Fix Rails 6.0 deprecation on class.parent (#2373)

* Fix Rails 6.0 deprecation on `class.parent`

* Update Changelog

* Switch travis to openJDK

* Lock bundler on appveyor

* Rejigger gemfile to fix sqlite issue

* Lock nokogiri for ruby < 2.4

* Use rubygems < 3 to fix travis

* Use specific bundler version and do not try to uninstall

Uninstalling bundler is not allowed since it is a default gem

* Lock rake for ruby < 2.2

* Downgrade rake further to support ruby 1.9.3

* Lock rake down further, and lock simplecov

* Fix rubocop/parser and minitest version deps in CI

* Lock sprockets version

* Try fixing jruby builds

* Try remove bad gem version for jruby on CI

* Try downgrading rubygems a different way

* Do not update rubygems on jruby

* Lock gems for jruby

* Fix sprockets version lock

.travis.yml

@@ -10,13 +10,13 @@ rvm:
   - jruby-9.1.5.0 # is precompiled per http://rubies.travis-ci.org/
 
 jdk:
-  - oraclejdk8
+  - openjdk8
 
 before_install:
-  - gem update --system
-  - rvm @global do gem uninstall bundler -a -x
+  - gem update --system 2.6.8
+  - if [ "$RUBY_VERSION" != "jruby-9.1.5.0" ] ; then update_rubygems ; fi 
   - rvm @global do gem install bundler -v 1.13.7
-install: bundle install --path=vendor/bundle --retry=3 --jobs=3
+install: bundle _1.13.7_ install --path=vendor/bundle --retry=3 --jobs=3
 cache:
   directories:
     - vendor/bundle

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ### [0-9-stable](https://github.com/rails-api/active_model_serializers/compare/v0.9.7...0-9-stable)
 
+- [#2373](https://github.com/rails-api/active_model_serializers/pull/2373) Fix Rails 6.0 deprecation warnings. (@supremebeing7)
+  
 ### [v0.9.7 (2017-05-01)](https://github.com/rails-api/active_model_serializers/compare/v0.9.6...v0.9.7)
 
 - [#2080](https://github.com/rails-api/active_model_serializers/pull/2080) remove `{ payload: nil }` from `!serialize.active_model_serializers` ActiveSupport::Notification. `payload` never had a value.  Changes, for example `{ serializer: 'ActiveModel::DefaultSerializer', payload: nil }` to be `{ serializer: 'ActiveModel::DefaultSerializer' }` (@yosiat)

Gemfile

@@ -33,8 +33,22 @@ if RUBY_VERSION < '2'
   gem 'mime-types', [ '>= 2.6.2', '< 3' ]
 end
 
-if RUBY_VERSION < '2.1'
-  gem 'nokogiri', '< 1.7'
+if ENV['CI']
+  if RUBY_VERSION < '2.4'
+    # Windows: An error occurred while installing nokogiri (1.8.0)
+    gem 'nokogiri', '< 1.7', platforms: @windows_platforms
+    # >= 4.0 requires ruby >= 2.5
+    gem 'sprockets', '< 4.0'
+  end
+
+  if RUBY_VERSION < '2.2'
+    # >= 12.3 and < 13 requires ruby >= 2.0, rake >= 13 requires ruby >= 2.2
+    gem 'rake', '< 12.3' 
+    # > 5.12 requires ruby >= 2.2
+    gem 'minitest', '< 5.12'
+    # >= 1.0 requires ruby >= 2.0
+    gem 'thor', '< 1.0'
+  end
 end
 
 # https://github.com/bundler/bundler/blob/89a8778c19269561926cea172acdcda241d26d23/lib/bundler/dependency.rb#L30-L54
@@ -50,12 +64,37 @@ group :bench do
 end
 
 group :test do
-  gem 'sqlite3',                          platform: (@windows_platforms + [:ruby])
-  gem 'activerecord-jdbcsqlite3-adapter', platform: :jruby
-
-  gem 'simplecov', '~> 0.10', require: false, group: :development
+  platforms(*(@windows_platforms + [:ruby])) do
+    if version == 'master' || version >= '6'
+      gem 'sqlite3', '~> 1.4'
+    else
+      gem 'sqlite3', '~> 1.3.13'
+    end
+  end
+  platforms :jruby do
+    if version == 'master' || version >= '6.0'
+      gem 'activerecord-jdbcsqlite3-adapter', github: 'jruby/activerecord-jdbc-adapter'
+    elsif version == '5.2'
+      gem 'activerecord-jdbcsqlite3-adapter', '~> 52.0'
+    elsif version == '5.1'
+      gem 'activerecord-jdbcsqlite3-adapter', '~> 51.0'
+    elsif version == '5.0'
+      gem 'activerecord-jdbcsqlite3-adapter', '~> 50.0'
+    else
+      gem 'activerecord-jdbcsqlite3-adapter', '~> 1.3.0'
+    end
+  end
 end
 
 group :development, :test do
+  unless ENV['CI']
     gem 'rubocop', '~> 0.34.0', require: false
   end
+  
+  # 0.12 requires ruby 2.4
+  if RUBY_VERSION < '2.4'
+    gem 'simplecov', '< 0.12', require: false
+  else
+    gem 'simplecov', '~> 0.10', require: false
+  end
+end

appveyor.yml

@@ -16,7 +16,7 @@ install:
   - SET PATH=C:\Ruby%ruby_version%\bin;%PATH%
   - ruby --version
   - gem --version
-  - gem install bundler
+  - gem install bundler -v 1.17.3
   - bundler --version
   - bundle platform
   - bundle install --path=vendor/bundle --retry=3 --jobs=3

lib/action_controller/serialization.rb

@@ -60,7 +60,15 @@ module ActionController
     private
 
     def namespace_for_serializer
-      @namespace_for_serializer ||= self.class.parent unless self.class.parent == Object
+      @namespace_for_serializer ||= namespace_for_class(self.class) unless namespace_for_class(self.class) == Object
+    end
+
+    def namespace_for_class(klass)
+      if Module.method_defined?(:module_parent)
+        klass.module_parent
+      else
+        klass.parent
+      end
     end
 
     def default_serializer(resource)