PyObject_GC_Resize doesn't check preheader size

[colesbury]

The PyObject_GC_Resize implementation in the main branch doesn't check if the object has a preheader:

cpython/Modules/gcmodule.c

Lines 2357 to 2358 in 0ef92d9

	PyGC_Head *g = AS_GC(op);
	g = (PyGC_Head *)PyObject_Realloc(g, sizeof(PyGC_Head) + basicsize);

The only internal use I see is by _PyTuple_Resize which doesn't have a preheader, but the PyObject_GC_Resize function is publicly documented.

Linked PRs

• gh-101408: PyObject_GC_Resize should calculate preheader size. #101741

[corona10]

@colesbury Patch is merged, but I left the issue open for the test code.

[erlend-aasland]

@corona10: what is the status on test code? 😄

[corona10]

@erlend-aasland Nah, let's close the issue until it needs (no bandwidth to work with these days)