gistfile1.txt

$ ./perl6-j -e'class C {...}; C.^add_attribute(Attribute, Attribute.new(:name<a>, :type(Any), :package(C))); class C { }'
org.perl6.nqp.sixmodel.reprs.P6OpaqueBaseInstance$NoSuchAttrException: No such attribute '$!name' for this object
<Internal error while creating backtrace: org.perl6.nqp.sixmodel.reprs.P6OpaqueBaseInstance$NoSuchAttrException: No such attribute '$!name' for this object   in block  at gen/jvm/CORE.setting:1299
  in method sink-all at gen/jvm/CORE.setting:2968
  in method sink at gen/jvm/CORE.setting:10694
  in method clone at gen/jvm/CORE.setting:1298
  in block  at gen/jvm/CORE.setting:17357
  in block  at gen/jvm/CORE.setting:17351
  in block  at gen/jvm/CORE.setting:17345
  in method nice at gen/jvm/CORE.setting:17342
  in method Str at gen/jvm/CORE.setting:17375
  in method Stringy at gen/jvm/CORE.setting:1181
  in sub infix:<~> at gen/jvm/CORE.setting:1621
  in block  at gen/jvm/CORE.setting:26993
  in code  at gen/jvm/CORE.setting:17474
  in block  at gen/jvm/CORE.setting:17474
  in method gist at gen/jvm/CORE.setting:17468
  in block  at gen/jvm/CORE.setting:17713
  in sub print_exception at gen/jvm/CORE.setting:17706
.
Please report this as a bug (mail to rakudobug@perl.org)
 and re-run with the --ll-exception command line option
to get more information about your error>