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I'm Jason, a web applications developer in the San Francisco Bay area.

Bundler Definitions

I’m currently starting work on a Ruby gem, ‘annotate_gemfile’, that will grab the title, description, homepage URL, or source URL for every defined gem, and then add them as an annotation / commented for each gem definition in the Gemfile.

As part of this exploration, I’m digging into the source for Bundler to try an understand how it imports details on the gems from the Gemfile, how it queries for details on each from RubyGems. Here are some discoveries I’m making.


This appears to return an initialized object with the Gemfile definitions loaded. Bundler.definition returns an instance of Bundler::Definition for the default Gemfile and default lock file (Gemfile.lock). Readable attributes of this “definition” are platforms, sources, ruby_version, and dependencies.

>> Bundler.definition.platforms
=> ["ruby"]

>> Bundler.definition.sources
=> [source at ., rubygems repository]

>> Bundler.definition.ruby_version
=> nil

>> Bundler.definition.dependencies
=> [<Bundler::Dependency type=:runtime name="annotate_gem" requirements=">= 0">, <Bundler::Dependency type=:development name="bundler" requirements="~> 1.3">, <Bundler::Dependency type=:development name="rake" requirements=">= 0">, <Bundler::Dependency type=:development name="rspec" requirements="~> 2.14.1">]


Bundler allows the specification for gems to be installed only on certain Ruby platforms. Options include different minor versions of Ruby (1.8, 1.9, 2.0) as well as differences between types of Ruby (MRI Ruby, Rubinius, jRuby, various Windows Ruby versions).


There appear to be three source types supported by Bundler.


A Bundler::Source::RubyGems object represents a RubyGems server. The default one is If you check your Gemfile, you’ll see a ‘source’ directive that points to the URL for the gem server with as the URL.

1.9.3p448 :044 > Bundler.definition.sources[1].class
 => Bundler::Source::Rubygems

1.9.3p448 :038 > Bundler.definition.sources[1]
 => rubygems repository

1.9.3p448 :039 > Bundler.definition.sources[1].name
 => "rubygems repository"

1.9.3p448 :040 > Bundler.definition.sources[1].options
 => {"remotes"=>[""]}

1.9.3p448 :041 > Bundler.definition.sources[1].remotes
 => [#<URI::HTTPS:0x007fb59138ea20 URL:>]

1.9.3p448 :042 > Bundler.definition.sources[1].caches
 => [#<Pathname:/Users/redconfetti/Sites/annotate_gemfile/vendor/cache>, "/Users/redconfetti/.rvm/gems/ruby-1.9.3-p448@annotate_gemfile/cache", "/Users/redconfetti/.rvm/gems/ruby-1.9.3-p448@global/cache"]

1.9.3p448 :043 > Bundler.definition.sources[1].dependency_names
 => ["rake", "annotate_gem", "bundler", "diff-lcs", "rspec-core", "rspec-expectations", "rspec-mocks", "rspec"]

The ‘dependency_names’ are the names of gems which rely on this RubyGem source server.


A Bundler::Source::Path object represents a local gem path. This source is from the local path of the Gemfile I’m developing. The ‘name’ appears to be the name of the dependency that relies on the “path” source.

1.9.3p448 :045 > Bundler.definition.sources[0].class
 => Bundler::Source::Path

1.9.3p448 :030 > Bundler.definition.sources[0].name
 => "annotate_gemfile"

1.9.3p448 :031 > Bundler.definition.sources[0].path
 => #<Pathname:.>

1.9.3p448 :032 > Bundler.definition.sources[0].options
 => {"path"=>"."}

1.9.3p448 :033 > Bundler.definition.sources[0]
 => source at .


A Bundler::Source::Git object represents a Git repository that provides the source code for a defined gem dependency.

2.0.0p247 :018 > Bundler.definition.sources[0].class
 => Bundler::Source::Git

2.0.0p247 :019 > Bundler.definition.sources[0].name
 => "bootstrap-sass"

2.0.0p247 :020 > Bundler.definition.sources[0].uri
 => ""

2.0.0p247 :021 > Bundler.definition.sources[0].ref
 => "master"

2.0.0p247 :022 > Bundler.definition.sources[0].branch
 => nil

2.0.0p247 :023 > Bundler.definition.sources[0].options
 => {"revision"=>"16da2ffb1fb98672f498b482c318db0cfb20a054", "uri"=>""}

2.0.0p247 :024 > Bundler.definition.sources[0].submodules
 => nil

2.0.0p247 :025 > Bundler.definition.sources[0].version
 => nil

As you can see, the ‘name’ attribute defines the gem that is dependent on this specific Git repository.

Ruby Version

Your Gemfile may include a specific Ruby version, which is expressed as a Bundler::RubyVersion object in the definition. Heroku requires the Ruby version for projects you are deploying to their platform.

# Gemfile
ruby '2.0.0'

# Console
2.0.0p247 :001 > Bundler.definition.ruby_version
 => #<Bundler::RubyVersion:0x007fe8c890a908 @version="2.0.0", @engine="ruby", @input_engine=nil, @engine_version="2.0.0">


This is the meat of the Gemfile, the dependencies which are represented as Bundler::Dependency objects.

1.9.3p448 :003 > Bundler.definition.dependencies[0]
 => <Bundler::Dependency type=:runtime name="annotate_gem" requirements=">= 0">

1.9.3p448 :004 > Bundler.definition.dependencies[1]
 => <Bundler::Dependency type=:development name="bundler" requirements="~> 1.3">

1.9.3p448 :005 > Bundler.definition.dependencies[2]
 => <Bundler::Dependency type=:development name="rake" requirements=">= 0">

1.9.3p448 :006 > Bundler.definition.dependencies[3]
 => <Bundler::Dependency type=:development name="rspec" requirements="~> 2.14.1">

It appears that dependencies do not specify a source if they are provided from a Ruby Gems server. Only if they are sourced from a Path or Git repository.

# Dependencies from my gem in development
1.9.3p448 :021 > Bundler.definition.dependencies[0]
 => <Bundler::Dependency type=:runtime name="annotate_gem" requirements=">= 0">

1.9.3p448 :022 > Bundler.definition.dependencies[0].source
 => source at .

1.9.3p448 :023 > Bundler.definition.dependencies[1]
 => <Bundler::Dependency type=:development name="bundler" requirements="~> 1.3">

1.9.3p448 :024 > Bundler.definition.dependencies[1].source
 => nil

# Bootstrap-Sass dependency from another project
2.0.0p247 :022 > Bundler.definition.dependencies[10].class
 => Bundler::Dependency

2.0.0p247 :023 > Bundler.definition.dependencies[10]
 => <Bundler::Dependency type=:runtime name="bootstrap-sass" requirements=">= 0">

2.0.0p247 :024 > Bundler.definition.dependencies[10].groups
 => [:default]

2.0.0p247 :025 > Bundler.definition.dependencies[10].source.class
 => Bundler::Source::Git