optionally remove empty nodes from AST

lib/liquid/block_body.rb

@@ -59,7 +59,7 @@ module Liquid
           end
           new_tag = tag.parse(tag_name, markup, tokenizer, parse_context)
 
-          next if new_tag.is_a?(Comment)
+          next if parse_context.omit_blank_nodes && blank_node?(new_tag)
 
           @blank &&= new_tag.blank?
           @nodelist << new_tag
@@ -157,7 +157,7 @@ module Liquid
           end
           new_tag = tag.parse(tag_name, markup, tokenizer, parse_context)
 
-          next if new_tag.is_a?(Comment)
+          next if parse_context.omit_blank_nodes && blank_node?(new_tag)
 
           @blank &&= new_tag.blank?
           @nodelist << new_tag
@@ -275,5 +275,18 @@ module Liquid
     def raise_missing_variable_terminator(token, parse_context)
       BlockBody.raise_missing_variable_terminator(token, parse_context)
     end
+
+    def blank_node?(node)
+      case node
+      when Comment
+        true
+      when BlockBody
+        true if node.nodelist.empty?
+      when Tag
+        node.nodelist.all? { |n| blank_node?(n) }
+      else
+        false
+      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, :omit_blank_nodes
 
     def initialize(options = Const::EMPTY_HASH)
       @environment = options.fetch(:environment, Environment.default)
@@ -12,6 +12,10 @@ module Liquid
       @locale   = @template_options[:locale] ||= I18n.new
       @warnings = []
 
+      # remove blank nodes such as
+      # comment tags, empty if tags, etc from the AST
+      @omit_blank_nodes = options.fetch(:omit_blank_nodes, false)
+
       self.depth   = 0
       self.partial = false
     end