New reify classes

[headius]

Work to unify variable and structural reification of Ruby classes. See #4643.

[kares]

there's org/jruby/gen to distinguish generated code, maybe it makes sense to use it as well (org.jruby.gen.specialize)?

[headius]

I agree this generated code should go into org.jruby.gen. The "org.jruby.specialize" was a typo on my part; it would have been specialized, which I think we will keep to separate the hand-written pieces from the generated stuff.

[ivoanjo]

I've just retried with this branch with the following testcase (from #4643)

class BrokenReify
  def to_s
    super
  end
end

puts BrokenReify.new.to_s

And it still causes a stack overflow. I believe the reason why it fails is still similar: it's because unlike other reification options (e.g. reify variables) we define the instance methods from the ruby class in the reified class, which is what breaks code which tries to call super.

I'm not sure what the is best choice here:

• One alternative would just to not add the instance methods
• Or they could be added, but using some name mangling (does any other part of JRuby really use them at all?)
• Or maybe the solution would be to hunt down and fix any assumptions that you can call kernel methods on the object instance e.g https://github.com/jruby/jruby/blob/9.1.10.0/core/src/main/java/org/jruby/RubyKernel.java#L1974-L1977 ).