Add `push.enabled` option to disable push notification calculation (#14551)

* Add initial option

* changelog

* Some more linting

changelog.d/14551.feature

@@ -0,0 +1 @@
+Add new `push.enabled` config option to allow opting out of push notification calculation.

docs/usage/configuration/config_documentation.md

@@ -3355,6 +3355,10 @@ Configuration settings related to push notifications
 This setting defines options for push notifications.
 
 This option has a number of sub-options. They are as follows:
+* `enable_push`: Enables or disables push notification calculation. Note, disabling this will also
+   stop unread counts being calculated for rooms. This mode of operation is intended
+   for homeservers which may only have bots or appservice users connected, or are otherwise
+   not interested in push/unread counters. This is enabled by default.
 * `include_content`: Clients requesting push notifications can either have the body of
    the message sent in the notification poke along with other details
    like the sender, or just the event ID and room ID (`event_id_only`).
@@ -3375,6 +3379,7 @@ This option has a number of sub-options. They are as follows:
 Example configuration:
 ```yaml
 push:
+  enable_push: true
   include_content: false
   group_unread_count_by_room: false
 ```

synapse/config/push.py

@@ -26,6 +26,7 @@ class PushConfig(Config):
     def read_config(self, config: JsonDict, **kwargs: Any) -> None:
         push_config = config.get("push") or {}
         self.push_include_content = push_config.get("include_content", True)
+        self.enable_push = push_config.get("enabled", True)
         self.push_group_unread_count_by_room = push_config.get(
             "group_unread_count_by_room", True
         )

synapse/push/bulk_push_rule_evaluator.py

@@ -106,6 +106,7 @@ class BulkPushRuleEvaluator:
         self.store = hs.get_datastores().main
         self.clock = hs.get_clock()
         self._event_auth_handler = hs.get_event_auth_handler()
+        self.should_calculate_push_rules = self.hs.config.push.enable_push
 
         self._related_event_match_enabled = self.hs.config.experimental.msc3664_enabled
 
@@ -269,6 +270,8 @@ class BulkPushRuleEvaluator:
         for each event, check if the message should increment the unread count, and
         insert the results into the event_push_actions_staging table.
         """
+        if not self.should_calculate_push_rules:
+            return
         # For batched events the power level events may not have been persisted yet,
         # so we pass in the batched events. Thus if the event cannot be found in the
         # database we can check in the batch.

tests/push/test_bulk_push_rule_evaluator.py

@@ -6,10 +6,11 @@ from synapse.rest import admin
 from synapse.rest.client import login, register, room
 from synapse.types import create_requester
 
-from tests import unittest
+from tests.test_utils import simple_async_mock
+from tests.unittest import HomeserverTestCase, override_config
 
 
-class TestBulkPushRuleEvaluator(unittest.HomeserverTestCase):
+class TestBulkPushRuleEvaluator(HomeserverTestCase):
 
     servlets = [
         admin.register_servlets_for_client_rest_resource,
@@ -72,3 +73,43 @@ class TestBulkPushRuleEvaluator(unittest.HomeserverTestCase):
         bulk_evaluator = BulkPushRuleEvaluator(self.hs)
         # should not raise
         self.get_success(bulk_evaluator.action_for_events_by_user([(event, context)]))
+
+    @override_config({"push": {"enabled": False}})
+    def test_action_for_event_by_user_disabled_by_config(self) -> None:
+        """Ensure that push rules are not calculated when disabled in the config"""
+        # Create a new user and room.
+        alice = self.register_user("alice", "pass")
+        token = self.login(alice, "pass")
+
+        room_id = self.helper.create_room_as(
+            alice, room_version=RoomVersions.V9.identifier, tok=token
+        )
+
+        # Alter the power levels in that room to include stringy and floaty levels.
+        # We need to suppress the validation logic or else it will reject these dodgy
+        # values. (Presumably this validation was not always present.)
+        event_creation_handler = self.hs.get_event_creation_handler()
+        requester = create_requester(alice)
+
+        # Create a new message event, and try to evaluate it under the dodgy
+        # power level event.
+        event, context = self.get_success(
+            event_creation_handler.create_event(
+                requester,
+                {
+                    "type": "m.room.message",
+                    "room_id": room_id,
+                    "content": {
+                        "msgtype": "m.text",
+                        "body": "helo",
+                    },
+                    "sender": alice,
+                },
+            )
+        )
+
+        bulk_evaluator = BulkPushRuleEvaluator(self.hs)
+        bulk_evaluator._action_for_event_by_user = simple_async_mock()  # type: ignore[assignment]
+        # should not raise
+        self.get_success(bulk_evaluator.action_for_events_by_user([(event, context)]))
+        bulk_evaluator._action_for_event_by_user.assert_not_called()