Cope with conditionally rendered form inputs

lib/phoenix_test/live.ex

@@ -461,8 +461,10 @@ defmodule PhoenixTest.Live do
     |> maybe_redirect(session)
   end
 
-  defp merged_form_data(session, form) do
-    FormData.merge(form.form_data, session.active_form.form_data)
+  defp merged_form_data(session, %Form{} = form) do
+    form.form_data
+    |> FormData.merge(session.active_form.form_data)
+    |> FormData.filter(fn %{name: name} -> name in Form.form_element_names(form) end)
   end
 
   def submit(session) do

test/phoenix_test/live_test.exs

@@ -1453,4 +1453,18 @@ defmodule PhoenixTest.LiveTest do
       |> refute_has("h2", text: "Where we test LiveView's async behavior", timeout: 250)
     end
   end
+
+  describe "conditionally rendered form fields" do
+    test "submitting after switching versions only includes the visible field", %{conn: conn} do
+      conn
+      |> visit("/live/conditional_form")
+      |> fill_in("Version A Text", with: "some value for A")
+      |> select("Version", option: "Version B")
+      |> fill_in("Version B Text", with: "some value for B")
+      |> click_button("Save")
+      |> assert_has("#form-data", text: "version_b_text: some value for B")
+      |> assert_has("#form-data", text: "version: b")
+      |> refute_has("#form-data", text: "version_a_text")
+    end
+  end
 end

test/support/web_app/conditional_form_live.ex

@@ -0,0 +1,69 @@
+defmodule PhoenixTest.WebApp.ConditionalFormLive do
+  @moduledoc false
+
+  use Phoenix.LiveView
+
+  def render(assigns) do
+    ~H"""
+    <h1>Conditional Form Test</h1>
+
+    <form id="conditional-form" phx-change="change-form" phx-submit="save-form">
+      <label for="version">Version</label>
+      <select id="version" name="version">
+        <option value="a">Version A</option>
+        <option value="b">Version B</option>
+      </select>
+
+      <label :if={@version == "a"} for="version_a_text">Version A Text</label>
+      <input
+        :if={@version == "a"}
+        id="version_a_text"
+        name="version_a_text"
+        value={@form_data["version_a_text"]}
+      />
+
+      <label :if={@version == "b"} for="version_b_text">Version B Text</label>
+      <input
+        :if={@version == "b"}
+        id="version_b_text"
+        name="version_b_text"
+        value={@form_data["version_b_text"]}
+      />
+
+      <button type="submit">Save</button>
+    </form>
+
+    <div :if={@form_saved} id="form-data">
+      <%= for {key, value} <- @submitted_data do %>
+        <span>{key}: {value}</span>
+      <% end %>
+    </div>
+    """
+  end
+
+  def mount(_params, _session, socket) do
+    {:ok,
+     assign(socket,
+       version: "a",
+       form_data: %{},
+       form_saved: false,
+       submitted_data: %{}
+     )}
+  end
+
+  def handle_event("change-form", form_data, socket) do
+    {:noreply,
+     assign(socket,
+       version: form_data["version"] || socket.assigns.version,
+       form_data: form_data
+     )}
+  end
+
+  def handle_event("save-form", form_data, socket) do
+    {:noreply,
+     assign(socket,
+       form_saved: true,
+       submitted_data: form_data
+     )}
+  end
+end

test/support/web_app/router.ex

@@ -43,6 +43,7 @@ defmodule PhoenixTest.WebApp.Router do
       live "/live/dynamic_form", DynamicFormLive
       live "/live/simple_ordinal_inputs", SimpleOrdinalInputsLive
       live "/live/nested", NestedLive
+      live "/live/conditional_form", ConditionalFormLive
     end
 
     scope "/auth" do