Support nil fields in forms (#2931)

lib/livebook/notebook/cell.ex

@@ -57,7 +57,7 @@ defmodule Livebook.Notebook.Cell do
   end
 
   def find_inputs_in_output({_idx, %{type: :control, attrs: %{type: :form, fields: fields}}}) do
-    Keyword.values(fields)
+    for {_field, input} <- fields, input != nil, do: input
   end
 
   def find_inputs_in_output({_idx, output}) when output.type in [:frame, :tabs, :grid] do

lib/livebook/runtime.ex

@@ -437,7 +437,7 @@ defprotocol Livebook.Runtime do
             }
           | %{
               type: :form,
-              fields: list({field :: atom(), input_output()}),
+              fields: list({field :: atom(), input_output() | nil}),
               submit: String.t() | nil,
               # Currently we always use true, but we can support
               # other tracking modes in the future

lib/livebook/session.ex

@@ -3311,8 +3311,9 @@ defmodule Livebook.Session do
 
         :form ->
           Map.update!(attrs, :fields, fn fields ->
-            Enum.map(fields, fn {field, attrs} ->
+            Enum.map(fields, fn
-              {field, normalize_runtime_output({:input, attrs})}
+              {field, nil} -> {field, nil}
+              {field, attrs} -> {field, normalize_runtime_output({:input, attrs})}
             end)
           end)
 

lib/livebook_web/live/output/control_form_component.ex

@@ -13,8 +13,9 @@ defmodule LivebookWeb.Output.ControlFormComponent do
     socket = assign(socket, assigns)
 
     data =
-      Map.new(assigns.control.attrs.fields, fn {field, input} ->
+      Map.new(assigns.control.attrs.fields, fn
-        {field, assigns.input_views[input.id].value}
+        {field, nil} -> {field, nil}
+        {field, input} -> {field, assigns.input_views[input.id].value}
       end)
 
     if prev_data != nil and data != prev_data do
@@ -38,6 +39,7 @@ defmodule LivebookWeb.Output.ControlFormComponent do
     <div class="flex flex-col space-y-3">
       <.live_component
         :for={{_field, input} <- @control.attrs.fields}
+        :if={input}
         module={LivebookWeb.Output.InputComponent}
         id={"#{@id}-#{input.id}"}
         input={input}
@@ -75,7 +77,7 @@ defmodule LivebookWeb.Output.ControlFormComponent do
   defp reset_inputs(socket) do
     values =
       for {field, input} <- socket.assigns.control.attrs.fields,
-          field in socket.assigns.control.attrs.reset_on_submit,
+          input != nil and field in socket.assigns.control.attrs.reset_on_submit,
           do: {input.id, input.attrs.default}
 
     send(self(), {:set_input_values, values, true})

test/livebook_web/live/session_live_test.exs

@@ -548,7 +548,8 @@ defmodule LivebookWeb.SessionLiveTest do
               id: "input1",
               destination: test,
               attrs: %{type: :text, default: "initial", label: "Name", debounce: :blur}
-            }
+            },
+            value: nil
           ],
           submit: "Send",
           report_changes: %{},
@@ -575,7 +576,8 @@ defmodule LivebookWeb.SessionLiveTest do
       |> element(~s/[data-el-outputs-container] button/, "Send")
       |> render_click()
 
-      assert_receive {:event, "control_ref1", %{data: %{name: "sherlock"}, type: :submit}}
+      assert_receive {:event, "control_ref1",
+                      %{data: %{name: "sherlock", value: nil}, type: :submit}}
     end
 
     test "file input", %{conn: conn, session: session, test: test} do