while using activerecord-sqlserver-adapter 3.1.5 with Rails 3.1 with …

…Arel 2.2.1 we encountered the error

  uninitialized constant Arel::Nodes::Visitors::DepthFirst
apparently Arel was trying to call a relative namespace with
  Visitors::DepthFirst.new(block).accept self
we fixed this by making it call an absolute namespace with
  ::Arel::Visitors::DepthFirst.new(block).accept self

lib/arel/nodes/node.rb

@@ -39,7 +39,7 @@ def to_sql engine = Table.engine
       def each &block
         return enum_for(:each) unless block_given?
 
-        Visitors::DepthFirst.new(block).accept self
+        ::Arel::Visitors::DepthFirst.new(block).accept self
       end
     end
   end