clear private HOOK_ID as soon as hook is destroyed

Fixes #3496.

When navigating from a sticky LiveView to another page that contains
a hook on an element with the same id, morphdom would merge the old
element into the new one and still find the old HOOK_ID in the element's
DOM.private data, leading to the new hook not initializing properly.

assets/js/phoenix_live_view/view_hook.js

@@ -33,7 +33,10 @@ export default class ViewHook {
   __mounted(){ this.mounted && this.mounted() }
   __updated(){ this.updated && this.updated() }
   __beforeUpdate(){ this.beforeUpdate && this.beforeUpdate() }
-  __destroyed(){ this.destroyed && this.destroyed() }
+  __destroyed(){
+    this.destroyed && this.destroyed()
+    DOM.deletePrivate(this.el, HOOK_ID) // https://github.com/phoenixframework/phoenix_live_view/issues/3496
+  }
   __reconnected(){
     if(this.__isDisconnected){
       this.__isDisconnected = false

test/e2e/support/issues/issue_3496.ex

@@ -0,0 +1,111 @@
+defmodule Phoenix.LiveViewTest.E2E.Issue3496.ALive do
+  # https://github.com/phoenixframework/phoenix_live_view/issues/3496
+
+  use Phoenix.LiveView
+
+  alias Phoenix.LiveView.JS
+
+  def base(assigns) do
+    ~H"""
+    <meta name="csrf-token" content={Plug.CSRFProtection.get_csrf_token()} />
+    <script src="/assets/phoenix/phoenix.min.js">
+    </script>
+    <script type="module">
+      import {LiveSocket} from "/assets/phoenix_live_view/phoenix_live_view.esm.js"
+
+      let csrfToken = document.querySelector("meta[name='csrf-token']").getAttribute("content");
+      let liveSocket = new LiveSocket("/live", window.Phoenix.Socket, {params: {_csrf_token: csrfToken}, hooks: {
+        MyHook: {
+          mounted() {
+            console.log("Hook mounted!")
+          }
+        }
+      }})
+      liveSocket.connect()
+      window.liveSocket = liveSocket
+    </script>
+    <style>
+      * { font-size: 1.1em; }
+    </style>
+    """
+  end
+
+  def with_sticky(assigns) do
+    ~H"""
+    <.base />
+
+    <div>
+      <%= @inner_content %>
+    </div>
+
+    <%= live_render(@socket, Phoenix.LiveViewTest.E2E.Issue3496.StickyLive,
+      id: "sticky",
+      sticky: true
+    ) %>
+    """
+  end
+
+  def without_sticky(assigns) do
+    ~H"""
+    <.base />
+
+    <div>
+      <%= @inner_content %>
+    </div>
+    """
+  end
+
+  def mount(_params, _session, socket) do
+    {:ok, socket, layout: {__MODULE__, :with_sticky}}
+  end
+
+  def render(assigns) do
+    ~H"""
+    <h1>Page A</h1>
+    <.link navigate="/issues/3496/b">Go to page B</.link>
+    """
+  end
+end
+
+defmodule Phoenix.LiveViewTest.E2E.Issue3496.BLive do
+  use Phoenix.LiveView
+
+  alias Phoenix.LiveView.JS
+
+  def mount(_params, _session, socket) do
+    {:ok, socket, layout: {Phoenix.LiveViewTest.E2E.Issue3496.ALive, :without_sticky}}
+  end
+
+  def render(assigns) do
+    ~H"""
+    <h1>Page B</h1>
+    <Phoenix.LiveViewTest.E2E.Issue3496.MyComponent.my_component />
+    """
+  end
+end
+
+defmodule Phoenix.LiveViewTest.E2E.Issue3496.StickyLive do
+  use Phoenix.LiveView
+
+  def mount(_params, _session, socket) do
+    {:ok, socket, layout: false}
+  end
+
+  def render(assigns) do
+    ~H"""
+    <div>
+      <Phoenix.LiveViewTest.E2E.Issue3496.MyComponent.my_component />
+    </div>
+    """
+  end
+end
+
+defmodule Phoenix.LiveViewTest.E2E.Issue3496.MyComponent do
+  use Phoenix.Component
+
+  def my_component(assigns) do
+    ~H"""
+    <div id="my-component" phx-hook="MyHook"></div>
+    """
+  end
+end

test/e2e/test_helper.exs

@@ -149,6 +149,8 @@ defmodule Phoenix.LiveViewTest.E2E.Router do
       live "/3194/other", Issue3194Live.OtherLive
       live "/3378", Issue3378.HomeLive
       live "/3448", Issue3448Live
+      live "/3496/a", Issue3496.ALive
+      live "/3496/b", Issue3496.BLive
     end
   end
 

test/e2e/tests/issues/3496.spec.js

@@ -0,0 +1,21 @@
+const { test, expect } = require("../../test-fixtures");
+const { syncLV } = require("../../utils");
+
+// https://github.com/phoenixframework/phoenix_live_view/issues/3496
+test("hook is initialized properly when reusing id between sticky and non sticky LiveViews", async ({ page }) => {
+  const logs = [];
+  page.on("console", (e) => logs.push(e.text()));
+  const errors = [];
+  page.on("pageerror", (err) => errors.push(err));
+
+  await page.goto("/issues/3496/a");
+  await syncLV(page);
+
+  await page.getByRole("link", { name: "Go to page B" }).click();
+  await syncLV(page);
+
+  expect(logs.filter(e => e.includes("Hook mounted!"))).toHaveLength(2);
+  expect(logs).not.toEqual(expect.arrayContaining([expect.stringMatching("no hook found for custom element")]));
+  // no uncaught exceptions
+  expect(errors).toEqual([]);
+});