Implement MSC3966: a push rule condition to check if an array contains a value (#3180)

* Support MSC3966 to match values in an array in push rule conditions.

* Update to stable identifiers.

* Appease the linter.

src/pushprocessor.ts

@@ -26,6 +26,7 @@ import {
     IContainsDisplayNameCondition,
     IEventMatchCondition,
     IEventPropertyIsCondition,
+    IEventPropertyContainsCondition,
     IPushRule,
     IPushRules,
     IRoomMemberCountCondition,
@@ -340,6 +341,8 @@ export class PushProcessor {
                 return this.eventFulfillsEventMatchCondition(cond, ev);
             case ConditionKind.EventPropertyIs:
                 return this.eventFulfillsEventPropertyIsCondition(cond, ev);
+            case ConditionKind.EventPropertyContains:
+                return this.eventFulfillsEventPropertyContains(cond, ev);
             case ConditionKind.ContainsDisplayName:
                 return this.eventFulfillsDisplayNameCondition(cond, ev);
             case ConditionKind.RoomMemberCount:
@@ -488,6 +491,24 @@ export class PushProcessor {
         return cond.value === this.valueForDottedKey(cond.key, ev);
     }
 
+    /**
+     * Check whether the given event matches the push rule condition by fetching
+     * the property from the event and comparing exactly against the condition's
+     * value.
+     * @param cond - The push rule condition to check for a match.
+     * @param ev - The event to check for a match.
+     */
+    private eventFulfillsEventPropertyContains(cond: IEventPropertyContainsCondition, ev: MatrixEvent): boolean {
+        if (!cond.key || cond.value === undefined) {
+            return false;
+        }
+        const val = this.valueForDottedKey(cond.key, ev);
+        if (!Array.isArray(val)) {
+            return false;
+        }
+        return val.includes(cond.value);
+    }
+
     private eventFulfillsCallStartedCondition(
         _cond: ICallStartedCondition | ICallStartedPrefixCondition,
         ev: MatrixEvent,