Fix stack level too deep error

Allow variables to start with contains in strict parser

.travis.yml

@@ -1,9 +1,9 @@
 language: ruby
 
 rvm:
-  - 2.0
   - 2.1
   - 2.2
+  - 2.3.3
   - ruby-head
   - jruby-head
 #  - rbx-2
@@ -19,6 +19,10 @@ matrix:
   allow_failures:
     - rvm: jruby-head
 
+install:
+  - gem install rainbow -v 2.2.1
+  - bundle install
+
 script: "bundle exec rake"
 
 notifications:

Gemfile

@@ -3,12 +3,15 @@ source 'https://rubygems.org'
 gemspec
 gem 'stackprof', platforms: :mri_21
 
+group :benchmark, :test do
+  gem 'benchmark-ips'
+end
+
 group :test do
   gem 'spy', '0.4.1'
-  gem 'benchmark-ips'
   gem 'rubocop', '0.34.2'
 
   platform :mri do
-    gem 'liquid-c', github: 'Shopify/liquid-c', ref: '2570693d8d03faa0df9160ec74348a7149436df3'
+    gem 'liquid-c', github: 'Shopify/liquid-c', ref: 'bd53db95de3d44d631e7c5a267c3d934e66107dd'
   end
 end

History.md

@@ -1,8 +1,10 @@
 # Liquid Change Log
 
-## 4.0.0 / not yet released / branch "master"
+## 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]
@@ -18,10 +20,13 @@
 * 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]

circle.yml

@@ -1,3 +1,3 @@
 machine:
   ruby:
-    version: ruby-2.0
+    version: ruby-2.1

lib/liquid.rb

@@ -24,6 +24,7 @@ module Liquid
   ArgumentSeparator           = ','.freeze
   FilterArgumentSeparator     = ':'.freeze
   VariableAttributeSeparator  = '.'.freeze
+  WhitespaceControl           = '-'.freeze
   TagStart                    = /\{\%/
   TagEnd                      = /\%\}/
   VariableSignature           = /\(?[\w\-\.\[\]]\)?/
@@ -34,7 +35,7 @@ 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

lib/liquid/block_body.rb

@@ -1,7 +1,7 @@
 module Liquid
   class BlockBody
-    FullToken = /\A#{TagStart}\s*(\w+)\s*(.*)?#{TagEnd}\z/om
+    FullToken = /\A#{TagStart}#{WhitespaceControl}?\s*(\w+)\s*(.*?)#{WhitespaceControl}?#{TagEnd}\z/om
-    ContentOfVariable = /\A#{VariableStart}(.*)#{VariableEnd}\z/om
+    ContentOfVariable = /\A#{VariableStart}#{WhitespaceControl}?(.*?)#{WhitespaceControl}?#{VariableEnd}\z/om
     TAGSTART = "{%".freeze
     VARSTART = "{{".freeze
 
@@ -18,6 +18,7 @@ module Liquid
         unless token.empty?
           case
           when token.start_with?(TAGSTART)
+            whitespace_handler(token, parse_context)
             if token =~ FullToken
               tag_name = $1
               markup = $2
@@ -35,9 +36,14 @@ module Liquid
               raise_missing_tag_terminator(token, parse_context)
             end
           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 =~ /\A\s*\z/)
           end
@@ -48,6 +54,16 @@ module Liquid
       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
@@ -80,7 +96,8 @@ module Liquid
           context.handle_error(e, token.line_number)
           output << nil
         rescue ::StandardError => e
-          output << context.handle_error(e, token.line_number)
+          line_number = token.is_a?(String) ? nil : token.line_number
+          output << context.handle_error(e, line_number)
         end
       end
 
@@ -90,7 +107,7 @@ module Liquid
     private
 
     def render_node(node, context)
-      node_output = (node.respond_to?(:render) ? node.render(context) : node)
+      node_output = node.is_a?(String) ? node : node.render(context)
       node_output = node_output.is_a?(Array) ? node_output.join : node_output.to_s
 
       context.resource_limits.render_length += node_output.length

lib/liquid/condition.rb

@@ -7,6 +7,7 @@ module Liquid
   #   c.evaluate #=> true
   #
   class Condition #:nodoc:
+    @@depth = 0
     @@operators = {
       '=='.freeze => ->(cond, left, right) {  cond.send(:equal_variables, left, right) },
       '!='.freeze => ->(cond, left, right) { !cond.send(:equal_variables, left, right) },
@@ -47,6 +48,11 @@ module Liquid
       when :or
         result || @child_condition.evaluate(context)
       when :and
+        @@depth += 1
+        if @@depth >= 500
+          @@depth = 0
+          raise StackLevelError, "Nesting too deep".freeze
+        end
         result && @child_condition.evaluate(context)
       else
         result
@@ -110,7 +116,7 @@ module Liquid
 
       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

lib/liquid/context.rb

@@ -13,7 +13,7 @@ module Liquid
   #   context['bob']  #=> nil  class Context
   class Context
     attr_reader :scopes, :errors, :registers, :environments, :resource_limits
-    attr_accessor :exception_handler, :template_name, :partial, :global_filter, :strict_variables, :strict_filters
+    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
@@ -27,8 +27,9 @@ module Liquid
 
       @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 = []
@@ -74,30 +75,11 @@ module Liquid
     end
 
     def handle_error(e, line_number = nil)
-      if e.is_a?(Liquid::Error)
+      e = internal_error unless e.is_a?(Liquid::Error)
-        e.template_name ||= template_name
+      e.template_name ||= template_name
-        e.line_number ||= line_number
+      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
       errors.push(e)
-      output || Liquid::Error.render(e)
+      exception_renderer.call(e).to_s
     end
 
     def invoke(method, *args)
@@ -178,7 +160,7 @@ module Liquid
     end
 
     # Fetches an object starting at the local scope and then moving up the hierachy
-    def find_variable(key)
+    def find_variable(key, raise_on_not_found: true)
       # This was changed from find() to find_index() because this is a very hot
       # path and find_index() is optimized in MRI to reduce object allocation
       index = @scopes.find_index { |s| s.key?(key) }
@@ -188,7 +170,7 @@ module Liquid
 
       if scope.nil?
         @environments.each do |e|
-          variable = lookup_and_evaluate(e, key)
+          variable = lookup_and_evaluate(e, key, raise_on_not_found: raise_on_not_found)
           unless variable.nil?
             scope = e
             break
@@ -197,7 +179,7 @@ module Liquid
       end
 
       scope ||= @environments.last || @scopes.last
-      variable ||= lookup_and_evaluate(scope, key)
+      variable ||= lookup_and_evaluate(scope, key, raise_on_not_found: raise_on_not_found)
 
       variable = variable.to_liquid
       variable.context = self if variable.respond_to?(:context=)
@@ -205,8 +187,8 @@ module Liquid
       variable
     end
 
-    def lookup_and_evaluate(obj, key)
+    def lookup_and_evaluate(obj, key, raise_on_not_found: true)
-      if @strict_variables && obj.respond_to?(:key?) && !obj.key?(key)
+      if @strict_variables && raise_on_not_found && obj.respond_to?(:key?) && !obj.key?(key)
         raise Liquid::UndefinedVariable, "undefined variable #{key}"
       end
 
@@ -221,6 +203,13 @@ module Liquid
 
     private
 
+    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/errors.rb

@@ -17,14 +17,6 @@ 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
@@ -60,4 +52,5 @@ module Liquid
   UndefinedDropMethod = Class.new(Error)
   UndefinedFilter = Class.new(Error)
   MethodOverrideError = Class.new(Error)
+  InternalError = Class.new(Error)
 end

lib/liquid/file_system.rb

@@ -8,8 +8,8 @@ module Liquid
   #
   # Example:
   #
-  # Liquid::Template.file_system = Liquid::LocalFileSystem.new(template_path)
+  #   Liquid::Template.file_system = Liquid::LocalFileSystem.new(template_path)
-  # liquid = Liquid::Template.parse(template)
+  #   liquid = Liquid::Template.parse(template)
   #
   # This will parse the template with a LocalFileSystem implementation rooted at 'template_path'.
   class BlankFileSystem
@@ -26,10 +26,10 @@ 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("mypartial")       # => "/some/path/_mypartial.liquid"
-  # file_system.full_path("dir/mypartial")   # => "/some/path/dir/_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.
@@ -37,9 +37,9 @@ 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

lib/liquid/lexer.rb

@@ -18,10 +18,10 @@ module Liquid
     DOUBLE_STRING_LITERAL = /"[^\"]*"/
     NUMBER_LITERAL = /-?\d+(\.\d+)?/
     DOTDOT = /\.\./
-    COMPARISON_OPERATOR = /==|!=|<>|<=?|>=?|contains/
+    COMPARISON_OPERATOR = /==|!=|<>|<=?|>=?|contains(?=\s)/
 
     def initialize(input)
-      @ss = StringScanner.new(input.rstrip)
+      @ss = StringScanner.new(input)
     end
 
     def tokenize
@@ -29,6 +29,7 @@ module Liquid
 
       until @ss.eos?
         @ss.skip(/\s*/)
+        break if @ss.eos?
         tok = case
         when t = @ss.scan(COMPARISON_OPERATOR) then [:comparison, t]
         when t = @ss.scan(SINGLE_STRING_LITERAL) then [:string, t]

lib/liquid/locales/en.yml

@@ -22,3 +22,5 @@
       tag_never_closed: "'%{block_name}' tag was never closed"
       meta_syntax_error: "Liquid syntax error: #{e.message}"
       table_row: "Syntax Error in 'table_row loop' - Valid syntax: table_row [item] in [collection] cols=3"
+    argument:
+      include: "Argument error in tag 'include' - Illegal template name"

lib/liquid/parse_context.rb

@@ -1,6 +1,6 @@
 module Liquid
   class ParseContext
-    attr_accessor :locale, :line_number
+    attr_accessor :locale, :line_number, :trim_whitespace
     attr_reader :partial, :warnings, :error_mode
 
     def initialize(options = {})

lib/liquid/standardfilters.rb

@@ -65,9 +65,10 @@ module Liquid
       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] + truncate_string_str : input_str
     end
 
     def truncatewords(input, words = 15, truncate_string = "...".freeze)
@@ -76,7 +77,7 @@ module Liquid
       words = Utils.to_integer(words)
       l = words - 1
       l = 0 if l < 0
-      wordlist.length > l ? wordlist[0..l].join(" ".freeze) + truncate_string : input
+      wordlist.length > l ? wordlist[0..l].join(" ".freeze) + truncate_string.to_s : input
     end
 
     # Split input string into an array of substrings separated by given pattern.
@@ -85,7 +86,7 @@ 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)
@@ -124,7 +125,15 @@ module Liquid
       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] }
+        ary.sort do |a, b|
+          a = a[property]
+          b = b[property]
+          if a && b
+            a <=> b
+          else
+            a ? -1 : 1
+          end
+        end
       end
     end
 
@@ -375,7 +384,7 @@ module Liquid
       end
 
       def join(glue)
-        to_a.join(glue)
+        to_a.join(glue.to_s)
       end
 
       def concat(args)

lib/liquid/strainer.rb

@@ -27,7 +27,7 @@ module Liquid
 
     def self.add_filter(filter)
       raise ArgumentError, "Expected module but got: #{filter.class}" unless filter.is_a?(Module)
-      unless self.class.include?(filter)
+      unless self.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(', ')}"
@@ -39,6 +39,7 @@ module Liquid
     end
 
     def self.global_filter(filter)
+      @@strainer_class_cache.clear
       @@global_strainer.add_filter(filter)
     end
 

lib/liquid/tags/for.rb

@@ -23,7 +23,7 @@ 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:
   #

lib/liquid/tags/include.rb

@@ -42,14 +42,15 @@ module Liquid
 
     def render(context)
       template_name = context.evaluate(@template_name_expr)
-      partial = load_cached_partial(template_name, context)
+      raise ArgumentError.new(options[:locale].t("errors.argument.include")) unless template_name
 
+      partial = load_cached_partial(template_name, context)
       context_variable_name = template_name.split('/'.freeze).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

lib/liquid/template.rb

@@ -69,6 +69,11 @@ 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
@@ -167,7 +172,7 @@ module Liquid
         c = args.shift
 
         if @rethrow_errors
-          c.exception_handler = ->(e) { raise }
+          c.exception_renderer = ->(e) { raise }
         end
 
         c
@@ -241,7 +246,7 @@ module Liquid
     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_handler = options[:exception_handler] if options[:exception_handler]
+      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

lib/liquid/version.rb

@@ -1,4 +1,4 @@
 # encoding: utf-8
 module Liquid
-  VERSION = "4.0.0.rc2"
+  VERSION = "4.0.0"
 end

liquid.gemspec

@@ -15,6 +15,7 @@ Gem::Specification.new do |s|
   s.license     = "MIT"
   # s.description = "A secure, non-evaling end user template engine with aesthetic markup."
 
+  s.required_ruby_version     = ">= 2.1.0"
   s.required_rubygems_version = ">= 1.3.7"
 
   s.test_files  = Dir.glob("{test}/**/*")
@@ -24,6 +25,6 @@ Gem::Specification.new do |s|
 
   s.require_path = "lib"
 
-  s.add_development_dependency 'rake'
+  s.add_development_dependency 'rake', '~> 11.3'
   s.add_development_dependency 'minitest'
 end

performance/benchmark.rb

@@ -5,7 +5,7 @@ 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 +13,6 @@ 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/theme_runner.rb

@@ -21,53 +21,100 @@ class ThemeRunner
     end
   end
 
-  # Load all templates into memory, do this now so that
+  # Initialize a new liquid ThemeRunner instance
-  # we don't profile IO.
+  # 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 |test_hash|
-
+      Liquid::Template.new.parse(test_hash[:liquid])
-    @tests.each do |liquid, layout, template_name|
+      Liquid::Template.new.parse(test_hash[:layout])
-      tmpl = Liquid::Template.new
-      tmpl.parse(liquid)
-      tmpl = Liquid::Template.new
-      tmpl.parse(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
+    each_test do |liquid, layout, assigns, page_template, template_name|
-    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))
       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))
-
+    tmpl
-    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
   end
 end

test/integration/error_handling_test.rb

@@ -97,6 +97,22 @@ class ErrorHandlingTest < Minitest::Test
     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(%q(
+          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
     template = Liquid::Template.parse('
         foobar
@@ -186,22 +202,40 @@ class ErrorHandlingTest < Minitest::Test
     end
   end
 
-  def test_exception_handler_with_string_result
+  def test_default_exception_renderer_with_internal_error
-    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
     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

test/integration/parsing_quirks_test.rb

@@ -115,4 +115,8 @@ 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/standard_filter_test.rb

@@ -115,15 +115,15 @@ 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
@@ -154,6 +154,7 @@ 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
@@ -169,6 +170,7 @@ class StandardFiltersTest < Minitest::Test
   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
@@ -176,6 +178,24 @@ 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_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_empty_array
     assert_equal [], @filters.sort([], "a")
   end

test/integration/tags/include_tag_test.rb

@@ -217,6 +217,17 @@ class IncludeTagTest < Minitest::Test
     end
   end
 
+  def test_render_raise_argument_error_when_template_is_undefined
+    assert_raises(Liquid::ArgumentError) do
+      template = Liquid::Template.parse('{% include undefined_variable %}')
+      template.render!
+    end
+    assert_raises(Liquid::ArgumentError) do
+      template = Liquid::Template.parse('{% include nil %}')
+      template.render!
+    end
+  end
+
   def test_including_via_variable_value
     assert_template_result "from TestFileSystem", "{% assign page = 'pick_a_source' %}{% include page %}"
 
@@ -224,4 +235,11 @@ class IncludeTagTest < Minitest::Test
 
     assert_template_result "Product: Draft 151cm ", "{% assign page = 'product' %}{% include page for foo %}", "foo" => { 'title' => 'Draft 151cm' }
   end
+
+  def test_including_with_strict_variables
+    template = Liquid::Template.parse("{% include 'simple' %}", error_mode: :warn)
+    template.render(nil, strict_variables: true)
+
+    assert_equal [], template.errors
+  end
 end # IncludeTagTest

test/integration/template_test.rb

@@ -215,16 +215,20 @@ class TemplateTest < Minitest::Test
     assert_equal 'ruby error in drop', e.message
   end
 
-  def test_exception_handler_doesnt_reraise_if_it_returns_false
+  def test_exception_renderer_that_returns_string
     exception = nil
-    Template.parse("{{ 1 | divided_by: 0 }}").render({}, exception_handler: ->(e) { exception = e; false })
+    handler = ->(e) { exception = e; '<!-- error -->' }
+
+    output = Template.parse("{{ 1 | divided_by: 0 }}").render({}, exception_renderer: handler)
+
     assert exception.is_a?(Liquid::ZeroDivisionError)
+    assert_equal '<!-- error -->', output
   end
 
-  def test_exception_handler_does_reraise_if_it_returns_true
+  def test_exception_renderer_that_raises
     exception = nil
     assert_raises(Liquid::ZeroDivisionError) do
-      Template.parse("{{ 1 | divided_by: 0 }}").render({}, exception_handler: ->(e) { exception = e; true })
+      Template.parse("{{ 1 | divided_by: 0 }}").render({}, exception_renderer: ->(e) { exception = e; raise })
     end
     assert exception.is_a?(Liquid::ZeroDivisionError)
   end

test/integration/trim_mode_test.rb

@@ -0,0 +1,525 @@
+require 'test_helper'
+
+class TrimModeTest < Minitest::Test
+  include Liquid
+
+  # Make sure the trim isn't applied to standard output
+  def test_standard_output
+    text = <<-END_TEMPLATE
+      <div>
+        <p>
+          {{ 'John' }}
+        </p>
+      </div>
+    END_TEMPLATE
+    expected = <<-END_EXPECTED
+      <div>
+        <p>
+          John
+        </p>
+      </div>
+    END_EXPECTED
+    assert_template_result(expected, text)
+  end
+
+  def test_variable_output_with_multiple_blank_lines
+    text = <<-END_TEMPLATE
+      <div>
+        <p>
+
+
+          {{- 'John' -}}
+
+
+        </p>
+      </div>
+    END_TEMPLATE
+    expected = <<-END_EXPECTED
+      <div>
+        <p>John</p>
+      </div>
+    END_EXPECTED
+    assert_template_result(expected, text)
+  end
+
+  def test_tag_output_with_multiple_blank_lines
+    text = <<-END_TEMPLATE
+      <div>
+        <p>
+
+
+          {%- if true -%}
+          yes
+          {%- endif -%}
+
+
+        </p>
+      </div>
+    END_TEMPLATE
+    expected = <<-END_EXPECTED
+      <div>
+        <p>yes</p>
+      </div>
+    END_EXPECTED
+    assert_template_result(expected, text)
+  end
+
+  # Make sure the trim isn't applied to standard tags
+  def test_standard_tags
+    whitespace = '          '
+    text = <<-END_TEMPLATE
+      <div>
+        <p>
+          {% if true %}
+          yes
+          {% endif %}
+        </p>
+      </div>
+    END_TEMPLATE
+    expected = <<-END_EXPECTED
+      <div>
+        <p>
+#{whitespace}
+          yes
+#{whitespace}
+        </p>
+      </div>
+    END_EXPECTED
+    assert_template_result(expected, text)
+
+    text = <<-END_TEMPLATE
+      <div>
+        <p>
+          {% if false %}
+          no
+          {% endif %}
+        </p>
+      </div>
+    END_TEMPLATE
+    expected = <<-END_EXPECTED
+      <div>
+        <p>
+#{whitespace}
+        </p>
+      </div>
+    END_EXPECTED
+    assert_template_result(expected, text)
+  end
+
+  # Make sure the trim isn't too agressive
+  def test_no_trim_output
+    text = '<p>{{- \'John\' -}}</p>'
+    expected = '<p>John</p>'
+    assert_template_result(expected, text)
+  end
+
+  # Make sure the trim isn't too agressive
+  def test_no_trim_tags
+    text = '<p>{%- if true -%}yes{%- endif -%}</p>'
+    expected = '<p>yes</p>'
+    assert_template_result(expected, text)
+
+    text = '<p>{%- if false -%}no{%- endif -%}</p>'
+    expected = '<p></p>'
+    assert_template_result(expected, text)
+  end
+
+  def test_single_line_outer_tag
+    text = '<p> {%- if true %} yes {% endif -%} </p>'
+    expected = '<p> yes </p>'
+    assert_template_result(expected, text)
+
+    text = '<p> {%- if false %} no {% endif -%} </p>'
+    expected = '<p></p>'
+    assert_template_result(expected, text)
+  end
+
+  def test_single_line_inner_tag
+    text = '<p> {% if true -%} yes {%- endif %} </p>'
+    expected = '<p> yes </p>'
+    assert_template_result(expected, text)
+
+    text = '<p> {% if false -%} no {%- endif %} </p>'
+    expected = '<p>  </p>'
+    assert_template_result(expected, text)
+  end
+
+  def test_single_line_post_tag
+    text = '<p> {% if true -%} yes {% endif -%} </p>'
+    expected = '<p> yes </p>'
+    assert_template_result(expected, text)
+
+    text = '<p> {% if false -%} no {% endif -%} </p>'
+    expected = '<p> </p>'
+    assert_template_result(expected, text)
+  end
+
+  def test_single_line_pre_tag
+    text = '<p> {%- if true %} yes {%- endif %} </p>'
+    expected = '<p> yes </p>'
+    assert_template_result(expected, text)
+
+    text = '<p> {%- if false %} no {%- endif %} </p>'
+    expected = '<p> </p>'
+    assert_template_result(expected, text)
+  end
+
+  def test_pre_trim_output
+    text = <<-END_TEMPLATE
+      <div>
+        <p>
+          {{- 'John' }}
+        </p>
+      </div>
+    END_TEMPLATE
+    expected = <<-END_EXPECTED
+      <div>
+        <p>John
+        </p>
+      </div>
+    END_EXPECTED
+    assert_template_result(expected, text)
+  end
+
+  def test_pre_trim_tags
+    text = <<-END_TEMPLATE
+      <div>
+        <p>
+          {%- if true %}
+          yes
+          {%- endif %}
+        </p>
+      </div>
+    END_TEMPLATE
+    expected = <<-END_EXPECTED
+      <div>
+        <p>
+          yes
+        </p>
+      </div>
+    END_EXPECTED
+    assert_template_result(expected, text)
+
+    text = <<-END_TEMPLATE
+      <div>
+        <p>
+          {%- if false %}
+          no
+          {%- endif %}
+        </p>
+      </div>
+    END_TEMPLATE
+    expected = <<-END_EXPECTED
+      <div>
+        <p>
+        </p>
+      </div>
+    END_EXPECTED
+    assert_template_result(expected, text)
+  end
+
+  def test_post_trim_output
+    text = <<-END_TEMPLATE
+      <div>
+        <p>
+          {{ 'John' -}}
+        </p>
+      </div>
+    END_TEMPLATE
+    expected = <<-END_EXPECTED
+      <div>
+        <p>
+          John</p>
+      </div>
+    END_EXPECTED
+    assert_template_result(expected, text)
+  end
+
+  def test_post_trim_tags
+    text = <<-END_TEMPLATE
+      <div>
+        <p>
+          {% if true -%}
+          yes
+          {% endif -%}
+        </p>
+      </div>
+    END_TEMPLATE
+    expected = <<-END_EXPECTED
+      <div>
+        <p>
+          yes
+          </p>
+      </div>
+    END_EXPECTED
+    assert_template_result(expected, text)
+
+    text = <<-END_TEMPLATE
+      <div>
+        <p>
+          {% if false -%}
+          no
+          {% endif -%}
+        </p>
+      </div>
+    END_TEMPLATE
+    expected = <<-END_EXPECTED
+      <div>
+        <p>
+          </p>
+      </div>
+    END_EXPECTED
+    assert_template_result(expected, text)
+  end
+
+  def test_pre_and_post_trim_tags
+    text = <<-END_TEMPLATE
+      <div>
+        <p>
+          {%- if true %}
+          yes
+          {% endif -%}
+        </p>
+      </div>
+    END_TEMPLATE
+    expected = <<-END_EXPECTED
+      <div>
+        <p>
+          yes
+          </p>
+      </div>
+    END_EXPECTED
+    assert_template_result(expected, text)
+
+    text = <<-END_TEMPLATE
+      <div>
+        <p>
+          {%- if false %}
+          no
+          {% endif -%}
+        </p>
+      </div>
+    END_TEMPLATE
+    expected = <<-END_EXPECTED
+      <div>
+        <p></p>
+      </div>
+    END_EXPECTED
+    assert_template_result(expected, text)
+  end
+
+  def test_post_and_pre_trim_tags
+    text = <<-END_TEMPLATE
+      <div>
+        <p>
+          {% if true -%}
+          yes
+          {%- endif %}
+        </p>
+      </div>
+    END_TEMPLATE
+    expected = <<-END_EXPECTED
+      <div>
+        <p>
+          yes
+        </p>
+      </div>
+    END_EXPECTED
+    assert_template_result(expected, text)
+
+    whitespace = '          '
+    text = <<-END_TEMPLATE
+      <div>
+        <p>
+          {% if false -%}
+          no
+          {%- endif %}
+        </p>
+      </div>
+    END_TEMPLATE
+    expected = <<-END_EXPECTED
+      <div>
+        <p>
+#{whitespace}
+        </p>
+      </div>
+    END_EXPECTED
+    assert_template_result(expected, text)
+  end
+
+  def test_trim_output
+    text = <<-END_TEMPLATE
+      <div>
+        <p>
+          {{- 'John' -}}
+        </p>
+      </div>
+    END_TEMPLATE
+    expected = <<-END_EXPECTED
+      <div>
+        <p>John</p>
+      </div>
+    END_EXPECTED
+    assert_template_result(expected, text)
+  end
+
+  def test_trim_tags
+    text = <<-END_TEMPLATE
+      <div>
+        <p>
+          {%- if true -%}
+          yes
+          {%- endif -%}
+        </p>
+      </div>
+    END_TEMPLATE
+    expected = <<-END_EXPECTED
+      <div>
+        <p>yes</p>
+      </div>
+    END_EXPECTED
+    assert_template_result(expected, text)
+
+    text = <<-END_TEMPLATE
+      <div>
+        <p>
+          {%- if false -%}
+          no
+          {%- endif -%}
+        </p>
+      </div>
+    END_TEMPLATE
+    expected = <<-END_EXPECTED
+      <div>
+        <p></p>
+      </div>
+    END_EXPECTED
+    assert_template_result(expected, text)
+  end
+
+  def test_whitespace_trim_output
+    text = <<-END_TEMPLATE
+      <div>
+        <p>
+          {{- 'John' -}},
+          {{- '30' -}}
+        </p>
+      </div>
+    END_TEMPLATE
+    expected = <<-END_EXPECTED
+      <div>
+        <p>John,30</p>
+      </div>
+    END_EXPECTED
+    assert_template_result(expected, text)
+  end
+
+  def test_whitespace_trim_tags
+    text = <<-END_TEMPLATE
+      <div>
+        <p>
+          {%- if true -%}
+          yes
+          {%- endif -%}
+        </p>
+      </div>
+    END_TEMPLATE
+    expected = <<-END_EXPECTED
+      <div>
+        <p>yes</p>
+      </div>
+    END_EXPECTED
+    assert_template_result(expected, text)
+
+    text = <<-END_TEMPLATE
+      <div>
+        <p>
+          {%- if false -%}
+          no
+          {%- endif -%}
+        </p>
+      </div>
+    END_TEMPLATE
+    expected = <<-END_EXPECTED
+      <div>
+        <p></p>
+      </div>
+    END_EXPECTED
+    assert_template_result(expected, text)
+  end
+
+  def test_complex_trim_output
+    text = <<-END_TEMPLATE
+      <div>
+        <p>
+          {{- 'John' -}}
+          {{- '30' -}}
+        </p>
+        <b>
+          {{ 'John' -}}
+          {{- '30' }}
+        </b>
+        <i>
+          {{- 'John' }}
+          {{ '30' -}}
+        </i>
+      </div>
+    END_TEMPLATE
+    expected = <<-END_EXPECTED
+      <div>
+        <p>John30</p>
+        <b>
+          John30
+        </b>
+        <i>John
+          30</i>
+      </div>
+    END_EXPECTED
+    assert_template_result(expected, text)
+  end
+
+  def test_complex_trim
+    text = <<-END_TEMPLATE
+      <div>
+        {%- if true -%}
+          {%- if true -%}
+            <p>
+              {{- 'John' -}}
+            </p>
+          {%- endif -%}
+        {%- endif -%}
+      </div>
+    END_TEMPLATE
+    expected = <<-END_EXPECTED
+      <div><p>John</p></div>
+    END_EXPECTED
+    assert_template_result(expected, text)
+  end
+
+  def test_raw_output
+    whitespace = '        '
+    text = <<-END_TEMPLATE
+      <div>
+        {% raw %}
+          {%- if true -%}
+            <p>
+              {{- 'John' -}}
+            </p>
+          {%- endif -%}
+        {% endraw %}
+      </div>
+    END_TEMPLATE
+    expected = <<-END_EXPECTED
+      <div>
+#{whitespace}
+          {%- if true -%}
+            <p>
+              {{- 'John' -}}
+            </p>
+          {%- endif -%}
+#{whitespace}
+      </div>
+    END_EXPECTED
+    assert_template_result(expected, text)
+  end
+end # TrimModeTest

test/unit/condition_unit_test.rb

@@ -64,6 +64,14 @@ class ConditionUnitTest < Minitest::Test
     assert_evaluates_argument_error '1', '<=', 0
   end
 
+  def test_hash_compare_backwards_compatibility
+    assert_equal nil, Condition.new({}, '>', 2).evaluate
+    assert_equal nil, Condition.new(2, '>', {}).evaluate
+    assert_equal false, Condition.new({}, '==', 2).evaluate
+    assert_equal true, Condition.new({ 'a' => 1 }, '==', { 'a' => 1 }).evaluate
+    assert_equal true, Condition.new({ 'a' => 2 }, 'contains', 'a').evaluate
+  end
+
   def test_contains_works_on_arrays
     @context = Liquid::Context.new
     @context['array'] = [1, 2, 3, 4, 5]
@@ -122,6 +130,17 @@ class ConditionUnitTest < Minitest::Test
     assert_equal false, condition.evaluate
   end
 
+  def test_maximum_recursion_depth
+    condition = Condition.new(1, '==', 1)
+
+    assert_raises(Liquid::StackLevelError) do
+      (1..510).each do
+        condition.evaluate
+        condition.and Condition.new(2, '==', 2)
+      end
+    end
+  end
+
   def test_should_allow_custom_proc_operator
     Condition.operators['starts_with'] = proc { |cond, left, right| left =~ %r{^#{right}} }
 

test/unit/lexer_unit_test.rb

@@ -19,7 +19,7 @@ class LexerUnitTest < Minitest::Test
   end
 
   def test_comparison
-    tokens = Lexer.new('== <> contains').tokenize
+    tokens = Lexer.new('== <> contains ').tokenize
     assert_equal [[:comparison, '=='], [:comparison, '<>'], [:comparison, 'contains'], [:end_of_string]], tokens
   end
 

test/unit/strainer_unit_test.rb

@@ -133,4 +133,32 @@ class StrainerUnitTest < Minitest::Test
     strainer.class.add_filter(PublicMethodOverrideFilter)
     assert strainer.class.filter_methods.include?('public_filter')
   end
+
+  module LateAddedFilter
+    def late_added_filter(input)
+      "filtered"
+    end
+  end
+
+  def test_global_filter_clears_cache
+    assert_equal 'input', Strainer.create(nil).invoke('late_added_filter', 'input')
+    Strainer.global_filter(LateAddedFilter)
+    assert_equal 'filtered', Strainer.create(nil).invoke('late_added_filter', 'input')
+  end
+
+  def test_add_filter_does_not_include_already_included_module
+    mod = Module.new do
+      class << self
+        attr_accessor :include_count
+        def included(mod)
+          self.include_count += 1
+        end
+      end
+      self.include_count = 0
+    end
+    strainer = Context.new.strainer
+    strainer.class.add_filter(mod)
+    strainer.class.add_filter(mod)
+    assert_equal 1, mod.include_count
+  end
 end # StrainerTest