gh-153205: Set MemoryError in stackref array conversion

Misc/NEWS.d/next/Core_and_Builtins/2026-07-07-04-16-48.gh-issue-153205.5fE8QZ.rst

@@ -0,0 +1,2 @@
+Fix a potential :exc:SystemError during vector calls when memory allocation fails.
+A :exc:MemoryError is now raised instead.

Python/ceval.c

@@ -1056,6 +1056,7 @@ _PyObjectArray_FromStackRefArray(_PyStackRef *input, Py_ssize_t nargs, PyObject
         // +1 in case PY_VECTORCALL_ARGUMENTS_OFFSET is set.
         result = PyMem_Malloc((nargs + 1) * sizeof(PyObject *));
         if (result == NULL) {
+            PyErr_NoMemory();
             return NULL;
         }
     }