A RubyGems plugin that generates binary (pre-compiled) gems.

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gem-compiler is a RubyGems plugin that helps generates binary gems from already existing ones without altering the original source code. It compiles Ruby C extensions and bundles the result into a new gem.

It uses an outside-in approach and leverages on existing RubyGems code to do it.

The result of the compilation is a binary gem built for your current platform, skipping the need of a compiler toolchain when installing it.


To install gem-compiler you need to use RubyGems:

$ gem install gem-compiler

Which will fetch and install the plugin. After that the compile command will be available through gem.


As requirement, gem-compiler can only compile local gems, either one you have generated from your projects or previously downloaded.

Fetching a gem

If you don't have the gem locally, you can use fetch to retrieve it first:

$ gem fetch yajl-ruby --platform=ruby
Fetching: yajl-ruby-1.1.0.gem (100%)
Downloaded yajl-ruby-1.1.0

Please note that I was explicit about which platform to fetch. This will avoid RubyGems attempt to download any existing binary gem for my current platform.

Compiling a gem

You need to tell RubyGems the filename of the gem you want to compile:

$ gem compile yajl-ruby-1.1.0.gem

The above command will unpack, compile any existing extensions found and repackage everything as a binary gem:

Unpacking gem: 'yajl-ruby-1.1.0' in temporary directory...
Building native extensions.  This could take a while...
  Successfully built RubyGem
  Name: yajl-ruby
  Version: 1.1.0
  File: yajl-ruby-1.1.0-x86-mingw32.gem

This new gem do not require a compiler, as shown when locally installed:

C:\> gem install --local yajl-ruby-1.1.0-x86-mingw32.gem
Successfully installed yajl-ruby-1.1.0-x86-mingw32
1 gem installed

There are native gems that will invalidate their own specification after compile process completes. This will not permit them be repackaged as binary gems. To workaround this problem you have the option to prune the package process:

$ gem fetch nokogiri --platform=ruby

Fetching: nokogiri- (100%)
Downloaded nokogiri-

$ gem compile nokogiri- --prune

Unpacking gem: 'nokogiri-' in temporary directory...
Building native extensions.  This could take a while...
  Successfully built RubyGem
  Name: nokogiri
  File: nokogiri-

$ gem install --local nokogiri-

Successfully installed nokogiri-
1 gem installed

Restrictions of binaries

Gems compiled with gem-compiler will be lock to the version of Ruby used to compile them.

This means that a gem compiled under Ruby 2.2 could only be installed under Ruby 2.2.

You can disable this by using --no-abi-lock option during compilation:

$ gem compile yajl-ruby-1.1.0.gem --no-abi-lock

Warning: this is not recommended since different versions of Ruby might expose different options on the API. The binary might be expecting specific features not present in the version of Ruby you're installing the binary gem into.

Compiling from Rake

Most of the times, as gem developer, you would like to generate both kind of gems at once. For that purpose, you can add a task for Rake similar to the one below:

desc "Generate a pre-compiled native gem"
task "gem:native" => ["gem"] do
  sh "gem compile #{gem_file}"

Of course, that assumes you have a task gem that generates the base gem required.


Ruby and RubyGems

It's assumed you have Ruby and RubyGems installed. gem-compiler requires RubyGems 1.8.x to properly work.

If you don't have RubyGems 1.8.x, you can upgrade by running:

$ gem update --system

A compiler

In order to compile a gem, you need a compiler toolchain installed. Depending on your Operating System you will have one already installed or will require additional steps to do it. Check your OS documentation about getting the right one.

If you're using Windows

For those using RubyInstaller-based builds, you will need to download the DevKit from their downloads page and follow the installation instructions.

To be sure your installation of Ruby is based on RubyInstaller, execute at the command prompt:

C:\> ruby --version

And from the output:

tcs-ruby 1.9.3p196 (2012-04-21, TCS patched 2012-04-21) [i386-mingw32]

If you see mingw32, that means you're using a RubyInstaller build (MinGW based).

Differences with rake-compiler

rake-compiler has provided to Ruby library authors a tool for compiling extensions and generating binary gems of their libraries.

You can consider rake-compiler's approach be an inside-out process. To do its magic, it requires library authors to modify their source code, adjust some structure and learn a series of commands.

While the ideal scenario is using a tool like rake-compiler that endorses convention over configuration, is not humanly possible change all the projects by snapping your fingers :wink:


The MIT License