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`Exception#cause` is difference behavior with CRuby 2.3.0 #3654

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hsbt opened this issue Feb 9, 2016 · 4 comments
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`Exception#cause` is difference behavior with CRuby 2.3.0 #3654

hsbt opened this issue Feb 9, 2016 · 4 comments

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@hsbt
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@hsbt hsbt commented Feb 9, 2016

I found difference behavior of Exception#cause with CRuby 2.3.0. I invoke following codes. There are part of Rake test code.

begin
  raise 'cause a'
rescue
  begin
    raise 'cause b'
  rescue => ex
    p [ex, ex.cause]
  end
end

begin
  begin
    raise 'cause a'
  rescue => a
    begin
      raise 'cause b'
    rescue
      raise a
    end
  end
rescue => ex
  p [ex, ex.cause]
end

I got following results.

% ruby -v cause.rb
jruby 9.0.5.0 (2.2.3) 2016-01-26 7bee00d Java HotSpot(TM) 64-Bit Server VM 25.72-b15 on 1.8.0_72-b15 +jit [darwin-x86_64]
[#<RuntimeError: cause b>, #<RuntimeError: cause a>]
[#<RuntimeError: cause a>, nil]

% ruby -v cause.rb
ruby 2.3.0p5 (2016-01-15 revision 53536) [x86_64-darwin15]
[#<RuntimeError: cause b>, #<RuntimeError: cause a>]
[#<RuntimeError: cause a>, #<RuntimeError: cause b>]

Is JRuby results intentional behavior? If it's yes, I will fix rake tests.

@enebo enebo added this to the JRuby 9.1.0.0 milestone Feb 9, 2016
@enebo enebo added the ir label Feb 9, 2016
@enebo
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@enebo enebo commented Feb 9, 2016

@hsbt I would say we are just doing the wrong thing here. We will fix it.

@headius
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@headius headius commented Feb 13, 2016

I'm not sure this is correct behavior in MRI, and I'll explain why.

In the differing case, a is not caused by b. They appear to be setting cause every time the exception is raised, which I'd consider a bug...since it would lose the original cause. An example of where this is broken:

begin
  begin
    raise 'a'
  rescue => a
    begin
      raise 'b'
    rescue => b
      p [b, b.cause]
      begin
        raise 'c'
      rescue
        raise b
      end
    end
  end
rescue
  p [$!, $!.cause]
end

And the output in JRuby 9.0.5.0 and MRI 2.3.0:

[] ~/projects/jruby $ rvm jruby-9.0.5.0 do ruby cause.rb
[#<RuntimeError: b>, #<RuntimeError: a>]
[#<RuntimeError: b>, #<RuntimeError: a>]

[] ~/projects/jruby $ ruby23 cause.rb
[#<RuntimeError: b>, #<RuntimeError: a>]
[#<RuntimeError: b>, #<RuntimeError: c>]

MRI is losing the original cause of the exception, without it being physically replaced.

I'm going to report this as a bug.

Interestingly, JRuby 9.1 (ruby-2.3 branch) appears to work like Ruby 2.3, so somewhere along the way we "fixed" this:

[] ~/projects/jruby $ jruby -v cause.rb
jruby 9.1.0.0-SNAPSHOT (2.3.0) 2016-02-13 8136dd9 Java HotSpot(TM) 64-Bit Server VM 25.60-b23 on 1.8.0_60-b27 +jit [darwin-x86_64]
[#<RuntimeError: b>, #<RuntimeError: a>]
[#<RuntimeError: b>, #<RuntimeError: c>]
@headius
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@headius headius commented Feb 13, 2016

Filed https://bugs.ruby-lang.org/issues/12068

If they disagree (and I will argue the point) then I guess we've already fixed this. If they agree, we'll need to reinstate 9.0.5.0's behavior.

@headius
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@headius headius commented Feb 14, 2016

They agreed, so we need to fix 9.1 to work like 9.0 did.

headius added a commit that referenced this issue Feb 14, 2016
@headius headius closed this Feb 14, 2016
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