metaclass-wo-basicsize-issue

metaclass-issue.c

#include <Python.h>
#include <structmember.h>

typedef struct {
    PyHeapTypeObject super;
    int meta_magic;
    int meta_member;
    char some_more[64];
} DummyMeta;

static PyTypeObject DummyMetaType = {
    PyVarObject_HEAD_INIT(&PyType_Type, 0)
    .tp_base = &PyType_Type,
    .tp_name = "mytest.DummyMeta",
    .tp_basicsize = sizeof(DummyMeta),
    .tp_flags = Py_TPFLAGS_DEFAULT,
};

typedef struct {
    PyObject_HEAD
    int member;
} DummyData;

static PyMemberDef members[] = {
        {"member", T_INT, offsetof(DummyData, member), 0, NULL},
        {NULL, 0, 0, 0, NULL},
};

static PyTypeObject DummyType = {
    PyVarObject_HEAD_INIT(&PyType_Type, 0)
    .tp_base = &PyType_Type,
    .tp_name = "mytest.Dummy",
    .tp_basicsize = sizeof(DummyData),
    .tp_flags = Py_TPFLAGS_DEFAULT,
    .tp_members = members,
};

// ...
// In module initialization:
if (PyType_Ready(&DummyMetaType))
    return;

Py_TYPE(&DummyType) = &DummyMetaType;
if (PyType_Ready(&DummyType))
    return;
// fails on Assertion `t_size >= b_size' failed on Python 3.8.5