push_notification: Return early if no device registered - w/o bouncer.

In 'send_push_notifications_legacy', when a user has no registered
devices:
* `uses_notification_bouncer()`=True: we log "Skipping..." and return.

* `uses_notification_bouncer()`=False: we make some function calls,
  which effectively does nothing.

It's better to have a common check (and log) early in the codepath.
This commit makes that change.

zerver/lib/push_notifications.py

@@ -590,13 +590,7 @@ def send_notifications_to_bouncer(
     android_devices: Sequence[DeviceToken],
     apple_devices: Sequence[DeviceToken],
 ) -> None:
-    if len(android_devices) + len(apple_devices) == 0:
-        logger.info(
-            "Skipping contacting the bouncer for user %s because there are no registered devices",
-            user_profile.id,
-        )
-
-        return
+    assert len(android_devices) + len(apple_devices) != 0
 
     post_data = {
         "user_uuid": str(user_profile.uuid),
@@ -1323,6 +1317,17 @@ def send_push_notifications_legacy(
         PushDeviceToken.objects.filter(user=user_profile, kind=PushDeviceToken.APNS).order_by("id")
     )
 
+    # Added this nocoverage check for this commit. We plan to add a commit
+    # which will remove the mocking of 'send_push_notifications_legacy'
+    # in 'test_e2ee_push_notifications' - and this case will be covered
+    # there as a part of that broader effort.
+    if len(android_devices) + len(apple_devices) == 0:  # nocoverage
+        logger.info(
+            "Skipping legacy push notifications for user %s because there are no registered devices",
+            user_profile.id,
+        )
+        return
+
     if uses_notification_bouncer():
         send_notifications_to_bouncer(
             user_profile, apns_payload, gcm_payload, gcm_options, android_devices, apple_devices

zerver/tests/test_handle_push_notification.py

@@ -362,6 +362,9 @@ class HandlePushNotificationTest(PushNotificationTestCase):
     @mock.patch("zerver.lib.push_notifications.push_notifications_configured", return_value=True)
     @override_settings(ZULIP_SERVICE_PUSH_NOTIFICATIONS=False, ZULIP_SERVICES=set())
     def test_read_message(self, mock_push_notifications: mock.MagicMock) -> None:
+        self.setup_apns_tokens()
+        self.setup_fcm_tokens()
+
         user_profile = self.example_user("hamlet")
         message = self.get_message(
             Recipient.PERSONAL,

zerver/tests/test_push_notifications.py

@@ -2138,23 +2138,6 @@ class TestGetGCMPayload(PushNotificationTestCase):
 
 
 class TestSendNotificationsToBouncer(PushNotificationTestCase):
-    def test_send_notifications_to_bouncer_when_no_devices(self) -> None:
-        user = self.example_user("hamlet")
-
-        with (
-            mock.patch("zerver.lib.remote_server.send_to_push_bouncer") as mock_send,
-            self.assertLogs("zerver.lib.push_notifications", level="INFO") as mock_logging_info,
-        ):
-            send_notifications_to_bouncer(
-                user, {"apns": True}, {"gcm": True}, {}, android_devices=[], apple_devices=[]
-            )
-
-        self.assertIn(
-            f"INFO:zerver.lib.push_notifications:Skipping contacting the bouncer for user {user.id} because there are no registered devices",
-            mock_logging_info.output,
-        )
-        mock_send.assert_not_called()
-
     @mock.patch("zerver.lib.remote_server.send_to_push_bouncer")
     def test_send_notifications_to_bouncer(self, mock_send: mock.MagicMock) -> None:
         user = self.example_user("hamlet")