Rails 3 to_json incompatible with JSON core library

It appears that Rails 3 changes the signature of to_json vs the JSON core lib. Unfortunately, this breaks ActiveRecord and other components when trying to use them outside of Rails. I've hit this with Sinatra, Sequel, and a couple other toolsets that rely on the core JSON library.

Here's one example backtrace from Sinatra:

ArgumentError: wrong number of arguments (2 for 1)
/Users/nwiger/Workspace/server/app/routes/message_routes.rb:6:in `to_json'
/Users/nwiger/Workspace/server/app/routes/message_routes.rb:6:in `block in <class:Main>'
/Users/nwiger/.rvm/gems/ruby-1.9.2-head/gems/sinatra-1.0/lib/sinatra/base.rb:865:in `call'
/Users/nwiger/.rvm/gems/ruby-1.9.2-head/gems/sinatra-1.0/lib/sinatra/base.rb:865:in `block in route'

The code that generated that was (AR3):

class Message < ActiveRecord::Base
  scope :unread, where(:is_read => false)

  def self.find_and_read_for(user_id)
    m = where(:user_id => user_id).unread.all
    update_all({:is_read => true}, ['id IN (?)', m]) unless m.empty?
    m
  end
end

Then in Sinatra:

# Return unread messages and mark read
get '/messages/read.json' do
  @messages = Message.find_and_read_for(current_user_id)
  @messages.to_json
end

The problem is that the JSON gem supports a *splat as its arg signature, whereas Rails 3 does not:

http://github.com/rails/rails/blob/master/activesupport/lib/active_...

It seems a simple patch to change that signature to this:

def to_json(*options)
  ActiveSupport::JSON.encode(self, options)
end

Would solve the issue.

I'm not sure why AR2 is not affected in the same way, since it appears to override to_json similarly, but I have seen this with a couple test apps now, and only with AR3.

Thanks,
Nate