Just clarifying the problem - even if you don't use Truffle, the fact that our jars come first on the classpath means they override anyone else trying to use their own version of those classes?

Maybe a solution is to only put the Truffle jars on the class path when the launcher sees -X+T.

@chrisseaton yes those jars in the truffle jar just forces everyone to use those versions of the libraries.

to add the truffle jar only on -X+T is one short term solution to make jruby and jruby-complete.jar and any embedded jruby behave the same way again. but in the long run truffle should use those jars in the same manner as the current jruby stdlib, i.e. require them, like jline and snakeyaml. not sure whether truffle core needs antlr itself - then there is no way around it.

Or we could re-namespace everything, or just Antlr.

I'll look into this options and update you here.

the snakeyaml is a different story as it implements psych and regular jruby uses the psych gem as default gem. truffle as it is right now does not allow to "overwrite" psych by installing the psych gem. not sure how much of it is a "temporary" solution to get yaml working.

I'll do the only adding Truffle to the classpath when -X+T is set today. That should fix all problems for anyone not using Truffle, right?

Fixed in e84c5e6.

I don't think we want to do any other shading or lazy loading at the moment, as the expected use-case for Truffle does not involve any user jars at the moment, so there's nothing to conflict with.