ES: proxy object setup for elasticsearch-rails

We no longer include Elasticsearch::Model, which would set up
those included modules. Therefore we have to do this manually.

Allow __transform to handle versions

config/initializers/elastic_client_setup.rb

@@ -5,9 +5,40 @@
 require 'gitlab/current_settings'
 
 Gitlab.ee do
+  require 'elasticsearch/model'
+
+  ### Modified from elasticsearch-model/lib/elasticsearch/model.rb
+
+  [
+    Elasticsearch::Model::Client::ClassMethods,
+    Elasticsearch::Model::Naming::ClassMethods,
+    Elasticsearch::Model::Indexing::ClassMethods,
+    Elasticsearch::Model::Searching::ClassMethods
+  ].each do |mod|
+    Elasticsearch::Model::Proxy::ClassMethodsProxy.include mod
+  end
+
+  [
+    Elasticsearch::Model::Client::InstanceMethods,
+    Elasticsearch::Model::Naming::InstanceMethods,
+    Elasticsearch::Model::Indexing::InstanceMethods,
+    Elasticsearch::Model::Serializing::InstanceMethods
+  ].each do |mod|
+    Elasticsearch::Model::Proxy::InstanceMethodsProxy.include mod
+  end
+
+  Elasticsearch::Model::Proxy::InstanceMethodsProxy.class_eval <<-CODE, __FILE__, __LINE__ + 1
+    def as_indexed_json(options={})
+      target.respond_to?(:as_indexed_json) ? target.__send__(:as_indexed_json, options) : super
+    end
+  CODE
+
+  ### Monkey patches
+
   Elasticsearch::Model::Response::Records.prepend GemExtensions::Elasticsearch::Model::Response::Records
   Elasticsearch::Model::Adapter::Multiple::Records.prepend GemExtensions::Elasticsearch::Model::Adapter::Multiple::Records
   Elasticsearch::Model::Indexing::InstanceMethods.prepend GemExtensions::Elasticsearch::Model::Indexing::InstanceMethods
+  Elasticsearch::Model::Adapter::ActiveRecord::Importing.prepend GemExtensions::Elasticsearch::Model::Adapter::ActiveRecord::Importing
 
   module Elasticsearch
     module Model

ee/lib/gem_extensions/elasticsearch/model/adapter/active_record/importing.rb

+# frozen_string_literal: true
+module GemExtensions
+  module Elasticsearch
+    module Model
+      module Adapter
+        module ActiveRecord
+          module Importing
+            def __transform
+              lambda { |model| { index: { _id: model.id, data: model.__elasticsearch__.version(version_namespace).as_indexed_json } } }
+            end
+          end
+        end
+      end
+    end
+  end
+end