[meta] SSS & PPS

[Hywan]

Here be dragons.

source

(that's a draft)

This is a meta issue to track the work about Simplified Sliding Sync (SSS) and Pragmatic Pragmatic Sync (PPS)

Simplified Sliding Sync

Synapse is implementing Sliding Sync natively. Since the Proxy implementation was experimental and was exposing too many features we now know we don't need, we call this project Simplified Sliding Sync.

Tasks

• Replace the sync ops by client-side sorting
  • feat(base) Client-side sorting, prelude: Implement Client::rooms_stream #3068
  • feat(ui): Client-side sorting in RoomList #3585
  • chore(sdk): Remove RoomListEntry and ops in Sliding Sync #3664
• Ruma support
  • feat(client-api): Draft support for simplified sliding sync ruma/ruma#1879
  • client-api: Implement MSC4186 ruma/ruma#1907
  • client-api: Add unstable-msc4186 inside the CHANGELOG ruma/ruma#1911
• Move the entire SDK to SSS, and be able to switch to SS at compile-time or runtime
  • feat: Migrate from Sliding Sync to Simplified Sliding Sync #3676
  • fix(sdk): Sliding sync rooms aren't restored from the cache #3702
• fix(sdk): Add m.room.create to bump_event_types for sliding sync #3724
• feat(sdk): Subscribe to many rooms only via Sliding Sync #3820
• Tiny collection of tiny small edits around Sliding Sync #3830
• feat(sdk): compute_limited is only useful for the SS proxy #3832
• fix(sdk): Remove SlidingSyncInner::past_positions #3833
• feat(sdk): Sliding sync has a timeout if all lists require a timeout #3853
• fix(sdk): Clear all sliding sync room subscriptions when session expires #3871
• feat(sdk): Do not send a room subscription that has already been sent #3874

Pragmatic Pragmatic Sync

Pragmatic Pragmatic Sync is another effort to extract some features of Sliding Sync into their own HTTP endpoints.

Tasks

• Replace Sliding Sync by /sync/e2ee
• Replace Sliding Sync by the improved /context

On the server-side

They are things missing or not working correctly on the server-side. We have nothing to do about it in the SDK, but it's important to list them so that we have a complete view of the project:

• Board
• SSS: read receipts are missing element-hq/element-x-ios#3106
• Sliding Sync: Add is_tombstoned: false filter in the defaults element-hq/synapse#17540

Release and Clean Up

Now it's time to clean up the old matrix_sdk::sliding_sync implementation.

Auto select SS or SSS

• [Story] EX: Migration to SSS element-hq/element-meta#2499
• Add a flag to /versions about SSS support element-hq/synapse#17571
• feat(sdk): Welcome sliding_sync::Version and sliding_sync::VersionBuilder #3889
• fix(api): Use the new sliding sync version API from the Rust SDK complement-crypto#128
• feat(sdk): Add Client::server #3908

Tasks

• Remove old features of Sliding Sync
• Remove potential intermediate feature flags
• Remove the experimental-sliding-sync feature flag:
  • feat: Remove the experimental-sliding-sync feature flag #4483
• test: Use Synapse with Simplified Sliding Sync in our integration tests #3698