@jesperronn does it make the same recommendation when run from MRI? I guess I would try against both and see if different stuff is recommended. I think that conversion will work (and is an icky suggestion IMHO -- ! with &. is super confusing to me) . I tried this and both JRuby and MRI works:

[" ", "d"].each do |s|
  ENV["LAWS"] = s

  ret = if ENV["LAWS"] && !ENV["LAWS"].match(/\A\s*\z/)
          puts "old true"
        end
  p ret

  ret = if !ENV["LAWS"]&.match(/\A\s*\z/)
          puts "new true"
        end
  p ret
end

Hello 👋 @jesperronn - 2.3 is the right pick for jruby-9.1.13.0.

I made this table of JRuby versions and their Ruby versions. @enebo, does such a table exist anywhere in the documentation?

No there is not. I was going to say I don't see the point in marking which MRI point release is which but upon reflection that might be useful for people.

Thanks @enebo and @olleolleolle for your help and support 👍. Yes, I got the same recommendation when running mri, and that actually triggered my question.

@olleolleolle thanks for sharing the compatibility table. Really helpful, also when updating.

A final thought could be to add in a future version, help for rubocop so that you would actually trigger s specific TargetRubyVersion based on the compatibility table.

That way, you could write (in .rubocop.yml):

TargetRubyVersion: jruby-9.1 

and it could (behind the scenes) translate it into mri 2.3

(I know this is not a feature request for this project, so closing the thread here :)