notifications: Correctly stringify pmUsers to fix navigation to group…

android/app/src/main/java/com/zulipmobile/notifications/FcmMessage.kt

@@ -51,7 +51,7 @@ sealed class Recipient {
      * pmUsers: the user IDs of all users in the conversation.
      */
     data class GroupPm(val pmUsers: Set<Int>) : Recipient() {
-        fun getPmUsersString() = pmUsers.sorted().joinToString { toString() }
+        fun getPmUsersString() = pmUsers.sorted().joinToString(separator=",") { it.toString() }
     }
 
     /** A stream message. */

android/app/src/test/java/com/zulipmobile/notifications/FcmMessageTest.kt

@@ -52,6 +52,19 @@ class FcmMessageTest : FcmMessageTestBase() {
     }
 }
 
+class RecipientTest : FcmMessageTestBase() {
+    @Test
+    fun `GroupPm#getPmUsersString gives the correct string`() {
+        expect.that(Recipient.GroupPm(pmUsers = setOf(123,234,345)).getPmUsersString())
+            .isEqualTo("123,234,345")
+    }
+    @Test
+    fun `GroupPm#getPmUsersString correctly reorders user ids`() {
+        expect.that(Recipient.GroupPm(pmUsers = setOf(234,123,23,345)).getPmUsersString())
+            .isEqualTo("23,123,234,345")
+    }
+}
+
 class MessageFcmMessageTest : FcmMessageTestBase() {
     object Example {
         val base = FcmMessageTestBase.Example.base.plus(sequenceOf(

src/notification/index.js

@@ -97,7 +97,8 @@ export const getNarrowFromNotificationData = (
   const emails = [];
   const idStrs = data.pm_users.split(',');
   for (let i = 0; i < idStrs.length; ++i) {
-    const user = usersById.get(+idStrs[i]);
+    const id = parseInt(idStrs[i], 10);
+    const user = usersById.get(id);
     if (!user) {
       return null;
     }