$ bin/jruby -Sgem install yard
$ bin/jruby lib/ruby/gems/shared/gems/yard-0.8.7.6/bin/yardoc --markup markdown --exclude truffle/src/main/ruby/core/truffle/cext/require\.rb --no-save --readme truffle/README.md truffle/src/main/ruby/core/truffle
[warn]: In file `truffle/src/main/ruby/core/truffle/debug.rb':12: Cannot resolve link to #break from text:
[warn]: ...{#break}...
Unhandled Java exception: IRReturnJump:<Static Type[864852424]: local [text=Truffle::Debug.break]:true>