dossier: fix rendering of piece_justificative in repetition

In repetitions we can't render the piece_justificative champ in the way
we do for normal champs (which was already a bit hackish).

Instead we render the whole form partial – and then extract the champ
from the form. In this way, we're sure to render the champ as it
appears in the form, without any hacks to reproduce the form structure.

app/helpers/application_helper.rb

@@ -49,6 +49,15 @@ module ApplicationHelper
     end
   end
 
+  def render_champ(champ)
+    champ_selector = ".editable-champ[data-champ-id=\"#{champ.id}\"]"
+    form_html = render 'shared/dossiers/edit', dossier: champ.dossier, apercu: false
+    champ_html = Nokogiri::HTML.fragment(form_html).at_css(champ_selector).to_s
+    # rubocop:disable Rails/OutputSafety
+    raw("document.querySelector('#{champ_selector}').outerHTML = \"#{escape_javascript(champ_html)}\";")
+    # rubocop:enable Rails/OutputSafety
+  end
+
   def remove_element(selector, timeout: 0, inner: false)
     script = "(function() {";
     script << "var el = document.querySelector('#{selector}');"

app/helpers/champ_helper.rb

@@ -33,7 +33,7 @@ module ChampHelper
   end
 
   def auto_attach_url(form, object)
-    if feature_enabled?(:autoupload_dossier_attachments) && object.is_a?(Champ) && object.public?
+    if feature_enabled?(:autoupload_dossier_attachments) && object.is_a?(Champ) && object.persisted? && object.public?
       champs_piece_justificative_url(object.id)
     end
   end

app/views/champs/piece_justificative/show.js.erb

@@ -1,15 +1,4 @@
-<% dossier = @champ.dossier %>
-
-<%= fields_for dossier do |form| %>
-  <%= form.fields_for :champs, dossier.champs.where(id: @champ.id), include_id: false do |champ_form| %>
-    <% render_to_element(".editable-champ[data-champ-id=\"#{@champ.id}\"]",
-      partial: 'shared/dossiers/editable_champs/editable_champ',
-      locals: {
-        champ: @champ,
-        form: champ_form
-      }) %>
-  <% end %>
-<% end %>
+<%= render_champ(@champ) %>
 
 <% attachment = @champ.piece_justificative_file.attachment %>
 <% if attachment.virus_scanner.pending? %>