Nice! We definitely want to get Fiddle working better. Long term it might make more sense to do a direct implementation atop jnr-ffi, but for now getting the FFI version working is probably best.

I splited two obvious errors into separate PRs
jruby/ruby#2 jruby/ruby#3

one more interesting failure

a string pointer #to_s should return a ruby string. That would be tricky to implement :)

Do you think there's any work remaining here or could we go ahead with a merge?

I have merged jruby/ruby#2 and jruby/ruby#3 across the two active branches jruby-ruby_2_5_7 and jruby-ruby_2_6_5 and incorporated their changes into the JRuby branches master and ruby-2.6.

I also figured out why the libc changes keeps disappearing: we were versioning lib/ruby/stdlib/fiddle/jruby.rb in both places when it's specific to JRuby, without any equivalent in CRuby, and subject to frequent updates. I modified all branches to reflect this, with messages about the proper versioning location added to jruby here and here.

(I see the spelling error now and will fix that).

I've also made sure that all changes from jruby/ruby's jruby-ruby_2_5_7 and jruby/jruby's master branch have been incorporated back into the jruby/ruby jruby-ruby_2_6_5 branch upon which the jruby/jruby ruby-2.6 branch is based. See jruby/ruby@afa0b25.

We need a better way to manage our patch set against CRuby's stdlib.

Do you think there's any work remaining here or could we go ahead with a merge?

there're still many broken parts, but I think it's ready for review

Everything here seems appropriate to me. I will merge and we can do other fixes in other PRs.