Assert in _Py_stackref_set_borrowed_from

Author: efimov-mikhail

Python/stackrefs.c

@@ -200,10 +200,6 @@ _Py_stackref_get_borrowed_from(_PyStackRef ref, const char *filename, int linenu
 void
 _Py_stackref_set_borrowed_from(_PyStackRef ref, _PyStackRef borrowed_from, const char *filename, int linenumber)
 {
-    if (PyStackRef_IsNull(borrowed_from)) {
-        return;
-    }
-
     assert(!PyStackRef_IsError(ref));
     PyInterpreterState *interp = PyInterpreterState_Get();
 
@@ -214,6 +210,11 @@ _Py_stackref_set_borrowed_from(_PyStackRef ref, _PyStackRef borrowed_from, const
             ref.index, filename, linenumber);
     }
 
+    assert(PyStackRef_IsNull(entry->borrowed_from));
+    if (PyStackRef_IsNull(borrowed_from)) {
+        return;
+    }
+
     TableEntry *entry_borrowed = _Py_hashtable_get(interp->open_stackrefs_table, (void *)borrowed_from.index);
     if (entry_borrowed == NULL) {
         _Py_FatalErrorFormat(__func__,