include dedicated error message for readonly work packages

app/contracts/work_packages/base_contract.rb

@@ -304,10 +304,18 @@ module WorkPackages
       end
     end
 
+    def readonly_attributes_unchanged
+      super.tap do
+        if already_in_readonly_status? && unauthenticated_changed.any?
+          # Better documentation on why a property is readonly.
+          errors.add :base, :readonly_status
+        end
+      end
+    end
+
     def reduce_by_writable_permissions(attributes)
-      # If we're in a readonly status and did not move into that status right now
-      # only allow other status transitions. But also prevent that if the associated version is closed.
-      if model.readonly_status? && !model.status_id_change
+      # If we're in a readonly status only allow other status transitions.
+      if already_in_readonly_status?
         super & %w(status status_id)
       else
         super
@@ -420,5 +428,10 @@ module WorkPackages
     def users_roles_in_project
       user.roles_for_project(model.project)
     end
+
+    # We're in a readonly status and did not move into that status right now.
+    def already_in_readonly_status?
+      model.readonly_status? && !model.status_id_change
+    end
   end
 end

config/locales/en.yml

@@ -801,6 +801,7 @@ en:
               does_not_exist: "The specified category does not exist."
             estimated_hours:
               only_values_greater_or_equal_zeroes_allowed: "must be >= 0."
+          readonly_status: 'The work package is in a readonly status so its attributes cannot be changed.'
         type:
           attributes:
             attribute_groups:

spec/contracts/work_packages/update_contract_spec.rb

@@ -42,7 +42,8 @@ describe WorkPackages::UpdateContract do
   let(:work_package) do
     FactoryBot.build_stubbed(:work_package,
                              project: work_package_project,
-                             type: type).tap do |wp|
+                             type: type,
+                             status: status).tap do |wp|
       wp_scope = double('wp scope')
 
       allow(WorkPackage)
@@ -58,6 +59,7 @@ describe WorkPackages::UpdateContract do
   end
   let(:user) { FactoryBot.build_stubbed(:user) }
   let(:type) { FactoryBot.build_stubbed(:type) }
+  let(:status) { FactoryBot.build_stubbed(:status) }
   let(:permissions) { %i[view_work_packages edit_work_packages assign_versions] }
 
   before do
@@ -337,4 +339,32 @@ describe WorkPackages::UpdateContract do
       end
     end
   end
+
+  describe 'readonly status' do
+    context 'with the status being readonly', with_ee: %i[readonly_work_packages] do
+      let(:status) { FactoryBot.build_stubbed(:status, is_readonly: true) }
+      let(:new_priority) { FactoryBot.build_stubbed(:priority) }
+
+      before do
+        work_package.priority = new_priority
+
+        contract.validate
+      end
+
+      it 'is invalid' do
+        expect(contract)
+          .not_to be_valid
+      end
+
+      it 'adds an error to the written to attribute' do
+        expect(contract.errors.symbols_for(:priority_id))
+          .to include(:error_readonly)
+      end
+
+      it 'adds an error to base to better explain' do
+        expect(contract.errors.symbols_for(:base))
+          .to include(:readonly_status)
+      end
+    end
+  end
 end