NameError (uninitialized constant Unzipper::Zip) but only on Heroku deploy (Rails)

Question

I have a class unzipper.rb that unzips a file using Rubyzip.

In my local environment, I can succesfully unzip a file without explictly including the dependency using require 'zip'

On Heroku though, I get an NameError (uninitialized constant Unzipper::Zip) which I could only resolve by using the explict require

Question: Why would this be necessary in the Heroku environment, but not on localhost? I was under the impression that Rails required all gems automatically.

app/services/unzipper.rb

require 'zip'  # Only required for Heroku. Works locally without!

class Unzipper

  OVERRIDE_FILES = true

  def initialize(file)
    @file = file
  end

  def self.unzip(file, &block)
    Unzipper.new(file).unzip(&block)
  end

  def unzip
    open_zip do |zip|
      yield extract_files(zip)
    end
  end

  private

  def open_zip(&block)
    ::Zip::File.open(@file.path, &block)
  end

  def extract_files(zip)
    files = []
    zip.each do |entry|
      path = "#{rails_temp_directory}/#{entry.name}"
      entry.extract(path) { OVERRIDE_FILES }
      files << path
    end
    files
  end

  def rails_temp_directory
    "#{Rails.root}/tmp"
  end
end

Heroku output when running bundler includes:

remote:        Using rubyzip 1.1.7

I verified both are using the same version of Ruby.

There is no initializer or environment config for Rubyzip.

Gemfile

source 'https://rubygems.org'

gem 'rails', '4.2.0'

gem 'pg', group: :production

gem 'sass-rails', '~> 5.0'
gem 'uglifier', '>= 1.3.0'
gem 'coffee-rails', '~> 4.1.0'
gem 'jquery-rails'
gem 'turbolinks'
gem 'jbuilder', '~> 2.0'
gem 'sdoc', '~> 0.4.0', group: :doc

gem 'slim-rails'

gem 'paperclip'
gem 'rest-client'

gem 'bootstrap-sass', '~> 3.3.3'

gem 'validates_serialized'

gem 'puma'

gem "nokogiri"
gem "cocoon"
gem 'sidekiq'
gem 'sinatra', :require => nil # For sidekiq web monitoring
gem 'aws-sdk', '< 2.0'
gem 'rails_12factor', group: :production
gem 'rubyzip'

group :development, :test do
  gem 'byebug'

  gem 'web-console', '~> 2.0'

  gem 'spring'

  gem 'sqlite3'

  gem 'shoulda-matchers'
  gem 'rspec-rails'
  gem 'factory_girl_rails'
  gem 'capybara'
  gem 'selenium-webdriver'
  gem 'database_cleaner'
  gem 'guard-rspec'
  gem 'faker'
end

group :test do 
  gem 'webmock'
end

ruby '2.2.0'

Answer 1

Rubyzip's main file name is different than its gem name, so you might have to specify it explicitly in the Gemfile:

gem 'rubyzip', require: 'zip'