Stabilise MSC4222: support the stable use_state_after identifiers on /sync

changelog.d/20170.feature

@@ -0,0 +1 @@
+Stabilise [MSC4222](https://github.com/matrix-org/matrix-spec-proposals/pull/4222): support the stable `use_state_after` query parameter and `state_after` response field on `/sync`, as per Matrix v1.16, and remove the `msc4222_enabled` experimental config flag.

docker/complement/conf/workers-shared-extra.yaml.j2

@@ -141,8 +141,6 @@ experimental_features:
   msc4306_enabled: true
   # Sticky Events
   msc4354_enabled: true
-  # `/sync` `state_after`
-  msc4222_enabled: true
 
 server_notices:
   system_mxid_localpart: _server

docs/admin_api/experimental_features.md

@@ -5,7 +5,6 @@ basis. The currently supported features are:
 - [MSC3881](https://github.com/matrix-org/matrix-spec-proposals/pull/3881): enable remotely toggling push notifications
 for another client
 - [MSC3575](https://github.com/matrix-org/matrix-spec-proposals/pull/3575): enable experimental sliding sync support
-- [MSC4222](https://github.com/matrix-org/matrix-spec-proposals/pull/4222): adding `state_after` to sync v2
 
 To use it, you will need to authenticate by providing an `access_token`
 for a server admin: see [Admin API](../usage/administration/admin_api/).

rust/src/config/mod.rs

@@ -70,7 +70,6 @@ pub struct ExperimentalConfig {
     pub msc4306_enabled: bool,
     pub msc4169_enabled: bool,
     pub msc4354_enabled: bool,
-    pub msc4222_enabled: bool,
     pub msc4491_enabled: bool,
     pub msc4143_enabled: bool,
     pub msc4446_enabled: bool,

rust/src/storage/store.rs

@@ -27,8 +27,6 @@ pub enum PerUserExperimentalFeature {
     MSC3881,
     #[serde(rename = "msc3575")]
     MSC3575,
-    #[serde(rename = "msc4222")]
-    MSC4222,
 }
 
 impl std::fmt::Display for PerUserExperimentalFeature {

synapse/config/experimental.py

@@ -256,9 +256,6 @@ def read_config(
         # MSC4210: Remove legacy mentions
         self.msc4210_enabled: bool = experimental.get("msc4210_enabled", False)
 
-        # MSC4222: Adding `state_after` to sync v2
-        self.msc4222_enabled: bool = experimental.get("msc4222_enabled", False)
-
         # MSC4076: Add `disable_badge_count`` to pusher configuration
         self.msc4076_enabled: bool = experimental.get("msc4076_enabled", False)
 

synapse/handlers/sync.py

@@ -139,6 +139,14 @@ class SyncConfig:
     is_guest: bool
     device_id: str | None
     use_state_after: bool
+    # Whether the client opted in to `state_after` via the unstable
+    # `org.matrix.msc4222.use_state_after` query parameter rather than the
+    # stable one, in which case the unstable response field name is used too.
+    # Only relevant when `use_state_after` is True.
+    #
+    # FIXME(unstable_state_after): Remove support for the unstable identifiers after 2027-09-01
+    # (to allow some time for the ecosystem to adapt to the stable identifiers)
+    use_unstable_state_after_name: bool = False
 
 
 @attr.s(slots=True, frozen=True, auto_attribs=True)

synapse/rest/admin/experimental_features.py

@@ -43,15 +43,12 @@ class ExperimentalFeature(str, Enum):
 
     MSC3881 = "msc3881"
     MSC3575 = "msc3575"
-    MSC4222 = "msc4222"
 
     def is_globally_enabled(self, config: "HomeServerConfig") -> bool:
         if self is ExperimentalFeature.MSC3881:
             return config.experimental.msc3881_enabled
         if self is ExperimentalFeature.MSC3575:
             return config.experimental.msc3575_enabled
-        if self is ExperimentalFeature.MSC4222:
-            return config.experimental.msc4222_enabled
 
         assert_never(self)
 

synapse/rest/client/sync.py

@@ -174,11 +174,12 @@ async def on_GET(self, request: SynapseRequest) -> tuple[int, JsonDict]:
         filter_id = parse_string(request, "filter")
         full_state = parse_boolean(request, "full_state", default=False)
 
-        use_state_after = False
-        if await self.store.is_feature_enabled(
-            user.to_string(), ExperimentalFeature.MSC4222
-        ):
-            use_state_after = parse_boolean(
+        use_state_after = parse_boolean(request, "use_state_after", default=False)
+        use_unstable_state_after_name = False
+        # FIXME(unstable_state_after): Remove support for the unstable identifiers after 2027-09-01
+        # (to allow some time for the ecosystem to adapt to the stable identifiers)
+        if not use_state_after:
+            use_state_after = use_unstable_state_after_name = parse_boolean(
                 request, "org.matrix.msc4222.use_state_after", default=False
             )
 
@@ -215,6 +216,7 @@ async def on_GET(self, request: SynapseRequest) -> tuple[int, JsonDict]:
             device_id,
             last_ignore_accdata_streampos,
             use_state_after,
+            use_unstable_state_after_name,
         )
 
         if filter_id is None:
@@ -252,6 +254,7 @@ async def on_GET(self, request: SynapseRequest) -> tuple[int, JsonDict]:
             is_guest=requester.is_guest,
             device_id=device_id,
             use_state_after=use_state_after,
+            use_unstable_state_after_name=use_unstable_state_after_name,
         )
 
         since_token = None
@@ -633,7 +636,12 @@ async def encode_room(
         # We either include a `state` or `state_after` field depending on
         # whether the client has opted in to the newer `state_after` behavior.
         if sync_config.use_state_after:
-            state_key_name = "org.matrix.msc4222.state_after"
+            # Clients which opted in via the unstable MSC4222 query parameter
+            # get the unstable field name back, for the transition period.
+            if sync_config.use_unstable_state_after_name:
+                state_key_name = "org.matrix.msc4222.state_after"
+            else:
+                state_key_name = "state_after"
         else:
             state_key_name = "state"
 

tests/rest/client/test_sync.py

@@ -33,7 +33,6 @@
     ReceiptTypes,
     RelationTypes,
 )
-from synapse.rest.admin.experimental_features import ExperimentalFeature
 from synapse.rest.client import devices, knock, login, read_marker, receipts, room, sync
 from synapse.server import HomeServer
 from synapse.types import JsonDict
@@ -767,6 +766,70 @@ def test_noop_sync_does_not_tightloop(self) -> None:
         self.assertEqual(channel.code, 200, channel.json_body)
 
 
+# FIXME(unstable_state_after): Remove this whole test case after 2027-09-01
+# and we drop support for the unstable variant of `state_after`
+class SyncStateAfterTestCase(unittest.HomeserverTestCase):
+    """
+    Tests for the `use_state_after` opt-in on `/sync` (MSC4222, stable as of
+    Matrix v1.16): the variant of the `state_after` field in the response should
+    match the stable/unstable query parameter the client opted in with.
+    """
+
+    servlets = [
+        synapse.rest.admin.register_servlets,
+        login.register_servlets,
+        room.register_servlets,
+        sync.register_servlets,
+    ]
+
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
+        self.user_id = self.register_user("user", "password")
+        self.access_token = self.login(self.user_id, "password")
+        self.room_id = self.helper.create_room_as(self.user_id, tok=self.access_token)
+
+    def _sync_room_keys(self, query_string: str) -> set[str]:
+        """Perform a sync with the given query string and return the keys of
+        our room's response object."""
+        channel = self.make_request(
+            "GET",
+            f"/sync{query_string}",
+            access_token=self.access_token,
+        )
+        self.assertEqual(channel.code, 200, channel.json_body)
+        return set(channel.json_body["rooms"]["join"][self.room_id].keys())
+
+    def test_state_without_opt_in(self) -> None:
+        """By default, room state comes down under the `state` key."""
+        room_keys = self._sync_room_keys("")
+        self.assertIn("state", room_keys)
+        self.assertNotIn("state_after", room_keys)
+        self.assertNotIn("org.matrix.msc4222.state_after", room_keys)
+
+    def test_state_after_stable_name(self) -> None:
+        """Opting in with the stable query parameter gives the stable field name."""
+        room_keys = self._sync_room_keys("?use_state_after=true")
+        self.assertIn("state_after", room_keys)
+        self.assertNotIn("state", room_keys)
+        self.assertNotIn("org.matrix.msc4222.state_after", room_keys)
+
+    def test_state_after_unstable_name(self) -> None:
+        """Opting in with the unstable query parameter gives the unstable field
+        name, for the transition period."""
+        room_keys = self._sync_room_keys("?org.matrix.msc4222.use_state_after=true")
+        self.assertIn("org.matrix.msc4222.state_after", room_keys)
+        self.assertNotIn("state", room_keys)
+        self.assertNotIn("state_after", room_keys)
+
+    def test_state_after_both_names(self) -> None:
+        """If a client opts in with both query parameters, the stable field name wins."""
+        room_keys = self._sync_room_keys(
+            "?use_state_after=true&org.matrix.msc4222.use_state_after=true"
+        )
+        self.assertIn("state_after", room_keys)
+        self.assertNotIn("state", room_keys)
+        self.assertNotIn("org.matrix.msc4222.state_after", room_keys)
+
+
 class DeviceListSyncTestCase(unittest.HomeserverTestCase):
     """
     Tests regarding device list (`device_lists`) changes.
@@ -1286,9 +1349,6 @@ class SyncStateAfterArchivedRoomTestCase(unittest.HomeserverTestCase):
         sync.register_servlets,
     ]
 
-    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
-        self.store = hs.get_datastores().main
-
     def test_archived_room_state_after_not_newer_than_leave(self) -> None:
         """`state_after` for a left room must be the state at the end of that
         room's timeline, i.e. at the user's leave point — never state from
@@ -1305,11 +1365,6 @@ def test_archived_room_state_after_not_newer_than_leave(self) -> None:
         bob = self.register_user("bob", "password")
         bob_tok = self.login("bob", "password")
 
-        # Opt Alice in to MSC4222.
-        self.get_success(
-            self.store.set_features_for_user(alice, {ExperimentalFeature.MSC4222: True})
-        )
-
         # Name the room to avoid heroes: those come from the *current*
         # summary — a separate leak path from the one under test.
         room_id = self.helper.create_room_as(
@@ -1338,7 +1393,7 @@ def test_archived_room_state_after_not_newer_than_leave(self) -> None:
                 }
             }
         )
-        sync_url = f"/sync?filter={sync_filter}&org.matrix.msc4222.use_state_after=true"
+        sync_url = f"/sync?filter={sync_filter}&use_state_after=true"
 
         # Initial sync.
         channel = self.make_request("GET", sync_url, access_token=alice_tok)
@@ -1368,7 +1423,7 @@ def test_archived_room_state_after_not_newer_than_leave(self) -> None:
         self.assertEqual(channel.code, 200, channel.result)
 
         left_room = channel.json_body["rooms"]["leave"][room_id]
-        state_after_events = left_room["org.matrix.msc4222.state_after"]["events"]
+        state_after_events = left_room["state_after"]["events"]
 
         # Post-leave state must not appear in `state_after`.
         self.assertNotIn(