf.is(vm.ctx.types.type_type) {
+            let num_args = args.args.len();
+            if num_args == 1 && args.kwargs.is_empty() {
+                return Ok(args.args[0].obj_type());
+            }
+            if num_args != 3 {
+                return Err(vm.new_type_error("type() takes 1 or 3 arguments".to_owned()));
+            }
+        }
+
+        let obj = if let Some(slot_new) = zelf.slots.new.load() {
+            slot_new(zelf.to_owned(), args.clone(), vm)?
+        } else {
+            return Err(vm.new_type_error(format!("cannot create '{}' instances", zelf.slots.name)));
+        };
+
+        if !obj.class().fast_issubclass(zelf) {
             return Ok(obj);
         }
 
-        let init = obj.class().mro_find_map(|cls| cls.slots.init.load());
-        if let Some(init_method) = init {
+        if let Some(init_method) = obj.class().slots.init.load() {
             init_method(obj.clone(), args, vm)?;
         }
         Ok(obj)
@@ -1700,6 +1729,40 @@ pub(crate) fn call_slot_new(
     args: FuncArgs,
     vm: &VirtualMachine,
 ) -> PyResult {
+    // Check DISALLOW_INSTANTIATION flag on subtype (the type being instantiated)
+    if subtype
+        .slots
+        .flags
+        .has_feature(PyTypeFlags::DISALLOW_INSTANTIATION)
+    {
+        return Err(vm.new_type_error(format!("cannot create '{}' instances", subtype.slot_name())));
+    }
+
+    // "is not safe" check (tp_new_wrapper logic)
+    // Check that the user doesn't do something silly and unsafe like
+    // object.__new__(dict). To do this, we check that the most derived base
+    // that's not a heap type is this type.
+    let mut staticbase = subtype.clone();
+    while staticbase.slots.flags.has_feature(PyTypeFlags::HEAPTYPE) {
+        if let Some(base) = staticbase.base.as_ref() {
+            staticbase = base.clone();
+        } else {
+            break;
+        }
+    }
+
+    // Check if staticbase's tp_new differs from typ's tp_new
+    let typ_new = typ.slots.new.load();
+    let staticbase_new = staticbase.slots.new.load();
+    if typ_new.map(|f| f as usize) != staticbase_new.map(|f| f as usize) {
+        return Err(vm.new_type_error(format!(
+            "{}.__new__({}) is not safe, use {}.__new__()",
+            typ.slot_name(),
+            subtype.slot_name(),
+            staticbase.slot_name()
+        )));
+    }
+
     let slot_new = typ
         .deref()
         .mro_find_map(|cls| cls.slots.new.load())

crates/vm/src/class.rs

@@ -116,13 +116,23 @@ pub trait PyClassImpl: PyClassDef {
             );
         }
 
-        if class.slots.new.load().is_some() {
-            let bound_new = Context::genesis().slot_new_wrapper.build_bound_method(
-                ctx,
-                class.to_owned().into(),
-                class,
-            );
-            class.set_attr(identifier!(ctx, __new__), bound_new.into());
+        // Don't add __new__ attribute if slot_new is inherited from object
+        // (Python doesn't add __new__ to __dict__ for inherited slots)
+        // Exception: object itself should have __new__ in its dict
+        if let Some(slot_new) = class.slots.new.load() {
+            let object_new = ctx.types.object_type.slots.new.load();
+            let is_object_itself = std::ptr::eq(class, ctx.types.object_type);
+            let is_inherited_from_object = !is_object_itself
+                && object_new.is_some_and(|obj_new| slot_new as usize == obj_new as usize);
+
+            if !is_inherited_from_object {
+                let bound_new = Context::genesis().slot_new_wrapper.build_bound_method(
+                    ctx,
+                    class.to_owned().into(),
+                    class,
+                );
+                class.set_attr(identifier!(ctx, __new__), bound_new.into());
+            }
         }
 
         if class.slots.hash.load().map_or(0, |h| h as usize) == hash_not_implemented as usize {

crates/vm/src/protocol/buffer.rs

@@ -9,7 +9,6 @@ use crate::{
     },
     object::PyObjectPayload,
     sliceable::SequenceIndexOp,
-    types::Unconstructible,
 };
 use itertools::Itertools;
 use std::{borrow::Cow, fmt::Debug, ops::Range};
@@ -402,7 +401,7 @@ pub struct VecBuffer {
     data: PyMutex<Vec<u8>>,
 }
 
-#[pyclass(flags(BASETYPE), with(Unconstructible))]
+#[pyclass(flags(BASETYPE, DISALLOW_INSTANTIATION))]
 impl VecBuffer {
     pub fn take(&self) -> Vec<u8> {
         std::mem::take(&mut self.data.lock())
@@ -417,8 +416,6 @@ impl From<Vec<u8>> for VecBuffer {
     }
 }
 
-impl Unconstructible for VecBuffer {}
-
 impl PyRef<VecBuffer> {
     pub fn into_pybuffer(self, readonly: bool) -> PyBuffer {
         let len = self.data.lock().len();

crates/vm/src/stdlib/ctypes/field.rs

@@ -1,6 +1,6 @@
 use crate::builtins::PyType;
 use crate::function::PySetterValue;
-use crate::types::{GetDescriptor, Representable, Unconstructible};
+use crate::types::{GetDescriptor, Representable};
 use crate::{AsObject, Py, PyObjectRef, PyResult, VirtualMachine};
 use num_traits::ToPrimitive;
 
@@ -85,8 +85,6 @@ impl Representable for PyCField {
     }
 }
 
-impl Unconstructible for PyCField {}
-
 impl GetDescriptor for PyCField {
     fn descr_get(
         zelf: PyObjectRef,
@@ -184,7 +182,7 @@ impl PyCField {
 
 #[pyclass(
     flags(DISALLOW_INSTANTIATION, IMMUTABLETYPE),
-    with(Unconstructible, Representable, GetDescriptor)
+    with(Representable, GetDescriptor)
 )]
 impl PyCField {
     #[pyslot]

crates/vm/src/stdlib/os.rs

@@ -167,7 +167,7 @@ pub(super) mod _os {
         ospath::{OsPath, OsPathOrFd, OutputMode},
         protocol::PyIterReturn,
         recursion::ReprGuard,
-        types::{IterNext, Iterable, PyStructSequence, Representable, SelfIter, Unconstructible},
+        types::{IterNext, Iterable, PyStructSequence, Representable, SelfIter},
         utils::ToCString,
         vm::VirtualMachine,
     };
@@ -570,7 +570,7 @@ pub(super) mod _os {
         ino: AtomicCell<Option<u64>>,
     }
 
-    #[pyclass(with(Representable, Unconstructible))]
+    #[pyclass(flags(DISALLOW_INSTANTIATION), with(Representable))]
     impl DirEntry {
         #[pygetset]
         fn name(&self, vm: &VirtualMachine) -> PyResult {
@@ -760,8 +760,6 @@ pub(super) mod _os {
             }
         }
     }
-    impl Unconstructible for DirEntry {}
-
     #[pyattr]
     #[pyclass(name = "ScandirIter")]
     #[derive(Debug, PyPayload)]
@@ -770,7 +768,7 @@ pub(super) mod _os {
         mode: OutputMode,
     }
 
-    #[pyclass(with(IterNext, Iterable, Unconstructible))]
+    #[pyclass(flags(DISALLOW_INSTANTIATION), with(IterNext, Iterable))]
     impl ScandirIterator {
         #[pymethod]
         fn close(&self) {
@@ -788,7 +786,6 @@ pub(super) mod _os {
             zelf.close()
         }
     }
-    impl Unconstructible for ScandirIterator {}
     impl SelfIter for ScandirIterator {}
     impl IterNext for ScandirIterator {
         fn next(zelf: &crate::Py<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {

crates/vm/src/types/slot.rs

@@ -922,15 +922,6 @@ pub trait DefaultConstructor: PyPayload + Default + std::fmt::Debug {
     }
 }
 
-/// For types that cannot be instantiated through Python code.
-#[pyclass]
-pub trait Unconstructible: PyPayload {
-    #[pyslot]
-    fn slot_new(cls: PyTypeRef, _args: FuncArgs, vm: &VirtualMachine) -> PyResult {
-        Err(vm.new_type_error(format!("cannot create '{}' instances", cls.slot_name())))
-    }
-}
-
 impl<T> Constructor for T
 where
     T: DefaultConstructor,