Fix dealloc implementation to collectly use subtype's tp_free

CHANGELOG.md

@@ -33,7 +33,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ### Fixed
 - Fix passing explicit `None` to `Option<T>` argument `#[pyfunction]` with a default value. [#936](https://github.com/PyO3/pyo3/pull/936)
-- Fix `PyClass.__new__`'s behavior when inherited by a Python class. [#990](https://github.com/PyO3/pyo3/pull/990)
+- Fix `PyClass.__new__`'s not respecting subclasses when inherited by a Python class. [#990](https://github.com/PyO3/pyo3/pull/990)
 
 ## [0.10.1] - 2020-05-14
 ### Fixed

examples/rustapi_module/tests/test_subclassing.py

@@ -7,10 +7,11 @@
 
 class SomeSubClass(Subclassable):
     def __str__(self):
-        return "Subclass"
+        return "SomeSubclass"
 
 
 def test_subclassing():
     if not PYPY:
         a = SomeSubClass()
-        assert str(a) == "Subclass"
+        assert str(a) == "SomeSubclass"
+        assert type(a) is SomeSubClass

pyo3-derive-backend/src/pymethod.rs

@@ -193,7 +193,7 @@ pub fn impl_wrap_new(cls: &syn::Type, spec: &FnSpec<'_>) -> TokenStream {
     quote! {
         #[allow(unused_mut)]
         unsafe extern "C" fn __wrap(
-            subcls: *mut pyo3::ffi::PyTypeObject,
+            subtype: *mut pyo3::ffi::PyTypeObject,
             _args: *mut pyo3::ffi::PyObject,
             _kwargs: *mut pyo3::ffi::PyObject) -> *mut pyo3::ffi::PyObject
         {
@@ -206,7 +206,7 @@ pub fn impl_wrap_new(cls: &syn::Type, spec: &FnSpec<'_>) -> TokenStream {
 
                 let _result = pyo3::derive_utils::IntoPyNewResult::into_pynew_result(#body)?;
                 let initializer = pyo3::PyClassInitializer::from(_result);
-                let cell = initializer.create_cell_from_subtype(_py, subcls)?;
+                let cell = initializer.create_cell_from_subtype(_py, subtype)?;
                 Ok(cell as *mut pyo3::ffi::PyObject)
             })
         }

src/freelist.rs

@@ -2,10 +2,9 @@
 
 //! Free allocation list
 
-use crate::ffi;
 use crate::pyclass::{tp_free_fallback, PyClassAlloc};
 use crate::type_object::{PyLayout, PyTypeInfo};
-use crate::Python;
+use crate::{ffi, AsPyPointer, FromPyPointer, PyAny, Python};
 use std::mem;
 use std::os::raw::c_void;
 
@@ -86,14 +85,15 @@ where
 
     unsafe fn dealloc(py: Python, self_: *mut Self::Layout) {
         (*self_).py_drop(py);
-
-        let obj = self_ as _;
-        if ffi::PyObject_CallFinalizerFromDealloc(obj) < 0 {
+        let obj = PyAny::from_borrowed_ptr_or_panic(py, self_ as _);
+        if Self::is_exact_instance(obj) && ffi::PyObject_CallFinalizerFromDealloc(obj.as_ptr()) < 0
+        {
+            // tp_finalize resurrected.
             return;
         }
 
-        if let Some(obj) = <Self as PyClassWithFreeList>::get_free_list().insert(obj) {
-            match Self::type_object_raw(py).tp_free {
+        if let Some(obj) = <Self as PyClassWithFreeList>::get_free_list().insert(obj.as_ptr()) {
+            match (*ffi::Py_TYPE(obj)).tp_free {
                 Some(free) => free(obj as *mut c_void),
                 None => tp_free_fallback(obj),
             }

src/instance.rs

@@ -59,7 +59,7 @@ where
         T::BaseLayout: PyBorrowFlagLayout<T::BaseType>,
     {
         let initializer = value.into();
-        let obj = unsafe { initializer.create_cell(py)? };
+        let obj = initializer.create_cell(py)?;
         let ob = unsafe { Py::from_owned_ptr(py, obj as _) };
         Ok(ob)
     }

src/pyclass.rs

@@ -1,10 +1,10 @@
 //! `PyClass` trait
 use crate::class::methods::{PyClassAttributeDef, PyMethodDefType, PyMethods};
 use crate::class::proto_methods::PyProtoMethods;
-use crate::conversion::{IntoPyPointer, ToPyObject};
+use crate::conversion::{AsPyPointer, FromPyPointer, IntoPyPointer, ToPyObject};
 use crate::pyclass_slots::{PyClassDict, PyClassWeakRef};
 use crate::type_object::{type_flags, PyLayout};
-use crate::types::PyDict;
+use crate::types::{PyAny, PyDict};
 use crate::{class, ffi, PyCell, PyErr, PyNativeType, PyResult, PyTypeInfo, Python};
 use std::ffi::CString;
 use std::os::raw::c_void;
@@ -42,14 +42,16 @@ pub trait PyClassAlloc: PyTypeInfo + Sized {
     /// `self_` must be a valid pointer to the Python heap.
     unsafe fn dealloc(py: Python, self_: *mut Self::Layout) {
         (*self_).py_drop(py);
-        let obj = self_ as _;
-        if ffi::PyObject_CallFinalizerFromDealloc(obj) < 0 {
+        let obj = PyAny::from_borrowed_ptr_or_panic(py, self_ as _);
+        if Self::is_exact_instance(obj) && ffi::PyObject_CallFinalizerFromDealloc(obj.as_ptr()) < 0
+        {
+            // tp_finalize resurrected.
             return;
         }
 
-        match Self::type_object_raw(py).tp_free {
-            Some(free) => free(obj as *mut c_void),
-            None => tp_free_fallback(obj),
+        match (*ffi::Py_TYPE(obj.as_ptr())).tp_free {
+            Some(free) => free(obj.as_ptr() as *mut c_void),
+            None => tp_free_fallback(obj.as_ptr()),
         }
     }
 }
@@ -66,8 +68,7 @@ fn tp_dealloc<T: PyClassAlloc>() -> Option<ffi::destructor> {
     Some(dealloc::<T>)
 }
 
-#[doc(hidden)]
-pub unsafe fn tp_free_fallback(obj: *mut ffi::PyObject) {
+pub(crate) unsafe fn tp_free_fallback(obj: *mut ffi::PyObject) {
     let ty = ffi::Py_TYPE(obj);
     if ffi::PyType_IS_GC(ty) != 0 {
         ffi::PyObject_GC_Del(obj as *mut c_void);

src/pyclass_init.rs

@@ -115,16 +115,19 @@ impl<T: PyClass> PyClassInitializer<T> {
     }
 
     // Create a new PyCell and initialize it.
-    pub(crate) unsafe fn create_cell(self, py: Python) -> PyResult<*mut PyCell<T>>
+    pub(crate) fn create_cell(self, py: Python) -> PyResult<*mut PyCell<T>>
     where
         T: PyClass,
         T::BaseLayout: PyBorrowFlagLayout<T::BaseType>,
     {
-        self.create_cell_from_subtype(py, T::type_object_raw(py) as *const _ as _)
+        unsafe { self.create_cell_from_subtype(py, T::type_object_raw(py) as *const _ as _) }
     }
 
     /// Create a new PyCell and initialize it given a typeobject `subtype`.
     /// Called by our `tp_new` generated by the `#[new]` attribute.
+    ///
+    /// # Safety
+    /// `cls` must be a subclass of T.
     pub unsafe fn create_cell_from_subtype(
         self,
         py: Python,