fix(graphql): detect custom champs in fragment definitions

spec/graphql/dossier_spec.rb

@@ -26,6 +26,16 @@ RSpec.describe Types::DossierType, type: :graphql do
     end
   end
 
+  describe 'dossier with champs' do
+    let(:procedure) { create(:procedure, :published, :with_commune, :with_address) }
+    let(:dossier) { create(:dossier, :accepte, :with_populated_champs, procedure: procedure) }
+    let(:query) { DOSSIER_WITH_CHAMPS_QUERY }
+    let(:variables) { { number: dossier.id } }
+
+    it { expect(data[:dossier][:champs][0][:__typename]).to eq "CommuneChamp" }
+    it { expect(data[:dossier][:champs][1][:__typename]).to eq "AddressChamp" }
+  end
+
   DOSSIER_QUERY = <<-GRAPHQL
   query($number: Int!) {
     dossier(number: $number) {
@@ -48,4 +58,35 @@ RSpec.describe Types::DossierType, type: :graphql do
     }
   }
   GRAPHQL
+
+  DOSSIER_WITH_CHAMPS_QUERY = <<-GRAPHQL
+  query($number: Int!) {
+    dossier(number: $number) {
+      id
+      number
+      champs {
+        id
+        label
+        __typename
+        ...CommuneChampFragment
+        ... on AddressChamp {
+          address {
+            ...AddressFragment
+          }
+        }
+      }
+    }
+  }
+  fragment CommuneChampFragment on CommuneChamp {
+    commune {
+      ...CommuneFragment
+    }
+  }
+  fragment CommuneFragment on Commune {
+    code
+  }
+  fragment AddressFragment on Address {
+    cityName
+  }
+  GRAPHQL
 end