Consolidate logic for parsing relations. (#12693)

Parse the `m.relates_to` event content field (which describes relations)
in a single place, this is used during:

* Event persistence.
* Validation of the Client-Server API.
* Fetching bundled aggregations.
* Processing of push rules.

Each of these separately implement the logic and each made slightly
different assumptions about what was valid. Some had minor / potential
bugs.

1 files changed, 3 insertions, 3 deletions

diff --git a/synapse/push/bulk_push_rule_evaluator.py b/synapse/push/bulk_push_rule_evaluator.py

index 0ffafc882b..4ac2c546bf 100644
--- a/synapse/push/bulk_push_rule_evaluator.py
+++ b/synapse/push/bulk_push_rule_evaluator.py
@@ -21,7 +21,7 @@ from prometheus_client import Counter
 
 from synapse.api.constants import EventTypes, Membership, RelationTypes
 from synapse.event_auth import get_user_power_level
-from synapse.events import EventBase
+from synapse.events import EventBase, relation_from_event
 from synapse.events.snapshot import EventContext
 from synapse.state import POWER_KEY
 from synapse.storage.databases.main.roommember import EventIdMembership
@@ -78,8 +78,8 @@ def _should_count_as_unread(event: EventBase, context: EventContext) -> bool:
         return False
 
     # Exclude edits.
-    relates_to = event.content.get("m.relates_to", {})
-    if relates_to.get("rel_type") == RelationTypes.REPLACE:
+    relates_to = relation_from_event(event)
+    if relates_to and relates_to.rel_type == RelationTypes.REPLACE:
         return False
 
     # Mark events that have a non-empty string body as unread.