Sliding Sync: Parameterize and add more tests for tracking changes to…

… required state (#17805)

Parameterize and add more tests for tracking changes to required state
(`_required_state_changes(...)`)

These are direct modifications to
#17785 and should be merged
into that PR.

changelog.d/17805.bugfix

@@ -0,0 +1 @@
+Fix bug with sliding sync where the server would not return state that was added to the `required_state` config.

synapse/handlers/sliding_sync/__init__.py

@@ -1313,6 +1313,13 @@ def _required_state_changes(
  prev_wildcard = prev_required_state_map.get(StateValues.WILDCARD, set())
  request_wildcard = request_required_state_map.get(StateValues.WILDCARD, set())
 
+ # If we were previously fetching everything ("*", "*"), always update the effective
+ # room required state config to match the request. And since we we're previously
+ # already fetching everything, we don't have to fetch anything now that they've
+ # narrowed.
+ if StateValues.WILDCARD in prev_wildcard:
+ return request_required_state_map, StateFilter.none()
+
  # If a event type wildcard has been added or removed we don't try and do
  # anything fancy, and instead always update the effective room required
  # state config to match the request.
@@ -1349,6 +1356,11 @@ def _required_state_changes(
  # Always update changes to include the newly added keys
  changes[event_type] = request_state_keys
 
+ if StateValues.WILDCARD in old_state_keys:
+ # We were previously fetching everything for this type, so we don't need to
+ # fetch anything new.
+ continue
+
  # Record the new state keys to fetch for this type.
  if StateValues.WILDCARD in request_state_keys:
  # If we have added a wildcard then we always just fetch everything.
@@ -1358,8 +1370,8 @@ def _required_state_changes(
  if state_key == StateValues.ME:
  added.append((event_type, user_id))
  elif state_key == StateValues.LAZY:
- # We handle lazy loading separately, so don't need to
- # explicitly add anything here.
+ # We handle lazy loading separately (outside this function), so
+ # don't need to explicitly add anything here.
  pass
  else:
  added.append((event_type, state_key))
@@ -1397,17 +1409,17 @@ def _required_state_changes(
  request_state_key_wildcard = StateValues.WILDCARD in request_state_keys
 
  if old_state_key_wildcard != request_state_key_wildcard:
- # If a wildcard has been added or removed we always update the
- # required state when any state with the same type has changed.
+ # If a state_key wildcard has been added or removed, we always update the
+ # effective room required state config to match the request.
  changes[event_type] = request_state_keys
  continue
 
  old_state_key_lazy = StateValues.LAZY in old_state_keys
  request_state_key_lazy = StateValues.LAZY in request_state_keys
 
  if old_state_key_lazy != request_state_key_lazy:
- # If a "$LAZY" has been added or removed we always update the
- # required state for simplicity.
+ # If a "$LAZY" has been added or removed we always update the effective room
+ # required state config to match the request.
  changes[event_type] = request_state_keys
  continue