fix(dossier): when a champ type changes on update, ensure we have an instance of the right class

app/models/concerns/dossier_champs_concern.rb

@@ -177,9 +177,11 @@ module DossierChampsConcern
       attributes[:value_json] = nil
       attributes[:external_id] = nil
       attributes[:data] = nil
+      champ = champ.becomes!(attributes[:type].constantize)
+      champ.save!
     end
 
-    reset_champs_cache
+    reset_champ_cache(champ)
 
     [champ, attributes]
   end
@@ -202,6 +204,11 @@ module DossierChampsConcern
     @project_champs_private = nil
   end
 
+  def reset_champ_cache(champ)
+    champs_by_public_id[champ.public_id]&.reload
+    reset_champs_cache
+  end
+
   def reload_champs_cache
     champs.reload if persisted?
     reset_champs_cache

spec/models/concerns/dossier_champs_concern_spec.rb

@@ -268,6 +268,25 @@ RSpec.describe DossierChampsConcern do
           }
         end
       end
+
+      context "champ with type change" do
+        let(:procedure) { create(:procedure, :published, types_de_champ_public: [{ type: :text, libelle: "Un champ text", stable_id: 99 }]) }
+        let(:dossier) { create(:dossier, :with_populated_champs, procedure:) }
+
+        before do
+          tdc = dossier.procedure.draft_revision.find_and_ensure_exclusive_use(99)
+          tdc.update!(type_champ: TypeDeChamp.type_champs.fetch(:checkbox))
+          dossier.procedure.publish_revision!
+          perform_enqueued_jobs
+          dossier.reload
+        end
+
+        it {
+          expect(subject.persisted?).to be_truthy
+          expect(subject.is_a?(Champs::CheckboxChamp)).to be_truthy
+          expect(subject.value).to be_nil
+        }
+      end
     end
 
     context "private champ" do
@@ -323,6 +342,27 @@ RSpec.describe DossierChampsConcern do
         expect(champ_994.value).to eq("Greer")
       }
     end
+
+    context "champ with type change" do
+      let(:procedure) { create(:procedure, :published, types_de_champ_public: [{ type: :text, libelle: "Un champ text", stable_id: 99 }]) }
+      let(:dossier) { create(:dossier, :with_populated_champs, procedure:) }
+      let(:attributes) { { "99" => { primary_value: "primary" } } }
+
+      before do
+        tdc = dossier.procedure.draft_revision.find_and_ensure_exclusive_use(99)
+        tdc.update!(type_champ: TypeDeChamp.type_champs.fetch(:linked_drop_down_list), drop_down_options: ["--primary--", "secondary"])
+        dossier.procedure.publish_revision!
+        perform_enqueued_jobs
+        dossier.reload
+      end
+
+      it {
+        subject
+        expect(dossier.champs.any?(&:changed_for_autosave?)).to be_truthy
+        expect(champ_99.changed?).to be_truthy
+        expect(champ_99.value).to eq('["primary",""]')
+      }
+    end
   end
 
   describe "#update_champs_attributes(private)" do