[3.15] gh-153205: Set MemoryError in stackref array conversion (GH-153206) (#153272)

gh-153205: Set `MemoryError` in stackref array conversion (GH-153206)
(cherry picked from commit 08759ff)

Co-authored-by: An Long <aisk@users.noreply.github.com>
Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>
Co-authored-by: sobolevn <mail@sobolevn.me>

Author: 4 people

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

@@ -1057,6 +1057,7 @@ _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;
         }
     }