How do I add conditional rubygem requirements to a gem specification?

Question

Is it possible to add a gem dependency only if the person is using a certain version of ruby?

Background: I\'m working on a fork of a project that u

Answer 1

hay ... i'm kind of a ruby newbie ... if this is the best way to do it.

any way ... i wish i can do that using only Ruby .... though u can use your operating system shell to do that, by using this in your program installer, just execute (works for Linux based operating systems):

$ruby --version

(u can execute that from a ruby installer file, just like: ruby --version) and put a possibility according to output, if it's 1.9.1 add an extra line to execute:

$ sudo gem install gem_name

else, just leave it be.

Answer 2

Checkout this tutorial in the Ruby Programming wikibook.

Tt shows how to install different versions of dependencies depending on what version of ruby the installee is using.

(short answer--it ain't as easy as it should be)

Answer 3

Gemspecs are just ruby files anyway, so you can execute any ruby code inside them, so:

spec.add_dependency = 'test-unit', '>= 2.0' if RUBY_VERSION =~ '1.9' 

EDIT: Specs run only on the builders machine.

Answer 4

Gem doesn't support conditional dependencies (except on gem builder's environment -as noted above), and bundler is not a viable option to solve this either - see https://github.com/carlhuda/bundler/issues/1281

Answer 5

I did this exact thing for a project. The trick is to add the script as an extension, which will then get executed at install time on the user's machine.

Here are code snippets and links to our github:

First, when in the gemspec (we're actually using a Rakefile to generate it, but the result ends up the same) source

# This file *needs* to be named this, there are other files 
#  for other extension processors
s.extensions << 'ext/mkrf_conf.rb'

And then the relevant lines in that mkrf_conf.rb source

require 'rubygems/dependency_installer.rb' 
inst = Gem::DependencyInstaller.new
inst.install "test-unit" if RUBY_VERSION > "1.9"

Answer 6

If you look at the gemspec documentation for add_dependency, there isn't an option for a ruby version. Perhaps you could use the post_install_message attribute to tell the user to install the gem if they're using ruby 1.9.