Error around the Enumerable::Enumerator class

[glarizza]

This may just be an error in my implementation, but I thought I'd paste it here to start the conversation.

I'm trying to require the CFPropertyList gem inside a provider that I'm using for Puppet. To do a 'safety check' for this, I created a Puppet 'feature' that will basically try to load the library and safely error-out if the lib isn't found.

The feature looks like so:

require 'puppet/util/feature'
Puppet.features.add(:cfpropertylist, :libs => ['CFPropertyList'])

In my provider code, I require the feature with:

confine :feature => :cfpropertylist

Cool, so when I try to run Puppet it complains about the feature not being available because the CFPropertyList library failed to load. Yikes. Okay, so I commented all the feature code out and just tried to require CFPropertyList at the top of my provider to see if I could expose more debugging messages. This bubbles up this stacktrace:

Notice: Compiled catalog for satori.local in environment production in 0.02 seconds
Error: Could not autoload puppet/feature/cfpropertylist: wrong number of arguments(1 for 0)
/Users/glarizza/src/puppet-property_list_key/vendor/ruby/1.9.1/gems/CFPropertyList-2.2.4/lib/rbCFPropertyList.rb:91:in `initialize'
/Users/glarizza/src/puppet-property_list_key/vendor/ruby/1.9.1/gems/CFPropertyList-2.2.4/lib/rbCFPropertyList.rb:91:in `new'
/Users/glarizza/src/puppet-property_list_key/vendor/ruby/1.9.1/gems/CFPropertyList-2.2.4/lib/rbCFPropertyList.rb:91:in `<top (required)>'
/Users/glarizza/src/puppet-property_list_key/vendor/ruby/1.9.1/gems/CFPropertyList-2.2.4/lib/CFPropertyList.rb:3:in `require'
/Users/glarizza/src/puppet-property_list_key/vendor/ruby/1.9.1/gems/CFPropertyList-2.2.4/lib/CFPropertyList.rb:3:in `<top (required)>'
/Users/glarizza/src/puppet-property_list_key/lib/puppet/feature/cfpropertylist.rb:2:in `require'
/Users/glarizza/src/puppet-property_list_key/lib/puppet/feature/cfpropertylist.rb:2:in `<top (required)>'

That's pointing back to the Enumerator::Enumerable hack that you used for the 1.8/1.9 codebase differences. So I jumped into IRB:

rirb(main):001:0> require 'puppet'
re=> true
irb(main):002:0> require 'CFPropertyList'
=> true
irb(main):015:0* begin
irb(main):016:1*   Enumerable::Enumerator.new([])
irb(main):017:1> rescue NameError => e
irb(main):018:1>   module Enumerable
irb(main):019:2>     class Enumerator
irb(main):020:3>     end
irb(main):021:2>   end
irb(main):022:1> end
ArgumentError: wrong number of arguments(1 for 0)
        from (irb):16:in `initialize'
        from (irb):16:in `new'
        from (irb):16
        from /opt/boxen/rbenv/versions/1.9.3-p392/bin/irb:12:in `<main>'

I then tried a brief hack that we'd talked about awhile back:

rirb(main):001:0> require 'puppet'
re=> true
irb(main):002:0> require 'CFPropertyList'
=> true
irb(main):003:0> begin
irb(main):004:1*   Enumerable::Enumerator.new([])
irb(main):005:1> rescue NameError => e
irb(main):006:1>   module Enumerable
irb(main):007:2>     class Enumerator
irb(main):008:3>       def initialize(*args)
irb(main):009:4>       end
irb(main):010:3>     end
irb(main):011:2>   end
irb(main):012:1> end
ArgumentError: wrong number of arguments(1 for 0)
        from (irb):4:in `initialize'
        from (irb):4:in `new'
        from (irb):4
        from /opt/boxen/rbenv/versions/1.9.3-p392/bin/irb:12:in `<main>'
irb(main):013:0>

I'm kinda stumped at the moment - it requires just fine in IRB but when I try to require the library inside the Puppet codebase I'm getting errors. I'm guessing maybe Puppet is doing some work with the Enumerable::Enumerator class, so I really need to track that down. Do you have any suggestions?

[dayglojesus]

Works in 1.8.7, rvm and OS X native MRI.

[dayglojesus]

Ooh, does not fly with Ruby 2.0! It's a bug.

[dayglojesus]

leela:~ itsvan$ irb -r cfpropertylist irb(main):001:0> begin irb(main):002:1* Enumerable::Enumerator.new([]) irb(main):003:1> rescue NameError => e irb(main):004:1> module Enumerable irb(main):005:2> class Enumerator irb(main):006:3> end irb(main):007:2> end irb(main):008:1> end ArgumentError: wrong number of arguments (1 for 0) from (irb):2:in initialize' from (irb):2:innew' from (irb):2 from /usr/bin/irb:12:in `

' irb(main):009:0>

[dayglojesus]

I think behaviour needs to be coerced based on Ruby version. In 1.9 and above, Enumerator.new wants a block…

begin
    Enumerable::Enumerator.new { [] }
rescue NameError => e
    module Enumerable
        class Enumerator
        end
    end
end

[dayglojesus]

The more I look at this block of code, the less I understand its purpose. Is it just scar tissue?

[glarizza]

@ckruse and I talked about this over email awhile back. In Ruby 1.8, Enumerator is covered in the Enumerable module while in 1.9 the class moved to the global namespace. To avoid problems, he creates the class if it doesn't exist so he can do:

when Array, Enumerator, Enumerable::Enumerator

The issue is with the default constructor that accepts no arguments

[dayglojesus]

I see, thanks.

[ckruse]

Hm, maybe we should change the check to

begin
  Enumerable::Enumerator.class
rescue NameError => e
  module Enumerable
    class Enumerator
    end
  end
end

This avoids the problem of different constructors. What do you guys think?

[dayglojesus]

There are may ways to quack a duck.

[ckruse]

I'm sorry, I don't understand?

I summarize what happend: I need to create Enumerable::Enumerator for backward compatibility if it doesn't exist. Therefore I check for existance by creating a new object. If it doesn't, it throws a NameError and I can rescue that. But since 2.0 it seems as if the constructor has changed. Therefore avoiding object creation and calling a method on the class object itself seems to be much more stable to me.

Am I missing something?

[dayglojesus]

Sorry, Christian, that was my awkward attempt at humor -- duck typing? ;)

What you propose will work, but if you simply want to discover if the class is defined all you need is:

begin
  Enumerable::Enumerator
rescue NameError
  module Enumerable
    class Enumerator
    end
  end
end

Perhaps more succinctly, simply:

module Enumerable
  class Enumerator
  end
end

Because it either exists or it doesn't. If it already exists, the code you see above does nothing to impact operation of the class. If it doesn't exist, the class will be defined.

[ckruse]

Good point! I didn't think anything of it.