Add more tests to cover types.Union

Author: uriyyo

Lib/test/test_types.py

@@ -668,10 +668,13 @@ def test_or_type_operator_with_TypeVar(self):
 
     def test_union_parameter_chaining(self):
         T = typing.TypeVar("T")
+        S = typing.TypeVar("S")
 
         self.assertEqual((float | list[T])[int], float | list[int])
         self.assertEqual(list[int | list[T]].__parameters__, (T,))
         self.assertEqual(list[int | list[T]][str], list[int | list[str]])
+        self.assertEqual((list[T] | list[S]).__parameters__, (T, S))
+        self.assertEqual((list[T] | list[S])[int, T], list[int] | list[T])
 
     def test_or_type_operator_with_forward(self):
         T = typing.TypeVar('T')

Objects/unionobject.c

@@ -443,7 +443,7 @@ static PyObject *
 union_getitem(PyObject *self, PyObject *item)
 {
     unionobject *alias = (unionobject *)self;
-    // do a lookup for __parameters__ so it gets populated (if not already)
+    // Populate __parameters__ if needed.
     if (alias->parameters == NULL) {
         alias->parameters = _Py_make_parameters(alias->args);
         if (alias->parameters == NULL) {