gh-148222: Fix NULL dereference bugs in genericaliasobject.c (#148226)

Author: prakashsellathurai

Misc/NEWS.d/next/Core_and_Builtins/2026-04-07-20-37-23.gh-issue-148222.uF4D4E.rst

@@ -0,0 +1 @@
+Fix vectorcall support in :class:`types.GenericAlias` when the underlying type does not support the vectorcall protocol. Fix possible leaks in :class:`types.GenericAlias` and :class:`types.UnionType` in case of memory error.

Objects/genericaliasobject.c

@@ -242,7 +242,6 @@ _Py_make_parameters(PyObject *args)
                     len += needed;
                     if (_PyTuple_Resize(&parameters, len) < 0) {
                         Py_DECREF(subparams);
-                        Py_DECREF(parameters);
                         Py_XDECREF(tuple_args);
                         return NULL;
                     }
@@ -650,7 +649,7 @@ ga_vectorcall(PyObject *self, PyObject *const *args,
               size_t nargsf, PyObject *kwnames)
 {
     gaobject *alias = (gaobject *) self;
-    PyObject *obj = PyVectorcall_Function(alias->origin)(alias->origin, args, nargsf, kwnames);
+    PyObject *obj = PyObject_Vectorcall(alias->origin, args, nargsf, kwnames);
     return set_orig_class(obj, self);
 }