Experimental support for MSC3772 (#12740)

Implements the following behind an experimental configuration flag:

* A new push rule kind for mutually related events.
* A new default push rule (`.m.rule.thread_reply`) under an unstable prefix.

This is missing part of MSC3772:

* The `.m.rule.thread_reply_to_me` push rule, this depends on MSC3664 / #11804.

1 files changed, 14 insertions, 0 deletions

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

index a17b35a605..4c7278b5a1 100644
--- a/synapse/push/baserules.py
+++ b/synapse/push/baserules.py
@@ -139,6 +139,7 @@ BASE_APPEND_CONTENT_RULES: List[Dict[str, Any]] = [
             {
                 "kind": "event_match",
                 "key": "content.body",
+                # Match the localpart of the requester's MXID.
                 "pattern_type": "user_localpart",
             }
         ],
@@ -191,6 +192,7 @@ BASE_APPEND_OVERRIDE_RULES: List[Dict[str, Any]] = [
                 "pattern": "invite",
                 "_cache_key": "_invite_member",
             },
+            # Match the requester's MXID.
             {"kind": "event_match", "key": "state_key", "pattern_type": "user_id"},
         ],
         "actions": [
@@ -351,6 +353,18 @@ BASE_APPEND_UNDERRIDE_RULES: List[Dict[str, Any]] = [
         ],
     },
     {
+        "rule_id": "global/underride/.org.matrix.msc3772.thread_reply",
+        "conditions": [
+            {
+                "kind": "org.matrix.msc3772.relation_match",
+                "rel_type": "m.thread",
+                # Match the requester's MXID.
+                "sender_type": "user_id",
+            }
+        ],
+        "actions": ["notify", {"set_tweak": "highlight", "value": False}],
+    },
+    {
         "rule_id": "global/underride/.m.rule.message",
         "conditions": [
             {