GH-92678: Fix tp_dictoffset inheritance. (GH-95596)

* Add test for inheriting explicit __dict__ and weakref.

* Restore 3.10 behavior for multiple inheritance of C extension classes that store their dictionary at the end of the struct.

1 files changed, 28 insertions, 0 deletions

diff --git a/Modules/_testcapi/heaptype.c b/Modules/_testcapi/heaptype.c
index 9fb0051..12889e8 100644
--- a/Modules/_testcapi/heaptype.c
+++ b/Modules/_testcapi/heaptype.c
@@ -737,6 +737,14 @@ static PyType_Spec HeapCTypeWithDict_spec = {
     HeapCTypeWithDict_slots
 };
 
+static PyType_Spec HeapCTypeWithDict2_spec = {
+    "_testcapi.HeapCTypeWithDict2",
+    sizeof(HeapCTypeWithDictObject),
+    0,
+    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
+    HeapCTypeWithDict_slots
+};
+
 static struct PyMemberDef heapctypewithnegativedict_members[] = {
     {"dictobj", T_OBJECT, offsetof(HeapCTypeWithDictObject, dict)},
     {"__dictoffset__", T_PYSSIZET, -(Py_ssize_t)sizeof(void*), READONLY},
@@ -796,6 +804,14 @@ static PyType_Spec HeapCTypeWithWeakref_spec = {
     HeapCTypeWithWeakref_slots
 };
 
+static PyType_Spec HeapCTypeWithWeakref2_spec = {
+    "_testcapi.HeapCTypeWithWeakref2",
+    sizeof(HeapCTypeWithWeakrefObject),
+    0,
+    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
+    HeapCTypeWithWeakref_slots
+};
+
 PyDoc_STRVAR(heapctypesetattr__doc__,
 "A heap type without GC, but with overridden __setattr__.\n\n"
 "The 'value' attribute is set to 10 in __init__ and updated via attribute setting.");
@@ -919,6 +935,12 @@ _PyTestCapi_Init_Heaptype(PyObject *m) {
     }
     PyModule_AddObject(m, "HeapCTypeWithDict", HeapCTypeWithDict);
 
+    PyObject *HeapCTypeWithDict2 = PyType_FromSpec(&HeapCTypeWithDict2_spec);
+    if (HeapCTypeWithDict2 == NULL) {
+        return -1;
+    }
+    PyModule_AddObject(m, "HeapCTypeWithDict2", HeapCTypeWithDict2);
+
     PyObject *HeapCTypeWithNegativeDict = PyType_FromSpec(&HeapCTypeWithNegativeDict_spec);
     if (HeapCTypeWithNegativeDict == NULL) {
         return -1;
@@ -931,6 +953,12 @@ _PyTestCapi_Init_Heaptype(PyObject *m) {
     }
     PyModule_AddObject(m, "HeapCTypeWithWeakref", HeapCTypeWithWeakref);
 
+    PyObject *HeapCTypeWithWeakref2 = PyType_FromSpec(&HeapCTypeWithWeakref2_spec);
+    if (HeapCTypeWithWeakref2 == NULL) {
+        return -1;
+    }
+    PyModule_AddObject(m, "HeapCTypeWithWeakref2", HeapCTypeWithWeakref2);
+
     PyObject *HeapCTypeWithBuffer = PyType_FromSpec(&HeapCTypeWithBuffer_spec);
     if (HeapCTypeWithBuffer == NULL) {
         return -1;