preserve order of appended items in stream (#2960)

Signed-off-by: Tw <tw19881113@gmail.com>

lib/phoenix_live_view/test/dom.ex

@@ -434,10 +434,9 @@ defmodule Phoenix.LiveViewTest.DOM do
           Enum.reduce(stream_inserts, children, fn {id, {ref, insert_at, _limit}}, acc ->
             old_index = Enum.find_index(acc, &(attribute(&1, "id") == id))
 
-            not_appended? =
-              is_nil(Enum.find_index(updated_appended, &(attribute(&1, "id") == id)))
+            appended? = Enum.any?(updated_appended, &(attribute(&1, "id") == id))
 
-            existing? = Enum.find_index(updated_existing_children, &(attribute(&1, "id") == id))
+            existing? = Enum.any?(updated_existing_children, &(attribute(&1, "id") == id))
             deleted? = MapSet.member?(stream_deletes, id)
 
             child =
@@ -453,11 +452,11 @@ defmodule Phoenix.LiveViewTest.DOM do
                 acc
 
               # skip added children that aren't ours if they are not being appended
-              not_appended? && parent_id && parent_id != container_id ->
+              not appended? && parent_id && parent_id != container_id ->
                 acc
 
               # do not append existing child if already present, only update in place
-              old_index && insert_at == -1 && existing? ->
+              old_index && insert_at == -1 && (existing? or appended?) ->
                 if deleted? do
                   acc |> List.delete_at(old_index) |> List.insert_at(insert_at, child)
                 else

test/phoenix_live_view/integrations/stream_test.exs

@@ -118,6 +118,14 @@ defmodule Phoenix.LiveView.StreamTest do
     refute lv |> element("#users div") |> has_element?()
   end
 
+  test "should preserve the order of appended items", %{conn: conn} do
+    {:ok, lv, _} = live(conn, "/stream")
+    assert lv |> element("#users div:last-child") |> render =~ "callan"
+
+    lv |> render_hook("append-users", %{})
+    assert lv |> element("#users div:last-child") |> render =~ "last_user"
+  end
+
   test "stream reset on patch", %{conn: conn} do
     {:ok, lv, _html} = live(conn, "/healthy/fruits")
 

test/support/live_views/streams.ex

@@ -41,6 +41,11 @@ defmodule Phoenix.LiveViewTest.StreamLive do
     %{id: 2, name: "callan"}
   ]
 
+  @append_users [
+    %{id: 4, name: "foo"},
+    %{id: 3, name: "last_user"},
+  ]
+
   def mount(_params, _session, socket) do
     {:ok,
      socket
@@ -88,6 +93,10 @@ defmodule Phoenix.LiveViewTest.StreamLive do
     {:noreply, stream(socket, :users, @users)}
   end
 
+  def handle_event("append-users", _, socket) do
+    {:noreply, stream(socket, :users, @append_users, at: -1)}
+  end
+
   def handle_event("admin-delete", %{"id" => dom_id}, socket) do
     {:noreply, stream_delete_by_dom_id(socket, :admins, dom_id)}
   end