Push pending events before redirecting

Previously, there was no way to handle both `push_event` and
`push_redirect` occuring in the same callback. The redirect would
prevent the events from being sent. This commit checks the diff for any
new events, and if they exist, sends them over the channel.

lib/phoenix_live_view/channel.ex

@@ -799,20 +799,23 @@ defmodule Phoenix.LiveView.Channel do
           |> Map.put(:to, to)
 
         new_state
+        |> push_pending_events_on_redirect(new_socket)
         |> push_redirect(opts, ref)
         |> stop_shutdown_redirect(:redirect, opts)
 
       {:redirect, %{to: _to} = opts} ->
         opts = copy_flash(new_state, flash, opts)
 
         new_state
+        |> push_pending_events_on_redirect(new_socket)
         |> push_redirect(opts, ref)
         |> stop_shutdown_redirect(:redirect, opts)
 
       {:live, :redirect, %{to: _to} = opts} ->
         opts = copy_flash(new_state, flash, opts)
 
         new_state
+        |> push_pending_events_on_redirect(new_socket)
         |> push_live_redirect(opts, ref, pending_diff_ack)
         |> stop_shutdown_redirect(:live_redirect, opts)
 
@@ -837,6 +840,12 @@ defmodule Phoenix.LiveView.Channel do
     end
   end
 
+  defp push_pending_events_on_redirect(state, socket) do
+    {:diff, diff, _new_state} = render_diff(state, socket, false)
+    if events = Map.get(diff, :e), do: push(state, "diff", %{:e => events})
+    state
+  end
+
   defp patch_params_and_action!(socket, %{to: to}) do
     destructure [path, query], :binary.split(to, ["?", "#"], [:global])
     to = %{socket.host_uri | path: path, query: query}

test/phoenix_live_view/integrations/event_test.exs

@@ -34,6 +34,29 @@ defmodule Phoenix.LiveView.EventTest do
       assert render(view) =~ "count: 123"
     end
 
+    test "supports events with redirects", %{conn: conn} do
+      {:ok, view, _html} = live(conn, "/events")
+
+      GenServer.call(
+        view.pid,
+        {:run,
+         fn socket ->
+           new_socket =
+             socket
+             |> Component.assign(count: 123)
+             |> LiveView.push_event("my-event", %{one: 1})
+             |> LiveView.push_event("my-event", %{one: 2})
+             |> LiveView.push_redirect(to: "/events")
+
+           {:reply, :ok, new_socket}
+         end}
+      )
+
+      assert_push_event(view, "my-event", %{one: 1})
+      assert_push_event(view, "my-event", %{one: 2})
+      assert_redirected(view, "/events")
+    end
+
     test "sends updates with no assigns diff", %{conn: conn} do
       {:ok, view, _html} = live(conn, "/events")