Errors with _id2ref when using frozen_string_literal magic comment?

[hainesr]

I have no idea what or where this bug really is, but as the behaviour I'm seeing is only in TruffleRuby I thought I'd submit here to see if you folks have any thoughts.

I am doing some work on rubyzip and I finally got around to adding the frozen_string_literal: true magic comment throughout the library. Now this is in place my CI is failing on TruffleRuby in GitHub Actions. This is the only change that has been made between a passing CI and failing CI:

• Passing: commit - CI
• Failing: commit - CI

Actions is using TruffleRuby version 21.1.0 and TruffleRuby-head, which are both failing. I have version 20.3.0 on my local machine and all works fine!

The error is as follows:

ZipFsFileNonmutatingTest#test_dirname:
RangeError: 0x0000000000000100 is not id value
    /home/runner/work/rubyzip/rubyzip/test/test_helper.rb:192:in `_id2ref'
    /home/runner/work/rubyzip/rubyzip/test/test_helper.rb:192:in `dirname'
    /home/runner/work/rubyzip/rubyzip/lib/zip/filesystem.rb:303:in `dirname'
    /home/runner/work/rubyzip/rubyzip/test/filesystem/file_nonmutating_test.rb:132:in `block in test_dirname'
    /home/runner/work/rubyzip/rubyzip/test/test_helper.rb:196:in `assert_forwarded'
    /home/runner/work/rubyzip/rubyzip/test/filesystem/file_nonmutating_test.rb:131:in `test_dirname'

Which is caused by a test that makes heavy use of meta-programming, unfortunately:

def test_dirname
  assert_forwarded(File, :dirname, 'ret_val', 'a/b/c/d') do
    @zip_file.file.dirname('a/b/c/d')
  end
end

assert_forwarded is where _id2ref is called and is defined here:

def assert_forwarded(object, method, ret_val, *expected_args)
  call_args = nil
  call_args_proc = proc { |args| call_args = args }
  object.instance_eval <<-END_EVAL, __FILE__, __LINE__ + 1
    alias #{method}_org #{method}
    def #{method}(*args)
      ObjectSpace._id2ref(#{call_args_proc.object_id}).call(args)
      ObjectSpace._id2ref(#{ret_val.object_id})
      end
  END_EVAL

  assert_equal(ret_val, yield) # Invoke test
  assert_equal(expected_args, call_args)
ensure
  object.instance_eval <<-END_EVAL, __FILE__, __LINE__ + 1
    undef #{method}
    alias #{method} #{method}_org
  END_EVAL
end

Any thoughts gratefully received! Many thanks.

[eregon]

Thank you for the detailed report!

The RangeError: 0x0000000000000100 is not id value means the object was not found.
I guess what's happening here is a side effect of using frozen_string_literal: true, which means some Strings now are the interned frozen literal strings (instead of regular mutable Strings), and those don't seem to be handled in ObjectSpace._id2ref yet (a bug).

[eregon]

A fix for existing TruffleRuby versions would be to avoid using ObjectSpace._id2ref (which is not recommended API anyway).
I think one here would be to use define_method with a block, and then there would be no need for object_id + _id2ref, the code could simply refer to variables captured by the block.

[hainesr]

Many thanks for your quick response!

I'm certainly not wedded to that code as it is - I'd be more than happy to refactor it once I am certain that I fully understand it (it's not mine originally, you see) 😄

Thanks!

[chrisseaton]

I think you'll find your _id2ref code possibly won't work on JRuby either.

irb(main):001:0> RUBY_DESCRIPTION
=> "jruby 9.2.17.0 (2.5.8) 2021-03-29 84d363da97 OpenJDK 64-Bit Server VM 16+36-2231 on 16+36-2231 +jit [darwin-x86_64]"
irb(main):002:0> string = 'foo'
=> "foo"
irb(main):003:0> ObjectSpace._id2ref(string.object_id)
(irb):3: warning: ObjectSpace is disabled; _id2ref only supports immediates, pass -X+O to enable
Traceback (most recent call last):
        7: from /Users/chrisseaton/.rubies/jruby-9.2.17.0/bin/irb:13:in `<main>'
        6: from org/jruby/RubyKernel.java:1189:in `catch'
        5: from org/jruby/RubyKernel.java:1189:in `catch'
        4: from org/jruby/RubyKernel.java:1442:in `loop'
        3: from org/jruby/RubyKernel.java:1048:in `eval'
        2: from (irb):3:in `evaluate'
        1: from org/jruby/RubyObjectSpace.java:113:in `_id2ref'
RangeError (0x00000000000007d2 is not id value)

[hainesr]

It does work with JRuby but we have to turn ObjectSpace on for the tests, which I know is not ideal. I'd be very happy to rid myself of that bit of code! I'll stare at it a bit tonight and see if I can figure out what it's doing...

[chrisseaton]

I can see what it's doing and why - it's hard to pass in a reference to an object to an eval string. If I have object foo, and I want to eval('foo.bar'), how do I pass foo in? That's what they're doing - eval('_id2ref(#{foo.object_id})'. You can fix this by passing the binding to eval, which then lets it directly reference foo, and using define_method rather than def so again it can capture foo from that binding.

[eregon]

Actually neither eval nor _id2ref are needed: rubyzip/rubyzip#483

[hainesr]

Thank you both @eregon, @chrisseaton for your attention and help with this!

[eregon]

Just to clarify, the _id2ref bug is fixed in beb45b8 (the issue was automatically closed by the commit fixing it).