fix LiveViewTest stream limit handling to match js

lib/phoenix_live_view/test/dom.ex

@@ -430,20 +430,35 @@ defmodule Phoenix.LiveViewTest.DOM do
       content_changed? && type == "stream" ->
         children = updated_existing_children ++ updated_appended
 
+        # we always reduce over all streams, even if only one of them is actually relevant
+        # for this container...
         new_children =
-          Enum.reduce(streams, children, fn item, acc ->
-            [ref, inserts, _deletes | _maybe_reset] = item
+          Enum.reduce(streams, updated_existing_children, fn item, acc ->
+            [ref, inserts, _deletes | maybe_reset] = item
+            reset = maybe_reset == [true]
+
+            # remove all children that are in a stream that was reset
+            acc =
+              if reset do
+                Enum.reject(acc, fn child ->
+                  item_ref = attribute(child, "data-phx-stream")
+                  item_ref == ref
+                end)
+              else
+                acc
+              end
 
-            Enum.reduce(inserts, acc, fn [id, insert_at, _limit], acc ->
-              old_index = Enum.find_index(acc, &(attribute(&1, "id") == id))
+            Enum.reduce(inserts, acc, fn [id, insert_at, limit], acc ->
+              old_index = Enum.find_index(children, &(attribute(&1, "id") == id))
+              current_index = Enum.find_index(acc, &(attribute(&1, "id") == id))
 
               appended? = Enum.any?(updated_appended, &(attribute(&1, "id") == id))
 
               existing? = Enum.any?(updated_existing_children, &(attribute(&1, "id") == id))
               deleted? = MapSet.member?(stream_deletes, id)
 
               child =
-                case old_index && Enum.at(acc, old_index) do
+                case old_index && Enum.at(children, old_index) do
                   nil -> nil
                   child -> set_attr(child, "data-phx-stream", ref)
                 end
@@ -459,19 +474,20 @@ defmodule Phoenix.LiveViewTest.DOM do
                   acc
 
                 # do not append existing child if already present, only update in place
-                old_index && insert_at == -1 && (existing? or appended?) ->
+                current_index && insert_at == -1 && (existing? or appended?) ->
                   if deleted? do
-                    acc |> List.delete_at(old_index) |> List.insert_at(insert_at, child)
+                    acc |> List.delete_at(current_index) |> List.insert_at(insert_at, child)
                   else
-                    List.replace_at(acc, old_index, child)
+                    List.replace_at(acc, current_index, child)
                   end
 
-                old_index && insert_at ->
-                  acc |> List.delete_at(old_index) |> List.insert_at(insert_at, child)
+                current_index && insert_at ->
+                  acc |> List.delete_at(current_index) |> List.insert_at(insert_at, child)
 
-                !old_index && insert_at ->
+                !current_index && insert_at ->
                   List.insert_at(acc, insert_at, child)
               end
+              |> maybe_apply_stream_limit(limit)
             end)
           end)
           |> Enum.reject(fn child ->
@@ -615,4 +631,10 @@ defmodule Phoenix.LiveViewTest.DOM do
     do: Enum.map(values, &normalize_attribute_order/1)
 
   defp normalize_attribute_order(value), do: value
+
+  defp maybe_apply_stream_limit(children, nil), do: children
+
+  defp maybe_apply_stream_limit(children, limit) do
+    Enum.take(children, limit)
+  end
 end

test/phoenix_live_view/integrations/stream_test.exs

@@ -336,6 +336,184 @@ defmodule Phoenix.LiveView.StreamTest do
            end) =~ ~r/streams can only be consumed directly by a for comprehension/
   end
 
+  describe "limit" do
+    test "limit is enforced on mount, but not dead render", %{conn: conn} do
+      conn = get(conn, "/stream/limit")
+      assert html_response(conn, 200) |> ids_in_ul_list() == [
+               "items-1",
+               "items-2",
+               "items-3",
+               "items-4",
+               "items-5",
+               "items-6",
+               "items-7",
+               "items-8",
+               "items-9",
+               "items-10"
+            ]
+
+      {:ok, _lv, html} = live(conn)
+
+      assert ids_in_ul_list(html) == [
+        "items-6",
+        "items-7",
+        "items-8",
+        "items-9",
+        "items-10"
+      ]
+    end
+
+    test "removes item at front when appending and limit is negative", %{conn: conn} do
+      {:ok, lv, _html} = live(conn, "/stream/limit")
+
+      assert lv |> render_hook("configure", %{"at" => "-1", "limit" => "-5"}) |> ids_in_ul_list()== [
+        "items-6",
+        "items-7",
+        "items-8",
+        "items-9",
+        "items-10"
+      ]
+
+      assert lv |> render_hook("insert_1") |> ids_in_ul_list()== [
+        "items-7",
+        "items-8",
+        "items-9",
+        "items-10",
+        "items-11"
+      ]
+
+      assert lv |> render_hook("insert_10") |> ids_in_ul_list()== [
+        "items-17",
+        "items-18",
+        "items-19",
+        "items-20",
+        "items-21"
+      ]
+    end
+
+    test "removes item at back when prepending and limit is positive", %{conn: conn} do
+      {:ok, lv, _html} = live(conn, "/stream/limit")
+
+      assert lv |> render_hook("configure", %{"at" => "0", "limit" => "5"}) |> ids_in_ul_list() == [
+        "items-10",
+        "items-9",
+        "items-8",
+        "items-7",
+        "items-6"
+      ]
+
+      assert lv |> render_hook("insert_1") |> ids_in_ul_list()== [
+        "items-11",
+        "items-10",
+        "items-9",
+        "items-8",
+        "items-7"
+      ]
+
+      assert lv |> render_hook("insert_10") |> ids_in_ul_list()== [
+        "items-21",
+        "items-20",
+        "items-19",
+        "items-18",
+        "items-17"
+      ]
+    end
+
+    test "does nothing if appending and positive limit is reached", %{conn: conn} do
+      {:ok, lv, _html} = live(conn, "/stream/limit")
+
+      assert lv |> render_hook("configure", %{"at" => "-1", "limit" => "5"}) |> ids_in_ul_list() == [
+        "items-1",
+        "items-2",
+        "items-3",
+        "items-4",
+        "items-5"
+      ]
+
+      # adding new items should do nothing, as the limit is reached
+      assert lv |> render_hook("insert_1") |> ids_in_ul_list()== [
+        "items-1",
+        "items-2",
+        "items-3",
+        "items-4",
+        "items-5"
+      ]
+
+      assert lv |> render_hook("insert_10") |> ids_in_ul_list() == [
+        "items-1",
+        "items-2",
+        "items-3",
+        "items-4",
+        "items-5"
+      ]
+    end
+
+    test "does nothing if prepending and negative limit is reached", %{conn: conn} do
+      {:ok, lv, _html} = live(conn, "/stream/limit")
+
+      assert lv |> render_hook("configure", %{"at" => "0", "limit" => "-5"}) |> ids_in_ul_list() == [
+        "items-5",
+        "items-4",
+        "items-3",
+        "items-2",
+        "items-1"
+      ]
+
+      # adding new items should do nothing, as the limit is reached
+      assert lv |> render_hook("insert_1") |> ids_in_ul_list()== [
+        "items-5",
+        "items-4",
+        "items-3",
+        "items-2",
+        "items-1"
+      ]
+
+      assert lv |> render_hook("insert_10") |> ids_in_ul_list() == [
+        "items-5",
+        "items-4",
+        "items-3",
+        "items-2",
+        "items-1"
+      ]
+    end
+
+    test "arbitrary index", %{conn: conn} do
+      {:ok, lv, _html} = live(conn, "/stream/limit")
+
+      assert lv |> render_hook("configure", %{"at" => "1", "limit" => "5"}) |> ids_in_ul_list() == [
+        "items-1",
+        "items-10",
+        "items-9",
+        "items-8",
+        "items-7"
+      ]
+
+      assert lv |> render_hook("insert_10") |> ids_in_ul_list()== [
+        "items-1",
+        "items-20",
+        "items-19",
+        "items-18",
+        "items-17"
+      ]
+
+      assert lv |> render_hook("configure", %{"at" => "1", "limit" => "-5"}) |> ids_in_ul_list() == [
+        "items-10",
+        "items-5",
+        "items-4",
+        "items-3",
+        "items-2"
+      ]
+
+      assert lv |> render_hook("insert_10") |> ids_in_ul_list() == [
+        "items-20",
+        "items-5",
+        "items-4",
+        "items-3",
+        "items-2"
+      ]
+    end
+  end
+
   defp assert_pruned_stream(lv) do
     stream = StreamLive.run(lv, fn socket -> {:reply, socket.assigns.streams.users, socket} end)
     assert stream.inserts == []

test/support/router.ex

@@ -126,6 +126,7 @@ defmodule Phoenix.LiveViewTest.Router do
     live "/stream", StreamLive
     live "/stream/reset", StreamResetLive
     live "/stream/reset-lc", StreamResetLCLive
+    live "/stream/limit", StreamLimitLive
 
     # healthy
     live "/healthy/:category", HealthyLive