finish thinking

synapse/storage/databases/main/events.py

@@ -2684,6 +2684,8 @@ class PersistEventsStore:
             elif event.type == EventTypes.Retention:
                 # Update the room_retention table.
                 self._store_retention_policy_for_room_txn(txn, event)
+            elif event.type == EventTypes.Member and event.content.get("org.matrix.msc4293.redact_events", False) == True:
+                self._try_store_member_redaction_txn(txn, event)
 
             self._handle_event_relations(txn, event)
 
@@ -2775,6 +2777,23 @@ class PersistEventsStore:
             },
         )
 
+    def _try_store_member_redaction_txn(self, txn: LoggingTransaction, event: EventBase) -> None:
+        # We only want to search for membership transitions which aren't kicks or bans
+        if event.membership != Membership.BAN and not (event.membership == Membership.LEAVE and event.sender != event.state_key):
+            # Not a membership event which is capable of redacting other events.
+            # See MSC4293 for details (as of May 28, 2025): https://github.com/matrix-org/matrix-spec-proposals/pull/4293
+            return
+
+        # We also want to filter out events where the sender can't actually redact (no permission to redact)
+        # TODO
+
+        # Find all the current events sent by this user
+        # TODO
+
+        # Insert them into the redactions table
+        # TODO
+
+
     def insert_labels_for_event_txn(
         self,
         txn: LoggingTransaction,

synapse/storage/schema/main/delta/92/06_redactions_multitarget.sql.postgres

@@ -0,0 +1,8 @@
+-- Create a unique index which *should* be fine because of the existing UNIQUE(event_id) preventing overlap
+ALTER TABLE ONLY redactions ADD CONSTRAINT redactions_event_id_redacts_key UNIQUE (event_id, redacts);
+
+-- Replace the index we're about to drop
+CREATE INDEX redactions_event_id ON redactions USING btree (event_id);
+
+-- Drop the old constraint
+ALTER TABLE ONLY redactions DROP CONSTRAINT redactions_event_id_key;

synapse/storage/schema/main/delta/92/06_redactions_multitarget.sql.sqlite

@@ -0,0 +1,9 @@
+-- sqlite is awful and requires rebuilding the table to drop the UNIQUE(event_id) constraint, so let's do that
+-- and build a new table with the constraints we want.
+CREATE TABLE redactions2 (event_id TEXT NOT NULL, redacts TEXT NOT NULL, have_censored BOOL NOT NULL DEFAULT false, received_ts BIGINT, UNIQUE(event_id, redacts));
+INSERT INTO redactions2 (event_id, redacts, have_censored, received_ts) SELECT r.event_id, r.redacts, r.have_censored, r.received_ts FROM redactions AS r;
+DROP INDEX redactions_redacts;
+DROP TABLE redactions;
+ALTER TABLE redactions2 RENAME TO redactions;
+CREATE INDEX redactions_redacts ON redactions(redacts);
+CREATE INDEX redactions_event_id ON redactions(event_id); -- replace the index we dropped