Implement MSC2176: Updated redaction rules (#8984)

An experimental room version ("org.matrix.msc2176") contains
the new redaction rules for testing.

Author: clokep

changelog.d/8984.feature

@@ -0,0 +1 @@
+Implement [MSC2176](https://github.com/matrix-org/matrix-doc/pull/2176) in an experimental room version.

synapse/api/room_versions.py

@@ -51,11 +51,11 @@ class RoomDisposition:
 class RoomVersion:
     """An object which describes the unique attributes of a room version."""
 
-    identifier = attr.ib()  # str; the identifier for this version
-    disposition = attr.ib()  # str; one of the RoomDispositions
-    event_format = attr.ib()  # int; one of the EventFormatVersions
-    state_res = attr.ib()  # int; one of the StateResolutionVersions
-    enforce_key_validity = attr.ib()  # bool
+    identifier = attr.ib(type=str)  # the identifier for this version
+    disposition = attr.ib(type=str)  # one of the RoomDispositions
+    event_format = attr.ib(type=int)  # one of the EventFormatVersions
+    state_res = attr.ib(type=int)  # one of the StateResolutionVersions
+    enforce_key_validity = attr.ib(type=bool)
 
     # bool: before MSC2261/MSC2432, m.room.aliases had special auth rules and redaction rules
     special_case_aliases_auth = attr.ib(type=bool)
@@ -64,9 +64,11 @@ class RoomVersion:
     # * Floats
     # * NaN, Infinity, -Infinity
     strict_canonicaljson = attr.ib(type=bool)
-    # bool: MSC2209: Check 'notifications' key while verifying
+    # MSC2209: Check 'notifications' key while verifying
     # m.room.power_levels auth rules.
     limit_notifications_power_levels = attr.ib(type=bool)
+    # MSC2174/MSC2176: Apply updated redaction rules algorithm.
+    msc2176_redaction_rules = attr.ib(type=bool)
 
 
 class RoomVersions:
@@ -79,6 +81,7 @@ class RoomVersions:
         special_case_aliases_auth=True,
         strict_canonicaljson=False,
         limit_notifications_power_levels=False,
+        msc2176_redaction_rules=False,
     )
     V2 = RoomVersion(
         "2",
@@ -89,6 +92,7 @@ class RoomVersions:
         special_case_aliases_auth=True,
         strict_canonicaljson=False,
         limit_notifications_power_levels=False,
+        msc2176_redaction_rules=False,
     )
     V3 = RoomVersion(
         "3",
@@ -99,6 +103,7 @@ class RoomVersions:
         special_case_aliases_auth=True,
         strict_canonicaljson=False,
         limit_notifications_power_levels=False,
+        msc2176_redaction_rules=False,
     )
     V4 = RoomVersion(
         "4",
@@ -109,6 +114,7 @@ class RoomVersions:
         special_case_aliases_auth=True,
         strict_canonicaljson=False,
         limit_notifications_power_levels=False,
+        msc2176_redaction_rules=False,
     )
     V5 = RoomVersion(
         "5",
@@ -119,6 +125,7 @@ class RoomVersions:
         special_case_aliases_auth=True,
         strict_canonicaljson=False,
         limit_notifications_power_levels=False,
+        msc2176_redaction_rules=False,
     )
     V6 = RoomVersion(
         "6",
@@ -129,6 +136,18 @@ class RoomVersions:
         special_case_aliases_auth=False,
         strict_canonicaljson=True,
         limit_notifications_power_levels=True,
+        msc2176_redaction_rules=False,
+    )
+    MSC2176 = RoomVersion(
+        "org.matrix.msc2176",
+        RoomDisposition.UNSTABLE,
+        EventFormatVersions.V3,
+        StateResolutionVersions.V2,
+        enforce_key_validity=True,
+        special_case_aliases_auth=False,
+        strict_canonicaljson=True,
+        limit_notifications_power_levels=True,
+        msc2176_redaction_rules=True,
     )
 
 
@@ -141,5 +160,6 @@ class RoomVersions:
         RoomVersions.V4,
         RoomVersions.V5,
         RoomVersions.V6,
+        RoomVersions.MSC2176,
     )
 }  # type: Dict[str, RoomVersion]

synapse/events/utils.py

@@ -79,13 +79,15 @@ def prune_event_dict(room_version: RoomVersion, event_dict: dict) -> dict:
         "state_key",
         "depth",
         "prev_events",
-        "prev_state",
         "auth_events",
         "origin",
         "origin_server_ts",
-        "membership",
     ]
 
+    # Room versions from before MSC2176 had additional allowed keys.
+    if not room_version.msc2176_redaction_rules:
+        allowed_keys.extend(["prev_state", "membership"])
+
     event_type = event_dict["type"]
 
     new_content = {}
@@ -98,6 +100,10 @@ def add_fields(*fields):
     if event_type == EventTypes.Member:
         add_fields("membership")
     elif event_type == EventTypes.Create:
+        # MSC2176 rules state that create events cannot be redacted.
+        if room_version.msc2176_redaction_rules:
+            return event_dict
+
         add_fields("creator")
     elif event_type == EventTypes.JoinRules:
         add_fields("join_rule")
@@ -112,10 +118,16 @@ def add_fields(*fields):
             "kick",
             "redact",
         )
+
+        if room_version.msc2176_redaction_rules:
+            add_fields("invite")
+
     elif event_type == EventTypes.Aliases and room_version.special_case_aliases_auth:
         add_fields("aliases")
     elif event_type == EventTypes.RoomHistoryVisibility:
         add_fields("history_visibility")
+    elif event_type == EventTypes.Redaction and room_version.msc2176_redaction_rules:
+        add_fields("redacts")
 
     allowed_fields = {k: v for k, v in event_dict.items() if k in allowed_keys}
 

synapse/handlers/room.py

@@ -365,7 +365,7 @@ async def clone_existing_room(
         creation_content = {
             "room_version": new_room_version.identifier,
             "predecessor": {"room_id": old_room_id, "event_id": tombstone_event_id},
-        }
+        }  # type: JsonDict
 
         # Check if old room was non-federatable