bpo-42576: Raise TypeError when passing in keyword arguments to GenericAlias (GH-23656)

Use `_PyArg_NoKeywords` instead of `_PyArg_NoKwnames` when checking the `kwds` tuple when creating `GenericAlias`. This fixes an interpreter crash when passing in keyword arguments to `GenericAlias`'s constructor.

Needs backport to 3.9.

Automerge-Triggered-By: GH:gvanrossum
(cherry picked from commit 804d6893b8)

Co-authored-by: kj <28750310+Fidget-Spinner@users.noreply.github.com>

Lib/test/test_genericalias.py

@@ -302,6 +302,11 @@ class BaseTest(unittest.TestCase):
                 alias = t[int]
                 self.assertEqual(ref(alias)(), alias)
 
+    def test_no_kwargs(self):
+        # bpo-42576
+        with self.assertRaises(TypeError):
+            GenericAlias(bad=float)
+
 
 if __name__ == "__main__":
     unittest.main()

Misc/NEWS.d/next/Core and Builtins/2020-12-05-22-34-47.bpo-42576.lEeEl7.rst

@@ -0,0 +1,3 @@
+``types.GenericAlias`` will now raise a ``TypeError`` when attempting to
+initialize with a keyword argument.  Previously, this would cause the
+interpreter to crash.  Patch by Ken Jin.

Objects/genericaliasobject.c

@@ -566,7 +566,7 @@ static PyGetSetDef ga_properties[] = {
 static PyObject *
 ga_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
 {
-    if (!_PyArg_NoKwnames("GenericAlias", kwds)) {
+    if (!_PyArg_NoKeywords("GenericAlias", kwds)) {
         return NULL;
     }
     if (!_PyArg_CheckPositional("GenericAlias", PyTuple_GET_SIZE(args), 2, 2)) {