Writing a Jeweler Rakefile that adds dependencies depending on RUBY_ENGINE (ruby or jruby)

I have a Rakefile that includes this:

Jeweler::Tasks.new do |gem|
  # ...
  gem.add_dependency('json')
end

The gemspec that this generates builds a gem that can't be installed on jruby because the 'json' gem is native.

For jruby, this would have to be:

Jeweler::Tasks.new do |gem|
  # ...
  gem.add_dependency('json-jruby')
end

How do I conditionally add th开发者_开发问答e dependency for 'json-jruby' when RUBY_ENGINE == 'java'?

It seems like my only option is to manually edit the gemspec file that jeweler generates to add the RUBY_ENGINE check. But I'd rather avoid this, since it kind of defeats the purpose of using jeweler in the first place.

Any ideas?

---

After some more digging around, I've come to the conclusion that the problem here isn't so much the limitation in Jeweler as it is a problem with how the json-jruby gem is named.

In a perfect world, the json-jruby gem should be named just json. That way when the gem file is built under JRuby (i.e. jgem build json-jruby.gem), the resulting gem file would be named json-1.4.3-universal-java-1.6.gem (RubyGems names the file based on the 'platform' property in the gemspec). When installed with the appropriate platform in the gem name, everything works transparently. There's no need to explicitly require json-jruby. RubyGems uses the appropriate version automatically.

I've contacted the maintainer of the json gem to see if he'd be willing to get json-1.4.3-universal-java-1.6.gem added to his gemcutter repo, but in the meantime you can download the drop-in jruby json gem here: http://roughest.net/json-1.4.3-universal-java-1.6.gem