Implement MSC3952: Intentional mentions (#14823)

MSC3952 defines push rules which searches for mentions in a list of
Matrix IDs in the event body, instead of searching the entire event
body for display name / local part.

This is implemented behind an experimental configuration flag and
does not yet implement the backwards compatibility pieces of the MSC.

4 files changed, 33 insertions, 1 deletions

diff --git a/synapse/api/constants.py b/synapse/api/constants.py
index 6f9239d21c..0f224b34cd 100644
--- a/synapse/api/constants.py
+++ b/synapse/api/constants.py
@@ -233,6 +233,9 @@ class EventContentFields:
     # The authorising user for joining a restricted room.
     AUTHORISING_USER: Final = "join_authorised_via_users_server"
 
+    # Use for mentioning users.
+    MSC3952_MENTIONS: Final = "org.matrix.msc3952.mentions"
+
     # an unspecced field added to to-device messages to identify them uniquely-ish
     TO_DEVICE_MSGID: Final = "org.matrix.msgid"
 
diff --git a/synapse/config/experimental.py b/synapse/config/experimental.py
index 2590c88cde..d2d0270ddd 100644
--- a/synapse/config/experimental.py
+++ b/synapse/config/experimental.py
@@ -168,3 +168,8 @@ class ExperimentalConfig(Config):
 
         # MSC3925: do not replace events with their edits
         self.msc3925_inhibit_edit = experimental.get("msc3925_inhibit_edit", False)
+
+        # MSC3952: Intentional mentions
+        self.msc3952_intentional_mentions = experimental.get(
+            "msc3952_intentional_mentions", False
+        )
diff --git a/synapse/push/bulk_push_rule_evaluator.py b/synapse/push/bulk_push_rule_evaluator.py
index f27ba64d53..deaec19564 100644
--- a/synapse/push/bulk_push_rule_evaluator.py
+++ b/synapse/push/bulk_push_rule_evaluator.py
@@ -22,13 +22,20 @@ from typing import (
     List,
     Mapping,
     Optional,
+    Set,
     Tuple,
     Union,
 )
 
 from prometheus_client import Counter
 
-from synapse.api.constants import MAIN_TIMELINE, EventTypes, Membership, RelationTypes
+from synapse.api.constants import (
+    MAIN_TIMELINE,
+    EventContentFields,
+    EventTypes,
+    Membership,
+    RelationTypes,
+)
 from synapse.api.room_versions import PushRuleRoomFlag, RoomVersion
 from synapse.event_auth import auth_types_for_event, get_user_power_level
 from synapse.events import EventBase, relation_from_event
@@ -342,8 +349,24 @@ class BulkPushRuleEvaluator:
             for user_id, level in notification_levels.items():
                 notification_levels[user_id] = int(level)
 
+        # Pull out any user and room mentions.
+        mentions = event.content.get(EventContentFields.MSC3952_MENTIONS)
+        user_mentions: Set[str] = set()
+        room_mention = False
+        if isinstance(mentions, dict):
+            # Remove out any non-string items and convert to a set.
+            user_mentions_raw = mentions.get("user_ids")
+            if isinstance(user_mentions_raw, list):
+                user_mentions = set(
+                    filter(lambda item: isinstance(item, str), user_mentions_raw)
+                )
+            # Room mention is only true if the value is exactly true.
+            room_mention = mentions.get("room") is True
+
         evaluator = PushRuleEvaluator(
             _flatten_dict(event, room_version=event.room_version),
+            user_mentions,
+            room_mention,
             room_member_count,
             sender_power_level,
             notification_levels,
diff --git a/synapse/storage/databases/main/push_rule.py b/synapse/storage/databases/main/push_rule.py
index 14ca167b34..466a1145b7 100644
--- a/synapse/storage/databases/main/push_rule.py
+++ b/synapse/storage/databases/main/push_rule.py
@@ -89,6 +89,7 @@ def _load_rules(
         msc1767_enabled=experimental_config.msc1767_enabled,
         msc3664_enabled=experimental_config.msc3664_enabled,
         msc3381_polls_enabled=experimental_config.msc3381_polls_enabled,
+        msc3952_intentional_mentions=experimental_config.msc3952_intentional_mentions,
     )
 
     return filtered_rules