Regression in 1.1.1 when using `render_submit/2` with a custom submitter on forms without IDs

[frerich]

Environment

• Elixir version (elixir -v): 1.18.3
• Phoenix version (mix deps): 1.8.0-rc.4
• Phoenix LiveView version (mix deps): 1.1.1
• Operating system: macOS 15.5
• Browsers you attempted to reproduce this bug on (the more the merrier): -
• Does the problem persist after removing "assets/node_modules" and trying again? Yes/no: -

Actual behavior

Calling Phoenix.LiveViewTest.render_submit/1 raises an error when using a custom submitter if the form has no ID.

To reproduce, add this test to e.g. test/phoenix_live_view/integrations/elements_test.exs:

    test "put_submitter/2 works on forms without IDs", %{live: view} do
      view
      |> element("form[data-name='form-without-id']")
      |> put_submitter("[name=button]")
      |> render_submit()
    end

Also, extend phoenix_live_view/test/support/live_views/elements.ex with a form which has no ID by adding:

    <form data-name="form-without-id" phx-submit="form-submit">
      <button name="button" type="submit">button</button>
    </form>

Running this test via mix test test/phoenix_live_view/integrations/elements_test.exs yields:

  1) test render_submit put_submitter/2 works on forms without IDs (Phoenix.LiveView.ElementsTest)
     test/phoenix_live_view/integrations/elements_test.exs:577
     ** (EXIT from #PID<0.366.0>) an exception was raised:

          ** (FunctionClauseError) no function clause matching in LazyHTML.from_tree/1

          The following arguments were given to LazyHTML.from_tree/1:

              # 1
              {"form", [{"data-name", "form-without-id"}, {"phx-submit", "form-submit"}], ["\n  ", {"button", [{"name", "button"}, {"type", "submit"}], ["button"]}, "\n"]}

          Attempted function clauses (showing 1 out of 1):

              def from_tree(tree) when is_list(tree)

          stacktrace:
            (lazy_html 0.1.3) lib/lazy_html.ex:188: LazyHTML.from_tree/1
            (phoenix_live_view 1.2.0-dev) lib/phoenix_live_view/test/client_proxy.ex:1319: Phoenix.LiveViewTest.ClientProxy.maybe_submitter/4
            (phoenix_live_view 1.2.0-dev) lib/phoenix_live_view/test/client_proxy.ex:1281: Phoenix.LiveViewTest.ClientProxy.maybe_values/4
            (phoenix_live_view 1.2.0-dev) lib/phoenix_live_view/test/client_proxy.ex:369: Phoenix.LiveViewTest.ClientProxy.handle_info/2
            (stdlib 6.2.2) gen_server.erl:2345: :gen_server.try_handle_info/3
            (stdlib 6.2.2) gen_server.erl:2433: :gen_server.handle_msg/6
            (stdlib 6.2.2) proc_lib.erl:329: :proc_lib.init_p_do_apply/3

Expected behavior

The test should succeed, no error should be printed.

Further observations

• This appears to be a regression since Phoenix LiveView 1.0.17.
• Omitting the Phoenix.LiveViewTest.put_submitter/2 call or adding a dummy ID (e.g. id="x") to the <form> element avoids the error.

[SteffenDE]

Thank you for the detailed description!