Prefer string interpolation in simple cases

Co-Authored-By: Dylan Thacker-Smith <dylan.smith@shopify.com>

.github/probots.yml

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

.gitignore

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

.rubocop.yml

@@ -1,125 +1,16 @@
-inherit_from: ./.rubocop_todo.yml
+inherit_from:
+  - https://shopify.github.io/ruby-style-guide/rubocop.yml
+  - .rubocop_todo.yml
+
+require: rubocop-performance
+
+Performance:
+  Enabled: true
 
 AllCops:
   Exclude:
-    - 'performance/shopify/*'
-    - 'pkg/**'
-
-Metrics/BlockNesting:
-  Max: 3
+    - 'vendor/bundle/**/*'
+      
+Naming/MethodName:
   Exclude:
-    - 'lib/liquid/block_body.rb'
-
-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
+    - 'example/server/liquid_servlet.rb'

.rubocop_todo.yml

@@ -1,72 +1,94 @@
-# This configuration was generated by `rubocop --auto-gen-config`
-# on 2015-06-08 18:16:16 +0000 using RuboCop version 0.32.0.
+# This configuration was generated by
+# `rubocop --auto-gen-config`
+# on 2019-09-11 06:34:25 +1000 using RuboCop version 0.74.0.
 # The point is for the user to remove these configuration records
 # one by one as the offenses are removed from the code base.
 # Note that changes in the inspected code, or installation of new
 # versions of RuboCop, may require this file to be generated again.
 
-# Offense count: 5
-Lint/NestedMethodDefinition:
-  Enabled: false
+# Offense count: 2
+Lint/AmbiguousOperator:
+  Exclude:
+    - 'test/unit/condition_unit_test.rb'
 
-# Offense count: 53
-Metrics/AbcSize:
-  Max: 58
+# Offense count: 21
+# Configuration parameters: AllowSafeAssignment.
+Lint/AssignmentInCondition:
+  Exclude:
+    - 'lib/liquid/block_body.rb'
+    - 'lib/liquid/lexer.rb'
+    - 'lib/liquid/standardfilters.rb'
+    - 'lib/liquid/tags/for.rb'
+    - 'lib/liquid/tags/if.rb'
+    - 'lib/liquid/tags/raw.rb'
+    - 'lib/liquid/variable.rb'
+    - 'performance/profile.rb'
+    - 'test/test_helper.rb'
+    - 'test/unit/tokenizer_unit_test.rb'
 
-# Offense count: 12
-Metrics/CyclomaticComplexity:
-  Max: 15
+# Offense count: 2
+# Cop supports --auto-correct.
+# Configuration parameters: EnforcedStyle.
+# SupportedStyles: runtime_error, standard_error
+Lint/InheritException:
+  Exclude:
+    - 'lib/liquid/interrupts.rb'
 
-# Offense count: 553
-# Configuration parameters: AllowURI, URISchemes.
+# Offense count: 2
+Lint/UselessAssignment:
+  Exclude:
+    - 'performance/shopify/database.rb'
+
+# Offense count: 1
+# Configuration parameters: CheckForMethodsWithNoSideEffects.
+Lint/Void:
+  Exclude:
+    - 'lib/liquid/parse_context.rb'
+
+# Offense count: 98
+# Cop supports --auto-correct.
+# Configuration parameters: AutoCorrect, AllowHeredoc, AllowURI, URISchemes, IgnoreCopDirectives, IgnoredPatterns.
+# URISchemes: http, https
 Metrics/LineLength:
   Max: 294
 
-# Offense count: 77
-# Configuration parameters: CountComments.
-Metrics/MethodLength:
-  Max: 46
+# Offense count: 44
+Naming/ConstantName:
+  Exclude:
+    - 'lib/liquid.rb'
+    - 'lib/liquid/block_body.rb'
+    - 'lib/liquid/tags/assign.rb'
+    - 'lib/liquid/tags/capture.rb'
+    - 'lib/liquid/tags/case.rb'
+    - 'lib/liquid/tags/cycle.rb'
+    - 'lib/liquid/tags/for.rb'
+    - 'lib/liquid/tags/if.rb'
+    - 'lib/liquid/tags/include.rb'
+    - 'lib/liquid/tags/raw.rb'
+    - 'lib/liquid/tags/table_row.rb'
+    - 'lib/liquid/variable.rb'
+    - 'performance/shopify/comment_form.rb'
+    - 'performance/shopify/paginate.rb'
+    - 'test/integration/tags/include_tag_test.rb'
 
-# Offense count: 6
-Metrics/PerceivedComplexity:
-  Max: 13
+# Offense count: 5
+Style/ClassVars:
+  Exclude:
+    - 'lib/liquid/condition.rb'
+    - 'lib/liquid/strainer.rb'
+    - 'lib/liquid/template.rb'
 
 # Offense count: 1
-Style/AccessorMethodName:
-  Enabled: false
+# Configuration parameters: AllowCoercion.
+Style/DateTime:
+  Exclude:
+    - 'test/unit/context_unit_test.rb'
 
-# 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
+# Offense count: 9
 # 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
+  Exclude:
+    - 'test/integration/error_handling_test.rb'
+    - 'test/integration/template_test.rb'
+    - 'test/unit/context_unit_test.rb'

.travis.yml

@@ -1,25 +1,30 @@
 language: ruby
+cache: bundler
 
 rvm:
-  - 2.0
-  - 2.1
-  - 2.2
+  - 2.4
+  - 2.5
+  - &latest_ruby 2.6
+  - 2.7
   - ruby-head
   - jruby-head
-#  - rbx-2
-
-sudo: false
-
-addons:
-  apt:
-    packages:
-    - libgmp3-dev
+  - truffleruby
 
 matrix:
+  include:
+    - rvm: *latest_ruby
+      script: bundle exec rake memory_profile:run
+      name: Profiling Memory Usage
   allow_failures:
+    - rvm: ruby-head
     - rvm: jruby-head
+    - rvm: truffleruby
 
-script: "bundle exec rake"
+branches:
+  only:
+    - master
+    - gh-pages
+    - /.*-stable/
 
 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 +1,27 @@
+# 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'
+  gem 'terminal-table'
 
-  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: 'master'
   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]

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 +75,40 @@ 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
+```
+
+### Usage tracking
+
+To help track usages of a feature or code path in production, we have released opt-in usage tracking. To enable this, we provide an empty `Liquid:: Usage.increment` method which you can customize to your needs. The feature is well suited to https://github.com/Shopify/statsd-instrument. However, the choice of implementation is up to you.
+
+Once you have enabled usage tracking, we recommend reporting any events through Github Issues that your system may be logging. It is highly likely this event has been added to consider deprecating or improving code specific to this event, so please raise any concerns.

Rakefile

@@ -1,29 +1,33 @@
+# frozen_string_literal: true
+
 require 'rake'
 require 'rake/testtask'
-$LOAD_PATH.unshift File.expand_path("../lib", __FILE__)
+$LOAD_PATH.unshift(File.expand_path("../lib", __FILE__))
 require "liquid/version"
 
-task default: [:rubocop, :test]
+task(default: [: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 +36,8 @@ 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
@@ -45,7 +49,7 @@ task :test do
   end
 end
 
-task gem: :build
+task(gem: :build)
 task :build do
   system "gem build liquid.gemspec"
 end
@@ -85,7 +89,14 @@ namespace :profile do
   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"
 end

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)

example/server/liquid_servlet.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class LiquidServlet < WEBrick::HTTPServlet::AbstractServlet
   def do_GET(req, res)
     handle(:get, req, res)
@@ -9,12 +11,12 @@ class LiquidServlet < WEBrick::HTTPServlet::AbstractServlet
 
   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"

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
@@ -21,9 +23,10 @@
 
 module Liquid
   FilterSeparator             = /\|/
-  ArgumentSeparator           = ','.freeze
-  FilterArgumentSeparator     = ':'.freeze
-  VariableAttributeSeparator  = '.'.freeze
+  ArgumentSeparator           = ','
+  FilterArgumentSeparator     = ':'
+  VariableAttributeSeparator  = '.'
+  WhitespaceControl           = '-'
   TagStart                    = /\{\%/
   TagEnd                      = /\%\}/
   VariableSignature           = /\(?[\w\-\.\[\]]\)?/
@@ -34,7 +37,7 @@ module Liquid
   QuotedString                = /"[^"]*"|'[^']*'/
   QuotedFragment              = /#{QuotedString}|(?:[^\s,\|'"]|#{QuotedString})+/o
   TagAttributes               = /(\w+)\s*\:\s*(#{QuotedFragment})/o
-  AnyStartingTag              = /\{\{|\{\%/
+  AnyStartingTag              = /#{TagStart}|#{VariableStart}/o
   PartialTemplateParser       = /#{TagStart}.*?#{TagEnd}|#{VariableStart}.*?#{VariableIncompleteEnd}/om
   TemplateParser              = /(#{PartialTemplateParser}|#{AnyStartingTag})/om
   VariableParser              = /\[[^\]]+\]|#{VariableSegment}+\??/o
@@ -44,6 +47,7 @@ module Liquid
 end
 
 require "liquid/version"
+require 'liquid/parse_tree_visitor'
 require 'liquid/lexer'
 require 'liquid/parser'
 require 'liquid/i18n'
@@ -72,6 +76,8 @@ require 'liquid/condition'
 require 'liquid/utils'
 require 'liquid/tokenizer'
 require 'liquid/parse_context'
+require 'liquid/partial_cache'
+require 'liquid/usage'
 
 # Load all the tags of the standard library
 #

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,
+      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))
+          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 +53,25 @@ module Liquid
     protected
 
     def parse_body(body, tokens)
-      body.parse(tokens, parse_context) do |end_tag_name, end_tag_params|
-        @blank &&= body.blank?
+      if parse_context.depth >= MAX_DEPTH
+        raise StackLevelError, "Nesting too deep"
+      end
+      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
-        unless end_tag_name
-          raise SyntaxError.new(parse_context.locale.t("errors.syntax.tag_never_closed".freeze, block_name: block_name))
+          return false if end_tag_name == block_delimiter
+          unless end_tag_name
+            raise SyntaxError, parse_context.locale.t("errors.syntax.tag_never_closed", block_name: block_name)
+          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)
         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 +1,13 @@
+# 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
+    LiquidTagToken = /\A\s*(\w+)\s*(.*?)\z/o
+    FullToken = /\A#{TagStart}#{WhitespaceControl}?(\s*)(\w+)(\s*)(.*?)#{WhitespaceControl}?#{TagEnd}\z/om
+    ContentOfVariable = /\A#{VariableStart}#{WhitespaceControl}?(.*?)#{WhitespaceControl}?#{VariableEnd}\z/om
+    WhitespaceOrNothing = /\A\s*\z/
+    TAGSTART = "{%"
+    VARSTART = "{{"
 
     attr_reader :nodelist
 
@@ -12,35 +16,34 @@ module Liquid
       @blank = true
     end
 
-    def parse(tokenizer, parse_context)
+    def parse(tokenizer, parse_context, &block)
       parse_context.line_number = tokenizer.line_number
+
+      if tokenizer.for_liquid_tag
+        parse_for_liquid_tag(tokenizer, parse_context, &block)
+      else
+        parse_for_document(tokenizer, parse_context, &block)
+      end
+    end
+
+    private def parse_for_liquid_tag(tokenizer, parse_context)
       while token = tokenizer.shift
-        unless token.empty?
-          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/)
+        unless token.empty? || token =~ WhitespaceOrNothing
+          unless token =~ LiquidTagToken
+            # line isn't empty but didn't match tag syntax, yield and let the
+            # caller raise a syntax error
+            return yield token, token
           end
+          tag_name = Regexp.last_match(1)
+          markup = Regexp.last_match(2)
+          unless tag = registered_tags[tag_name]
+            # end parsing if we reach an unknown tag and let the caller decide
+            # determine how to proceed
+            return yield tag_name, markup
+          end
+          new_tag = tag.parse(tag_name, markup, tokenizer, parse_context)
+          @blank &&= new_tag.blank?
+          @nodelist << new_tag
         end
         parse_context.line_number = tokenizer.line_number
       end
@@ -48,53 +51,121 @@ module Liquid
       yield nil, nil
     end
 
+    private def parse_for_document(tokenizer, parse_context, &block)
+      while token = tokenizer.shift
+        next if token.empty?
+        case
+        when token.start_with?(TAGSTART)
+          whitespace_handler(token, parse_context)
+          unless token =~ FullToken
+            raise_missing_tag_terminator(token, parse_context)
+          end
+          tag_name = Regexp.last_match(2)
+          markup = Regexp.last_match(4)
+
+          if parse_context.line_number
+            # newlines inside the tag should increase the line number,
+            # particularly important for multiline {% liquid %} tags
+            parse_context.line_number += Regexp.last_match(1).count("\n") + Regexp.last_match(3).count("\n")
+          end
+
+          if tag_name == 'liquid'
+            liquid_tag_tokenizer = Tokenizer.new(markup, line_number: parse_context.line_number, for_liquid_tag: true)
+            next parse_for_liquid_tag(liquid_tag_tokenizer, parse_context, &block)
+          end
+
+          unless tag = registered_tags[tag_name]
+            # end parsing if we reach an unknown tag and let the caller decide
+            # determine how to proceed
+            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?(VARSTART)
+          whitespace_handler(token, parse_context)
+          @nodelist << create_variable(token, parse_context)
+          @blank = false
+        else
+          if parse_context.trim_whitespace
+            token.lstrip!
+          end
+          parse_context.trim_whitespace = false
+          @nodelist << token
+          @blank &&= !!(token =~ WhitespaceOrNothing)
+        end
+        parse_context.line_number = tokenizer.line_number
+      end
+
+      yield nil, nil
+    end
+
+    def whitespace_handler(token, parse_context)
+      if token[2] == WhitespaceControl
+        previous_token = @nodelist.last
+        if previous_token.is_a?(String)
+          previous_token.rstrip!
+        end
+      end
+      parse_context.trim_whitespace = (token[-3] == WhitespaceControl)
+    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)
@@ -106,11 +177,11 @@ 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: TagEnd.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: VariableEnd.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
   #
@@ -8,49 +10,55 @@ module Liquid
   #
   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|
+      '==' => ->(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
     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
   #
@@ -12,28 +14,39 @@ 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_reader :scopes, :errors, :registers, :environments, :resource_limits, :static_registers, :static_environments
+    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
-      @scopes           = [(outer_scope || {})]
-      @registers        = registers
-      @errors           = []
-      @partial          = false
-      @resource_limits  = resource_limits || ResourceLimits.new(Template.default_resource_limits)
+    # rubocop:disable Metrics/ParameterLists
+    def self.build(environments: {}, outer_scope: {}, registers: {}, rethrow_errors: false, resource_limits: nil, static_registers: {}, static_environments: {})
+      new(environments, outer_scope, registers, rethrow_errors, resource_limits, static_registers, static_environments)
+    end
+
+    def initialize(environments = {}, outer_scope = {}, registers = {}, rethrow_errors = false, resource_limits = nil, static_registers = {}, static_environments = {})
+      @environments = [environments]
+      @environments.flatten!
+
+      @static_environments = [static_environments].flat_map(&:freeze).freeze
+      @scopes              = [(outer_scope || {})]
+      @registers           = registers
+      @static_registers    = static_registers.freeze
+      @errors              = []
+      @partial             = false
+      @strict_variables    = false
+      @resource_limits     = resource_limits || ResourceLimits.new(Template.default_resource_limits)
+      @base_scope_depth    = 0
       squash_instance_assigns_with_environments
 
-      @this_stack_used = false
-
+      self.exception_renderer = Template.default_exception_renderer
       if rethrow_errors
-        self.exception_handler = ->(e) { raise }
+        self.exception_renderer = ->(_e) { raise }
       end
 
       @interrupts = []
       @filters = []
       @global_filter = nil
     end
+    # rubocop:enable Metrics/ParameterLists
 
     def warnings
       @warnings ||= []
@@ -73,30 +86,11 @@ 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 +100,7 @@ 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
+      check_overflow
     end
 
     # Merge a hash of variables in the current local scope
@@ -128,19 +122,30 @@ module Liquid
     #   end
     #
     #   context['var]  #=> nil
-    def stack(new_scope = nil)
-      old_stack_used = @this_stack_used
-      if new_scope
-        push(new_scope)
-        @this_stack_used = true
-      else
-        @this_stack_used = false
-      end
-
+    def stack(new_scope = {})
+      push(new_scope)
       yield
     ensure
-      pop if @this_stack_used
-      @this_stack_used = old_stack_used
+      pop
+    end
+
+    # Creates a new context inheriting resource limits, filters, environment etc.,
+    # but with an isolated scope.
+    def new_isolated_subcontext
+      check_overflow
+
+      Context.build(
+        resource_limits: resource_limits,
+        static_environments: static_environments,
+        static_registers: static_registers
+      ).tap do |subcontext|
+        subcontext.base_scope_depth = base_scope_depth + 1
+        subcontext.exception_renderer = exception_renderer
+        subcontext.filters = @filters
+        subcontext.strainer = nil
+        subcontext.errors = errors
+        subcontext.warnings = warnings
+      end
     end
 
     def clear_instance_assigns
@@ -149,10 +154,6 @@ module Liquid
 
     # Only allow String, Numeric, Hash, Array, Proc, Boolean or <tt>Liquid::Drop</tt>
     def []=(key, value)
-      unless @this_stack_used
-        @this_stack_used = true
-        push({})
-      end
       @scopes[0][key] = value
     end
 
@@ -177,43 +178,76 @@ 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) }
-      scope = @scopes[index] if index
 
-      variable = nil
-
-      if scope.nil?
-        @environments.each do |e|
-          variable = lookup_and_evaluate(e, key)
-          unless variable.nil?
-            scope = e
-            break
-          end
-        end
+      variable = if index
+        lookup_and_evaluate(@scopes[index], key, raise_on_not_found: raise_on_not_found)
+      else
+        try_variable_find_in_environments(key, raise_on_not_found: raise_on_not_found)
       end
 
-      scope ||= @environments.last || @scopes.last
-      variable ||= lookup_and_evaluate(scope, key)
-
       variable = variable.to_liquid
       variable.context = self if variable.respond_to?(:context=)
 
       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)
+      if @strict_variables && raise_on_not_found && obj.respond_to?(:key?) && !obj.key?(key)
+        raise Liquid::UndefinedVariable, "undefined variable #{key}"
+      end
+
+      value = obj[key]
+
+      if value.is_a?(Proc) && obj.respond_to?(:[]=)
+        obj[key] = value.arity == 0 ? value.call : value.call(self)
       else
         value
       end
     end
 
+    protected
+
+    attr_writer :base_scope_depth, :warnings, :errors, :strainer, :filters
+
     private
 
+    attr_reader :base_scope_depth
+
+    def try_variable_find_in_environments(key, raise_on_not_found:)
+      @environments.each do |environment|
+        found_variable = lookup_and_evaluate(environment, key, raise_on_not_found: raise_on_not_found)
+        if !found_variable.nil? || @strict_variables && raise_on_not_found
+          return found_variable
+        end
+      end
+      @static_environments.each do |environment|
+        found_variable = lookup_and_evaluate(environment, key, raise_on_not_found: raise_on_not_found)
+        if !found_variable.nil? || @strict_variables && raise_on_not_found
+          return found_variable
+        end
+      end
+      nil
+    end
+
+    def check_overflow
+      raise StackLevelError, "Nesting too deep" if overflow?
+    end
+
+    def overflow?
+      base_scope_depth + @scopes.length > Block::MAX_DEPTH
+    end
+
+    def internal_error
+      # raise and catch to set backtrace and cause on exception
+      raise Liquid::InternalError, 'internal'
+    rescue Liquid::InternalError => exc
+      exc
+    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 +26,9 @@ 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 +64,17 @@ 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?]
         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
@@ -5,7 +7,7 @@ module Liquid
     attr_accessor :markup_context
 
     def to_s(with_prefix = true)
-      str = ""
+      str = +""
       str << message_prefix if with_prefix
       str << super()
 
@@ -17,22 +19,14 @@ module Liquid
       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
@@ -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
+    DOUBLE_QUOTED_STRING = /\A"(.*)"\z/m
+    INTEGERS_REGEX       = /\A(-?\d+)\z/
+    FLOATS_REGEX         = /\A(-?\d[\d\.]+)\z/
+    RANGES_REGEX         = /\A\((\S+)\.\.(\S+)\)\z/
 
     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.
   #
@@ -8,8 +10,8 @@ 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
@@ -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

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'yaml'
 
 module Liquid
@@ -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

@@ -1,10 +1,12 @@
+# 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
 

lib/liquid/lexer.rb

@@ -1,41 +1,44 @@
+# 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
-    }
+      '|' => :pipe,
+      '.' => :dot,
+      ':' => :colon,
+      ',' => :comma,
+      '[' => :open_square,
+      ']' => :close_square,
+      '(' => :open_round,
+      ')' => :close_round,
+      '?' => :question,
+      '-' => :dash,
+    }.freeze
     IDENTIFIER = /[a-zA-Z_][\w-]*\??/
     SINGLE_STRING_LITERAL = /'[^\']*'/
     DOUBLE_STRING_LITERAL = /"[^\"]*"/
     NUMBER_LITERAL = /-?\d+(\.\d+)?/
     DOTDOT = /\.\./
-    COMPARISON_OPERATOR = /==|!=|<>|<=?|>=?|contains/
+    COMPARISON_OPERATOR = /==|!=|<>|<=?|>=?|contains(?=\s)/
+    WHITESPACE_OR_NOTHING = /\s*/
 
     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]

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 +22,6 @@
       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"
+      render: "Syntax error in tag 'render' - Template name must be a quoted string"
+    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
 
@@ -27,7 +30,7 @@ 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)
@@ -44,11 +46,14 @@ module Liquid
       tok[0] == type
     end
 
+    SINGLE_TOKEN_EXPRESSION_TYPES = [:string, :number].freeze
+    private_constant :SINGLE_TOKEN_EXPRESSION_TYPES
+
     def expression
       token = @tokens[@p]
       if token[0] == :id
         variable_signature
-      elsif [:string, :number].include? token[0]
+      elsif SINGLE_TOKEN_EXPRESSION_TYPES.include?(token[0])
         consume
       elsif token.first == :open_round
         consume
@@ -63,10 +68,10 @@ module Liquid
     end
 
     def argument
-      str = ""
+      str = +""
       # might be a keyword argument (identifier: expression)
       if look(:id) && look(:colon, 1)
-        str << consume << consume << ' '.freeze
+        str << consume << consume << ' '
       end
 
       str << expression

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/partial_cache.rb

@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+module Liquid
+  class PartialCache
+    def self.load(template_name, context:, parse_context:)
+      cached_partials = (context.registers[:cached_partials] ||= {})
+      cached = cached_partials[template_name]
+      return cached if cached
+
+      file_system = (context.registers[:file_system] ||= Liquid::Template.file_system)
+      source = file_system.read_template_file(template_name)
+      parse_context.partial = true
+
+      partial = Liquid::Template.parse(source, parse_context)
+      cached_partials[template_name] = partial
+    ensure
+      parse_context.partial = false
+    end
+  end
+end

lib/liquid/profiler.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'liquid/profiler/hooks'
 
 module Liquid

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

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Liquid
   class ResourceLimits
     attr_accessor :render_length, :render_score, :assign_score,

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
-    }
+      '&' => '&amp;',
+      '>' => '&gt;',
+      '<' => '&lt;',
+      '"' => '&quot;',
+      "'" => '&#39;',
+    }.freeze
     HTML_ESCAPE_ONCE_REGEXP = /["><']|&(?!([a-zA-Z]+|(#\d+));)/
+    STRIP_HTML_BLOCKS = Regexp.union(
+      %r{<script.*?</script>}m,
+      /<!--.*?-->/m,
+      %r{<style.*?</style>}m
+    )
+    STRIP_HTML_TAGS = /<.*?>/m
 
     # 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 +74,23 @@ 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 +99,7 @@ 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 +115,19 @@ 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 +135,19 @@ 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 +156,40 @@ 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 +203,11 @@ 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 +222,15 @@ 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 +243,32 @@ 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 +277,9 @@ module Liquid
     end
 
     def concat(input, array)
+      unless array.respond_to?(:to_ary)
+        raise ArgumentError, "concat filter requires an array argument"
+      end
       InputIterator.new(input).concat(array)
     end
 
@@ -232,7 +290,7 @@ 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
@@ -292,6 +350,12 @@ 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, :+)
@@ -341,8 +405,25 @@ 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?
+        Usage.increment("default_filter_received_false_value") if input == false # See https://github.com/Shopify/liquid/issues/1127
         default_value
       else
         input
@@ -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
@@ -26,14 +28,20 @@ module Liquid
     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)
+      @@strainer_class_cache.clear
       @@global_strainer.add_filter(filter)
     end
 
@@ -48,6 +56,8 @@ module Liquid
     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
@@ -5,8 +7,8 @@ module Liquid
     include ParserSwitching
 
     class << self
-      def parse(tag_name, markup, tokenizer, options)
-        tag = new(tag_name, markup, options)
+      def parse(tag_name, markup, tokenizer, parse_context)
+        tag = new(tag_name, markup, parse_context)
         tag.parse(tokenizer)
         tag
       end
@@ -33,7 +35,15 @@ 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.
   #
@@ -10,30 +12,54 @@ module Liquid
   class Assign < Tag
     Syntax = /(#{VariableSignature}+)\s*=\s*(.*)\s*/om
 
+    def self.syntax_error_translation_key
+      "errors.syntax.assign"
+    end
+
+    attr_reader :to, :from
+
     def initialize(tag_name, markup, options)
       super
       if markup =~ Syntax
-        @to = $1
-        @from = Variable.new($2, options)
+        @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(self.class.syntax_error_translation_key)
       end
     end
 
-    def render(context)
+    def render_to_output_buffer(context, output)
       val = @from.render(context)
       context.scopes.last[@to] = val
-
-      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.
   #
@@ -16,17 +18,18 @@ module Liquid
     def initialize(tag_name, markup, options)
       super
       if markup =~ Syntax
-        @to = $1
+        @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
 
+    attr_reader :blocks, :left
+
     def initialize(tag_name, markup, options)
       super
       @blocks = []
 
       if markup =~ Syntax
-        @left = Expression.parse($1)
+        @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 +29,28 @@ 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)
-      context.stack do
-        execute_else_block = true
+    def render_to_output_buffer(context, output)
+      execute_else_block = true
 
-        output = ''
-        @blocks.each do |block|
-          if block.else?
-            return block.attachment.render(context) if execute_else_block
-          elsif block.evaluate(context)
-            execute_else_block = false
-            output << block.attachment.render(context)
-          end
+      @blocks.each do |block|
+        if block.else?
+          block.attachment.render_to_output_buffer(context, output) if execute_else_block
+        elsif block.evaluate(context)
+          execute_else_block = false
+          block.attachment.render_to_output_buffer(context, output)
         end
-        output
       end
+
+      output
     end
 
     private
@@ -60,12 +60,12 @@ module Liquid
 
       while markup
         unless markup =~ WhenSyntax
-          raise SyntaxError.new(options[:locale].t("errors.syntax.case_invalid_when".freeze))
+          raise SyntaxError, options[:locale].t("errors.syntax.case_invalid_when")
         end
 
-        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
@@ -73,14 +73,20 @@ module Liquid
 
     def record_else_condition(markup)
       unless markup.strip.empty?
-        raise SyntaxError.new(options[:locale].t("errors.syntax.case_invalid_else".freeze))
+        raise SyntaxError, options[:locale].t("errors.syntax.case_invalid_else")
       end
 
       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

@@ -1,7 +1,9 @@
+# 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)
@@ -12,5 +14,5 @@ module Liquid
     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.
   #
@@ -15,32 +17,43 @@ module Liquid
     SimpleSyntax = /\A#{QuotedFragment}+/o
     NamedSyntax  = /\A(#{QuotedFragment})\s*\:\s*(.*)/om
 
+    attr_reader :variables
+
     def initialize(tag_name, markup, options)
       super
       case markup
       when NamedSyntax
-        @variables = variables_from_string($2)
-        @name = Expression.parse($1)
+        @variables = variables_from_string(Regexp.last_match(2))
+        @name = Expression.parse(Regexp.last_match(1))
       when SimpleSyntax
         @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 += 1
-        iteration  = 0 if iteration >= @variables.size
-        context.registers[:cycle][key] = iteration
-        result
+      key = context.evaluate(@name)
+      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
+
+      output
     end
 
     private
@@ -48,9 +61,15 @@ module Liquid
     def variables_from_string(markup)
       markup.split(',').collect do |var|
         var =~ /\s*(#{QuotedFragment})\s*/o
-        $1 ? Expression.parse($1) : nil
+        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/echo.rb

@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+
+module Liquid
+  # Echo outputs an expression
+  #
+  #   {% echo monkey %}
+  #   {% echo user.name %}
+  #
+  # This is identical to variable output syntax, like {{ foo }}, but works
+  # inside {% liquid %} tags. The full syntax is supported, including filters:
+  #
+  #   {% echo user | link %}
+  #
+  class Echo < Tag
+    def initialize(tag_name, markup, parse_context)
+      super
+      @variable = Variable.new(markup, parse_context)
+    end
+
+    def render(context)
+      @variable.render_to_output_buffer(context, +'')
+    end
+  end
+
+  Template.register_tag('echo', Echo)
+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:
   #
@@ -46,10 +48,14 @@ module Liquid
   class For < Block
     Syntax = /\A(#{VariableSegment}+)\s+in\s+(#{QuotedFragment}+)\s*(reversed)?/o
 
+    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)
@@ -62,49 +68,51 @@ 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
+        @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|
           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)
@@ -115,19 +123,28 @@ 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 +154,64 @@ 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
   #
@@ -12,12 +14,18 @@ module Liquid
   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)
+    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 ['elsif', 'else'].include?(tag)
         push_block(tag, markup)
       else
         super
       end
     end
 
-    def render(context)
-      context.stack do
-        @blocks.each do |block|
-          if block.evaluate(context)
-            return block.attachment.render(context)
-          end
+    def render_to_output_buffer(context, output)
+      @blocks.each do |block|
+        if block.evaluate(context)
+          return block.attachment.render_to_output_buffer(context, output)
         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)
@@ -63,17 +66,17 @@ module Liquid
 
     def lax_parse(markup)
       expressions = markup.scan(ExpressionsAndOperators)
-      raise(SyntaxError.new(options[:locale].t("errors.syntax.if".freeze))) unless expressions.pop =~ Syntax
+      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($1), $2, Expression.parse($3))
-        raise(SyntaxError.new(options[:locale].t("errors.syntax.if".freeze))) unless BOOLEAN_OPERATORS.include?(operator)
+        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.send(operator, condition)
         condition = new_condition
       end
@@ -83,17 +86,20 @@ 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)
@@ -105,7 +111,13 @@ module Liquid
         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 +1,19 @@
+# frozen_string_literal: true
+
 module Liquid
   class Ifchanged < Block
-    def render(context)
-      context.stack do
-        output = super
+    def render_to_output_buffer(context, output)
+      block_output = +''
+      super(context, block_output)
 
-        if output != context.registers[:ifchanged]
-          context.registers[:ifchanged] = output
-          output
-        else
-          ''.freeze
-        end
+      if block_output != context.registers[:ifchanged]
+        context.registers[:ifchanged] = block_output
+        output << block_output
       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
   #
@@ -16,13 +18,15 @@ module Liquid
   class Include < Tag
     Syntax = /(#{QuotedFragment}+)(\s+(?:with|for)\s+(#{QuotedFragment}+))?/o
 
+    attr_reader :template_name_expr, :variable_name_expr, :attributes
+
     def initialize(tag_name, markup, options)
       super
 
       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)
@@ -33,23 +37,29 @@ module Liquid
         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 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 = PartialCache.load(
+        template_name,
+        context: context,
+        parse_context: parse_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
@@ -63,50 +73,35 @@ 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
-    end
 
-    private
+      output
+    end
 
     alias_method :parse_context, :options
     private :parse_context
 
-    def load_cached_partial(template_name, context)
-      cached_partials = context.registers[:cached_partials] || {}
-
-      if cached = cached_partials[template_name]
-        return cached
+    class ParseTreeVisitor < Liquid::ParseTreeVisitor
+      def children
+        [
+          @node.template_name_expr,
+          @node.variable_name_expr,
+        ] + @node.attributes.values
       end
-      source = read_template_from_file_system(context)
-      begin
-        parse_context.partial = true
-        partial = Liquid::Template.parse(source, parse_context)
-      ensure
-        parse_context.partial = false
-      end
-      cached_partials[template_name] = partial
-      context.registers[:cached_partials] = cached_partials
-      partial
-    end
-
-    def read_template_from_file_system(context)
-      file_system = context.registers[:file_system] || Liquid::Template.file_system
-
-      file_system.read_template_file(context.evaluate(@template_name_expr))
     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 +22,14 @@ 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

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Liquid
   class Raw < Block
     Syntax = /\A\s*\z/
@@ -6,26 +8,25 @@ module Liquid
     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 = ''
+      @body = +''
       while token = tokens.shift
         if token =~ FullTokenPossiblyInvalid
-          @body << $1 if $1 != "".freeze
-          return if block_delimiter == $2
+          @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 +36,15 @@ module Liquid
     def blank?
       @body.empty?
     end
+
+    protected
+
+    def ensure_valid_markup(tag_name, markup, parse_context)
+      unless markup =~ Syntax
+        raise SyntaxError, parse_context.locale.t("errors.syntax.tag_unexpected_args", tag: tag_name)
+      end
+    end
   end
 
-  Template.register_tag('raw'.freeze, Raw)
+  Template.register_tag('raw', Raw)
 end

lib/liquid/tags/render.rb

@@ -0,0 +1,56 @@
+# frozen_string_literal: true
+
+module Liquid
+  class Render < Tag
+    SYNTAX = /(#{QuotedString})#{QuotedFragment}*/o
+
+    attr_reader :template_name_expr, :attributes
+
+    def initialize(tag_name, markup, options)
+      super
+
+      raise SyntaxError, options[:locale].t("errors.syntax.render") unless markup =~ SYNTAX
+
+      template_name = Regexp.last_match(1)
+
+      @template_name_expr = Expression.parse(template_name)
+
+      @attributes = {}
+      markup.scan(TagAttributes) do |key, value|
+        @attributes[key] = Expression.parse(value)
+      end
+    end
+
+    def render_to_output_buffer(context, output)
+      # Though we evaluate this here we will only ever parse it as a string literal.
+      template_name = context.evaluate(@template_name_expr)
+      raise ArgumentError, options[:locale].t("errors.argument.include") unless template_name
+
+      partial = PartialCache.load(
+        template_name,
+        context: context,
+        parse_context: parse_context
+      )
+
+      inner_context = context.new_isolated_subcontext
+      inner_context.template_name = template_name
+      inner_context.partial = true
+      @attributes.each do |key, value|
+        inner_context[key] = context.evaluate(value)
+      end
+      partial.render_to_output_buffer(inner_context, output)
+
+      output
+    end
+
+    class ParseTreeVisitor < Liquid::ParseTreeVisitor
+      def children
+        [
+          @node.template_name_expr,
+        ] + @node.attributes.values
+      end
+    end
+  end
+
+  Template.register_tag('render', Render)
+end

lib/liquid/tags/table_row.rb

@@ -1,54 +1,67 @@
+# frozen_string_literal: true
+
 module Liquid
   class TableRow < Block
     Syntax = /(\w+)\s+in\s+(#{QuotedFragment}+)/o
 
+    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)
+        @variable_name = Regexp.last_match(1)
+        @collection_name = Expression.parse(Regexp.last_match(2))
         @attributes = {}
         markup.scan(TagAttributes) 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}\">"
+            output << "</tr>\n<tr class=\"row#{tablerowloop.row + 1}\">"
           end
 
           tablerowloop.send(:increment!)
         end
       end
-      result << "</tr>\n"
-      result
+
+      output << "</tr>\n"
+      output
+    end
+
+    class ParseTreeVisitor < Liquid::ParseTreeVisitor
+      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 +8,23 @@ module Liquid
   #   {% unless x < 0 %} x is greater than zero {% endunless %}
   #
   class Unless < If
-    def render(context)
-      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
-
-        # After the first condition unless works just like if
-        @blocks[1..-1].each do |block|
-          if block.evaluate(context)
-            return block.attachment.render(context)
-          end
-        end
-
-        ''.freeze
+    def render_to_output_buffer(context, output)
+      # First condition is interpreted backwards ( if not )
+      first_block = @blocks.first
+      unless first_block.evaluate(context)
+        return first_block.attachment.render_to_output_buffer(context, output)
       end
+
+      # After the first condition unless works just like if
+      @blocks[1..-1].each do |block|
+        if block.evaluate(context)
+          return block.attachment.render_to_output_buffer(context, output)
+        end
+      end
+
+      output
     end
   end
 
-  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
@@ -19,8 +21,10 @@ module Liquid
     @@file_system = BlankFileSystem.new
 
     class TagRegistry
+      include Enumerable
+
       def initialize
-        @tags  = {}
+        @tags = {}
         @cache = {}
       end
 
@@ -41,10 +45,14 @@ 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
 
@@ -63,6 +71,11 @@ module Liquid
       # :error raises an error when tainted output is used
       attr_writer :taint_mode
 
+      attr_accessor :default_exception_renderer
+      Template.default_exception_renderer = lambda do |exception|
+        exception
+      end
+
       def file_system
         @@file_system
       end
@@ -80,11 +93,11 @@ 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 +120,7 @@ module Liquid
     end
 
     def initialize
+      @rethrow_errors = false
       @resource_limits = ResourceLimits.new(self.class.default_resource_limits)
     end
 
@@ -153,14 +167,14 @@ 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 }
+          c.exception_renderer = ->(_e) { raise }
         end
 
         c
@@ -175,18 +189,16 @@ module Liquid
         raise ArgumentError, "Expected Hash or Liquid::Context as parameter"
       end
 
+      output = nil
+
       case args.last
       when Hash
         options = args.pop
+        output = options[:output] if options[:output]
 
         registers.merge!(options[:registers]) if options[:registers].is_a?(Hash)
 
-        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 +209,9 @@ 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 +224,10 @@ module Liquid
       render(*args)
     end
 
+    def render_to_output_buffer(context, output)
+      render(context, output: output)
+    end
+
     private
 
     def tokenize(source)
@@ -235,5 +250,13 @@ 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

@@ -1,29 +1,37 @@
+# frozen_string_literal: true
+
 module Liquid
   class Tokenizer
-    attr_reader :line_number
+    attr_reader :line_number, :for_liquid_tag
 
-    def initialize(source, line_numbers = false)
+    def initialize(source, line_numbers = false, line_number: nil, for_liquid_tag: false)
       @source = source
-      @line_number = 1 if line_numbers
+      @line_number = line_number || (line_numbers ? 1 : nil)
+      @for_liquid_tag = for_liquid_tag
       @tokens = tokenize
     end
 
     def shift
-      token = @tokens.shift
-      @line_number += token.count("\n") if @line_number && token
+      (token = @tokens.shift) || return
+
+      if @line_number
+        @line_number += @for_liquid_tag ? 1 : token.count("\n")
+      end
+
       token
     end
 
     private
 
     def tokenize
-      @source = @source.source if @source.respond_to?(:source)
       return [] if @source.to_s.empty?
 
+      return @source.split("\n") if @for_liquid_tag
+
       tokens = @source.split(TemplateParser)
 
       # removes the rogue empty element at the beginning of the array
-      tokens.shift if tokens[0] && tokens[0].empty?
+      tokens.shift if tokens[0]&.empty?
 
       tokens
     end

lib/liquid/usage.rb

@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+module Liquid
+  module Usage
+    def self.increment(name)
+    end
+  end
+end

lib/liquid/utils.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Liquid
   module Utils
     def self.slice_collection(collection, from, to)
@@ -46,13 +48,17 @@ module Liquid
     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
 
@@ -65,7 +71,7 @@ module Liquid
       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
+    FilterMarkupRegex = /#{FilterSeparator}\s*(.*)/om
     FilterParser = /(?:\s+|#{QuotedFragment}|#{ArgumentSeparator})+/o
+    FilterArgsRegex = /(?:#{FilterArgumentSeparator}|#{ArgumentSeparator})\s*((?:\w+\s*\:\s*)?#{QuotedFragment})/o
+    JustTagAttributes = /\A#{TagAttributes}\z/o
+    MarkupWithQuotedFragment = /(#{QuotedFragment})(.*)/om
+
     attr_accessor :filters, :name, :line_number
     attr_reader :parse_context
     alias_method :options, :parse_context
+
     include ParserSwitching
 
     def initialize(markup, parse_context)
@@ -35,17 +43,17 @@ module Liquid
 
     def lax_parse(markup)
       @filters = []
-      return unless markup =~ /(#{QuotedFragment})(.*)/om
+      return unless markup =~ MarkupWithQuotedFragment
 
-      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 =~ FilterMarkupRegex
+        filters = Regexp.last_match(1).scan(FilterParser)
         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(FilterArgsRegex).flatten
           @filters << parse_filter_expressions(filtername, filterargs)
         end
       end
@@ -79,31 +87,43 @@ 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(JustTagAttributes)
+          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|
@@ -132,5 +152,11 @@ 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]
+    COMMAND_METHODS = ['size', 'first', 'last'].freeze
 
     attr_reader :name, :lookups
 
@@ -14,7 +16,7 @@ module Liquid
 
       name = lookups.shift
       if name =~ SQUARE_BRACKETED
-        name = Expression.parse($1)
+        name = Expression.parse(Regexp.last_match(1))
       end
       @name = name
 
@@ -24,7 +26,7 @@ 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
@@ -55,9 +57,11 @@ 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 +80,11 @@ 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 +1,6 @@
 # encoding: utf-8
+# frozen_string_literal: true
+
 module Liquid
-  VERSION = "4.0.0.rc1"
+  VERSION = "4.0.3"
 end

liquid.gemspec

@@ -1,6 +1,8 @@
 # encoding: utf-8
+# frozen_string_literal: true
+
 lib = File.expand_path('../lib/', __FILE__)
-$LOAD_PATH.unshift lib unless $LOAD_PATH.include?(lib)
+$LOAD_PATH.unshift(lib) unless $LOAD_PATH.include?(lib)
 
 require "liquid/version"
 
@@ -15,6 +17,7 @@ Gem::Specification.new do |s|
   s.license     = "MIT"
   # s.description = "A secure, non-evaling end user template engine with aesthetic markup."
 
+  s.required_ruby_version     = ">= 2.4.0"
   s.required_rubygems_version = ">= 1.3.7"
 
   s.test_files  = Dir.glob("{test}/**/*")
@@ -24,6 +27,6 @@ Gem::Specification.new do |s|
 
   s.require_path = "lib"
 
-  s.add_development_dependency 'rake'
-  s.add_development_dependency 'minitest'
+  s.add_development_dependency('rake', '~> 11.3')
+  s.add_development_dependency('minitest')
 end

performance/benchmark.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'benchmark/ips'
 require_relative 'theme_runner'
 
@@ -5,7 +7,7 @@ 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
@@ -13,5 +15,6 @@ Benchmark.ips do |x|
   puts
 
   x.report("parse:") { profiler.compile }
-  x.report("parse & run:") { profiler.run }
+  x.report("render:") { profiler.render }
+  x.report("parse & render:") { profiler.run }
 end

performance/memory_profile.rb

@@ -0,0 +1,63 @@
+# frozen_string_literal: true
+
+require 'benchmark/ips'
+require 'memory_profiler'
+require 'terminal-table'
+require_relative 'theme_runner'
+
+class Profiler
+  LOG_LABEL   = "Profiling: ".rjust(14).freeze
+  REPORTS_DIR = File.expand_path('.memprof', __dir__).freeze
+
+  def self.run
+    puts
+    yield new
+  end
+
+  def initialize
+    @allocated = []
+    @retained  = []
+    @headings  = []
+  end
+
+  def profile(phase, &block)
+    print LOG_LABEL
+    print "#{phase}.. ".ljust(10)
+    report = MemoryProfiler.report(&block)
+    puts 'Done.'
+    @headings  << phase.capitalize
+    @allocated << "#{report.scale_bytes(report.total_allocated_memsize)} (#{report.total_allocated} objects)"
+    @retained  << "#{report.scale_bytes(report.total_retained_memsize)} (#{report.total_retained} objects)"
+
+    return if ENV['CI']
+
+    require 'fileutils'
+    report_file = File.join(REPORTS_DIR, "#{sanitize(phase)}.txt")
+    FileUtils.mkdir_p(REPORTS_DIR)
+    report.pretty_print(to_file: report_file, scale_bytes: true)
+  end
+
+  def tabulate
+    table = Terminal::Table.new(headings: @headings.unshift('Phase')) do |t|
+      t << @allocated.unshift('Total allocated')
+      t << @retained.unshift('Total retained')
+    end
+
+    puts
+    puts table
+    puts "\nDetailed report(s) saved to #{REPORTS_DIR}/" unless ENV['CI']
+  end
+
+  def sanitize(string)
+    string.downcase.gsub(/[\W]/, '-').squeeze('-')
+  end
+end
+
+Liquid::Template.error_mode = ARGV.first.to_sym if ARGV.first
+
+runner = ThemeRunner.new
+Profiler.run do |x|
+  x.profile('parse') { runner.compile }
+  x.profile('render') { runner.render }
+  x.tabulate
+end

performance/profile.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'stackprof'
 require_relative 'theme_runner'
 

performance/shopify/comment_form.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class CommentForm < Liquid::Block
   Syntax = /(#{Liquid::VariableSignature}+)/
 
@@ -5,14 +7,14 @@ class CommentForm < Liquid::Block
     super
 
     if markup =~ Syntax
-      @variable_name = $1
+      @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
@@ -16,9 +18,10 @@ 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; }
-        assigns
+      db = db.each_with_object({}) do |(key, values), assigns|
+        assigns[key] = values.each_with_object({}) do |v, h|
+          h[v['handle']] = v
+        end
       end
 
       # Some standard direct accessors so that the specialized templates
@@ -30,8 +33,8 @@ module Database
 
       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
+        'item_count' => db['line_items'].values.inject(0) { |sum, item| sum += item['quantity'] },
+        'items' => db['line_items'].values,
       }
 
       db
@@ -40,6 +43,6 @@ 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 +1,14 @@
+# 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

@@ -1,13 +1,15 @@
+# frozen_string_literal: true
+
 class Paginate < Liquid::Block
-  Syntax     = /(#{Liquid::QuotedFragment})\s*(by\s*(\d+))?/
+  Syntax = /(#{Liquid::QuotedFragment})\s*(by\s*(\d+))?/
 
   def initialize(tag_name, markup, options)
     super
 
     if markup =~ Syntax
-      @collection_name = $1
-      @page_size = if $2
-        $3.to_i
+      @collection_name = Regexp.last_match(1)
+      @page_size = if Regexp.last_match(2)
+        Regexp.last_match(3).to_i
       else
         20
       end
@@ -17,27 +19,27 @@ class Paginate < Liquid::Block
         @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
 

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}"
@@ -52,7 +54,7 @@ module ShopFilter
   end
 
   def product_img_url(url, style = 'small')
-    unless url =~ /\Aproducts\/([\w\-\_]+)\.(\w{2,4})/
+    unless url =~ %r{\Aproducts/([\w\-\_]+)\.(\w{2,4})}
       raise ArgumentError, 'filter "size" can only be called on product images'
     end
 
@@ -60,7 +62,7 @@ module ShopFilter
     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 +72,14 @@ 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

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
@@ -31,7 +32,9 @@ class BlankTest < Minitest::Test
   end
 
   def test_new_tags_are_not_blank_by_default
-    assert_template_result(" " * N, wrap_in_for("{% foobar %}"))
+    with_custom_tag('foobar', FoobarTag) do
+      assert_template_result(" " * N, wrap_in_for("{% foobar %}"))
+    end
   end
 
   def test_loops_are_blank

test/integration/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

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

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

test/integration/drop_test.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 
 class ContextDrop < Liquid::Drop
@@ -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}"
     end
   end
 
@@ -48,7 +50,7 @@ class ProductDrop < Liquid::Drop
   end
 
   def user_input
-    "foo".taint
+    (+"foo").taint
   end
 
   protected
@@ -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
@@ -241,7 +243,7 @@ class DropsTest < Minitest::Test
   end
 
   def test_some_enumerable_methods_still_get_invoked
-    [ :count, :max ].each do |method|
+    [: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)
@@ -250,7 +252,7 @@ class DropsTest < Minitest::Test
 
     assert_equal "yes", Liquid::Template.parse("{% if collection contains 3 %}yes{% endif %}").render!('collection' => RealEnumerableDrop.new)
 
-    [ :min, :first ].each do |method|
+    [: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)

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
@@ -106,8 +122,7 @@ class ErrorHandlingTest < Minitest::Test
         bla
             ',
       error_mode: :warn,
-      line_numbers: true
-                                     )
+      line_numbers: true)
 
     assert_equal ['Liquid syntax error (line 4): Unexpected character = in "1 =! 2"'],
       template.warnings.map(&:message)
@@ -123,8 +138,7 @@ class ErrorHandlingTest < Minitest::Test
           bla
                 ',
         error_mode: :strict,
-        line_numbers: true
-                            )
+        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
@@ -186,26 +199,44 @@ 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 = ->(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 = ->(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)
+    def read_template_file(_template_path)
       "{{ errors.argument_error }}"
     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
 
@@ -26,7 +28,7 @@ class FiltersTest < Minitest::Test
   include Liquid
 
   module OverrideObjectMethodFilter
-    def tap(input)
+    def tap(_input)
       "tap overridden"
     end
   end
@@ -149,7 +151,7 @@ class FiltersTest < Minitest::Test
     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
 

test/integration/hash_ordering_test.rb

@@ -1,18 +1,20 @@
+# 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

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
 
@@ -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
 

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(
+      ["test", "infilter"],
+      visit(%({{ test | split: infilter }}))
+    )
+  end
+
+  def test_dynamic_variable
+    assert_equal(
+      ["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

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 
 class ParsingQuirksTest < Minitest::Test
@@ -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
 
@@ -115,4 +117,8 @@ class ParsingQuirksTest < Minitest::Test
       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
@@ -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
 
@@ -145,7 +147,7 @@ class RenderProfilingTest < Minitest::Test
 
   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.render!("collection" => ["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 )
@@ -59,4 +65,18 @@ class SecurityTest < Minitest::Test
 
     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 +1,5 @@
 # encoding: utf-8
+# frozen_string_literal: true
 
 require 'test_helper'
 
@@ -17,7 +18,7 @@ class TestThing
     "woot: #{@foo}"
   end
 
-  def [](whatever)
+  def [](_whatever)
     to_s
   end
 
@@ -37,7 +38,17 @@ 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
 
@@ -105,21 +116,29 @@ class StandardFiltersTest < Minitest::Test
     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 '12341', @filters.truncate("1234567890", 5, 1)
   end
 
   def test_split
     assert_equal ['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 ['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 +147,22 @@ 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
@@ -144,6 +171,7 @@ class StandardFiltersTest < Minitest::Test
     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 'one two1', @filters.truncatewords("one two three", 2, 1)
   end
 
   def test_strip_html
@@ -154,11 +182,15 @@ class StandardFiltersTest < Minitest::Test
     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
@@ -166,16 +198,114 @@ class StandardFiltersTest < Minitest::Test
     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 ["a", "B", "c", "D"], @filters.sort_natural(["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 ["a", "b", "c", "X", "Y", "Z"], @filters.sort_natural(["X", "Y", "Z", "a", "b", "c"])
+  end
+
   def test_sort_empty_array
     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")
   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
@@ -197,10 +327,34 @@ class StandardFiltersTest < Minitest::Test
     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")
   end
 
+  def test_compact_invalid_property
+    foo = [
+      [1],
+      [2],
+      [3],
+    ]
+
+    assert_raises Liquid::ArgumentError do
+      @filters.compact(foo, "bar")
+    end
+  end
+
   def test_reverse
     assert_equal [4, 3, 2, 1], @filters.reverse([1, 2, 3, 4])
   end
@@ -227,7 +381,7 @@ class StandardFiltersTest < Minitest::Test
 
   def test_map_on_hashes
     assert_template_result "4217", '{{ thing | map: "foo" | map: "bar" }}',
-      "thing" => { "foo" => [ { "bar" => 42 }, { "bar" => 17 } ] }
+      "thing" => { "foo" => [{ "bar" => 42 }, { "bar" => 17 }] }
   end
 
   def test_legacy_map_on_hashes_with_dynamic_key
@@ -244,7 +398,7 @@ class StandardFiltersTest < Minitest::Test
 
   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]
   end
@@ -252,10 +406,10 @@ class StandardFiltersTest < Minitest::Test
   def test_map_over_drops_returning_procs
     drops = [
       {
-        "proc" => ->{ "foo" },
+        "proc" => -> { "foo" },
       },
       {
-        "proc" => ->{ "bar" },
+        "proc" => -> { "bar" },
       },
     ]
     templ = '{{ drops | map: "proc" }}'
@@ -266,6 +420,29 @@ class StandardFiltersTest < Minitest::Test
     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
   end
@@ -296,11 +473,11 @@ class StandardFiltersTest < Minitest::Test
     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 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")
 
@@ -313,8 +490,8 @@ class StandardFiltersTest < Minitest::Test
   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
@@ -364,20 +541,38 @@ class StandardFiltersTest < Minitest::Test
   def test_plus
     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 "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 "-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
@@ -391,6 +586,8 @@ class StandardFiltersTest < Minitest::Test
     assert_raises(Liquid::ZeroDivisionError) do
       assert_template_result "4", "{{ 1 | modulo: 0 }}"
     end
+
+    assert_template_result "5", "{{ price | divided_by:2 }}", 'price' => NumberLikeThing.new(10)
   end
 
   def test_modulo
@@ -398,6 +595,8 @@ class StandardFiltersTest < Minitest::Test
     assert_raises(Liquid::ZeroDivisionError) do
       assert_template_result "4", "{{ 1 | modulo: 0 }}"
     end
+
+    assert_template_result "1", "{{ price | modulo:2 }}", 'price' => NumberLikeThing.new(3)
   end
 
   def test_round
@@ -407,6 +606,9 @@ class StandardFiltersTest < Minitest::Test
     assert_raises(Liquid::FloatDomainError) do
       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
@@ -415,6 +617,8 @@ class StandardFiltersTest < Minitest::Test
     assert_raises(Liquid::FloatDomainError) do
       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
@@ -423,6 +627,30 @@ class StandardFiltersTest < Minitest::Test
     assert_raises(Liquid::FloatDomainError) do
       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
@@ -436,8 +664,7 @@ 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
@@ -466,6 +693,78 @@ 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