Remove hasnling false scopes

Remove lazy load stacks and instead only create a new scope when a tag is known to need one

.gitignore

@@ -7,3 +7,4 @@ pkg
 .ruby-version
 Gemfile.lock
 .bundle
+.byebug_history

.rubocop.yml

@@ -2,9 +2,15 @@ inherit_from:
   - .rubocop_todo.yml
   - ./.rubocop_todo.yml
 
+require: rubocop-performance
+
+Performance:
+  Enabled: true
+
 AllCops:
   Exclude:
     - 'performance/shopify/*'
+    - 'vendor/bundle/**/*'
     - 'pkg/**'
 
 Metrics/BlockNesting:
@@ -79,9 +85,6 @@ Style/TrailingCommaInArrayLiteral:
 Style/TrailingCommaInHashLiteral:
   Enabled: false
 
-Layout/IndentHash:
-  EnforcedStyle: consistent
-
 Style/FormatString:
   Enabled: false
 
@@ -106,9 +109,6 @@ Style/RegexpLiteral:
 Style/SymbolLiteral:
   Enabled: false
 
-Performance/Count:
-  Enabled: false
-
 Naming/ConstantName:
   Enabled: false
 

.rubocop_todo.yml

@@ -1,6 +1,6 @@
 # This configuration was generated by
 # `rubocop --auto-gen-config`
-# on 2019-03-19 11:04:37 -0400 using RuboCop version 0.53.0.
+# on 2019-08-29 00:43:36 +1000 using RuboCop version 0.74.0.
 # The point is for the user to remove these configuration records
 # one by one as the offenses are removed from the code base.
 # Note that changes in the inspected code, or installation of new
@@ -8,16 +8,67 @@
 
 # Offense count: 1
 # Cop supports --auto-correct.
-# Configuration parameters: Include, TreatCommentsAsGroupSeparators.
+# Configuration parameters: TreatCommentsAsGroupSeparators, Include.
 # Include: **/*.gemspec
 Gemspec/OrderedDependencies:
   Exclude:
     - 'liquid.gemspec'
 
+# Offense count: 1
+# Configuration parameters: Include.
+# Include: **/*.gemspec, 
+Gemspec/RequiredRubyVersion:
+  Exclude:
+    - 'liquid.gemspec'
+
+# Offense count: 124
+# Cop supports --auto-correct.
+# Configuration parameters: EnforcedStyle, IndentationWidth.
+# SupportedStyles: with_first_argument, with_fixed_indentation
+Layout/AlignArguments:
+  Enabled: false
+
+# Offense count: 7
+# Cop supports --auto-correct.
+# Configuration parameters: AllowMultipleStyles, EnforcedHashRocketStyle, EnforcedColonStyle, EnforcedLastArgumentHashStyle.
+# SupportedHashRocketStyles: key, separator, table
+# SupportedColonStyles: key, separator, table
+# SupportedLastArgumentHashStyles: always_inspect, always_ignore, ignore_implicit, ignore_explicit
+Layout/AlignHash:
+  Exclude:
+    - 'lib/liquid/condition.rb'
+    - 'lib/liquid/expression.rb'
+    - 'test/unit/context_unit_test.rb'
+
+# Offense count: 6
+# Cop supports --auto-correct.
+Layout/ClosingHeredocIndentation:
+  Exclude:
+    - 'test/integration/tags/for_tag_test.rb'
+
+# Offense count: 27
+# Cop supports --auto-correct.
+Layout/EmptyLineAfterGuardClause:
+  Exclude:
+    - 'lib/liquid/block.rb'
+    - 'lib/liquid/block_body.rb'
+    - 'lib/liquid/context.rb'
+    - 'lib/liquid/drop.rb'
+    - 'lib/liquid/lexer.rb'
+    - 'lib/liquid/parser.rb'
+    - 'lib/liquid/standardfilters.rb'
+    - 'lib/liquid/strainer.rb'
+    - 'lib/liquid/tags/for.rb'
+    - 'lib/liquid/tags/if.rb'
+    - 'lib/liquid/tags/include.rb'
+    - 'lib/liquid/utils.rb'
+    - 'lib/liquid/variable.rb'
+    - 'lib/liquid/variable_lookup.rb'
+
 # Offense count: 5
 # Cop supports --auto-correct.
 # Configuration parameters: EnforcedStyle.
-# SupportedStyles: auto_detection, squiggly, active_support, powerpack, unindent
+# SupportedStyles: squiggly, active_support, powerpack, unindent
 Layout/IndentHeredoc:
   Exclude:
     - 'test/integration/tags/for_tag_test.rb'
@@ -32,6 +83,13 @@ Layout/MultilineMethodCallBraceLayout:
     - 'test/integration/error_handling_test.rb'
     - 'test/unit/strainer_unit_test.rb'
 
+# Offense count: 1
+# Cop supports --auto-correct.
+# Configuration parameters: AllowForAlignment.
+Layout/SpaceAroundOperators:
+  Exclude:
+    - 'lib/liquid/condition.rb'
+
 # Offense count: 2
 # Cop supports --auto-correct.
 # Configuration parameters: EnforcedStyle.
@@ -46,35 +104,33 @@ Lint/Void:
   Exclude:
     - 'lib/liquid/parse_context.rb'
 
-# Offense count: 54
+# Offense count: 53
 Metrics/AbcSize:
   Max: 56
 
 # Offense count: 12
 Metrics/CyclomaticComplexity:
-  Max: 12
+  Max: 13
 
-# Offense count: 112
+# Offense count: 118
-# Configuration parameters: CountComments.
+# Configuration parameters: CountComments, ExcludedMethods.
 Metrics/MethodLength:
-  Max: 37
+  Max: 38
 
-# Offense count: 8
+# Offense count: 9
 Metrics/PerceivedComplexity:
   Max: 11
 
-# Offense count: 52
+# Offense count: 1
-# Configuration parameters: Blacklist.
+# Cop supports --auto-correct.
-# Blacklist: END, (?-mix:EO[A-Z]{1})
+# Configuration parameters: PreferredName.
-Naming/HeredocDelimiterNaming:
+Naming/RescuedExceptionsVariableName:
   Exclude:
-    - 'test/integration/assign_test.rb'
+    - 'lib/liquid/context.rb'
-    - 'test/integration/capture_test.rb'
-    - 'test/integration/trim_mode_test.rb'
 
-# Offense count: 23
+# Offense count: 20
 # Configuration parameters: MinNameLength, AllowNamesEndingInNumbers, AllowedNames, ForbiddenNames.
-# AllowedNames: io, id
+# AllowedNames: io, id, to, by, on, in, at, ip, db
 Naming/UncommunicativeMethodParamName:
   Exclude:
     - 'example/server/example_servlet.rb'
@@ -82,14 +138,22 @@ Naming/UncommunicativeMethodParamName:
     - 'lib/liquid/context.rb'
     - 'lib/liquid/standardfilters.rb'
     - 'lib/liquid/tags/if.rb'
-    - 'lib/liquid/utils.rb'
     - 'lib/liquid/variable.rb'
     - 'test/integration/filter_test.rb'
     - 'test/integration/standard_filter_test.rb'
-    - 'test/integration/tags/for_tag_test.rb'
     - 'test/integration/template_test.rb'
     - 'test/unit/condition_unit_test.rb'
 
+# Offense count: 5
+# Configuration parameters: EnforcedStyle.
+# SupportedStyles: inline, group
+Style/AccessModifierDeclarations:
+  Exclude:
+    - 'lib/liquid/block_body.rb'
+    - 'lib/liquid/tag.rb'
+    - 'lib/liquid/tags/include.rb'
+    - 'test/unit/strainer_unit_test.rb'
+
 # Offense count: 10
 # Cop supports --auto-correct.
 # Configuration parameters: EnforcedStyle.
@@ -117,15 +181,9 @@ Style/ConditionalAssignment:
     - 'lib/liquid/errors.rb'
 
 # Offense count: 1
-Style/DateTime:
-  Exclude:
-    - 'test/unit/context_unit_test.rb'
-
-# Offense count: 2
 # Cop supports --auto-correct.
 Style/EmptyCaseCondition:
   Exclude:
-    - 'lib/liquid/block_body.rb'
     - 'lib/liquid/lexer.rb'
 
 # Offense count: 5
@@ -163,6 +221,13 @@ Style/FormatStringToken:
     - 'test/integration/filter_test.rb'
     - 'test/integration/hash_ordering_test.rb'
 
+# Offense count: 106
+# Cop supports --auto-correct.
+# Configuration parameters: EnforcedStyle.
+# SupportedStyles: always, never
+Style/FrozenStringLiteralComment:
+  Enabled: false
+
 # Offense count: 14
 # Configuration parameters: MinBodyLength.
 Style/GuardClause:
@@ -180,6 +245,13 @@ Style/GuardClause:
     - 'lib/liquid/variable.rb'
     - 'test/unit/tokenizer_unit_test.rb'
 
+# Offense count: 53
+# Cop supports --auto-correct.
+# Configuration parameters: EnforcedStyle.
+# SupportedStyles: literals, strict
+Style/MutableConstant:
+  Enabled: false
+
 # Offense count: 1
 # Cop supports --auto-correct.
 # Configuration parameters: EnforcedStyle, MinBodyLength.
@@ -188,9 +260,9 @@ Style/Next:
   Exclude:
     - 'lib/liquid/tags/for.rb'
 
-# Offense count: 4
+# Offense count: 13
 # Cop supports --auto-correct.
-# Configuration parameters: AutoCorrect, EnforcedStyle.
+# Configuration parameters: AutoCorrect, EnforcedStyle, IgnoredMethods.
 # SupportedStyles: predicate, comparison
 Style/NumericPredicate:
   Exclude:
@@ -199,6 +271,8 @@ Style/NumericPredicate:
     - 'lib/liquid/forloop_drop.rb'
     - 'lib/liquid/standardfilters.rb'
     - 'lib/liquid/tablerowloop_drop.rb'
+    - 'test/integration/standard_filter_test.rb'
+    - 'test/integration/template_test.rb'
 
 # Offense count: 14
 # Cop supports --auto-correct.
@@ -216,6 +290,16 @@ Style/RedundantSelf:
   Exclude:
     - 'lib/liquid/strainer.rb'
 
+# Offense count: 3
+# Cop supports --auto-correct.
+# Configuration parameters: ConvertCodeThatCanStartToReturnNil, Whitelist.
+# Whitelist: present?, blank?, presence, try, try!
+Style/SafeNavigation:
+  Exclude:
+    - 'lib/liquid/drop.rb'
+    - 'lib/liquid/strainer.rb'
+    - 'lib/liquid/tokenizer.rb'
+
 # Offense count: 9
 # Cop supports --auto-correct.
 # Configuration parameters: AllowAsExpressionSeparator.
@@ -253,8 +337,9 @@ Style/WhileUntilModifier:
   Exclude:
     - 'lib/liquid/tags/case.rb'
 
-# Offense count: 640
+# Offense count: 665
-# Configuration parameters: AllowHeredoc, AllowURI, URISchemes, IgnoreCopDirectives, IgnoredPatterns.
+# Cop supports --auto-correct.
+# Configuration parameters: AutoCorrect, AllowHeredoc, AllowURI, URISchemes, IgnoreCopDirectives, IgnoredPatterns.
 # URISchemes: http, https
 Metrics/LineLength:
   Max: 294

.travis.yml

@@ -1,29 +1,26 @@
 language: ruby
 
 rvm:
-  - 2.1
-  - 2.2
-  - 2.3
   - 2.4
   - 2.5
+  - &latest_ruby 2.6
+  - 2.7
   - ruby-head
   - jruby-head
-#  - rbx-2
+  - truffleruby
 
-sudo: false
-
-addons:
-  apt:
-    packages:
-    - libgmp3-dev
 
 matrix:
+  include:
+    - rvm: *latest_ruby
+      script: bundle exec rake memory_profile:run
+      name: Profiling Memory Usage
   allow_failures:
     - rvm: ruby-head
     - rvm: jruby-head
+    - rvm: truffleruby
 
-install:
+cache: bundler
-  - bundle install
 
 script: bundle exec rake
 

Gemfile

@@ -8,16 +8,18 @@ gemspec
 group :benchmark, :test do
   gem 'benchmark-ips'
   gem 'memory_profiler'
+  gem 'terminal-table'
 
-  install_if -> { RUBY_PLATFORM !~ /mingw|mswin|java/ } do
+  install_if -> { RUBY_PLATFORM !~ /mingw|mswin|java/ && RUBY_ENGINE != 'truffleruby' } do
     gem 'stackprof'
   end
 end
 
 group :test do
-  gem 'rubocop', '~> 0.53.0'
+  gem 'rubocop', '~> 0.74.0', require: false
+  gem 'rubocop-performance', require: false
 
-  platform :mri do
+  platform :mri, :truffleruby do
-    gem 'liquid-c', github: 'Shopify/liquid-c', ref: '9168659de45d6d576fce30c735f857e597fa26f6'
+    gem 'liquid-c', github: 'Shopify/liquid-c', ref: 'liquid-tag'
   end
 end

Rakefile

@@ -19,8 +19,10 @@ task :warn_test do
 end
 
 task :rubocop do
-  require 'rubocop/rake_task'
+  if RUBY_ENGINE == 'ruby'
-  RuboCop::RakeTask.new
+    require 'rubocop/rake_task'
+    RuboCop::RakeTask.new
+  end
 end
 
 desc 'runs test suite with both strict and lax parsers'
@@ -32,8 +34,8 @@ task :test do
   Rake::Task['base_test'].reenable
   Rake::Task['base_test'].invoke
 
-  if RUBY_ENGINE == 'ruby'
+  if RUBY_ENGINE == 'ruby' || RUBY_ENGINE == 'truffleruby'
-    ENV['LIQUID-C'] = '1'
+    ENV['LIQUID_C'] = '1'
 
     ENV['LIQUID_PARSER_MODE'] = 'lax'
     Rake::Task['base_test'].reenable

lib/liquid/block.rb

@@ -13,6 +13,7 @@ module Liquid
       end
     end
 
+    # For backwards compatibility
     def render(context)
       @body.render(context)
     end

lib/liquid/block_body.rb

@@ -1,6 +1,7 @@
 module Liquid
   class BlockBody
-    FullToken = /\A#{TagStart}#{WhitespaceControl}?\s*(\w+)\s*(.*?)#{WhitespaceControl}?#{TagEnd}\z/om
+    LiquidTagToken = /\A\s*(\w+)\s*(.*?)\z/o
+    FullToken = /\A#{TagStart}#{WhitespaceControl}?(\s*)(\w+)(\s*)(.*?)#{WhitespaceControl}?#{TagEnd}\z/om
     ContentOfVariable = /\A#{VariableStart}#{WhitespaceControl}?(.*?)#{WhitespaceControl}?#{VariableEnd}\z/om
     WhitespaceOrNothing = /\A\s*\z/
     TAGSTART = "{%".freeze
@@ -13,8 +14,42 @@ module Liquid
       @blank = true
     end
 
-    def parse(tokenizer, parse_context)
+    def parse(tokenizer, parse_context, &block)
       parse_context.line_number = tokenizer.line_number
+
+      if tokenizer.for_liquid_tag
+        parse_for_liquid_tag(tokenizer, parse_context, &block)
+      else
+        parse_for_document(tokenizer, parse_context, &block)
+      end
+    end
+
+    private def parse_for_liquid_tag(tokenizer, parse_context)
+      while token = tokenizer.shift
+        unless token.empty? || token =~ WhitespaceOrNothing
+          unless token =~ LiquidTagToken
+            # line isn't empty but didn't match tag syntax, yield and let the
+            # caller raise a syntax error
+            return yield token, token
+          end
+          tag_name = $1
+          markup = $2
+          unless tag = registered_tags[tag_name]
+            # end parsing if we reach an unknown tag and let the caller decide
+            # determine how to proceed
+            return yield tag_name, markup
+          end
+          new_tag = tag.parse(tag_name, markup, tokenizer, parse_context)
+          @blank &&= new_tag.blank?
+          @nodelist << new_tag
+        end
+        parse_context.line_number = tokenizer.line_number
+      end
+
+      yield nil, nil
+    end
+
+    private def parse_for_document(tokenizer, parse_context, &block)
       while token = tokenizer.shift
         next if token.empty?
         case
@@ -23,9 +58,20 @@ module Liquid
           unless token =~ FullToken
             raise_missing_tag_terminator(token, parse_context)
           end
-          tag_name = $1
+          tag_name = $2
-          markup = $2
+          markup = $4
-          # fetch the tag from registered blocks
+
+          if parse_context.line_number
+            # newlines inside the tag should increase the line number,
+            # particularly important for multiline {% liquid %} tags
+            parse_context.line_number += $1.count("\n".freeze) + $3.count("\n".freeze)
+          end
+
+          if tag_name == 'liquid'.freeze
+            liquid_tag_tokenizer = Tokenizer.new(markup, line_number: parse_context.line_number, for_liquid_tag: true)
+            next parse_for_liquid_tag(liquid_tag_tokenizer, parse_context, &block)
+          end
+
           unless tag = registered_tags[tag_name]
             # end parsing if we reach an unknown tag and let the caller decide
             # determine how to proceed
@@ -67,19 +113,23 @@ module Liquid
     end
 
     def render(context)
-      output = []
+      render_to_output_buffer(context, '')
+    end
+
+    def render_to_output_buffer(context, output)
       context.resource_limits.render_score += @nodelist.length
 
       idx = 0
       while node = @nodelist[idx]
+        previous_output_size = output.bytesize
+
         case node
         when String
-          check_resources(context, node)
           output << node
         when Variable
-          render_node_to_output(node, output, context)
+          render_node(context, output, node)
         when Block
-          render_node_to_output(node, output, context, node.blank?)
+          render_node(context, node.blank? ? '' : output, node)
           break if context.interrupt? # might have happened in a for-block
         when Continue, Break
           # If we get an Interrupt that means the block must stop processing. An
@@ -88,34 +138,30 @@ module Liquid
           context.push_interrupt(node.interrupt)
           break
         else # Other non-Block tags
-          render_node_to_output(node, output, context)
+          render_node(context, output, node)
           break if context.interrupt? # might have happened through an include
         end
         idx += 1
+
+        raise_if_resource_limits_reached(context, output.bytesize - previous_output_size)
       end
 
-      output.join
+      output
     end
 
     private
 
-    def render_node_to_output(node, output, context, skip_output = false)
+    def render_node(context, output, node)
-      node_output = node.render(context)
+      node.render_to_output_buffer(context, output)
-      node_output = node_output.is_a?(Array) ? node_output.join : node_output.to_s
-      check_resources(context, node_output)
-      output << node_output unless skip_output
-    rescue MemoryError => e
-      raise e
     rescue UndefinedVariable, UndefinedDropMethod, UndefinedFilter => e
       context.handle_error(e, node.line_number)
-      output << nil
     rescue ::StandardError => e
       line_number = node.is_a?(String) ? nil : node.line_number
       output << context.handle_error(e, line_number)
     end
 
-    def check_resources(context, node_output)
+    def raise_if_resource_limits_reached(context, length)
-      context.resource_limits.render_length += node_output.bytesize
+      context.resource_limits.render_length += length
       return unless context.resource_limits.reached?
       raise MemoryError.new("Memory limits exceeded".freeze)
     end

lib/liquid/context.rb

@@ -25,8 +25,6 @@ module Liquid
       @resource_limits  = resource_limits || ResourceLimits.new(Template.default_resource_limits)
       squash_instance_assigns_with_environments
 
-      @this_stack_used = false
-
       self.exception_renderer = Template.default_exception_renderer
       if rethrow_errors
         self.exception_renderer = ->(e) { raise }
@@ -111,19 +109,11 @@ module Liquid
     #   end
     #
     #   context['var]  #=> nil
-    def stack(new_scope = nil)
+    def stack(new_scope = {})
-      old_stack_used = @this_stack_used
+      push(new_scope)
-      if new_scope
-        push(new_scope)
-        @this_stack_used = true
-      else
-        @this_stack_used = false
-      end
-
       yield
     ensure
-      pop if @this_stack_used
+      pop
-      @this_stack_used = old_stack_used
     end
 
     def clear_instance_assigns
@@ -132,10 +122,6 @@ module Liquid
 
     # Only allow String, Numeric, Hash, Array, Proc, Boolean or <tt>Liquid::Drop</tt>
     def []=(key, value)
-      unless @this_stack_used
-        @this_stack_used = true
-        push({})
-      end
       @scopes[0][key] = value
     end
 

lib/liquid/parser.rb

@@ -44,11 +44,14 @@ module Liquid
       tok[0] == type
     end
 
+    SINGLE_TOKEN_EXPRESSION_TYPES = [:string, :number].freeze
+    private_constant :SINGLE_TOKEN_EXPRESSION_TYPES
+
     def expression
       token = @tokens[@p]
       if token[0] == :id
         variable_signature
-      elsif [:string, :number].include? token[0]
+      elsif SINGLE_TOKEN_EXPRESSION_TYPES.include? token[0]
         consume
       elsif token.first == :open_round
         consume

lib/liquid/profiler/hooks.rb

@@ -1,23 +1,23 @@
 module Liquid
   class BlockBody
-    def render_node_with_profiling(node, output, context, skip_output = false)
+    def render_node_with_profiling(context, output, node)
       Profiler.profile_node_render(node) do
-        render_node_without_profiling(node, output, context, skip_output)
+        render_node_without_profiling(context, output, node)
       end
     end
 
-    alias_method :render_node_without_profiling, :render_node_to_output
+    alias_method :render_node_without_profiling, :render_node
-    alias_method :render_node_to_output, :render_node_with_profiling
+    alias_method :render_node, :render_node_with_profiling
   end
 
   class Include < Tag
-    def render_with_profiling(context)
+    def render_to_output_buffer_with_profiling(context, output)
       Profiler.profile_children(context.evaluate(@template_name_expr).to_s) do
-        render_without_profiling(context)
+        render_to_output_buffer_without_profiling(context, output)
       end
     end
 
-    alias_method :render_without_profiling, :render
+    alias_method :render_to_output_buffer_without_profiling, :render_to_output_buffer
-    alias_method :render, :render_with_profiling
+    alias_method :render_to_output_buffer, :render_to_output_buffer_with_profiling
   end
 end

lib/liquid/standardfilters.rb

@@ -79,7 +79,7 @@ module Liquid
       truncate_string_str = truncate_string.to_s
       l = length - truncate_string_str.length
       l = 0 if l < 0
-      input_str.length > length ? input_str[0...l] + truncate_string_str : input_str
+      input_str.length > length ? input_str[0...l].concat(truncate_string_str) : input_str
     end
 
     def truncatewords(input, words = 15, truncate_string = "...".freeze)
@@ -88,7 +88,7 @@ module Liquid
       words = Utils.to_integer(words)
       l = words - 1
       l = 0 if l < 0
-      wordlist.length > l ? wordlist[0..l].join(" ".freeze) + truncate_string.to_s : input
+      wordlist.length > l ? wordlist[0..l].join(" ".freeze).concat(truncate_string.to_s) : input
     end
 
     # Split input string into an array of substrings separated by given pattern.

lib/liquid/tag.rb

@@ -5,8 +5,8 @@ module Liquid
     include ParserSwitching
 
     class << self
-      def parse(tag_name, markup, tokenizer, options)
+      def parse(tag_name, markup, tokenizer, parse_context)
-        tag = new(tag_name, markup, options)
+        tag = new(tag_name, markup, parse_context)
         tag.parse(tokenizer)
         tag
       end
@@ -36,6 +36,14 @@ module Liquid
       ''.freeze
     end
 
+    # For backwards compatibility with custom tags. In a future release, the semantics
+    # of the `render_to_output_buffer` method will become the default and the `render`
+    # method will be removed.
+    def render_to_output_buffer(context, output)
+      output << render(context)
+      output
+    end
+
     def blank?
       false
     end

lib/liquid/tags/assign.rb

@@ -10,6 +10,10 @@ module Liquid
   class Assign < Tag
     Syntax = /(#{VariableSignature}+)\s*=\s*(.*)\s*/om
 
+    def self.syntax_error_translation_key
+      "errors.syntax.assign".freeze
+    end
+
     attr_reader :to, :from
 
     def initialize(tag_name, markup, options)
@@ -18,15 +22,15 @@ module Liquid
         @to = $1
         @from = Variable.new($2, options)
       else
-        raise SyntaxError.new options[:locale].t("errors.syntax.assign".freeze)
+        raise SyntaxError.new(options[:locale].t(self.class.syntax_error_translation_key))
       end
     end
 
-    def render(context)
+    def render_to_output_buffer(context, output)
       val = @from.render(context)
       context.scopes.last[@to] = val
       context.resource_limits.assign_score += assign_score_of(val)
-      ''.freeze
+      output
     end
 
     def blank?

lib/liquid/tags/capture.rb

@@ -22,11 +22,12 @@ module Liquid
       end
     end
 
-    def render(context)
+    def render_to_output_buffer(context, output)
-      output = super
+      previous_output_size = output.bytesize
+      super
       context.scopes.last[@to] = output
-      context.resource_limits.assign_score += output.bytesize
+      context.resource_limits.assign_score += (output.bytesize - previous_output_size)
-      ''.freeze
+      output
     end
 
     def blank?

lib/liquid/tags/case.rb

@@ -38,21 +38,19 @@ module Liquid
       end
     end
 
-    def render(context)
+    def render_to_output_buffer(context, output)
-      context.stack do
+      execute_else_block = true
-        execute_else_block = true
 
-        output = ''
+      @blocks.each do |block|
-        @blocks.each do |block|
+        if block.else?
-          if block.else?
+          block.attachment.render_to_output_buffer(context, output) if execute_else_block
-            return block.attachment.render(context) if execute_else_block
+        elsif block.evaluate(context)
-          elsif block.evaluate(context)
+          execute_else_block = false
-            execute_else_block = false
+          block.attachment.render_to_output_buffer(context, output)
-            output << block.attachment.render(context)
-          end
         end
-        output
       end
+
+      output
     end
 
     private

lib/liquid/tags/comment.rb

@@ -1,7 +1,7 @@
 module Liquid
   class Comment < Block
-    def render(_context)
+    def render_to_output_buffer(_context, output)
-      ''.freeze
+      output
     end
 
     def unknown_tag(_tag, _markup, _tokens)

lib/liquid/tags/cycle.rb

@@ -31,18 +31,27 @@ module Liquid
       end
     end
 
-    def render(context)
+    def render_to_output_buffer(context, output)
       context.registers[:cycle] ||= {}
 
-      context.stack do
+      key = context.evaluate(@name)
-        key = context.evaluate(@name)
+      iteration = context.registers[:cycle][key].to_i
-        iteration = context.registers[:cycle][key].to_i
+
-        result = context.evaluate(@variables[iteration])
+      val = context.evaluate(@variables[iteration])
-        iteration += 1
+
-        iteration  = 0 if iteration >= @variables.size
+      if val.is_a?(Array)
-        context.registers[:cycle][key] = iteration
+        val = val.join
-        result
+      elsif !val.is_a?(String)
+        val = val.to_s
       end
+
+      output << val
+
+      iteration += 1
+      iteration  = 0 if iteration >= @variables.size
+      context.registers[:cycle][key] = iteration
+
+      output
     end
 
     private

lib/liquid/tags/decrement.rb

@@ -23,11 +23,12 @@ module Liquid
       @variable = markup.strip
     end
 
-    def render(context)
+    def render_to_output_buffer(context, output)
       value = context.environments.first[@variable] ||= 0
       value -= 1
       context.environments.first[@variable] = value
-      value.to_s
+      output << value.to_s
+      output
     end
   end
 

lib/liquid/tags/echo.rb

@@ -0,0 +1,24 @@
+module Liquid
+  # Echo outputs an expression
+  #
+  #   {% echo monkey %}
+  #   {% echo user.name %}
+  #
+  # This is identical to variable output syntax, like {{ foo }}, but works
+  # inside {% liquid %} tags. The full syntax is supported, including filters:
+  #
+  #   {% echo user | link %}
+  #
+  class Echo < Tag
+    def initialize(tag_name, markup, parse_context)
+      super
+      @variable = Variable.new(markup, parse_context)
+    end
+
+    def render(context)
+      @variable.render_to_output_buffer(context, '')
+    end
+  end
+
+  Template.register_tag('echo'.freeze, Echo)
+end

lib/liquid/tags/for.rb

@@ -70,14 +70,16 @@ module Liquid
       @else_block = BlockBody.new
     end
 
-    def render(context)
+    def render_to_output_buffer(context, output)
       segment = collection_segment(context)
 
       if segment.empty?
-        render_else(context)
+        render_else(context, output)
       else
-        render_segment(context, segment)
+        render_segment(context, output, segment)
       end
+
+      output
     end
 
     protected
@@ -150,12 +152,10 @@ module Liquid
       segment
     end
 
-    def render_segment(context, segment)
+    def render_segment(context, output, segment)
       for_stack = context.registers[:for_stack] ||= []
       length = segment.length
 
-      result = ''
-
       context.stack do
         loop_vars = Liquid::ForloopDrop.new(@name, length, for_stack[-1])
 
@@ -166,7 +166,7 @@ module Liquid
 
           segment.each do |item|
             context[@variable_name] = item
-            result << @for_block.render(context)
+            @for_block.render_to_output_buffer(context, output)
             loop_vars.send(:increment!)
 
             # Handle any interrupts if they exist.
@@ -181,7 +181,7 @@ module Liquid
         end
       end
 
-      result
+      output
     end
 
     def set_attribute(key, expr)
@@ -197,8 +197,12 @@ module Liquid
       end
     end
 
-    def render_else(context)
+    def render_else(context, output)
-      @else_block ? @else_block.render(context) : ''.freeze
+      if @else_block
+        @else_block.render_to_output_buffer(context, output)
+      else
+        output
+      end
     end
 
     class ParseTreeVisitor < Liquid::ParseTreeVisitor

lib/liquid/tags/if.rb

@@ -39,15 +39,14 @@ module Liquid
       end
     end
 
-    def render(context)
+    def render_to_output_buffer(context, output)
-      context.stack do
+      @blocks.each do |block|
-        @blocks.each do |block|
+        if block.evaluate(context)
-          if block.evaluate(context)
+          return block.attachment.render_to_output_buffer(context, output)
-            return block.attachment.render(context)
-          end
         end
-        ''.freeze
       end
+
+      output
     end
 
     private

lib/liquid/tags/ifchanged.rb

@@ -1,16 +1,15 @@
 module Liquid
   class Ifchanged < Block
-    def render(context)
+    def render_to_output_buffer(context, output)
-      context.stack do
+      block_output = ''
-        output = super
+      super(context, block_output)
 
-        if output != context.registers[:ifchanged]
+      if block_output != context.registers[:ifchanged]
-          context.registers[:ifchanged] = output
+        context.registers[:ifchanged] = block_output
-          output
+        output << block_output
-        else
-          ''.freeze
-        end
       end
+
+      output
     end
   end
 

lib/liquid/tags/include.rb

@@ -42,7 +42,7 @@ module Liquid
     def parse(_tokens)
     end
 
-    def render(context)
+    def render_to_output_buffer(context, output)
       template_name = context.evaluate(@template_name_expr)
       raise ArgumentError.new(options[:locale].t("errors.argument.include")) unless template_name
 
@@ -66,19 +66,21 @@ module Liquid
           end
 
           if variable.is_a?(Array)
-            variable.collect do |var|
+            variable.each do |var|
               context[context_variable_name] = var
-              partial.render(context)
+              partial.render_to_output_buffer(context, output)
             end
           else
             context[context_variable_name] = variable
-            partial.render(context)
+            partial.render_to_output_buffer(context, output)
           end
         end
       ensure
         context.template_name = old_template_name
         context.partial = old_partial
       end
+
+      output
     end
 
     private

lib/liquid/tags/increment.rb

@@ -20,10 +20,11 @@ module Liquid
       @variable = markup.strip
     end
 
-    def render(context)
+    def render_to_output_buffer(context, output)
       value = context.environments.first[@variable] ||= 0
       context.environments.first[@variable] = value + 1
-      value.to_s
+      output << value.to_s
+      output
     end
   end
 

lib/liquid/tags/raw.rb

@@ -22,8 +22,9 @@ module Liquid
       raise SyntaxError.new(parse_context.locale.t("errors.syntax.tag_never_closed".freeze, block_name: block_name))
     end
 
-    def render(_context)
+    def render_to_output_buffer(_context, output)
-      @body
+      output << @body
+      output
     end
 
     def nodelist

lib/liquid/tags/table_row.rb

@@ -18,7 +18,7 @@ module Liquid
       end
     end
 
-    def render(context)
+    def render_to_output_buffer(context, output)
       collection = context.evaluate(@collection_name) or return ''.freeze
 
       from = @attributes.key?('offset'.freeze) ? context.evaluate(@attributes['offset'.freeze]).to_i : 0
@@ -30,7 +30,7 @@ module Liquid
 
       cols = context.evaluate(@attributes['cols'.freeze]).to_i
 
-      result = "<tr class=\"row1\">\n"
+      output << "<tr class=\"row1\">\n"
       context.stack do
         tablerowloop = Liquid::TablerowloopDrop.new(length, cols)
         context['tablerowloop'.freeze] = tablerowloop
@@ -38,17 +38,20 @@ module Liquid
         collection.each do |item|
           context[@variable_name] = item
 
-          result << "<td class=\"col#{tablerowloop.col}\">" << super << '</td>'
+          output << "<td class=\"col#{tablerowloop.col}\">"
+          super
+          output << '</td>'
 
           if tablerowloop.col_last && !tablerowloop.last
-            result << "</tr>\n<tr class=\"row#{tablerowloop.row + 1}\">"
+            output << "</tr>\n<tr class=\"row#{tablerowloop.row + 1}\">"
           end
 
           tablerowloop.send(:increment!)
         end
       end
-      result << "</tr>\n"
+
-      result
+      output << "</tr>\n"
+      output
     end
 
     class ParseTreeVisitor < Liquid::ParseTreeVisitor

lib/liquid/tags/unless.rb

@@ -6,23 +6,21 @@ module Liquid
   #   {% unless x < 0 %} x is greater than zero {% endunless %}
   #
   class Unless < If
-    def render(context)
+    def render_to_output_buffer(context, output)
-      context.stack do
+      # First condition is interpreted backwards ( if not )
-        # First condition is interpreted backwards ( if not )
+      first_block = @blocks.first
-        first_block = @blocks.first
+      unless first_block.evaluate(context)
-        unless first_block.evaluate(context)
+        return first_block.attachment.render_to_output_buffer(context, output)
-          return first_block.attachment.render(context)
-        end
-
-        # After the first condition unless works just like if
-        @blocks[1..-1].each do |block|
-          if block.evaluate(context)
-            return block.attachment.render(context)
-          end
-        end
-
-        ''.freeze
       end
+
+      # After the first condition unless works just like if
+      @blocks[1..-1].each do |block|
+        if block.evaluate(context)
+          return block.attachment.render_to_output_buffer(context, output)
+        end
+      end
+
+      output
     end
   end
 

lib/liquid/template.rb

@@ -50,7 +50,7 @@ module Liquid
       private
 
       def lookup_class(name)
-        name.split("::").reject(&:empty?).reduce(Object) { |scope, const| scope.const_get(const) }
+        Object.const_get(name)
       end
     end
 
@@ -187,9 +187,12 @@ module Liquid
         raise ArgumentError, "Expected Hash or Liquid::Context as parameter"
       end
 
+      output = nil
+
       case args.last
       when Hash
         options = args.pop
+        output = options[:output] if options[:output]
 
         registers.merge!(options[:registers]) if options[:registers].is_a?(Hash)
 
@@ -204,10 +207,9 @@ module Liquid
       begin
         # render the nodelist.
         # for performance reasons we get an array back here. join will make a string out of it.
-        result = with_profiling(context) do
+        with_profiling(context) do
-          @root.render(context)
+          @root.render_to_output_buffer(context, output || '')
         end
-        result.respond_to?(:join) ? result.join : result
       rescue Liquid::MemoryError => e
         context.handle_error(e)
       ensure
@@ -220,6 +222,10 @@ module Liquid
       render(*args)
     end
 
+    def render_to_output_buffer(context, output)
+      render(context, output: output)
+    end
+
     private
 
     def tokenize(source)

lib/liquid/tokenizer.rb

@@ -1,25 +1,31 @@
 module Liquid
   class Tokenizer
-    attr_reader :line_number
+    attr_reader :line_number, :for_liquid_tag
 
-    def initialize(source, line_numbers = false)
+    def initialize(source, line_numbers = false, line_number: nil, for_liquid_tag: false)
       @source = source
-      @line_number = line_numbers ? 1 : nil
+      @line_number = line_number || (line_numbers ? 1 : nil)
+      @for_liquid_tag = for_liquid_tag
       @tokens = tokenize
     end
 
     def shift
-      token = @tokens.shift
+      token = @tokens.shift or return
-      @line_number += token.count("\n") if @line_number && token
+
+      if @line_number
+        @line_number += @for_liquid_tag ? 1 : token.count("\n")
+      end
+
       token
     end
 
     private
 
     def tokenize
-      @source = @source.source if @source.respond_to?(:source)
       return [] if @source.to_s.empty?
 
+      return @source.split("\n") if @for_liquid_tag
+
       tokens = @source.split(TemplateParser)
 
       # removes the rogue empty element at the beginning of the array

lib/liquid/variable.rb

@@ -85,12 +85,23 @@ module Liquid
       end
 
       obj = context.apply_global_filter(obj)
-
       taint_check(context, obj)
-
       obj
     end
 
+    def render_to_output_buffer(context, output)
+      obj = render(context)
+
+      if obj.is_a?(Array)
+        output << obj.join
+      elsif obj.nil?
+      else
+        output << obj.to_s
+      end
+
+      output
+    end
+
     private
 
     def parse_filter_expressions(filter_name, unparsed_args)

liquid.gemspec

@@ -16,7 +16,7 @@ Gem::Specification.new do |s|
   s.license     = "MIT"
   # s.description = "A secure, non-evaling end user template engine with aesthetic markup."
 
-  s.required_ruby_version     = ">= 2.1.0"
+  s.required_ruby_version     = ">= 2.4.0"
   s.required_rubygems_version = ">= 1.3.7"
 
   s.test_files  = Dir.glob("{test}/**/*")

performance/memory_profile.rb

@@ -2,25 +2,62 @@
 
 require 'benchmark/ips'
 require 'memory_profiler'
+require 'terminal-table'
 require_relative 'theme_runner'
 
-def profile(phase, &block)
+class Profiler
-  puts
+  LOG_LABEL   = "Profiling: ".rjust(14).freeze
-  puts "#{phase}:"
+  REPORTS_DIR = File.expand_path('.memprof', __dir__).freeze
-  puts
 
-  report = MemoryProfiler.report(&block)
+  def self.run
+    puts
+    yield new
+  end
 
-  report.pretty_print(
+  def initialize
-    color_output: true,
+    @allocated = []
-    scale_bytes: true,
+    @retained  = []
-    detailed_report: true
+    @headings  = []
-  )
+  end
+
+  def profile(phase, &block)
+    print LOG_LABEL
+    print "#{phase}.. ".ljust(10)
+    report = MemoryProfiler.report(&block)
+    puts 'Done.'
+    @headings  << phase.capitalize
+    @allocated << "#{report.scale_bytes(report.total_allocated_memsize)} (#{report.total_allocated} objects)"
+    @retained  << "#{report.scale_bytes(report.total_retained_memsize)} (#{report.total_retained} objects)"
+
+    return if ENV['CI']
+
+    require 'fileutils'
+    report_file = File.join(REPORTS_DIR, "#{sanitize(phase)}.txt")
+    FileUtils.mkdir_p(REPORTS_DIR)
+    report.pretty_print(to_file: report_file, scale_bytes: true)
+  end
+
+  def tabulate
+    table = Terminal::Table.new(headings: @headings.unshift('Phase')) do |t|
+      t << @allocated.unshift('Total allocated')
+      t << @retained.unshift('Total retained')
+    end
+
+    puts
+    puts table
+    puts "\nDetailed report(s) saved to #{REPORTS_DIR}/" unless ENV['CI']
+  end
+
+  def sanitize(string)
+    string.downcase.gsub(/[\W]/, '-').squeeze('-')
+  end
 end
 
 Liquid::Template.error_mode = ARGV.first.to_sym if ARGV.first
 
-profiler = ThemeRunner.new
+runner = ThemeRunner.new
-
+Profiler.run do |x|
-profile("Parsing") { profiler.compile }
+  x.profile('parse') { runner.compile }
-profile("Rendering") { profiler.render }
+  x.profile('render') { runner.render }
+  x.tabulate
+end

performance/shopify/comment_form.rb

@@ -12,7 +12,7 @@ class CommentForm < Liquid::Block
     end
   end
 
-  def render(context)
+  def render_to_output_buffer(context, output)
     article = context[@variable_name]
 
     context.stack do
@@ -23,7 +23,9 @@ class CommentForm < Liquid::Block
         'email'  => context['comment.email'],
         'body'   => context['comment.body']
       }
-      wrap_in_form(article, render_all(@nodelist, context))
+
+      output << wrap_in_form(article, render_all(@nodelist, context, output))
+      output
     end
   end
 

performance/shopify/paginate.rb

@@ -21,7 +21,7 @@ class Paginate < Liquid::Block
     end
   end
 
-  def render(context)
+  def render_to_output_buffer(context, output)
     @context = context
 
     context.stack do

test/integration/blank_test.rb

@@ -1,11 +1,10 @@
 require 'test_helper'
 
 class FoobarTag < Liquid::Tag
-  def render(*args)
+  def render_to_output_buffer(context, output)
-    " "
+    output << ' '
+    output
   end
-
-  Liquid::Template.register_tag('foobar', FoobarTag)
 end
 
 class BlankTestFileSystem
@@ -31,7 +30,9 @@ class BlankTest < Minitest::Test
   end
 
   def test_new_tags_are_not_blank_by_default
-    assert_template_result(" " * N, wrap_in_for("{% foobar %}"))
+    with_custom_tag('foobar', FoobarTag) do
+      assert_template_result(" " * N, wrap_in_for("{% foobar %}"))
+    end
   end
 
   def test_loops_are_blank

test/integration/tags/echo_test.rb

@@ -0,0 +1,11 @@
+require 'test_helper'
+
+class EchoTest < Minitest::Test
+  include Liquid
+
+  def test_echo_outputs_its_input
+    assert_template_result('BAR', <<~LIQUID, { 'variable-name' => 'bar' })
+      {%- echo variable-name | upcase -%}
+    LIQUID
+  end
+end

test/integration/tags/include_tag_test.rb

@@ -66,8 +66,9 @@ class CustomInclude < Liquid::Tag
   def parse(tokens)
   end
 
-  def render(context)
+  def render_to_output_buffer(context, output)
-    @template_name[1..-2]
+    output << @template_name[1..-2]
+    output
   end
 end
 

test/integration/tags/liquid_tag_test.rb

@@ -0,0 +1,104 @@
+require 'test_helper'
+
+class LiquidTagTest < Minitest::Test
+  include Liquid
+
+  def test_liquid_tag
+    assert_template_result('1 2 3', <<~LIQUID, 'array' => [1, 2, 3])
+      {%- liquid
+        echo array | join: " "
+      -%}
+    LIQUID
+
+    assert_template_result('1 2 3', <<~LIQUID, 'array' => [1, 2, 3])
+      {%- liquid
+        for value in array
+          echo value
+          unless forloop.last
+            echo " "
+          endunless
+        endfor
+      -%}
+    LIQUID
+
+    assert_template_result('4 8 12 6', <<~LIQUID, 'array' => [1, 2, 3])
+      {%- liquid
+        for value in array
+          assign double_value = value | times: 2
+          echo double_value | times: 2
+          unless forloop.last
+            echo " "
+          endunless
+        endfor
+
+        echo " "
+        echo double_value
+      -%}
+    LIQUID
+
+    assert_template_result('abc', <<~LIQUID)
+      {%- liquid echo "a" -%}
+      b
+      {%- liquid echo "c" -%}
+    LIQUID
+  end
+
+  def test_liquid_tag_errors
+    assert_match_syntax_error("syntax error (line 1): Unknown tag 'error'", <<~LIQUID)
+      {%- liquid error no such tag -%}
+    LIQUID
+
+    assert_match_syntax_error("syntax error (line 7): Unknown tag 'error'", <<~LIQUID)
+      {{ test }}
+
+      {%-
+      liquid
+        for value in array
+
+          error no such tag
+        endfor
+      -%}
+    LIQUID
+
+    assert_match_syntax_error("syntax error (line 2): Unknown tag '!!! the guards are vigilant'", <<~LIQUID)
+      {%- liquid
+        !!! the guards are vigilant
+      -%}
+    LIQUID
+
+    assert_match_syntax_error("syntax error (line 4): 'for' tag was never closed", <<~LIQUID)
+      {%- liquid
+        for value in array
+          echo 'forgot to close the for tag'
+      -%}
+    LIQUID
+  end
+
+  def test_line_number_is_correct_after_a_blank_token
+    assert_match_syntax_error("syntax error (line 3): Unknown tag 'error'", "{% liquid echo ''\n\n error %}")
+    assert_match_syntax_error("syntax error (line 3): Unknown tag 'error'", "{% liquid echo ''\n  \n error %}")
+  end
+
+  def test_cannot_open_blocks_living_past_a_liquid_tag
+    assert_match_syntax_error("syntax error (line 3): 'if' tag was never closed", <<~LIQUID)
+      {%- liquid
+        if true
+      -%}
+      {%- endif -%}
+    LIQUID
+  end
+
+  def test_quirk_can_close_blocks_created_before_a_liquid_tag
+    assert_template_result("42", <<~LIQUID)
+      {%- if true -%}
+      42
+      {%- liquid endif -%}
+    LIQUID
+  end
+
+  def test_liquid_tag_in_raw
+    assert_template_result("{% liquid echo 'test' %}\n", <<~LIQUID)
+      {% raw %}{% liquid echo 'test' %}{% endraw %}
+    LIQUID
+  end
+end

test/test_helper.rb

@@ -14,7 +14,7 @@ if env_mode = ENV['LIQUID_PARSER_MODE']
 end
 Liquid::Template.error_mode = mode
 
-if ENV['LIQUID-C'] == '1'
+if ENV['LIQUID_C'] == '1'
   puts "-- LIQUID C"
   require 'liquid/c'
 end
@@ -37,18 +37,18 @@ module Minitest
     include Liquid
 
     def assert_template_result(expected, template, assigns = {}, message = nil)
-      assert_equal expected, Template.parse(template).render!(assigns), message
+      assert_equal expected, Template.parse(template, line_numbers: true).render!(assigns), message
     end
 
     def assert_template_result_matches(expected, template, assigns = {}, message = nil)
       return assert_template_result(expected, template, assigns, message) unless expected.is_a? Regexp
 
-      assert_match expected, Template.parse(template).render!(assigns), message
+      assert_match expected, Template.parse(template, line_numbers: true).render!(assigns), message
     end
 
     def assert_match_syntax_error(match, template, assigns = {})
       exception = assert_raises(Liquid::SyntaxError) do
-        Template.parse(template).render(assigns)
+        Template.parse(template, line_numbers: true).render(assigns)
       end
       assert_match match, exception.message
     end
@@ -84,6 +84,13 @@ module Minitest
     ensure
       Liquid::Template.error_mode = old_mode
     end
+
+    def with_custom_tag(tag_name, tag_class)
+      Liquid::Template.register_tag(tag_name, tag_class)
+      yield
+    ensure
+      Liquid::Template.tags.delete(tag_name)
+    end
   end
 end
 

test/unit/block_unit_test.rb

@@ -44,10 +44,47 @@ class BlockUnitTest < Minitest::Test
   end
 
   def test_with_custom_tag
-    Liquid::Template.register_tag("testtag", Block)
+    with_custom_tag('testtag', Block) do
-    assert Liquid::Template.parse("{% testtag %} {% endtesttag %}")
+      assert Liquid::Template.parse("{% testtag %} {% endtesttag %}")
-  ensure
+    end
-    Liquid::Template.tags.delete('testtag')
+  end
+
+  def test_custom_block_tags_have_a_default_render_to_output_buffer_method_for_backwards_compatibility
+    klass1 = Class.new(Block) do
+      def render(*)
+        'hello'
+      end
+    end
+
+    with_custom_tag('blabla', klass1) do
+      template = Liquid::Template.parse("{% blabla %} bla {% endblabla %}")
+
+      assert_equal 'hello', template.render
+
+      buf = ''
+      output = template.render({}, output: buf)
+      assert_equal 'hello', output
+      assert_equal 'hello', buf
+      assert_equal buf.object_id, output.object_id
+    end
+
+    klass2 = Class.new(klass1) do
+      def render(*)
+        'foo' + super + 'bar'
+      end
+    end
+
+    with_custom_tag('blabla', klass2) do
+      template = Liquid::Template.parse("{% blabla %} foo {% endblabla %}")
+
+      assert_equal 'foohellobar', template.render
+
+      buf = ''
+      output = template.render({}, output: buf)
+      assert_equal 'foohellobar', output
+      assert_equal 'foohellobar', buf
+      assert_equal buf.object_id, output.object_id
+    end
   end
 
   private

test/unit/tag_unit_test.rb

@@ -18,4 +18,42 @@ class TagUnitTest < Minitest::Test
     tag = Tag.parse("some_tag", "", Tokenizer.new(""), ParseContext.new)
     assert_equal 'some_tag', tag.tag_name
   end
+
+  def test_custom_tags_have_a_default_render_to_output_buffer_method_for_backwards_compatibility
+    klass1 = Class.new(Tag) do
+      def render(*)
+        'hello'
+      end
+    end
+
+    with_custom_tag('blabla', klass1) do
+      template = Liquid::Template.parse("{% blabla %}")
+
+      assert_equal 'hello', template.render
+
+      buf = ''
+      output = template.render({}, output: buf)
+      assert_equal 'hello', output
+      assert_equal 'hello', buf
+      assert_equal buf.object_id, output.object_id
+    end
+
+    klass2 = Class.new(klass1) do
+      def render(*)
+        'foo' + super + 'bar'
+      end
+    end
+
+    with_custom_tag('blabla', klass2) do
+      template = Liquid::Template.parse("{% blabla %}")
+
+      assert_equal 'foohellobar', template.render
+
+      buf = ''
+      output = template.render({}, output: buf)
+      assert_equal 'foohellobar', output
+      assert_equal 'foohellobar', buf
+      assert_equal buf.object_id, output.object_id
+    end
+  end
 end