jruby環境でgem install ruby-debug-baseとすると下記のようなエラーが出てくると思います。 Building native extensions. This could take a while... WARNING: JRuby does not support native extensions or the `mkmf' library. Check wiki.jruby.org for alternatives. extconf.rb:16: undefined method `create_makefile' for main:Object (NoMethodError) ERROR: Error installing ruby-debug-base: ERROR: Failed to build gem native extension. "C:/P