Fix `have_seen_event` cache not being invalidated (#13863)

Fix https://github.com/matrix-org/synapse/issues/13856
Fix https://github.com/matrix-org/synapse/issues/13865

> Discovered while trying to make Synapse fast enough for [this MSC2716 test for importing many batches](https://github.com/matrix-org/complement/pull/214#discussion_r741678240). As an example, disabling the `have_seen_event` cache saves 10 seconds for each `/messages` request in that MSC2716 Complement test because we're not making as many federation requests for `/state` (speeding up `have_seen_event` itself is related to https://github.com/matrix-org/synapse/issues/13625) 
> 
> But this will also make `/messages` faster in general so we can include it in the [faster `/messages` milestone](https://github.com/matrix-org/synapse/milestone/11).
> 
> *-- https://github.com/matrix-org/synapse/issues/13856*


### The problem

`_invalidate_caches_for_event` doesn't run in monolith mode which means we never even tried to clear the `have_seen_event` and other caches. And even in worker mode, it only runs on the workers, not the master (AFAICT).

Additionally there was bug with the key being wrong so `_invalidate_caches_for_event` never invalidates the `have_seen_event` cache even when it does run.

Because we were using the `@cachedList` wrong, it was putting items in the cache under keys like `((room_id, event_id),)` with a `set` in a `set` (ex. `(('!TnCIJPKzdQdUlIyXdQ:test', '$Iu0eqEBN7qcyF1S9B3oNB3I91v2o5YOgRNPwi_78s-k'),)`) and we we're trying to invalidate with just `(room_id, event_id)` which did nothing.

1 files changed, 32 insertions, 1 deletions

diff --git a/tests/util/caches/test_descriptors.py b/tests/util/caches/test_descriptors.py
index 48e616ac74..90861fe522 100644
--- a/tests/util/caches/test_descriptors.py
+++ b/tests/util/caches/test_descriptors.py
@@ -13,7 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 import logging
-from typing import Set
+from typing import Iterable, Set, Tuple
 from unittest import mock
 
 from twisted.internet import defer, reactor
@@ -1008,3 +1008,34 @@ class CachedListDescriptorTestCase(unittest.TestCase):
             obj.inner_context_was_finished, "Tried to restart a finished logcontext"
         )
         self.assertEqual(current_context(), SENTINEL_CONTEXT)
+
+    def test_num_args_mismatch(self):
+        """
+        Make sure someone does not accidentally use @cachedList on a method with
+        a mismatch in the number args to the underlying single cache method.
+        """
+
+        class Cls:
+            @descriptors.cached(tree=True)
+            def fn(self, room_id, event_id):
+                pass
+
+            # This is wrong ❌. `@cachedList` expects to be given the same number
+            # of arguments as the underlying cached function, just with one of
+            # the arguments being an iterable
+            @descriptors.cachedList(cached_method_name="fn", list_name="keys")
+            def list_fn(self, keys: Iterable[Tuple[str, str]]):
+                pass
+
+            # Corrected syntax ✅
+            #
+            # @cachedList(cached_method_name="fn", list_name="event_ids")
+            # async def list_fn(
+            #     self, room_id: str, event_ids: Collection[str],
+            # )
+
+        obj = Cls()
+
+        # Make sure this raises an error about the arg mismatch
+        with self.assertRaises(Exception):
+            obj.list_fn([("foo", "bar")])