Implement Fiber#raise

[eregon]

It's part of the new 2.7 methods: #2004
And it's used notably by socketry/io-event#2
cc @ioquatix

[ioquatix]

Thanks, and also allow Fiber#transfer and Fiber#resume/yield interleaved.

[eregon]

The change for Fiber#transfer allowed in more cases is only in Ruby 3.0+ though, right?

[ioquatix]

The change for Fiber#transfer allowed in more cases is only in Ruby 3.0+ though, right?

It is purely additive, it won't break Ruby 2.x

[eregon]

Looking at Fiber specs, it seems there would be specs that break if we change the behavior of Fiber#transfer while reporting RUBY_VERSION as 2.7:
https://github.com/oracle/truffleruby/blob/master/spec/ruby/library/fiber/transfer_spec.rb
https://github.com/oracle/truffleruby/blob/master/spec/ruby/library/fiber/resume_spec.rb

Is it needed by https://github.com/socketry/event ?

[ioquatix]

The event library needs the following:

• Fiber#raise (for cancellation)
• Fiber#transfer (for non-blocking operation)

For new version of async (currently unreleased prototype) which depends on event, Fiber#resume and Fiber#yield is not used. It's purely for user code. Depending on how you implemented lazy enumerator, this may be a problem. From user point of view, semantics remain unchanged.

[eregon]

Fiber#raise was implemented in 52f7d8b by @bjfish.
If we need to allow more cases for transfer to pass tests/specs of event or async, could you create a separate issue?

[eregon]

Looks like the event specs need Fiber#raise to be allowed after Fiber#transfer: socketry/io-event#5 (comment)
That's a change of Ruby 3 as well: https://github.com/ruby/ruby/pull/3795/files#diff-f5e06781d15d3a6c16eef4cb49eebc310820bead3672ed84608c84958ae5da14R2341-R2343
=> #2342

[ioquatix]

Yes, Fiber#raise must do the right thing in order to transfer back to the fiber.