tl;dr jruby in Gentoo will have to go unless we get volunteers to help us with the jruby 1.7 series.
jruby has been available in Gentoo since 2004 and is currently at version 1.6.8. People following jruby will realize that this is a problem: the latest upstream version is 1.7.12 as of this writing. The 1.6 series is also based on ruby 1.8.7 by default. This is a problem since we have removed ruby 1.8 from the tree altogether, and support for it in ruby packages is disappearing fast. jruby 1.6 has a 1.9 mode, but that is based on ruby 1.9.2 where most packages expect at least 1.9.3. We are currently experimenting with defaulting to 1.9.2 mode to extend the 1.6 series. In short, more and more packages that currently have jruby target will loose it on updates since it simply is no longer compatible with jruby 1.7 and in its current state jruby in Gentoo is ready for a slow and agonizing descent. Or we could just be quick about it and mask it soon.
Why not just update to jruby 1.7, you might wonder? We have bug 442230 to track this update, but unfortunately it turns out that it is not easy to add the 1.7 series of jruby to Gentoo. The biggest stumbling block here is that the 1.7 build system is based on Maven. Using Maven is not well supported in Gentoo, mostly because Maven requires the ability to download code during its build phase and does not play very nice with Gentoo's package structure in general. It may be possible to fix this, but that requires good knowledge of Java and Ruby on Gentoo. Currently we don't have any developers capable of both, and passing the code back and forth isn't very practical and proves to go very slow in practice.
So we are looking for a volunteer who wants to pick up this project, and help us bring the jruby 1.7 series to Gentoo. If you see this as a step to become a Gentoo developer than that's great and we can mentor you. If you see this as an interesting one-off project to help out with, that's great too. Once 1.7 is in the tree it should not be a big deal to keep up with new versions. Feel free to drop by in #gentoo-ruby to discuss this with us if you are interested. Our ruby overlay holds the current work-in-progress on jruby 1.7.
If no-one volunteers, unless a magical break-through suddenly appears, we will most likely be forced to mask jruby and remove it from the tree. Help us to not do that!