There's a (minor) Java integration regression since 9.4.7.0 caused by 31f1ed6 (fix for #8156)

Environment Information

• JRuby version 9.4.8.0

Consider the sample script trying to utilize the "duck-typing" Java auto-interface impl feature:

class Run1
  class << self
    def run; puts self end
  end
end

class Run2 < Run1; end
class Run3 < Run1; end

#java.lang.Thread.new(Run1).start
java.lang.Thread.new(Run2).start
java.lang.Thread.new(Run3).start

The script will print a Ruby constant initialization warning (will get printed the amount of times there are sub-classes since the impl proxy will be cached once per RubyClass):

impl_repro.rb:12: warning: already initialized constant org.jruby.gen::InterfaceImpl1353309827

The internal (interface implementation) proxy class ends up being stored in Ruby land, this did not happen previously.

p.s. There might be other Java proxy path worth checking, whether they end up eagerly setting their class proxy wrappers in Ruby land, effectively preventing garbage collection of such classes...