Fix YAML dump/load issues with SqlLiteral node.

lib/arel/nodes/sql_literal.rb

@@ -1,14 +1,25 @@
 # frozen_string_literal: true
+
+require 'forwardable'
+
 module Arel
   module Nodes
-    class SqlLiteral < String
+    class SqlLiteral
       include Arel::Expressions
       include Arel::Predications
       include Arel::AliasPredication
       include Arel::OrderPredications
+      extend Forwardable
+
+      def_delegators :@string,
+                     :===, :==, :to_str, :to_s, :gsub, :inspect, :hash
+
+      def eql?(val)
+        self == val
+      end
 
-      def encode_with(coder)
-        coder.scalar = self.to_s
+      def initialize(string)
+        @string = string
       end
     end
   end

lib/arel/update_manager.rb

@@ -42,7 +42,8 @@ def where expr
     end
 
     def set values
-      if String === values
+      case values
+      when String, Nodes::SqlLiteral
         @ast.values = [values]
       else
         @ast.values = values.map { |column,value|

test/nodes/test_sql_literal.rb

@@ -65,8 +65,11 @@ def compile node
 
       describe 'serialization' do
         it 'serializes into YAML' do
-          yaml_literal = SqlLiteral.new('foo').to_yaml
-          assert_equal('foo', YAML.load(yaml_literal))
+          literal = SqlLiteral.new('foo')
+          yaml_literal = literal.to_yaml
+          revived = YAML.load(yaml_literal)
+          assert_equal(literal, revived)
+          revived.must_be_kind_of Arel::Nodes::SqlLiteral
         end
       end
     end