Add performance rubocop and fixes

Reduce allocations while registering Liquid tags

.github/probots.yml

@@ -0,0 +1,2 @@
+enabled:
+  - cla

.gitignore

@@ -4,6 +4,8 @@
 pkg
 *.rbc
 .rvmrc
+.idea
 .ruby-version
 Gemfile.lock
 .bundle
+.byebug_history

.rubocop.yml

@@ -1,125 +1,10 @@
-inherit_from: ./.rubocop_todo.yml
+inherit_from:
+  - .rubocop.shopify.yml
 
-AllCops:
-  Exclude:
-    - 'performance/shopify/*'
-    - 'pkg/**'
+require: rubocop-performance
 
-Metrics/BlockNesting:
-  Max: 3
-  Exclude:
-    - 'lib/liquid/block_body.rb'
+Performance:
+  Enabled: true
 
-Metrics/ModuleLength:
-  Enabled: false
-
-Metrics/ClassLength:
-  Enabled: false
-
-Lint/AssignmentInCondition:
-  Enabled: false
-
-Lint/AmbiguousOperator:
-  Enabled: false
-
-Lint/AmbiguousRegexpLiteral:
-  Enabled: false
-
-Lint/ParenthesesAsGroupedExpression:
-  Enabled: false
-
-Lint/UnusedBlockArgument:
-  Enabled: false
-
-Lint/EndAlignment:
-  AlignWith: variable
-
-Lint/UnusedMethodArgument:
-  Enabled: false
-
-Style/SingleLineBlockParams:
-  Enabled: false
-
-Style/DoubleNegation:
-  Enabled: false
-
-Style/StringLiteralsInInterpolation:
-  Enabled: false
-
-Style/AndOr:
-  Enabled: false
-
-Style/SignalException:
-  Enabled: false
-
-Style/StringLiterals:
-  Enabled: false
-
-Style/BracesAroundHashParameters:
-  Enabled: false
-
-Style/NumericLiterals:
-  Enabled: false
-
-Style/SpaceInsideBrackets:
-  Enabled: false
-
-Style/SpaceBeforeBlockBraces:
-  Enabled: false
-
-Style/Documentation:
-  Enabled: false
-
-Style/ClassAndModuleChildren:
-  Enabled: false
-
-Style/TrailingComma:
-  Enabled: false
-
-Style/IndentHash:
-  EnforcedStyle: consistent
-
-Style/FormatString:
-  Enabled: false
-
-Style/AlignParameters:
-  EnforcedStyle: with_fixed_indentation
-
-Style/MultilineOperationIndentation:
-  EnforcedStyle: indented
-
-Style/IfUnlessModifier:
-  Enabled: false
-
-Style/RaiseArgs:
-  Enabled: false
-
-Style/DeprecatedHashMethods:
-  Enabled: false
-
-Style/RegexpLiteral:
-  Enabled: false
-
-Style/SymbolLiteral:
-  Enabled: false
-
-Performance/Count:
-  Enabled: false
-
-Style/ConstantName:
-  Enabled: false
-
-Style/CaseIndentation:
-  Enabled: false
-
-Style/ClassVars:
-  Enabled: false
-
-Style/PerlBackrefs:
-  Enabled: false
-
-Style/TrivialAccessors:
-  AllowPredicates: true
-
-Style/WordArray:
-  Enabled: false
+Metrics/LineLength:
+  Enabled: false

.rubocop_todo.yml

@@ -1,72 +0,0 @@
-# This configuration was generated by `rubocop --auto-gen-config`
-# on 2015-06-08 18:16:16 +0000 using RuboCop version 0.32.0.
-# 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
-# versions of RuboCop, may require this file to be generated again.
-
-# Offense count: 5
-Lint/NestedMethodDefinition:
-  Enabled: false
-
-# Offense count: 53
-Metrics/AbcSize:
-  Max: 58
-
-# Offense count: 12
-Metrics/CyclomaticComplexity:
-  Max: 15
-
-# Offense count: 553
-# Configuration parameters: AllowURI, URISchemes.
-Metrics/LineLength:
-  Max: 294
-
-# Offense count: 77
-# Configuration parameters: CountComments.
-Metrics/MethodLength:
-  Max: 46
-
-# Offense count: 6
-Metrics/PerceivedComplexity:
-  Max: 13
-
-# Offense count: 1
-Style/AccessorMethodName:
-  Enabled: false
-
-# Offense count: 1
-# Cop supports --auto-correct.
-Style/ClosingParenthesisIndentation:
-  Enabled: false
-
-# Offense count: 3
-# Configuration parameters: MinBodyLength.
-Style/GuardClause:
-  Enabled: false
-
-# Offense count: 4
-# Configuration parameters: EnforcedStyle, SupportedStyles.
-Style/MethodName:
-  Enabled: false
-
-# Offense count: 1
-Style/MultilineBlockChain:
-  Enabled: false
-
-# Offense count: 2
-# Configuration parameters: EnforcedStyle, MinBodyLength, SupportedStyles.
-Style/Next:
-  Enabled: false
-
-# Offense count: 7
-# Cop supports --auto-correct.
-# Configuration parameters: AllowAsExpressionSeparator.
-Style/Semicolon:
-  Enabled: false
-
-# Offense count: 1
-# Cop supports --auto-correct.
-# Configuration parameters: MaxLineLength.
-Style/WhileUntilModifier:
-  Enabled: false

.travis.yml

@@ -1,12 +1,13 @@
 language: ruby
 
 rvm:
-  - 2.0
-  - 2.1
-  - 2.2
+  - 2.4
+  - 2.5
+  - 2.6
+  - 2.7
   - ruby-head
   - jruby-head
-#  - rbx-2
+  - truffleruby
 
 sudo: false
 
@@ -17,9 +18,13 @@ addons:
 
 matrix:
   allow_failures:
+    - rvm: ruby-head
     - rvm: jruby-head
 
-script: "bundle exec rake"
+install:
+  - bundle install
+
+script: bundle exec rake
 
 notifications:
   disable: true

CONTRIBUTING.md

@@ -4,23 +4,22 @@
 
 * Bugfixes
 * Performance improvements
-* Features which are likely to be useful to the majority of Liquid users
+* Features that are likely to be useful to the majority of Liquid users
 
 ## Things we won't merge
 
-* Code which introduces considerable performance degrations
-* Code which touches performance critical parts of Liquid and comes without benchmarks
-* Features which are not important for most people (we want to keep the core Liquid code small and tidy)
-* Features which can easily be implemented on top of Liquid (for example as a custom filter or custom filesystem)
-* Code which comes without tests
-* Code which breaks existing tests
+* Code that introduces considerable performance degrations
+* Code that touches performance-critical parts of Liquid and comes without benchmarks
+* Features that are not important for most people (we want to keep the core Liquid code small and tidy)
+* Features that can easily be implemented on top of Liquid (for example as a custom filter or custom filesystem)
+* Code that does not include tests
+* Code that breaks existing tests
 
 ## Workflow
 
 * Fork the Liquid repository
 * Create a new branch in your fork
-* If it makes sense, add tests for your code and run a performance benchmark
-* Make sure all tests pass
+* If it makes sense, add tests for your code and/or run a performance benchmark
+* Make sure all tests pass (`bundle exec rake`)
 * Create a pull request
-* In the description, ping one of [@boourns](https://github.com/boourns), [@fw42](https://github.com/fw42), [@camilo](https://github.com/camilo), [@dylanahsmith](https://github.com/dylanahsmith), or [@arthurnn](https://github.com/arthurnn) and ask for a code review.
 

Gemfile

@@ -1,14 +1,26 @@
+# frozen_string_literal: true
+
 source 'https://rubygems.org'
+git_source(:github) do |repo_name|
+  "https://github.com/#{repo_name}.git"
+end
 
 gemspec
-gem 'stackprof', platforms: :mri_21
 
-group :test do
-  gem 'spy', '0.4.1'
+group :benchmark, :test do
   gem 'benchmark-ips'
-  gem 'rubocop', '0.34.2'
+  gem 'memory_profiler'
 
-  platform :mri do
-    gem 'liquid-c', github: 'Shopify/liquid-c', ref: '2570693d8d03faa0df9160ec74348a7149436df3'
+  install_if -> { RUBY_PLATFORM !~ /mingw|mswin|java/ && RUBY_ENGINE != 'truffleruby' } do
+    gem 'stackprof'
+  end
+end
+
+group :test do
+  gem 'rubocop', '~> 0.74.0', require: false
+  gem 'rubocop-performance', require: false
+
+  platform :mri, :truffleruby do
+    gem 'liquid-c', github: 'Shopify/liquid-c', ref: '7ba926791ef8411984d0f3e41c6353fd716041c6'
   end
 end

History.md

@@ -1,8 +1,65 @@
 # Liquid Change Log
 
-## 4.0.0 / not yet released / branch "master"
+## 4.0.3 / 2019-03-12
+
+### Fixed
+* Fix break and continue tags inside included templates in loops (#1072) [Justin Li]
+
+## 4.0.2 / 2019-03-08
 
 ### Changed
+* Add `where` filter (#1026) [Samuel Doiron]
+* Add `ParseTreeVisitor` to iterate the Liquid AST (#1025) [Stephen Paul Weber]
+* Improve `strip_html` performance (#1032) [printercu]
+
+### Fixed
+* Add error checking for invalid combinations of inputs to sort, sort_natural, where, uniq, map, compact filters (#1059) [Garland Zhang]
+* Validate the character encoding in url_decode (#1070) [Clayton Smith]
+
+## 4.0.1 / 2018-10-09
+
+### Changed
+* Add benchmark group in Gemfile (#855) [Jerry Liu]
+* Allow benchmarks to benchmark render by itself (#851) [Jerry Liu]
+* Avoid calling `line_number` on String node when rescuing a render error. (#860) [Dylan Thacker-Smith]
+* Avoid duck typing to detect whether to call render on a node. [Dylan Thacker-Smith]
+* Clarify spelling of `reversed` on `for` block tag (#843) [Mark Crossfield]
+* Replace recursion with loop to avoid potential stack overflow from malicious input (#891, #892) [Dylan Thacker-Smith]
+* Limit block tag nesting to 100 (#894) [Dylan Thacker-Smith]
+* Replace `assert_equal nil` with `assert_nil` (#895) [Dylan Thacker-Smith]
+* Remove Spy Gem (#896) [Dylan Thacker-Smith]
+* Add `collection_name` and `variable_name` reader to `For` block (#909)
+* Symbols render as strings (#920) [Justin Li]
+* Remove default value from Hash objects (#932) [Maxime Bedard]
+* Remove one level of nesting (#944) [Dylan Thacker-Smith]
+* Update Rubocop version (#952) [Justin Li]
+* Add `at_least` and `at_most` filters (#954, #958) [Nithin Bekal]
+* Add a regression test for a liquid-c trim mode bug (#972) [Dylan Thacker-Smith]
+* Use https rather than git protocol to fetch liquid-c [Dylan Thacker-Smith]
+* Add tests against Ruby 2.4 (#963) and 2.5 (#981)
+* Replace RegExp literals with constants (#988) [Ashwin Maroli]
+* Replace unnecessary `#each_with_index` with `#each` (#992) [Ashwin Maroli]
+* Improve the unexpected end delimiter message for block tags. (#1003) [Dylan Thacker-Smith]
+* Refactor and optimize rendering (#1005) [Christopher Aue]
+* Add installation instruction (#1006) [Ben Gift]
+* Remove Circle CI (#1010)
+* Rename deprecated `BigDecimal.new` to `BigDecimal` (#1024) [Koichi ITO]
+* Rename deprecated Rubocop name (#1027) [Justin Li]
+
+### Fixed
+* Handle `join` filter on non String joiners (#857) [Richard Monette]
+* Fix duplicate inclusion condition logic error of `Liquid::Strainer.add_filter` method (#861)
+* Fix `escape`, `url_encode`, `url_decode` not handling non-string values (#898) [Thierry Joyal]
+* Fix raise when variable is defined but nil when using `strict_variables` [Pascal Betz]
+* Fix `sort` and `sort_natural` to handle arrays with nils (#930) [Eric Chan]
+
+## 4.0.0 / 2016-12-14 / branch "4-0-stable"
+
+### Changed
+* Render an opaque internal error by default for non-Liquid::Error (#835) [Dylan Thacker-Smith]
+* Ruby 2.0 support dropped (#832) [Dylan Thacker-Smith]
+* Add to_number Drop method to allow custom drops to work with number filters (#731)
+* Add strict_variables and strict_filters options to detect undefined references (#691)
 * Improve loop performance (#681) [Florian Weingarten]
 * Rename Drop method `before_method` to `liquid_method_missing` (#661) [Thierry Joyal]
 * Add url_decode filter to invert url_encode (#645) [Larry Archer]
@@ -16,9 +73,13 @@
 * Add concat filter to concatenate arrays (#429) [Diogo Beato]
 * Ruby 1.9 support dropped (#491) [Justin Li]
 * Liquid::Template.file_system's read_template_file method is no longer passed the context. (#441) [James Reid-Smith]
-* Remove support for `liquid_methods`
+* Remove `liquid_methods` (See https://github.com/Shopify/liquid/pull/568 for replacement)
+* Liquid::Template.register_filter raises when the module overrides registered public methods as private or protected (#705) [Gaurav Chande]
 
 ### Fixed
+
+* Fix variable names being detected as an operator when starting with contains (#788) [Michael Angell]
+* Fix include tag used with strict_variables (#828) [QuickPay]
 * Fix map filter when value is a Proc (#672) [Guillaume Malette]
 * Fix truncate filter when value is not a string (#672) [Guillaume Malette]
 * Fix behaviour of escape filter when input is nil (#665) [Tanel Jakobsoo]
@@ -213,7 +274,7 @@ Yanked from rubygems, as it contained too many changes that broke compatibility.
 * Fixed bad error reporting when a filter called a method which doesn't exist. Liquid told you that it couldn't find the filter which was obviously misleading [Tobias Luetke]
 * Removed count helper from standard lib. use size [Tobias Luetke]
 * Fixed bug with string filter parameters failing to tolerate commas in strings. [Paul Hammond]
-* Improved filter parameters. Filter parameters are now context sensitive; Types are resolved according to the rules of the context. Multiple parameters are now separated by the Liquid::ArgumentSeparator: , by default [Paul Hammond]
+* Improved filter parameters. Filter parameters are now context sensitive; Types are resolved according to the rules of the context. Multiple parameters are now separated by the Liquid::ARGUMENT_SEPARATOR: , by default [Paul Hammond]
     {{ 'Typo' | link_to: 'http://typo.leetsoft.com', 'Typo - a modern weblog engine' }}
 * Added Liquid::Drop. A base class which you can use for exporting proxy objects to liquid which can acquire more data when used in liquid. [Tobias Luetke]
 

README.md

@@ -42,6 +42,8 @@ Liquid is a template engine which was written with very specific requirements:
 
 ## How to use Liquid
 
+Install Liquid by adding `gem 'liquid'` to your gemfile.
+
 Liquid supports a very simple API based around the Liquid::Template class.
 For standard use you can just pass it the content of a file and call render with a parameters hash.
 
@@ -73,3 +75,34 @@ This is useful for doing things like enabling strict mode only in the theme edit
 
 It is recommended that you enable `:strict` or `:warn` mode on new apps to stop invalid templates from being created.
 It is also recommended that you use it in the template editors of existing apps to give editors better error messages.
+
+### Undefined variables and filters
+
+By default, the renderer doesn't raise or in any other way notify you if some variables or filters are missing, i.e. not passed to the `render` method.
+You can improve this situation by passing `strict_variables: true` and/or `strict_filters: true` options to the `render` method.
+When one of these options is set to true, all errors about undefined variables and undefined filters will be stored in `errors` array of a `Liquid::Template` instance.
+Here are some examples:
+
+```ruby
+template = Liquid::Template.parse("{{x}} {{y}} {{z.a}} {{z.b}}")
+template.render({ 'x' => 1, 'z' => { 'a' => 2 } }, { strict_variables: true })
+#=> '1  2 ' # when a variable is undefined, it's rendered as nil
+template.errors
+#=> [#<Liquid::UndefinedVariable: Liquid error: undefined variable y>, #<Liquid::UndefinedVariable: Liquid error: undefined variable b>]
+```
+
+```ruby
+template = Liquid::Template.parse("{{x | filter1 | upcase}}")
+template.render({ 'x' => 'foo' }, { strict_filters: true })
+#=> '' # when at least one filter in the filter chain is undefined, a whole expression is rendered as nil
+template.errors
+#=> [#<Liquid::UndefinedFilter: Liquid error: undefined filter filter1>]
+```
+
+If you want to raise on a first exception instead of pushing all of them in `errors`, you can use `render!` method:
+
+```ruby
+template = Liquid::Template.parse("{{x}} {{y}}")
+template.render!({ 'x' => 1}, { strict_variables: true })
+#=> Liquid::UndefinedVariable: Liquid error: undefined variable y
+```

Rakefile

@@ -1,29 +1,33 @@
+# frozen_string_literal: true
+
 require 'rake'
 require 'rake/testtask'
-$LOAD_PATH.unshift File.expand_path("../lib", __FILE__)
-require "liquid/version"
+$LOAD_PATH.unshift(File.expand_path('lib', __dir__))
+require 'liquid/version'
 
-task default: [:rubocop, :test]
+task(default: %i[test rubocop])
 
-desc 'run test suite with default parser'
+desc('run test suite with default parser')
 Rake::TestTask.new(:base_test) do |t|
   t.libs << '.' << 'lib' << 'test'
   t.test_files = FileList['test/{integration,unit}/**/*_test.rb']
   t.verbose = false
 end
 
-desc 'run test suite with warn error mode'
+desc('run test suite with warn error mode')
 task :warn_test do
   ENV['LIQUID_PARSER_MODE'] = 'warn'
   Rake::Task['base_test'].invoke
 end
 
 task :rubocop do
-  require 'rubocop/rake_task'
-  RuboCop::RakeTask.new
+  if RUBY_ENGINE == 'ruby'
+    require 'rubocop/rake_task'
+    RuboCop::RakeTask.new
+  end
 end
 
-desc 'runs test suite with both strict and lax parsers'
+desc('runs test suite with both strict and lax parsers')
 task :test do
   ENV['LIQUID_PARSER_MODE'] = 'lax'
   Rake::Task['base_test'].invoke
@@ -32,8 +36,9 @@ task :test do
   Rake::Task['base_test'].reenable
   Rake::Task['base_test'].invoke
 
-  if RUBY_ENGINE == 'ruby'
-    ENV['LIQUID-C'] = '1'
+  if RUBY_ENGINE == 'ruby' || RUBY_ENGINE == 'truffleruby'
+
+    ENV['LIQUID_C'] = '1'
 
     ENV['LIQUID_PARSER_MODE'] = 'lax'
     Rake::Task['base_test'].reenable
@@ -45,9 +50,9 @@ task :test do
   end
 end
 
-task gem: :build
+task(gem: :build)
 task :build do
-  system "gem build liquid.gemspec"
+  system 'gem build liquid.gemspec'
 end
 
 task install: :build do
@@ -56,38 +61,45 @@ end
 
 task release: :build do
   system "git tag -a v#{Liquid::VERSION} -m 'Tagging #{Liquid::VERSION}'"
-  system "git push --tags"
+  system 'git push --tags'
   system "gem push liquid-#{Liquid::VERSION}.gem"
   system "rm liquid-#{Liquid::VERSION}.gem"
 end
 
 namespace :benchmark do
-  desc "Run the liquid benchmark with lax parsing"
+  desc 'Run the liquid benchmark with lax parsing'
   task :run do
-    ruby "./performance/benchmark.rb lax"
+    ruby './performance/benchmark.rb lax'
   end
 
-  desc "Run the liquid benchmark with strict parsing"
+  desc 'Run the liquid benchmark with strict parsing'
   task :strict do
-    ruby "./performance/benchmark.rb strict"
+    ruby './performance/benchmark.rb strict'
   end
 end
 
 namespace :profile do
-  desc "Run the liquid profile/performance coverage"
+  desc 'Run the liquid profile/performance coverage'
   task :run do
-    ruby "./performance/profile.rb"
+    ruby './performance/profile.rb'
   end
 
-  desc "Run the liquid profile/performance coverage with strict parsing"
+  desc 'Run the liquid profile/performance coverage with strict parsing'
   task :strict do
-    ruby "./performance/profile.rb strict"
+    ruby './performance/profile.rb strict'
   end
 end
 
-desc "Run example"
+namespace :memory_profile do
+  desc 'Run memory profiler'
+  task :run do
+    ruby './performance/memory_profile.rb'
+  end
+end
+
+desc('Run example')
 task :example do
-  ruby "-w -d -Ilib example/server/server.rb"
+  ruby '-w -d -Ilib example/server/server.rb'
 end
 
 task :console do

circle.yml

@@ -1,3 +0,0 @@
-machine:
-  ruby:
-    version: ruby-2.0

example/server/example_servlet.rb

@@ -1,6 +1,8 @@
+# frozen_string_literal: true
+
 module ProductsFilter
   def price(integer)
-    sprintf("$%.2d USD", integer / 100.0)
+    format('$%.2d USD', integer / 100.0)
   end
 
   def prettyprint(text)
@@ -28,17 +30,17 @@ class Servlet < LiquidServlet
   private
 
   def products_list
-    [{ 'name' => 'Arbor Draft', 'price' => 39900, 'description' => 'the *arbor draft* is a excellent product' },
-     { 'name' => 'Arbor Element', 'price' => 40000, 'description' => 'the *arbor element* rocks for freestyling' },
-     { 'name' => 'Arbor Diamond', 'price' => 59900, 'description' => 'the *arbor diamond* is a made up product because im obsessed with arbor and have no creativity' }]
+    [{ 'name' => 'Arbor Draft', 'price' => 39_900, 'description' => 'the *arbor draft* is a excellent product' },
+     { 'name' => 'Arbor Element', 'price' => 40_000, 'description' => 'the *arbor element* rocks for freestyling' },
+     { 'name' => 'Arbor Diamond', 'price' => 59_900, 'description' => 'the *arbor diamond* is a made up product because im obsessed with arbor and have no creativity' }]
   end
 
   def more_products_list
-    [{ 'name' => 'Arbor Catalyst', 'price' => 39900, 'description' => 'the *arbor catalyst* is an advanced drop-through for freestyle and flatground performance and versatility' },
-     { 'name' => 'Arbor Fish', 'price' => 40000, 'description' => 'the *arbor fish* is a compact pin that features an extended wheelbase and time-honored teardrop shape' }]
+    [{ 'name' => 'Arbor Catalyst', 'price' => 39_900, 'description' => 'the *arbor catalyst* is an advanced drop-through for freestyle and flatground performance and versatility' },
+     { 'name' => 'Arbor Fish', 'price' => 40_000, 'description' => 'the *arbor fish* is a compact pin that features an extended wheelbase and time-honored teardrop shape' }]
   end
 
   def description
-    "List of Products ~ This is a list of products with price and description."
+    'List of Products ~ This is a list of products with price and description.'
   end
 end

example/server/liquid_servlet.rb

@@ -1,23 +1,28 @@
+# frozen_string_literal: true
+
 class LiquidServlet < WEBrick::HTTPServlet::AbstractServlet
-  def do_GET(req, res)
+  def get(req, res)
     handle(:get, req, res)
   end
 
-  def do_POST(req, res)
+  def post(req, res)
     handle(:post, req, res)
   end
 
+  alias_method :do_GET, :get
+  alias_method :do_POST, :post
+
   private
 
-  def handle(type, req, res)
+  def handle(_type, req, res)
     @request = req
     @response = res
 
     @request.path_info =~ /(\w+)\z/
-    @action = $1 || 'index'
+    @action = Regexp.last_match(1) || 'index'
     @assigns = send(@action) if respond_to?(@action)
 
-    @response['Content-Type'] = "text/html"
+    @response['Content-Type'] = 'text/html'
     @response.status = 200
     @response.body = Liquid::Template.parse(read_template).render(@assigns, filters: [ProductsFilter])
   end

example/server/server.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'webrick'
 require 'rexml/document'
 
@@ -8,5 +10,5 @@ require_relative 'example_servlet'
 # Setup webrick
 server = WEBrick::HTTPServer.new(Port: ARGV[1] || 3000)
 server.mount('/', Servlet)
-trap("INT"){ server.shutdown }
+trap('INT') { server.shutdown }
 server.start

lib/liquid.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2005 Tobias Luetke
 #
 # Permission is hereby granted, free of charge, to any person obtaining
@@ -20,30 +22,32 @@
 # WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 
 module Liquid
-  FilterSeparator             = /\|/
-  ArgumentSeparator           = ','.freeze
-  FilterArgumentSeparator     = ':'.freeze
-  VariableAttributeSeparator  = '.'.freeze
-  TagStart                    = /\{\%/
-  TagEnd                      = /\%\}/
-  VariableSignature           = /\(?[\w\-\.\[\]]\)?/
-  VariableSegment             = /[\w\-]/
-  VariableStart               = /\{\{/
-  VariableEnd                 = /\}\}/
-  VariableIncompleteEnd       = /\}\}?/
-  QuotedString                = /"[^"]*"|'[^']*'/
-  QuotedFragment              = /#{QuotedString}|(?:[^\s,\|'"]|#{QuotedString})+/o
-  TagAttributes               = /(\w+)\s*\:\s*(#{QuotedFragment})/o
-  AnyStartingTag              = /\{\{|\{\%/
-  PartialTemplateParser       = /#{TagStart}.*?#{TagEnd}|#{VariableStart}.*?#{VariableIncompleteEnd}/om
-  TemplateParser              = /(#{PartialTemplateParser}|#{AnyStartingTag})/om
-  VariableParser              = /\[[^\]]+\]|#{VariableSegment}+\??/o
+  FILTER_SEPARATOR = /\|/.freeze
+  ARGUMENT_SEPARATOR = ','
+  FILTER_ARGUMENT_SEPARATOR = ':'
+  VARIABLE_ATTRIBUTE_SEPARATOR = '.'
+  WHITESPACE_CONTROL = '-'
+  TAG_START = /\{\%/.freeze
+  TAG_END = /\%\}/.freeze
+  VARIABLE_SIGNATURE = /\(?[\w\-\.\[\]]\)?/.freeze
+  VARIABLE_SEGMENT = /[\w\-]/.freeze
+  VARIABLE_START = /\{\{/.freeze
+  VARIABLE_END = /\}\}/.freeze
+  VARIABLE_INCOMPLETE_END = /\}\}?/.freeze
+  QUOTED_STRING = /"[^"]*"|'[^']*'/.freeze
+  QUOTED_FRAGMENT = /#{QUOTED_STRING}|(?:[^\s,\|'"]|#{QUOTED_STRING})+/o.freeze
+  TAG_ATTRIBUTES = /(\w+)\s*\:\s*(#{QUOTED_FRAGMENT})/o.freeze
+  ANY_STARTING_TAG = /#{TAG_START}|#{VARIABLE_START}/o.freeze
+  PARTIAL_TEMPLATE_PARSER = /#{TAG_START}.*?#{TAG_END}|#{VARIABLE_START}.*?#{VARIABLE_INCOMPLETE_END}/om.freeze
+  TEMPLATE_PARSER = /(#{PARTIAL_TEMPLATE_PARSER}|#{ANY_STARTING_TAG})/om.freeze
+  VARIABLE_PARSER = /\[[^\]]+\]|#{VARIABLE_SEGMENT}+\??/o.freeze
 
   singleton_class.send(:attr_accessor, :cache_classes)
   self.cache_classes = true
 end
 
-require "liquid/version"
+require 'liquid/version'
+require 'liquid/parse_tree_visitor'
 require 'liquid/lexer'
 require 'liquid/parser'
 require 'liquid/i18n'

lib/liquid/block.rb

@@ -1,5 +1,9 @@
+# frozen_string_literal: true
+
 module Liquid
   class Block < Tag
+    MAX_DEPTH = 100
+
     def initialize(tag_name, markup, options)
       super
       @blank = true
@@ -11,6 +15,7 @@ module Liquid
       end
     end
 
+    # For backwards compatibility
     def render(context)
       @body.render(context)
     end
@@ -24,16 +29,16 @@ module Liquid
     end
 
     def unknown_tag(tag, _params, _tokens)
-      case tag
-      when 'else'.freeze
-        raise SyntaxError.new(parse_context.locale.t("errors.syntax.unexpected_else".freeze,
-          block_name: block_name))
-      when 'end'.freeze
-        raise SyntaxError.new(parse_context.locale.t("errors.syntax.invalid_delimiter".freeze,
-          block_name: block_name,
-          block_delimiter: block_delimiter))
+      if tag == 'else'
+        raise SyntaxError, parse_context.locale.t('errors.syntax.unexpected_else',
+                                                  block_name: block_name)
+      elsif tag.start_with?('end')
+        raise SyntaxError, parse_context.locale.t('errors.syntax.invalid_delimiter',
+                                                  tag: tag,
+                                                  block_name: block_name,
+                                                  block_delimiter: block_delimiter)
       else
-        raise SyntaxError.new(parse_context.locale.t("errors.syntax.unknown_tag".freeze, tag: tag))
+        raise SyntaxError, parse_context.locale.t('errors.syntax.unknown_tag', tag: tag)
       end
     end
 
@@ -48,17 +53,22 @@ module Liquid
     protected
 
     def parse_body(body, tokens)
-      body.parse(tokens, parse_context) do |end_tag_name, end_tag_params|
-        @blank &&= body.blank?
+      raise StackLevelError, 'Nesting too deep' if parse_context.depth >= MAX_DEPTH
 
-        return false if end_tag_name == block_delimiter
-        unless end_tag_name
-          raise SyntaxError.new(parse_context.locale.t("errors.syntax.tag_never_closed".freeze, block_name: block_name))
+      parse_context.depth += 1
+      begin
+        body.parse(tokens, parse_context) do |end_tag_name, end_tag_params|
+          @blank &&= body.blank?
+
+          return false if end_tag_name == block_delimiter
+          raise SyntaxError, parse_context.locale.t('errors.syntax.tag_never_closed', block_name: block_name) unless end_tag_name
+
+          # this tag is not registered with the system
+          # pass it to the current block for special handling or error reporting
+          unknown_tag(end_tag_name, end_tag_params, tokens)
         end
-
-        # this tag is not registered with the system
-        # pass it to the current block for special handling or error reporting
-        unknown_tag(end_tag_name, end_tag_params, tokens)
+      ensure
+        parse_context.depth -= 1
       end
 
       true

lib/liquid/block_body.rb

@@ -1,9 +1,12 @@
+# frozen_string_literal: true
+
 module Liquid
   class BlockBody
-    FullToken = /\A#{TagStart}\s*(\w+)\s*(.*)?#{TagEnd}\z/om
-    ContentOfVariable = /\A#{VariableStart}(.*)#{VariableEnd}\z/om
-    TAGSTART = "{%".freeze
-    VARSTART = "{{".freeze
+    FULL_TOKEN = /\A#{TAG_START}#{WHITESPACE_CONTROL}?\s*(\w+)\s*(.*?)#{WHITESPACE_CONTROL}?#{TAG_END}\z/om.freeze
+    CONTENT_OF_VARIABLE = /\A#{VARIABLE_START}#{WHITESPACE_CONTROL}?(.*?)#{WHITESPACE_CONTROL}?#{VARIABLE_END}\z/om.freeze
+    WHITESPACE_OR_NOTHING = /\A\s*\z/.freeze
+    TAG_START = '{%'
+    VAR_START = '{{'
 
     attr_reader :nodelist
 
@@ -14,33 +17,34 @@ module Liquid
 
     def parse(tokenizer, parse_context)
       parse_context.line_number = tokenizer.line_number
-      while token = tokenizer.shift
-        unless token.empty?
-          case
-          when token.start_with?(TAGSTART)
-            if token =~ FullToken
-              tag_name = $1
-              markup = $2
-              # fetch the tag from registered blocks
-              if tag = registered_tags[tag_name]
-                new_tag = tag.parse(tag_name, markup, tokenizer, parse_context)
-                @blank &&= new_tag.blank?
-                @nodelist << new_tag
-              else
-                # end parsing if we reach an unknown tag and let the caller decide
-                # determine how to proceed
-                return yield tag_name, markup
-              end
-            else
-              raise_missing_tag_terminator(token, parse_context)
-            end
-          when token.start_with?(VARSTART)
-            @nodelist << create_variable(token, parse_context)
-            @blank = false
-          else
-            @nodelist << token
-            @blank &&= !!(token =~ /\A\s*\z/)
+      while (token = tokenizer.shift)
+        next if token.empty?
+
+        case
+        when token.start_with?(TAG_START)
+          whitespace_handler(token, parse_context)
+          raise_missing_tag_terminator(token, parse_context) unless token =~ FULL_TOKEN
+          tag_name = Regexp.last_match(1)
+          markup = Regexp.last_match(2)
+          # fetch the tag from registered blocks
+          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
+        when token.start_with?(VAR_START)
+          whitespace_handler(token, parse_context)
+          @nodelist << create_variable(token, parse_context)
+          @blank = false
+        else
+          token.lstrip! if parse_context.trim_whitespace
+          parse_context.trim_whitespace = false
+          @nodelist << token
+          @blank &&= token.match?(WHITESPACE_OR_NOTHING)
         end
         parse_context.line_number = tokenizer.line_number
       end
@@ -48,57 +52,75 @@ module Liquid
       yield nil, nil
     end
 
+    def whitespace_handler(token, parse_context)
+      if token[2] == WHITESPACE_CONTROL
+        previous_token = @nodelist.last
+        previous_token.rstrip! if previous_token.is_a?(String)
+      end
+      parse_context.trim_whitespace = (token[-3] == WHITESPACE_CONTROL)
+    end
+
     def blank?
       @blank
     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
 
-      @nodelist.each do |token|
-        # Break out if we have any unhanded interrupts.
-        break if context.interrupt?
+      idx = 0
+      while (node = @nodelist[idx])
+        previous_output_size = output.bytesize
 
-        begin
+        case node
+        when String
+          output << node
+        when Variable
+          render_node(context, output, node)
+        when Block
+          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
           # Interrupt is any command that stops block execution such as {% break %}
           # or {% continue %}
-          if token.is_a?(Continue) || token.is_a?(Break)
-            context.push_interrupt(token.interrupt)
-            break
-          end
-
-          node_output = render_node(token, context)
-
-          unless token.is_a?(Block) && token.blank?
-            output << node_output
-          end
-        rescue MemoryError => e
-          raise e
-        rescue ::StandardError => e
-          output << context.handle_error(e, token.line_number)
+          context.push_interrupt(node.interrupt)
+          break
+        else # Other non-Block tags
+          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(node, context)
-      node_output = (node.respond_to?(:render) ? node.render(context) : node)
-      node_output = node_output.is_a?(Array) ? node_output.join : node_output.to_s
+    def render_node(context, output, node)
+      node.render_to_output_buffer(context, output)
+    rescue UndefinedVariable, UndefinedDropMethod, UndefinedFilter => e
+      context.handle_error(e, node.line_number)
+    rescue ::StandardError => e
+      line_number = node.is_a?(String) ? nil : node.line_number
+      output << context.handle_error(e, line_number)
+    end
 
-      context.resource_limits.render_length += node_output.length
-      if context.resource_limits.reached?
-        raise MemoryError.new("Memory limits exceeded".freeze)
-      end
-      node_output
+    def raise_if_resource_limits_reached(context, length)
+      context.resource_limits.render_length += length
+      return unless context.resource_limits.reached?
+
+      raise MemoryError, 'Memory limits exceeded'
     end
 
     def create_variable(token, parse_context)
-      token.scan(ContentOfVariable) do |content|
+      token.scan(CONTENT_OF_VARIABLE) do |content|
         markup = content.first
         return Variable.new(markup, parse_context)
       end
@@ -106,11 +128,11 @@ module Liquid
     end
 
     def raise_missing_tag_terminator(token, parse_context)
-      raise SyntaxError.new(parse_context.locale.t("errors.syntax.tag_termination".freeze, token: token, tag_end: TagEnd.inspect))
+      raise SyntaxError, parse_context.locale.t('errors.syntax.tag_termination', token: token, tag_end: TAG_END.inspect)
     end
 
     def raise_missing_variable_terminator(token, parse_context)
-      raise SyntaxError.new(parse_context.locale.t("errors.syntax.variable_termination".freeze, token: token, tag_end: VariableEnd.inspect))
+      raise SyntaxError, parse_context.locale.t('errors.syntax.variable_termination', token: token, tag_end: VARIABLE_END.inspect)
     end
 
     def registered_tags

lib/liquid/condition.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Liquid
   # Container for liquid nodes which conveniently wraps decision making logic
   #
@@ -7,50 +9,56 @@ module Liquid
   #   c.evaluate #=> true
   #
   class Condition #:nodoc:
-    @@operators = {
-      '=='.freeze => ->(cond, left, right) {  cond.send(:equal_variables, left, right) },
-      '!='.freeze => ->(cond, left, right) { !cond.send(:equal_variables, left, right) },
-      '<>'.freeze => ->(cond, left, right) { !cond.send(:equal_variables, left, right) },
-      '<'.freeze  => :<,
-      '>'.freeze  => :>,
-      '>='.freeze => :>=,
-      '<='.freeze => :<=,
-      'contains'.freeze => lambda do |cond, left, right|
+    @operators = {
+      '==' => ->(cond, left, right) {  cond.send(:equal_variables, left, right) },
+      '!=' => ->(cond, left, right) { !cond.send(:equal_variables, left, right) },
+      '<>' => ->(cond, left, right) { !cond.send(:equal_variables, left, right) },
+      '<' => :<,
+      '>' => :>,
+      '>=' => :>=,
+      '<=' => :<=,
+      'contains' => lambda do |_cond, left, right|
         if left && right && left.respond_to?(:include?)
           right = right.to_s if left.is_a?(String)
           left.include?(right)
         else
           false
         end
-      end
+      end,
     }
 
-    def self.operators
-      @@operators
+    class << self
+      attr_accessor :operators
     end
 
-    attr_reader :attachment
+    attr_reader :attachment, :child_condition
     attr_accessor :left, :operator, :right
 
     def initialize(left = nil, operator = nil, right = nil)
       @left = left
       @operator = operator
       @right = right
-      @child_relation  = nil
+      @child_relation = nil
       @child_condition = nil
     end
 
     def evaluate(context = Context.new)
-      result = interpret_condition(left, right, operator, context)
+      condition = self
+      result = nil
+      loop do
+        result = interpret_condition(condition.left, condition.right, condition.operator, context)
 
-      case @child_relation
-      when :or
-        result || @child_condition.evaluate(context)
-      when :and
-        result && @child_condition.evaluate(context)
-      else
-        result
+        case condition.child_relation
+        when :or
+          break if result
+        when :and
+          break unless result
+        else
+          break
+        end
+        condition = condition.child_condition
       end
+      result
     end
 
     def or(condition)
@@ -72,9 +80,13 @@ module Liquid
     end
 
     def inspect
-      "#<Condition #{[@left, @operator, @right].compact.join(' '.freeze)}>"
+      "#<Condition #{[@left, @operator, @right].compact.join(' ')}>"
     end
 
+    protected
+
+    attr_reader :child_relation
+
     private
 
     def equal_variables(left, right)
@@ -106,18 +118,27 @@ module Liquid
       left = context.evaluate(left)
       right = context.evaluate(right)
 
-      operation = self.class.operators[op] || raise(Liquid::ArgumentError.new("Unknown operator #{op}"))
+      operation = self.class.operators[op] || raise(Liquid::ArgumentError, "Unknown operator #{op}")
 
       if operation.respond_to?(:call)
         operation.call(self, left, right)
-      elsif left.respond_to?(operation) && right.respond_to?(operation)
+      elsif left.respond_to?(operation) && right.respond_to?(operation) && !left.is_a?(Hash) && !right.is_a?(Hash)
         begin
           left.send(operation, right)
         rescue ::ArgumentError => e
-          raise Liquid::ArgumentError.new(e.message)
+          raise Liquid::ArgumentError, e.message
         end
       end
     end
+
+    class ParseTreeVisitor < Liquid::ParseTreeVisitor
+      def children
+        [
+          @node.left, @node.right,
+          @node.child_condition, @node.attachment
+        ].compact
+      end
+    end
   end
 
   class ElseCondition < Condition

lib/liquid/context.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Liquid
   # Context keeps the variable stack and resolves variables, as well as keywords
   #
@@ -13,7 +15,7 @@ module Liquid
   #   context['bob']  #=> nil  class Context
   class Context
     attr_reader :scopes, :errors, :registers, :environments, :resource_limits
-    attr_accessor :exception_handler, :template_name, :partial, :global_filter
+    attr_accessor :exception_renderer, :template_name, :partial, :global_filter, :strict_variables, :strict_filters
 
     def initialize(environments = {}, outer_scope = {}, registers = {}, rethrow_errors = false, resource_limits = nil)
       @environments     = [environments].flatten
@@ -21,14 +23,14 @@ module Liquid
       @registers        = registers
       @errors           = []
       @partial          = false
+      @strict_variables = false
       @resource_limits  = resource_limits || ResourceLimits.new(Template.default_resource_limits)
       squash_instance_assigns_with_environments
 
       @this_stack_used = false
 
-      if rethrow_errors
-        self.exception_handler = ->(e) { raise }
-      end
+      self.exception_renderer = Template.default_exception_renderer
+      self.exception_renderer = ->(_e) { raise } if rethrow_errors
 
       @interrupts = []
       @filters = []
@@ -73,30 +75,11 @@ module Liquid
     end
 
     def handle_error(e, line_number = nil)
-      if e.is_a?(Liquid::Error)
-        e.template_name ||= template_name
-        e.line_number ||= line_number
-      end
-
-      output = nil
-
-      if exception_handler
-        result = exception_handler.call(e)
-        case result
-        when Exception
-          e = result
-          if e.is_a?(Liquid::Error)
-            e.template_name ||= template_name
-            e.line_number ||= line_number
-          end
-        when String
-          output = result
-        else
-          raise if result
-        end
-      end
+      e = internal_error unless e.is_a?(Liquid::Error)
+      e.template_name ||= template_name
+      e.line_number ||= line_number
       errors.push(e)
-      output || Liquid::Error.render(e)
+      exception_renderer.call(e).to_s
     end
 
     def invoke(method, *args)
@@ -106,7 +89,7 @@ module Liquid
     # Push new local scope on the stack. use <tt>Context#stack</tt> instead
     def push(new_scope = {})
       @scopes.unshift(new_scope)
-      raise StackLevelError, "Nesting too deep".freeze if @scopes.length > 100
+      raise StackLevelError, 'Nesting too deep' if @scopes.length > Block::MAX_DEPTH
     end
 
     # Merge a hash of variables in the current local scope
@@ -117,6 +100,7 @@ module Liquid
     # Pop from the stack. use <tt>Context#stack</tt> instead
     def pop
       raise ContextError if @scopes.size == 1
+
       @scopes.shift
     end
 
@@ -177,7 +161,7 @@ module Liquid
     end
 
     # Fetches an object starting at the local scope and then moving up the hierachy
-    def find_variable(key)
+    def find_variable(key, raise_on_not_found: true)
       # This was changed from find() to find_index() because this is a very hot
       # path and find_index() is optimized in MRI to reduce object allocation
       index = @scopes.find_index { |s| s.key?(key) }
@@ -187,8 +171,10 @@ module Liquid
 
       if scope.nil?
         @environments.each do |e|
-          variable = lookup_and_evaluate(e, key)
-          unless variable.nil?
+          variable = lookup_and_evaluate(e, key, raise_on_not_found: raise_on_not_found)
+          # When lookup returned a value OR there is no value but the lookup also did not raise
+          # then it is the value we are looking for.
+          if !variable.nil? || @strict_variables && raise_on_not_found
             scope = e
             break
           end
@@ -196,7 +182,7 @@ module Liquid
       end
 
       scope ||= @environments.last || @scopes.last
-      variable ||= lookup_and_evaluate(scope, key)
+      variable ||= lookup_and_evaluate(scope, key, raise_on_not_found: raise_on_not_found)
 
       variable = variable.to_liquid
       variable.context = self if variable.respond_to?(:context=)
@@ -204,9 +190,13 @@ module Liquid
       variable
     end
 
-    def lookup_and_evaluate(obj, key)
-      if (value = obj[key]).is_a?(Proc) && obj.respond_to?(:[]=)
-        obj[key] = (value.arity == 0) ? value.call : value.call(self)
+    def lookup_and_evaluate(obj, key, raise_on_not_found: true)
+      raise Liquid::UndefinedVariable, "undefined variable #{key}" if @strict_variables && raise_on_not_found && obj.respond_to?(:key?) && !obj.key?(key)
+
+      value = obj[key]
+
+      if value.is_a?(Proc) && obj.respond_to?(:[]=)
+        obj[key] = value.arity == 0 ? value.call : value.call(self)
       else
         value
       end
@@ -214,6 +204,13 @@ module Liquid
 
     private
 
+    def internal_error
+      # raise and catch to set backtrace and cause on exception
+      raise Liquid::InternalError, 'internal'
+    rescue Liquid::InternalError => e
+      e
+    end
+
     def squash_instance_assigns_with_environments
       @scopes.last.each_key do |k|
         @environments.each do |env|

lib/liquid/document.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Liquid
   class Document < BlockBody
     def self.parse(tokens, parse_context)
@@ -7,7 +9,7 @@ module Liquid
     end
 
     def parse(tokens, parse_context)
-      super do |end_tag_name, end_tag_params|
+      super do |end_tag_name, _end_tag_params|
         unknown_tag(end_tag_name, parse_context) if end_tag_name
       end
     rescue SyntaxError => e
@@ -17,10 +19,10 @@ module Liquid
 
     def unknown_tag(tag, parse_context)
       case tag
-      when 'else'.freeze, 'end'.freeze
-        raise SyntaxError.new(parse_context.locale.t("errors.syntax.unexpected_outer_tag".freeze, tag: tag))
+      when 'else', 'end'
+        raise SyntaxError, parse_context.locale.t('errors.syntax.unexpected_outer_tag', tag: tag)
       else
-        raise SyntaxError.new(parse_context.locale.t("errors.syntax.unknown_tag".freeze, tag: tag))
+        raise SyntaxError, parse_context.locale.t('errors.syntax.unknown_tag', tag: tag)
       end
     end
   end

lib/liquid/drop.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'set'
 
 module Liquid
@@ -24,8 +26,10 @@ module Liquid
     attr_writer :context
 
     # Catch all for the method
-    def liquid_method_missing(_method)
-      nil
+    def liquid_method_missing(method)
+      return nil unless @context&.strict_variables
+
+      raise Liquid::UndefinedDropMethod, "undefined method #{method}"
     end
 
     # called by liquid to invoke a drop
@@ -61,16 +65,17 @@ module Liquid
     end
 
     def self.invokable_methods
-      unless @invokable_methods
+      @invokable_methods ||= begin
         blacklist = Liquid::Drop.public_instance_methods + [:each]
+
         if include?(Enumerable)
           blacklist += Enumerable.public_instance_methods
-          blacklist -= [:sort, :count, :first, :min, :max, :include?]
+          blacklist -= %i[sort count first min max include?]
         end
+
         whitelist = [:to_liquid] + (public_instance_methods - blacklist)
-        @invokable_methods = Set.new(whitelist.map(&:to_s))
+        Set.new(whitelist.map(&:to_s))
       end
-      @invokable_methods
     end
   end
 end

lib/liquid/errors.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Liquid
   class Error < ::StandardError
     attr_accessor :line_number
@@ -5,43 +7,35 @@ module Liquid
     attr_accessor :markup_context
 
     def to_s(with_prefix = true)
-      str = ""
+      str = +''
       str << message_prefix if with_prefix
       str << super()
 
       if markup_context
-        str << " "
+        str << ' '
         str << markup_context
       end
 
       str
     end
 
-    def self.render(e)
-      if e.is_a?(Liquid::Error)
-        e.to_s
-      else
-        "Liquid error: #{e}"
-      end
-    end
-
     private
 
     def message_prefix
-      str = ""
-      if is_a?(SyntaxError)
-        str << "Liquid syntax error"
+      str = +''
+      str << if is_a?(SyntaxError)
+        'Liquid syntax error'
       else
-        str << "Liquid error"
+        'Liquid error'
       end
 
       if line_number
-        str << " ("
-        str << template_name << " " if template_name
-        str << "line " << line_number.to_s << ")"
+        str << ' ('
+        str << template_name << ' ' if template_name
+        str << 'line ' << line_number.to_s << ')'
       end
 
-      str << ": "
+      str << ': '
       str
     end
   end
@@ -56,4 +50,9 @@ module Liquid
   MemoryError = Class.new(Error)
   ZeroDivisionError = Class.new(Error)
   FloatDomainError = Class.new(Error)
+  UndefinedVariable = Class.new(Error)
+  UndefinedDropMethod = Class.new(Error)
+  UndefinedFilter = Class.new(Error)
+  MethodOverrideError = Class.new(Error)
+  InternalError = Class.new(Error)
 end

lib/liquid/expression.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Liquid
   class Expression
     class MethodLiteral
@@ -14,28 +16,32 @@ module Liquid
     end
 
     LITERALS = {
-      nil => nil, 'nil'.freeze => nil, 'null'.freeze => nil, ''.freeze => nil,
-      'true'.freeze  => true,
-      'false'.freeze => false,
-      'blank'.freeze => MethodLiteral.new(:blank?, '').freeze,
-      'empty'.freeze => MethodLiteral.new(:empty?, '').freeze
-    }
+      nil => nil, 'nil' => nil, 'null' => nil, '' => nil,
+      'true' => true,
+      'false' => false,
+      'blank' => MethodLiteral.new(:blank?, '').freeze,
+      'empty' => MethodLiteral.new(:empty?, '').freeze
+    }.freeze
+
+    SINGLE_QUOTED_STRING = /\A'(.*)'\z/m.freeze
+    DOUBLE_QUOTED_STRING = /\A"(.*)"\z/m.freeze
+    INTEGERS_REGEX       = /\A(-?\d+)\z/.freeze
+    FLOATS_REGEX         = /\A(-?\d[\d\.]+)\z/.freeze
+    RANGES_REGEX         = /\A\((\S+)\.\.(\S+)\)\z/.freeze
 
     def self.parse(markup)
       if LITERALS.key?(markup)
         LITERALS[markup]
       else
         case markup
-        when /\A'(.*)'\z/m # Single quoted strings
-          $1
-        when /\A"(.*)"\z/m # Double quoted strings
-          $1
-        when /\A(-?\d+)\z/ # Integer and floats
-          $1.to_i
-        when /\A\((\S+)\.\.(\S+)\)\z/ # Ranges
-          RangeLookup.parse($1, $2)
-        when /\A(-?\d[\d\.]+)\z/ # Floats
-          $1.to_f
+        when SINGLE_QUOTED_STRING, DOUBLE_QUOTED_STRING
+          Regexp.last_match(1)
+        when INTEGERS_REGEX
+          Regexp.last_match(1).to_i
+        when RANGES_REGEX
+          RangeLookup.parse(Regexp.last_match(1), Regexp.last_match(2))
+        when FLOATS_REGEX
+          Regexp.last_match(1).to_f
         else
           VariableLookup.parse(markup)
         end

lib/liquid/extensions.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'time'
 require 'date'
 
@@ -7,6 +9,12 @@ class String # :nodoc:
   end
 end
 
+class Symbol # :nodoc:
+  def to_liquid
+    to_s
+  end
+end
+
 class Array # :nodoc:
   def to_liquid
     self
@@ -25,6 +33,12 @@ class Numeric # :nodoc:
   end
 end
 
+class Range # :nodoc:
+  def to_liquid
+    self
+  end
+end
+
 class Time # :nodoc:
   def to_liquid
     self

lib/liquid/file_system.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Liquid
   # A Liquid file system is a way to let your templates retrieve other templates for use with the include tag.
   #
@@ -8,14 +10,14 @@ module Liquid
   #
   # Example:
   #
-  # Liquid::Template.file_system = Liquid::LocalFileSystem.new(template_path)
-  # liquid = Liquid::Template.parse(template)
+  #   Liquid::Template.file_system = Liquid::LocalFileSystem.new(template_path)
+  #   liquid = Liquid::Template.parse(template)
   #
   # This will parse the template with a LocalFileSystem implementation rooted at 'template_path'.
   class BlankFileSystem
     # Called by Liquid to retrieve a template file
     def read_template_file(_template_path)
-      raise FileSystemError, "This liquid context does not allow includes."
+      raise FileSystemError, 'This liquid context does not allow includes.'
     end
   end
 
@@ -26,10 +28,10 @@ module Liquid
   #
   # Example:
   #
-  # file_system = Liquid::LocalFileSystem.new("/some/path")
+  #   file_system = Liquid::LocalFileSystem.new("/some/path")
   #
-  # file_system.full_path("mypartial")       # => "/some/path/_mypartial.liquid"
-  # file_system.full_path("dir/mypartial")   # => "/some/path/dir/_mypartial.liquid"
+  #   file_system.full_path("mypartial")       # => "/some/path/_mypartial.liquid"
+  #   file_system.full_path("dir/mypartial")   # => "/some/path/dir/_mypartial.liquid"
   #
   # Optionally in the second argument you can specify a custom pattern for template filenames.
   # The Kernel::sprintf format specification is used.
@@ -37,14 +39,14 @@ module Liquid
   #
   # Example:
   #
-  # file_system = Liquid::LocalFileSystem.new("/some/path", "%s.html")
+  #   file_system = Liquid::LocalFileSystem.new("/some/path", "%s.html")
   #
-  # file_system.full_path("index") # => "/some/path/index.html"
+  #   file_system.full_path("index") # => "/some/path/index.html"
   #
   class LocalFileSystem
     attr_accessor :root
 
-    def initialize(root, pattern = "_%s.liquid".freeze)
+    def initialize(root, pattern = '_%s.liquid')
       @root = root
       @pattern = pattern
     end
@@ -57,15 +59,15 @@ module Liquid
     end
 
     def full_path(template_path)
-      raise FileSystemError, "Illegal template name '#{template_path}'" unless template_path =~ /\A[^.\/][a-zA-Z0-9_\/]+\z/
+      raise FileSystemError, "Illegal template name '#{template_path}'" unless template_path =~ %r{\A[^./][a-zA-Z0-9_/]+\z}
 
-      full_path = if template_path.include?('/'.freeze)
+      full_path = if template_path.include?('/')
         File.join(root, File.dirname(template_path), @pattern % File.basename(template_path))
       else
         File.join(root, @pattern % template_path)
       end
 
-      raise FileSystemError, "Illegal template path '#{File.expand_path(full_path)}'" unless File.expand_path(full_path) =~ /\A#{File.expand_path(root)}/
+      raise FileSystemError, "Illegal template path '#{File.expand_path(full_path)}'" unless File.expand_path(full_path).start_with?(File.expand_path(root))
 
       full_path
     end

lib/liquid/forloop_drop.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Liquid
   class ForloopDrop < Drop
     def initialize(name, length, parentloop)

lib/liquid/i18n.rb

@@ -1,8 +1,10 @@
+# frozen_string_literal: true
+
 require 'yaml'
 
 module Liquid
   class I18n
-    DEFAULT_LOCALE = File.join(File.expand_path(__dir__), "locales", "en.yml")
+    DEFAULT_LOCALE = File.join(File.expand_path(__dir__), 'locales', 'en.yml')
 
     TranslationError = Class.new(StandardError)
 
@@ -26,13 +28,13 @@ module Liquid
     def interpolate(name, vars)
       name.gsub(/%\{(\w+)\}/) do
         # raise TranslationError, "Undefined key #{$1} for interpolation in translation #{name}"  unless vars[$1.to_sym]
-        "#{vars[$1.to_sym]}"
+        (vars[Regexp.last_match(1).to_sym]).to_s
       end
     end
 
     def deep_fetch_translation(name)
-      name.split('.'.freeze).reduce(locale) do |level, cur|
-        level[cur] or raise TranslationError, "Translation for #{name} does not exist in locale #{path}"
+      name.split('.').reduce(locale) do |level, cur|
+        level[cur] || raise(TranslationError, "Translation for #{name} does not exist in locale #{path}")
       end
     end
   end

lib/liquid/interrupts.rb

@@ -1,16 +1,18 @@
+# frozen_string_literal: true
+
 module Liquid
   # An interrupt is any command that breaks processing of a block (ex: a for loop).
   class Interrupt
     attr_reader :message
 
     def initialize(message = nil)
-      @message = message || "interrupt".freeze
+      @message = message || 'interrupt'
     end
   end
 
   # Interrupt that is thrown whenever a {% break %} is called.
-  class BreakInterrupt < Interrupt; end
+  class BreakInterrupt < RuntimeError; end
 
   # Interrupt that is thrown whenever a {% continue %} is called.
-  class ContinueInterrupt < Interrupt; end
+  class ContinueInterrupt < RuntimeError; end
 end

lib/liquid/legacy.rb

@@ -0,0 +1,79 @@
+# frozen_string_literal: true
+
+module Liquid
+  FilterSeparator = FILTER_SEPARATOR
+  ArgumentSeparator = ARGUMENT_SEPARATOR
+  FilterArgumentSeparator = FILTER_ARGUMENT_SEPARATOR
+  VariableAttributeSeparator = VARIABLE_ATTRIBUTE_SEPARATOR
+  WhitespaceControl = WHITESPACE_CONTROL
+  TagStart = TAG_START
+  TagEnd = TAG_END
+  VariableSignature = VARIABLE_SIGNATURE
+  VariableSegment = VARIABLE_SEGMENT
+  VariableStart = VARIABLE_START
+  VariableEnd = VARIABLE_END
+  VariableIncompleteEnd = VARIABLE_INCOMPLETE_END
+  QuotedString = QUOTED_STRING
+  QuotedFragment = QUOTED_FRAGMENT
+  TagAttributes = TAG_ATTRIBUTES
+  AnyStartingTag = ANY_STARTING_TAG
+  PartialTemplateParser = PARTIAL_TEMPLATE_PARSER
+  TemplateParser = TEMPLATE_PARSER
+  VariableParser = VARIABLE_PARSER
+
+  class BlockBody
+    FullToken = FULL_TOKEN
+    ContentOfVariable = CONTENT_OF_VARIABLE
+    WhitespaceOrNothing = WHITESPACE_OR_NOTHING
+    TAGSTART = TAG_START
+    VARSTART = VAR_START
+  end
+
+  class Assign < Tag
+    Syntax = SYNTAX
+  end
+
+  class Capture < Block
+    Syntax = SYNTAX
+  end
+
+  class Case < Block
+    Syntax     = SYNTAX
+    WhenSyntax = WHEN_SYNTAX
+  end
+
+  class Cycle < Tag
+    SimpleSyntax = SIMPLE_SYNTAX
+    NamedSyntax  = NAMED_SYNTAX
+  end
+
+  class For < Block
+    Syntax = SYNTAX
+  end
+
+  class If < Block
+    Syntax = SYNTAX
+    ExpressionsAndOperators = EXPRESSIONS_AND_OPERATORS
+  end
+
+  class Include < Tag
+    Syntax = SYNTAX
+  end
+
+  class Raw < Block
+    Syntax = SYNTAX
+    FullTokenPossiblyInvalid = FULL_TOKEN_POSSIBLY_INVALID
+  end
+
+  class TableRow < Block
+    Syntax = SYNTAX
+  end
+
+  class Variable
+    FilterMarkupRegex = FILTER_MARKUP_REGEX
+    FilterParser = FILTER_PARSER
+    FilterArgsRegex = FILTER_ARGS_REGEX
+    JustTagAttributes = JUST_TAG_ATTRIBUTES
+    MarkupWithQuotedFragment = MARKUP_WITH_QUOTED_FRAGMENT
+  end
+end

lib/liquid/lexer.rb

@@ -1,44 +1,48 @@
-require "strscan"
+# frozen_string_literal: true
+
+require 'strscan'
 module Liquid
   class Lexer
     SPECIALS = {
-      '|'.freeze => :pipe,
-      '.'.freeze => :dot,
-      ':'.freeze => :colon,
-      ','.freeze => :comma,
-      '['.freeze => :open_square,
-      ']'.freeze => :close_square,
-      '('.freeze => :open_round,
-      ')'.freeze => :close_round,
-      '?'.freeze => :question,
-      '-'.freeze => :dash
-    }
-    IDENTIFIER = /[a-zA-Z_][\w-]*\??/
-    SINGLE_STRING_LITERAL = /'[^\']*'/
-    DOUBLE_STRING_LITERAL = /"[^\"]*"/
-    NUMBER_LITERAL = /-?\d+(\.\d+)?/
-    DOTDOT = /\.\./
-    COMPARISON_OPERATOR = /==|!=|<>|<=?|>=?|contains/
+      '|' => :pipe,
+      '.' => :dot,
+      ':' => :colon,
+      ',' => :comma,
+      '[' => :open_square,
+      ']' => :close_square,
+      '(' => :open_round,
+      ')' => :close_round,
+      '?' => :question,
+      '-' => :dash,
+    }.freeze
+    IDENTIFIER = /[a-zA-Z_][\w-]*\??/.freeze
+    SINGLE_STRING_LITERAL = /'[^\']*'/.freeze
+    DOUBLE_STRING_LITERAL = /"[^\"]*"/.freeze
+    NUMBER_LITERAL = /-?\d+(\.\d+)?/.freeze
+    DOTDOT = /\.\./.freeze
+    COMPARISON_OPERATOR = /==|!=|<>|<=?|>=?|contains(?=\s)/.freeze
+    WHITESPACE_OR_NOTHING = /\s*/.freeze
 
     def initialize(input)
-      @ss = StringScanner.new(input.rstrip)
+      @ss = StringScanner.new(input)
     end
 
     def tokenize
       @output = []
 
       until @ss.eos?
-        @ss.skip(/\s*/)
-        tok = case
-        when t = @ss.scan(COMPARISON_OPERATOR) then [:comparison, t]
-        when t = @ss.scan(SINGLE_STRING_LITERAL) then [:string, t]
-        when t = @ss.scan(DOUBLE_STRING_LITERAL) then [:string, t]
-        when t = @ss.scan(NUMBER_LITERAL) then [:number, t]
-        when t = @ss.scan(IDENTIFIER) then [:id, t]
-        when t = @ss.scan(DOTDOT) then [:dotdot, t]
+        @ss.skip(WHITESPACE_OR_NOTHING)
+        break if @ss.eos?
+
+        tok = if (t = @ss.scan(COMPARISON_OPERATOR)) then [:comparison, t]
+        elsif (t = @ss.scan(SINGLE_STRING_LITERAL)) then [:string, t]
+        elsif (t = @ss.scan(DOUBLE_STRING_LITERAL)) then [:string, t]
+        elsif (t = @ss.scan(NUMBER_LITERAL)) then [:number, t]
+        elsif (t = @ss.scan(IDENTIFIER)) then [:id, t]
+        elsif (t = @ss.scan(DOTDOT)) then [:dotdot, t]
         else
           c = @ss.getch
-          if s = SPECIALS[c]
+          if (s = SPECIALS[c])
             [s, c]
           else
             raise SyntaxError, "Unexpected character #{c}"

lib/liquid/locales/en.yml

@@ -14,7 +14,7 @@
       if: "Syntax Error in tag 'if' - Valid syntax: if [expression]"
       include: "Error in tag 'include' - Valid syntax: include '[template]' (with|for) [object|collection]"
       unknown_tag: "Unknown tag '%{tag}'"
-      invalid_delimiter: "'end' is not a valid delimiter for %{block_name} tags. use %{block_delimiter}"
+      invalid_delimiter: "'%{tag}' is not a valid delimiter for %{block_name} tags. use %{block_delimiter}"
       unexpected_else: "%{block_name} tag does not expect 'else' tag"
       unexpected_outer_tag: "Unexpected outer '%{tag}' tag"
       tag_termination: "Tag '%{token}' was not properly terminated with regexp: %{tag_end}"
@@ -22,3 +22,5 @@
       tag_never_closed: "'%{block_name}' tag was never closed"
       meta_syntax_error: "Liquid syntax error: #{e.message}"
       table_row: "Syntax Error in 'table_row loop' - Valid syntax: table_row [item] in [collection] cols=3"
+    argument:
+      include: "Argument error in tag 'include' - Illegal template name"

lib/liquid/parse_context.rb

@@ -1,12 +1,15 @@
+# frozen_string_literal: true
+
 module Liquid
   class ParseContext
-    attr_accessor :partial, :locale, :line_number
-    attr_reader :warnings, :error_mode
+    attr_accessor :locale, :line_number, :trim_whitespace, :depth
+    attr_reader :partial, :warnings, :error_mode
 
     def initialize(options = {})
       @template_options = options ? options.dup : {}
       @locale = @template_options[:locale] ||= I18n.new
       @warnings = []
+      self.depth = 0
       self.partial = false
     end
 
@@ -18,7 +21,6 @@ module Liquid
       @partial = value
       @options = value ? partial_options : @template_options
       @error_mode = @options[:error_mode] || Template.error_mode
-      value
     end
 
     def partial_options
@@ -27,7 +29,7 @@ module Liquid
         if dont_pass == true
           { locale: locale }
         elsif dont_pass.is_a?(Array)
-          @template_options.reject { |k, v| dont_pass.include?(k) }
+          @template_options.reject { |k, _v| dont_pass.include?(k) }
         else
           @template_options
         end

lib/liquid/parse_tree_visitor.rb

@@ -0,0 +1,42 @@
+# frozen_string_literal: true
+
+module Liquid
+  class ParseTreeVisitor
+    def self.for(node, callbacks = Hash.new(proc {}))
+      if defined?(node.class::ParseTreeVisitor)
+        node.class::ParseTreeVisitor
+      else
+        self
+      end.new(node, callbacks)
+    end
+
+    def initialize(node, callbacks)
+      @node = node
+      @callbacks = callbacks
+    end
+
+    def add_callback_for(*classes, &block)
+      callback = block
+      callback = ->(node, _) { yield node } if block.arity.abs == 1
+      callback = ->(_, _) { yield } if block.arity.zero?
+      classes.each { |klass| @callbacks[klass] = callback }
+      self
+    end
+
+    def visit(context = nil)
+      children.map do |node|
+        item, new_context = @callbacks[node.class].call(node, context)
+        [
+          item,
+          ParseTreeVisitor.for(node, @callbacks).visit(new_context || context),
+        ]
+      end
+    end
+
+    protected
+
+    def children
+      @node.respond_to?(:nodelist) ? Array(@node.nodelist) : []
+    end
+  end
+end

lib/liquid/parser.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Liquid
   class Parser
     def initialize(input)
@@ -12,9 +14,8 @@ module Liquid
 
     def consume(type = nil)
       token = @tokens[@p]
-      if type && token[0] != type
-        raise SyntaxError, "Expected #{type} but found #{@tokens[@p].first}"
-      end
+      raise SyntaxError, "Expected #{type} but found #{@tokens[@p].first}" if type && token[0] != type
+
       @p += 1
       token[1]
     end
@@ -25,6 +26,7 @@ module Liquid
     def consume?(type)
       token = @tokens[@p]
       return false unless token && token[0] == type
+
       @p += 1
       token[1]
     end
@@ -34,6 +36,7 @@ module Liquid
       token = @tokens[@p]
       return false unless token && token[0] == :id
       return false unless token[1] == str
+
       @p += 1
       token[1]
     end
@@ -41,14 +44,18 @@ module Liquid
     def look(type, ahead = 0)
       tok = @tokens[@p + ahead]
       return false unless tok
+
       tok[0] == type
     end
 
+    SINGLE_TOKEN_EXPRESSION_TYPES = %i[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
@@ -63,11 +70,9 @@ module Liquid
     end
 
     def argument
-      str = ""
+      str = +''
       # might be a keyword argument (identifier: expression)
-      if look(:id) && look(:colon, 1)
-        str << consume << consume << ' '.freeze
-      end
+      str << consume << consume << ' ' if look(:id) && look(:colon, 1)
 
       str << expression
       str

lib/liquid/parser_switching.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Liquid
   module ParserSwitching
     def parse_with_selected_parser(markup)

lib/liquid/profiler.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'liquid/profiler/hooks'
 
 module Liquid
@@ -97,9 +99,9 @@ module Liquid
     end
 
     def initialize
-      @partial_stack = ["<root>"]
+      @partial_stack = ['<root>']
 
-      @root_timing = Timing.new("", current_partial)
+      @root_timing = Timing.new('', current_partial)
       @timing_stack = [@root_timing]
 
       @render_start_at = Time.now

lib/liquid/profiler/hooks.rb

@@ -1,8 +1,10 @@
+# frozen_string_literal: true
+
 module Liquid
   class BlockBody
-    def render_node_with_profiling(node, context)
+    def render_node_with_profiling(context, output, node)
       Profiler.profile_node_render(node) do
-        render_node_without_profiling(node, context)
+        render_node_without_profiling(context, output, node)
       end
     end
 
@@ -11,13 +13,13 @@ module Liquid
   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, :render_with_profiling
+    alias_method :render_to_output_buffer_without_profiling, :render_to_output_buffer
+    alias_method :render_to_output_buffer, :render_to_output_buffer_with_profiling
   end
 end

lib/liquid/range_lookup.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Liquid
   class RangeLookup
     def self.parse(start_markup, end_markup)

lib/liquid/resource_limits.rb

@@ -1,7 +1,9 @@
+# frozen_string_literal: true
+
 module Liquid
   class ResourceLimits
     attr_accessor :render_length, :render_score, :assign_score,
-      :render_length_limit, :render_score_limit, :assign_score_limit
+                  :render_length_limit, :render_score_limit, :assign_score_limit
 
     def initialize(limits)
       @render_length_limit = limits[:render_length_limit]

lib/liquid/standardfilters.rb

@@ -1,16 +1,24 @@
+# frozen_string_literal: true
+
 require 'cgi'
 require 'bigdecimal'
 
 module Liquid
   module StandardFilters
     HTML_ESCAPE = {
-      '&'.freeze => '&'.freeze,
-      '>'.freeze => '>'.freeze,
-      '<'.freeze => '&lt;'.freeze,
-      '"'.freeze => '&quot;'.freeze,
-      "'".freeze => '&#39;'.freeze
-    }
-    HTML_ESCAPE_ONCE_REGEXP = /["><']|&(?!([a-zA-Z]+|(#\d+));)/
+      '&' => '&amp;',
+      '>' => '&gt;',
+      '<' => '&lt;',
+      '"' => '&quot;',
+      "'" => '&#39;',
+    }.freeze
+    HTML_ESCAPE_ONCE_REGEXP = /["><']|&(?!([a-zA-Z]+|(#\d+));)/.freeze
+    STRIP_HTML_BLOCKS = Regexp.union(
+      %r{<script.*?</script>}m,
+      /<!--.*?-->/m,
+      %r{<style.*?</style>}m
+    )
+    STRIP_HTML_TAGS = /<.*?>/m.freeze
 
     # Return the size of an array or of an string
     def size(input)
@@ -33,7 +41,7 @@ module Liquid
     end
 
     def escape(input)
-      CGI.escapeHTML(input).untaint unless input.nil?
+      CGI.escapeHTML(input.to_s).untaint unless input.nil?
     end
     alias_method :h, :escape
 
@@ -42,11 +50,16 @@ module Liquid
     end
 
     def url_encode(input)
-      CGI.escape(input) unless input.nil?
+      CGI.escape(input.to_s) unless input.nil?
     end
 
     def url_decode(input)
-      CGI.unescape(input) unless input.nil?
+      return if input.nil?
+
+      result = CGI.unescape(input.to_s)
+      raise Liquid::ArgumentError, "invalid byte sequence in #{result.encoding}" unless result.valid_encoding?
+
+      result
     end
 
     def slice(input, offset, length = nil)
@@ -61,22 +74,25 @@ module Liquid
     end
 
     # Truncate a string down to x characters
-    def truncate(input, length = 50, truncate_string = "...".freeze)
+    def truncate(input, length = 50, truncate_string = '...')
       return if input.nil?
+
       input_str = input.to_s
       length = Utils.to_integer(length)
-      l = length - truncate_string.length
+      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 : 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)
+    def truncatewords(input, words = 15, truncate_string = '...')
       return if input.nil?
+
       wordlist = input.to_s.split
       words = Utils.to_integer(words)
       l = words - 1
       l = 0 if l < 0
-      wordlist.length > l ? wordlist[0..l].join(" ".freeze) + truncate_string : input
+      wordlist.length > l ? wordlist[0..l].join(' ').concat(truncate_string.to_s) : input
     end
 
     # Split input string into an array of substrings separated by given pattern.
@@ -85,7 +101,7 @@ module Liquid
     #   <div class="summary">{{ post | split '//' | first }}</div>
     #
     def split(input, pattern)
-      input.to_s.split(pattern)
+      input.to_s.split(pattern.to_s)
     end
 
     def strip(input)
@@ -101,17 +117,19 @@ module Liquid
     end
 
     def strip_html(input)
-      empty = ''.freeze
-      input.to_s.gsub(/<script.*?<\/script>/m, empty).gsub(/<!--.*?-->/m, empty).gsub(/<style.*?<\/style>/m, empty).gsub(/<.*?>/m, empty)
+      empty = ''
+      result = input.to_s.gsub(STRIP_HTML_BLOCKS, empty)
+      result.gsub!(STRIP_HTML_TAGS, empty)
+      result
     end
 
     # Remove all newlines from the string
     def strip_newlines(input)
-      input.to_s.gsub(/\r?\n/, ''.freeze)
+      input.to_s.gsub(/\r?\n/, '')
     end
 
     # Join elements of the array with certain character between them
-    def join(input, glue = ' '.freeze)
+    def join(input, glue = ' ')
       InputIterator.new(input).join(glue)
     end
 
@@ -119,14 +137,19 @@ module Liquid
     # provide optional property with which to sort an array of hashes or drops
     def sort(input, property = nil)
       ary = InputIterator.new(input)
+
+      return [] if ary.empty?
+
       if property.nil?
-        ary.sort
-      elsif ary.empty? # The next two cases assume a non-empty array.
-        []
-      elsif ary.first.respond_to?(:[]) && !ary.first[property].nil?
-        ary.sort { |a, b| a[property] <=> b[property] }
-      elsif ary.first.respond_to?(property)
-        ary.sort { |a, b| a.send(property) <=> b.send(property) }
+        ary.sort do |a, b|
+          nil_safe_compare(a, b)
+        end
+      elsif ary.all? { |el| el.respond_to?(:[]) }
+        begin
+          ary.sort { |a, b| nil_safe_compare(a[property], b[property]) }
+        rescue TypeError
+          raise_property_error(property)
+        end
       end
     end
 
@@ -135,14 +158,40 @@ module Liquid
     def sort_natural(input, property = nil)
       ary = InputIterator.new(input)
 
+      return [] if ary.empty?
+
       if property.nil?
-        ary.sort { |a, b| a.casecmp(b) }
-      elsif ary.empty? # The next two cases assume a non-empty array.
+        ary.sort do |a, b|
+          nil_safe_casecmp(a, b)
+        end
+      elsif ary.all? { |el| el.respond_to?(:[]) }
+        begin
+          ary.sort { |a, b| nil_safe_casecmp(a[property], b[property]) }
+        rescue TypeError
+          raise_property_error(property)
+        end
+      end
+    end
+
+    # Filter the elements of an array to those with a certain property value.
+    # By default the target is any truthy value.
+    def where(input, property, target_value = nil)
+      ary = InputIterator.new(input)
+
+      if ary.empty?
         []
-      elsif ary.first.respond_to?(:[]) && !ary.first[property].nil?
-        ary.sort { |a, b| a[property].casecmp(b[property]) }
-      elsif ary.first.respond_to?(property)
-        ary.sort { |a, b| a.send(property).casecmp(b.send(property)) }
+      elsif ary.first.respond_to?(:[]) && target_value.nil?
+        begin
+          ary.select { |item| item[property] }
+        rescue TypeError
+          raise_property_error(property)
+        end
+      elsif ary.first.respond_to?(:[])
+        begin
+          ary.select { |item| item[property] == target_value }
+        rescue TypeError
+          raise_property_error(property)
+        end
       end
     end
 
@@ -156,7 +205,11 @@ module Liquid
       elsif ary.empty? # The next two cases assume a non-empty array.
         []
       elsif ary.first.respond_to?(:[])
-        ary.uniq{ |a| a[property] }
+        begin
+          ary.uniq { |a| a[property] }
+        rescue TypeError
+          raise_property_error(property)
+        end
       end
     end
 
@@ -171,13 +224,15 @@ module Liquid
       InputIterator.new(input).map do |e|
         e = e.call if e.is_a?(Proc)
 
-        if property == "to_liquid".freeze
+        if property == 'to_liquid'
           e
         elsif e.respond_to?(:[])
           r = e[property]
           r.is_a?(Proc) ? r.call : r
         end
       end
+    rescue TypeError
+      raise_property_error(property)
     end
 
     # Remove nils within an array
@@ -190,30 +245,32 @@ module Liquid
       elsif ary.empty? # The next two cases assume a non-empty array.
         []
       elsif ary.first.respond_to?(:[])
-        ary.reject{ |a| a[property].nil? }
-      elsif ary.first.respond_to?(property)
-        ary.reject { |a| a.send(property).nil? }
+        begin
+          ary.reject { |a| a[property].nil? }
+        rescue TypeError
+          raise_property_error(property)
+        end
       end
     end
 
     # Replace occurrences of a string with another
-    def replace(input, string, replacement = ''.freeze)
+    def replace(input, string, replacement = '')
       input.to_s.gsub(string.to_s, replacement.to_s)
     end
 
     # Replace the first occurrences of a string with another
-    def replace_first(input, string, replacement = ''.freeze)
+    def replace_first(input, string, replacement = '')
       input.to_s.sub(string.to_s, replacement.to_s)
     end
 
     # remove a substring
     def remove(input, string)
-      input.to_s.gsub(string.to_s, ''.freeze)
+      input.to_s.gsub(string.to_s, '')
     end
 
     # remove the first occurrences of a substring
     def remove_first(input, string)
-      input.to_s.sub(string.to_s, ''.freeze)
+      input.to_s.sub(string.to_s, '')
     end
 
     # add one string to another
@@ -222,6 +279,8 @@ module Liquid
     end
 
     def concat(input, array)
+      raise ArgumentError, 'concat filter requires an array argument' unless array.respond_to?(:to_ary)
+
       InputIterator.new(input).concat(array)
     end
 
@@ -232,7 +291,7 @@ module Liquid
 
     # Add <br /> tags in front of all newlines in input string
     def newline_to_br(input)
-      input.to_s.gsub(/\n/, "<br />\n".freeze)
+      input.to_s.gsub(/\n/, "<br />\n")
     end
 
     # Reformat a date using Ruby's core Time#strftime( string ) -> string
@@ -269,7 +328,7 @@ module Liquid
     def date(input, format)
       return input if format.to_s.empty?
 
-      return input unless date = Utils.to_date(input)
+      return input unless (date = Utils.to_date(input))
 
       date.strftime(format.to_s)
     end
@@ -292,6 +351,12 @@ module Liquid
       array.last if array.respond_to?(:last)
     end
 
+    # absolute value
+    def abs(input)
+      result = Utils.to_number(input).abs
+      result.is_a?(BigDecimal) ? result.to_f : result
+    end
+
     # addition
     def plus(input, operand)
       apply_operation(input, operand, :+)
@@ -341,7 +406,23 @@ module Liquid
       raise Liquid::FloatDomainError, e.message
     end
 
-    def default(input, default_value = ''.freeze)
+    def at_least(input, n)
+      min_value = Utils.to_number(n)
+
+      result = Utils.to_number(input)
+      result = min_value if min_value > result
+      result.is_a?(BigDecimal) ? result.to_f : result
+    end
+
+    def at_most(input, n)
+      max_value = Utils.to_number(n)
+
+      result = Utils.to_number(input)
+      result = max_value if max_value < result
+      result.is_a?(BigDecimal) ? result.to_f : result
+    end
+
+    def default(input, default_value = '')
       if !input || input.respond_to?(:empty?) && input.empty?
         default_value
       else
@@ -351,11 +432,31 @@ module Liquid
 
     private
 
+    def raise_property_error(property)
+      raise Liquid::ArgumentError, "cannot select the property '#{property}'"
+    end
+
     def apply_operation(input, operand, operation)
       result = Utils.to_number(input).send(operation, Utils.to_number(operand))
       result.is_a?(BigDecimal) ? result.to_f : result
     end
 
+    def nil_safe_compare(a, b)
+      if !a.nil? && !b.nil?
+        a <=> b
+      else
+        a.nil? ? 1 : -1
+      end
+    end
+
+    def nil_safe_casecmp(a, b)
+      if !a.nil? && !b.nil?
+        a.to_s.casecmp(b.to_s)
+      else
+        a.nil? ? 1 : -1
+      end
+    end
+
     class InputIterator
       include Enumerable
 
@@ -372,11 +473,11 @@ module Liquid
       end
 
       def join(glue)
-        to_a.join(glue)
+        to_a.join(glue.to_s)
       end
 
       def concat(args)
-        to_a.concat args
+        to_a.concat(args)
       end
 
       def reverse

lib/liquid/strainer.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'set'
 
 module Liquid
@@ -7,12 +9,12 @@ module Liquid
   # The Strainer only allows method calls defined in filters given to it via Strainer.global_filter,
   # Context#add_filters or Template.register_filter
   class Strainer #:nodoc:
-    @@global_strainer = Class.new(Strainer) do
+    @global_strainer = Class.new(Strainer) do
       @filter_methods = Set.new
     end
-    @@strainer_class_cache = Hash.new do |hash, filters|
-      hash[filters] = Class.new(@@global_strainer) do
-        @filter_methods = @@global_strainer.filter_methods.dup
+    @strainer_class_cache = Hash.new do |hash, filters|
+      hash[filters] = Class.new(@global_strainer) do
+        @filter_methods = Strainer.global_strainer.filter_methods.dup
         filters.each { |f| add_filter(f) }
       end
     end
@@ -22,19 +24,27 @@ module Liquid
     end
 
     class << self
+      attr_accessor :strainer_class_cache, :global_strainer
       attr_reader :filter_methods
     end
 
     def self.add_filter(filter)
-      raise ArgumentError, "Expected module but got: #{f.class}" unless filter.is_a?(Module)
-      unless self.class.include?(filter)
-        send(:include, filter)
-        @filter_methods.merge(filter.public_instance_methods.map(&:to_s))
+      raise ArgumentError, "Expected module but got: #{filter.class}" unless filter.is_a?(Module)
+
+      unless include?(filter)
+        invokable_non_public_methods = (filter.private_instance_methods + filter.protected_instance_methods).select { |m| invokable?(m) }
+        if invokable_non_public_methods.any?
+          raise MethodOverrideError, "Filter overrides registered public methods as non public: #{invokable_non_public_methods.join(', ')}"
+        else
+          send(:include, filter)
+          @filter_methods.merge(filter.public_instance_methods.map(&:to_s))
+        end
       end
     end
 
     def self.global_filter(filter)
-      @@global_strainer.add_filter(filter)
+      @strainer_class_cache.clear
+      @global_strainer.add_filter(filter)
     end
 
     def self.invokable?(method)
@@ -42,12 +52,14 @@ module Liquid
     end
 
     def self.create(context, filters = [])
-      @@strainer_class_cache[filters].new(context)
+      @strainer_class_cache[filters].new(context)
     end
 
     def invoke(method, *args)
       if self.class.invokable?(method)
         send(method, *args)
+      elsif @context&.strict_filters
+        raise Liquid::UndefinedFilter, "undefined filter #{method}"
       else
         args.first
       end

lib/liquid/tablerowloop_drop.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Liquid
   class TablerowloopDrop < Drop
     def initialize(length, cols)

lib/liquid/tag.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Liquid
   class Tag
     attr_reader :nodelist, :tag_name, :line_number, :parse_context
@@ -21,8 +23,7 @@ module Liquid
       @line_number = parse_context.line_number
     end
 
-    def parse(_tokens)
-    end
+    def parse(_tokens); end
 
     def raw
       "#{@tag_name} #{@markup}"
@@ -33,7 +34,15 @@ module Liquid
     end
 
     def render(_context)
-      ''.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?

lib/liquid/tags/assign.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Liquid
   # Assign sets a variable in your template.
   #
@@ -8,32 +10,52 @@ module Liquid
   #  {{ foo }}
   #
   class Assign < Tag
-    Syntax = /(#{VariableSignature}+)\s*=\s*(.*)\s*/om
+    SYNTAX = /(#{VARIABLE_SIGNATURE}+)\s*=\s*(.*)\s*/om.freeze
+
+    attr_reader :to, :from
 
     def initialize(tag_name, markup, options)
       super
-      if markup =~ Syntax
-        @to = $1
-        @from = Variable.new($2, options)
+      if markup =~ SYNTAX
+        @to = Regexp.last_match(1)
+        @from = Variable.new(Regexp.last_match(2), options)
       else
-        raise SyntaxError.new options[:locale].t("errors.syntax.assign".freeze)
+        raise SyntaxError, options[:locale].t('errors.syntax.assign')
       end
     end
 
-    def render(context)
+    def render_to_output_buffer(context, output)
       val = @from.render(context)
       context.scopes.last[@to] = val
-
-      inc = val.instance_of?(String) || val.instance_of?(Array) || val.instance_of?(Hash) ? val.length : 1
-      context.resource_limits.assign_score += inc
-
-      ''.freeze
+      context.resource_limits.assign_score += assign_score_of(val)
+      output
     end
 
     def blank?
       true
     end
+
+    private
+
+    def assign_score_of(val)
+      if val.instance_of?(String)
+        val.bytesize
+      elsif val.instance_of?(Array) || val.instance_of?(Hash)
+        sum = 1
+        # Uses #each to avoid extra allocations.
+        val.each { |child| sum += assign_score_of(child) }
+        sum
+      else
+        1
+      end
+    end
+
+    class ParseTreeVisitor < Liquid::ParseTreeVisitor
+      def children
+        [@node.from]
+      end
+    end
   end
 
-  Template.register_tag('assign'.freeze, Assign)
+  Template.register_tag('assign', Assign)
 end

lib/liquid/tags/break.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Liquid
   # Break tag to be used to break out of a for loop.
   #
@@ -14,5 +16,5 @@ module Liquid
     end
   end
 
-  Template.register_tag('break'.freeze, Break)
+  Template.register_tag('break', Break)
 end

lib/liquid/tags/capture.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Liquid
   # Capture stores the result of a block into a variable without rendering it inplace.
   #
@@ -11,22 +13,23 @@ module Liquid
   # in a sidebar or footer.
   #
   class Capture < Block
-    Syntax = /(#{VariableSignature}+)/o
+    SYNTAX = /(#{VARIABLE_SIGNATURE}+)/o.freeze
 
     def initialize(tag_name, markup, options)
       super
-      if markup =~ Syntax
-        @to = $1
+      if markup =~ SYNTAX
+        @to = Regexp.last_match(1)
       else
-        raise SyntaxError.new(options[:locale].t("errors.syntax.capture"))
+        raise SyntaxError, options[:locale].t('errors.syntax.capture')
       end
     end
 
-    def render(context)
-      output = super
+    def render_to_output_buffer(context, output)
+      previous_output_size = output.bytesize
+      super
       context.scopes.last[@to] = output
-      context.resource_limits.assign_score += output.length
-      ''.freeze
+      context.resource_limits.assign_score += (output.bytesize - previous_output_size)
+      output
     end
 
     def blank?
@@ -34,5 +37,5 @@ module Liquid
     end
   end
 
-  Template.register_tag('capture'.freeze, Capture)
+  Template.register_tag('capture', Capture)
 end

lib/liquid/tags/case.rb

@@ -1,24 +1,26 @@
+# frozen_string_literal: true
+
 module Liquid
   class Case < Block
-    Syntax     = /(#{QuotedFragment})/o
-    WhenSyntax = /(#{QuotedFragment})(?:(?:\s+or\s+|\s*\,\s*)(#{QuotedFragment}.*))?/om
+    SYNTAX = /(#{QUOTED_FRAGMENT})/o.freeze
+    WHEN_SYNTAX = /(#{QUOTED_FRAGMENT})(?:(?:\s+or\s+|\s*\,\s*)(#{QUOTED_FRAGMENT}.*))?/om.freeze
+
+    attr_reader :blocks, :left
 
     def initialize(tag_name, markup, options)
       super
       @blocks = []
 
-      if markup =~ Syntax
-        @left = Expression.parse($1)
+      if markup =~ SYNTAX
+        @left = Expression.parse(Regexp.last_match(1))
       else
-        raise SyntaxError.new(options[:locale].t("errors.syntax.case".freeze))
+        raise SyntaxError, options[:locale].t('errors.syntax.case')
       end
     end
 
     def parse(tokens)
       body = BlockBody.new
-      while parse_body(body, tokens)
-        body = @blocks.last.attachment
-      end
+      body = @blocks.last.attachment while parse_body(body, tokens)
     end
 
     def nodelist
@@ -27,30 +29,30 @@ module Liquid
 
     def unknown_tag(tag, markup, tokens)
       case tag
-      when 'when'.freeze
+      when 'when'
         record_when_condition(markup)
-      when 'else'.freeze
+      when 'else'
         record_else_condition(markup)
       else
         super
       end
     end
 
-    def render(context)
+    def render_to_output_buffer(context, output)
       context.stack do
         execute_else_block = true
 
-        output = ''
         @blocks.each do |block|
           if block.else?
-            return block.attachment.render(context) if execute_else_block
+            block.attachment.render_to_output_buffer(context, output) if execute_else_block
           elsif block.evaluate(context)
             execute_else_block = false
-            output << block.attachment.render(context)
+            block.attachment.render_to_output_buffer(context, output)
           end
         end
-        output
       end
+
+      output
     end
 
     private
@@ -59,28 +61,30 @@ module Liquid
       body = BlockBody.new
 
       while markup
-        unless markup =~ WhenSyntax
-          raise SyntaxError.new(options[:locale].t("errors.syntax.case_invalid_when".freeze))
-        end
+        raise SyntaxError, options[:locale].t('errors.syntax.case_invalid_when') unless markup =~ WHEN_SYNTAX
 
-        markup = $2
+        markup = Regexp.last_match(2)
 
-        block = Condition.new(@left, '=='.freeze, Expression.parse($1))
+        block = Condition.new(@left, '==', Expression.parse(Regexp.last_match(1)))
         block.attach(body)
         @blocks << block
       end
     end
 
     def record_else_condition(markup)
-      unless markup.strip.empty?
-        raise SyntaxError.new(options[:locale].t("errors.syntax.case_invalid_else".freeze))
-      end
+      raise SyntaxError, options[:locale].t('errors.syntax.case_invalid_else') unless markup.strip.empty?
 
       block = ElseCondition.new
       block.attach(BlockBody.new)
       @blocks << block
     end
+
+    class ParseTreeVisitor < Liquid::ParseTreeVisitor
+      def children
+        [@node.left] + @node.blocks
+      end
+    end
   end
 
-  Template.register_tag('case'.freeze, Case)
+  Template.register_tag('case', Case)
 end

lib/liquid/tags/comment.rb

@@ -1,16 +1,17 @@
+# frozen_string_literal: true
+
 module Liquid
   class Comment < Block
-    def render(_context)
-      ''.freeze
+    def render_to_output_buffer(_context, output)
+      output
     end
 
-    def unknown_tag(_tag, _markup, _tokens)
-    end
+    def unknown_tag(_tag, _markup, _tokens); end
 
     def blank?
       true
     end
   end
 
-  Template.register_tag('comment'.freeze, Comment)
+  Template.register_tag('comment', Comment)
 end

lib/liquid/tags/continue.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Liquid
   # Continue tag to be used to break out of a for loop.
   #
@@ -14,5 +16,5 @@ module Liquid
     end
   end
 
-  Template.register_tag('continue'.freeze, Continue)
+  Template.register_tag('continue', Continue)
 end

lib/liquid/tags/cycle.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Liquid
   # Cycle is usually used within a loop to alternate between values, like colors or DOM classes.
   #
@@ -12,45 +14,64 @@ module Liquid
   #    <div class="green"> Item five</div>
   #
   class Cycle < Tag
-    SimpleSyntax = /\A#{QuotedFragment}+/o
-    NamedSyntax  = /\A(#{QuotedFragment})\s*\:\s*(.*)/om
+    SIMPLE_SYNTAX = /\A#{QUOTED_FRAGMENT}+/o.freeze
+    NAMED_SYNTAX  = /\A(#{QUOTED_FRAGMENT})\s*\:\s*(.*)/om.freeze
+
+    attr_reader :variables
 
     def initialize(tag_name, markup, options)
       super
       case markup
-      when NamedSyntax
-        @variables = variables_from_string($2)
-        @name = Expression.parse($1)
-      when SimpleSyntax
+      when NAMED_SYNTAX
+        @variables = variables_from_string(Regexp.last_match(2))
+        @name = Expression.parse(Regexp.last_match(1))
+      when SIMPLE_SYNTAX
         @variables = variables_from_string(markup)
         @name = @variables.to_s
       else
-        raise SyntaxError.new(options[:locale].t("errors.syntax.cycle".freeze))
+        raise SyntaxError, options[:locale].t('errors.syntax.cycle')
       end
     end
 
-    def render(context)
-      context.registers[:cycle] ||= Hash.new(0)
+    def render_to_output_buffer(context, output)
+      context.registers[:cycle] ||= {}
 
       context.stack do
         key = context.evaluate(@name)
-        iteration = context.registers[:cycle][key]
-        result = context.evaluate(@variables[iteration])
+        iteration = context.registers[:cycle][key].to_i
+
+        val = context.evaluate(@variables[iteration])
+
+        if val.is_a?(Array)
+          val = val.join
+        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
-        result
       end
+
+      output
     end
 
     private
 
     def variables_from_string(markup)
       markup.split(',').collect do |var|
-        var =~ /\s*(#{QuotedFragment})\s*/o
-        $1 ? Expression.parse($1) : nil
+        var =~ /\s*(#{QUOTED_FRAGMENT})\s*/o
+        Regexp.last_match(1) ? Expression.parse(Regexp.last_match(1)) : nil
       end.compact
     end
+
+    class ParseTreeVisitor < Liquid::ParseTreeVisitor
+      def children
+        Array(@node.variables)
+      end
+    end
   end
 
   Template.register_tag('cycle', Cycle)

lib/liquid/tags/decrement.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Liquid
   # decrement is used in a place where one needs to insert a counter
   #     into a template, and needs the counter to survive across
@@ -23,13 +25,14 @@ 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
 
-  Template.register_tag('decrement'.freeze, Decrement)
+  Template.register_tag('decrement', Decrement)
 end

lib/liquid/tags/for.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Liquid
   # "For" iterates over an array or collection.
   # Several useful variables are available to you within the loop.
@@ -23,7 +25,7 @@ module Liquid
   #      {{ item.name }}
   #    {% end %}
   #
-  #  To reverse the for loop simply use {% for item in collection reversed %}
+  #  To reverse the for loop simply use {% for item in collection reversed %} (note that the flag's spelling is different to the filter `reverse`)
   #
   # == Available variables:
   #
@@ -44,16 +46,21 @@ module Liquid
   # forloop.parentloop:: Provides access to the parent loop, if present.
   #
   class For < Block
-    Syntax = /\A(#{VariableSegment}+)\s+in\s+(#{QuotedFragment}+)\s*(reversed)?/o
+    SYNTAX = /\A(#{VARIABLE_SEGMENT}+)\s+in\s+(#{QUOTED_FRAGMENT}+)\s*(reversed)?/o.freeze
+
+    attr_reader :collection_name, :variable_name, :limit, :from
 
     def initialize(tag_name, markup, options)
       super
+      @from = @limit = nil
       parse_with_selected_parser(markup)
       @for_block = BlockBody.new
+      @else_block = nil
     end
 
     def parse(tokens)
       return unless parse_body(@for_block, tokens)
+
       parse_body(@else_block, tokens)
     end
 
@@ -62,50 +69,55 @@ module Liquid
     end
 
     def unknown_tag(tag, markup, tokens)
-      return super unless tag == 'else'.freeze
+      return super unless tag == 'else'
+
       @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
 
     def lax_parse(markup)
-      if markup =~ Syntax
-        @variable_name = $1
-        collection_name = $2
-        @reversed = !!$3
+      if markup =~ SYNTAX
+        @variable_name = Regexp.last_match(1)
+        collection_name = Regexp.last_match(2)
+        @reversed = !!Regexp.last_match(3)
         @name = "#{@variable_name}-#{collection_name}"
         @collection_name = Expression.parse(collection_name)
-        markup.scan(TagAttributes) do |key, value|
+        markup.scan(TAG_ATTRIBUTES) do |key, value|
           set_attribute(key, value)
         end
       else
-        raise SyntaxError.new(options[:locale].t("errors.syntax.for".freeze))
+        raise SyntaxError, options[:locale].t('errors.syntax.for')
       end
     end
 
     def strict_parse(markup)
       p = Parser.new(markup)
       @variable_name = p.consume(:id)
-      raise SyntaxError.new(options[:locale].t("errors.syntax.for_invalid_in".freeze)) unless p.id?('in'.freeze)
+      raise SyntaxError, options[:locale].t('errors.syntax.for_invalid_in') unless p.id?('in')
+
       collection_name = p.expression
       @name = "#{@variable_name}-#{collection_name}"
       @collection_name = Expression.parse(collection_name)
-      @reversed = p.id?('reversed'.freeze)
+      @reversed = p.id?('reversed')
 
       while p.look(:id) && p.look(:colon, 1)
-        unless attribute = p.id?('limit'.freeze) || p.id?('offset'.freeze)
-          raise SyntaxError.new(options[:locale].t("errors.syntax.for_invalid_attribute".freeze))
+        unless (attribute = p.id?('limit') || p.id?('offset'))
+          raise SyntaxError, options[:locale].t('errors.syntax.for_invalid_attribute')
         end
+
         p.consume
         set_attribute(attribute, p.expression)
       end
@@ -115,19 +127,28 @@ module Liquid
     private
 
     def collection_segment(context)
-      offsets = context.registers[:for] ||= Hash.new(0)
+      offsets = context.registers[:for] ||= {}
 
       from = if @from == :continue
         offsets[@name].to_i
       else
-        context.evaluate(@from).to_i
+        from_value = context.evaluate(@from)
+        if from_value.nil?
+          0
+        else
+          Utils.to_integer(from_value)
+        end
       end
 
       collection = context.evaluate(@collection_name)
       collection = collection.to_a if collection.is_a?(Range)
 
-      limit = context.evaluate(@limit)
-      to = limit ? limit.to_i + from : nil
+      limit_value = context.evaluate(@limit)
+      to = if limit_value.nil?
+        nil
+      else
+        Utils.to_integer(limit_value) + from
+      end
 
       segment = Utils.slice_collection(collection, from, to)
       segment.reverse! if @reversed
@@ -137,57 +158,65 @@ 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])
 
         for_stack.push(loop_vars)
 
         begin
-          context['forloop'.freeze] = loop_vars
+          context['forloop'] = loop_vars
 
-          segment.each_with_index do |item, index|
+          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.
-            if context.interrupt?
-              interrupt = context.pop_interrupt
-              break if interrupt.is_a? BreakInterrupt
-              next if interrupt.is_a? ContinueInterrupt
-            end
+            next unless context.interrupt?
+
+            interrupt = context.pop_interrupt
+            break if interrupt.is_a?(BreakInterrupt)
+            next if interrupt.is_a?(ContinueInterrupt)
           end
         ensure
           for_stack.pop
         end
       end
 
-      result
+      output
     end
 
     def set_attribute(key, expr)
       case key
-      when 'offset'.freeze
-        @from = if expr == 'continue'.freeze
+      when 'offset'
+        @from = if expr == 'continue'
           :continue
         else
           Expression.parse(expr)
         end
-      when 'limit'.freeze
+      when 'limit'
         @limit = Expression.parse(expr)
       end
     end
 
-    def render_else(context)
-      @else_block ? @else_block.render(context) : ''.freeze
+    def render_else(context, output)
+      if @else_block
+        @else_block.render_to_output_buffer(context, output)
+      else
+        output
+      end
+    end
+
+    class ParseTreeVisitor < Liquid::ParseTreeVisitor
+      def children
+        (super + [@node.limit, @node.from, @node.collection_name]).compact
+      end
     end
   end
 
-  Template.register_tag('for'.freeze, For)
+  Template.register_tag('for', For)
 end

lib/liquid/tags/if.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Liquid
   # If is the conditional block
   #
@@ -10,14 +12,20 @@ module Liquid
   #    There are {% if count < 5 %} less {% else %} more {% endif %} items than you need.
   #
   class If < Block
-    Syntax = /(#{QuotedFragment})\s*([=!<>a-z_]+)?\s*(#{QuotedFragment})?/o
-    ExpressionsAndOperators = /(?:\b(?:\s?and\s?|\s?or\s?)\b|(?:\s*(?!\b(?:\s?and\s?|\s?or\s?)\b)(?:#{QuotedFragment}|\S+)\s*)+)/o
-    BOOLEAN_OPERATORS = %w(and or)
+    SYNTAX = /(#{QUOTED_FRAGMENT})\s*([=!<>a-z_]+)?\s*(#{QUOTED_FRAGMENT})?/o.freeze
+    EXPRESSIONS_AND_OPERATORS = /(?:\b(?:\s?and\s?|\s?or\s?)\b|(?:\s*(?!\b(?:\s?and\s?|\s?or\s?)\b)(?:#{QUOTED_FRAGMENT}|\S+)\s*)+)/o.freeze
+    BOOLEAN_OPERATORS = %w[and or].freeze
+
+    attr_reader :blocks
 
     def initialize(tag_name, markup, options)
       super
       @blocks = []
-      push_block('if'.freeze, markup)
+      push_block('if', markup)
+    end
+
+    def nodelist
+      @blocks.map(&:attachment)
     end
 
     def parse(tokens)
@@ -25,33 +33,28 @@ module Liquid
       end
     end
 
-    def nodelist
-      @blocks.map(&:attachment)
-    end
-
     def unknown_tag(tag, markup, tokens)
-      if ['elsif'.freeze, 'else'.freeze].include?(tag)
+      if %w[elsif else].include?(tag)
         push_block(tag, markup)
       else
         super
       end
     end
 
-    def render(context)
+    def render_to_output_buffer(context, output)
       context.stack do
         @blocks.each do |block|
-          if block.evaluate(context)
-            return block.attachment.render(context)
-          end
+          return block.attachment.render_to_output_buffer(context, output) if block.evaluate(context)
         end
-        ''.freeze
       end
+
+      output
     end
 
     private
 
     def push_block(tag, markup)
-      block = if tag == 'else'.freeze
+      block = if tag == 'else'
         ElseCondition.new
       else
         parse_with_selected_parser(markup)
@@ -62,18 +65,19 @@ module Liquid
     end
 
     def lax_parse(markup)
-      expressions = markup.scan(ExpressionsAndOperators)
-      raise(SyntaxError.new(options[:locale].t("errors.syntax.if".freeze))) unless expressions.pop =~ Syntax
+      expressions = markup.scan(EXPRESSIONS_AND_OPERATORS)
+      raise SyntaxError, options[:locale].t('errors.syntax.if') unless expressions.pop =~ SYNTAX
 
-      condition = Condition.new(Expression.parse($1), $2, Expression.parse($3))
+      condition = Condition.new(Expression.parse(Regexp.last_match(1)), Regexp.last_match(2), Expression.parse(Regexp.last_match(3)))
 
       until expressions.empty?
         operator = expressions.pop.to_s.strip
 
-        raise(SyntaxError.new(options[:locale].t("errors.syntax.if".freeze))) unless expressions.pop.to_s =~ Syntax
+        raise SyntaxError, options[:locale].t('errors.syntax.if') unless expressions.pop.to_s =~ SYNTAX
+
+        new_condition = Condition.new(Expression.parse(Regexp.last_match(1)), Regexp.last_match(2), Expression.parse(Regexp.last_match(3)))
+        raise SyntaxError, options[:locale].t('errors.syntax.if') unless BOOLEAN_OPERATORS.include?(operator)
 
-        new_condition = Condition.new(Expression.parse($1), $2, Expression.parse($3))
-        raise(SyntaxError.new(options[:locale].t("errors.syntax.if".freeze))) unless BOOLEAN_OPERATORS.include?(operator)
         new_condition.send(operator, condition)
         condition = new_condition
       end
@@ -83,29 +87,38 @@ module Liquid
 
     def strict_parse(markup)
       p = Parser.new(markup)
-      condition = parse_binary_comparison(p)
+      condition = parse_binary_comparisons(p)
       p.consume(:end_of_string)
       condition
     end
 
-    def parse_binary_comparison(p)
+    def parse_binary_comparisons(p)
       condition = parse_comparison(p)
-      if op = (p.id?('and'.freeze) || p.id?('or'.freeze))
-        condition.send(op, parse_binary_comparison(p))
+      first_condition = condition
+      while (op = (p.id?('and') || p.id?('or')))
+        child_condition = parse_comparison(p)
+        condition.send(op, child_condition)
+        condition = child_condition
       end
-      condition
+      first_condition
     end
 
     def parse_comparison(p)
       a = Expression.parse(p.expression)
-      if op = p.consume?(:comparison)
+      if (op = p.consume?(:comparison))
         b = Expression.parse(p.expression)
         Condition.new(a, op, b)
       else
         Condition.new(a)
       end
     end
+
+    class ParseTreeVisitor < Liquid::ParseTreeVisitor
+      def children
+        @node.blocks
+      end
+    end
   end
 
-  Template.register_tag('if'.freeze, If)
+  Template.register_tag('if', If)
 end

lib/liquid/tags/ifchanged.rb

@@ -1,18 +1,21 @@
+# frozen_string_literal: true
+
 module Liquid
   class Ifchanged < Block
-    def render(context)
+    def render_to_output_buffer(context, output)
       context.stack do
-        output = super
+        block_output = +''
+        super(context, block_output)
 
-        if output != context.registers[:ifchanged]
-          context.registers[:ifchanged] = output
-          output
-        else
-          ''.freeze
+        if block_output != context.registers[:ifchanged]
+          context.registers[:ifchanged] = block_output
+          output << block_output
         end
       end
+
+      output
     end
   end
 
-  Template.register_tag('ifchanged'.freeze, Ifchanged)
+  Template.register_tag('ifchanged', Ifchanged)
 end

lib/liquid/tags/include.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Liquid
   # Include allows templates to relate with other templates
   #
@@ -14,42 +16,44 @@ module Liquid
   #   {% include 'product' for products %}
   #
   class Include < Tag
-    Syntax = /(#{QuotedFragment}+)(\s+(?:with|for)\s+(#{QuotedFragment}+))?/o
+    SYNTAX = /(#{QUOTED_FRAGMENT}+)(\s+(?:with|for)\s+(#{QUOTED_FRAGMENT}+))?/o.freeze
+
+    attr_reader :template_name_expr, :variable_name_expr, :attributes
 
     def initialize(tag_name, markup, options)
       super
 
-      if markup =~ Syntax
+      if markup =~ SYNTAX
 
-        template_name = $1
-        variable_name = $3
+        template_name = Regexp.last_match(1)
+        variable_name = Regexp.last_match(3)
 
         @variable_name_expr = variable_name ? Expression.parse(variable_name) : nil
         @template_name_expr = Expression.parse(template_name)
         @attributes = {}
 
-        markup.scan(TagAttributes) do |key, value|
+        markup.scan(TAG_ATTRIBUTES) do |key, value|
           @attributes[key] = Expression.parse(value)
         end
 
       else
-        raise SyntaxError.new(options[:locale].t("errors.syntax.include".freeze))
+        raise SyntaxError, options[:locale].t('errors.syntax.include')
       end
     end
 
-    def parse(_tokens)
-    end
+    def parse(_tokens); end
 
-    def render(context)
+    def render_to_output_buffer(context, output)
       template_name = context.evaluate(@template_name_expr)
-      partial = load_cached_partial(template_name, context)
+      raise ArgumentError, options[:locale].t('errors.argument.include') unless template_name
 
-      context_variable_name = template_name.split('/'.freeze).last
+      partial = load_cached_partial(template_name, context)
+      context_variable_name = template_name.split('/').last
 
       variable = if @variable_name_expr
         context.evaluate(@variable_name_expr)
       else
-        context.find_variable(template_name)
+        context.find_variable(template_name, raise_on_not_found: false)
       end
 
       old_template_name = context.template_name
@@ -63,19 +67,21 @@ 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
@@ -86,9 +92,10 @@ module Liquid
     def load_cached_partial(template_name, context)
       cached_partials = context.registers[:cached_partials] || {}
 
-      if cached = cached_partials[template_name]
+      if (cached = cached_partials[template_name])
         return cached
       end
+
       source = read_template_from_file_system(context)
       begin
         parse_context.partial = true
@@ -106,7 +113,16 @@ module Liquid
 
       file_system.read_template_file(context.evaluate(@template_name_expr))
     end
+
+    class ParseTreeVisitor < Liquid::ParseTreeVisitor
+      def children
+        [
+          @node.template_name_expr,
+          @node.variable_name_expr,
+        ] + @node.attributes.values
+      end
+    end
   end
 
-  Template.register_tag('include'.freeze, Include)
+  Template.register_tag('include', Include)
 end

lib/liquid/tags/increment.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Liquid
   # increment is used in a place where one needs to insert a counter
   #     into a template, and needs the counter to survive across
@@ -20,12 +22,13 @@ 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
 
-  Template.register_tag('increment'.freeze, Increment)
+  Template.register_tag('increment', Increment)
 end

lib/liquid/tags/raw.rb

@@ -1,31 +1,32 @@
+# frozen_string_literal: true
+
 module Liquid
   class Raw < Block
-    Syntax = /\A\s*\z/
-    FullTokenPossiblyInvalid = /\A(.*)#{TagStart}\s*(\w+)\s*(.*)?#{TagEnd}\z/om
+    SYNTAX = /\A\s*\z/.freeze
+    FULL_TOKEN_POSSIBLY_INVALID = /\A(.*)#{TAG_START}\s*(\w+)\s*(.*)?#{TAG_END}\z/om.freeze
 
     def initialize(tag_name, markup, parse_context)
       super
 
-      unless markup =~ Syntax
-        raise SyntaxError.new(parse_context.locale.t("errors.syntax.tag_unexpected_args".freeze, tag: tag_name))
-      end
+      ensure_valid_markup(tag_name, markup, parse_context)
     end
 
     def parse(tokens)
-      @body = ''
-      while token = tokens.shift
-        if token =~ FullTokenPossiblyInvalid
-          @body << $1 if $1 != "".freeze
-          return if block_delimiter == $2
+      @body = +''
+      while (token = tokens.shift)
+        if token =~ FULL_TOKEN_POSSIBLY_INVALID
+          @body << Regexp.last_match(1) if Regexp.last_match(1) != ''
+          return if block_delimiter == Regexp.last_match(2)
         end
         @body << token unless token.empty?
       end
 
-      raise SyntaxError.new(parse_context.locale.t("errors.syntax.tag_never_closed".freeze, block_name: block_name))
+      raise SyntaxError, parse_context.locale.t('errors.syntax.tag_never_closed', block_name: block_name)
     end
 
-    def render(_context)
-      @body
+    def render_to_output_buffer(_context, output)
+      output << @body
+      output
     end
 
     def nodelist
@@ -35,7 +36,13 @@ module Liquid
     def blank?
       @body.empty?
     end
+
+    protected
+
+    def ensure_valid_markup(tag_name, markup, parse_context)
+      raise SyntaxError, parse_context.locale.t('errors.syntax.tag_unexpected_args', tag: tag_name) unless markup =~ SYNTAX
+    end
   end
 
-  Template.register_tag('raw'.freeze, Raw)
+  Template.register_tag('raw', Raw)
 end

lib/liquid/tags/table_row.rb

@@ -1,54 +1,65 @@
+# frozen_string_literal: true
+
 module Liquid
   class TableRow < Block
-    Syntax = /(\w+)\s+in\s+(#{QuotedFragment}+)/o
+    SYNTAX = /(\w+)\s+in\s+(#{QUOTED_FRAGMENT}+)/o.freeze
+
+    attr_reader :variable_name, :collection_name, :attributes
 
     def initialize(tag_name, markup, options)
       super
-      if markup =~ Syntax
-        @variable_name = $1
-        @collection_name = Expression.parse($2)
+      if markup =~ SYNTAX
+        @variable_name = Regexp.last_match(1)
+        @collection_name = Expression.parse(Regexp.last_match(2))
         @attributes = {}
-        markup.scan(TagAttributes) do |key, value|
+        markup.scan(TAG_ATTRIBUTES) do |key, value|
           @attributes[key] = Expression.parse(value)
         end
       else
-        raise SyntaxError.new(options[:locale].t("errors.syntax.table_row".freeze))
+        raise SyntaxError, options[:locale].t('errors.syntax.table_row')
       end
     end
 
-    def render(context)
-      collection = context.evaluate(@collection_name) or return ''.freeze
+    def render_to_output_buffer(context, output)
+      (collection = context.evaluate(@collection_name)) || (return '')
 
-      from = @attributes.key?('offset'.freeze) ? context.evaluate(@attributes['offset'.freeze]).to_i : 0
-      to = @attributes.key?('limit'.freeze) ? from + context.evaluate(@attributes['limit'.freeze]).to_i : nil
+      from = @attributes.key?('offset') ? context.evaluate(@attributes['offset']).to_i : 0
+      to = @attributes.key?('limit') ? from + context.evaluate(@attributes['limit']).to_i : nil
 
       collection = Utils.slice_collection(collection, from, to)
 
       length = collection.length
 
-      cols = context.evaluate(@attributes['cols'.freeze]).to_i
+      cols = context.evaluate(@attributes['cols']).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
+        context['tablerowloop'] = tablerowloop
 
-        collection.each_with_index do |item, index|
+        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}\">"
-          end
+          output << "</tr>\n<tr class=\"row#{tablerowloop.row + 1}\">" if tablerowloop.col_last && !tablerowloop.last
 
           tablerowloop.send(:increment!)
         end
       end
-      result << "</tr>\n"
-      result
+
+      output << "</tr>\n"
+      output
+    end
+
+    class ParseTreeVisitor < Liquid::ParseTreeVisitor
+      def children
+        super + @node.attributes.values + [@node.collection_name]
+      end
     end
   end
 
-  Template.register_tag('tablerow'.freeze, TableRow)
+  Template.register_tag('tablerow', TableRow)
 end

lib/liquid/tags/unless.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require_relative 'if'
 
 module Liquid
@@ -6,25 +8,21 @@ 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_block = @blocks.first
-        unless first_block.evaluate(context)
-          return first_block.attachment.render(context)
-        end
+        return first_block.attachment.render_to_output_buffer(context, output) unless first_block.evaluate(context)
 
         # 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
+          return block.attachment.render_to_output_buffer(context, output) if block.evaluate(context)
         end
-
-        ''.freeze
       end
+
+      output
     end
   end
 
-  Template.register_tag('unless'.freeze, Unless)
+  Template.register_tag('unless', Unless)
 end

lib/liquid/template.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Liquid
   # Templates are central to liquid.
   # Interpretating templates is a two step process. First you compile the
@@ -16,11 +18,17 @@ module Liquid
     attr_accessor :root
     attr_reader :resource_limits, :warnings
 
-    @@file_system = BlankFileSystem.new
+    @file_system = BlankFileSystem.new
+
+    class << self
+      attr_accessor :file_system
+    end
 
     class TagRegistry
+      include Enumerable
+
       def initialize
-        @tags  = {}
+        @tags = {}
         @cache = {}
       end
 
@@ -41,10 +49,14 @@ module Liquid
         @cache.delete(tag_name)
       end
 
+      def each(&block)
+        @tags.each(&block)
+      end
+
       private
 
       def lookup_class(name)
-        name.split("::").reject(&:empty?).reduce(Object) { |scope, const| scope.const_get(const) }
+        Object.const_get(name)
       end
     end
 
@@ -63,12 +75,9 @@ module Liquid
       # :error raises an error when tainted output is used
       attr_writer :taint_mode
 
-      def file_system
-        @@file_system
-      end
-
-      def file_system=(obj)
-        @@file_system = obj
+      attr_accessor :default_exception_renderer
+      Template.default_exception_renderer = lambda do |exception|
+        exception
       end
 
       def register_tag(name, klass)
@@ -80,11 +89,11 @@ module Liquid
       end
 
       def error_mode
-        @error_mode || :lax
+        @error_mode ||= :lax
       end
 
       def taint_mode
-        @taint_mode || :lax
+        @taint_mode ||= :lax
       end
 
       # Pass a module with filter methods which should be available
@@ -107,6 +116,7 @@ module Liquid
     end
 
     def initialize
+      @rethrow_errors = false
       @resource_limits = ResourceLimits.new(self.class.default_resource_limits)
     end
 
@@ -153,15 +163,13 @@ module Liquid
     #    filters and tags and might be useful to integrate liquid more with its host application
     #
     def render(*args)
-      return ''.freeze if @root.nil?
+      return '' if @root.nil?
 
       context = case args.first
       when Liquid::Context
         c = args.shift
 
-        if @rethrow_errors
-          c.exception_handler = ->(e) { raise }
-        end
+        c.exception_renderer = ->(_e) { raise } if @rethrow_errors
 
         c
       when Liquid::Drop
@@ -172,21 +180,19 @@ module Liquid
       when nil
         Context.new(assigns, instance_assigns, registers, @rethrow_errors, @resource_limits)
       else
-        raise ArgumentError, "Expected Hash or Liquid::Context as parameter"
+        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)
 
-        context.add_filters(options[:filters]) if options[:filters]
-
-        context.global_filter = options[:global_filter] if options[:global_filter]
-
-        context.exception_handler = options[:exception_handler] if options[:exception_handler]
-
+        apply_options_to_context(context, options)
       when Module, Array
         context.add_filters(args.pop)
       end
@@ -197,10 +203,9 @@ 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
-          @root.render(context)
+        with_profiling(context) do
+          @root.render_to_output_buffer(context, output || +'')
         end
-        result.respond_to?(:join) ? result.join : result
       rescue Liquid::MemoryError => e
         context.handle_error(e)
       ensure
@@ -213,6 +218,10 @@ module Liquid
       render(*args)
     end
 
+    def render_to_output_buffer(context, output)
+      render(context, output: output)
+    end
+
     private
 
     def tokenize(source)
@@ -235,5 +244,13 @@ module Liquid
         yield
       end
     end
+
+    def apply_options_to_context(context, options)
+      context.add_filters(options[:filters]) if options[:filters]
+      context.global_filter = options[:global_filter] if options[:global_filter]
+      context.exception_renderer = options[:exception_renderer] if options[:exception_renderer]
+      context.strict_variables = options[:strict_variables] if options[:strict_variables]
+      context.strict_filters = options[:strict_filters] if options[:strict_filters]
+    end
   end
 end

lib/liquid/tokenizer.rb

@@ -1,10 +1,12 @@
+# frozen_string_literal: true
+
 module Liquid
   class Tokenizer
     attr_reader :line_number
 
     def initialize(source, line_numbers = false)
       @source = source
-      @line_number = 1 if line_numbers
+      @line_number = line_numbers ? 1 : nil
       @tokens = tokenize
     end
 
@@ -20,10 +22,10 @@ module Liquid
       @source = @source.source if @source.respond_to?(:source)
       return [] if @source.to_s.empty?
 
-      tokens = @source.split(TemplateParser)
+      tokens = @source.split(TEMPLATE_PARSER)
 
       # removes the rogue empty element at the beginning of the array
-      tokens.shift if tokens[0] && tokens[0].empty?
+      tokens.shift if tokens[0]&.empty?
 
       tokens
     end

lib/liquid/utils.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Liquid
   module Utils
     def self.slice_collection(collection, from, to)
@@ -19,13 +21,9 @@ module Liquid
       return [] unless collection.respond_to?(:each)
 
       collection.each do |item|
-        if to && to <= index
-          break
-        end
+        break if to && to <= index
 
-        if from <= index
-          segments << item
-        end
+        segments << item if from <= index
 
         index += 1
       end
@@ -35,24 +33,29 @@ module Liquid
 
     def self.to_integer(num)
       return num if num.is_a?(Integer)
+
       num = num.to_s
       begin
         Integer(num)
       rescue ::ArgumentError
-        raise Liquid::ArgumentError, "invalid integer"
+        raise Liquid::ArgumentError, 'invalid integer'
       end
     end
 
     def self.to_number(obj)
       case obj
       when Float
-        BigDecimal.new(obj.to_s)
+        BigDecimal(obj.to_s)
       when Numeric
         obj
       when String
-        (obj.strip =~ /\A\d+\.\d+\z/) ? BigDecimal.new(obj) : obj.to_i
+        obj.strip =~ /\A-?\d+\.\d+\z/ ? BigDecimal(obj) : obj.to_i
       else
-        0
+        if obj.respond_to?(:to_number)
+          obj.to_number
+        else
+          0
+        end
       end
     end
 
@@ -61,11 +64,12 @@ module Liquid
 
       if obj.is_a?(String)
         return nil if obj.empty?
+
         obj = obj.downcase
       end
 
       case obj
-      when 'now'.freeze, 'today'.freeze
+      when 'now', 'today'
         Time.now
       when /\A\d+\z/, Integer
         Time.at(obj.to_i)

lib/liquid/variable.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Liquid
   # Holds variables. Variables are only loaded "just in time"
   # and are not evaluated as part of the render stage
@@ -10,10 +12,16 @@ module Liquid
   #   {{ user | link }}
   #
   class Variable
-    FilterParser = /(?:\s+|#{QuotedFragment}|#{ArgumentSeparator})+/o
+    FILTER_MARKUP_REGEX = /#{FILTER_SEPARATOR}\s*(.*)/om.freeze
+    FILTER_PARSER = /(?:\s+|#{QUOTED_FRAGMENT}|#{ARGUMENT_SEPARATOR})+/o.freeze
+    FILTER_ARGS_REGEX = /(?:#{FILTER_ARGUMENT_SEPARATOR}|#{ARGUMENT_SEPARATOR})\s*((?:\w+\s*\:\s*)?#{QUOTED_FRAGMENT})/o.freeze
+    JUST_TAG_ATTRIBUTES = /\A#{TAG_ATTRIBUTES}\z/o.freeze
+    MARKUP_WITH_QUOTED_FRAGMENT = /(#{QUOTED_FRAGMENT})(.*)/om.freeze
+
     attr_accessor :filters, :name, :line_number
     attr_reader :parse_context
     alias_method :options, :parse_context
+
     include ParserSwitching
 
     def initialize(markup, parse_context)
@@ -35,17 +43,18 @@ module Liquid
 
     def lax_parse(markup)
       @filters = []
-      return unless markup =~ /(#{QuotedFragment})(.*)/om
+      return unless markup =~ MARKUP_WITH_QUOTED_FRAGMENT
 
-      name_markup = $1
-      filter_markup = $2
+      name_markup = Regexp.last_match(1)
+      filter_markup = Regexp.last_match(2)
       @name = Expression.parse(name_markup)
-      if filter_markup =~ /#{FilterSeparator}\s*(.*)/om
-        filters = $1.scan(FilterParser)
+      if filter_markup =~ FILTER_MARKUP_REGEX
+        filters = Regexp.last_match(1).scan(FILTER_PARSER)
         filters.each do |f|
           next unless f =~ /\w+/
+
           filtername = Regexp.last_match(0)
-          filterargs = f.scan(/(?:#{FilterArgumentSeparator}|#{ArgumentSeparator})\s*((?:\w+\s*\:\s*)?#{QuotedFragment})/o).flatten
+          filterargs = f.scan(FILTER_ARGS_REGEX).flatten
           @filters << parse_filter_expressions(filtername, filterargs)
         end
       end
@@ -79,31 +88,43 @@ 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)
       filter_args = []
-      keyword_args = {}
+      keyword_args = nil
       unparsed_args.each do |a|
-        if matches = a.match(/\A#{TagAttributes}\z/o)
+        if (matches = a.match(JUST_TAG_ATTRIBUTES))
+          keyword_args ||= {}
           keyword_args[matches[1]] = Expression.parse(matches[2])
         else
           filter_args << Expression.parse(a)
         end
       end
       result = [filter_name, filter_args]
-      result << keyword_args unless keyword_args.empty?
+      result << keyword_args if keyword_args
       result
     end
 
     def evaluate_filter_expressions(context, filter_args, filter_kwargs)
-      parsed_args = filter_args.map{ |expr| context.evaluate(expr) }
+      parsed_args = filter_args.map { |expr| context.evaluate(expr) }
       if filter_kwargs
         parsed_kwargs = {}
         filter_kwargs.each do |key, expr|
@@ -118,7 +139,7 @@ module Liquid
       return unless obj.tainted?
       return if Template.taint_mode == :lax
 
-      @markup =~ QuotedFragment
+      @markup =~ QUOTED_FRAGMENT
       name = Regexp.last_match(0)
 
       error = TaintedError.new("variable '#{name}' is tainted and was not escaped")
@@ -132,5 +153,11 @@ module Liquid
         raise error
       end
     end
+
+    class ParseTreeVisitor < Liquid::ParseTreeVisitor
+      def children
+        [@node.name] + @node.filters.flatten
+      end
+    end
   end
 end

lib/liquid/variable_lookup.rb

@@ -1,7 +1,9 @@
+# frozen_string_literal: true
+
 module Liquid
   class VariableLookup
-    SQUARE_BRACKETED = /\A\[(.*)\]\z/m
-    COMMAND_METHODS = ['size'.freeze, 'first'.freeze, 'last'.freeze]
+    SQUARE_BRACKETED = /\A\[(.*)\]\z/m.freeze
+    COMMAND_METHODS = %w[size first last].freeze
 
     attr_reader :name, :lookups
 
@@ -10,12 +12,10 @@ module Liquid
     end
 
     def initialize(markup)
-      lookups = markup.scan(VariableParser)
+      lookups = markup.scan(VARIABLE_PARSER)
 
       name = lookups.shift
-      if name =~ SQUARE_BRACKETED
-        name = Expression.parse($1)
-      end
+      name = Expression.parse(Regexp.last_match(1)) if name =~ SQUARE_BRACKETED
       @name = name
 
       @lookups = lookups
@@ -24,7 +24,7 @@ module Liquid
       @lookups.each_index do |i|
         lookup = lookups[i]
         if lookup =~ SQUARE_BRACKETED
-          lookups[i] = Expression.parse($1)
+          lookups[i] = Expression.parse(Regexp.last_match(1))
         elsif COMMAND_METHODS.include?(lookup)
           @command_flags |= 1 << i
         end
@@ -41,8 +41,8 @@ module Liquid
         # If object is a hash- or array-like object we look for the
         # presence of the key and if its available we return it
         if object.respond_to?(:[]) &&
-            ((object.respond_to?(:key?) && object.key?(key)) ||
-             (object.respond_to?(:fetch) && key.is_a?(Integer)))
+           ((object.respond_to?(:key?) && object.key?(key)) ||
+            (object.respond_to?(:fetch) && key.is_a?(Integer)))
 
           # if its a proc we will replace the entry with the proc
           res = context.lookup_and_evaluate(object, key)
@@ -55,9 +55,12 @@ module Liquid
           object = object.send(key).to_liquid
 
           # No key was present with the desired value and it wasn't one of the directly supported
-          # keywords either. The only thing we got left is to return nil
+          # keywords either. The only thing we got left is to return nil or
+          # raise an exception if `strict_variables` option is set to true
         else
-          return nil
+          return nil unless context.strict_variables
+
+          raise Liquid::UndefinedVariable, "undefined variable #{key}"
         end
 
         # If we are dealing with a drop here we have to
@@ -76,5 +79,11 @@ module Liquid
     def state
       [@name, @lookups, @command_flags]
     end
+
+    class ParseTreeVisitor < Liquid::ParseTreeVisitor
+      def children
+        @node.lookups
+      end
+    end
   end
 end

lib/liquid/version.rb

@@ -1,4 +1,5 @@
-# encoding: utf-8
+# frozen_string_literal: true
+
 module Liquid
-  VERSION = "4.0.0.rc1"
+  VERSION = '4.0.3'
 end

liquid.gemspec

@@ -1,29 +1,31 @@
-# encoding: utf-8
-lib = File.expand_path('../lib/', __FILE__)
-$LOAD_PATH.unshift lib unless $LOAD_PATH.include?(lib)
+# frozen_string_literal: true
 
-require "liquid/version"
+lib = File.expand_path('lib', __dir__)
+$LOAD_PATH.unshift(lib) unless $LOAD_PATH.include?(lib)
+
+require 'liquid/version'
 
 Gem::Specification.new do |s|
-  s.name        = "liquid"
+  s.name        = 'liquid'
   s.version     = Liquid::VERSION
   s.platform    = Gem::Platform::RUBY
-  s.summary     = "A secure, non-evaling end user template engine with aesthetic markup."
-  s.authors     = ["Tobias Lütke"]
-  s.email       = ["tobi@leetsoft.com"]
-  s.homepage    = "http://www.liquidmarkup.org"
-  s.license     = "MIT"
+  s.summary     = 'A secure, non-evaling end user template engine with aesthetic markup.'
+  s.authors     = ['Tobias Lütke']
+  s.email       = ['tobi@leetsoft.com']
+  s.homepage    = 'http://www.liquidmarkup.org'
+  s.license     = 'MIT'
   # s.description = "A secure, non-evaling end user template engine with aesthetic markup."
 
-  s.required_rubygems_version = ">= 1.3.7"
+  s.required_ruby_version     = '>= 2.4.0'
+  s.required_rubygems_version = '>= 1.3.7'
 
-  s.test_files  = Dir.glob("{test}/**/*")
-  s.files       = Dir.glob("{lib}/**/*") + %w(LICENSE README.md)
+  s.test_files  = Dir.glob('{test}/**/*')
+  s.files       = Dir.glob('{lib}/**/*') + %w[LICENSE README.md]
 
-  s.extra_rdoc_files = ["History.md", "README.md"]
+  s.extra_rdoc_files = ['History.md', 'README.md']
 
-  s.require_path = "lib"
+  s.require_path = 'lib'
 
-  s.add_development_dependency 'rake'
-  s.add_development_dependency 'minitest'
+  s.add_development_dependency('minitest')
+  s.add_development_dependency('rake', '~> 11.3')
 end

performance/benchmark.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'benchmark/ips'
 require_relative 'theme_runner'
 
@@ -5,13 +7,14 @@ Liquid::Template.error_mode = ARGV.first.to_sym if ARGV.first
 profiler = ThemeRunner.new
 
 Benchmark.ips do |x|
-  x.time = 60
+  x.time = 10
   x.warmup = 5
 
   puts
   puts "Running benchmark for #{x.time} seconds (with #{x.warmup} seconds warmup)."
   puts
 
-  x.report("parse:") { profiler.compile }
-  x.report("parse & run:") { profiler.run }
+  x.report('parse:') { profiler.compile }
+  x.report('render:') { profiler.render }
+  x.report('parse & render:') { profiler.run }
 end

performance/memory_profile.rb

@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+
+require 'benchmark/ips'
+require 'memory_profiler'
+require_relative 'theme_runner'
+
+def profile(phase, &block)
+  puts
+  puts "#{phase}:"
+  puts
+
+  report = MemoryProfiler.report(&block)
+
+  report.pretty_print(
+    color_output: true,
+    scale_bytes: true,
+    detailed_report: true
+  )
+end
+
+Liquid::Template.error_mode = ARGV.first.to_sym if ARGV.first
+
+profiler = ThemeRunner.new
+
+profile('Parsing') { profiler.compile }
+profile('Rendering') { profiler.render }

performance/profile.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'stackprof'
 require_relative 'theme_runner'
 
@@ -5,7 +7,7 @@ Liquid::Template.error_mode = ARGV.first.to_sym if ARGV.first
 profiler = ThemeRunner.new
 profiler.run
 
-[:cpu, :object].each do |profile_type|
+%i[cpu object].each do |profile_type|
   puts "Profiling in #{profile_type} mode..."
   results = StackProf.run(mode: profile_type) do
     200.times do
@@ -13,12 +15,12 @@ profiler.run
     end
   end
 
-  if profile_type == :cpu && graph_filename = ENV['GRAPH_FILENAME']
+  if profile_type == :cpu && (graph_filename = ENV['GRAPH_FILENAME'])
     File.open(graph_filename, 'w') do |f|
       StackProf::Report.new(results).print_graphviz(nil, f)
     end
   end
 
   StackProf::Report.new(results).print_text(false, 20)
-  File.write(ENV['FILENAME'] + "." + profile_type.to_s, Marshal.dump(results)) if ENV['FILENAME']
+  File.write(ENV['FILENAME'] + '.' + profile_type.to_s, Marshal.dump(results)) if ENV['FILENAME']
 end

performance/shopify/comment_form.rb

@@ -1,18 +1,20 @@
+# frozen_string_literal: true
+
 class CommentForm < Liquid::Block
-  Syntax = /(#{Liquid::VariableSignature}+)/
+  SYNTAX = /(#{Liquid::VARIABLE_SIGNATURE}+)/.freeze
 
   def initialize(tag_name, markup, options)
     super
 
-    if markup =~ Syntax
-      @variable_name = $1
+    if markup =~ SYNTAX
+      @variable_name = Regexp.last_match(1)
       @attributes = {}
     else
-      raise SyntaxError.new("Syntax Error in 'comment_form' - Valid syntax: comment_form [article]")
+      raise SyntaxError, "Syntax Error in 'comment_form' - Valid syntax: comment_form [article]"
     end
   end
 
-  def render(context)
+  def render_to_output_buffer(context, output)
     article = context[@variable_name]
 
     context.stack do
@@ -20,10 +22,12 @@ class CommentForm < Liquid::Block
         'posted_successfully?' => context.registers[:posted_successfully],
         'errors' => context['comment.errors'],
         'author' => context['comment.author'],
-        'email'  => context['comment.email'],
-        'body'   => context['comment.body']
+        '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/database.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'yaml'
 
 module Database
@@ -16,8 +18,11 @@ module Database
       end
 
       # key the tables by handles, as this is how liquid expects it.
-      db = db.inject({}) do |assigns, (key, values)|
-        assigns[key] = values.inject({}) { |h, v| h[v['handle']] = v; h; }
+      db = db.each_with_object({}) do |(key, values), assigns|
+        assigns[key] = values.each_with_object({}) do |v, h|
+          h[v['handle']] = v
+          h
+        end
         assigns
       end
 
@@ -29,9 +34,9 @@ module Database
       db['article']    = db['blog']['articles'].first
 
       db['cart']       = {
-        'total_price' => db['line_items'].values.inject(0) { |sum, item| sum += item['line_price'] * item['quantity'] },
-        'item_count'  => db['line_items'].values.inject(0) { |sum, item| sum += item['quantity'] },
-        'items'       => db['line_items'].values
+        'total_price' => db['line_items'].values.inject(0) { |sum, item| sum + item['line_price'] * item['quantity'] },
+        'item_count' => db['line_items'].values.inject(0) { |sum, item| sum + item['quantity'] },
+        'items' => db['line_items'].values,
       }
 
       db
@@ -40,6 +45,6 @@ module Database
 end
 
 if __FILE__ == $PROGRAM_NAME
-  p Database.tables['collections']['frontpage'].keys
+  p(Database.tables['collections']['frontpage'].keys)
   # p Database.tables['blog']['articles']
 end

performance/shopify/json_filter.rb

@@ -1,7 +1,9 @@
+# frozen_string_literal: true
+
 require 'json'
 
 module JsonFilter
   def json(object)
-    JSON.dump(object.reject { |k, v| k == "collections" })
+    JSON.dump(object.reject { |k, _v| k == 'collections' })
   end
 end

performance/shopify/liquid.rb

@@ -1,4 +1,6 @@
-$:.unshift __dir__ + '/../../lib'
+# frozen_string_literal: true
+
+$LOAD_PATH.unshift(__dir__ + '/../../lib')
 require_relative '../../lib/liquid'
 
 require_relative 'comment_form'
@@ -9,11 +11,11 @@ require_relative 'shop_filter'
 require_relative 'tag_filter'
 require_relative 'weight_filter'
 
-Liquid::Template.register_tag 'paginate', Paginate
-Liquid::Template.register_tag 'form', CommentForm
+Liquid::Template.register_tag('paginate', Paginate)
+Liquid::Template.register_tag('form', CommentForm)
 
-Liquid::Template.register_filter JsonFilter
-Liquid::Template.register_filter MoneyFilter
-Liquid::Template.register_filter WeightFilter
-Liquid::Template.register_filter ShopFilter
-Liquid::Template.register_filter TagFilter
+Liquid::Template.register_filter(JsonFilter)
+Liquid::Template.register_filter(MoneyFilter)
+Liquid::Template.register_filter(WeightFilter)
+Liquid::Template.register_filter(ShopFilter)
+Liquid::Template.register_filter(TagFilter)

performance/shopify/money_filter.rb

@@ -1,12 +1,16 @@
+# frozen_string_literal: true
+
 module MoneyFilter
   def money_with_currency(money)
     return '' if money.nil?
-    sprintf("$ %.2f USD", money / 100.0)
+
+    format('$ %.2f USD', money / 100.0)
   end
 
   def money(money)
     return '' if money.nil?
-    sprintf("$ %.2f", money / 100.0)
+
+    format('$ %.2f', money / 100.0)
   end
 
   private

performance/shopify/paginate.rb

@@ -1,49 +1,51 @@
+# frozen_string_literal: true
+
 class Paginate < Liquid::Block
-  Syntax     = /(#{Liquid::QuotedFragment})\s*(by\s*(\d+))?/
+  SYNTAX = /(#{Liquid::QUOTED_FRAGMENT})\s*(by\s*(\d+))?/.freeze
 
   def initialize(tag_name, markup, options)
     super
 
-    if markup =~ Syntax
-      @collection_name = $1
-      @page_size = if $2
-        $3.to_i
+    if markup =~ SYNTAX
+      @collection_name = Regexp.last_match(1)
+      @page_size = if Regexp.last_match(2)
+        Regexp.last_match(3).to_i
       else
         20
       end
 
       @attributes = { 'window_size' => 3 }
-      markup.scan(Liquid::TagAttributes) do |key, value|
+      markup.scan(Liquid::TAG_ATTRIBUTES) do |key, value|
         @attributes[key] = value
       end
     else
-      raise SyntaxError.new("Syntax Error in tag 'paginate' - Valid syntax: paginate [collection] by number")
+      raise SyntaxError, "Syntax Error in tag 'paginate' - Valid syntax: paginate [collection] by number"
     end
   end
 
-  def render(context)
+  def render_to_output_buffer(context, output)
     @context = context
 
     context.stack do
-      current_page  = context['current_page'].to_i
+      current_page = context['current_page'].to_i
 
       pagination = {
-        'page_size'      => @page_size,
-        'current_page'   => 5,
-        'current_offset' => @page_size * 5
+        'page_size' => @page_size,
+        'current_page' => 5,
+        'current_offset' => @page_size * 5,
       }
 
       context['paginate'] = pagination
 
-      collection_size  = context[@collection_name].size
+      collection_size = context[@collection_name].size
 
-      raise ArgumentError.new("Cannot paginate array '#{@collection_name}'. Not found.") if collection_size.nil?
+      raise ArgumentError, "Cannot paginate array '#{@collection_name}'. Not found." if collection_size.nil?
 
       page_count = (collection_size.to_f / @page_size.to_f).to_f.ceil + 1
 
       pagination['items']      = collection_size
       pagination['pages']      = page_count - 1
-      pagination['previous']   = link('&laquo; Previous', current_page - 1)  unless 1 >= current_page
+      pagination['previous']   = link('&laquo; Previous', current_page - 1)  unless current_page <= 1
       pagination['next']       = link('Next &raquo;', current_page + 1)      unless page_count <= current_page + 1
       pagination['parts']      = []
 
@@ -59,6 +61,7 @@ class Paginate < Liquid::Block
             pagination['parts'] << link(page, page)
           elsif page <= current_page - @attributes['window_size'] || page >= current_page + @attributes['window_size']
             next if hellip_break
+
             pagination['parts'] << no_link('&hellip;')
             hellip_break = true
             next
@@ -85,6 +88,6 @@ class Paginate < Liquid::Block
   end
 
   def current_url
-    "/collections/frontpage"
+    '/collections/frontpage'
   end
 end

performance/shopify/shop_filter.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ShopFilter
   def asset_url(input)
     "/files/1/[shop_id]/[shop_id]/assets/#{input}"
@@ -15,15 +17,15 @@ module ShopFilter
     %(<script src="#{url}" type="text/javascript"></script>)
   end
 
-  def stylesheet_tag(url, media = "all")
+  def stylesheet_tag(url, media = 'all')
     %(<link href="#{url}" rel="stylesheet" type="text/css"  media="#{media}"  />)
   end
 
-  def link_to(link, url, title = "")
+  def link_to(link, url, title = '')
     %(<a href="#{url}" title="#{title}">#{link}</a>)
   end
 
-  def img_tag(url, alt = "")
+  def img_tag(url, alt = '')
     %(<img src="#{url}" alt="#{alt}" />)
   end
 
@@ -52,15 +54,13 @@ module ShopFilter
   end
 
   def product_img_url(url, style = 'small')
-    unless url =~ /\Aproducts\/([\w\-\_]+)\.(\w{2,4})/
-      raise ArgumentError, 'filter "size" can only be called on product images'
-    end
+    raise ArgumentError, 'filter "size" can only be called on product images' unless url =~ %r{\Aproducts/([\w\-\_]+)\.(\w{2,4})}
 
     case style
     when 'original'
       return '/files/shops/random_number/' + url
     when 'grande', 'large', 'medium', 'compact', 'small', 'thumb', 'icon'
-      "/files/shops/random_number/products/#{$1}_#{style}.#{$2}"
+      "/files/shops/random_number/products/#{Regexp.last_match(1)}_#{style}.#{Regexp.last_match(2)}"
     else
       raise ArgumentError, 'valid parameters for filter "size" are: original, grande, large, medium, compact, small, thumb and icon '
     end
@@ -70,16 +70,14 @@ module ShopFilter
     html = []
     html << %(<span class="prev">#{link_to(paginate['previous']['title'], paginate['previous']['url'])}</span>) if paginate['previous']
 
-    for part in paginate['parts']
-
-      if part['is_link']
-        html << %(<span class="page">#{link_to(part['title'], part['url'])}</span>)
+    paginate['parts'].each do |part|
+      html << if part['is_link']
+        %(<span class="page">#{link_to(part['title'], part['url'])}</span>)
       elsif part['title'].to_i == paginate['current_page'].to_i
-        html << %(<span class="page current">#{part['title']}</span>)
+        %(<span class="page current">#{part['title']}</span>)
       else
-        html << %(<span class="deco">#{part['title']}</span>)
+        %(<span class="deco">#{part['title']}</span>)
       end
-
     end
 
     html << %(<span class="next">#{link_to(paginate['next']['title'], paginate['next']['url'])}</span>) if paginate['next']

performance/shopify/tag_filter.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module TagFilter
   def link_to_tag(label, tag)
     "<a title=\"Show tag #{tag}\" href=\"/collections/#{@context['handle']}/#{tag}\">#{label}</a>"
@@ -13,11 +15,11 @@ module TagFilter
 
   def link_to_add_tag(label, tag)
     tags = (@context['current_tags'] + [tag]).uniq
-    "<a title=\"Show tag #{tag}\" href=\"/collections/#{@context['handle']}/#{tags.join("+")}\">#{label}</a>"
+    "<a title=\"Show tag #{tag}\" href=\"/collections/#{@context['handle']}/#{tags.join('+')}\">#{label}</a>"
   end
 
   def link_to_remove_tag(label, tag)
     tags = (@context['current_tags'] - [tag]).uniq
-    "<a title=\"Show tag #{tag}\" href=\"/collections/#{@context['handle']}/#{tags.join("+")}\">#{label}</a>"
+    "<a title=\"Show tag #{tag}\" href=\"/collections/#{@context['handle']}/#{tags.join('+')}\">#{label}</a>"
   end
 end

performance/shopify/weight_filter.rb

@@ -1,6 +1,8 @@
+# frozen_string_literal: true
+
 module WeightFilter
   def weight(grams)
-    sprintf("%.2f", grams / 1000)
+    format('%.2f', grams / 1000)
   end
 
   def weight_with_unit(grams)

performance/theme_runner.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # This profiler run simulates Shopify.
 # We are looking in the tests directory for liquid files and render them within the designated layout file.
 # We will also export a substantial database to liquid which the templates can render values of.
@@ -21,53 +23,100 @@ class ThemeRunner
     end
   end
 
-  # Load all templates into memory, do this now so that
-  # we don't profile IO.
+  # Initialize a new liquid ThemeRunner instance
+  # Will load all templates into memory, do this now so that we don't profile IO.
   def initialize
     @tests = Dir[__dir__ + '/tests/**/*.liquid'].collect do |test|
       next if File.basename(test) == 'theme.liquid'
 
       theme_path = File.dirname(test) + '/theme.liquid'
-
-      [File.read(test), (File.file?(theme_path) ? File.read(theme_path) : nil), test]
+      {
+        liquid: File.read(test),
+        layout: (File.file?(theme_path) ? File.read(theme_path) : nil),
+        template_name: test,
+      }
     end.compact
+
+    compile_all_tests
   end
 
+  # `compile` will test just the compilation portion of liquid without any templates
   def compile
-    # Dup assigns because will make some changes to them
-
-    @tests.each do |liquid, layout, template_name|
-      tmpl = Liquid::Template.new
-      tmpl.parse(liquid)
-      tmpl = Liquid::Template.new
-      tmpl.parse(layout)
+    @tests.each do |test_hash|
+      Liquid::Template.new.parse(test_hash[:liquid])
+      Liquid::Template.new.parse(test_hash[:layout])
     end
   end
 
+  # `run` is called to benchmark rendering and compiling at the same time
   def run
-    # Dup assigns because will make some changes to them
-    assigns = Database.tables.dup
-
-    @tests.each do |liquid, layout, template_name|
-      # Compute page_tempalte outside of profiler run, uninteresting to profiler
-      page_template = File.basename(template_name, File.extname(template_name))
+    each_test do |liquid, layout, assigns, page_template, template_name|
       compile_and_render(liquid, layout, assigns, page_template, template_name)
     end
   end
 
+  # `render` is called to benchmark just the render portion of liquid
+  def render
+    @compiled_tests.each do |test|
+      tmpl = test[:tmpl]
+      assigns = test[:assigns]
+      layout = test[:layout]
+
+      if layout
+        assigns['content_for_layout'] = tmpl.render!(assigns)
+        layout.render!(assigns)
+      else
+        tmpl.render!(assigns)
+      end
+    end
+  end
+
+  private
+
   def compile_and_render(template, layout, assigns, page_template, template_file)
+    compiled_test = compile_test(template, layout, assigns, page_template, template_file)
+    assigns['content_for_layout'] = compiled_test[:tmpl].render!(assigns)
+    compiled_test[:layout].render!(assigns) if layout
+  end
+
+  def compile_all_tests
+    @compiled_tests = []
+    each_test do |liquid, layout, assigns, page_template, template_name|
+      @compiled_tests << compile_test(liquid, layout, assigns, page_template, template_name)
+    end
+    @compiled_tests
+  end
+
+  def compile_test(template, layout, assigns, page_template, template_file)
+    tmpl = init_template(page_template, template_file)
+    parsed_template = tmpl.parse(template).dup
+
+    if layout
+      parsed_layout = tmpl.parse(layout)
+      { tmpl: parsed_template, assigns: assigns, layout: parsed_layout }
+    else
+      { tmpl: parsed_template, assigns: assigns }
+    end
+  end
+
+  # utility method with similar functionality needed in `compile_all_tests` and `run`
+  def each_test
+    # Dup assigns because will make some changes to them
+    assigns = Database.tables.dup
+
+    @tests.each do |test_hash|
+      # Compute page_template outside of profiler run, uninteresting to profiler
+      page_template = File.basename(test_hash[:template_name], File.extname(test_hash[:template_name]))
+      yield(test_hash[:liquid], test_hash[:layout], assigns, page_template, test_hash[:template_name])
+    end
+  end
+
+  # set up a new Liquid::Template object for use in `compile_and_render` and `compile_test`
+  def init_template(page_template, template_file)
     tmpl = Liquid::Template.new
     tmpl.assigns['page_title'] = 'Page title'
     tmpl.assigns['template'] = page_template
     tmpl.registers[:file_system] = ThemeRunner::FileSystem.new(File.dirname(template_file))
-
-    content_for_layout = tmpl.parse(template).render!(assigns)
-
-    if layout
-      assigns['content_for_layout'] = content_for_layout
-      tmpl.parse(layout).render!(assigns)
-    else
-      content_for_layout
-    end
+    tmpl
   end
 end

test/integration/assign_test.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 
 class AssignTest < Minitest::Test
@@ -10,29 +12,29 @@ class AssignTest < Minitest::Test
     END_TEMPLATE
     template = Template.parse(template_source)
     rendered = template.render!
-    assert_equal "Print this-thing", rendered.strip
+    assert_equal 'Print this-thing', rendered.strip
   end
 
   def test_assigned_variable
     assert_template_result('.foo.',
-      '{% assign foo = values %}.{{ foo[0] }}.',
-      'values' => %w(foo bar baz))
+                           '{% assign foo = values %}.{{ foo[0] }}.',
+                           'values' => %w[foo bar baz])
 
     assert_template_result('.bar.',
-      '{% assign foo = values %}.{{ foo[1] }}.',
-      'values' => %w(foo bar baz))
+                           '{% assign foo = values %}.{{ foo[1] }}.',
+                           'values' => %w[foo bar baz])
   end
 
   def test_assign_with_filter
     assert_template_result('.bar.',
-      '{% assign foo = values | split: "," %}.{{ foo[1] }}.',
-      'values' => "foo,bar,baz")
+                           '{% assign foo = values | split: "," %}.{{ foo[1] }}.',
+                           'values' => 'foo,bar,baz')
   end
 
   def test_assign_syntax_error
     assert_match_syntax_error(/assign/,
-      '{% assign foo not values %}.',
-      'values' => "foo,bar,baz")
+                              '{% assign foo not values %}.',
+                              'values' => 'foo,bar,baz')
   end
 
   def test_assign_uses_error_mode

test/integration/blank_test.rb

@@ -1,11 +1,12 @@
+# frozen_string_literal: true
+
 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
@@ -31,76 +32,78 @@ 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
-    assert_template_result("", wrap_in_for(" "))
+    assert_template_result('', wrap_in_for(' '))
   end
 
   def test_if_else_are_blank
-    assert_template_result("", "{% if true %} {% elsif false %} {% else %} {% endif %}")
+    assert_template_result('', '{% if true %} {% elsif false %} {% else %} {% endif %}')
   end
 
   def test_unless_is_blank
-    assert_template_result("", wrap("{% unless true %} {% endunless %}"))
+    assert_template_result('', wrap('{% unless true %} {% endunless %}'))
   end
 
   def test_mark_as_blank_only_during_parsing
-    assert_template_result(" " * (N + 1), wrap(" {% if false %} this never happens, but still, this block is not blank {% endif %}"))
+    assert_template_result(' ' * (N + 1), wrap(' {% if false %} this never happens, but still, this block is not blank {% endif %}'))
   end
 
   def test_comments_are_blank
-    assert_template_result("", wrap(" {% comment %} whatever {% endcomment %} "))
+    assert_template_result('', wrap(' {% comment %} whatever {% endcomment %} '))
   end
 
   def test_captures_are_blank
-    assert_template_result("", wrap(" {% capture foo %} whatever {% endcapture %} "))
+    assert_template_result('', wrap(' {% capture foo %} whatever {% endcapture %} '))
   end
 
   def test_nested_blocks_are_blank_but_only_if_all_children_are
-    assert_template_result("", wrap(wrap(" ")))
+    assert_template_result('', wrap(wrap(' ')))
     assert_template_result("\n       but this is not " * (N + 1),
-      wrap('{% if true %} {% comment %} this is blank {% endcomment %} {% endif %}
+                           wrap('{% if true %} {% comment %} this is blank {% endcomment %} {% endif %}
       {% if true %} but this is not {% endif %}'))
   end
 
   def test_assigns_are_blank
-    assert_template_result("", wrap(' {% assign foo = "bar" %} '))
+    assert_template_result('', wrap(' {% assign foo = "bar" %} '))
   end
 
   def test_whitespace_is_blank
-    assert_template_result("", wrap(" "))
-    assert_template_result("", wrap("\t"))
+    assert_template_result('', wrap(' '))
+    assert_template_result('', wrap("\t"))
   end
 
   def test_whitespace_is_not_blank_if_other_stuff_is_present
-    body = "     x "
+    body = '     x '
     assert_template_result(body * (N + 1), wrap(body))
   end
 
   def test_increment_is_not_blank
-    assert_template_result(" 0" * 2 * (N + 1), wrap("{% assign foo = 0 %} {% increment foo %} {% decrement foo %}"))
+    assert_template_result(' 0' * 2 * (N + 1), wrap('{% assign foo = 0 %} {% increment foo %} {% decrement foo %}'))
   end
 
   def test_cycle_is_not_blank
-    assert_template_result("  " * ((N + 1) / 2) + " ", wrap("{% cycle ' ', ' ' %}"))
+    assert_template_result('  ' * ((N + 1) / 2) + ' ', wrap("{% cycle ' ', ' ' %}"))
   end
 
   def test_raw_is_not_blank
-    assert_template_result("  " * (N + 1), wrap(" {% raw %} {% endraw %}"))
+    assert_template_result('  ' * (N + 1), wrap(' {% raw %} {% endraw %}'))
   end
 
   def test_include_is_blank
     Liquid::Template.file_system = BlankTestFileSystem.new
-    assert_template_result "foobar" * (N + 1), wrap("{% include 'foobar' %}")
-    assert_template_result " foobar " * (N + 1), wrap("{% include ' foobar ' %}")
-    assert_template_result "   " * (N + 1), wrap(" {% include ' ' %} ")
+    assert_template_result 'foobar' * (N + 1), wrap("{% include 'foobar' %}")
+    assert_template_result ' foobar ' * (N + 1), wrap("{% include ' foobar ' %}")
+    assert_template_result '   ' * (N + 1), wrap(" {% include ' ' %} ")
   end
 
   def test_case_is_blank
-    assert_template_result("", wrap(" {% assign foo = 'bar' %} {% case foo %} {% when 'bar' %} {% when 'whatever' %} {% else %} {% endcase %} "))
-    assert_template_result("", wrap(" {% assign foo = 'else' %} {% case foo %} {% when 'bar' %} {% when 'whatever' %} {% else %} {% endcase %} "))
-    assert_template_result("   x  " * (N + 1), wrap(" {% assign foo = 'else' %} {% case foo %} {% when 'bar' %} {% when 'whatever' %} {% else %} x {% endcase %} "))
+    assert_template_result('', wrap(" {% assign foo = 'bar' %} {% case foo %} {% when 'bar' %} {% when 'whatever' %} {% else %} {% endcase %} "))
+    assert_template_result('', wrap(" {% assign foo = 'else' %} {% case foo %} {% when 'bar' %} {% when 'whatever' %} {% else %} {% endcase %} "))
+    assert_template_result('   x  ' * (N + 1), wrap(" {% assign foo = 'else' %} {% case foo %} {% when 'bar' %} {% when 'whatever' %} {% else %} x {% endcase %} "))
   end
 end

test/integration/block_test.rb

@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+require 'test_helper'
+
+class BlockTest < Minitest::Test
+  include Liquid
+
+  def test_unexpected_end_tag
+    exc = assert_raises(SyntaxError) do
+      Template.parse('{% if true %}{% endunless %}')
+    end
+    assert_equal exc.message, "Liquid syntax error: 'endunless' is not a valid delimiter for if tags. use endif"
+  end
+end

test/integration/capture_test.rb

@@ -1,10 +1,12 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 
 class CaptureTest < Minitest::Test
   include Liquid
 
   def test_captures_block_content_in_variable
-    assert_template_result("test string", "{% capture 'var' %}test string{% endcapture %}{{var}}", {})
+    assert_template_result('test string', "{% capture 'var' %}test string{% endcapture %}{{var}}", {})
   end
 
   def test_capture_with_hyphen_in_variable_name
@@ -14,7 +16,7 @@ class CaptureTest < Minitest::Test
     END_TEMPLATE
     template = Template.parse(template_source)
     rendered = template.render!
-    assert_equal "Print this-thing", rendered.strip
+    assert_equal 'Print this-thing', rendered.strip
   end
 
   def test_capture_to_variable_from_outer_scope_if_existing
@@ -30,7 +32,7 @@ class CaptureTest < Minitest::Test
     END_TEMPLATE
     template = Template.parse(template_source)
     rendered = template.render!
-    assert_equal "test-string", rendered.gsub(/\s/, '')
+    assert_equal 'test-string', rendered.gsub(/\s/, '')
   end
 
   def test_assigning_from_capture
@@ -45,6 +47,6 @@ class CaptureTest < Minitest::Test
     END_TEMPLATE
     template = Template.parse(template_source)
     rendered = template.render!
-    assert_equal "3-3", rendered.gsub(/\s/, '')
+    assert_equal '3-3', rendered.gsub(/\s/, '')
   end
 end # CaptureTest

test/integration/context_test.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 
 class ContextTest < Minitest::Test

test/integration/document_test.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 
 class DocumentTest < Minitest::Test
@@ -5,14 +7,14 @@ class DocumentTest < Minitest::Test
 
   def test_unexpected_outer_tag
     exc = assert_raises(SyntaxError) do
-      Template.parse("{% else %}")
+      Template.parse('{% else %}')
     end
     assert_equal exc.message, "Liquid syntax error: Unexpected outer 'else' tag"
   end
 
   def test_unknown_tag
     exc = assert_raises(SyntaxError) do
-      Template.parse("{% foo %}")
+      Template.parse('{% foo %}')
     end
     assert_equal exc.message, "Liquid syntax error: Unknown tag 'foo'"
   end

test/integration/drop_test.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 
 class ContextDrop < Liquid::Drop
@@ -21,7 +23,7 @@ end
 class ProductDrop < Liquid::Drop
   class TextDrop < Liquid::Drop
     def array
-      ['text1', 'text2']
+      %w[text1 text2]
     end
 
     def text
@@ -31,7 +33,7 @@ class ProductDrop < Liquid::Drop
 
   class CatchallDrop < Liquid::Drop
     def liquid_method_missing(method)
-      'catchall_method: ' << method.to_s
+      +'catchall_method: ' << method.to_s
     end
   end
 
@@ -48,13 +50,13 @@ class ProductDrop < Liquid::Drop
   end
 
   def user_input
-    "foo".taint
+    (+'foo').taint
   end
 
   protected
 
   def callmenot
-    "protected"
+    'protected'
   end
 end
 
@@ -139,17 +141,17 @@ class DropsTest < Minitest::Test
   end
 
   def test_drop_does_only_respond_to_whitelisted_methods
-    assert_equal "", Liquid::Template.parse("{{ product.inspect }}").render!('product' => ProductDrop.new)
-    assert_equal "", Liquid::Template.parse("{{ product.pretty_inspect }}").render!('product' => ProductDrop.new)
-    assert_equal "", Liquid::Template.parse("{{ product.whatever }}").render!('product' => ProductDrop.new)
-    assert_equal "", Liquid::Template.parse('{{ product | map: "inspect" }}').render!('product' => ProductDrop.new)
-    assert_equal "", Liquid::Template.parse('{{ product | map: "pretty_inspect" }}').render!('product' => ProductDrop.new)
-    assert_equal "", Liquid::Template.parse('{{ product | map: "whatever" }}').render!('product' => ProductDrop.new)
+    assert_equal '', Liquid::Template.parse('{{ product.inspect }}').render!('product' => ProductDrop.new)
+    assert_equal '', Liquid::Template.parse('{{ product.pretty_inspect }}').render!('product' => ProductDrop.new)
+    assert_equal '', Liquid::Template.parse('{{ product.whatever }}').render!('product' => ProductDrop.new)
+    assert_equal '', Liquid::Template.parse('{{ product | map: "inspect" }}').render!('product' => ProductDrop.new)
+    assert_equal '', Liquid::Template.parse('{{ product | map: "pretty_inspect" }}').render!('product' => ProductDrop.new)
+    assert_equal '', Liquid::Template.parse('{{ product | map: "whatever" }}').render!('product' => ProductDrop.new)
   end
 
   def test_drops_respond_to_to_liquid
-    assert_equal "text1", Liquid::Template.parse("{{ product.to_liquid.texts.text }}").render!('product' => ProductDrop.new)
-    assert_equal "text1", Liquid::Template.parse('{{ product | map: "to_liquid" | map: "texts" | map: "text" }}').render!('product' => ProductDrop.new)
+    assert_equal 'text1', Liquid::Template.parse('{{ product.to_liquid.texts.text }}').render!('product' => ProductDrop.new)
+    assert_equal 'text1', Liquid::Template.parse('{{ product | map: "to_liquid" | map: "texts" | map: "text" }}').render!('product' => ProductDrop.new)
   end
 
   def test_text_drop
@@ -173,12 +175,12 @@ class DropsTest < Minitest::Test
   end
 
   def test_context_drop
-    output = Liquid::Template.parse(' {{ context.bar }} ').render!('context' => ContextDrop.new, 'bar' => "carrot")
+    output = Liquid::Template.parse(' {{ context.bar }} ').render!('context' => ContextDrop.new, 'bar' => 'carrot')
     assert_equal ' carrot ', output
   end
 
   def test_nested_context_drop
-    output = Liquid::Template.parse(' {{ product.context.foo }} ').render!('product' => ProductDrop.new, 'foo' => "monkey")
+    output = Liquid::Template.parse(' {{ product.context.foo }} ').render!('product' => ProductDrop.new, 'foo' => 'monkey')
     assert_equal ' monkey ', output
   end
 
@@ -188,7 +190,7 @@ class DropsTest < Minitest::Test
   end
 
   def test_object_methods_not_allowed
-    [:dup, :clone, :singleton_class, :eval, :class_eval, :inspect].each do |method|
+    %i[dup clone singleton_class eval class_eval inspect].each do |method|
       output = Liquid::Template.parse(" {{ product.#{method} }} ").render!('product' => ProductDrop.new)
       assert_equal '  ', output
     end
@@ -201,9 +203,9 @@ class DropsTest < Minitest::Test
   end
 
   def test_scope_though_proc
-    assert_equal '1', Liquid::Template.parse('{{ s }}').render!('context' => ContextDrop.new, 's' => proc{ |c| c['context.scopes'] })
-    assert_equal '2', Liquid::Template.parse('{%for i in dummy%}{{ s }}{%endfor%}').render!('context' => ContextDrop.new, 's' => proc{ |c| c['context.scopes'] }, 'dummy' => [1])
-    assert_equal '3', Liquid::Template.parse('{%for i in dummy%}{%for i in dummy%}{{ s }}{%endfor%}{%endfor%}').render!('context' => ContextDrop.new, 's' => proc{ |c| c['context.scopes'] }, 'dummy' => [1])
+    assert_equal '1', Liquid::Template.parse('{{ s }}').render!('context' => ContextDrop.new, 's' => proc { |c| c['context.scopes'] })
+    assert_equal '2', Liquid::Template.parse('{%for i in dummy%}{{ s }}{%endfor%}').render!('context' => ContextDrop.new, 's' => proc { |c| c['context.scopes'] }, 'dummy' => [1])
+    assert_equal '3', Liquid::Template.parse('{%for i in dummy%}{%for i in dummy%}{{ s }}{%endfor%}{%endfor%}').render!('context' => ContextDrop.new, 's' => proc { |c| c['context.scopes'] }, 'dummy' => [1])
   end
 
   def test_scope_with_assigns
@@ -232,7 +234,7 @@ class DropsTest < Minitest::Test
   end
 
   def test_enumerable_drop_will_invoke_liquid_method_missing_for_clashing_method_names
-    ["select", "each", "map", "cycle"].each do |method|
+    %w[select each map cycle].each do |method|
       assert_equal method.to_s, Liquid::Template.parse("{{collection.#{method}}}").render!('collection' => EnumerableDrop.new)
       assert_equal method.to_s, Liquid::Template.parse("{{collection[\"#{method}\"]}}").render!('collection' => EnumerableDrop.new)
       assert_equal method.to_s, Liquid::Template.parse("{{collection.#{method}}}").render!('collection' => RealEnumerableDrop.new)
@@ -241,20 +243,20 @@ class DropsTest < Minitest::Test
   end
 
   def test_some_enumerable_methods_still_get_invoked
-    [ :count, :max ].each do |method|
-      assert_equal "3", Liquid::Template.parse("{{collection.#{method}}}").render!('collection' => RealEnumerableDrop.new)
-      assert_equal "3", Liquid::Template.parse("{{collection[\"#{method}\"]}}").render!('collection' => RealEnumerableDrop.new)
-      assert_equal "3", Liquid::Template.parse("{{collection.#{method}}}").render!('collection' => EnumerableDrop.new)
-      assert_equal "3", Liquid::Template.parse("{{collection[\"#{method}\"]}}").render!('collection' => EnumerableDrop.new)
+    %i[count max].each do |method|
+      assert_equal '3', Liquid::Template.parse("{{collection.#{method}}}").render!('collection' => RealEnumerableDrop.new)
+      assert_equal '3', Liquid::Template.parse("{{collection[\"#{method}\"]}}").render!('collection' => RealEnumerableDrop.new)
+      assert_equal '3', Liquid::Template.parse("{{collection.#{method}}}").render!('collection' => EnumerableDrop.new)
+      assert_equal '3', Liquid::Template.parse("{{collection[\"#{method}\"]}}").render!('collection' => EnumerableDrop.new)
     end
 
-    assert_equal "yes", Liquid::Template.parse("{% if collection contains 3 %}yes{% endif %}").render!('collection' => RealEnumerableDrop.new)
+    assert_equal 'yes', Liquid::Template.parse('{% if collection contains 3 %}yes{% endif %}').render!('collection' => RealEnumerableDrop.new)
 
-    [ :min, :first ].each do |method|
-      assert_equal "1", Liquid::Template.parse("{{collection.#{method}}}").render!('collection' => RealEnumerableDrop.new)
-      assert_equal "1", Liquid::Template.parse("{{collection[\"#{method}\"]}}").render!('collection' => RealEnumerableDrop.new)
-      assert_equal "1", Liquid::Template.parse("{{collection.#{method}}}").render!('collection' => EnumerableDrop.new)
-      assert_equal "1", Liquid::Template.parse("{{collection[\"#{method}\"]}}").render!('collection' => EnumerableDrop.new)
+    %i[min first].each do |method|
+      assert_equal '1', Liquid::Template.parse("{{collection.#{method}}}").render!('collection' => RealEnumerableDrop.new)
+      assert_equal '1', Liquid::Template.parse("{{collection[\"#{method}\"]}}").render!('collection' => RealEnumerableDrop.new)
+      assert_equal '1', Liquid::Template.parse("{{collection.#{method}}}").render!('collection' => EnumerableDrop.new)
+      assert_equal '1', Liquid::Template.parse("{{collection[\"#{method}\"]}}").render!('collection' => EnumerableDrop.new)
     end
   end
 
@@ -267,7 +269,7 @@ class DropsTest < Minitest::Test
   end
 
   def test_default_to_s_on_drops
-    assert_equal 'ProductDrop', Liquid::Template.parse("{{ product }}").render!('product' => ProductDrop.new)
+    assert_equal 'ProductDrop', Liquid::Template.parse('{{ product }}').render!('product' => ProductDrop.new)
     assert_equal 'EnumerableDrop', Liquid::Template.parse('{{ collection }}').render!('collection' => EnumerableDrop.new)
   end
 end # DropsTest

test/integration/error_handling_test.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 
 class ErrorHandlingTest < Minitest::Test
@@ -83,18 +85,32 @@ class ErrorHandlingTest < Minitest::Test
 
   def test_with_line_numbers_adds_numbers_to_parser_errors
     err = assert_raises(SyntaxError) do
-      Liquid::Template.parse(%q(
+      Liquid::Template.parse('
           foobar
 
           {% "cat" | foobar %}
 
           bla
-        ),
-        line_numbers: true
-      )
+        ',
+                             line_numbers: true)
     end
 
-    assert_match /Liquid syntax error \(line 4\)/, err.message
+    assert_match(/Liquid syntax error \(line 4\)/, err.message)
+  end
+
+  def test_with_line_numbers_adds_numbers_to_parser_errors_with_whitespace_trim
+    err = assert_raises(SyntaxError) do
+      Liquid::Template.parse('
+          foobar
+
+          {%- "cat" | foobar -%}
+
+          bla
+        ',
+                             line_numbers: true)
+    end
+
+    assert_match(/Liquid syntax error \(line 4\)/, err.message)
   end
 
   def test_parsing_warn_with_line_numbers_adds_numbers_to_lexer_errors
@@ -105,12 +121,11 @@ class ErrorHandlingTest < Minitest::Test
 
         bla
             ',
-      error_mode: :warn,
-      line_numbers: true
-                                     )
+                                      error_mode: :warn,
+                                      line_numbers: true)
 
     assert_equal ['Liquid syntax error (line 4): Unexpected character = in "1 =! 2"'],
-      template.warnings.map(&:message)
+                 template.warnings.map(&:message)
   end
 
   def test_parsing_strict_with_line_numbers_adds_numbers_to_lexer_errors
@@ -122,9 +137,8 @@ class ErrorHandlingTest < Minitest::Test
 
           bla
                 ',
-        error_mode: :strict,
-        line_numbers: true
-                            )
+                             error_mode: :strict,
+                             line_numbers: true)
     end
 
     assert_equal 'Liquid syntax error (line 4): Unexpected character = in "1 =! 2"', err.message
@@ -141,8 +155,7 @@ class ErrorHandlingTest < Minitest::Test
 
           bla
                 ',
-        line_numbers: true
-                            )
+                             line_numbers: true)
     end
 
     assert_equal "Liquid syntax error (line 5): Unknown tag 'foo'", err.message
@@ -186,27 +199,51 @@ class ErrorHandlingTest < Minitest::Test
     end
   end
 
-  def test_exception_handler_with_string_result
-    template = Liquid::Template.parse('This is an argument error: {{ errors.argument_error }}')
-    output = template.render({ 'errors' => ErrorDrop.new }, exception_handler: ->(e) { '' })
-    assert_equal 'This is an argument error: ', output
-    assert_equal [ArgumentError], template.errors.map(&:class)
-  end
-
-  class InternalError < Liquid::Error
-  end
-
-  def test_exception_handler_with_exception_result
+  def test_default_exception_renderer_with_internal_error
     template = Liquid::Template.parse('This is a runtime error: {{ errors.runtime_error }}', line_numbers: true)
-    handler = ->(e) { e.is_a?(Liquid::Error) ? e : InternalError.new('internal') }
-    output = template.render({ 'errors' => ErrorDrop.new }, exception_handler: handler)
+
+    output = template.render('errors' => ErrorDrop.new)
+
     assert_equal 'This is a runtime error: Liquid error (line 1): internal', output
-    assert_equal [InternalError], template.errors.map(&:class)
+    assert_equal [Liquid::InternalError], template.errors.map(&:class)
+  end
+
+  def test_setting_default_exception_renderer
+    old_exception_renderer = Liquid::Template.default_exception_renderer
+    exceptions = []
+    Liquid::Template.default_exception_renderer = lambda { |e|
+      exceptions << e
+      ''
+    }
+    template = Liquid::Template.parse('This is a runtime error: {{ errors.argument_error }}')
+
+    output = template.render('errors' => ErrorDrop.new)
+
+    assert_equal 'This is a runtime error: ', output
+    assert_equal [Liquid::ArgumentError], template.errors.map(&:class)
+  ensure
+    Liquid::Template.default_exception_renderer = old_exception_renderer if old_exception_renderer
+  end
+
+  def test_exception_renderer_exposing_non_liquid_error
+    template = Liquid::Template.parse('This is a runtime error: {{ errors.runtime_error }}', line_numbers: true)
+    exceptions = []
+    handler = lambda { |e|
+      exceptions << e
+      e.cause
+    }
+
+    output = template.render({ 'errors' => ErrorDrop.new }, exception_renderer: handler)
+
+    assert_equal 'This is a runtime error: runtime error', output
+    assert_equal [Liquid::InternalError], exceptions.map(&:class)
+    assert_equal exceptions, template.errors
+    assert_equal '#<RuntimeError: runtime error>', exceptions.first.cause.inspect
   end
 
   class TestFileSystem
-    def read_template_file(template_path)
-      "{{ errors.argument_error }}"
+    def read_template_file(_template_path)
+      '{{ errors.argument_error }}'
     end
   end
 
@@ -221,6 +258,6 @@ class ErrorHandlingTest < Minitest::Test
       Liquid::Template.file_system = old_file_system
     end
     assert_equal "Argument error:\nLiquid error (product line 1): argument error", page
-    assert_equal "product", template.errors.first.template_name
+    assert_equal 'product', template.errors.first.template_name
   end
 end

test/integration/filter_test.rb

@@ -1,24 +1,26 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 
 module MoneyFilter
   def money(input)
-    sprintf(' %d$ ', input)
+    format(' %d$ ', input)
   end
 
   def money_with_underscore(input)
-    sprintf(' %d$ ', input)
+    format(' %d$ ', input)
   end
 end
 
 module CanadianMoneyFilter
   def money(input)
-    sprintf(' %d$ CAD ', input)
+    format(' %d$ CAD ', input)
   end
 end
 
 module SubstituteFilter
   def substitute(input, params = {})
-    input.gsub(/%\{(\w+)\}/) { |match| params[$1] }
+    input.gsub(/%\{(\w+)\}/) { |_match| params[Regexp.last_match(1)] }
   end
 end
 
@@ -26,8 +28,8 @@ class FiltersTest < Minitest::Test
   include Liquid
 
   module OverrideObjectMethodFilter
-    def tap(input)
-      "tap overridden"
+    def tap(_input)
+      'tap overridden'
     end
   end
 
@@ -39,13 +41,13 @@ class FiltersTest < Minitest::Test
     @context['var'] = 1000
     @context.add_filters(MoneyFilter)
 
-    assert_equal ' 1000$ ', Template.parse("{{var | money}}").render(@context)
+    assert_equal ' 1000$ ', Template.parse('{{var | money}}').render(@context)
   end
 
   def test_underscore_in_filter_name
     @context['var'] = 1000
     @context.add_filters(MoneyFilter)
-    assert_equal ' 1000$ ', Template.parse("{{var | money_with_underscore}}").render(@context)
+    assert_equal ' 1000$ ', Template.parse('{{var | money_with_underscore}}').render(@context)
   end
 
   def test_second_filter_overwrites_first
@@ -53,43 +55,43 @@ class FiltersTest < Minitest::Test
     @context.add_filters(MoneyFilter)
     @context.add_filters(CanadianMoneyFilter)
 
-    assert_equal ' 1000$ CAD ', Template.parse("{{var | money}}").render(@context)
+    assert_equal ' 1000$ CAD ', Template.parse('{{var | money}}').render(@context)
   end
 
   def test_size
     @context['var'] = 'abcd'
     @context.add_filters(MoneyFilter)
 
-    assert_equal '4', Template.parse("{{var | size}}").render(@context)
+    assert_equal '4', Template.parse('{{var | size}}').render(@context)
   end
 
   def test_join
     @context['var'] = [1, 2, 3, 4]
 
-    assert_equal "1 2 3 4", Template.parse("{{var | join}}").render(@context)
+    assert_equal '1 2 3 4', Template.parse('{{var | join}}').render(@context)
   end
 
   def test_sort
     @context['value'] = 3
     @context['numbers'] = [2, 1, 4, 3]
-    @context['words'] = ['expected', 'as', 'alphabetic']
-    @context['arrays'] = ['flower', 'are']
-    @context['case_sensitive'] = ['sensitive', 'Expected', 'case']
+    @context['words'] = %w[expected as alphabetic]
+    @context['arrays'] = %w[flower are]
+    @context['case_sensitive'] = %w[sensitive Expected case]
 
-    assert_equal '1 2 3 4', Template.parse("{{numbers | sort | join}}").render(@context)
-    assert_equal 'alphabetic as expected', Template.parse("{{words | sort | join}}").render(@context)
-    assert_equal '3', Template.parse("{{value | sort}}").render(@context)
-    assert_equal 'are flower', Template.parse("{{arrays | sort | join}}").render(@context)
-    assert_equal 'Expected case sensitive', Template.parse("{{case_sensitive | sort | join}}").render(@context)
+    assert_equal '1 2 3 4', Template.parse('{{numbers | sort | join}}').render(@context)
+    assert_equal 'alphabetic as expected', Template.parse('{{words | sort | join}}').render(@context)
+    assert_equal '3', Template.parse('{{value | sort}}').render(@context)
+    assert_equal 'are flower', Template.parse('{{arrays | sort | join}}').render(@context)
+    assert_equal 'Expected case sensitive', Template.parse('{{case_sensitive | sort | join}}').render(@context)
   end
 
   def test_sort_natural
-    @context['words'] = ['case', 'Assert', 'Insensitive']
+    @context['words'] = %w[case Assert Insensitive]
     @context['hashes'] = [{ 'a' => 'A' }, { 'a' => 'b' }, { 'a' => 'C' }]
     @context['objects'] = [TestObject.new('A'), TestObject.new('b'), TestObject.new('C')]
 
     # Test strings
-    assert_equal 'Assert case Insensitive', Template.parse("{{words | sort_natural | join}}").render(@context)
+    assert_equal 'Assert case Insensitive', Template.parse('{{words | sort_natural | join}}').render(@context)
 
     # Test hashes
     assert_equal 'A b C', Template.parse("{{hashes | sort_natural: 'a' | map: 'a' | join}}").render(@context)
@@ -104,7 +106,7 @@ class FiltersTest < Minitest::Test
     @context['objects'] = [TestObject.new('A'), TestObject.new(nil), TestObject.new('C')]
 
     # Test strings
-    assert_equal 'a b c', Template.parse("{{words | compact | join}}").render(@context)
+    assert_equal 'a b c', Template.parse('{{words | compact | join}}').render(@context)
 
     # Test hashes
     assert_equal 'A C', Template.parse("{{hashes | compact: 'a' | map: 'a' | join}}").render(@context)
@@ -114,27 +116,27 @@ class FiltersTest < Minitest::Test
   end
 
   def test_strip_html
-    @context['var'] = "<b>bla blub</a>"
+    @context['var'] = '<b>bla blub</a>'
 
-    assert_equal "bla blub", Template.parse("{{ var | strip_html }}").render(@context)
+    assert_equal 'bla blub', Template.parse('{{ var | strip_html }}').render(@context)
   end
 
   def test_strip_html_ignore_comments_with_html
-    @context['var'] = "<!-- split and some <ul> tag --><b>bla blub</a>"
+    @context['var'] = '<!-- split and some <ul> tag --><b>bla blub</a>'
 
-    assert_equal "bla blub", Template.parse("{{ var | strip_html }}").render(@context)
+    assert_equal 'bla blub', Template.parse('{{ var | strip_html }}').render(@context)
   end
 
   def test_capitalize
-    @context['var'] = "blub"
+    @context['var'] = 'blub'
 
-    assert_equal "Blub", Template.parse("{{ var | capitalize }}").render(@context)
+    assert_equal 'Blub', Template.parse('{{ var | capitalize }}').render(@context)
   end
 
   def test_nonexistent_filter_is_ignored
     @context['var'] = 1000
 
-    assert_equal '1000', Template.parse("{{ var | xyzzy }}").render(@context)
+    assert_equal '1000', Template.parse('{{ var | xyzzy }}').render(@context)
   end
 
   def test_filter_with_keyword_arguments
@@ -146,10 +148,10 @@ class FiltersTest < Minitest::Test
   end
 
   def test_override_object_method_in_filter
-    assert_equal "tap overridden", Template.parse("{{var | tap}}").render!({ 'var' => 1000 }, filters: [OverrideObjectMethodFilter])
+    assert_equal 'tap overridden', Template.parse('{{var | tap}}').render!({ 'var' => 1000 }, filters: [OverrideObjectMethodFilter])
 
     # tap still treated as a non-existent filter
-    assert_equal "1000", Template.parse("{{var | tap}}").render!({ 'var' => 1000 })
+    assert_equal '1000', Template.parse('{{var | tap}}').render!('var' => 1000)
   end
 end
 
@@ -158,15 +160,15 @@ class FiltersInTemplate < Minitest::Test
 
   def test_local_global
     with_global_filter(MoneyFilter) do
-      assert_equal " 1000$ ", Template.parse("{{1000 | money}}").render!(nil, nil)
-      assert_equal " 1000$ CAD ", Template.parse("{{1000 | money}}").render!(nil, filters: CanadianMoneyFilter)
-      assert_equal " 1000$ CAD ", Template.parse("{{1000 | money}}").render!(nil, filters: [CanadianMoneyFilter])
+      assert_equal ' 1000$ ', Template.parse('{{1000 | money}}').render!(nil, nil)
+      assert_equal ' 1000$ CAD ', Template.parse('{{1000 | money}}').render!(nil, filters: CanadianMoneyFilter)
+      assert_equal ' 1000$ CAD ', Template.parse('{{1000 | money}}').render!(nil, filters: [CanadianMoneyFilter])
     end
   end
 
   def test_local_filter_with_deprecated_syntax
-    assert_equal " 1000$ CAD ", Template.parse("{{1000 | money}}").render!(nil, CanadianMoneyFilter)
-    assert_equal " 1000$ CAD ", Template.parse("{{1000 | money}}").render!(nil, [CanadianMoneyFilter])
+    assert_equal ' 1000$ CAD ', Template.parse('{{1000 | money}}').render!(nil, CanadianMoneyFilter)
+    assert_equal ' 1000$ CAD ', Template.parse('{{1000 | money}}').render!(nil, [CanadianMoneyFilter])
   end
 end # FiltersTest
 

test/integration/hash_ordering_test.rb

@@ -1,23 +1,25 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 
-module MoneyFilter
-  def money(input)
-    sprintf(' %d$ ', input)
-  end
-end
-
-module CanadianMoneyFilter
-  def money(input)
-    sprintf(' %d$ CAD ', input)
-  end
-end
-
 class HashOrderingTest < Minitest::Test
+  module MoneyFilter
+    def money(input)
+      format(' %d$ ', input)
+    end
+  end
+
+  module CanadianMoneyFilter
+    def money(input)
+      format(' %d$ CAD ', input)
+    end
+  end
+
   include Liquid
 
   def test_global_register_order
     with_global_filter(MoneyFilter, CanadianMoneyFilter) do
-      assert_equal " 1000$ CAD ", Template.parse("{{1000 | money}}").render(nil, nil)
+      assert_equal ' 1000$ CAD ', Template.parse('{{1000 | money}}').render(nil, nil)
     end
   end
 end

test/integration/legacy_test.rb

@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+require 'test_helper'
+require 'liquid/legacy'
+
+class FiltersTest < Minitest::Test
+  include Liquid
+
+  def test_constants
+    assert_equal Liquid::FilterSeparator, Liquid::FILTER_SEPARATOR
+    assert_equal Liquid::BlockBody::ContentOfVariable, Liquid::BlockBody::CONTENT_OF_VARIABLE
+  end
+end

test/integration/output_test.rb

@@ -1,7 +1,9 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 
 module FunnyFilter
-  def make_funny(input)
+  def make_funny(_input)
     'LOL'
   end
 
@@ -9,11 +11,11 @@ module FunnyFilter
     "LOL: #{input}"
   end
 
-  def add_smiley(input, smiley = ":-)")
+  def add_smiley(input, smiley = ':-)')
     "#{input} #{smiley}"
   end
 
-  def add_tag(input, tag = "p", id = "foo")
+  def add_tag(input, tag = 'p', id = 'foo')
     %(<#{tag} id="#{id}">#{input}</#{tag}>)
   end
 
@@ -32,7 +34,7 @@ class OutputTest < Minitest::Test
   def setup
     @assigns = {
       'best_cars' => 'bmw',
-      'car' => { 'bmw' => 'good', 'gm' => 'bad' }
+      'car' => { 'bmw' => 'good', 'gm' => 'bad' },
     }
   end
 
@@ -45,9 +47,9 @@ class OutputTest < Minitest::Test
 
   def test_variable_traversing_with_two_brackets
     text = %({{ site.data.menu[include.menu][include.locale] }})
-    assert_equal "it works!", Template.parse(text).render!(
-      "site" => { "data" => { "menu" => { "foo" => { "bar" => "it works!" } } } },
-      "include" => { "menu" => "foo", "locale" => "bar" }
+    assert_equal 'it works!', Template.parse(text).render!(
+      'site' => { 'data' => { 'menu' => { 'foo' => { 'bar' => 'it works!' } } } },
+      'include' => { 'menu' => 'foo', 'locale' => 'bar' }
     )
   end
 

test/integration/parse_tree_visitor_test.rb

@@ -0,0 +1,247 @@
+# frozen_string_literal: true
+
+require 'test_helper'
+
+class ParseTreeVisitorTest < Minitest::Test
+  include Liquid
+
+  def test_variable
+    assert_equal(
+      ['test'],
+      visit(%({{ test }}))
+    )
+  end
+
+  def test_varible_with_filter
+    assert_equal(
+      %w[test infilter],
+      visit(%({{ test | split: infilter }}))
+    )
+  end
+
+  def test_dynamic_variable
+    assert_equal(
+      %w[test inlookup],
+      visit(%({{ test[inlookup] }}))
+    )
+  end
+
+  def test_if_condition
+    assert_equal(
+      ['test'],
+      visit(%({% if test %}{% endif %}))
+    )
+  end
+
+  def test_complex_if_condition
+    assert_equal(
+      ['test'],
+      visit(%({% if 1 == 1 and 2 == test %}{% endif %}))
+    )
+  end
+
+  def test_if_body
+    assert_equal(
+      ['test'],
+      visit(%({% if 1 == 1 %}{{ test }}{% endif %}))
+    )
+  end
+
+  def test_unless_condition
+    assert_equal(
+      ['test'],
+      visit(%({% unless test %}{% endunless %}))
+    )
+  end
+
+  def test_complex_unless_condition
+    assert_equal(
+      ['test'],
+      visit(%({% unless 1 == 1 and 2 == test %}{% endunless %}))
+    )
+  end
+
+  def test_unless_body
+    assert_equal(
+      ['test'],
+      visit(%({% unless 1 == 1 %}{{ test }}{% endunless %}))
+    )
+  end
+
+  def test_elsif_condition
+    assert_equal(
+      ['test'],
+      visit(%({% if 1 == 1 %}{% elsif test %}{% endif %}))
+    )
+  end
+
+  def test_complex_elsif_condition
+    assert_equal(
+      ['test'],
+      visit(%({% if 1 == 1 %}{% elsif 1 == 1 and 2 == test %}{% endif %}))
+    )
+  end
+
+  def test_elsif_body
+    assert_equal(
+      ['test'],
+      visit(%({% if 1 == 1 %}{% elsif 2 == 2 %}{{ test }}{% endif %}))
+    )
+  end
+
+  def test_else_body
+    assert_equal(
+      ['test'],
+      visit(%({% if 1 == 1 %}{% else %}{{ test }}{% endif %}))
+    )
+  end
+
+  def test_case_left
+    assert_equal(
+      ['test'],
+      visit(%({% case test %}{% endcase %}))
+    )
+  end
+
+  def test_case_condition
+    assert_equal(
+      ['test'],
+      visit(%({% case 1 %}{% when test %}{% endcase %}))
+    )
+  end
+
+  def test_case_when_body
+    assert_equal(
+      ['test'],
+      visit(%({% case 1 %}{% when 2 %}{{ test }}{% endcase %}))
+    )
+  end
+
+  def test_case_else_body
+    assert_equal(
+      ['test'],
+      visit(%({% case 1 %}{% else %}{{ test }}{% endcase %}))
+    )
+  end
+
+  def test_for_in
+    assert_equal(
+      ['test'],
+      visit(%({% for x in test %}{% endfor %}))
+    )
+  end
+
+  def test_for_limit
+    assert_equal(
+      ['test'],
+      visit(%({% for x in (1..5) limit: test %}{% endfor %}))
+    )
+  end
+
+  def test_for_offset
+    assert_equal(
+      ['test'],
+      visit(%({% for x in (1..5) offset: test %}{% endfor %}))
+    )
+  end
+
+  def test_for_body
+    assert_equal(
+      ['test'],
+      visit(%({% for x in (1..5) %}{{ test }}{% endfor %}))
+    )
+  end
+
+  def test_tablerow_in
+    assert_equal(
+      ['test'],
+      visit(%({% tablerow x in test %}{% endtablerow %}))
+    )
+  end
+
+  def test_tablerow_limit
+    assert_equal(
+      ['test'],
+      visit(%({% tablerow x in (1..5) limit: test %}{% endtablerow %}))
+    )
+  end
+
+  def test_tablerow_offset
+    assert_equal(
+      ['test'],
+      visit(%({% tablerow x in (1..5) offset: test %}{% endtablerow %}))
+    )
+  end
+
+  def test_tablerow_body
+    assert_equal(
+      ['test'],
+      visit(%({% tablerow x in (1..5) %}{{ test }}{% endtablerow %}))
+    )
+  end
+
+  def test_cycle
+    assert_equal(
+      ['test'],
+      visit(%({% cycle test %}))
+    )
+  end
+
+  def test_assign
+    assert_equal(
+      ['test'],
+      visit(%({% assign x = test %}))
+    )
+  end
+
+  def test_capture
+    assert_equal(
+      ['test'],
+      visit(%({% capture x %}{{ test }}{% endcapture %}))
+    )
+  end
+
+  def test_include
+    assert_equal(
+      ['test'],
+      visit(%({% include test %}))
+    )
+  end
+
+  def test_include_with
+    assert_equal(
+      ['test'],
+      visit(%({% include "hai" with test %}))
+    )
+  end
+
+  def test_include_for
+    assert_equal(
+      ['test'],
+      visit(%({% include "hai" for test %}))
+    )
+  end
+
+  def test_preserve_tree_structure
+    assert_equal(
+      [[nil, [
+        [nil, [[nil, [['other', []]]]]],
+        ['test', []],
+        ['xs', []],
+      ]]],
+      traversal(%({% for x in xs offset: test %}{{ other }}{% endfor %})).visit
+    )
+  end
+
+  private
+
+  def traversal(template)
+    ParseTreeVisitor
+      .for(Template.parse(template).root)
+      .add_callback_for(VariableLookup, &:name)
+  end
+
+  def visit(template)
+    traversal(template).visit.flatten.compact
+  end
+end

test/integration/parsing_quirks_test.rb

@@ -1,41 +1,43 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 
 class ParsingQuirksTest < Minitest::Test
   include Liquid
 
   def test_parsing_css
-    text = " div { font-weight: bold; } "
+    text = ' div { font-weight: bold; } '
     assert_equal text, Template.parse(text).render!
   end
 
   def test_raise_on_single_close_bracet
     assert_raises(SyntaxError) do
-      Template.parse("text {{method} oh nos!")
+      Template.parse('text {{method} oh nos!')
     end
   end
 
   def test_raise_on_label_and_no_close_bracets
     assert_raises(SyntaxError) do
-      Template.parse("TEST {{ ")
+      Template.parse('TEST {{ ')
     end
   end
 
   def test_raise_on_label_and_no_close_bracets_percent
     assert_raises(SyntaxError) do
-      Template.parse("TEST {% ")
+      Template.parse('TEST {% ')
     end
   end
 
   def test_error_on_empty_filter
-    assert Template.parse("{{test}}")
+    assert Template.parse('{{test}}')
 
     with_error_mode(:lax) do
-      assert Template.parse("{{|test}}")
+      assert Template.parse('{{|test}}')
     end
 
     with_error_mode(:strict) do
-      assert_raises(SyntaxError) { Template.parse("{{|test}}") }
-      assert_raises(SyntaxError) { Template.parse("{{test |a|b|}}") }
+      assert_raises(SyntaxError) { Template.parse('{{|test}}') }
+      assert_raises(SyntaxError) { Template.parse('{{test |a|b|}}') }
     end
   end
 
@@ -51,20 +53,20 @@ class ParsingQuirksTest < Minitest::Test
   def test_unexpected_characters_syntax_error
     with_error_mode(:strict) do
       assert_raises(SyntaxError) do
-        markup = "true && false"
+        markup = 'true && false'
         Template.parse("{% if #{markup} %} YES {% endif %}")
       end
       assert_raises(SyntaxError) do
-        markup = "false || true"
+        markup = 'false || true'
         Template.parse("{% if #{markup} %} YES {% endif %}")
       end
     end
   end
 
   def test_no_error_on_lax_empty_filter
-    assert Template.parse("{{test |a|b|}}", error_mode: :lax)
-    assert Template.parse("{{test}}", error_mode: :lax)
-    assert Template.parse("{{|test|}}", error_mode: :lax)
+    assert Template.parse('{{test |a|b|}}', error_mode: :lax)
+    assert Template.parse('{{test}}', error_mode: :lax)
+    assert Template.parse('{{|test|}}', error_mode: :lax)
   end
 
   def test_meaningless_parens_lax
@@ -77,9 +79,9 @@ class ParsingQuirksTest < Minitest::Test
 
   def test_unexpected_characters_silently_eat_logic_lax
     with_error_mode(:lax) do
-      markup = "true && false"
+      markup = 'true && false'
       assert_template_result(' YES ', "{% if #{markup} %} YES {% endif %}")
-      markup = "false || true"
+      markup = 'false || true'
       assert_template_result('', "{% if #{markup} %} YES {% endif %}")
     end
   end
@@ -99,7 +101,7 @@ class ParsingQuirksTest < Minitest::Test
       # After the messed up quotes a filter without parameters (reverse) should work
       # but one with parameters (remove) shouldn't be detected.
       assert_template_result('here',  "{{ 'hi there' | split:\"t\"\" | reverse | first}}")
-      assert_template_result('hi ',  "{{ 'hi there' | split:\"t\"\" | remove:\"i\" | first}}")
+      assert_template_result('hi ', "{{ 'hi there' | split:\"t\"\" | remove:\"i\" | first}}")
     end
   end
 
@@ -112,7 +114,11 @@ class ParsingQuirksTest < Minitest::Test
 
   def test_extra_dots_in_ranges
     with_error_mode(:lax) do
-      assert_template_result('12345', "{% for i in (1...5) %}{{ i }}{% endfor %}")
+      assert_template_result('12345', '{% for i in (1...5) %}{{ i }}{% endfor %}')
     end
   end
+
+  def test_contains_in_id
+    assert_template_result(' YES ', '{% if containsallshipments == true %} YES {% endif %}', 'containsallshipments' => true)
+  end
 end # ParsingQuirksTest

test/integration/render_profiling_test.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 
 class RenderProfilingTest < Minitest::Test
@@ -72,7 +74,7 @@ class RenderProfilingTest < Minitest::Test
     t = Template.parse("{% include 'a_template' %}", profile: true)
     t.render!
 
-    assert t.profiler.total_render_time >= 0, "Total render time was not calculated"
+    assert t.profiler.total_render_time >= 0, 'Total render time was not calculated'
   end
 
   def test_profiling_uses_include_to_mark_children
@@ -89,7 +91,7 @@ class RenderProfilingTest < Minitest::Test
 
     include_node = t.profiler[1]
     include_node.children.each do |child|
-      assert_equal "a_template", child.partial
+      assert_equal 'a_template', child.partial
     end
   end
 
@@ -99,12 +101,12 @@ class RenderProfilingTest < Minitest::Test
 
     a_template = t.profiler[1]
     a_template.children.each do |child|
-      assert_equal "a_template", child.partial
+      assert_equal 'a_template', child.partial
     end
 
     b_template = t.profiler[2]
     b_template.children.each do |child|
-      assert_equal "b_template", child.partial
+      assert_equal 'b_template', child.partial
     end
   end
 
@@ -114,12 +116,12 @@ class RenderProfilingTest < Minitest::Test
 
     a_template1 = t.profiler[1]
     a_template1.children.each do |child|
-      assert_equal "a_template", child.partial
+      assert_equal 'a_template', child.partial
     end
 
     a_template2 = t.profiler[2]
     a_template2.children.each do |child|
-      assert_equal "a_template", child.partial
+      assert_equal 'a_template', child.partial
     end
   end
 
@@ -128,7 +130,7 @@ class RenderProfilingTest < Minitest::Test
     t.render!
 
     timing_count = 0
-    t.profiler.each do |timing|
+    t.profiler.each do |_timing|
       timing_count += 1
     end
 
@@ -136,7 +138,7 @@ class RenderProfilingTest < Minitest::Test
   end
 
   def test_profiling_marks_children_of_if_blocks
-    t = Template.parse("{% if true %} {% increment test %} {{ test }} {% endif %}", profile: true)
+    t = Template.parse('{% if true %} {% increment test %} {{ test }} {% endif %}', profile: true)
     t.render!
 
     assert_equal 1, t.profiler.length
@@ -144,8 +146,8 @@ class RenderProfilingTest < Minitest::Test
   end
 
   def test_profiling_marks_children_of_for_blocks
-    t = Template.parse("{% for item in collection %} {{ item }} {% endfor %}", profile: true)
-    t.render!({ "collection" => ["one", "two"] })
+    t = Template.parse('{% for item in collection %} {{ item }} {% endfor %}', profile: true)
+    t.render!('collection' => %w[one two])
 
     assert_equal 1, t.profiler.length
     # Will profile each invocation of the for block

test/integration/security_test.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 
 module SecurityFilter
@@ -9,6 +11,10 @@ end
 class SecurityTest < Minitest::Test
   include Liquid
 
+  def setup
+    @assigns = {}
+  end
+
   def test_no_instance_eval
     text = %( {{ '1+1' | instance_eval }} )
     expected = %( 1+1 )
@@ -53,10 +59,24 @@ class SecurityTest < Minitest::Test
     current_symbols = Symbol.all_symbols
 
     assigns = { 'drop' => Drop.new }
-    assert_equal "", Template.parse("{{ drop.custom_method_1 }}", assigns).render!
-    assert_equal "", Template.parse("{{ drop.custom_method_2 }}", assigns).render!
-    assert_equal "", Template.parse("{{ drop.custom_method_3 }}", assigns).render!
+    assert_equal '', Template.parse('{{ drop.custom_method_1 }}', assigns).render!
+    assert_equal '', Template.parse('{{ drop.custom_method_2 }}', assigns).render!
+    assert_equal '', Template.parse('{{ drop.custom_method_3 }}', assigns).render!
 
     assert_equal [], (Symbol.all_symbols - current_symbols)
   end
+
+  def test_max_depth_nested_blocks_does_not_raise_exception
+    depth = Liquid::Block::MAX_DEPTH
+    code = '{% if true %}' * depth + 'rendered' + '{% endif %}' * depth
+    assert_equal 'rendered', Template.parse(code).render!
+  end
+
+  def test_more_than_max_depth_nested_blocks_raises_exception
+    depth = Liquid::Block::MAX_DEPTH + 1
+    code = '{% if true %}' * depth + 'rendered' + '{% endif %}' * depth
+    assert_raises(Liquid::StackLevelError) do
+      Template.parse(code).render!
+    end
+  end
 end # SecurityTest

test/integration/standard_filter_test.rb

@@ -1,4 +1,4 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 require 'test_helper'
 
@@ -17,7 +17,7 @@ class TestThing
     "woot: #{@foo}"
   end
 
-  def [](whatever)
+  def [](_whatever)
     to_s
   end
 
@@ -29,7 +29,7 @@ end
 
 class TestDrop < Liquid::Drop
   def test
-    "testfoo"
+    'testfoo'
   end
 end
 
@@ -37,7 +37,17 @@ class TestEnumerable < Liquid::Drop
   include Enumerable
 
   def each(&block)
-    [ { "foo" => 1, "bar" => 2 }, { "foo" => 2, "bar" => 1 }, { "foo" => 3, "bar" => 3 } ].each(&block)
+    [{ 'foo' => 1, 'bar' => 2 }, { 'foo' => 2, 'bar' => 1 }, { 'foo' => 3, 'bar' => 3 }].each(&block)
+  end
+end
+
+class NumberLikeThing < Liquid::Drop
+  def initialize(amount)
+    @amount = amount
+  end
+
+  def to_number
+    @amount
   end
 end
 
@@ -55,12 +65,12 @@ class StandardFiltersTest < Minitest::Test
   end
 
   def test_downcase
-    assert_equal 'testing', @filters.downcase("Testing")
+    assert_equal 'testing', @filters.downcase('Testing')
     assert_equal '', @filters.downcase(nil)
   end
 
   def test_upcase
-    assert_equal 'TESTING', @filters.upcase("Testing")
+    assert_equal 'TESTING', @filters.upcase('Testing')
     assert_equal '', @filters.upcase(nil)
   end
 
@@ -81,22 +91,22 @@ class StandardFiltersTest < Minitest::Test
       @filters.slice('foobar', nil)
     end
     assert_raises(Liquid::ArgumentError) do
-      @filters.slice('foobar', 0, "")
+      @filters.slice('foobar', 0, '')
     end
   end
 
   def test_slice_on_arrays
     input = 'foobar'.split(//)
-    assert_equal %w(o o b), @filters.slice(input, 1, 3)
-    assert_equal %w(o o b a r), @filters.slice(input, 1, 1000)
-    assert_equal %w(), @filters.slice(input, 1, 0)
-    assert_equal %w(o), @filters.slice(input, 1, 1)
-    assert_equal %w(b a r), @filters.slice(input, 3, 3)
-    assert_equal %w(a r), @filters.slice(input, -2, 2)
-    assert_equal %w(a r), @filters.slice(input, -2, 1000)
-    assert_equal %w(r), @filters.slice(input, -1)
-    assert_equal %w(), @filters.slice(input, 100, 10)
-    assert_equal %w(), @filters.slice(input, -100, 10)
+    assert_equal %w[o o b], @filters.slice(input, 1, 3)
+    assert_equal %w[o o b a r], @filters.slice(input, 1, 1000)
+    assert_equal %w[], @filters.slice(input, 1, 0)
+    assert_equal %w[o], @filters.slice(input, 1, 1)
+    assert_equal %w[b a r], @filters.slice(input, 3, 3)
+    assert_equal %w[a r], @filters.slice(input, -2, 2)
+    assert_equal %w[a r], @filters.slice(input, -2, 1000)
+    assert_equal %w[r], @filters.slice(input, -1)
+    assert_equal %w[], @filters.slice(input, 100, 10)
+    assert_equal %w[], @filters.slice(input, -100, 10)
   end
 
   def test_truncate
@@ -104,22 +114,30 @@ class StandardFiltersTest < Minitest::Test
     assert_equal '1234567890', @filters.truncate('1234567890', 20)
     assert_equal '...', @filters.truncate('1234567890', 0)
     assert_equal '1234567890', @filters.truncate('1234567890')
-    assert_equal "测试...", @filters.truncate("测试测试测试测试", 5)
+    assert_equal '测试...', @filters.truncate('测试测试测试测试', 5)
+    assert_equal '12341', @filters.truncate('1234567890', 5, 1)
   end
 
   def test_split
-    assert_equal ['12', '34'], @filters.split('12~34', '~')
+    assert_equal %w[12 34], @filters.split('12~34', '~')
     assert_equal ['A? ', ' ,Z'], @filters.split('A? ~ ~ ~ ,Z', '~ ~ ~')
     assert_equal ['A?Z'], @filters.split('A?Z', '~')
-    # Regexp works although Liquid does not support.
-    assert_equal ['A', 'Z'], @filters.split('AxZ', /x/)
     assert_equal [], @filters.split(nil, ' ')
+    assert_equal %w[A Z], @filters.split('A1Z', 1)
   end
 
   def test_escape
     assert_equal '&lt;strong&gt;', @filters.escape('<strong>')
-    assert_equal nil, @filters.escape(nil)
+    assert_equal '1', @filters.escape(1)
+    assert_equal '2001-02-03', @filters.escape(Date.new(2001, 2, 3))
+    assert_nil @filters.escape(nil)
+  end
+
+  def test_h
     assert_equal '&lt;strong&gt;', @filters.h('<strong>')
+    assert_equal '1', @filters.h(1)
+    assert_equal '2001-02-03', @filters.h(Date.new(2001, 2, 3))
+    assert_nil @filters.h(nil)
   end
 
   def test_escape_once
@@ -128,14 +146,22 @@ class StandardFiltersTest < Minitest::Test
 
   def test_url_encode
     assert_equal 'foo%2B1%40example.com', @filters.url_encode('foo+1@example.com')
-    assert_equal nil, @filters.url_encode(nil)
+    assert_equal '1', @filters.url_encode(1)
+    assert_equal '2001-02-03', @filters.url_encode(Date.new(2001, 2, 3))
+    assert_nil @filters.url_encode(nil)
   end
 
   def test_url_decode
     assert_equal 'foo bar', @filters.url_decode('foo+bar')
     assert_equal 'foo bar', @filters.url_decode('foo%20bar')
     assert_equal 'foo+1@example.com', @filters.url_decode('foo%2B1%40example.com')
-    assert_equal nil, @filters.url_decode(nil)
+    assert_equal '1', @filters.url_decode(1)
+    assert_equal '2001-02-03', @filters.url_decode(Date.new(2001, 2, 3))
+    assert_nil @filters.url_decode(nil)
+    exception = assert_raises Liquid::ArgumentError do
+      @filters.url_decode('%ff')
+    end
+    assert_equal 'Liquid error: invalid byte sequence in UTF-8', exception.message
   end
 
   def test_truncatewords
@@ -143,62 +169,189 @@ class StandardFiltersTest < Minitest::Test
     assert_equal 'one two...', @filters.truncatewords('one two three', 2)
     assert_equal 'one two three', @filters.truncatewords('one two three')
     assert_equal 'Two small (13&#8221; x 5.5&#8221; x 10&#8221; high) baskets fit inside one large basket (13&#8221;...', @filters.truncatewords('Two small (13&#8221; x 5.5&#8221; x 10&#8221; high) baskets fit inside one large basket (13&#8221; x 16&#8221; x 10.5&#8221; high) with cover.', 15)
-    assert_equal "测试测试测试测试", @filters.truncatewords('测试测试测试测试', 5)
+    assert_equal '测试测试测试测试', @filters.truncatewords('测试测试测试测试', 5)
+    assert_equal 'one two1', @filters.truncatewords('one two three', 2, 1)
   end
 
   def test_strip_html
-    assert_equal 'test', @filters.strip_html("<div>test</div>")
+    assert_equal 'test', @filters.strip_html('<div>test</div>')
     assert_equal 'test', @filters.strip_html("<div id='test'>test</div>")
     assert_equal '', @filters.strip_html("<script type='text/javascript'>document.write('some stuff');</script>")
     assert_equal '', @filters.strip_html("<style type='text/css'>foo bar</style>")
     assert_equal 'test', @filters.strip_html("<div\nclass='multiline'>test</div>")
     assert_equal 'test', @filters.strip_html("<!-- foo bar \n test -->test")
     assert_equal '', @filters.strip_html(nil)
+
+    # Quirk of the existing implementation
+    assert_equal 'foo;', @filters.strip_html('<<<script </script>script>foo;</script>')
   end
 
   def test_join
     assert_equal '1 2 3 4', @filters.join([1, 2, 3, 4])
     assert_equal '1 - 2 - 3 - 4', @filters.join([1, 2, 3, 4], ' - ')
+    assert_equal '1121314', @filters.join([1, 2, 3, 4], 1)
   end
 
   def test_sort
     assert_equal [1, 2, 3, 4], @filters.sort([4, 3, 2, 1])
-    assert_equal [{ "a" => 1 }, { "a" => 2 }, { "a" => 3 }, { "a" => 4 }], @filters.sort([{ "a" => 4 }, { "a" => 3 }, { "a" => 1 }, { "a" => 2 }], "a")
+    assert_equal [{ 'a' => 1 }, { 'a' => 2 }, { 'a' => 3 }, { 'a' => 4 }], @filters.sort([{ 'a' => 4 }, { 'a' => 3 }, { 'a' => 1 }, { 'a' => 2 }], 'a')
+  end
+
+  def test_sort_with_nils
+    assert_equal [1, 2, 3, 4, nil], @filters.sort([nil, 4, 3, 2, 1])
+    assert_equal [{ 'a' => 1 }, { 'a' => 2 }, { 'a' => 3 }, { 'a' => 4 }, {}], @filters.sort([{ 'a' => 4 }, { 'a' => 3 }, {}, { 'a' => 1 }, { 'a' => 2 }], 'a')
+  end
+
+  def test_sort_when_property_is_sometimes_missing_puts_nils_last
+    input = [
+      { 'price' => 4, 'handle' => 'alpha' },
+      { 'handle' => 'beta' },
+      { 'price' => 1, 'handle' => 'gamma' },
+      { 'handle' => 'delta' },
+      { 'price' => 2, 'handle' => 'epsilon' },
+    ]
+    expectation = [
+      { 'price' => 1, 'handle' => 'gamma' },
+      { 'price' => 2, 'handle' => 'epsilon' },
+      { 'price' => 4, 'handle' => 'alpha' },
+      { 'handle' => 'delta' },
+      { 'handle' => 'beta' },
+    ]
+    assert_equal expectation, @filters.sort(input, 'price')
+  end
+
+  def test_sort_natural
+    assert_equal %w[a B c D], @filters.sort_natural(%w[c D a B])
+    assert_equal [{ 'a' => 'a' }, { 'a' => 'B' }, { 'a' => 'c' }, { 'a' => 'D' }], @filters.sort_natural([{ 'a' => 'D' }, { 'a' => 'c' }, { 'a' => 'a' }, { 'a' => 'B' }], 'a')
+  end
+
+  def test_sort_natural_with_nils
+    assert_equal ['a', 'B', 'c', 'D', nil], @filters.sort_natural([nil, 'c', 'D', 'a', 'B'])
+    assert_equal [{ 'a' => 'a' }, { 'a' => 'B' }, { 'a' => 'c' }, { 'a' => 'D' }, {}], @filters.sort_natural([{ 'a' => 'D' }, { 'a' => 'c' }, {}, { 'a' => 'a' }, { 'a' => 'B' }], 'a')
+  end
+
+  def test_sort_natural_when_property_is_sometimes_missing_puts_nils_last
+    input = [
+      { 'price' => '4', 'handle' => 'alpha' },
+      { 'handle' => 'beta' },
+      { 'price' => '1', 'handle' => 'gamma' },
+      { 'handle' => 'delta' },
+      { 'price' => 2, 'handle' => 'epsilon' },
+    ]
+    expectation = [
+      { 'price' => '1', 'handle' => 'gamma' },
+      { 'price' => 2, 'handle' => 'epsilon' },
+      { 'price' => '4', 'handle' => 'alpha' },
+      { 'handle' => 'delta' },
+      { 'handle' => 'beta' },
+    ]
+    assert_equal expectation, @filters.sort_natural(input, 'price')
+  end
+
+  def test_sort_natural_case_check
+    input = [
+      { 'key' => 'X' },
+      { 'key' => 'Y' },
+      { 'key' => 'Z' },
+      { 'fake' => 't' },
+      { 'key' => 'a' },
+      { 'key' => 'b' },
+      { 'key' => 'c' },
+    ]
+    expectation = [
+      { 'key' => 'a' },
+      { 'key' => 'b' },
+      { 'key' => 'c' },
+      { 'key' => 'X' },
+      { 'key' => 'Y' },
+      { 'key' => 'Z' },
+      { 'fake' => 't' },
+    ]
+    assert_equal expectation, @filters.sort_natural(input, 'key')
+    assert_equal %w[a b c X Y Z], @filters.sort_natural(%w[X Y Z a b c])
   end
 
   def test_sort_empty_array
-    assert_equal [], @filters.sort([], "a")
+    assert_equal [], @filters.sort([], 'a')
+  end
+
+  def test_sort_invalid_property
+    foo = [
+      [1],
+      [2],
+      [3],
+    ]
+
+    assert_raises Liquid::ArgumentError do
+      @filters.sort(foo, 'bar')
+    end
   end
 
   def test_sort_natural_empty_array
-    assert_equal [], @filters.sort_natural([], "a")
+    assert_equal [], @filters.sort_natural([], 'a')
+  end
+
+  def test_sort_natural_invalid_property
+    foo = [
+      [1],
+      [2],
+      [3],
+    ]
+
+    assert_raises Liquid::ArgumentError do
+      @filters.sort_natural(foo, 'bar')
+    end
   end
 
   def test_legacy_sort_hash
-    assert_equal [{ a: 1, b: 2 }], @filters.sort({ a: 1, b: 2 })
+    assert_equal [{ a: 1, b: 2 }], @filters.sort(a: 1, b: 2)
   end
 
   def test_numerical_vs_lexicographical_sort
     assert_equal [2, 10], @filters.sort([10, 2])
-    assert_equal [{ "a" => 2 }, { "a" => 10 }], @filters.sort([{ "a" => 10 }, { "a" => 2 }], "a")
-    assert_equal ["10", "2"], @filters.sort(["10", "2"])
-    assert_equal [{ "a" => "10" }, { "a" => "2" }], @filters.sort([{ "a" => "10" }, { "a" => "2" }], "a")
+    assert_equal [{ 'a' => 2 }, { 'a' => 10 }], @filters.sort([{ 'a' => 10 }, { 'a' => 2 }], 'a')
+    assert_equal %w[10 2], @filters.sort(%w[10 2])
+    assert_equal [{ 'a' => '10' }, { 'a' => '2' }], @filters.sort([{ 'a' => '10' }, { 'a' => '2' }], 'a')
   end
 
   def test_uniq
-    assert_equal ["foo"], @filters.uniq("foo")
+    assert_equal ['foo'], @filters.uniq('foo')
     assert_equal [1, 3, 2, 4], @filters.uniq([1, 1, 3, 2, 3, 1, 4, 3, 2, 1])
-    assert_equal [{ "a" => 1 }, { "a" => 3 }, { "a" => 2 }], @filters.uniq([{ "a" => 1 }, { "a" => 3 }, { "a" => 1 }, { "a" => 2 }], "a")
+    assert_equal [{ 'a' => 1 }, { 'a' => 3 }, { 'a' => 2 }], @filters.uniq([{ 'a' => 1 }, { 'a' => 3 }, { 'a' => 1 }, { 'a' => 2 }], 'a')
     testdrop = TestDrop.new
     assert_equal [testdrop], @filters.uniq([testdrop, TestDrop.new], 'test')
   end
 
   def test_uniq_empty_array
-    assert_equal [], @filters.uniq([], "a")
+    assert_equal [], @filters.uniq([], 'a')
+  end
+
+  def test_uniq_invalid_property
+    foo = [
+      [1],
+      [2],
+      [3],
+    ]
+
+    assert_raises Liquid::ArgumentError do
+      @filters.uniq(foo, 'bar')
+    end
   end
 
   def test_compact_empty_array
-    assert_equal [], @filters.compact([], "a")
+    assert_equal [], @filters.compact([], 'a')
+  end
+
+  def test_compact_invalid_property
+    foo = [
+      [1],
+      [2],
+      [3],
+    ]
+
+    assert_raises Liquid::ArgumentError do
+      @filters.compact(foo, 'bar')
+    end
   end
 
   def test_reverse
@@ -210,64 +363,87 @@ class StandardFiltersTest < Minitest::Test
   end
 
   def test_map
-    assert_equal [1, 2, 3, 4], @filters.map([{ "a" => 1 }, { "a" => 2 }, { "a" => 3 }, { "a" => 4 }], 'a')
+    assert_equal [1, 2, 3, 4], @filters.map([{ 'a' => 1 }, { 'a' => 2 }, { 'a' => 3 }, { 'a' => 4 }], 'a')
     assert_template_result 'abc', "{{ ary | map:'foo' | map:'bar' }}",
-      'ary' => [{ 'foo' => { 'bar' => 'a' } }, { 'foo' => { 'bar' => 'b' } }, { 'foo' => { 'bar' => 'c' } }]
+                           'ary' => [{ 'foo' => { 'bar' => 'a' } }, { 'foo' => { 'bar' => 'b' } }, { 'foo' => { 'bar' => 'c' } }]
   end
 
   def test_map_doesnt_call_arbitrary_stuff
-    assert_template_result "", '{{ "foo" | map: "__id__" }}'
-    assert_template_result "", '{{ "foo" | map: "inspect" }}'
+    assert_template_result '', '{{ "foo" | map: "__id__" }}'
+    assert_template_result '', '{{ "foo" | map: "inspect" }}'
   end
 
   def test_map_calls_to_liquid
     t = TestThing.new
-    assert_template_result "woot: 1", '{{ foo | map: "whatever" }}', "foo" => [t]
+    assert_template_result 'woot: 1', '{{ foo | map: "whatever" }}', 'foo' => [t]
   end
 
   def test_map_on_hashes
-    assert_template_result "4217", '{{ thing | map: "foo" | map: "bar" }}',
-      "thing" => { "foo" => [ { "bar" => 42 }, { "bar" => 17 } ] }
+    assert_template_result '4217', '{{ thing | map: "foo" | map: "bar" }}',
+                           'thing' => { 'foo' => [{ 'bar' => 42 }, { 'bar' => 17 }] }
   end
 
   def test_legacy_map_on_hashes_with_dynamic_key
     template = "{% assign key = 'foo' %}{{ thing | map: key | map: 'bar' }}"
-    hash = { "foo" => { "bar" => 42 } }
-    assert_template_result "42", template, "thing" => hash
+    hash = { 'foo' => { 'bar' => 42 } }
+    assert_template_result '42', template, 'thing' => hash
   end
 
   def test_sort_calls_to_liquid
     t = TestThing.new
-    Liquid::Template.parse('{{ foo | sort: "whatever" }}').render("foo" => [t])
-    assert t.foo > 0
+    Liquid::Template.parse('{{ foo | sort: "whatever" }}').render('foo' => [t])
+    assert t.foo.positive?
   end
 
   def test_map_over_proc
     drop = TestDrop.new
-    p = proc{ drop }
+    p = proc { drop }
     templ = '{{ procs | map: "test" }}'
-    assert_template_result "testfoo", templ, "procs" => [p]
+    assert_template_result 'testfoo', templ, 'procs' => [p]
   end
 
   def test_map_over_drops_returning_procs
     drops = [
       {
-        "proc" => ->{ "foo" },
+        'proc' => -> { 'foo' },
       },
       {
-        "proc" => ->{ "bar" },
+        'proc' => -> { 'bar' },
       },
     ]
     templ = '{{ drops | map: "proc" }}'
-    assert_template_result "foobar", templ, "drops" => drops
+    assert_template_result 'foobar', templ, 'drops' => drops
   end
 
   def test_map_works_on_enumerables
-    assert_template_result "123", '{{ foo | map: "foo" }}', "foo" => TestEnumerable.new
+    assert_template_result '123', '{{ foo | map: "foo" }}', 'foo' => TestEnumerable.new
+  end
+
+  def test_map_returns_empty_on_2d_input_array
+    foo = [
+      [1],
+      [2],
+      [3],
+    ]
+
+    assert_raises Liquid::ArgumentError do
+      @filters.map(foo, 'bar')
+    end
+  end
+
+  def test_map_returns_empty_with_no_property
+    foo = [
+      [1],
+      [2],
+      [3],
+    ]
+    assert_raises Liquid::ArgumentError do
+      @filters.map(foo, nil)
+    end
   end
 
   def test_sort_works_on_enumerables
-    assert_template_result "213", '{{ foo | sort: "bar" | map: "foo" }}', "foo" => TestEnumerable.new
+    assert_template_result '213', '{{ foo | sort: "bar" | map: "foo" }}', 'foo' => TestEnumerable.new
   end
 
   def test_first_and_last_call_to_liquid
@@ -276,45 +452,45 @@ class StandardFiltersTest < Minitest::Test
   end
 
   def test_truncate_calls_to_liquid
-    assert_template_result "wo...", '{{ foo | truncate: 5 }}', "foo" => TestThing.new
+    assert_template_result 'wo...', '{{ foo | truncate: 5 }}', 'foo' => TestThing.new
   end
 
   def test_date
-    assert_equal 'May', @filters.date(Time.parse("2006-05-05 10:00:00"), "%B")
-    assert_equal 'June', @filters.date(Time.parse("2006-06-05 10:00:00"), "%B")
-    assert_equal 'July', @filters.date(Time.parse("2006-07-05 10:00:00"), "%B")
+    assert_equal 'May', @filters.date(Time.parse('2006-05-05 10:00:00'), '%B')
+    assert_equal 'June', @filters.date(Time.parse('2006-06-05 10:00:00'), '%B')
+    assert_equal 'July', @filters.date(Time.parse('2006-07-05 10:00:00'), '%B')
 
-    assert_equal 'May', @filters.date("2006-05-05 10:00:00", "%B")
-    assert_equal 'June', @filters.date("2006-06-05 10:00:00", "%B")
-    assert_equal 'July', @filters.date("2006-07-05 10:00:00", "%B")
+    assert_equal 'May', @filters.date('2006-05-05 10:00:00', '%B')
+    assert_equal 'June', @filters.date('2006-06-05 10:00:00', '%B')
+    assert_equal 'July', @filters.date('2006-07-05 10:00:00', '%B')
 
-    assert_equal '2006-07-05 10:00:00', @filters.date("2006-07-05 10:00:00", "")
-    assert_equal '2006-07-05 10:00:00', @filters.date("2006-07-05 10:00:00", "")
-    assert_equal '2006-07-05 10:00:00', @filters.date("2006-07-05 10:00:00", "")
-    assert_equal '2006-07-05 10:00:00', @filters.date("2006-07-05 10:00:00", nil)
+    assert_equal '2006-07-05 10:00:00', @filters.date('2006-07-05 10:00:00', '')
+    assert_equal '2006-07-05 10:00:00', @filters.date('2006-07-05 10:00:00', '')
+    assert_equal '2006-07-05 10:00:00', @filters.date('2006-07-05 10:00:00', '')
+    assert_equal '2006-07-05 10:00:00', @filters.date('2006-07-05 10:00:00', nil)
 
-    assert_equal '07/05/2006', @filters.date("2006-07-05 10:00:00", "%m/%d/%Y")
+    assert_equal '07/05/2006', @filters.date('2006-07-05 10:00:00', '%m/%d/%Y')
 
-    assert_equal "07/16/2004", @filters.date("Fri Jul 16 01:00:00 2004", "%m/%d/%Y")
-    assert_equal "#{Date.today.year}", @filters.date('now', '%Y')
-    assert_equal "#{Date.today.year}", @filters.date('today', '%Y')
-    assert_equal "#{Date.today.year}", @filters.date('Today', '%Y')
+    assert_equal '07/16/2004', @filters.date('Fri Jul 16 01:00:00 2004', '%m/%d/%Y')
+    assert_equal Date.today.year.to_s, @filters.date('now', '%Y')
+    assert_equal Date.today.year.to_s, @filters.date('today', '%Y')
+    assert_equal Date.today.year.to_s, @filters.date('Today', '%Y')
 
-    assert_equal nil, @filters.date(nil, "%B")
+    assert_nil @filters.date(nil, '%B')
 
-    assert_equal '', @filters.date('', "%B")
+    assert_equal '', @filters.date('', '%B')
 
-    with_timezone("UTC") do
-      assert_equal "07/05/2006", @filters.date(1152098955, "%m/%d/%Y")
-      assert_equal "07/05/2006", @filters.date("1152098955", "%m/%d/%Y")
+    with_timezone('UTC') do
+      assert_equal '07/05/2006', @filters.date(1_152_098_955, '%m/%d/%Y')
+      assert_equal '07/05/2006', @filters.date('1152098955', '%m/%d/%Y')
     end
   end
 
   def test_first_last
     assert_equal 1, @filters.first([1, 2, 3])
     assert_equal 3, @filters.last([1, 2, 3])
-    assert_equal nil, @filters.first([])
-    assert_equal nil, @filters.last([])
+    assert_nil @filters.first([])
+    assert_nil @filters.last([])
   end
 
   def test_replace
@@ -326,10 +502,10 @@ class StandardFiltersTest < Minitest::Test
   end
 
   def test_remove
-    assert_equal '   ', @filters.remove("a a a a", 'a')
-    assert_equal '   ', @filters.remove("1 1 1 1", 1)
-    assert_equal 'a a a', @filters.remove_first("a a a a", 'a ')
-    assert_equal ' 1 1 1', @filters.remove_first("1 1 1 1", 1)
+    assert_equal '   ', @filters.remove('a a a a', 'a')
+    assert_equal '   ', @filters.remove('1 1 1 1', 1)
+    assert_equal 'a a a', @filters.remove_first('a a a a', 'a ')
+    assert_equal ' 1 1 1', @filters.remove_first('1 1 1 1', 1)
     assert_template_result 'a a a', "{{ 'a a a a' | remove_first: 'a ' }}"
   end
 
@@ -338,97 +514,148 @@ class StandardFiltersTest < Minitest::Test
   end
 
   def test_strip
-    assert_template_result 'ab c', "{{ source | strip }}", 'source' => " ab c  "
-    assert_template_result 'ab c', "{{ source | strip }}", 'source' => " \tab c  \n \t"
+    assert_template_result 'ab c', '{{ source | strip }}', 'source' => ' ab c  '
+    assert_template_result 'ab c', '{{ source | strip }}', 'source' => " \tab c  \n \t"
   end
 
   def test_lstrip
-    assert_template_result 'ab c  ', "{{ source | lstrip }}", 'source' => " ab c  "
-    assert_template_result "ab c  \n \t", "{{ source | lstrip }}", 'source' => " \tab c  \n \t"
+    assert_template_result 'ab c  ', '{{ source | lstrip }}', 'source' => ' ab c  '
+    assert_template_result "ab c  \n \t", '{{ source | lstrip }}', 'source' => " \tab c  \n \t"
   end
 
   def test_rstrip
-    assert_template_result " ab c", "{{ source | rstrip }}", 'source' => " ab c  "
-    assert_template_result " \tab c", "{{ source | rstrip }}", 'source' => " \tab c  \n \t"
+    assert_template_result ' ab c', '{{ source | rstrip }}', 'source' => ' ab c  '
+    assert_template_result " \tab c", '{{ source | rstrip }}', 'source' => " \tab c  \n \t"
   end
 
   def test_strip_newlines
-    assert_template_result 'abc', "{{ source | strip_newlines }}", 'source' => "a\nb\nc"
-    assert_template_result 'abc', "{{ source | strip_newlines }}", 'source' => "a\r\nb\nc"
+    assert_template_result 'abc', '{{ source | strip_newlines }}', 'source' => "a\nb\nc"
+    assert_template_result 'abc', '{{ source | strip_newlines }}', 'source' => "a\r\nb\nc"
   end
 
   def test_newlines_to_br
-    assert_template_result "a<br />\nb<br />\nc", "{{ source | newline_to_br }}", 'source' => "a\nb\nc"
+    assert_template_result "a<br />\nb<br />\nc", '{{ source | newline_to_br }}', 'source' => "a\nb\nc"
   end
 
   def test_plus
-    assert_template_result "2", "{{ 1 | plus:1 }}"
-    assert_template_result "2.0", "{{ '1' | plus:'1.0' }}"
+    assert_template_result '2', '{{ 1 | plus:1 }}'
+    assert_template_result '2.0', "{{ '1' | plus:'1.0' }}"
+
+    assert_template_result '5', "{{ price | plus:'2' }}", 'price' => NumberLikeThing.new(3)
   end
 
   def test_minus
-    assert_template_result "4", "{{ input | minus:operand }}", 'input' => 5, 'operand' => 1
-    assert_template_result "2.3", "{{ '4.3' | minus:'2' }}"
+    assert_template_result '4', '{{ input | minus:operand }}', 'input' => 5, 'operand' => 1
+    assert_template_result '2.3', "{{ '4.3' | minus:'2' }}"
+
+    assert_template_result '5', "{{ price | minus:'2' }}", 'price' => NumberLikeThing.new(7)
+  end
+
+  def test_abs
+    assert_template_result '17', '{{ 17 | abs }}'
+    assert_template_result '17', '{{ -17 | abs }}'
+    assert_template_result '17', "{{ '17' | abs }}"
+    assert_template_result '17', "{{ '-17' | abs }}"
+    assert_template_result '0', '{{ 0 | abs }}'
+    assert_template_result '0', "{{ '0' | abs }}"
+    assert_template_result '17.42', '{{ 17.42 | abs }}'
+    assert_template_result '17.42', '{{ -17.42 | abs }}'
+    assert_template_result '17.42', "{{ '17.42' | abs }}"
+    assert_template_result '17.42', "{{ '-17.42' | abs }}"
   end
 
   def test_times
-    assert_template_result "12", "{{ 3 | times:4 }}"
-    assert_template_result "0", "{{ 'foo' | times:4 }}"
-
-    assert_template_result "6", "{{ '2.1' | times:3 | replace: '.','-' | plus:0}}"
-
-    assert_template_result "7.25", "{{ 0.0725 | times:100 }}"
+    assert_template_result '12', '{{ 3 | times:4 }}'
+    assert_template_result '0', "{{ 'foo' | times:4 }}"
+    assert_template_result '6', "{{ '2.1' | times:3 | replace: '.','-' | plus:0}}"
+    assert_template_result '7.25', '{{ 0.0725 | times:100 }}'
+    assert_template_result '-7.25', '{{ "-0.0725" | times:100 }}'
+    assert_template_result '7.25', '{{ "-0.0725" | times: -100 }}'
+    assert_template_result '4', '{{ price | times:2 }}', 'price' => NumberLikeThing.new(2)
   end
 
   def test_divided_by
-    assert_template_result "4", "{{ 12 | divided_by:3 }}"
-    assert_template_result "4", "{{ 14 | divided_by:3 }}"
+    assert_template_result '4', '{{ 12 | divided_by:3 }}'
+    assert_template_result '4', '{{ 14 | divided_by:3 }}'
 
-    assert_template_result "5", "{{ 15 | divided_by:3 }}"
-    assert_equal "Liquid error: divided by 0", Template.parse("{{ 5 | divided_by:0 }}").render
+    assert_template_result '5', '{{ 15 | divided_by:3 }}'
+    assert_equal 'Liquid error: divided by 0', Template.parse('{{ 5 | divided_by:0 }}').render
 
-    assert_template_result "0.5", "{{ 2.0 | divided_by:4 }}"
+    assert_template_result '0.5', '{{ 2.0 | divided_by:4 }}'
     assert_raises(Liquid::ZeroDivisionError) do
-      assert_template_result "4", "{{ 1 | modulo: 0 }}"
+      assert_template_result '4', '{{ 1 | modulo: 0 }}'
     end
+
+    assert_template_result '5', '{{ price | divided_by:2 }}', 'price' => NumberLikeThing.new(10)
   end
 
   def test_modulo
-    assert_template_result "1", "{{ 3 | modulo:2 }}"
+    assert_template_result '1', '{{ 3 | modulo:2 }}'
     assert_raises(Liquid::ZeroDivisionError) do
-      assert_template_result "4", "{{ 1 | modulo: 0 }}"
+      assert_template_result '4', '{{ 1 | modulo: 0 }}'
     end
+
+    assert_template_result '1', '{{ price | modulo:2 }}', 'price' => NumberLikeThing.new(3)
   end
 
   def test_round
-    assert_template_result "5", "{{ input | round }}", 'input' => 4.6
-    assert_template_result "4", "{{ '4.3' | round }}"
-    assert_template_result "4.56", "{{ input | round: 2 }}", 'input' => 4.5612
+    assert_template_result '5', '{{ input | round }}', 'input' => 4.6
+    assert_template_result '4', "{{ '4.3' | round }}"
+    assert_template_result '4.56', '{{ input | round: 2 }}', 'input' => 4.5612
     assert_raises(Liquid::FloatDomainError) do
-      assert_template_result "4", "{{ 1.0 | divided_by: 0.0 | round }}"
+      assert_template_result '4', '{{ 1.0 | divided_by: 0.0 | round }}'
     end
+
+    assert_template_result '5', '{{ price | round }}', 'price' => NumberLikeThing.new(4.6)
+    assert_template_result '4', '{{ price | round }}', 'price' => NumberLikeThing.new(4.3)
   end
 
   def test_ceil
-    assert_template_result "5", "{{ input | ceil }}", 'input' => 4.6
-    assert_template_result "5", "{{ '4.3' | ceil }}"
+    assert_template_result '5', '{{ input | ceil }}', 'input' => 4.6
+    assert_template_result '5', "{{ '4.3' | ceil }}"
     assert_raises(Liquid::FloatDomainError) do
-      assert_template_result "4", "{{ 1.0 | divided_by: 0.0 | ceil }}"
+      assert_template_result '4', '{{ 1.0 | divided_by: 0.0 | ceil }}'
     end
+
+    assert_template_result '5', '{{ price | ceil }}', 'price' => NumberLikeThing.new(4.6)
   end
 
   def test_floor
-    assert_template_result "4", "{{ input | floor }}", 'input' => 4.6
-    assert_template_result "4", "{{ '4.3' | floor }}"
+    assert_template_result '4', '{{ input | floor }}', 'input' => 4.6
+    assert_template_result '4', "{{ '4.3' | floor }}"
     assert_raises(Liquid::FloatDomainError) do
-      assert_template_result "4", "{{ 1.0 | divided_by: 0.0 | floor }}"
+      assert_template_result '4', '{{ 1.0 | divided_by: 0.0 | floor }}'
     end
+
+    assert_template_result '5', '{{ price | floor }}', 'price' => NumberLikeThing.new(5.4)
+  end
+
+  def test_at_most
+    assert_template_result '4', '{{ 5 | at_most:4 }}'
+    assert_template_result '5', '{{ 5 | at_most:5 }}'
+    assert_template_result '5', '{{ 5 | at_most:6 }}'
+
+    assert_template_result '4.5', '{{ 4.5 | at_most:5 }}'
+    assert_template_result '5', '{{ width | at_most:5 }}', 'width' => NumberLikeThing.new(6)
+    assert_template_result '4', '{{ width | at_most:5 }}', 'width' => NumberLikeThing.new(4)
+    assert_template_result '4', '{{ 5 | at_most: width }}', 'width' => NumberLikeThing.new(4)
+  end
+
+  def test_at_least
+    assert_template_result '5', '{{ 5 | at_least:4 }}'
+    assert_template_result '5', '{{ 5 | at_least:5 }}'
+    assert_template_result '6', '{{ 5 | at_least:6 }}'
+
+    assert_template_result '5', '{{ 4.5 | at_least:5 }}'
+    assert_template_result '6', '{{ width | at_least:5 }}', 'width' => NumberLikeThing.new(6)
+    assert_template_result '5', '{{ width | at_least:5 }}', 'width' => NumberLikeThing.new(4)
+    assert_template_result '6', '{{ 5 | at_least: width }}', 'width' => NumberLikeThing.new(6)
   end
 
   def test_append
     assigns = { 'a' => 'bc', 'b' => 'd' }
     assert_template_result('bcd', "{{ a | append: 'd'}}", assigns)
-    assert_template_result('bcd', "{{ a | append: b}}", assigns)
+    assert_template_result('bcd', '{{ a | append: b}}', assigns)
   end
 
   def test_concat
@@ -436,8 +663,7 @@ class StandardFiltersTest < Minitest::Test
     assert_equal [1, 2, 'a'],  @filters.concat([1, 2], ['a'])
     assert_equal [1, 2, 10],   @filters.concat([1, 2], [10])
 
-    assert_raises(TypeError) do
-      # no implicit conversion of Fixnum into Array
+    assert_raises(Liquid::ArgumentError, 'concat filter requires an array argument') do
       @filters.concat([1, 2], 10)
     end
   end
@@ -445,16 +671,16 @@ class StandardFiltersTest < Minitest::Test
   def test_prepend
     assigns = { 'a' => 'bc', 'b' => 'a' }
     assert_template_result('abc', "{{ a | prepend: 'a'}}", assigns)
-    assert_template_result('abc', "{{ a | prepend: b}}", assigns)
+    assert_template_result('abc', '{{ a | prepend: b}}', assigns)
   end
 
   def test_default
-    assert_equal "foo", @filters.default("foo", "bar")
-    assert_equal "bar", @filters.default(nil, "bar")
-    assert_equal "bar", @filters.default("", "bar")
-    assert_equal "bar", @filters.default(false, "bar")
-    assert_equal "bar", @filters.default([], "bar")
-    assert_equal "bar", @filters.default({}, "bar")
+    assert_equal 'foo', @filters.default('foo', 'bar')
+    assert_equal 'bar', @filters.default(nil, 'bar')
+    assert_equal 'bar', @filters.default('', 'bar')
+    assert_equal 'bar', @filters.default(false, 'bar')
+    assert_equal 'bar', @filters.default([], 'bar')
+    assert_equal 'bar', @filters.default({}, 'bar')
   end
 
   def test_cannot_access_private_methods
@@ -466,6 +692,78 @@ class StandardFiltersTest < Minitest::Test
     assert_template_result('abc', "{{ 'abc' | date: '%D' }}")
   end
 
+  def test_where
+    input = [
+      { 'handle' => 'alpha', 'ok' => true },
+      { 'handle' => 'beta', 'ok' => false },
+      { 'handle' => 'gamma', 'ok' => false },
+      { 'handle' => 'delta', 'ok' => true },
+    ]
+
+    expectation = [
+      { 'handle' => 'alpha', 'ok' => true },
+      { 'handle' => 'delta', 'ok' => true },
+    ]
+
+    assert_equal expectation, @filters.where(input, 'ok', true)
+    assert_equal expectation, @filters.where(input, 'ok')
+  end
+
+  def test_where_no_key_set
+    input = [
+      { 'handle' => 'alpha', 'ok' => true },
+      { 'handle' => 'beta' },
+      { 'handle' => 'gamma' },
+      { 'handle' => 'delta', 'ok' => true },
+    ]
+
+    expectation = [
+      { 'handle' => 'alpha', 'ok' => true },
+      { 'handle' => 'delta', 'ok' => true },
+    ]
+
+    assert_equal expectation, @filters.where(input, 'ok', true)
+    assert_equal expectation, @filters.where(input, 'ok')
+  end
+
+  def test_where_non_array_map_input
+    assert_equal [{ 'a' => 'ok' }], @filters.where({ 'a' => 'ok' }, 'a', 'ok')
+    assert_equal [], @filters.where({ 'a' => 'not ok' }, 'a', 'ok')
+  end
+
+  def test_where_indexable_but_non_map_value
+    assert_raises(Liquid::ArgumentError) { @filters.where(1, 'ok', true) }
+    assert_raises(Liquid::ArgumentError) { @filters.where(1, 'ok') }
+  end
+
+  def test_where_non_boolean_value
+    input = [
+      { 'message' => 'Bonjour!', 'language' => 'French' },
+      { 'message' => 'Hello!', 'language' => 'English' },
+      { 'message' => 'Hallo!', 'language' => 'German' },
+    ]
+
+    assert_equal [{ 'message' => 'Bonjour!', 'language' => 'French' }], @filters.where(input, 'language', 'French')
+    assert_equal [{ 'message' => 'Hallo!', 'language' => 'German' }], @filters.where(input, 'language', 'German')
+    assert_equal [{ 'message' => 'Hello!', 'language' => 'English' }], @filters.where(input, 'language', 'English')
+  end
+
+  def test_where_array_of_only_unindexable_values
+    assert_nil @filters.where([nil], 'ok', true)
+    assert_nil @filters.where([nil], 'ok')
+  end
+
+  def test_where_no_target_value
+    input = [
+      { 'foo' => false },
+      { 'foo' => true },
+      { 'foo' => 'for sure' },
+      { 'bar' => true },
+    ]
+
+    assert_equal [{ 'foo' => true }, { 'foo' => 'for sure' }], @filters.where(input, 'foo')
+  end
+
   private
 
   def with_timezone(tz)

test/integration/tags/break_tag_test.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 
 class BreakTagTest < Minitest::Test

test/integration/tags/continue_tag_test.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 
 class ContinueTagTest < Minitest::Test

test/integration/tags/for_tag_test.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 
 class ThingWithValue < Liquid::Drop
@@ -23,16 +25,16 @@ class ForTagTest < Minitest::Test
   yo
 
 HERE
-    template = <<HERE
-{%for item in array%}
-  yo
-{%endfor%}
-HERE
+    template = <<~HERE
+      {%for item in array%}
+        yo
+      {%endfor%}
+    HERE
     assert_template_result(expected, template, 'array' => [1, 2, 3])
   end
 
   def test_for_reversed
-    assigns = { 'array' => [ 1, 2, 3] }
+    assigns = { 'array' => [1, 2, 3] }
     assert_template_result('321', '{%for item in array reversed %}{{item}}{%endfor%}', assigns)
   end
 
@@ -40,31 +42,31 @@ HERE
     assert_template_result(' 1  2  3 ', '{%for item in (1..3) %} {{item}} {%endfor%}')
 
     assert_raises(Liquid::ArgumentError) do
-      Template.parse('{% for i in (a..2) %}{% endfor %}').render!("a" => [1, 2])
+      Template.parse('{% for i in (a..2) %}{% endfor %}').render!('a' => [1, 2])
     end
 
-    assert_template_result(' 0  1  2  3 ', '{% for item in (a..3) %} {{item}} {% endfor %}', "a" => "invalid integer")
+    assert_template_result(' 0  1  2  3 ', '{% for item in (a..3) %} {{item}} {% endfor %}', 'a' => 'invalid integer')
   end
 
   def test_for_with_variable_range
-    assert_template_result(' 1  2  3 ', '{%for item in (1..foobar) %} {{item}} {%endfor%}', "foobar" => 3)
+    assert_template_result(' 1  2  3 ', '{%for item in (1..foobar) %} {{item}} {%endfor%}', 'foobar' => 3)
   end
 
   def test_for_with_hash_value_range
-    foobar = { "value" => 3 }
-    assert_template_result(' 1  2  3 ', '{%for item in (1..foobar.value) %} {{item}} {%endfor%}', "foobar" => foobar)
+    foobar = { 'value' => 3 }
+    assert_template_result(' 1  2  3 ', '{%for item in (1..foobar.value) %} {{item}} {%endfor%}', 'foobar' => foobar)
   end
 
   def test_for_with_drop_value_range
     foobar = ThingWithValue.new
-    assert_template_result(' 1  2  3 ', '{%for item in (1..foobar.value) %} {{item}} {%endfor%}', "foobar" => foobar)
+    assert_template_result(' 1  2  3 ', '{%for item in (1..foobar.value) %} {{item}} {%endfor%}', 'foobar' => foobar)
   end
 
   def test_for_with_variable
     assert_template_result(' 1  2  3 ', '{%for item in array%} {{item}} {%endfor%}', 'array' => [1, 2, 3])
     assert_template_result('123', '{%for item in array%}{{item}}{%endfor%}', 'array' => [1, 2, 3])
     assert_template_result('123', '{% for item in array %}{{item}}{% endfor %}', 'array' => [1, 2, 3])
-    assert_template_result('abcd', '{%for item in array%}{{item}}{%endfor%}', 'array' => ['a', 'b', 'c', 'd'])
+    assert_template_result('abcd', '{%for item in array%}{{item}}{%endfor%}', 'array' => %w[a b c d])
     assert_template_result('a b c', '{%for item in array%}{{item}}{%endfor%}', 'array' => ['a', ' ', 'b', ' ', 'c'])
     assert_template_result('abc', '{%for item in array%}{{item}}{%endfor%}', 'array' => ['a', '', 'b', '', 'c'])
   end
@@ -72,8 +74,8 @@ HERE
   def test_for_helpers
     assigns = { 'array' => [1, 2, 3] }
     assert_template_result(' 1/3  2/3  3/3 ',
-      '{%for item in array%} {{forloop.index}}/{{forloop.length}} {%endfor%}',
-      assigns)
+                           '{%for item in array%} {{forloop.index}}/{{forloop.length}} {%endfor%}',
+                           assigns)
     assert_template_result(' 1  2  3 ', '{%for item in array%} {{forloop.index}} {%endfor%}', assigns)
     assert_template_result(' 0  1  2 ', '{%for item in array%} {{forloop.index0}} {%endfor%}', assigns)
     assert_template_result(' 2  1  0 ', '{%for item in array%} {{forloop.rindex0}} {%endfor%}', assigns)
@@ -85,8 +87,8 @@ HERE
   def test_for_and_if
     assigns = { 'array' => [1, 2, 3] }
     assert_template_result('+--',
-      '{%for item in array%}{% if forloop.first %}+{% else %}-{% endif %}{%endfor%}',
-      assigns)
+                           '{%for item in array%}{% if forloop.first %}+{% else %}-{% endif %}{%endfor%}',
+                           assigns)
   end
 
   def test_for_else
@@ -103,6 +105,34 @@ HERE
     assert_template_result('3456', '{%for i in array limit: 4 offset: 2 %}{{ i }}{%endfor%}', assigns)
   end
 
+  def test_limiting_with_invalid_limit
+    assigns = { 'array' => [1, 2, 3, 4, 5, 6, 7, 8, 9, 0] }
+    template = <<-MKUP
+      {% for i in array limit: true offset: 1 %}
+        {{ i }}
+      {% endfor %}
+    MKUP
+
+    exception = assert_raises(Liquid::ArgumentError) do
+      Template.parse(template).render!(assigns)
+    end
+    assert_equal('Liquid error: invalid integer', exception.message)
+  end
+
+  def test_limiting_with_invalid_offset
+    assigns = { 'array' => [1, 2, 3, 4, 5, 6, 7, 8, 9, 0] }
+    template = <<-MKUP
+      {% for i in array limit: 1 offset: true %}
+        {{ i }}
+      {% endfor %}
+    MKUP
+
+    exception = assert_raises(Liquid::ArgumentError) do
+      Template.parse(template).render!(assigns)
+    end
+    assert_equal('Liquid error: invalid integer', exception.message)
+  end
+
   def test_dynamic_variable_limiting
     assigns = { 'array' => [1, 2, 3, 4, 5, 6, 7, 8, 9, 0] }
     assigns['limit'] = 2
@@ -129,14 +159,14 @@ HERE
       {%for i in array.items offset:continue limit: 3 %}{{i}}{%endfor%}
       next
       {%for i in array.items offset:continue limit: 3 %}{{i}}{%endfor%}
-      MKUP
+    MKUP
     expected = <<-XPCTD
       123
       next
       456
       next
       789
-      XPCTD
+    XPCTD
     assert_template_result(expected, markup, assigns)
   end
 
@@ -148,18 +178,18 @@ HERE
       {%for i in array.items offset:continue limit:3 %}{{i}}{%endfor%}
       next
       {%for i in array.items offset:continue limit:1 %}{{i}}{%endfor%}
-      MKUP
+    MKUP
     expected = <<-XPCTD
       123
       next
       456
       next
       7
-      XPCTD
+    XPCTD
     assert_template_result(expected, markup, assigns)
   end
 
-  def test_pause_resume_BIG_limit
+  def test_pause_resume_big_limit
     assigns = { 'array' => { 'items' => [1, 2, 3, 4, 5, 6, 7, 8, 9, 0] } }
     markup = <<-MKUP
       {%for i in array.items limit:3 %}{{i}}{%endfor%}
@@ -167,18 +197,18 @@ HERE
       {%for i in array.items offset:continue limit:3 %}{{i}}{%endfor%}
       next
       {%for i in array.items offset:continue limit:1000 %}{{i}}{%endfor%}
-      MKUP
+    MKUP
     expected = <<-XPCTD
       123
       next
       456
       next
       7890
-      XPCTD
+    XPCTD
     assert_template_result(expected, markup, assigns)
   end
 
-  def test_pause_resume_BIG_offset
+  def test_pause_resume_big_offset
     assigns = { 'array' => { 'items' => [1, 2, 3, 4, 5, 6, 7, 8, 9, 0] } }
     markup = '{%for i in array.items limit:3 %}{{i}}{%endfor%}
       next
@@ -197,19 +227,19 @@ HERE
     assigns = { 'array' => { 'items' => [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] } }
 
     markup = '{% for i in array.items %}{% break %}{% endfor %}'
-    expected = ""
+    expected = ''
     assert_template_result(expected, markup, assigns)
 
     markup = '{% for i in array.items %}{{ i }}{% break %}{% endfor %}'
-    expected = "1"
+    expected = '1'
     assert_template_result(expected, markup, assigns)
 
     markup = '{% for i in array.items %}{% break %}{{ i }}{% endfor %}'
-    expected = ""
+    expected = ''
     assert_template_result(expected, markup, assigns)
 
     markup = '{% for i in array.items %}{{ i }}{% if i > 3 %}{% break %}{% endif %}{% endfor %}'
-    expected = "1234"
+    expected = '1234'
     assert_template_result(expected, markup, assigns)
 
     # tests to ensure it only breaks out of the local for loop
@@ -237,23 +267,23 @@ HERE
     assigns = { 'array' => { 'items' => [1, 2, 3, 4, 5] } }
 
     markup = '{% for i in array.items %}{% continue %}{% endfor %}'
-    expected = ""
+    expected = ''
     assert_template_result(expected, markup, assigns)
 
     markup = '{% for i in array.items %}{{ i }}{% continue %}{% endfor %}'
-    expected = "12345"
+    expected = '12345'
     assert_template_result(expected, markup, assigns)
 
     markup = '{% for i in array.items %}{% continue %}{{ i }}{% endfor %}'
-    expected = ""
+    expected = ''
     assert_template_result(expected, markup, assigns)
 
     markup = '{% for i in array.items %}{% if i > 3 %}{% continue %}{% endif %}{{ i }}{% endfor %}'
-    expected = "123"
+    expected = '123'
     assert_template_result(expected, markup, assigns)
 
     markup = '{% for i in array.items %}{% if i == 3 %}{% continue %}{% else %}{{ i }}{% endif %}{% endfor %}'
-    expected = "1245"
+    expected = '1245'
     assert_template_result(expected, markup, assigns)
 
     # tests to ensure it only continues the local for loop and not all of them.
@@ -282,41 +312,41 @@ HERE
     # the functionality for backwards compatibility
 
     assert_template_result('test string',
-      '{%for val in string%}{{val}}{%endfor%}',
-      'string' => "test string")
+                           '{%for val in string%}{{val}}{%endfor%}',
+                           'string' => 'test string')
 
     assert_template_result('test string',
-      '{%for val in string limit:1%}{{val}}{%endfor%}',
-      'string' => "test string")
+                           '{%for val in string limit:1%}{{val}}{%endfor%}',
+                           'string' => 'test string')
 
     assert_template_result('val-string-1-1-0-1-0-true-true-test string',
-      '{%for val in string%}' \
-      '{{forloop.name}}-' \
-      '{{forloop.index}}-' \
-      '{{forloop.length}}-' \
-      '{{forloop.index0}}-' \
-      '{{forloop.rindex}}-' \
-      '{{forloop.rindex0}}-' \
-      '{{forloop.first}}-' \
-      '{{forloop.last}}-' \
-      '{{val}}{%endfor%}',
-      'string' => "test string")
+                           '{%for val in string%}' \
+                           '{{forloop.name}}-' \
+                           '{{forloop.index}}-' \
+                           '{{forloop.length}}-' \
+                           '{{forloop.index0}}-' \
+                           '{{forloop.rindex}}-' \
+                           '{{forloop.rindex0}}-' \
+                           '{{forloop.first}}-' \
+                           '{{forloop.last}}-' \
+                           '{{val}}{%endfor%}',
+                           'string' => 'test string')
   end
 
   def test_for_parentloop_references_parent_loop
     assert_template_result('1.1 1.2 1.3 2.1 2.2 2.3 ',
-      '{% for inner in outer %}{% for k in inner %}' \
-      '{{ forloop.parentloop.index }}.{{ forloop.index }} ' \
-      '{% endfor %}{% endfor %}',
-      'outer' => [[1, 1, 1], [1, 1, 1]])
+                           '{% for inner in outer %}{% for k in inner %}' \
+                           '{{ forloop.parentloop.index }}.{{ forloop.index }} ' \
+                           '{% endfor %}{% endfor %}',
+                           'outer' => [[1, 1, 1], [1, 1, 1]])
   end
 
   def test_for_parentloop_nil_when_not_present
     assert_template_result('.1 .2 ',
-      '{% for inner in outer %}' \
-      '{{ forloop.parentloop.index }}.{{ forloop.index }} ' \
-      '{% endfor %}',
-      'outer' => [[1, 1, 1], [1, 1, 1]])
+                           '{% for inner in outer %}' \
+                           '{{ forloop.parentloop.index }}.{{ forloop.index }} ' \
+                           '{% endfor %}',
+                           'outer' => [[1, 1, 1], [1, 1, 1]])
   end
 
   def test_inner_for_over_empty_input
@@ -324,7 +354,7 @@ HERE
   end
 
   def test_blank_string_not_iterable
-    assert_template_result('', "{% for char in characters %}I WILL NOT BE OUTPUT{% endfor %}", 'characters' => '')
+    assert_template_result('', '{% for char in characters %}I WILL NOT BE OUTPUT{% endfor %}', 'characters' => '')
   end
 
   def test_bad_variable_naming_in_for_loop