Allow making operations on sifters and having them in a group

lib/squeel/dsl.rb

@@ -86,7 +86,7 @@ def _(expr)
     # @param [Symbol, Nodes::Stub] name The name of the sifter defined in the model.
     # @return [Nodes::Sifter] The sifter node
     def sift(name, *args)
-      Nodes::Sifter.new name.to_sym, args
+      Nodes::Grouping.new(Nodes::Sifter.new(name.to_sym, args))
     end
 
     # Node generation inside DSL blocks.

lib/squeel/nodes/key_path.rb

@@ -125,7 +125,7 @@ def op(operator, other)
       def sift(name, *args)
         if Stub === endpoint || Join === endpoint
           @path << Sifter.new(name, args)
-          self
+          Grouping.new(self)
         else
           no_method_error :sift
         end

lib/squeel/nodes/stub.rb

@@ -108,7 +108,7 @@ def inner
       # Create a keypath with a sifter as its endpoint
       # @return [KeyPath] The new KeyPath
       def sift(name, *args)
-        KeyPath.new([self, Sifter.new(name, args)])
+        Grouping.new(KeyPath.new([self, Sifter.new(name, args)]))
       end
 
       # Create an outer Join node for the association named by this Stub

lib/squeel/visitors/visitor.rb

@@ -362,6 +362,10 @@ def visit_Squeel_Nodes_Operation(o, parent)
         op
       end
 
+      def visit_Squeel_Nodes_Sifter(o, parent)
+        visit(context.base.active_record.send("sifter_#{o.name}", *o.args), parent)
+      end
+
       # Visit an Active Record Relation, returning an Arel::SelectManager
       # @param [ActiveRecord::Relation] o The Relation to visit
       # @param parent The parent object in the context