GH-100342: check for allocation failure in AC *args parsing (#100343)

Author: kumaraditya303

Lib/test/clinic.test

@@ -3781,6 +3781,9 @@ test_vararg_and_posonly(PyObject *module, PyObject *const *args, Py_ssize_t narg
     }
     a = args[0];
     __clinic_args = PyTuple_New(nargs - 1);
+    if (!__clinic_args) {
+        goto exit;
+    }
     for (Py_ssize_t i = 0; i < nargs - 1; ++i) {
         PyTuple_SET_ITEM(__clinic_args, i, Py_NewRef(args[1 + i]));
     }
@@ -3793,7 +3796,7 @@ exit:
 
 static PyObject *
 test_vararg_and_posonly_impl(PyObject *module, PyObject *a, PyObject *args)
-/*[clinic end generated code: output=081a953b8cbe7617 input=08dc2bf7afbf1613]*/
+/*[clinic end generated code: output=79b75dc07decc8d6 input=08dc2bf7afbf1613]*/
 
 /*[clinic input]
 test_vararg

Misc/NEWS.d/next/Tools-Demos/2022-12-19-10-08-53.gh-issue-100342.qDFlQG.rst

@@ -0,0 +1 @@
+Add missing ``NULL`` check for possible allocation failure in ``*args`` parsing in Argument Clinic.

Modules/clinic/_testclinic.c.h

@@ -960,12 +960,16 @@ def parser_body(prototype, *fields, declarations=''):
                     if not new_or_init:
                         parser_code.append(normalize_snippet("""
                             %s = PyTuple_New(%s);
+                            if (!%s) {{
+                                goto exit;
+                            }}
                             for (Py_ssize_t i = 0; i < %s; ++i) {{
                                 PyTuple_SET_ITEM(%s, i, Py_NewRef(args[%d + i]));
                             }}
                             """ % (
                                 p.converter.parser_name,
                                 left_args,
+                                p.converter.parser_name,
                                 left_args,
                                 p.converter.parser_name,
                                 max_pos