Issue #9311 has been updated by Aman Gupta.


> This causes singleton_class? to no longer show in the Module.methods list (I suspect because of the new method cache invalidation stuff?):

This has nothing to do with method cache, but is instead caused by ActiveSupport marking :singleton_class? as private.

    >> Module.methods.include?(:singleton_class?)
    => true
    
    >> class Class; def singleton_class?() super end; end
    >> Module.methods.include?(:singleton_class?)
    => true
    
    >> class Class; private :singleton_class?; end
    >> Module.methods.include?(:singleton_class?)
    => false


----------------------------------------
Bug #9311: module_function breaks on `singleton_class?`
https://bugs.ruby-lang.org/issues/9311#change-44375

* Author: Chris Heald
* Status: Rejected
* Priority: Normal
* Assignee: 
* Category: 
* Target version: 
* ruby -v: -
* Backport: 
----------------------------------------
=begin
When trying to use Sass 3.3.0-rc2 with Rails 3.x, an error similar to the one below is produced:

    [6] pry(Sass::Util)> Sass::Util.methods.grep /singleton_class/
    => [:singleton_class?, :singleton_class]
    [7] pry(Sass::Util)> Sass::Util.method_function :singleton_class?
    NoMethodError: undefined method `method_function' for Sass::Util:Module
    from (pry):6:in `<module:Util>'

This is actually pretty trivially reproduced via:

    2.1.0 :001 > module Foo
    2.1.0 :002?>   methods.grep(/singleton/).each {|x| module_function x }
    2.1.0 :003?>   end
    NameError: undefined method `singleton_class?' for module `Foo'
            from (irb):2:in `module_function'
            from (irb):2:in `block in <module:Foo>'
            from (irb):2:in `each'
            from (irb):2:in `<module:Foo>'
            from (irb):1
            from /usr/local/rvm/rubies/ruby-2.1.0/bin/irb:11:in `<main>'

Now, Sass performs the following:

    (Sass::Util.methods - Module.methods).each {|method| module_function method }

This succeeds if you don't include ActiveSupport, but ActiveSupport extends Class with the following:

    class Class
      private
      def singleton_class?
        ancestors.first != self
      end
    end

This causes `singleton_class?` to no longer show in the `Module.methods` list (I suspect because of the new method cache invalidation stuff?):

    2.1.0 :001 > Module.methods.sort
     => [... :singleton_class, :singleton_class?, :singleton_method, :singleton_methods, :superclass, ...]
    2.1.0 :002 > class Class
    2.1.0 :003?>         private
    2.1.0 :004?>         def singleton_class?
    2.1.0 :005?>             ancestors.first != self
    2.1.0 :006?>           end
    2.1.0 :007?>       end
     => :singleton_class?
    2.1.0 :008 > Module.methods.sort
     => [... :singleton_class, :singleton_method, :singleton_methods, :superclass, ...]
     
Since it's no longer in the Module.methods list, Sass attempts to `module_function` it and the whole thing blows up.

This is fixable in both Sass and ActiveSupport (which I'll file tickets for), but it feels like this is a Ruby bug. Doing something similar in 2.0 (which doesn't have `singleton_class?`) results in the following:

    2.0.0p247 :001 > class Class
    2.0.0p247 :002?>   private
    2.0.0p247 :003?>   def singleton_class
    2.0.0p247 :004?>     false
    2.0.0p247 :005?>     end
    2.0.0p247 :006?>   end
     => nil
    2.0.0p247 :007 > module Foo
    2.0.0p247 :008?>   module_function :singleton_class
    2.0.0p247 :009?>   end
     => Foo
    2.0.0p247 :010 > Foo.singleton_class
     => #<Class:Foo>

Which seems to work just fine.
=end


---Files--------------------------------
bug9311-test.diff (568 Bytes)


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