Make CanCan 1.6 + arel 2.0 work with multiple scopes

gistfile1.rb

require "cancan/model_adapters/active_record_adapter"

class CanCan::ModelAdapters::ActiveRecordAdapter

  # disable the error when multiple conditions with scopes are used
  def override_scope
    return false
  end
  
  # convert where-clauses from relations into sql strings which will be merged by the cancan  merge_conditions logic 
  def tableized_conditions_with_relations(*args)
    if args.first.kind_of?(ActiveRecord::Relation)
      base_class = @model_class.unscoped
      arel = args.first.arel
      
      arel.where_clauses.join(" AND ")
    else
      tableized_conditions_without_relations(*args)
    end
  end
  alias_method_chain :tableized_conditions, :relations unless method_defined? :tableized_conditions_without_relations
  
  
  # convert join-clauses from relations into sql strings which will be merged by the cancan merge_joins logic
  def joins_with_relations
    arr = joins_without_relations || []
    arr.concat(@rules.map(&:conditions).select{|c| c.kind_of?(ActiveRecord::Relation)}.map do |rel|
      arel = rel.arel
      arel.ast.cores.each{|c| convert_join(c)}
      arel.join_sql
    end)
    
    arr.delete_if{|e| e.blank?}
    arr = nil if arr.empty?

    arr 
  end
  alias_method_chain :joins, :relations unless method_defined? :joins_without_relations



  private

  # helper that traverses a arel AST to turn inner into outer joins
  def convert_join(ast)
    ast.froms = convert_join(ast.froms) if ast.is_a? Arel::Nodes::SelectCore
    
    if ast.is_a? Arel::Nodes::Join
      ast.left = convert_join(ast.left)
      ast.right = convert_join(ast.right)
    end
    
    return Arel::Nodes::OuterJoin.new(ast.left,ast.right,ast.constraint) if ast.is_a? Arel::Nodes::InnerJoin 
    
    ast
  end
  
end