Minor @cachedList enhancements (#9975)

- use a tuple rather than a list for the iterable that is passed into the
  wrapped function, for performance

- test that we can pass an iterable and that keys are correctly deduped.

tests/util/caches/test_descriptors.py

@@ -666,18 +666,20 @@ class CachedListDescriptorTestCase(unittest.TestCase):
         with LoggingContext("c1") as c1:
             obj = Cls()
             obj.mock.return_value = {10: "fish", 20: "chips"}
+
+            # start the lookup off
             d1 = obj.list_fn([10, 20], 2)
             self.assertEqual(current_context(), SENTINEL_CONTEXT)
             r = yield d1
             self.assertEqual(current_context(), c1)
-            obj.mock.assert_called_once_with([10, 20], 2)
+            obj.mock.assert_called_once_with((10, 20), 2)
             self.assertEqual(r, {10: "fish", 20: "chips"})
             obj.mock.reset_mock()
 
             # a call with different params should call the mock again
             obj.mock.return_value = {30: "peas"}
             r = yield obj.list_fn([20, 30], 2)
-            obj.mock.assert_called_once_with([30], 2)
+            obj.mock.assert_called_once_with((30,), 2)
             self.assertEqual(r, {20: "chips", 30: "peas"})
             obj.mock.reset_mock()
 
@@ -692,6 +694,15 @@ class CachedListDescriptorTestCase(unittest.TestCase):
             obj.mock.assert_not_called()
             self.assertEqual(r, {10: "fish", 20: "chips", 30: "peas"})
 
+            # we should also be able to use a (single-use) iterable, and should
+            # deduplicate the keys
+            obj.mock.reset_mock()
+            obj.mock.return_value = {40: "gravy"}
+            iterable = (x for x in [10, 40, 40])
+            r = yield obj.list_fn(iterable, 2)
+            obj.mock.assert_called_once_with((40,), 2)
+            self.assertEqual(r, {10: "fish", 40: "gravy"})
+
     @defer.inlineCallbacks
     def test_invalidate(self):
         """Make sure that invalidation callbacks are called."""
@@ -717,7 +728,7 @@ class CachedListDescriptorTestCase(unittest.TestCase):
         # cache miss
         obj.mock.return_value = {10: "fish", 20: "chips"}
         r1 = yield obj.list_fn([10, 20], 2, on_invalidate=invalidate0)
-        obj.mock.assert_called_once_with([10, 20], 2)
+        obj.mock.assert_called_once_with((10, 20), 2)
         self.assertEqual(r1, {10: "fish", 20: "chips"})
         obj.mock.reset_mock()