Phoenix LiveView form does not show errors on polymorphic_embeds_many fields

[anjou-low]

Hi and thanks for the great work !

I'm trying to create a form for a schema which has polymorphic_embeds_many field using polymorphic_embed_inputs_for but the validation errors are not shown on the inner forms when I use the base input core component.

Below is a minimum example using the schemas defined in the documentation (MyApp.Channel.Email and MyApp.Channel.SMS are omitted for brevity) and the code for my LiveView.

Inputing invalid values in the inner fields does not show any error while it does for the outer field. Am I doing something wrong with the way I build my form ?

After looking around a bit, I see that the errors are properly set on the inner fields but they are not displayed and this is related to the use of Phoenix.Component.used_input?/1 in the input core component. I was able to make it work by modifying a few lines of to_form in PolymorphicEmbed.HTML.Helpers but I'd like to know if I am properly constructing my form before going there.

defmodule MyApp.Reminder do
  use Ecto.Schema
  import Ecto.Changeset
  import PolymorphicEmbed

  schema "reminders" do
    field :date, :utc_datetime
    field :text, :string

    polymorphic_embeds_many :channels,
      types: [
        sms: MyApp.Channel.SMS,
        email: MyApp.Channel.Email
      ],
      on_type_not_found: :raise,
      on_replace: :delete
  end

  def changeset(struct, values) do
    struct
    |> cast(values, [:date, :text])
    |> cast_polymorphic_embed(:channels, required: true)
    |> validate_required(:date)
  end
end

defmodule PolembedWeb.ReminderLive.Index do
  use PolembedWeb, :live_view

  import PolymorphicEmbed.HTML.Helpers
  alias MyApp.Reminder

  @impl true
  def mount(_params, _session, socket) do
    form =
      Reminder.changeset(%Reminder{}, %{
        "channels" => [
          %{"__type__" => "sms", "number" => "32"},
          %{"__type__" => "email"}
        ]
      })
      |> to_form()

    {:ok, assign(socket, form: form)}
  end

  @impl true
  def handle_event("validate", %{"reminder" => reminder_params}, socket) do
    form = Reminder.changeset(%Reminder{}, reminder_params) |> to_form(action: :validate)
    {:noreply, assign(socket, form: form)}
  end

  @impl true
  def handle_event("save", _params, socket) do
    {:noreply, socket}
  end

  @impl true
  def render(assigns) do
    ~H"""
    <.form for={@form} id="reminders-form" phx-change="validate" phx-submit="save">
      <.input field={@form[:date]} type="date" label="Name" />
      <.polymorphic_embed_inputs_for :let={channel} field={@form[:channels]}>
        <%= case source_module(channel) do %>
          <% MyApp.Channel.SMS -> %>
            <.input field={channel[:number]} type="number" label="Number" />
          <% MyApp.Channel.Email -> %>
            <.input field={channel[:address]} type="text" label="Address" />
        <% end %>
      </.polymorphic_embed_inputs_for>
    </.form>
    """
  end
end

[nduitz]

@anjou-low Hey, i can confirm the issue with Phoenix.Component.used_input?/1.
Could you elaborate what changes you did to to_form to make it work?