Add a concept of default push rules, using it for tombstone notifications

src/pushprocessor.js

@@ -23,6 +23,37 @@ import {escapeRegExp, globToRegexp} from "./utils";
 
 const RULEKINDS_IN_ORDER = ['override', 'content', 'room', 'sender', 'underride'];
 
+// The default override rules to apply when calculating actions for an event. These
+// defaults apply under no other circumstances to avoid confusing the client with server
+// state. We do this for two reasons:
+//   1. Synapse is unlikely to send us the push rule in an incremental sync - see
+//      https://github.com/matrix-org/synapse/pull/4867#issuecomment-481446072 for
+//      more details.
+//   2. We often want to start using push rules ahead of the server supporting them,
+//      and so we can put them here.
+const DEFAULT_OVERRIDE_RULES = [
+    {
+        // For homeservers which don't support MSC1930 yet
+        rule_id: ".m.rule.tombstone",
+        default: true,
+        enabled: true,
+        conditions: [
+            {
+                kind: "event_match",
+                key: "type",
+                pattern: "m.room.tombstone",
+            },
+        ],
+        actions: [
+            "notify",
+            {
+                set_tweak: "highlight",
+                value: true,
+            },
+        ],
+    },
+];
+
 /**
  * Construct a Push Processor.
  * @constructor
@@ -312,6 +343,33 @@ function PushProcessor(client) {
         return actionObj;
     };
 
+    const applyRuleDefaults = function(clientRuleset) {
+        // Deep clone the object before we mutate it
+        const ruleset = JSON.parse(JSON.stringify(clientRuleset));
+
+        if (!clientRuleset['global']) {
+            clientRuleset['global'] = {};
+        }
+        if (!clientRuleset['global']['override']) {
+            clientRuleset['global']['override'] = [];
+        }
+
+        // Apply default overrides
+        const globalOverrides = clientRuleset['global']['override'];
+        for (const override of DEFAULT_OVERRIDE_RULES) {
+            const existingRule = globalOverrides
+                .find((r) => r.rule_id === override.rule_id);
+
+            if (!existingRule) {
+                const ruleId = override.rule_id;
+                console.warn(`Adding default global override for ${ruleId}`);
+                globalOverrides.push(override);
+            }
+        }
+
+        return ruleset;
+    };
+
     this.ruleMatchesEvent = function(rule, ev) {
         let ret = true;
         for (let i = 0; i < rule.conditions.length; ++i) {
@@ -331,7 +389,8 @@ function PushProcessor(client) {
      * @return {PushAction}
      */
     this.actionsForEvent = function(ev) {
-        return pushActionsForEventAndRulesets(ev, client.pushRules);
+        const rules = applyRuleDefaults(client.pushRules);
+        return pushActionsForEventAndRulesets(ev, rules);
     };
 
     /**