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gh-94731: Revert to C-style casts for _Py_CAST #94782

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Merged
encukou merged 8 commits into from
Jul 14, 2022
Merged

gh-94731: Revert to C-style casts for _Py_CAST #94782

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f09b8c6
gh-94731: Add a failing test
encukou Jul 12, 2022
3faf13d
gh-94731: Use C-style casts for _Py_CAST, even in C++
encukou Jul 12, 2022
b3b4ec8
Add a blurb
encukou Jul 12, 2022
498e8bb
Also allow the -Wzero-as-null-pointer-constant warning
encukou Jul 12, 2022
b13e464
Workaround for C++ compilers that don't support designated initializers
encukou Jul 13, 2022
c6945f1
Rename the type variable (ipotype was a hold-over from the original r…
encukou Jul 13, 2022
713bf7d
Punt on C++ sanitizing builds for now
encukou Jul 13, 2022
021c03d
Make the skip work if PY_CFLAGS is not set
encukou Jul 13, 2022
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gh-94731: Add a failing test 
Co-Authored-By: da-woods <dw-git@d-woods.co.uk>
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@encukou @da-woods
encukou and da-woods committed Jul 12, 2022
commit f09b8c638bf07a3bfa605d62baa4fa18a47a848e
75 changes: 72 additions & 3 deletions Lib/test/_testcppext.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -12,6 +12,9 @@
# define NAME _testcpp03ext
#endif

#define _STR(NAME) #NAME
#define STR(NAME) _STR(NAME)

PyDoc_STRVAR(_testcppext_add_doc,
"add(x, y)\n"
"\n"
Expand Down Expand Up @@ -123,11 +126,76 @@ test_unicode(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
Py_RETURN_NONE;
}

/* Test a `new`-allocated object with a virtual method.
* (https://github.com/python/cpython/issues/94731) */

class VirtualPyObject : public PyObject {
public:
VirtualPyObject();
virtual ~VirtualPyObject() {
delete [] internal_data;
--instance_count;
}
virtual void set_internal_data() {
internal_data[0] = 1;
}
static void dealloc(PyObject* o) {
delete static_cast<VirtualPyObject*>(o);
}

// Number of "living" instances
static int instance_count;
private:
// buffer that can get corrupted
int* internal_data;
};

int VirtualPyObject::instance_count = 0;

PyType_Slot VirtualPyObject_Slots[] = {
{Py_tp_free, (void*)VirtualPyObject::dealloc},
{0, _Py_NULL},
};

PyType_Spec VirtualPyObject_Spec = {
.name = STR(NAME) ".VirtualPyObject",
.basicsize = sizeof(VirtualPyObject),
.flags = Py_TPFLAGS_DEFAULT,
.slots = VirtualPyObject_Slots,
};

VirtualPyObject::VirtualPyObject() {
// Create a temporary type (just so we don't need to store it)
PyObject *ipotype = PyType_FromSpec(&VirtualPyObject_Spec);
// no good way to signal failure from a C++ constructor, so use assert
// for error handling
assert(ipotype);
assert(PyObject_Init(this, (PyTypeObject *)ipotype));
Py_DECREF(ipotype);

@da-woods da-woods Jul 13, 2022

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Suggested change
PyObject *ipotype = PyType_FromSpec(&VirtualPyObject_Spec);
// no good way to signal failure from a C++ constructor, so use assert
// for error handling
assert(ipotype);
assert(PyObject_Init(this, (PyTypeObject *)ipotype));
Py_DECREF(ipotype);
PyObject *vpotype = PyType_FromSpec(&VirtualPyObject_Spec);
// no good way to signal failure from a C++ constructor, so use assert
// for error handling
assert(vpotype);
assert(PyObject_Init(this, (PyTypeObject *)vpotype));
Py_DECREF(vpotype);

Just suggesting changing the name slightly here to match the name you used from the class. I think the i from ipotype was a hold-over from the name I used.

@encukou encukou Jul 13, 2022

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Thanks! It's a local variable now so I'll just name it type :)

internal_data = new int[50];
++instance_count;
}

static PyObject *
test_virtual_object(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
{
VirtualPyObject* obj = new VirtualPyObject();
obj->set_internal_data();
Py_DECREF(obj);
if (VirtualPyObject::instance_count != 0) {
return PyErr_Format(
PyExc_AssertionError,
"instance_count should be 0, got %d",
VirtualPyObject::instance_count);
}
Py_RETURN_NONE;
}

static PyMethodDef _testcppext_methods[] = {
{"add", _testcppext_add, METH_VARARGS, _testcppext_add_doc},
{"test_api_casts", test_api_casts, METH_NOARGS, _Py_NULL},
{"test_unicode", test_unicode, METH_NOARGS, _Py_NULL},
{"test_virtual_object", test_virtual_object, METH_NOARGS, _Py_NULL},
// Note: _testcppext_exec currently runs all test functions directly.
// When adding a new one, add a call there.

Expand All @@ -152,6 +220,10 @@ _testcppext_exec(PyObject *module)
if (!result) return -1;
Py_DECREF(result);

result = PyObject_CallMethod(module, "test_virtual_object", "");
if (!result) return -1;
Py_DECREF(result);

return 0;
}

Expand All @@ -163,9 +235,6 @@ static PyModuleDef_Slot _testcppext_slots[] = {

PyDoc_STRVAR(_testcppext_doc, "C++ test extension.");

#define _STR(NAME) #NAME
#define STR(NAME) _STR(NAME)

static struct PyModuleDef _testcppext_module = {
PyModuleDef_HEAD_INIT, // m_base
STR(NAME), // m_name
Expand Down