feat(join): use join_description as the join-form field label

lib/mv_web/live/join_live.ex

@@ -8,6 +8,7 @@ defmodule MvWeb.JoinLive do
   alias Ash.Resource.Info
   alias Mv.Membership
   alias Mv.Membership.CustomFieldLookup
+  alias MvWeb.Helpers.JoinDescriptionRenderer
   alias MvWeb.JoinRateLimit
   alias MvWeb.Translations.MemberFields
 
@@ -96,14 +97,20 @@ defmodule MvWeb.JoinLive do
                           class="checkbox checkbox-sm"
                         />
                         <span class="label-text">
-                          {field.label}<span :if={field.required} aria-hidden="true"> *</span>
+                          {render_field_label(field)}<span
+                            :if={field.required}
+                            aria-hidden="true"
+                          > *</span>
                         </span>
                       </label>
                     <% else %>
                       <div>
                         <label for={"join-field-#{field.id}"} class="label">
                           <span class="label-text">
-                            {field.label}<span :if={field.required} aria-hidden="true"> *</span>
+                            {render_field_label(field)}<span
+                              :if={field.required}
+                              aria-hidden="true"
+                            > *</span>
                           </span>
                         </label>
                         <input
@@ -237,6 +244,17 @@ defmodule MvWeb.JoinLive do
      |> assign(:form, to_form(params, as: "join"))}
   end
 
+  # Renders a join field's label. When a custom field has a join_description it is
+  # rendered with auto-linked URLs/Markdown; otherwise the plain field label is used.
+  # Safe: join_description is admin-set settings content, never end-user input, and
+  # JoinDescriptionRenderer escapes all non-link text (only emits <a href> tags).
+  defp render_field_label(%{join_description: join_description})
+       when is_binary(join_description) do
+    JoinDescriptionRenderer.render(join_description)
+  end
+
+  defp render_field_label(%{label: label}), do: label
+
   defp build_join_fields_with_labels(allowlist) do
     member_field_strings = Mv.Constants.member_fields() |> Enum.map(&Atom.to_string/1)
     custom_field_by_id = custom_field_map(allowlist, member_field_strings)
@@ -249,20 +267,36 @@ defmodule MvWeb.JoinLive do
   defp build_join_field(id, required, member_field_strings, custom_field_by_id) do
     if id in member_field_strings do
       label = MemberFields.label(String.to_existing_atom(id))
-      %{id: id, label: label, required: required, input_type: member_field_input_type(id)}
+
+      %{
+        id: id,
+        label: label,
+        required: required,
+        input_type: member_field_input_type(id),
+        join_description: nil
+      }
     else
       custom_field = Map.get(custom_field_by_id, id)
       label = if custom_field, do: custom_field.name, else: gettext("Field")
       input_type = custom_field_input_type(custom_field && custom_field.value_type)
 
-      %{id: id, label: label, required: required, input_type: input_type}
+      %{
+        id: id,
+        label: label,
+        required: required,
+        input_type: input_type,
+        join_description: custom_field && custom_field.join_description
+      }
     end
   end
 
   defp custom_field_map(allowlist, _member_field_strings) do
     allowlist
     |> Enum.map(& &1.id)
-    |> CustomFieldLookup.fetch_map_by_ids(authorize?: false, select: [:id, :name, :value_type])
+    |> CustomFieldLookup.fetch_map_by_ids(
+      authorize?: false,
+      select: [:id, :name, :value_type, :join_description]
+    )
   end
 
   defp initial_form_params(join_fields) do

test/mv_web/live/join_live_test.exs

@@ -165,6 +165,34 @@ defmodule MvWeb.JoinLiveTest do
                custom_field.name
              )
     end
+
+    @tag role: :unauthenticated
+    test "renders join_description with rendered link as label when set", %{conn: conn} do
+      {:ok, settings} = Membership.get_settings()
+      system_actor = Mv.Helpers.SystemActor.get_system_actor()
+
+      {:ok, custom_field} =
+        Membership.create_custom_field(
+          %{
+            name: "DSGVO",
+            value_type: :boolean,
+            join_description: "Akzeptiere die [Datenschutzerklärung](https://example.com/dsgvo)"
+          },
+          actor: system_actor
+        )
+
+      {:ok, _} =
+        Membership.update_settings(settings, %{
+          join_form_enabled: true,
+          join_form_field_ids: ["email", custom_field.id],
+          join_form_field_required: %{"email" => true, custom_field.id => false}
+        })
+
+      {:ok, _view, html} = live(conn, "/join")
+
+      assert html =~ ~s(<a href="https://example.com/dsgvo">Datenschutzerklärung</a>)
+      assert html =~ "Akzeptiere die"
+    end
   end
 
   describe "join field input types" do