Refactor the Optimizer class no visit the AST

Just takes care of Variables for now.

Increases performance.

lib/liquid/document.rb

@@ -5,7 +5,7 @@ module Liquid
     def self.parse(tokens, parse_context)
       doc = new(parse_context)
       doc.parse(tokens, parse_context)
-      Optimizer.new.optimize(doc)
+      doc
     end
 
     attr_reader :parse_context, :body

lib/liquid/optimizer.rb

@@ -2,54 +2,18 @@
 
 module Liquid
   class Optimizer
-    def optimize(node)
-      case node
-      when Liquid::Template       then optimize(node.root.body)
-      when Liquid::Document       then optimize(node.body)
-      when Liquid::BlockBody      then optimize_block(node)
-      when Liquid::Variable       then optimize_variable(node)
-      when Liquid::Assign         then optimize_assign(node)
-      when Liquid::For            then optimize_for(node)
-      when Liquid::If             then optimize_if(node)
-      end
-      node
-    end
+    class << self
+      attr_accessor :enabled
 
-    def optimize_block(block)
-      block.nodelist.each { |node| optimize(node) }
-    end
+      def optimize_variable(node)
+        return unless enabled
 
-    def optimize_variable(node)
-      # Turn chained `| append: "..."| append: "..."`, into a single `append_all: [...]`
-      if node.filters.size > 1 && node.filters.all? { |f, _| f == "append" }
-        node.filters = [["append_all", node.filters.map { |f, (arg)| arg }]]
-      end
-    end
-
-    def optimize_assign(node)
-      optimize(node.from)
-    end
-
-    def optimize_for(node)
-      optimize(node.collection_name)
-      optimize_block(node)
-    end
-
-    def optimize_if(node)
-      node.blocks.each do |block|
-        optimize_condition(block)
-        optimize(block.attachment)
-      end
-    end
-
-    def optimize_condition(node)
-      case node
-      when Liquid::ElseCondition
-        # noop
-      when Liquid::Condition
-        optimize(node.left)
-        optimize(node.right) if node.right
+        # Turn chained `| append: "..."| append: "..."`, into a single `append_all: [...]`
+        if node.filters.size > 1 && node.filters.all? { |f, _| f == "append" }
+          node.filters = [["append_all", node.filters.map { |f, (arg)| arg }]]
+        end
       end
     end
+    self.enabled = true
   end
 end

lib/liquid/variable.rb

@@ -31,6 +31,8 @@ module Liquid
       @line_number   = parse_context.line_number
 
       parse_with_selected_parser(markup)
+
+      Optimizer.optimize_variable(self)
     end
 
     def raw