WIP: Loom

lib/liquid.rb

@@ -86,3 +86,4 @@ require 'liquid/partial_cache'
 require 'liquid/usage'
 require 'liquid/registers'
 require 'liquid/template_factory'
+require 'liquid/loom'

lib/liquid/block_body.rb

@@ -31,10 +31,11 @@ module Liquid
       end
     end
 
-    def freeze
-      @nodelist.freeze
-      super
-    end
+    # TODO: Freeze the nodelist after optimization
+    # def freeze
+    #   @nodelist.freeze
+    #   super
+    # end
 
     private def parse_for_liquid_tag(tokenizer, parse_context)
       while (token = tokenizer.shift)
@@ -154,6 +155,12 @@ module Liquid
           end
           new_tag = tag.parse(tag_name, markup, tokenizer, parse_context)
           @blank &&= new_tag.blank?
+
+          if parse_context.eager_optimize
+            next if new_tag.nodelist&.all? { !_1.is_a?(String) && _1.nodelist.empty? } # this is an empty block
+            next if new_tag.is_a?(If) && new_tag.blocks.empty? # this is an empty If block
+          end
+
           @nodelist << new_tag
         when token.start_with?(VARSTART)
           whitespace_handler(token, parse_context)

lib/liquid/loom.rb

@@ -0,0 +1,71 @@
+# frozen_string_literal: true
+
+module Liquid
+  class Loom
+    class << self
+      def optimize(template)
+        new(template).optimize
+      end
+    end
+
+    def initialize template
+      @root = template.root
+    end
+
+    def optimize
+      merge_if_blocks
+    end
+
+    def merge_if_blocks
+      nodelist_list = [@root.nodelist]
+
+      while nodelist_list.any?
+        next_nodelist_list = []
+
+        nodelist_list.each do |nodelist|
+          i = 0
+          while i < nodelist.length
+            node = nodelist[i]
+            chain_if_blocks(nodelist, node, i) if node.is_a?(If)
+            i += 1
+          end
+        end
+
+        nodelist_list = next_nodelist_list
+      end
+    end
+
+    private
+
+    def chain_if_blocks(nodelist, first_if_node, first_if_index)
+      used_variables = Set.new
+
+      # only check the top level Condition (ignore children conditions for now)
+      first_if_node.blocks.each do |condition|
+        used_variables << condition.left
+        used_variables << condition.right if condition.right
+      end
+
+      if_blocks = []
+
+      nodelist[first_if_index + 1..-1].each do |node|
+        break unless node.is_a?(If)
+
+        # check if the variables used in the current block are used in the previous block
+        first_if_node.blocks.each do |condition|
+          if used_variables.include?(condition.left) || (condition.right && used_variables.include?(condition.right))
+            break
+          end
+        end
+
+        if_blocks << node
+      end
+
+      nodelist.delete_if { |node| if_blocks.include?(node) }
+
+      if_blocks.each do |if_block|
+        first_if_node.blocks << if_block.blocks.first
+      end
+    end
+  end
+end

lib/liquid/parse_context.rb

@@ -3,7 +3,7 @@
 module Liquid
   class ParseContext
     attr_accessor :locale, :line_number, :trim_whitespace, :depth
-    attr_reader :partial, :warnings, :error_mode, :environment
+    attr_reader :partial, :warnings, :error_mode, :environment, :eager_optimize
 
     def initialize(options = Const::EMPTY_HASH)
       @environment = options.fetch(:environment, Environment.default)
@@ -11,6 +11,7 @@ module Liquid
 
       @locale   = @template_options[:locale] ||= I18n.new
       @warnings = []
+      @eager_optimize = options.fetch(:eager_optimize, ENV["OPTIMIZE"] == "true")
 
       self.depth   = 0
       self.partial = false

lib/liquid/tags/if.rb

@@ -23,6 +23,7 @@ module Liquid
     def initialize(tag_name, markup, options)
       super
       @blocks = []
+      @has_else_block = false
       push_block('if', markup)
     end
 
@@ -33,17 +34,44 @@ module Liquid
     def parse(tokens)
       while parse_body(@blocks.last.attachment, tokens)
       end
-      @blocks.reverse_each do |block|
-        block.attachment.remove_blank_strings if blank?
-        block.attachment.freeze
+
+      if parse_context.eager_optimize && definitive_false_statement?
+        @blocks.clear
+      else
+        @blocks.reverse_each do |block|
+          block.attachment.remove_blank_strings if blank?
+          block.attachment.freeze
+        end
       end
     end
 
+    def definitive_false_statement?
+      # check if any blocks have variable lookups
+      @blocks.each do |condition|
+        return false if condition.left.is_a?(VariableLookup) || condition.right&.is_a?(VariableLookup)
+
+        child_condition = condition.child_condition
+
+        while child_condition
+          return false if child_condition&.left.is_a?(VariableLookup) || child_condition&.right&.is_a?(VariableLookup)
+          child_condition = child_condition.child_condition
+        end
+      end
+
+      # check if all blocks are false
+      @blocks.each do |condition|
+        return false if condition.evaluate
+      end
+
+      true
+    end
+
     ELSE_TAG_NAMES = ['elsif', 'else'].freeze
     private_constant :ELSE_TAG_NAMES
 
     def unknown_tag(tag, markup, tokens)
       if ELSE_TAG_NAMES.include?(tag)
+        @has_else_block = true
         push_block(tag, markup)
       else
         super

lib/liquid/template.rb

@@ -82,7 +82,11 @@ module Liquid
       # See Liquid::Profiler for more information
       def parse(source, options = {})
         environment = options[:environment] || Environment.default
-        new(environment: environment).parse(source, options)
+        template = new(environment: environment).parse(source, options)
+
+        Loom.optimize(template) if options[:eager_optimize]
+
+        template
       end
     end