How do I find out all the dependencies of a gem?

Question

I have been trying to find out dependencies for a ruby-gem. I know that gem dependency command will let me know about the dependencies of the gem. But I want to do more than

Answer 1

$ gem dependency nokogiri -R

for example will give you a list like

  Gem nokogiri-1.6.0
  hoe (~> 2.16, development)
  hoe-bundler (>= 1.1, development)
  hoe-debugging (>= 1.0.3, development)
  hoe-gemspec (>= 1.0, development)
  hoe-git (>= 1.4, development)
  mini_portile (~> 0.5.0)
  minitest (~> 2.2.2, development)
  racc (>= 1.4.6, development)
  rake (>= 0.9, development)
  rake-compiler (~> 0.8.0, development)
  rdoc (~> 3.10, development)
  rexical (>= 1.0.5, development)
  Used by
    haml-4.0.3 (nokogiri (>= 0, development))
    mime-types-1.23 (nokogiri (~> 1.5, development))
    redcarpet-2.3.0 (nokogiri (>= 0, development))
    tilt-1.4.1 (nokogiri (>= 0, development))

that Include reverse dependencies in the output

More on $ gem dependencyhttp://guides.rubygems.org/command-reference/#gem_dependency

update

According to the research I have done on web, and after having asked about this subject to my colleagues and others I went to conclusion, that there is no way one can currently use $ gem dependency to find out the complete recursive list of a gem dependencies.

Writing a ruby gem similar to one that you have indicated in your updated question should not be very complicated. I believe one can do this by writing a simple recursive loop and by fetching gem information, perhaps in a desirable format.

I think I give up on this about this subject, but somebody could start a bounty for somebody else (not me) who could think of "the best way to get recursive gem dependencies" other than https://www.gemlou.pe which I think is nice.

Answer 2

following class will recursively get gem dependencies (note its proof of concept so it does not do anything fancy, but its a good starting point). for documentation please refer rubydocs: Gem::Dependency and Gem::Specification

class GemRequirements
  def initialize(name, version = nil)
    @gem = Gem::Dependency.new(name, version)
  end

  def dependency_tree
    @dependency_tree ||= {}.merge(get_dependency(@gem))
  end

  private

  def get_dependency(gem_dependency)
    spec = gem_dependency.matching_specs.first
    dep_key = "#{gem_dependency.name} #{spec.version}"
    hash = { dep_key => {} }
    spec.runtime_dependencies.each do |spec_dependency|
      spec_dependency_spec = spec_dependency.matching_specs.first
      spec_dep_key = "#{spec_dependency.name} #{spec_dependency_spec.version}"
      hash[dep_key][spec_dep_key] = get_dependency(spec_dependency)
    end
    hash
  end
end

you can use it programatically in your app or from ruby console:

r = GemRequirements.new 'rails'
r.dependency_tree  
=> {"rails 3.2.12"=>
  {"activesupport 3.2.12"=>
    {"activesupport 3.2.12"=>
      {"i18n 0.6.4"=>{"i18n 0.6.4"=>{}},
       "multi_json 1.8.2"=>{"multi_json 1.8.2"=>{}}}},
   "actionpack 3.2.12"=>
    {"actionpack 3.2.12"=>
      {"activesupport 3.2.12"=>
        {"activesupport 3.2.12"=>
          {"i18n 0.6.4"=>{"i18n 0.6.4"=>{}},
           "multi_json 1.8.2"=>{"multi_json 1.8.2"=>{}}}},
       "activemodel 3.2.12"=>
        {"activemodel 3.2.12"=>
          {"activesupport 3.2.12"=>
            {"activesupport 3.2.12"=>
              {"i18n 0.6.4"=>{"i18n 0.6.4"=>{}},
               "multi_json 1.8.2"=>{"multi_json 1.8.2"=>{}}}},
           "builder 3.0.4"=>{"builder 3.0.4"=>{}}}},
       "rack-cache 1.2"=>
        {"rack-cache 1.2"=>{"rack 1.4.5"=>{"rack 1.4.5"=>{}}}},
       "builder 3.0.4"=>{"builder 3.0.4"=>{}},
       "rack 1.4.5"=>{"rack 1.4.5"=>{}},
       "rack-test 0.6.2"=>
        {"rack-test 0.6.2"=>{"rack 1.4.5"=>{"rack 1.4.5"=>{}}}},
       "journey 1.0.4"=>{"journey 1.0.4"=>{}},
       "sprockets 2.2.2"=>
        {"sprockets 2.2.2"=>
          {"hike 1.2.1"=>{"hike 1.2.1"=>{}},
           "multi_json 1.8.2"=>{"multi_json 1.8.2"=>{}},
           "rack 1.4.5"=>{"rack 1.4.5"=>{}},
           "tilt 1.4.1"=>{"tilt 1.4.1"=>{}}}},
       "erubis 2.7.0"=>{"erubis 2.7.0"=>{}}}},
   "activerecord 3.2.12"=>
    {"activerecord 3.2.12"=>
      {"activesupport 3.2.12"=>
        {"activesupport 3.2.12"=>
          {"i18n 0.6.4"=>{"i18n 0.6.4"=>{}},
           "multi_json 1.8.2"=>{"multi_json 1.8.2"=>{}}}},
       "activemodel 3.2.12"=>
        {"activemodel 3.2.12"=>
          {"activesupport 3.2.12"=>
            {"activesupport 3.2.12"=>
              {"i18n 0.6.4"=>{"i18n 0.6.4"=>{}},
               "multi_json 1.8.2"=>{"multi_json 1.8.2"=>{}}}},
           "builder 3.0.4"=>{"builder 3.0.4"=>{}}}},
       "arel 3.0.2"=>{"arel 3.0.2"=>{}},
       "tzinfo 0.3.37"=>{"tzinfo 0.3.37"=>{}}}},
   "activeresource 3.2.12"=>
    {"activeresource 3.2.12"=>
      {"activesupport 3.2.12"=>
        {"activesupport 3.2.12"=>
          {"i18n 0.6.4"=>{"i18n 0.6.4"=>{}},
           "multi_json 1.8.2"=>{"multi_json 1.8.2"=>{}}}},
       "activemodel 3.2.12"=>
        {"activemodel 3.2.12"=>
          {"activesupport 3.2.12"=>
            {"activesupport 3.2.12"=>
              {"i18n 0.6.4"=>{"i18n 0.6.4"=>{}},
               "multi_json 1.8.2"=>{"multi_json 1.8.2"=>{}}}},
           "builder 3.0.4"=>{"builder 3.0.4"=>{}}}}}},
   "actionmailer 3.2.12"=>
    {"actionmailer 3.2.12"=>
      {"actionpack 3.2.12"=>
        {"actionpack 3.2.12"=>
          {"activesupport 3.2.12"=>
            {"activesupport 3.2.12"=>
              {"i18n 0.6.4"=>{"i18n 0.6.4"=>{}},
               "multi_json 1.8.2"=>{"multi_json 1.8.2"=>{}}}},
           "activemodel 3.2.12"=>
            {"activemodel 3.2.12"=>
              {"activesupport 3.2.12"=>
                {"activesupport 3.2.12"=>
                  {"i18n 0.6.4"=>{"i18n 0.6.4"=>{}},
                   "multi_json 1.8.2"=>{"multi_json 1.8.2"=>{}}}},
               "builder 3.0.4"=>{"builder 3.0.4"=>{}}}},
           "rack-cache 1.2"=>
            {"rack-cache 1.2"=>{"rack 1.4.5"=>{"rack 1.4.5"=>{}}}},
           "builder 3.0.4"=>{"builder 3.0.4"=>{}},
           "rack 1.4.5"=>{"rack 1.4.5"=>{}},
           "rack-test 0.6.2"=>
            {"rack-test 0.6.2"=>{"rack 1.4.5"=>{"rack 1.4.5"=>{}}}},
           "journey 1.0.4"=>{"journey 1.0.4"=>{}},
           "sprockets 2.2.2"=>
            {"sprockets 2.2.2"=>
              {"hike 1.2.1"=>{"hike 1.2.1"=>{}},
               "multi_json 1.8.2"=>{"multi_json 1.8.2"=>{}},
               "rack 1.4.5"=>{"rack 1.4.5"=>{}},
               "tilt 1.4.1"=>{"tilt 1.4.1"=>{}}}},
           "erubis 2.7.0"=>{"erubis 2.7.0"=>{}}}},
       "mail 2.4.4"=>
        {"mail 2.4.4"=>
          {"mime-types 1.21"=>{"mime-types 1.21"=>{}},
           "treetop 1.4.12"=>
            {"treetop 1.4.12"=>{"polyglot 0.3.3"=>{"polyglot 0.3.3"=>{}}}},
           "i18n 0.6.4"=>{"i18n 0.6.4"=>{}}}}}},
   "railties 3.2.12"=>
    {"railties 3.2.12"=>
      {"rake 10.1.0"=>{"rake 10.1.0"=>{}},
       "rack-ssl 1.3.3"=>
        {"rack-ssl 1.3.3"=>{"rack 1.4.5"=>{"rack 1.4.5"=>{}}}},
       "thor 0.18.1"=>{"thor 0.18.1"=>{}},
       "rdoc 3.12.2"=>{"rdoc 3.12.2"=>{"json 1.8.1"=>{"json 1.8.1"=>{}}}},
       "activesupport 3.2.12"=>
        {"activesupport 3.2.12"=>
          {"i18n 0.6.4"=>{"i18n 0.6.4"=>{}},
           "multi_json 1.8.2"=>{"multi_json 1.8.2"=>{}}}},
       "actionpack 3.2.12"=>
        {"actionpack 3.2.12"=>
          {"activesupport 3.2.12"=>
            {"activesupport 3.2.12"=>
              {"i18n 0.6.4"=>{"i18n 0.6.4"=>{}},
               "multi_json 1.8.2"=>{"multi_json 1.8.2"=>{}}}},
           "activemodel 3.2.12"=>
            {"activemodel 3.2.12"=>
              {"activesupport 3.2.12"=>
                {"activesupport 3.2.12"=>
                  {"i18n 0.6.4"=>{"i18n 0.6.4"=>{}},
                   "multi_json 1.8.2"=>{"multi_json 1.8.2"=>{}}}},
               "builder 3.0.4"=>{"builder 3.0.4"=>{}}}},
           "rack-cache 1.2"=>
            {"rack-cache 1.2"=>{"rack 1.4.5"=>{"rack 1.4.5"=>{}}}},
           "builder 3.0.4"=>{"builder 3.0.4"=>{}},
           "rack 1.4.5"=>{"rack 1.4.5"=>{}},
           "rack-test 0.6.2"=>
            {"rack-test 0.6.2"=>{"rack 1.4.5"=>{"rack 1.4.5"=>{}}}},
           "journey 1.0.4"=>{"journey 1.0.4"=>{}},
           "sprockets 2.2.2"=>
            {"sprockets 2.2.2"=>
              {"hike 1.2.1"=>{"hike 1.2.1"=>{}},
               "multi_json 1.8.2"=>{"multi_json 1.8.2"=>{}},
               "rack 1.4.5"=>{"rack 1.4.5"=>{}},
               "tilt 1.4.1"=>{"tilt 1.4.1"=>{}}}},
           "erubis 2.7.0"=>{"erubis 2.7.0"=>{}}}}}},
   "bundler 1.3.5"=>{"bundler 1.3.5"=>{}}}}