问题的来源--sidekiq 4.1.3中的提交中有如下这么一个commit
sidekiq依赖于sinatra，在这个提交中，sinatra由development_dependency提升为dependency, 导致升级sidekiq后，
bundle install正常，当时启动或者重启sidekiq失败，发现sinatra依赖1.4.x版本。
翻遍了个整个网络，找到如下两篇文件
github中关于dependency的讨论还是挺多的(囧，文章好长)
rubygems官方说明
首先看一下sidekiq的gemspec文件
# -*- encoding: utf-8 -*-
require File.expand_path('../lib/sidekiq/version', __FILE__)
Gem::Specification.new do |gem|
gem.authors = ["Mike Perham"]
gem.email = ["mperham@gmail.com"]
gem.summary = "Simple, efficient background processing for Ruby"
gem.description = "Simple, efficient background processing for Ruby."
gem.homepage = "http://sidekiq.org"
gem.license = "LGPL-3.0"
gem.executables = ['sidekiq', 'sidekiqctl']
gem.files = `git ls-files | grep -Ev '^(myapp|examples)'`.split("\n")
gem.test_files = `git ls-files -- test/*`.split("\n")
gem.name = "sidekiq"
gem.require_paths = ["lib"]
gem.version = Sidekiq::VERSION
gem.add_dependency 'redis', '~> 3.2', '>= 3.2.1'
gem.add_dependency 'connection_pool', '~> 2.2', '>= 2.2.0'
gem.add_dependency 'concurrent-ruby', '~> 1.0'
gem.add_dependency 'rack-protection', '>= 1.5.0'
gem.add_development_dependency 'redis-namespace', '~> 1.5', '>= 1.5.2'
gem.add_development_dependency 'minitest', '~> 5.7', '>= 5.7.0'
gem.add_development_dependency 'rake', '~> 10.0'
gem.add_development_dependency 'rails', '>= 3.2.0'
end
该gemspec中指定了runtime dependency和development dependency。
runtime dependency有redis, connection_pool, concurrent-ruby, rack-protection这些都是sidekiq运行时所必需的
development dependency有redis-namepace, minitest, rake, rake, rails是sidekiq build(启动)以及test所需要的
那么gem install安装的时候如何安装所有的依赖呢？
可用过
gem install --dev sidekiq或者gem install --development-all sidekiq， 前者会安装development dependency， 后者会安装包括依赖的依赖。development dependency默认不会被安装，并且当gem被require的时候，它们不会被激活(加载)
