The fork of msgpack-rpc-ruby that the rb_call uses, namely https://github.com/yohm/msgpack-rpc-ruby, does not have its issues configured. Therefore there is no place to submit bug reports.
$ bundle install
Fetching https://github.com/yohm/msgpack-rpc-ruby.git
Resolving dependencies...
Fetching gem metadata from https://rubygems.org/..
Fetching cool.io 1.4.6
Fetching msgpack 1.0.3
Installing msgpack 1.0.3 with native extensions
Installing cool.io 1.4.6 with native extensions
Gem::Ext::BuildError: ERROR: Failed to build gem native extension.
[....]
In file included from cool.io_ext.c:11:
cool.io.h:11:10: fatal error: rubyio.h: No such file or directory
11 | #include "rubyio.h"
| ^~~~~~~~~~
compilation terminated.
make: *** [Makefile:246: cool.io_ext.o] Error 1
[...]
An error occurred while installing cool.io (1.4.6), and Bundler cannot continue.
In Gemfile:
msgpack-rpc was resolved to 0.5.4, which depends on
cool.io
The fork of msgpack-rpc-ruby that the rb_call uses, namely https://github.com/yohm/msgpack-rpc-ruby, does not have its issues configured. Therefore there is no place to submit bug reports.