Truffleruby: Exception#cause behaves differently under MRI

[deepj]

This issue is reported in JRuby https://github.com/jruby/jruby/issues/4239 reported by @nateberkopec

To reproduce (TruffleRuby 1.0.0 RC 11):

def build_exception_with_cause
  begin
    1 / 0
  rescue ZeroDivisionError
    1 / 0
  end
rescue ZeroDivisionError => exception
  return exception
end

exc = build_exception_with_cause
exc.cause

exc.cause would return #<ZeroDivisionError: divided by 0> not nil in case of TruffleRuby.

[eregon]

Thank you for the report.
I can reproduce the bug on master.

[eregon]

A slightly clearer reproducer:

def build_exception_with_cause
  begin
    raise "first"
  rescue
    1 / 0
  end
rescue ZeroDivisionError => exception
  return exception
end

exc = build_exception_with_cause
p exc.cause

i.e., ZeroDivisionError doesn't capture the cause.
Swapping them works, i.e., exceptions from raise capture the cause.

[deepj]

This causes an issue in Sidekiq on this place https://github.com/mperham/sidekiq/blob/master/lib/sidekiq/processor.rb#L176

Due to this, plenty tests fail.

[deepj]

@eregon @chrisseaton when this issue is quick to fix, please try to fix it to RC13. This fixes almost or all failed tests in Sidekiq. Sidekiq depends heavily on this behaviour.

[eregon]

I'll take a look at this.

[eregon]

Fixed by ee80ecd1002495f06b6da6855221919fab9611bc.
@deepj Thanks for the report, I took the occasion to fix a couple more Exception#cause-related bugs.