Bust `_membership_stream_cache` cache when current state changes (#17732)

This is particularly a problem in a state reset scenario where the membership
might change without a corresponding event.

This PR is targeting a scenario where a state reset happens which causes
room membership to change. Previously, the cache would just hold onto
stale data and now we properly bust the cache in this scenario.

We have a few tests for these scenarios which you can see are now fixed
because we can remove the `FIXME` where we were previously manually
busting the cache in the test itself.

This is a general Synapse thing so by it's nature it helps out Sliding
Sync.

Fix https://github.com/element-hq/synapse/issues/17368

Prerequisite for https://github.com/element-hq/synapse/issues/17929

---

Match when are busting `_curr_state_delta_stream_cache`

1 files changed, 3 insertions, 1 deletions

diff --git a/synapse/storage/_base.py b/synapse/storage/_base.py

index e14d711c76..7251e72e3a 100644
--- a/synapse/storage/_base.py
+++ b/synapse/storage/_base.py
@@ -86,7 +86,9 @@ class SQLBaseStore(metaclass=ABCMeta):
         """
 
     def _invalidate_state_caches(
-        self, room_id: str, members_changed: Collection[str]
+        self,
+        room_id: str,
+        members_changed: Collection[str],
     ) -> None:
         """Invalidates caches that are based on the current state, but does
         not stream invalidations down replication.