bpo-33583: Add note in PyObject_GC_Resize() doc (GH-7021)
(cherry picked from commit 1179f4b40f375af5c59cd4b6be9cc313fa0e1a37)
Co-authored-by: INADA Naoki <methane@users.noreply.github.com>
diff --git a/Doc/c-api/gcsupport.rst b/Doc/c-api/gcsupport.rst
index 9438fea..18ecd07 100644
--- a/Doc/c-api/gcsupport.rst
+++ b/Doc/c-api/gcsupport.rst
@@ -56,7 +56,7 @@
.. c:function:: TYPE* PyObject_GC_Resize(TYPE, PyVarObject *op, Py_ssize_t newsize)
Resize an object allocated by :c:func:`PyObject_NewVar`. Returns the
- resized object or *NULL* on failure.
+ resized object or *NULL* on failure. *op* must not be tracked by the collector yet.
.. versionchanged:: 2.5
This function used an :c:type:`int` type for *newsize*. This might
diff --git a/Modules/gcmodule.c b/Modules/gcmodule.c
index 916e481..19011c4 100644
--- a/Modules/gcmodule.c
+++ b/Modules/gcmodule.c
@@ -1539,6 +1539,7 @@
{
const size_t basicsize = _PyObject_VAR_SIZE(Py_TYPE(op), nitems);
PyGC_Head *g = AS_GC(op);
+ assert(!IS_TRACKED(op));
if (basicsize > PY_SSIZE_T_MAX - sizeof(PyGC_Head))
return (PyVarObject *)PyErr_NoMemory();
g = (PyGC_Head *)PyObject_REALLOC(g, sizeof(PyGC_Head) + basicsize);