Jeweler: Craft the perfect RubyGem

Jeweler provides the noble ruby developer with two primary features:

  • a library for managing and releasing RubyGem projects
  • a scaffold generator for starting new RubyGem projects

Hello, world

Use RubyGems to install the heck out of jeweler to get started: 

$ gem install jeweler

With jeweler installed, you can use the jeweler command to generate a new project. For the most basic use, just give it a name:

$ jeweler hello-gem

This requires some Git configuration (like name, email, GitHub account, etc), but jeweler will prompt along the way.

Your new hello-gem gem is ready in the hello-gem directory. Take a peek, and you'll see several files and directories

  • Rakefile setup for jeweler, running tests, generating documentation, and releasing to rubygems.org
  • README.rdoc with contribution guidelines and copyright info crediting you
  • LICENSE with the MIT licensed crediting you
  • Gemfile with development dependencies filled in
  • lib/hello-gem.rb waiting for you to code
  • test/ containing a (failing) shoulda test suite shoulda

More jeweler options

The jeweler command supports a lot of options. Mostly, they are for generating baked in support for this test framework, or that.

Check out jeweler --help for the most up to date options.

Hello, rake tasks

Beyond just editing source code, you'll be interacting with your gem using rake a lot. To see all the tasks available with a brief description, you can run:

$ rake -T

You'll need a version before you can start installing your gem locally. The easiest way is with the version:write Rake task. Let's imagine you start with 0.1.0

$ rake version:write MAJOR=0 MINOR=1 PATCH=0

You can now go forth and develop, now that there's an initial version defined. Eventually, you should install and test the gem:

$ rake install

The install rake task builds the gem and gem installs it. You're all set if you're using RVM, but you may need to run it with sudo if you have a system-installed ruby:

$ sudo rake install

Releasing

At last, it's time to ship it! Make sure you have everything committed and pushed, then go wild:

$ rake release

This will automatically:

  • Generate hello-gem.gemspec and commit it
  • Use git to tag v0.1.0 and push it
  • Build hello-gem-0.1.0.gem and push it to rubygems.org

Version bumping

It feels good to release code. Do it, do it often. But before that, bump the version. Then release it. There's a few ways to update the version:

# version:write like before
$ rake version:write MAJOR=0 MINOR=3 PATCH=0

# bump just major, ie 0.1.0 -> 1.0.0
$ rake version:bump:major

# bump just minor, ie 0.1.0 -> 0.2.0
$ rake version:bump:minor

# bump just patch, ie 0.1.0 -> 0.1.1
$ rake version:bump:patch

Then it's the same release we used before:

$ rake release

Customizing your gem

If you've been following along so far, your gem is just a blank slate. You're going to need to make it colorful and full of metadata.

You can customize your gem by updating your Rakefile. With a newly generated project, it will look something like this:

require 'jeweler'
Jeweler::Tasks.new do |gem|
  # gem is a Gem::Specification... see http://docs.rubygems.org/read/chapter/20 for more options
  gem.name = "whatwhatwhat"
  gem.summary = %Q{TODO: one-line summary of your gem}
  gem.description = %Q{TODO: longer description of your gem}
  gem.email = "[email protected]"
  gem.homepage = "http://github.com/technicalpickles/whatwhatwhat"
  gem.authors = ["Joshua Nichols"]
end
Jeweler::RubygemsDotOrgTasks.new

It's crucial to understand the gem object is just a Gem::Specification. You can read up about it at docs.rubygems.org/read/chapter/20. This is the most basic way of specifying a gem, Jeweler-managed or not. Jeweler just exposes this to you, in addition to providing some reasonable defaults, which we'll explore now.

Project information

gem.name = "whatwhatwhat"

Every gem has a name. Among other things, the gem name is how you are able to gem install it. Reference

gem.summary = %Q{TODO: one-line summary of your gem}

This is a one line summary of your gem. This is displayed, for example, when you use gem list --details or view it on rubygems.org.

gem.description = %Q{TODO: longer description of your gem}

Description is a longer description. Scholars ascertain that knowledge of where the description is used was lost centuries ago.

gem.email = "[email protected]"

This should be a way to get a hold of you regarding the gem.

gem.homepage = "http://github.com/technicalpickles/whatwhatwhat"

The homepage should have more information about your gem. The jeweler generator guesses this based on the assumption your code lives on GitHub, using your Git configuration to find your GitHub username. This is displayed by gem list --details and on rubygems.org.

gem.authors = ["Joshua Nichols"]

Hey, this is you, the author (or me in this case). The jeweler generator also guesses this from your Git configuration. This is displayed by gem list --details and on rubygems.org.

Files

The quickest way to add more files is to git add them. Jeweler uses your Git repository to populate your gem's files by including added and committed and excluding .gitignored. In most cases, this is reasonable enough.

If you need to tweak the files, that's cool. Jeweler populates gem.files as a Rake::FileList. It's like a normal array, except you can include and exclude file globs:

gem.files.exclude 'tmp' # exclude temporary directory
gem.files.include 'lib/foo/bar.rb' # explicitly include lib/foo/bar.rb

If that's not enough, you can just set gem.files outright

gem.files = Dir.glob('lib/**/*.rb')

Dependencies

Dependencies let you define other gems that your gem needs to function. gem install your-gem will install your-gem's dependencies along with it, and when you use your-gem in an application, the dependencies will be made available. Use gem.add_dependency to register them. Reference

gem.add_dependency 'nokogiri'

This will ensure a version of nokogiri is installed, but it doesn't require anything more than that. You can provide extra args to be more specific:

gem.add_dependency 'nokogiri', '= 1.2.1' # exactly version 1.2.1
gem.add_dependency 'nokogiri', '>= 1.2.1' # greater than or equal to 1.2.1, ie, 1.2.1, 1.2.2, 1.3.0, 2.0.0, etc
gem.add_dependency 'nokogiri', '>= 1.2.1', '< 1.3.0' # greater than or equal to 1.2.1, but less than 1.3.0
gem.add_dependency 'nokogiri', '~> 1.2.1' # same thing, but more concise

When specifying which version is required, there's a bit of the condunrum. You want to allow the most versions possible, but you want to be sure they are compatible. Using >= 1.2.1 is fine most of the time, except until the point that 2.0.0 comes out and totally breaks backwards the API. That's when it's good to use ~> 1.2.1, which requires any version in the 1.2 family, starting with 1.2.1.

Executables

Executables let your gem install shell commands. Just put any executable scripts in the bin/ directory, make sure they are added using git, and Jeweler will take care of the rest.

When you need more finely grained control over it, you can set it yourself:

gem.executables = ['foo'] # note, it's the file name relative to `bin/`, not the project root

Versioning

We discussed earlier how to bump the version. The rake tasks are really just convience methods for manipulating the VERSION file. It just contains a version string, like 1.2.3.

VERSION is a convention used by Jeweler, and is used to populate gem.version. You can actually set this yourself, and Jeweler won't try to override it:

gem.version = '1.2.3'

A common pattern is to have this in a version constant in your library. This is convenient, because users of the library can query the version they are using at runtime.

# in lib/foo/version.rb
class Foo
  module Version
    MAJOR = 1
    MINOR = 2
    PATCH = 3
    BUILD = 'pre3'

    STRING = [MAJOR, MINOR, PATCH, BUILD].compact.join('.')
  end
end

# in Rakefile
require 'jeweler'
require './lib/foo/version.rb'
Jeweler::Tasks.new do |gem|
  # snip
  gem.version = Foo::Version::STRING
end

Rake tasks

Jeweler lives inside of Rake. As a result, they are dear friends. But, that friendship doesn't interfere with typical Rake operations.

That means you can define your own namespaces, tasks, or use third party Rake libraries without cause for concern.

Contributing to Jeweler

  • Check out the latest master to make sure the feature hasn't been implemented or the bug hasn't been fixed yet
  • Ask on the mailing list for feedback on your proposal, to see if somebody else has done it.
  • Check out the issue tracker to make sure someone already hasn't requested it and/or contributed it
  • Fork the project
  • Start a feature/bugfix branch
  • Commit and push until you are happy with your contribution
  • Make sure to add tests for the feature/bugfix. This is important so I don't break it in a future version unintentionally.
  • Please try not to mess with the Rakefile, version, or history. If you want to have your own version, or is otherwise necessary, that is fine, but please isolate it to its own commit so I can cherry-pick around it.

Copyright (c) 2008-2010 Josh Nichols. See LICENSE for details.