Nest encrypted attribute types within serialized types

Make the order in which `serializes :foo` and `encrypts :foo` are called
irrelevant by always nesting the encrypted attribute type inside the
serialized type.

This required switching from `DelegateClass` to `SimpleDelegator` so
that object we are delegating to can be replaced.

To ensure that the serialized type survives YAML serialization (there's
a test for this), we need to implement init_with to call __setobj__.

activerecord/lib/active_record/encryption/encryptable_record.rb

@@ -88,7 +88,15 @@ def encrypt_attribute(name, key_provider: nil, key: nil, deterministic: false, s
               scheme = scheme_for key_provider: key_provider, key: key, deterministic: deterministic, support_unencrypted_data: support_unencrypted_data, \
                 downcase: downcase, ignore_case: ignore_case, previous: previous, compress: compress, compressor: compressor, **context_properties
 
-              ActiveRecord::Encryption::EncryptedAttributeType.new(scheme: scheme, cast_type: cast_type, default: columns_hash[name.to_s]&.default)
+              if cast_type.serialized?
+                cast_type.tap do |serialized_type|
+                  serialized_type.replace_serialized_subtype do |current_subtype|
+                    ActiveRecord::Encryption::EncryptedAttributeType.new(scheme: scheme, cast_type: current_subtype, default: columns_hash[name.to_s]&.default)
+                  end
+                end
+              else
+                ActiveRecord::Encryption::EncryptedAttributeType.new(scheme: scheme, cast_type: cast_type, default: columns_hash[name.to_s]&.default)
+              end
             end
 
             preserve_original_encrypted(name) if ignore_case

activerecord/lib/active_record/type/serialized.rb

@@ -2,7 +2,7 @@
 
 module ActiveRecord
   module Type
-    class Serialized < DelegateClass(ActiveModel::Type::Value) # :nodoc:
+    class Serialized < SimpleDelegator # :nodoc:
       undef to_yaml if method_defined?(:to_yaml)
 
       include ActiveModel::Type::Helpers::Mutable
@@ -12,7 +12,14 @@ class Serialized < DelegateClass(ActiveModel::Type::Value) # :nodoc:
       def initialize(subtype, coder)
         @subtype = subtype
         @coder = coder
-        super(subtype)
+        __setobj__(subtype)
+      end
+
+      def init_with(coder) # :nodoc:
+        # Ensures YAML deserialization calls __setobj__
+        @subtype = coder["subtype"]
+        @coder = coder["coder"]
+        __setobj__(subtype)
       end
 
       def deserialize(value)
@@ -57,6 +64,11 @@ def serialized? # :nodoc:
         true
       end
 
+      def replace_serialized_subtype(&block) # :nodoc:
+        @subtype = block.call(subtype)
+        __setobj__(@subtype)
+      end
+
       private
         def default_value?(value)
           value == coder.load(nil)