Add support for changing the actions for default rules

See matrix-org/matrix-doc#283

Works by adding dummy rules to the push rules table with a negative priority class and then using those rules to clobber the default rule actions when adding the default rules in ``list_with_base_rules``

synapse/rest/client/v1/push_rule.py

@@ -22,7 +22,7 @@ from .base import ClientV1RestServlet, client_path_patterns
 from synapse.storage.push_rule import (
     InconsistentRuleException, RuleNotFoundException
 )
-import synapse.push.baserules as baserules
+from synapse.push.baserules import list_with_base_rules, BASE_RULE_IDS
 from synapse.push.rulekinds import (
     PRIORITY_CLASS_MAP, PRIORITY_CLASS_INVERSE_MAP
 )
@@ -55,6 +55,10 @@ class PushRuleRestServlet(ClientV1RestServlet):
             yield self.set_rule_attr(requester.user.to_string(), spec, content)
             defer.returnValue((200, {}))
 
+        if spec['rule_id'].startswith('.'):
+            # Rule ids starting with '.' are reserved for server default rules.
+            raise SynapseError(400, "cannot add new rule_ids that start with '.'")
+
         try:
             (conditions, actions) = _rule_tuple_from_request_object(
                 spec['template'],
@@ -128,7 +132,7 @@ class PushRuleRestServlet(ClientV1RestServlet):
             ruleslist.append(rule)
 
         # We're going to be mutating this a lot, so do a deep copy
-        ruleslist = copy.deepcopy(baserules.list_with_base_rules(ruleslist))
+        ruleslist = copy.deepcopy(list_with_base_rules(ruleslist))
 
         rules = {'global': {}, 'device': {}}
 
@@ -197,6 +201,18 @@ class PushRuleRestServlet(ClientV1RestServlet):
             return self.hs.get_datastore().set_push_rule_enabled(
                 user_id, namespaced_rule_id, val
             )
+        elif spec['attr'] == 'actions':
+            actions = val.get('actions')
+            _check_actions(actions)
+            namespaced_rule_id = _namespaced_rule_id_from_spec(spec)
+            rule_id = spec['rule_id']
+            is_default_rule = rule_id.startswith(".")
+            if is_default_rule:
+                if namespaced_rule_id not in BASE_RULE_IDS:
+                    raise SynapseError(404, "Unknown rule %r" % (namespaced_rule_id,))
+            return self.hs.get_datastore().set_push_rule_actions(
+                user_id, namespaced_rule_id, actions, is_default_rule
+            )
         else:
             raise UnrecognizedRequestError()
 
@@ -274,6 +290,15 @@ def _rule_tuple_from_request_object(rule_template, rule_id, req_obj):
         raise InvalidRuleException("No actions found")
     actions = req_obj['actions']
 
+    _check_actions(actions)
+
+    return conditions, actions
+
+
+def _check_actions(actions):
+    if not isinstance(actions, list):
+        raise InvalidRuleException("No actions found")
+
     for a in actions:
         if a in ['notify', 'dont_notify', 'coalesce']:
             pass
@@ -282,8 +307,6 @@ def _rule_tuple_from_request_object(rule_template, rule_id, req_obj):
         else:
             raise InvalidRuleException("Unrecognised action")
 
-    return conditions, actions
-
 
 def _add_empty_priority_class_arrays(d):
     for pc in PRIORITY_CLASS_MAP.keys():