Based on [MSC3575](https://github.com/matrix-org/matrix-spec-proposals/pull/3575): Sliding Sync
This iteration only focuses on returning the list of room IDs in the sliding window API (without sorting/filtering).
Rooms appear in the Sliding sync response based on:
- `invite`, `join`, `knock`, `ban` membership events
- Kicks (`leave` membership events where `sender` is different from the `user_id`/`state_key`)
- `newly_left` (rooms that were left during the given token range, > `from_token` and <= `to_token`)
- In order for bans/kicks to not show up, you need to `/forget` those rooms. This doesn't modify the event itself though and only adds the `forgotten` flag to `room_memberships` in Synapse. There isn't a way to tell when a room was forgotten at the moment so we can't factor it into the from/to range.
### Example request
`POST http://localhost:8008/_matrix/client/unstable/org.matrix.msc3575/sync`
```json
{
"lists": {
"foo-list": {
"ranges": [ [0, 99] ],
"sort": [ "by_notification_level", "by_recency", "by_name" ],
"required_state": [
["m.room.join_rules", ""],
["m.room.history_visibility", ""],
["m.space.child", "*"]
],
"timeline_limit": 100
}
}
}
```
Response:
```json
{
"next_pos": "s58_224_0_13_10_1_1_16_0_1",
"lists": {
"foo-list": {
"count": 1,
"ops": [
{
"op": "SYNC",
"range": [0, 99],
"room_ids": [
"!MmgikIyFzsuvtnbvVG:my.synapse.linux.server"
]
}
]
}
},
"rooms": {},
"extensions": {}
}
```
Before, the problem scenario would get caught in one of the assertions because
we expect the to_token <= membership_snapshot_token or vice-versa but it's
possible the tokens are intertwined and neither is ahead of each other.
Especially since the `instance_map` in `membership_snapshot_token` is made up
from the `stream_ordering` of membership events at various stream positions
and processed on different instances (not current stream positions).
We get into trouble when stream positions are lagging between workers and our
now/`to_token` doesn't cleanly compare to `membership_snapshot_token`.
What we really want to assert is that the `to_token` <= the stream positions
at the time we asked for the room membership snapshot. Since
`get_rooms_for_local_user_where_membership_is()` doesn't return that
information, the closest we can get is to get the stream positions before we
ask for the room membership snapshot and consider that good enough to compare
against.
The new implementation catches the problem with an assert
but I think it's possible to make it work as well.
```
SYNAPSE_POSTGRES=1 SYNAPSE_POSTGRES_USER=postgres SYNAPSE_TEST_LOG_LEVEL=INFO poetry run trial tests.handlers.test_sliding_sync.GetSyncRoomIdsForUserEventShardTestCase
```
Use fully-qualified `PersistedEventPosition` (`instance_name` and `stream_ordering`) when returning `RoomsForUser` to facilitate proper comparisons and `RoomStreamToken` generation.
Spawning from https://github.com/element-hq/synapse/pull/17187 where we want to utilize this change
