When redacting, keep event fields around that maintain the historical event structure intact (MSC2716) (#10538)

* Keep event fields that maintain the historical event structure intact

Fix https://github.com/matrix-org/synapse/issues/10521

* Add changelog

* Bump room version

* Better changelog text

* Fix up room version after develop merge

3 files changed, 40 insertions, 6 deletions

diff --git a/changelog.d/10538.feature b/changelog.d/10538.feature
new file mode 100644
index 0000000000..120c8e8ca0
--- /dev/null
+++ b/changelog.d/10538.feature
@@ -0,0 +1 @@
+Add support for new redaction rules for historical events specified in [MSC2716](https://github.com/matrix-org/matrix-doc/pull/2716).
diff --git a/synapse/api/room_versions.py b/synapse/api/room_versions.py
index f32a40ba4a..11280c4462 100644
--- a/synapse/api/room_versions.py
+++ b/synapse/api/room_versions.py
@@ -76,6 +76,8 @@ class RoomVersion:
     # MSC2716: Adds m.room.power_levels -> content.historical field to control
     # whether "insertion", "chunk", "marker" events can be sent
     msc2716_historical = attr.ib(type=bool)
+    # MSC2716: Adds support for redacting "insertion", "chunk", and "marker" events
+    msc2716_redactions = attr.ib(type=bool)
 
 
 class RoomVersions:
@@ -92,6 +94,7 @@ class RoomVersions:
         msc3083_join_rules=False,
         msc2403_knocking=False,
         msc2716_historical=False,
+        msc2716_redactions=False,
     )
     V2 = RoomVersion(
         "2",
@@ -106,6 +109,7 @@ class RoomVersions:
         msc3083_join_rules=False,
         msc2403_knocking=False,
         msc2716_historical=False,
+        msc2716_redactions=False,
     )
     V3 = RoomVersion(
         "3",
@@ -120,6 +124,7 @@ class RoomVersions:
         msc3083_join_rules=False,
         msc2403_knocking=False,
         msc2716_historical=False,
+        msc2716_redactions=False,
     )
     V4 = RoomVersion(
         "4",
@@ -134,6 +139,7 @@ class RoomVersions:
         msc3083_join_rules=False,
         msc2403_knocking=False,
         msc2716_historical=False,
+        msc2716_redactions=False,
     )
     V5 = RoomVersion(
         "5",
@@ -148,6 +154,7 @@ class RoomVersions:
         msc3083_join_rules=False,
         msc2403_knocking=False,
         msc2716_historical=False,
+        msc2716_redactions=False,
     )
     V6 = RoomVersion(
         "6",
@@ -162,6 +169,7 @@ class RoomVersions:
         msc3083_join_rules=False,
         msc2403_knocking=False,
         msc2716_historical=False,
+        msc2716_redactions=False,
     )
     MSC2176 = RoomVersion(
         "org.matrix.msc2176",
@@ -176,6 +184,7 @@ class RoomVersions:
         msc3083_join_rules=False,
         msc2403_knocking=False,
         msc2716_historical=False,
+        msc2716_redactions=False,
     )
     V7 = RoomVersion(
         "7",
@@ -190,6 +199,22 @@ class RoomVersions:
         msc3083_join_rules=False,
         msc2403_knocking=True,
         msc2716_historical=False,
+        msc2716_redactions=False,
+    )
+    V8 = RoomVersion(
+        "8",
+        RoomDisposition.STABLE,
+        EventFormatVersions.V3,
+        StateResolutionVersions.V2,
+        enforce_key_validity=True,
+        special_case_aliases_auth=False,
+        strict_canonicaljson=True,
+        limit_notifications_power_levels=True,
+        msc2176_redaction_rules=False,
+        msc3083_join_rules=True,
+        msc2403_knocking=True,
+        msc2716_historical=False,
+        msc2716_redactions=False,
     )
     MSC2716 = RoomVersion(
         "org.matrix.msc2716",
@@ -204,10 +229,11 @@ class RoomVersions:
         msc3083_join_rules=False,
         msc2403_knocking=True,
         msc2716_historical=True,
+        msc2716_redactions=False,
     )
-    V8 = RoomVersion(
-        "8",
-        RoomDisposition.STABLE,
+    MSC2716v2 = RoomVersion(
+        "org.matrix.msc2716v2",
+        RoomDisposition.UNSTABLE,
         EventFormatVersions.V3,
         StateResolutionVersions.V2,
         enforce_key_validity=True,
@@ -215,9 +241,10 @@ class RoomVersions:
         strict_canonicaljson=True,
         limit_notifications_power_levels=True,
         msc2176_redaction_rules=False,
-        msc3083_join_rules=True,
+        msc3083_join_rules=False,
         msc2403_knocking=True,
-        msc2716_historical=False,
+        msc2716_historical=True,
+        msc2716_redactions=True,
     )
 
 
diff --git a/synapse/events/utils.py b/synapse/events/utils.py
index a0c07f62f4..b6da2f60af 100644
--- a/synapse/events/utils.py
+++ b/synapse/events/utils.py
@@ -17,7 +17,7 @@ from typing import Any, Mapping, Union
 
 from frozendict import frozendict
 
-from synapse.api.constants import EventTypes, RelationTypes
+from synapse.api.constants import EventContentFields, EventTypes, RelationTypes
 from synapse.api.errors import Codes, SynapseError
 from synapse.api.room_versions import RoomVersion
 from synapse.util.async_helpers import yieldable_gather_results
@@ -135,6 +135,12 @@ def prune_event_dict(room_version: RoomVersion, event_dict: dict) -> dict:
         add_fields("history_visibility")
     elif event_type == EventTypes.Redaction and room_version.msc2176_redaction_rules:
         add_fields("redacts")
+    elif room_version.msc2716_redactions and event_type == EventTypes.MSC2716_INSERTION:
+        add_fields(EventContentFields.MSC2716_NEXT_CHUNK_ID)
+    elif room_version.msc2716_redactions and event_type == EventTypes.MSC2716_CHUNK:
+        add_fields(EventContentFields.MSC2716_CHUNK_ID)
+    elif room_version.msc2716_redactions and event_type == EventTypes.MSC2716_MARKER:
+        add_fields(EventContentFields.MSC2716_MARKER_INSERTION)
 
     allowed_fields = {k: v for k, v in event_dict.items() if k in allowed_keys}