Phoenix_live_view: Test helper form/3 doesnt allow hidden input values to be set.

[glennr]

Hi! I ran into this head-scratcher...

Environment

• Elixir version (elixir -v):

Erlang/OTP 22 [erts-10.7.2] [source] [64-bit] [smp:16:16] [ds:16:16:10] [async-threads:1]

Elixir 1.10.3 (compiled with Erlang/OTP 22)

• Phoenix version (mix deps):

phoenix 1.5.3 (Hex package) (mix)

• Phoenix LiveView version (mix deps): phoenix_live_view 0.13.3 (Hex package) (mix)
• NodeJS version (node -v): v12.15.0
• NPM version (npm -v): 6.13.4
• Operating system: Ubuntu
• Browsers you attempted to reproduce this bug on (the more the merrier): n/a
• Does the problem persist after removing "assets/node_modules" and trying again? Yes/no: Yes.

Actual behavior

Seeing this error in my liveview tests

     ** (ArgumentError) value for hidden "submittedButton" must be one of [""], got: "submit-and-next"             
     code: |> render_submit()                   
     stacktrace:                                                                                                   
       (phoenix_live_view 0.13.3) lib/phoenix_live_view/test/live_view_test.ex:873: Phoenix.LiveViewTest.call/2     
       test/brmbl_web/live/owner/process_chain_live_test.exs:133: (test)                                                                         

for this bit of test code:

      assert {:ok, _, html} =
               index_live
               |> form("#chain-form",
                 process_chain: %{name: name, description: descr},
                 submittedButton: "submit-and-next"
               )
               |> render_submit()
               |> follow_redirect(
                 conn,
                 Routes.owner_process_chain_index_path(conn, :new)
               )

and this html:

  <%= f = form_for @changeset, "#",
id: "chain-form",
phx_target: @myself,
phx_change: "validate",
phx_submit: "save" %>

[[[  ... form fields removed for brevity ]]]

      <input type="hidden" name="submittedButton" value="" />
      <%= submit @button_label, name: "submit-only", phx_hook: "SetButtonState", phx_disable_with: "Adding...", class: "btn btn-primary lift"%>
      <%= if @save_and_add_button_label do %>
        <%= submit @save_and_add_button_label, name: "submit-and-next", phx_hook: "SetButtonState", phx_disable_with: "Adding...", class: "btn btn-primary lift"%>
      <% end %>
</div>

and this event handler:

  def handle_event(
        "save",
        %{"process_chain" => chain_params, "submittedButton" => button},
        socket
      ) do
    save_process_chain(socket, socket.assigns.action, chain_params, button)
  end

Expected behavior

form/3 should allow the hidden input's value to be set.

For more context: I'm the hidden input field to determine which form button was pressed per https://github.com/phoenixframework/phoenix_live_view/issues/511#issuecomment-563875328

The feature in question works perfectly in the browser - so either a problem with LiveViewTest form/3's handling of hidden form inputs, or I'm using it incorrectly?

[josevalim]

Yes, this is intentional, since form is meant to mimic what the user can actually do. You can pass hidden values directly as the third value of render_submit/render_change:

view |> form(..., ...) |> render_submit(%{"hidden_value" => "example"})

Let me know if you run into any issues.

[glennr]

Whoa - thanks for the quick reply!

That indeed fixed it.

Root cause: something between my keyboard and my chair.

[josevalim]

Root cause: something between my keyboard and my chair.

I disagree. :) It is definitely a corner case and we don't have docs for it. Would you like to send a PR that improves the docs for form to help the next human that may run into this scenario? thanks!

[glennr]

@josevalim it's my pleasure. PR above ^^