From c72325277a254f114fe77d6421ba06ddab4ef60d Mon Sep 17 00:00:00 2001
From: Ryuta Kamizono <kamipo@gmail.com>
Date: Thu, 28 Jan 2021 11:18:14 +0900
Subject: [PATCH] Provide a way `decorate_attribute` for attribute type
 decoration

Just an implementation for https://github.com/rails/rails/pull/41139#discussion_r565752925.
---
 activerecord/lib/active_record/attributes.rb   |  6 ++++++
 .../test/cases/serialized_attribute_test.rb    | 18 ++++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/activerecord/lib/active_record/attributes.rb b/activerecord/lib/active_record/attributes.rb
index fa075d1cdf9fd..30347bc6b7a70 100644
--- a/activerecord/lib/active_record/attributes.rb
+++ b/activerecord/lib/active_record/attributes.rb
@@ -266,6 +266,12 @@ def load_schema! # :nodoc:
         end
       end
 
+      def decorate_attribute(name, type_name, default: NO_DEFAULT_PROVIDED, **options)
+        attribute(name, default: default) do |subtype|
+          Type.lookup(type_name, **options, subtype: subtype, adapter: Type.adapter_name_from(self))
+        end
+      end
+
       private
         NO_DEFAULT_PROVIDED = Object.new # :nodoc:
         private_constant :NO_DEFAULT_PROVIDED
diff --git a/activerecord/test/cases/serialized_attribute_test.rb b/activerecord/test/cases/serialized_attribute_test.rb
index a750e572ecea9..35a17ddada352 100644
--- a/activerecord/test/cases/serialized_attribute_test.rb
+++ b/activerecord/test/cases/serialized_attribute_test.rb
@@ -424,6 +424,24 @@ def changed_in_place?(old, new)
     end
   end
 
+  def test_decorate_attribute_on_serialized_attribute
+    old_registry = ActiveRecord::Type.registry
+    ActiveRecord::Type.registry = ActiveRecord::Type.registry.dup
+    ActiveRecord::Type.register :encrypted, EncryptedType
+
+    klass = Class.new(ActiveRecord::Base) do
+      self.table_name = Topic.table_name
+      store :content
+      decorate_attribute :content, :encrypted
+    end
+
+    topic = klass.create!(content: { trial: true })
+
+    assert_equal({ "trial" => true }, topic.content)
+  ensure
+    ActiveRecord::Type.registry = old_registry
+  end
+
   def test_decorated_type_with_type_for_attribute
     old_registry = ActiveRecord::Type.registry
     ActiveRecord::Type.registry = ActiveRecord::Type.registry.dup