byebug: `rb_tr_error': rb_tracepoint_new not implemented

[deepj]

Hello,
I'm getting with truffleruby 1.0.0-rc8 on macOS 10.14 the following issue when I'm trying to use byebug (10.0.2). Since byebug is a recommended tool for debugging in Rails =>
https://guides.rubyonrails.org/debugging_rails_applications.html#debugging-with-the-byebug-gem

It'd be worth to take a look at Tracepoint API support in C gems by Truffleruby.

How to reproduce it:

require 'byebug'

byebug

puts 'Hello byebug'

The error:

/Users/graal/slave/e/truffleruby/src/main/c/cext/ruby.c:in `rb_tr_error': rb_tracepoint_new not implemented (RuntimeError)
	from /Users/graal/slave/e/truffleruby/src/main/c/cext/ruby.c:in `rb_tracepoint_new'
	from ~/.gem/truffleruby/2.4.4/gems/byebug-10.0.2/ext/byebug/byebug.c:501:in `register_tracepoints'
	from ~/.gem/truffleruby/2.4.4/gems/byebug-10.0.2/ext/byebug/byebug.c:711:in `Start'
	from ~/.rubies/truffleruby-1.0.0-rc8/lib/truffle/truffle/cext.rb:221:in `execute_without_conversion'
	from ~/.rubies/truffleruby-1.0.0-rc8/lib/truffle/truffle/cext.rb:221:in `execute_with_mutex'
	from ~/.rubies/truffleruby-1.0.0-rc8/lib/truffle/truffle/cext_ruby.rb:36:in `start'
	from ~/.gem/truffleruby/2.4.4/gems/byebug-10.0.2/lib/byebug/attacher.rb:16:in `attach'
	from ~/.gem/truffleruby/2.4.4/gems/byebug-10.0.2/lib/byebug/attacher.rb:38:in `byebug'

[chrisseaton]

We do support trace points from Ruby, even in optimised code, so we should be able to provide this from C as well. Thanks for the issue.

[deepj]

@chrisseaton I guess it would be interesting to have working byebug since it's a recommended tool for debugging in Rails. But there is a question how it will work under Truffleruby. But I have some doubts when I look at https://github.com/deivid-rodriguez/byebug/tree/master/ext/byebug

[eregon]

As reported in #1528 by @deepj, this also happens for the web-console gem (one of default Rails dependencies):

web-console uses the bindex gem (accessing exception bindings) which uses rb_tracepoint_new. The gem doesn't support TruffleRuby itself but it's easy to add the support.

[deepj]

@chrisseaton @eregon I've noticed of your last work on TracePoint support. If it's not too much work, is it possible to provide some support TracePoint API to C extensions?

[chrisseaton]

In order to support byebug? Do you mean code like this? https://github.com/deivid-rodriguez/byebug/blob/af25ece0b5a43fd857d19a45206653d0c402cd10/ext/byebug/byebug.c#L78

[deepj]

@chrisseaton yes, I'd like to see byebug to work and to try on TruffleRuby

[chrisseaton]

Ok I'll mark this as priority as well, but I don't think it's as easily achievable as the others. We should try to fix this set now and then ask for more if we have time. Let us know if you want to swap one priority issue out for another.

[chrisseaton]

Sorry I'm going to have to de-priortise this. I've taken a look and it's not realistic to get it done soon. It uses a ton of C APIs that we don't have yet, and the underlying TracePoint implementation also is not totally complete.

TruffleRuby includes it's own Chrome-based debugger, and we'd recommend that for now.