Refactor the Optimizer class no visit the AST

Just takes care of Variables for now.

Increases performance.

lib/liquid.rb

@@ -84,6 +84,7 @@ require 'liquid/usage'
 require 'liquid/register'
 require 'liquid/static_registers'
 require 'liquid/template_factory'
+require 'liquid/optimizer'
 
 # Load all the tags of the standard library
 #

lib/liquid/optimizer.rb

@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+module Liquid
+  class Optimizer
+    class << self
+      attr_accessor :enabled
+
+      def optimize_variable(node)
+        return unless enabled
+
+        # 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/standardfilters.rb

@@ -281,6 +281,10 @@ module Liquid
       input.to_s + string.to_s
     end
 
+    def append_all(input, *items)
+      input.to_s + items.join
+    end
+
     def concat(input, array)
       unless array.respond_to?(:to_ary)
         raise ArgumentError, "concat filter requires an array argument"

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

test/unit/optimizer_test.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+require 'test_helper'
+
+class OptimizerUnitTest < Minitest::Test
+  include Liquid
+
+  def test_combines_append_filters
+    optimizer = Optimizer.new
+    var = Variable.new('hello | append: "a" | append: b', ParseContext.new)
+    var = optimizer.optimize(var)
+    assert_equal([
+      ['append_all', ["a", VariableLookup.new("b")]]
+    ], var.filters)
+  end
+end