ruby - Why does Rails 4.2 + responders keeps telling me to add responders to the Gemfile?

Question

I'm upgrading a Rails 4.1.8 app (also using rails-api ~> 0.3.1) to 4.2.0.rc2 and would like to retain the respond_with functionality. I've added responders to the Gemfile, but when I bin/rake spec, I get:

/Users/sloveless/.gem/ruby/2.1.0/gems/actionpack-4.2.0.rc2/lib/action_controller/metal/mime_responds.rb:10:in `respond_to': The controller-level `respond_to' feature has been extracted to the `responders` gem. Add it to your Gemfile to continue using this feature: (NoMethodError)
  gem 'responders', '~> 2.0'
Consult the Rails upgrade guide for details.
    from /Users/sloveless/Development/twilight/app/controllers/application_controller.rb:6:in `<class:ApplicationController>'
    from /Users/sloveless/Development/twilight/app/controllers/application_controller.rb:1:in `<top (required)>'
    from /Users/sloveless/.gem/ruby/2.1.0/gems/activesupport-4.2.0.rc2/lib/active_support/dependencies.rb:274:in `require'
    from /Users/sloveless/.gem/ruby/2.1.0/gems/activesupport-4.2.0.rc2/lib/active_support/dependencies.rb:274:in `block in require'
    from /Users/sloveless/.gem/ruby/2.1.0/gems/activesupport-4.2.0.rc2/lib/active_support/dependencies.rb:240:in `load_dependency'
    from /Users/sloveless/.gem/ruby/2.1.0/gems/activesupport-4.2.0.rc2/lib/active_support/dependencies.rb:274:in `require'
    from /Users/sloveless/.gem/ruby/2.1.0/gems/activesupport-4.2.0.rc2/lib/active_support/dependencies.rb:360:in `require_or_load'
    from /Users/sloveless/.gem/ruby/2.1.0/gems/activesupport-4.2.0.rc2/lib/active_support/dependencies.rb:494:in `load_missing_constant'
    from /Users/sloveless/.gem/ruby/2.1.0/gems/activesupport-4.2.0.rc2/lib/active_support/dependencies.rb:184:in `const_missing'
    from /Users/sloveless/Development/twilight/app/controllers/zone_maps_controller.rb:1:in `<top (required)>'
    from /Users/sloveless/.gem/ruby/2.1.0/gems/activesupport-4.2.0.rc2/lib/active_support/dependencies.rb:274:in `require'
    from /Users/sloveless/.gem/ruby/2.1.0/gems/activesupport-4.2.0.rc2/lib/active_support/dependencies.rb:274:in `block in require'
    from /Users/sloveless/.gem/ruby/2.1.0/gems/activesupport-4.2.0.rc2/lib/active_support/dependencies.rb:240:in `load_dependency'
    from /Users/sloveless/.gem/ruby/2.1.0/gems/activesupport-4.2.0.rc2/lib/active_support/dependencies.rb:274:in `require'
    from /Users/sloveless/.gem/ruby/2.1.0/gems/activesupport-4.2.0.rc2/lib/active_support/dependencies.rb:360:in `require_or_load'
    from /Users/sloveless/.gem/ruby/2.1.0/gems/activesupport-4.2.0.rc2/lib/active_support/dependencies.rb:494:in `load_missing_constant'
    from /Users/sloveless/.gem/ruby/2.1.0/gems/activesupport-4.2.0.rc2/lib/active_support/dependencies.rb:184:in `const_missing'
    from /Users/sloveless/Development/twilight/spec/controllers/zone_maps_controller_spec.rb:3:in `<top (required)>'
    from /Users/sloveless/.gem/ruby/2.1.0/gems/activesupport-4.2.0.rc2/lib/active_support/dependencies.rb:268:in `load'
    from /Users/sloveless/.gem/ruby/2.1.0/gems/activesupport-4.2.0.rc2/lib/active_support/dependencies.rb:268:in `block in load'
    from /Users/sloveless/.gem/ruby/2.1.0/gems/activesupport-4.2.0.rc2/lib/active_support/dependencies.rb:240:in `load_dependency'
    from /Users/sloveless/.gem/ruby/2.1.0/gems/activesupport-4.2.0.rc2/lib/active_support/dependencies.rb:268:in `load'
    from /Users/sloveless/.gem/ruby/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/configuration.rb:1105:in `block in load_spec_files'
    from /Users/sloveless/.gem/ruby/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/configuration.rb:1105:in `each'
    from /Users/sloveless/.gem/ruby/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/configuration.rb:1105:in `load_spec_files'
    from /Users/sloveless/.gem/ruby/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/runner.rb:96:in `setup'
    from /Users/sloveless/.gem/ruby/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/runner.rb:84:in `run'
    from /Users/sloveless/.gem/ruby/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/runner.rb:69:in `run'
    from /Users/sloveless/.gem/ruby/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/runner.rb:37:in `invoke'
    from /Users/sloveless/.gem/ruby/2.1.0/gems/rspec-core-3.1.7/exe/rspec:4:in `<top (required)>'
    from /Users/sloveless/.gem/ruby/2.1.0/gems/activesupport-4.2.0.rc2/lib/active_support/dependencies.rb:268:in `load'
    from /Users/sloveless/.gem/ruby/2.1.0/gems/activesupport-4.2.0.rc2/lib/active_support/dependencies.rb:268:in `block in load'
    from /Users/sloveless/.gem/ruby/2.1.0/gems/activesupport-4.2.0.rc2/lib/active_support/dependencies.rb:240:in `load_dependency'
    from /Users/sloveless/.gem/ruby/2.1.0/gems/activesupport-4.2.0.rc2/lib/active_support/dependencies.rb:268:in `load'
    from /Users/sloveless/.gem/ruby/2.1.0/gems/spring-commands-rspec-1.0.3/lib/spring/commands/rspec.rb:18:in `call'
    from /Users/sloveless/.rubies/ruby-2.1.0/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
    from /Users/sloveless/.rubies/ruby-2.1.0/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
    from -e:1:in `<main>'

Any ideas why I might be getting this? ...and, of course, how I can get around it?

Pertinent files:

# app/application_controller.rb
class ApplicationController < ActionController::API
  include ActionController::MimeResponds
  include ActionController::ImplicitRender
  include SentientController

  respond_to :json

  # (Custom responder)
  self.responder = HTTPErrors::Responder
  before_action :set_locale

  private

  def set_locale
    I18n.locale = http_accept_language.compatible_language_from(I18n.available_locales)
  end
end






# Gemfile
source 'https://rubygems.org'

gem 'rails', '4.2.0.rc2'
gem 'rails-api', '~> 0.3.1'

# Other utils
gem 'uuidtools'

# Serializing things
gem 'active_model_serializers', '~> 0.8.2'

# Persisting things
gem 'pg', '~> 0.17.1'
# gem 'activerecord-postgis-adapter', '~> 2.2.1'
# gem 'redis'

# Controller & routing things
gem 'http_accept_language', '~> 2.0.2'
gem 'kaminari'
gem 'rack-cors', require: 'rack/cors'
gem 'responders', '~> 2.0'

group :development do
  gem 'brakeman', require: false
  gem 'guard-bundler'
  gem 'guard-rails'
  gem 'guard-rspec'
  gem 'guard-rubocop'
  gem 'rails_best_practices'
  gem 'rubocop', require: false
  gem 'quiet_assets'
  gem 'web-console', '~> 2.0'
end

group :development, :test do
  gem 'bullet'
  gem 'byebug'
  gem 'factory_girl_rails'
  gem 'faker'
  gem 'pry-rails'
  gem 'pry-rescue'
  gem 'pry-stack_explorer'
  gem 'rspec-rails'
  gem 'puma'
  gem 'spring'
  gem 'spring-commands-rspec'
end

group :test do
  gem 'json_spec'
  gem 'shoulda-matchers'
end

group :production do
  gem 'newrelic_rpm'
end

Edit: To no surprise, this happens when I manually make a request, not just during testing.

Answer 1

The following worked for me using rails-api / active_model_serializers 0.8.3:

Remove

include ActionController::MimeResponds
include ActionController::ImplicitRender

Add

include ActionController::RespondWith

See this discussion on github.