added a module for visiting and transforming bind values

lib/arel/visitors/bind_visitor.rb

@@ -0,0 +1,24 @@
+module Arel
+  module Visitors
+    module BindVisitor
+      def initialize target
+        @block = nil
+        super
+      end
+
+      def accept node, &block
+        @block = block if block_given?
+        super
+      end
+
+      private
+      def visit_Arel_Nodes_BindParam o
+        if @block
+          @block.call
+        else
+          super
+        end
+      end
+    end
+  end
+end

lib/arel/visitors/to_sql.rb

@@ -108,7 +108,7 @@ key on UpdateManager using UpdateManager#key=
       def visit_Arel_Nodes_Values o
         "VALUES (#{o.expressions.zip(o.columns).map { |value, attr|
           if Nodes::SqlLiteral === value
-            visit_Arel_Nodes_SqlLiteral value
+            visit value
           else
             quote(value, attr && column_for(attr))
           end
@@ -133,7 +133,7 @@ key on UpdateManager using UpdateManager#key=
           (visit(o.set_quantifier) if o.set_quantifier),
           ("#{o.projections.map { |x| visit x }.join ', '}" unless o.projections.empty?),
           ("FROM #{visit(o.source)}" if o.source && !o.source.empty?),
-          ("WHERE #{o.wheres.map { |x| accept x }.join ' AND ' }" unless o.wheres.empty?),
+          ("WHERE #{o.wheres.map { |x| visit x }.join ' AND ' }" unless o.wheres.empty?),
           ("GROUP BY #{o.groups.map { |x| visit x }.join ', ' }" unless o.groups.empty?),
           (visit(o.having) if o.having),
         ].compact.join ' '

test/visitors/test_bind_visitor.rb

@@ -0,0 +1,39 @@
+require 'helper'
+require 'arel/visitors/bind_visitor'
+
+module Arel
+  module Visitors
+    class TestBindVisitor < MiniTest::Unit::TestCase
+      def test_visitor_yields_on_binds
+        visitor = Class.new(Arel::Visitors::Visitor) {
+          def initialize omg
+          end
+
+          include Arel::Visitors::BindVisitor
+        }.new nil
+
+        bp = Nodes::BindParam.new 'omg'
+        called = false
+        visitor.accept(bp) { called = true }
+        assert called
+      end
+
+      def test_visitor_only_yields_on_binds
+        visitor = Class.new(Arel::Visitors::Visitor) {
+          def initialize omg
+          end
+
+          include Arel::Visitors::BindVisitor
+        }.new(nil)
+
+        bp = Arel.sql 'omg'
+        called = false
+
+        assert_raises(TypeError) {
+          visitor.accept(bp) { called = true }
+        }
+        refute called
+      end
+    end
+  end
+end