gh-101408: PyObject_GC_Resize should calculate preheader size.

[corona10]

• Issue: PyObject_GC_Resize doesn't check preheader size #101408

[corona10]

@pablogsal @colesbury Can you please take a look?

[colesbury]

This LGTM!

Minor: I don't think this needs backport to 3.10 or 3.11. I think the preheader feature was introduced in 3.12.

[corona10]

This LGTM!

Thank you, I will wait for the @pablogsal review too :)

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @corona10 for commit a09708c 🤖

If you want to schedule another build, you need to add the :hammer: test-with-refleak-buildbots label again.

[corona10]

The refleak is not related to this PR, I am finding out the which PR cause the leak.

[pablogsal]

Thanks a lot for tacking this @corona10 and thanks for the catch @colesbury!

I would be more comfortable if we could have a test in testcapi that uses this API, among other things so we don't regress in the future if we keep changing things.

[corona10]

I would be more comfortable if we could have a test in testcapi that uses this API, among other things so we don't regress in the future if we keep changing things.

Okay, I will finalize the PR by end of this weekend. :)

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @corona10 for commit 27566ab 🤖

If you want to schedule another build, you need to add the :hammer: test-with-refleak-buildbots label again.

[corona10]

@pablogsal

Hi Pablo, I succeeded in adding the test code for the normal PyObject_GC_Resize case.
But looks hard to create the test code for Py_TPFLAGS_PREHEADER.
Do you have any recommended way for this case?

static PyObject *
test_pyobject_gc(PyObject *self, PyObject *Py_UNUSED(ignored))
{
    PyTupleObject *obj = PyObject_GC_NewVar(PyTupleObject, &PyTuple_Type, 3);
    obj->ob_item[0] = Py_NewRef(Py_None);
    obj->ob_item[1] = Py_NewRef(Py_None);
    obj->ob_item[2] = Py_NewRef(Py_None);

    if (obj == NULL) {
        goto alloc_failed;
    }
    if (Py_SIZE(obj) != 3) {
        Py_DECREF(obj);
        PyErr_SetString(PyExc_RuntimeError, "Invalid Py_SIZE(obj)");
        return NULL;
    }

    PyTupleObject *new_obj = PyObject_GC_Resize(PyTupleObject, obj, 6);
    if (new_obj == NULL) {
        Py_DECREF(obj);
        goto alloc_failed;
    }

    new_obj->ob_item[3] = Py_NewRef(Py_None);
    new_obj->ob_item[4] = Py_NewRef(Py_None);
    new_obj->ob_item[5] = Py_NewRef(Py_None);
    if (Py_SIZE(new_obj) != 6) {
        Py_DECREF(new_obj);
        PyErr_SetString(PyExc_RuntimeError, "Invalid Py_SIZE(new_obj)");
        return NULL;
    }

    Py_DECREF(new_obj);
    Py_RETURN_NONE;

alloc_failed:
    PyErr_NoMemory();
    return NULL;
}

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @corona10 for commit 896c5ba 🤖

If you want to schedule another build, you need to add the 🔨 test-with-refleak-buildbots label again.

[corona10]

@pablogsal I think that this PR should be merged before 3.12 is officially released, I will let the issue as opened for test code and merging this PR.

[vstinner]

No one wrote code since April, maybe it's time to abandon the idea of having tests and just close the issue?