Include whether the requesting users has responded to an MSC3440 thread

[clokep]

Per an update to MSC3440. (Note that we're going to be consistent and not use a camel-case version as suggested there.)

[clokep]

This seems like it might not be super feasible since we don't have the requesting user when serializing events. We could probably pass through the user to those places, but I'm not sure if that is desirable (in terms of caching and such). What do we think of this?

Relevant code is near:

• synapse/synapse/events/utils.py

  Lines 467 to 480 in ba00e20

  	if self._msc3440_enabled:
  	(
  	thread_count,
  	latest_thread_event,
  	) = await self.store.get_thread_summary(event_id)
  	if latest_thread_event:
  	r = serialized_event["unsigned"].setdefault("m.relations", {})
  	r[RelationTypes.THREAD] = {
  	# Don't bundle aggregations as this could recurse forever.
  	"latest_event": await self.serialize_event(
  	latest_thread_event, time_now, bundle_aggregations=False
  	),
  	"count": thread_count,
  	}

  , which calls

• synapse/synapse/storage/databases/main/relations.py

  Lines 273 to 327 in ba00e20

  	async def get_thread_summary(
  	self, event_id: str
  	) -> Tuple[int, Optional[EventBase]]:
  	"""Get the number of threaded replies, the senders of those replies, and
  	the latest reply (if any) for the given event.
  	Args:
  	event_id: The original event ID
  	Returns:
  	The number of items in the thread and the most recent response, if any.
  	"""
  	def _get_thread_summary_txn(txn) -> Tuple[int, Optional[str]]:
  	# Fetch the count of threaded events and the latest event ID.
  	# TODO Should this only allow m.room.message events.
  	sql = """
  	SELECT event_id
  	FROM event_relations
  	INNER JOIN events USING (event_id)
  	WHERE
  	relates_to_id = ?
  	AND relation_type = ?
  	ORDER BY topological_ordering DESC, stream_ordering DESC
  	LIMIT 1
  	"""
  	txn.execute(sql, (event_id, RelationTypes.THREAD))
  	row = txn.fetchone()
  	if row is None:
  	return 0, None
  	latest_event_id = row[0]
  	sql = """
  	SELECT COALESCE(COUNT(event_id), 0)
  	FROM event_relations
  	WHERE
  	relates_to_id = ?
  	AND relation_type = ?
  	"""
  	txn.execute(sql, (event_id, RelationTypes.THREAD))
  	count = txn.fetchone()[0]
  	return count, latest_event_id
  	count, latest_event_id = await self.db_pool.runInteraction(
  	"get_thread_summary", _get_thread_summary_txn
  	)
  	latest_event = None
  	if latest_event_id:
  	latest_event = await self.get_event(latest_event_id, allow_none=True)
  	return count, latest_event

[clokep]

This is not necessary, the filtering adding to MSC3440 is meant to be used for this purpose.

[clokep]

We might need to do this for thread previews in the timeline.