Switch to use `class_attribute`:

- Since `ActiveModel::Error` can now be inherited by
  `ActiveModel::NestedError`, when the latter generates a
  `full_message`, the `i18n_customize_full_message` accessor set in
  the parent class is not set.

  This commit fixes that by using a `class_attribute` instead.

1 files changed, 13 insertions, 0 deletions

diff --git a/activemodel/test/cases/validations/i18n_validation_test.rb b/activemodel/test/cases/validations/i18n_validation_test.rb
index ea5b335f44..c81649f493 100644
--- a/activemodel/test/cases/validations/i18n_validation_test.rb
+++ b/activemodel/test/cases/validations/i18n_validation_test.rb
@@ -59,6 +59,19 @@ class I18nValidationTest < ActiveModel::TestCase
     assert_equal "Name test cannot be blank", person.errors.full_message(:name_test, "cannot be blank")
   end
 
+  def test_errors_full_messages_on_nested_error_uses_attribute_format
+    ActiveModel::Error.i18n_customize_full_message = true
+    I18n.backend.store_translations("en", activemodel: {
+      errors: { models: { person: { attributes: { gender: "Gender" } } } },
+      attributes: { "person/contacts": { gender: "Gender" } }
+    })
+
+    person = person_class.new
+    error = ActiveModel::Error.new(person, :gender, "can't be blank")
+    person.errors.import(error, attribute: "person[0].contacts.gender")
+    assert_equal ["Gender can't be blank"], person.errors.full_messages
+  end
+
   def test_errors_full_messages_uses_attribute_format
     ActiveModel::Error.i18n_customize_full_message = true