refactor(dossier): use champ id as champ attributes key

app/models/champ.rb

@@ -137,6 +137,23 @@ class Champ < ApplicationRecord
     "#{html_id}-input"
   end
 
+  # A predictable string to use when generating an input name for this champ.
+  #
+  # Rail's FormBuilder can auto-generate input names, using the form "dossier[champs_attributes][5]",
+  # where [5] is the index of the field in the form.
+  # However the field index makes it difficult to render a single field, independent from the ordering of the others.
+  #
+  # Luckily, this is only used to make the name unique, but the actual value is ignored when Rails parses nested
+  # attributes. So instead of the field index, this method uses the champ id; which gives us an independent and
+  # predictable input name.
+  def input_name
+    if parent_id
+      "#{parent.input_name}[#{champs_attributes_accessor}][#{id}]"
+    else
+      "dossier[#{champs_attributes_accessor}][#{id}]"
+    end
+  end
+
   def labelledby_id
     "#{html_id}-label"
   end
@@ -169,6 +186,14 @@ class Champ < ApplicationRecord
     "#{stable_id}-#{id}"
   end
 
+  def champs_attributes_accessor
+    if private?
+      "champs_private_attributes"
+    else
+      "champs_attributes"
+    end
+  end
+
   def needs_dossier_id?
     !dossier_id && parent_id
   end

app/views/instructeurs/dossiers/annotations_privees.html.haml

@@ -6,10 +6,9 @@
   - if @dossier.champs_private.present?
     %section
       = form_for @dossier, url: annotations_instructeur_dossier_path(@dossier.procedure, @dossier), html: { class: 'form' } do |f|
-        = f.fields_for :champs_private, f.object.champs_private do |champ_form|
-          - champ = champ_form.object
-          = render partial: "shared/dossiers/editable_champs/editable_champ",
-            locals: { champ: champ, form: champ_form, seen_at: @annotations_privees_seen_at }
+        - @dossier.champs_private.each do |champ|
+          = fields_for champ.input_name, champ do |form|
+            = render partial: "shared/dossiers/editable_champs/editable_champ", locals: { form: form, champ: champ, seen_at: @annotations_privees_seen_at }
 
         .send-wrapper
           = f.submit 'Sauvegarder', class: 'button primary send', data: { disable: true }

app/views/shared/dossiers/_edit.html.haml

@@ -35,10 +35,9 @@
         dossier.procedure.groupe_instructeurs.order(:label).map { |gi| [gi.label, gi.id] },
         { include_blank: dossier.brouillon? }
 
-    = f.fields_for :champs, dossier.champs do |champ_form|
-      - champ = champ_form.object
-      = render partial: "shared/dossiers/editable_champs/editable_champ",
-        locals: { champ: champ, form: champ_form }
+    - dossier.champs.each do |champ|
+      = fields_for champ.input_name, champ do |form|
+        = render partial: "shared/dossiers/editable_champs/editable_champ", locals: { form: form, champ: champ }
 
     - if !dossier.for_procedure_preview?
       .dossier-edit-sticky-footer

app/views/shared/dossiers/editable_champs/_editable_champ.html.haml

@@ -8,5 +8,6 @@
     = render partial: 'shared/dossiers/editable_champs/champ_label', locals: { form: form, champ: champ, seen_at: defined?(seen_at) ? seen_at : nil }
   - if champ.type_champ == "titre_identite"
     %p.notice  Carte nationale d’identité (uniquement le recto), passeport, titre de séjour ou autre justificatif d’identité. Formats acceptés : jpg/png
-  = render partial: "shared/dossiers/editable_champs/#{champ.type_champ}",
-    locals: { champ: champ, form: form }
+
+  = form.hidden_field :id, value: champ.id
+  = render partial: "shared/dossiers/editable_champs/#{champ.type_champ}", locals: { form: form, champ: champ }