Add strict2 let closures for Liquid composition

Keep the historical blank-body inline-error suppression for lax and strict parse modes, but stop suppressing the rendered error text when the template was parsed in strict2. Raised-error rendering continues to raise in all modes.

Store the resolved template error mode on the render context while a template renders so BlockBody can distinguish strict2 from compatibility modes when deciding whether a blank tag should hide inline error text.

Add integration coverage for lax/strict suppression, strict2 non-suppression across blank body forms, nonblank bodies, and raised-error behavior.

.github/workflows/liquid.yml

@@ -22,6 +22,7 @@ jobs:
             }
           - { ruby: 4.0, allowed-failure: false, rubyopt: "--yjit" }
           - { ruby: 4.0, allowed-failure: false, rubyopt: "--zjit" }
+          - { ruby: truffleruby, allowed-failure: false }
 
           # Head can have failures due to being in development
           - { ruby: head, allowed-failure: true }
@@ -35,7 +36,7 @@ jobs:
     name: Test Ruby ${{ matrix.entry.ruby }} ${{ matrix.entry.rubyopt }} --${{ matrix.entry.allowed-failure && 'allowed-failure' || 'strict' }}
     steps:
       - uses: actions/checkout@f43a0e5ff2bd294095638e18286ca9a3d1956744 # v3.6.0
-      - uses: ruby/setup-ruby@a25f1e45f0e65a92fcb1e95e8847f78fb0a7197a # v1.273.0
+      - uses: ruby/setup-ruby@319994f95fa847cf3fb3cd3dbe89f6dcde9f178f # v1.295.0
         with:
           ruby-version: ${{ matrix.entry.ruby }}
           bundler-cache: true
@@ -51,7 +52,7 @@ jobs:
       BUNDLE_WITH: spec
     steps:
       - uses: actions/checkout@f43a0e5ff2bd294095638e18286ca9a3d1956744 # v3.6.0
-      - uses: ruby/setup-ruby@a25f1e45f0e65a92fcb1e95e8847f78fb0a7197a # v1.273.0
+      - uses: ruby/setup-ruby@319994f95fa847cf3fb3cd3dbe89f6dcde9f178f # v1.295.0
         with:
           bundler-cache: true
           bundler: latest
@@ -66,7 +67,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@f43a0e5ff2bd294095638e18286ca9a3d1956744 # v3.6.0
-      - uses: ruby/setup-ruby@a25f1e45f0e65a92fcb1e95e8847f78fb0a7197a # v1.273.0
+      - uses: ruby/setup-ruby@319994f95fa847cf3fb3cd3dbe89f6dcde9f178f # v1.295.0
         with:
           bundler-cache: true
       - run: bundle exec rake memory_profile:run

.ruby-version

@@ -1 +1 @@
-3.4.1
+4.0.2

Gemfile

@@ -32,7 +32,7 @@ group :test do
 end
 
 group :spec do
-  # TODO: temporary - using cp-gate-lax-specs-ai branch until lax specs are properly gated
-  gem 'liquid-spec', github: 'Shopify/liquid-spec', branch: 'cp-gate-lax-specs-ai'
+  # Using feature branch until https://github.com/Shopify/liquid-spec/pull/144 is merged
+  gem 'liquid-spec', github: 'Shopify/liquid-spec', branch: 'self-drop-env-lookup-specs'
   gem 'activesupport', require: false
 end

History.md

@@ -1,37 +1,16 @@
 # Liquid Change Log
 
-## 6.0.0
+## 5.13.0
 
-### Architectural changes
-
-### Features
-* (TODO) Add support for boolean expressions everywhere
-  * As variable output `{{ a or b }}`
-  * As filter argument `{{ collection | where: 'prop', a or b }}`
-  * As tag argument `{% render 'snip', enabled: a or b %}`
-  * As conditional tag argument `{% if cond %}` (extending previous behaviour)
-* (TODO) Add support for subexpression prioritization and associativity
-  * In ascending order of priority:
-    * Logical: `and`, `or` (right to left)
-    * Equality: `==`, `!=`, `<>` (left to right)
-    * Comparison: `>`, `>=`, `<`, `<=`, `contains` (left to right)
-  - For example, this is now supported
-    * `{{ a > b == c < d or e == f }}` which is equivalent to
-    * `{{ ((a > b) == (c < d)) or (e == f) }}`
-- (TODO) Add support for parenthesized expressions
-  * e.g. `(a or b) and c`
-
-### Breaking changes
-* The Environment's `error_mode` option has been removed.
-  * `:warn` is no longer supported
-  * `:lax` and `lax_parse` is no longer supported
-  * `:strict` and `strict_parse` is no longer supported
-  * `strict2_parse` is renamed to `parse_markup`
-* The `warnings` system has been removed.
-
-### Migrating from `^5.11.0`
-- In custom tags that include `ParserSwitching`, rename `strict2_parse` to `parse_markup`
-- Remove code depending on `:error_mode`
+* Add TruffleRuby in CI [Benoit Daloze]
+* Skip slow test raising many exceptions on non-CRuby [Benoit Daloze]
+* Reject bare-bracket syntax in strict2 and introduce `self` keyword by [Alok Swamy]
+* Add strict2_parse to assign and capture tags by [Alok Swamy]
+* Add strict2_parse to increment and decrement tags by [Alok Swamy]
+* Update liquid-spec adapters for `missing_features` [Ian Ker-Seymer]
+* Prevent `SelfDrop` context mutation across render boundaries [Guilherme Carreiro]
+* Fix `SelfDrop` equality [Guilherme Carreiro]
+* Let environment `self` shadow `SelfDrop` [Ian Ker-Seymer]
 
 ## 5.11.0
 * Revert the Inline Snippets tag (#2001), treat its inclusion in the latest Liquid release as a bug, and allow for feedback on RFC#1916 to better support Liquid developers [Guilherme Carreiro]

README.md

@@ -93,6 +93,75 @@ LIQUID
 
 By using Environments, you ensure that custom tags and filters are only available in the contexts where they are needed, making your Liquid templates more robust and easier to manage. For smaller projects, a global environment is available via `Liquid::Environment.default`.
 
+### Error Modes
+
+Setting the error mode of Liquid lets you specify how strictly you want your templates to be interpreted.
+Normally the parser is very lax and will accept almost anything without error. Unfortunately this can make
+it very hard to debug and can lead to unexpected behaviour.
+
+Liquid also comes with different parsers that can be used when editing templates to give better error messages
+when templates are invalid. You can enable this new parser like this:
+
+```ruby
+Liquid::Environment.default.error_mode = :strict2 # Raises a SyntaxError when invalid syntax is used in all tags
+Liquid::Environment.default.error_mode = :strict  # Raises a SyntaxError when invalid syntax is used in some tags
+Liquid::Environment.default.error_mode = :warn    # Adds strict errors to template.errors but continues as normal
+Liquid::Environment.default.error_mode = :lax     # The default mode, accepts almost anything.
+```
+
+If you want to set the error mode only on specific templates you can pass `:error_mode` as an option to `parse`:
+```ruby
+Liquid::Template.parse(source, error_mode: :strict)
+```
+This is useful for doing things like enabling strict mode only in the theme editor.
+
+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.
+
+### Strict2 bindings and closures
+
+In `error_mode: :strict2`, `let` binds a value or defines a callable Liquid body:
+
+```liquid
+{% let count = 1 %}
+{% let title(step) %}
+  {% let count = count | plus: step %}
+  {{ count }}
+{% endlet %}
+{{ title(2) }}
+```
+
+Each call has fresh locals and writable parameters. Captures read the latest parent
+bindings. `set name = expression` updates the nearest local binding, or creates a
+shadow at the invocation root when the name is captured or absent. Initializers run
+before installing the new binding. Loops have fresh `let` bindings each iteration
+and can shadow outer names; conditional branches share their surrounding scope.
+Duplicate `let` declarations in one scope
+and `assign` inside closure bodies are parse errors. Calls accept positional
+arguments and invoke only Liquid closures.
+
+Custom `Liquid::Block` subclasses can use the same body rules:
+
+```ruby
+def parse(tokens)
+  @closure_body = parse_closure_body(tokens)
+end
+
+def render_to_output_buffer(context, output)
+  body = @closure_body.bind(context)
+  exports = body.invoke(context, output: output)
+  exports['title']&.render_to_output_buffer(context, output, ['Hello'])
+  output
+end
+```
+
+`invoke` renders into the supplied buffer and returns direct-child body-form `let`
+bindings by name. Value bindings and declarations nested in control flow are not
+exported. Each invocation has fresh state; bind the body at render time rather than
+caching a closure on the parsed tag. For parameterized bodies, pass
+`parameters: ['name']` to `parse_closure_body`, then pass an argument array as the
+second argument to `invoke`. The syntax remains visible to `ParseTreeVisitor`.
+
 ### 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.

Rakefile

@@ -33,12 +33,29 @@ task :rubocop do
   end
 end
 
-desc('runs test suite')
+desc('runs test suite with lax, strict, and strict2 parsers')
 task :test do
+  ENV['LIQUID_PARSER_MODE'] = 'lax'
+  Rake::Task['base_test'].invoke
+
+  ENV['LIQUID_PARSER_MODE'] = 'strict'
+  Rake::Task['base_test'].reenable
+  Rake::Task['base_test'].invoke
+
+  ENV['LIQUID_PARSER_MODE'] = 'strict2'
   Rake::Task['base_test'].reenable
   Rake::Task['base_test'].invoke
 
   if RUBY_ENGINE == 'ruby' || RUBY_ENGINE == 'truffleruby'
+    ENV['LIQUID_PARSER_MODE'] = 'lax'
+    Rake::Task['integration_test'].reenable
+    Rake::Task['integration_test'].invoke
+
+    ENV['LIQUID_PARSER_MODE'] = 'strict'
+    Rake::Task['integration_test'].reenable
+    Rake::Task['integration_test'].invoke
+
+    ENV['LIQUID_PARSER_MODE'] = 'strict2'
     Rake::Task['integration_test'].reenable
     Rake::Task['integration_test'].invoke
   end
@@ -61,11 +78,24 @@ task release: :build do
 end
 
 namespace :benchmark do
-  desc "Run the liquid benchmark"
-  task :run do
-    ruby "./performance/benchmark.rb"
+  desc "Run the liquid benchmark with lax parsing"
+  task :lax do
+    ruby "./performance/benchmark.rb lax"
   end
 
+  desc "Run the liquid benchmark with strict parsing"
+  task :strict do
+    ruby "./performance/benchmark.rb strict"
+  end
+
+  desc "Run the liquid benchmark with strict2 parsing"
+  task :strict2 do
+    ruby "./performance/benchmark.rb strict2"
+  end
+
+  desc "Run the liquid benchmark with lax, strict, and strict2 parsing"
+  task run: [:lax, :strict, :strict2]
+
   desc "Run unit benchmarks"
   namespace :unit do
     task :all do
@@ -96,6 +126,11 @@ namespace :profile do
   task :run do
     ruby "./performance/profile.rb"
   end
+
+  desc "Run the liquid profile/performance coverage with strict parsing"
+  task :strict do
+    ruby "./performance/profile.rb strict"
+  end
 end
 
 namespace :memory_profile do
@@ -116,6 +151,8 @@ end
 
 desc('run liquid-spec suite across all adapters')
 task :spec do
-  adapters = Dir['./spec/*.rb'].join(',')
-  sh "bundle exec liquid-spec matrix --adapters=#{adapters} --reference=ruby_liquid"
+  Dir['./spec/*.rb'].sort.each do |adapter|
+    puts "=== Running #{adapter} ==="
+    sh 'bundle', 'exec', 'liquid-spec', 'run', adapter, '--no-max-failures'
+  end
 end

lib/liquid.rb

@@ -58,6 +58,9 @@ require 'liquid/parser_switching'
 require 'liquid/tag'
 require 'liquid/block'
 require 'liquid/parse_tree_visitor'
+require 'liquid/closure_body'
+require 'liquid/closure'
+require 'liquid/call_expression'
 require 'liquid/interrupts'
 require 'liquid/tags'
 require "liquid/environment"
@@ -65,6 +68,7 @@ require 'liquid/lexer'
 require 'liquid/parser'
 require 'liquid/i18n'
 require 'liquid/drop'
+require 'liquid/self_drop'
 require 'liquid/tablerowloop_drop'
 require 'liquid/forloop_drop'
 require 'liquid/extensions'

lib/liquid/block.rb

@@ -10,10 +10,13 @@ module Liquid
     end
 
     def parse(tokens)
-      @body = new_body
-      while parse_body(@body, tokens)
-      end
-      @body.freeze
+      parse_block_body(tokens)
+    end
+
+    # Parse an external block body with closure validation and lexical declarations.
+    def parse_closure_body(tokens, parameters: Const::EMPTY_ARRAY)
+      parse_context.with_closure(parameters) { parse_block_body(tokens) }
+      ClosureBody.new(@body, parameters)
     end
 
     # For backwards compatibility
@@ -66,6 +69,13 @@ module Liquid
 
     private
 
+    def parse_block_body(tokens)
+      @body = new_body
+      while parse_body(@body, tokens)
+      end
+      @body.freeze
+    end
+
     # @api public
     def new_body
       parse_context.new_block_body

lib/liquid/block_body.rb

@@ -99,7 +99,9 @@ module Liquid
         context.handle_error(exc, line_number)
       else
         error_message = context.handle_error(exc, line_number)
-        unless blank_tag # conditional for backwards compatibility
+        error_mode = context.registers.static[:template_error_mode]
+        suppress_error_text = blank_tag && error_mode != :strict2 && error_mode != :rigid
+        unless suppress_error_text # blank-tag suppression is kept for backwards compatibility outside strict2
           output << error_message
         end
       end

lib/liquid/call_expression.rb

@@ -0,0 +1,33 @@
+# frozen_string_literal: true
+
+module Liquid
+  class CallExpression
+    attr_reader :target, :arguments
+
+    def initialize(target, arguments)
+      @target = target.freeze
+      @arguments = arguments.freeze
+      freeze
+    end
+
+    def evaluate(context)
+      context.resource_limits.with_capture do
+        render_to_output_buffer(context, +'')
+      end
+    end
+
+    def render_to_output_buffer(context, output)
+      closure = context.evaluate(@target)
+      raise Liquid::ArgumentError, "Expected a Liquid closure" unless closure.is_a?(Closure)
+
+      arguments = @arguments.map { |argument| context.evaluate(argument) }
+      closure.render_to_output_buffer(context, output, arguments)
+    end
+
+    class ParseTreeVisitor < Liquid::ParseTreeVisitor
+      def children
+        [@node.target] + @node.arguments
+      end
+    end
+  end
+end

lib/liquid/closure.rb

@@ -0,0 +1,96 @@
+# frozen_string_literal: true
+
+module Liquid
+  # A render-time value. Captures retain binding hashes, not copies of their values.
+  class Closure
+    def initialize(body, parameters, context)
+      @body = body
+      @parameters = parameters
+      @scopes = context.scopes.dup
+      @environments = context.environments.dup
+      @static_environments = context.static_environments
+    end
+
+    # Render into the supplied buffer and return direct-child body-form let bindings.
+    def invoke(context, arguments = Const::EMPTY_ARRAY, output: +'')
+      invocation = render_invocation(context, arguments, output)
+      @body.exports(invocation)
+    end
+
+    def render_to_output_buffer(context, output, arguments = Const::EMPTY_ARRAY)
+      render_invocation(context, arguments, output)
+      output
+    end
+
+    def to_liquid
+      self
+    end
+
+    def to_s
+      ''
+    end
+
+    private
+
+    def render_invocation(context, arguments, output)
+      unless arguments.length == @parameters.length
+        raise Liquid::ArgumentError, "Expected #{@parameters.length} closure arguments, got #{arguments.length}"
+      end
+
+      invocation = context.new_closure_subcontext(@scopes, @environments, @static_environments)
+      @parameters.each_with_index { |name, index| invocation[name] = arguments[index] }
+      @body.render_to_output_buffer(invocation, output)
+      invocation
+    end
+
+    # @api private
+    class CapturedBindings
+      def initialize(scopes, environments, context)
+        @scopes = scopes
+        @environments = environments
+        @context = context
+        @locals = {}
+      end
+
+      def key?(name)
+        local_key?(name) || @environments.any? { |environment| environment.key?(name) }
+      end
+
+      def local_key?(name)
+        @locals.key?(name) || @scopes.any? { |scope| scope.key?(name) } ||
+          @environments.any? { |environment| environment.is_a?(CapturedBindings) && environment.local_key?(name) }
+      end
+
+      def []=(name, value)
+        @locals[name] = value
+      end
+
+      def [](name)
+        find_variable(name, @context, raise_on_not_found: false)
+      end
+
+      def find_variable(name, context, raise_on_not_found: true)
+        return context.lookup_and_evaluate(@locals, name, raise_on_not_found: raise_on_not_found) if @locals.key?(name)
+
+        scope = @scopes.find { |candidate| candidate.key?(name) }
+        return context.lookup_and_evaluate(scope, name, raise_on_not_found: raise_on_not_found) if scope
+
+        find_in_environments(name, context, raise_on_not_found: raise_on_not_found)
+      end
+
+      private
+
+      def find_in_environments(name, context, raise_on_not_found:)
+        @environments.each do |environment|
+          if environment.is_a?(CapturedBindings)
+            return environment.find_variable(name, context, raise_on_not_found: raise_on_not_found)
+          end
+
+          value = context.lookup_and_evaluate(environment, name, raise_on_not_found: raise_on_not_found)
+          return value if !value.nil? || context.strict_variables && raise_on_not_found
+        end
+        nil
+      end
+    end
+  end
+end

lib/liquid/closure_body.rb

@@ -0,0 +1,31 @@
+# frozen_string_literal: true
+
+module Liquid
+  # Parsed syntax shared by let and closure-aware custom blocks.
+  class ClosureBody
+    attr_reader :body
+
+    def initialize(body, parameters = Const::EMPTY_ARRAY)
+      @body = body
+      @parameters = parameters.dup.freeze
+      @exports = body.nodelist.select { |node| node.is_a?(Let) && node.body_form? }.map(&:to).freeze
+      freeze
+    end
+
+    def bind(context)
+      Closure.new(self, @parameters, context)
+    end
+
+    def render_to_output_buffer(context, output)
+      @body.render_to_output_buffer(context, output)
+    end
+
+    def exports(context)
+      context.scopes.last.slice(*@exports)
+    end
+
+    def nodelist
+      @body.nodelist
+    end
+  end
+end

lib/liquid/context.rb

@@ -60,6 +60,10 @@ module Liquid
     end
     # rubocop:enable Metrics/ParameterLists
 
+    def warnings
+      @warnings ||= []
+    end
+
     def strainer
       @strainer ||= @environment.create_strainer(self, @filters)
     end
@@ -153,10 +157,45 @@ module Liquid
         subcontext.filters  = @filters
         subcontext.strainer = nil
         subcontext.errors   = errors
+        subcontext.warnings = warnings
         subcontext.disabled_tags = @disabled_tags
       end
     end
 
+    # @api private
+    def new_closure_subcontext(scopes, environments, static_environments)
+      new_isolated_subcontext.tap do |invocation|
+        captures = Closure::CapturedBindings.new(scopes, environments + static_environments, invocation)
+        invocation.captured_bindings = captures
+        invocation.environments = [captures]
+        invocation.static_environments = static_environments
+        invocation.strict_variables = strict_variables
+        invocation.strict_filters = strict_filters
+        invocation.global_filter = global_filter
+        invocation.template_name = template_name
+        invocation.partial = partial
+        invocation.base_scope_depth = base_scope_depth + @scopes.length
+      end
+    end
+
+    # @api private
+    def with_binding_scope
+      previous_root = @binding_root
+      stack do
+        @binding_root = @scopes.first
+        yield
+      end
+    ensure
+      @binding_root = previous_root
+    end
+
+    # @api private
+    def set_local(name, value)
+      root = @binding_root || @scopes.last
+      scope = @scopes.find { |owned| owned.key?(name) || owned.equal?(root) }
+      scope[name] = value
+    end
+
     def clear_instance_assigns
       @scopes[0] = {}
     end
@@ -182,6 +221,15 @@ module Liquid
       find_variable(key, raise_on_not_found: false) != nil
     end
 
+    # Checks whether a variable is defined in any scope, including nil-valued keys.
+    # Unlike #key?, this uses Hash#key? so that variables explicitly set to nil
+    # are still considered defined.
+    def variable_defined?(key)
+      @scopes.any? { |s| s.key?(key) } ||
+        @environments.any? { |e| e.key?(key) } ||
+        @static_environments.any? { |e| e.key?(key) }
+    end
+
     def evaluate(object)
       object.respond_to?(:evaluate) ? object.evaluate(self) : object
     end
@@ -192,12 +240,21 @@ module Liquid
       # path and find_index() is optimized in MRI to reduce object allocation
       index = @scopes.find_index { |s| s.key?(key) }
 
+      fallback_to_self_drop = key == Expression::SELF && index.nil? && !@captured_bindings&.local_key?(key)
+
       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)
+        try_variable_find_in_environments(
+          key,
+          raise_on_not_found: raise_on_not_found && !fallback_to_self_drop,
+        )
       end
 
+      # `self` resolves to a SelfDrop (enabling `self['var']` lookups),
+      # but only after the normal environment lookup doesn't find a value.
+      return @self_drop ||= SelfDrop.new(self) if fallback_to_self_drop && variable.nil?
+
       # update variable's context before invoking #to_liquid
       variable.context = self if variable.respond_to?(:context=)
 
@@ -239,13 +296,17 @@ module Liquid
 
     protected
 
-    attr_writer :base_scope_depth, :errors, :strainer, :filters, :disabled_tags
+    attr_writer :base_scope_depth, :warnings, :errors, :strainer, :filters, :disabled_tags, :environments, :static_environments, :captured_bindings
 
     private
 
     attr_reader :base_scope_depth
 
     def try_variable_find_in_environments(key, raise_on_not_found:)
+      if @captured_bindings
+        return @captured_bindings.find_variable(key, self, raise_on_not_found: raise_on_not_found)
+      end
+
       @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

lib/liquid/document.rb

@@ -20,7 +20,9 @@ module Liquid
     end
 
     def parse(tokenizer, parse_context)
-      while parse_body(tokenizer)
+      @local_bindings = parse_context.with_document_scope do
+        while parse_body(tokenizer)
+        end
       end
       @body.freeze
     rescue SyntaxError => e
@@ -38,7 +40,9 @@ module Liquid
     end
 
     def render_to_output_buffer(context, output)
-      @body.render_to_output_buffer(context, output)
+      return @body.render_to_output_buffer(context, output) unless @local_bindings
+
+      context.with_binding_scope { @body.render_to_output_buffer(context, output) }
     end
 
     def render(context)

lib/liquid/environment.rb

@@ -4,6 +4,10 @@ module Liquid
   # The Environment is the container for all configuration options of Liquid, such as
   # the registered tags, filters, and the default error mode.
   class Environment
+    # The default error mode for all templates. This can be overridden on a
+    # per-template basis.
+    attr_accessor :error_mode
+
     # The tags that are available to use in the template.
     attr_accessor :tags
 
@@ -29,14 +33,17 @@ module Liquid
       #  the template.
       # @param file_system The default file system that is used
       #  to load templates from.
+      # @param error_mode [Symbol] The default error mode for all templates
+      #  (either :strict2, :strict, :warn, or :lax).
       # @param exception_renderer [Proc] The exception renderer that is used to
       #   render exceptions.
       # @yieldparam environment [Environment] The environment instance that is being built.
       # @return [Environment] The new environment instance.
-      def build(tags: nil, file_system: nil, exception_renderer: nil)
+      def build(tags: nil, file_system: nil, error_mode: nil, exception_renderer: nil)
         ret = new
         ret.tags = tags if tags
         ret.file_system = file_system if file_system
+        ret.error_mode = error_mode if error_mode
         ret.exception_renderer = exception_renderer if exception_renderer
         yield ret if block_given?
         ret.freeze
@@ -68,6 +75,7 @@ module Liquid
     # @api private
     def initialize
       @tags = Tags::STANDARD_TAGS.dup
+      @error_mode = :lax
       @strainer_template = Class.new(StrainerTemplate).tap do |klass|
         klass.add_filter(StandardFilters)
       end

lib/liquid/expression.rb

@@ -2,6 +2,8 @@
 
 module Liquid
   class Expression
+    SELF = 'self'
+
     LITERALS = {
       nil => nil,
       'nil' => nil,
@@ -11,6 +13,9 @@ module Liquid
       'false' => false,
       'blank' => '',
       'empty' => '',
+      # in lax mode, minus sign can be a VariableLookup
+      # For simplicity and performace, we treat it like a literal
+      '-' => VariableLookup.parse("-", nil).freeze,
     }.freeze
 
     DOT = ".".ord
@@ -31,6 +36,7 @@ module Liquid
 
       def parse(markup, ss = StringScanner.new(""), cache = nil)
         return unless markup
+        return markup unless markup.is_a?(String)
 
         markup = markup.strip # markup can be a frozen string
 

lib/liquid/lexer.rb

@@ -2,6 +2,7 @@
 
 module Liquid
   class Lexer
+    ASSIGN = [:assign, "="].freeze
     CLOSE_ROUND = [:close_round, ")"].freeze
     CLOSE_SQUARE = [:close_square, "]"].freeze
     COLON = [:colon, ":"].freeze
@@ -133,6 +134,8 @@ module Liquid
             if (peeked_byte = ss.peek_byte) && (found = sub_table[peeked_byte])
               output << found
               ss.scan_byte
+            elsif peeked == "=".ord && ss.peek_byte != "<".ord && ss.peek_byte != ">".ord && ss.peek_byte != "!".ord
+              output << ASSIGN
             else
               raise_syntax_error(start_pos, ss)
             end

lib/liquid/parse_context.rb

@@ -3,13 +3,14 @@
 module Liquid
   class ParseContext
     attr_accessor :locale, :line_number, :trim_whitespace, :depth
-    attr_reader :partial, :environment
+    attr_reader :partial, :warnings, :error_mode, :environment
 
     def initialize(options = Const::EMPTY_HASH)
       @environment = options.fetch(:environment, Environment.default)
       @template_options = options ? options.dup : {}
 
-      @locale = @template_options[:locale] ||= I18n.new
+      @locale   = @template_options[:locale] ||= I18n.new
+      @warnings = []
 
       # constructing new StringScanner in Lexer, Tokenizer, etc is expensive
       # This StringScanner will be shared by all of them
@@ -37,7 +38,11 @@ module Liquid
 
     def new_parser(input)
       @string_scanner.string = input
-      Parser.new(@string_scanner)
+      Parser.new(
+        @string_scanner,
+        reject_bare_brackets: @error_mode == :strict2 || @error_mode == :rigid,
+        allow_calls: @error_mode == :strict2,
+      )
     end
 
     def new_tokenizer(source, start_line_number: nil, for_liquid_tag: false)
@@ -54,19 +59,73 @@ module Liquid
     end
 
     def parse_expression(markup, safe: false)
-      # markup MUST come from a string returned by the parser
-      # (e.g., parser.expression). We're not calling the parser here to
-      # prevent redundant parser overhead. The `safe` opt-in
-      # exists to ensure it is not accidentally still called with
-      # the result of a regex.
-      raise Liquid::InternalError, "unsafe parse_expression cannot be used" unless safe
+      if !safe && @error_mode == :strict2
+        # parse_expression is a widely used API. To maintain backward
+        # compatibility while raising awareness about strict2 parser standards,
+        # the safe flag supports API users make a deliberate decision.
+        #
+        # In strict2 mode, markup MUST come from parser.expression, which returns
+        # markup or a parsed callable node. We're not calling the parser here to
+        # prevent redundant parser overhead.
+        raise Liquid::InternalError, "unsafe parse_expression cannot be used in strict2 mode"
+      end
 
       Expression.parse(markup, @string_scanner, @expression_cache)
     end
 
+    def with_document_scope(&block)
+      previous_usage = @uses_local_bindings
+      @uses_local_bindings = false
+      with_lexical_scope(&block)
+      @uses_local_bindings
+    ensure
+      @uses_local_bindings = previous_usage
+    end
+
+    def with_lexical_scope(parameters = Const::EMPTY_ARRAY)
+      previous_scope = @lexical_scope
+      @lexical_scope = parameters.to_h { |name| [name, true] }
+      yield
+    ensure
+      @lexical_scope = previous_scope
+    end
+
+    def local_declarations?
+      @lexical_scope && !@lexical_scope.empty?
+    end
+
+    def declare_local(name)
+      @lexical_scope ||= {}
+      raise SyntaxError, "Duplicate let declaration '#{name}'" if @lexical_scope.key?(name)
+
+      @lexical_scope[name] = true
+    end
+
+    def with_closure(parameters = Const::EMPTY_ARRAY, &block)
+      require_closures!
+      previous_closure = @in_closure
+      @in_closure = true
+      with_lexical_scope(parameters, &block)
+    ensure
+      @in_closure = previous_closure
+    end
+
+    def in_closure?
+      @in_closure
+    end
+
+    def require_closures!
+      @uses_local_bindings = true
+      return if @error_mode == :strict2
+
+      raise SyntaxError, "Closures require strict2 mode"
+    end
+
     def partial=(value)
       @partial = value
       @options = value ? partial_options : @template_options
+
+      @error_mode = @options[:error_mode] || @environment.error_mode
     end
 
     def partial_options

lib/liquid/parser.rb

@@ -2,10 +2,12 @@
 
 module Liquid
   class Parser
-    def initialize(input)
+    def initialize(input, reject_bare_brackets: false, allow_calls: false)
       ss = input.is_a?(StringScanner) ? input : StringScanner.new(input)
       @tokens = Lexer.tokenize(ss)
       @p      = 0 # pointer to current location
+      @reject_bare_brackets = reject_bare_brackets
+      @allow_calls = allow_calls
     end
 
     def jump(point)
@@ -50,9 +52,14 @@ module Liquid
       token = @tokens[@p]
       case token[0]
       when :id
+        return callable_or_lookup if @allow_calls
+
         str = consume
         str << variable_lookups
       when :open_square
+        if @reject_bare_brackets
+          raise SyntaxError, "Bare bracket access is not allowed. Use #{Expression::SELF}['...'] instead"
+        end
         str = consume.dup
         str << expression
         str << consume(:close_square)
@@ -65,12 +72,41 @@ module Liquid
         consume(:dotdot)
         last = expression
         consume(:close_round)
+        return RangeLookup.new(Expression.parse(first), Expression.parse(last)) unless first.is_a?(String) && last.is_a?(String)
+
         "(#{first}..#{last})"
       else
         raise SyntaxError, "#{token} is not a valid expression"
       end
     end
 
+    def expression_with_markup
+      start = @p
+      # Parsing lookups appends to consumed identifier strings.
+      markup_tokens = @tokens[start...-1].map { |token| token[1].dup }
+      value = expression
+      markup = value.is_a?(String) ? value : markup_tokens.take(@p - start).join
+      [value, markup]
+    end
+
+    def remaining_markup
+      @tokens[@p...-1].map { |token| token[1] }.join(' ')
+    end
+
+    def parameters
+      parameters = []
+      return parameters unless consume?(:open_round)
+
+      unless look(:close_round)
+        parameters << consume(:id)
+        parameters << consume(:id) while consume?(:comma) && !look(:close_round)
+      end
+      consume(:close_round)
+      raise SyntaxError, "Duplicate closure parameter" unless parameters.uniq.length == parameters.length
+
+      parameters
+    end
+
     def argument
       str = +""
       # might be a keyword argument (identifier: expression)
@@ -98,5 +134,46 @@ module Liquid
       end
       str
     end
+
+    private
+
+    def callable_or_lookup
+      target = callable_lookups(consume(:id))
+      return target unless consume?(:open_round)
+
+      arguments = []
+      unless look(:close_round)
+        arguments << Expression.parse(expression)
+        arguments << Expression.parse(expression) while consume?(:comma) && !look(:close_round)
+      end
+      consume(:close_round)
+      target = VariableLookup.parse(target) if target.is_a?(String)
+      CallExpression.new(target, arguments)
+    end
+
+    def callable_lookups(target)
+      loop do
+        if consume?(:dot)
+          target = append_lookup(target, consume(:id), command: true)
+          next
+        end
+        break unless consume?(:open_square)
+
+        key = expression
+        consume(:close_square)
+        target = append_lookup(target, key)
+      end
+      target
+    end
+
+    def append_lookup(target, key, command: false)
+      if target.is_a?(String) && key.is_a?(String)
+        return target << (command ? ".#{key}" : "[#{key}]")
+      end
+
+      target = VariableLookup.parse(target) if target.is_a?(String)
+      target.add_lookup(command ? key : Expression.parse(key), command: command)
+      target
+    end
   end
 end

lib/liquid/parser_switching.rb

@@ -2,15 +2,74 @@
 
 module Liquid
   module ParserSwitching
+    # Do not use this.
+    #
+    # It's basically doing the same thing the {#parse_with_selected_parser},
+    # except this will try the strict parser regardless of the error mode,
+    # and fall back to the lax parser if the error mode is lax or warn,
+    # except when in strict2 mode where it uses the strict2 parser.
+    #
+    # @deprecated Use {#parse_with_selected_parser} instead.
+    def strict_parse_with_error_mode_fallback(markup)
+      return strict2_parse_with_error_context(markup) if strict2_mode?
+
+      strict_parse_with_error_context(markup)
+    rescue SyntaxError => e
+      case parse_context.error_mode
+      when :rigid
+        rigid_warn
+        raise
+      when :strict2
+        raise
+      when :strict
+        raise
+      when :warn
+        parse_context.warnings << e
+      end
+      lax_parse(markup)
+    end
+
     def parse_with_selected_parser(markup)
-      parse_markup(markup)
+      case parse_context.error_mode
+      when :rigid   then rigid_warn && strict2_parse_with_error_context(markup)
+      when :strict2 then strict2_parse_with_error_context(markup)
+      when :strict  then strict_parse_with_error_context(markup)
+      when :lax     then lax_parse(markup)
+      when :warn
+        begin
+          strict2_parse_with_error_context(markup)
+        rescue SyntaxError => e
+          parse_context.warnings << e
+          lax_parse(markup)
+        end
+      end
+    end
+
+    def strict2_mode?
+      parse_context.error_mode == :strict2 || parse_context.error_mode == :rigid
+    end
+
+    private
+
+    def rigid_warn
+      Deprecations.warn(':rigid', ':strict2')
+    end
+
+    def strict2_parse_with_error_context(markup)
+      strict2_parse(markup)
     rescue SyntaxError => e
       e.line_number    = line_number
       e.markup_context = markup_context(markup)
       raise e
     end
 
-    private
+    def strict_parse_with_error_context(markup)
+      strict_parse(markup)
+    rescue SyntaxError => e
+      e.line_number    = line_number
+      e.markup_context = markup_context(markup)
+      raise e
+    end
 
     def markup_context(markup)
       "in \"#{markup.strip}\""

lib/liquid/partial_cache.rb

@@ -4,7 +4,7 @@ module Liquid
   class PartialCache
     def self.load(template_name, context:, parse_context:)
       cached_partials = context.registers[:cached_partials]
-      cache_key = template_name.to_s
+      cache_key = "#{template_name}:#{parse_context.error_mode}"
       cached = cached_partials[cache_key]
       return cached if cached
 

lib/liquid/resource_limits.rb

@@ -2,24 +2,39 @@
 
 module Liquid
   class ResourceLimits
-    attr_accessor :render_length_limit, :render_score_limit, :assign_score_limit
-    attr_reader :render_score, :assign_score
+    attr_accessor :render_length_limit,
+      :render_score_limit,
+      :assign_score_limit,
+      :cumulative_render_score_limit,
+      :cumulative_assign_score_limit
+    attr_reader :render_score,
+      :assign_score,
+      :cumulative_render_score,
+      :cumulative_assign_score
 
     def initialize(limits)
-      @render_length_limit = limits[:render_length_limit]
-      @render_score_limit  = limits[:render_score_limit]
-      @assign_score_limit  = limits[:assign_score_limit]
+      @render_length_limit           = limits[:render_length_limit]
+      @render_score_limit            = limits[:render_score_limit]
+      @assign_score_limit            = limits[:assign_score_limit]
+      @cumulative_render_score_limit = limits[:cumulative_render_score_limit]
+      @cumulative_assign_score_limit = limits[:cumulative_assign_score_limit]
+      @cumulative_render_score = 0
+      @cumulative_assign_score = 0
       reset
     end
 
     def increment_render_score(amount)
       @render_score += amount
+      @cumulative_render_score += amount
       raise_limits_reached if @render_score_limit && @render_score > @render_score_limit
+      raise_limits_reached if @cumulative_render_score_limit && @cumulative_render_score > @cumulative_render_score_limit
     end
 
     def increment_assign_score(amount)
       @assign_score += amount
+      @cumulative_assign_score += amount
       raise_limits_reached if @assign_score_limit && @assign_score > @assign_score_limit
+      raise_limits_reached if @cumulative_assign_score_limit && @cumulative_assign_score > @cumulative_assign_score_limit
     end
 
     # update either render_length or assign_score based on whether or not the writes are captured
@@ -47,6 +62,8 @@ module Liquid
       @reached_limit = false
       @last_capture_length = nil
       @render_score = @assign_score = 0
+      raise_limits_reached if @cumulative_render_score_limit && @cumulative_render_score > @cumulative_render_score_limit
+      raise_limits_reached if @cumulative_assign_score_limit && @cumulative_assign_score > @cumulative_assign_score_limit
     end
 
     def with_capture

lib/liquid/self_drop.rb

@@ -0,0 +1,54 @@
+# frozen_string_literal: true
+
+module Liquid
+  # @liquid_public_docs
+  # @liquid_type object
+  # @liquid_name self
+  # @liquid_summary
+  #   Provides access to variables through the current scope chain.
+  # @liquid_description
+  #   The `self` object resolves variables through the normal lookup hierarchy
+  #   (local > file > global) without exposing filters, interrupts, errors,
+  #   or other context internals. It's used when bare bracket notation
+  #   (`['variable']`) needs to be replaced with an explicit variable lookup.
+  #
+  #   If `self` is explicitly assigned as a local variable (e.g. `{% assign self = 'value' %}`),
+  #   then the local value takes precedence over the `self` object.
+  # @liquid_access global
+  class SelfDrop < Drop
+    def initialize(self_context)
+      super()
+      @self_context = self_context
+    end
+
+    def [](key)
+      @self_context.find_variable(key)
+    rescue UndefinedVariable
+      nil
+    end
+
+    def key?(key)
+      @self_context.variable_defined?(key)
+    end
+
+    def to_liquid
+      self
+    end
+
+    def ==(other)
+      other.is_a?(SelfDrop) && other.self_context.equal?(@self_context)
+    end
+
+    alias_method :eql?, :==
+
+    def hash
+      @self_context.object_id.hash
+    end
+
+    protected
+
+    attr_reader :self_context
+
+    undef context=
+  end
+end

lib/liquid/standardfilters.rb

@@ -8,10 +8,19 @@ module Liquid
     MAX_I32 = (1 << 31) - 1
     private_constant :MAX_I32
 
-    MIN_I64 = -(1 << 63)
-    MAX_I64 = (1 << 63) - 1
-    I64_RANGE = MIN_I64..MAX_I64
-    private_constant :MIN_I64, :MAX_I64, :I64_RANGE
+    supports_64bit_indices = begin
+      [][1 << 33, 1 << 33]
+      true
+    rescue RangeError
+      false
+    end
+
+    INDEX_RANGE = if supports_64bit_indices
+      (-(1 << 63))..((1 << 63) - 1)
+    else
+      (-(1 << 31))..((1 << 31) - 1)
+    end
+    private_constant :INDEX_RANGE
 
     HTML_ESCAPE = {
       '&' => '&amp;',
@@ -214,11 +223,11 @@ module Liquid
           Utils.to_s(input).slice(offset, length) || ''
         end
       rescue RangeError
-        if I64_RANGE.cover?(length) && I64_RANGE.cover?(offset)
+        if INDEX_RANGE.cover?(length) && INDEX_RANGE.cover?(offset)
           raise # unexpected error
         end
-        offset = offset.clamp(I64_RANGE)
-        length = length.clamp(I64_RANGE)
+        offset = offset.clamp(INDEX_RANGE)
+        length = length.clamp(INDEX_RANGE)
         retry
       end
     end
@@ -293,6 +302,19 @@ module Liquid
       input.split(pattern)
     end
 
+    # @liquid_public_docs
+    # @liquid_type filter
+    # @liquid_category string
+    # @liquid_summary
+    #   Removes leading and trailing whitespace and collapses consecutive whitespace to a single space.
+    # @liquid_syntax string | squish
+    # @liquid_return [string]
+    def squish(input)
+      return if input.nil?
+
+      Utils.to_s(input).strip.gsub(/\s+/, ' ')
+    end
+
     # @liquid_public_docs
     # @liquid_type filter
     # @liquid_category string

lib/liquid/tags.rb

@@ -7,6 +7,8 @@ require_relative "tags/break"
 require_relative "tags/inline_comment"
 require_relative "tags/for"
 require_relative "tags/assign"
+require_relative "tags/let"
+require_relative "tags/set"
 require_relative "tags/ifchanged"
 require_relative "tags/case"
 require_relative "tags/include"
@@ -37,6 +39,8 @@ module Liquid
       'case' => Case,
       'ifchanged' => Ifchanged,
       'assign' => Assign,
+      'let' => Let,
+      'set' => SetTag,
       'for' => For,
       '#' => InlineComment,
       'break' => Break,

lib/liquid/tags/assign.rb

@@ -18,6 +18,8 @@ module Liquid
   # @liquid_syntax_keyword variable_name The name of the variable being created.
   # @liquid_syntax_keyword value The value you want to assign to the variable.
   class Assign < Tag
+    include ParserSwitching
+
     Syntax = /(#{VariableSignature}+)\s*=\s*(.*)\s*/om
 
     # @api private
@@ -29,6 +31,12 @@ module Liquid
 
     def initialize(tag_name, markup, parse_context)
       super
+      raise SyntaxError, "assign is not allowed in closure bodies" if parse_context.in_closure?
+
+      parse_with_selected_parser(markup)
+    end
+
+    def lax_parse(markup)
       if markup =~ Syntax
         @to   = Regexp.last_match(1)
         @from = Variable.new(Regexp.last_match(2), parse_context)
@@ -37,10 +45,29 @@ module Liquid
       end
     end
 
+    def strict_parse(markup)
+      lax_parse(markup)
+    end
+
+    def strict2_parse(markup)
+      unless markup =~ Syntax
+        self.class.raise_syntax_error(parse_context)
+      end
+
+      lhs = Regexp.last_match(1).strip
+      rhs = Regexp.last_match(2)
+
+      p = @parse_context.new_parser(lhs)
+      @to = p.consume(:id)
+      p.consume(:end_of_string)
+
+      @from = Variable.new(rhs, parse_context)
+    end
+
     def render_to_output_buffer(context, output)
       val = @from.render(context)
       context.scopes.last[@to] = val
-      context.resource_limits.increment_assign_score(assign_score_of(val))
+      context.resource_limits.increment_assign_score(self.class.assign_score_of(val))
       output
     end
 
@@ -48,9 +75,8 @@ module Liquid
       true
     end
 
-    private
-
-    def assign_score_of(val)
+    # @api private
+    def self.assign_score_of(val)
       if val.instance_of?(String)
         val.bytesize
       elsif val.instance_of?(Array)

lib/liquid/tags/capture.rb

@@ -20,10 +20,18 @@ module Liquid
   # @liquid_syntax_keyword variable The name of the variable being created.
   # @liquid_syntax_keyword value The value you want to assign to the variable.
   class Capture < Block
+    include ParserSwitching
+
     Syntax = /(#{VariableSignature}+)/o
 
+    attr_reader :to
+
     def initialize(tag_name, markup, options)
       super
+      parse_with_selected_parser(markup)
+    end
+
+    def lax_parse(markup)
       if markup =~ Syntax
         @to = Regexp.last_match(1)
       else
@@ -31,6 +39,16 @@ module Liquid
       end
     end
 
+    def strict_parse(markup)
+      lax_parse(markup)
+    end
+
+    def strict2_parse(markup)
+      p = @parse_context.new_parser(markup.strip)
+      @to = p.consume(:id)
+      p.consume(:end_of_string)
+    end
+
     def render_to_output_buffer(context, output)
       context.resource_limits.with_capture do
         capture_output = render(context)

lib/liquid/tags/case.rb

@@ -23,6 +23,9 @@ module Liquid
   # @liquid_syntax_keyword second_expression An expression to be rendered when the variable's value matches `second_value`.
   # @liquid_syntax_keyword third_expression An expression to be rendered when the variable's value has no match.
   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)
@@ -83,19 +86,35 @@ module Liquid
 
     private
 
-    def parse_markup(markup)
+    def strict2_parse(markup)
       parser = @parse_context.new_parser(markup)
       @left = safe_parse_expression(parser)
       parser.consume(:end_of_string)
     end
 
+    def strict_parse(markup)
+      lax_parse(markup)
+    end
+
+    def lax_parse(markup)
+      if markup =~ Syntax
+        @left = parse_expression(Regexp.last_match(1))
+      else
+        raise SyntaxError, options[:locale].t("errors.syntax.case")
+      end
+    end
+
     def record_when_condition(markup)
       body = new_body
 
-      parse_when(markup, body)
+      if strict2_mode?
+        parse_strict2_when(markup, body)
+      else
+        parse_lax_when(markup, body)
+      end
     end
 
-    def parse_when(markup, body)
+    def parse_strict2_when(markup, body)
       parser = @parse_context.new_parser(markup)
 
       loop do
@@ -110,6 +129,20 @@ module Liquid
       parser.consume(:end_of_string)
     end
 
+    def parse_lax_when(markup, body)
+      while markup
+        unless markup =~ WhenSyntax
+          raise SyntaxError, options[:locale].t("errors.syntax.case_invalid_when")
+        end
+
+        markup = Regexp.last_match(2)
+
+        block = Condition.new(@left, '==', Condition.parse_expression(parse_context, Regexp.last_match(1)))
+        block.attach(body)
+        @blocks << block
+      end
+    end
+
     def record_else_condition(markup)
       unless markup.strip.empty?
         raise SyntaxError, options[:locale].t("errors.syntax.case_invalid_else")

lib/liquid/tags/cycle.rb

@@ -15,6 +15,8 @@ module Liquid
   # @liquid_syntax
   #   {% cycle string, string, ... %}
   class Cycle < Tag
+    SimpleSyntax = /\A#{QuotedFragment}+/o
+    NamedSyntax  = /\A(#{QuotedFragment})\s*\:\s*(.*)/om
     UNNAMED_CYCLE_PATTERN = /\w+:0x\h{8}/
 
     attr_reader :variables
@@ -54,7 +56,7 @@ module Liquid
     private
 
     # cycle [name:] expression(, expression)*
-    def parse_markup(markup)
+    def strict2_parse(markup)
       p = @parse_context.new_parser(markup)
 
       @variables = []
@@ -89,6 +91,35 @@ module Liquid
       end
     end
 
+    def strict_parse(markup)
+      lax_parse(markup)
+    end
+
+    def lax_parse(markup)
+      case markup
+      when NamedSyntax
+        @variables = variables_from_string(Regexp.last_match(2))
+        @name      = parse_expression(Regexp.last_match(1))
+        @is_named = true
+      when SimpleSyntax
+        @variables = variables_from_string(markup)
+        @name      = @variables.to_s
+        @is_named = !@name.match?(UNNAMED_CYCLE_PATTERN)
+      else
+        raise SyntaxError, options[:locale].t("errors.syntax.cycle")
+      end
+    end
+
+    def variables_from_string(markup)
+      markup.split(',').collect do |var|
+        var =~ /\s*(#{QuotedFragment})\s*/o
+        next unless Regexp.last_match(1)
+
+        var = parse_expression(Regexp.last_match(1))
+        maybe_dup_lookup(var)
+      end.compact
+    end
+
     # For backwards compatibility, whenever a lookup is used in an unnamed cycle,
     # we make it so that the @variables.to_s produces different strings for cycles
     # called with the same arguments (since @variables.to_s is used as the cycle counter key)

lib/liquid/tags/decrement.rb

@@ -23,13 +23,29 @@ module Liquid
   #   {% decrement variable_name %}
   # @liquid_syntax_keyword variable_name The name of the variable being decremented.
   class Decrement < Tag
+    include ParserSwitching
+
     attr_reader :variable_name
 
     def initialize(tag_name, markup, options)
       super
+      parse_with_selected_parser(markup)
+    end
+
+    def lax_parse(markup)
       @variable_name = markup.strip
     end
 
+    def strict_parse(markup)
+      lax_parse(markup)
+    end
+
+    def strict2_parse(markup)
+      p = @parse_context.new_parser(markup.strip)
+      @variable_name = p.consume(:id)
+      p.consume(:end_of_string)
+    end
+
     def render_to_output_buffer(context, output)
       counter_environment = context.environments.first
       value = counter_environment[@variable_name] || 0

lib/liquid/tags/for.rb

@@ -25,6 +25,8 @@ module Liquid
   # @liquid_optional_param range [untyped] A custom numeric range to iterate over.
   # @liquid_optional_param reversed [untyped] Iterate in reverse order.
   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)
@@ -36,15 +38,10 @@ module Liquid
     end
 
     def parse(tokens)
-      if parse_body(@for_block, tokens)
-        parse_body(@else_block, tokens)
+      parse_context.with_lexical_scope do
+        parse_loop(tokens)
+        @has_local_declarations = parse_context.local_declarations?
       end
-      if blank?
-        @else_block&.remove_blank_strings
-        @for_block.remove_blank_strings
-      end
-      @else_block&.freeze
-      @for_block.freeze
     end
 
     def nodelist
@@ -70,15 +67,30 @@ module Liquid
 
     protected
 
-    def parse_markup(markup)
+    def lax_parse(markup)
+      if markup =~ Syntax
+        @variable_name   = Regexp.last_match(1)
+        collection_name  = Regexp.last_match(2)
+        @reversed        = !!Regexp.last_match(3)
+        @name            = "#{@variable_name}-#{collection_name}"
+        @collection_name = parse_expression(collection_name)
+        markup.scan(TagAttributes) do |key, value|
+          set_attribute(key, value)
+        end
+      else
+        raise SyntaxError, options[:locale].t("errors.syntax.for")
+      end
+    end
+
+    def strict_parse(markup)
       p = @parse_context.new_parser(markup)
       @variable_name = p.consume(:id)
       raise SyntaxError, options[:locale].t("errors.syntax.for_invalid_in") unless p.id?('in')
 
-      collection_name  = p.expression
+      collection_name, collection_markup = p.expression_with_markup
       @collection_name = parse_expression(collection_name, safe: true)
 
-      @name     = "#{@variable_name}-#{collection_name}"
+      @name     = "#{@variable_name}-#{collection_markup}"
       @reversed = p.id?('reversed')
 
       while p.look(:comma) || p.look(:id)
@@ -94,6 +106,22 @@ module Liquid
 
     private
 
+    def parse_loop(tokens)
+      if parse_body(@for_block, tokens)
+        parse_body(@else_block, tokens)
+      end
+      if blank?
+        @else_block&.remove_blank_strings
+        @for_block.remove_blank_strings
+      end
+      @else_block&.freeze
+      @for_block.freeze
+    end
+
+    def strict2_parse(markup)
+      strict_parse(markup)
+    end
+
     def collection_segment(context)
       offsets = context.registers[:for] ||= {}
 
@@ -140,7 +168,7 @@ module Liquid
 
           segment.each do |item|
             context[@variable_name] = item
-            @for_block.render_to_output_buffer(context, output)
+            render_iteration(context, output)
             loop_vars.send(:increment!)
 
             # Handle any interrupts if they exist.
@@ -157,6 +185,12 @@ module Liquid
       output
     end
 
+    def render_iteration(context, output)
+      return @for_block.render_to_output_buffer(context, output) unless @has_local_declarations
+
+      context.stack { @for_block.render_to_output_buffer(context, output) }
+    end
+
     def set_attribute(key, expr, safe: false)
       case key
       when 'offset'
@@ -171,11 +205,10 @@ module Liquid
     end
 
     def render_else(context, output)
-      if @else_block
-        @else_block.render_to_output_buffer(context, output)
-      else
-        output
-      end
+      return output unless @else_block
+      return @else_block.render_to_output_buffer(context, output) unless @has_local_declarations
+
+      context.stack { @else_block.render_to_output_buffer(context, output) }
     end
 
     class ParseTreeVisitor < Liquid::ParseTreeVisitor

lib/liquid/tags/if.rb

@@ -14,6 +14,10 @@ module Liquid
   # @liquid_syntax_keyword condition The condition to evaluate.
   # @liquid_syntax_keyword expression The expression to render if the condition is met.
   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).freeze
+
     attr_reader :blocks
 
     def initialize(tag_name, markup, options)
@@ -62,6 +66,10 @@ module Liquid
 
     private
 
+    def strict2_parse(markup)
+      strict_parse(markup)
+    end
+
     def push_block(tag, markup)
       block = if tag == 'else'
         ElseCondition.new
@@ -77,7 +85,27 @@ module Liquid
       Condition.parse_expression(parse_context, markup, safe: safe)
     end
 
-    def parse_markup(markup)
+    def lax_parse(markup)
+      expressions = markup.scan(ExpressionsAndOperators)
+      raise SyntaxError, options[:locale].t("errors.syntax.if") unless expressions.pop =~ Syntax
+
+      condition = Condition.new(parse_expression(Regexp.last_match(1)), Regexp.last_match(2), parse_expression(Regexp.last_match(3)))
+
+      until expressions.empty?
+        operator = expressions.pop.to_s.strip
+
+        raise SyntaxError, options[:locale].t("errors.syntax.if") unless expressions.pop.to_s =~ Syntax
+
+        new_condition = Condition.new(parse_expression(Regexp.last_match(1)), Regexp.last_match(2), parse_expression(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
+
+      condition
+    end
+
+    def strict_parse(markup)
       p = @parse_context.new_parser(markup)
       condition = parse_binary_comparisons(p)
       p.consume(:end_of_string)

lib/liquid/tags/include.rb

@@ -20,6 +20,10 @@ module Liquid
   class Include < Tag
     prepend Tag::Disableable
 
+    FOR = 'for'
+    SYNTAX = /(#{QuotedFragment}+)(\s+(with|#{FOR})\s+(#{QuotedFragment}+))?(\s+(?:as)\s+(#{VariableSegment}+))?/o
+    Syntax = SYNTAX
+
     attr_reader :template_name_expr, :variable_name_expr, :attributes
 
     def initialize(tag_name, markup, options)
@@ -81,12 +85,18 @@ module Liquid
     alias_method :parse_context, :options
     private :parse_context
 
-    def parse_markup(markup)
+    def for_loop?
+      @is_for_loop
+    end
+
+    def strict2_parse(markup)
       p = @parse_context.new_parser(markup)
 
       @template_name_expr = safe_parse_expression(p)
-      @variable_name_expr = safe_parse_expression(p) if p.id?("for") || p.id?("with")
+      with_or_for         = p.id?("for") || p.id?("with")
+      @variable_name_expr = safe_parse_expression(p) if with_or_for
       @alias_name         = p.consume(:id) if p.id?("as")
+      @is_for_loop        = (with_or_for == FOR)
 
       p.consume?(:comma)
 
@@ -101,6 +111,31 @@ module Liquid
       p.consume(:end_of_string)
     end
 
+    def strict_parse(markup)
+      lax_parse(markup)
+    end
+
+    def lax_parse(markup)
+      if markup =~ SYNTAX
+        template_name = Regexp.last_match(1)
+        with_or_for   = Regexp.last_match(3)
+        variable_name = Regexp.last_match(4)
+
+        @alias_name         = Regexp.last_match(6)
+        @variable_name_expr = variable_name ? parse_expression(variable_name) : nil
+        @template_name_expr = parse_expression(template_name)
+        @is_for_loop        = (with_or_for == FOR)
+        @attributes         = {}
+
+        markup.scan(TagAttributes) do |key, value|
+          @attributes[key] = parse_expression(value)
+        end
+
+      else
+        raise SyntaxError, options[:locale].t("errors.syntax.include")
+      end
+    end
+
     class ParseTreeVisitor < Liquid::ParseTreeVisitor
       def children
         [

lib/liquid/tags/increment.rb

@@ -23,13 +23,29 @@ module Liquid
   #   {% increment variable_name %}
   # @liquid_syntax_keyword variable_name The name of the variable being incremented.
   class Increment < Tag
+    include ParserSwitching
+
     attr_reader :variable_name
 
     def initialize(tag_name, markup, options)
       super
+      parse_with_selected_parser(markup)
+    end
+
+    def lax_parse(markup)
       @variable_name = markup.strip
     end
 
+    def strict_parse(markup)
+      lax_parse(markup)
+    end
+
+    def strict2_parse(markup)
+      p = @parse_context.new_parser(markup.strip)
+      @variable_name = p.consume(:id)
+      p.consume(:end_of_string)
+    end
+
     def render_to_output_buffer(context, output)
       counter_environment = context.environments.first
       value = counter_environment[@variable_name] || 0

lib/liquid/tags/let.rb

@@ -0,0 +1,54 @@
+# frozen_string_literal: true
+
+module Liquid
+  class Let < Block
+    attr_reader :to, :from, :parameters, :closure_body
+
+    def initialize(tag_name, markup, parse_context)
+      super
+      parse_context.require_closures!
+      parser = parse_context.new_parser(markup)
+      @to = parser.consume(:id)
+      if parser.consume?(:assign)
+        raise SyntaxError, "Expected let initializer" if parser.look(:end_of_string)
+
+        @from = Variable.new(parser, parse_context)
+      else
+        @parameters = parser.parameters.freeze
+        parser.consume(:end_of_string)
+      end
+      parse_context.declare_local(@to)
+    end
+
+    def parse(tokens)
+      return unless body_form?
+
+      @closure_body = parse_closure_body(tokens, parameters: @parameters)
+    end
+
+    def body_form?
+      @from.nil?
+    end
+
+    def nodelist
+      body_form? ? super : Const::EMPTY_ARRAY
+    end
+
+    def render_to_output_buffer(context, output)
+      value = body_form? ? @closure_body.bind(context) : @from.render(context)
+      context.resource_limits.increment_assign_score(Assign.assign_score_of(value))
+      context[@to] = value
+      output
+    end
+
+    def blank?
+      true
+    end
+
+    class ParseTreeVisitor < Liquid::ParseTreeVisitor
+      def children
+        @node.body_form? ? [@node.closure_body] : [@node.from]
+      end
+    end
+  end
+end

lib/liquid/tags/render.rb

@@ -27,6 +27,7 @@ module Liquid
   # @liquid_syntax_keyword filename The name of the snippet to render, without the `.liquid` extension.
   class Render < Tag
     FOR = 'for'
+    SYNTAX = /(#{QuotedString}+)(\s+(with|#{FOR})\s+(#{QuotedFragment}+))?(\s+(?:as)\s+(#{VariableSegment}+))?/o
 
     disable_tags "include"
 
@@ -84,10 +85,10 @@ module Liquid
     end
 
     # render (string) (with|for expression)? (as id)? (key: value)*
-    def parse_markup(markup)
+    def strict2_parse(markup)
       p = @parse_context.new_parser(markup)
 
-      @template_name_expr = parse_expression(template_name(p), safe: true)
+      @template_name_expr = parse_expression(strict2_template_name(p), safe: true)
       with_or_for         = p.id?("for") || p.id?("with")
       @variable_name_expr = safe_parse_expression(p) if with_or_for
       @alias_name         = p.consume(:id) if p.id?("as")
@@ -106,10 +107,32 @@ module Liquid
       p.consume(:end_of_string)
     end
 
-    def template_name(p)
+    def strict2_template_name(p)
       p.consume(:string)
     end
 
+    def strict_parse(markup)
+      lax_parse(markup)
+    end
+
+    def lax_parse(markup)
+      raise SyntaxError, options[:locale].t("errors.syntax.render") unless markup =~ SYNTAX
+
+      template_name = Regexp.last_match(1)
+      with_or_for = Regexp.last_match(3)
+      variable_name = Regexp.last_match(4)
+
+      @alias_name = Regexp.last_match(6)
+      @variable_name_expr = variable_name ? parse_expression(variable_name) : nil
+      @template_name_expr = parse_expression(template_name)
+      @is_for_loop = (with_or_for == FOR)
+
+      @attributes = {}
+      markup.scan(TagAttributes) do |key, value|
+        @attributes[key] = parse_expression(value)
+      end
+    end
+
     class ParseTreeVisitor < Liquid::ParseTreeVisitor
       def children
         [

lib/liquid/tags/set.rb

@@ -0,0 +1,39 @@
+# frozen_string_literal: true
+
+module Liquid
+  class SetTag < Tag
+    attr_reader :to, :from
+
+    def initialize(tag_name, markup, parse_context)
+      super
+      parse_context.require_closures!
+      parser = parse_context.new_parser(markup)
+      @to = parser.consume(:id)
+      parser.consume(:assign)
+      raise SyntaxError, "Expected set initializer" if parser.look(:end_of_string)
+
+      @from = Variable.new(parser, parse_context)
+    end
+
+    def render_to_output_buffer(context, output)
+      value = if context.variable_defined?(@to)
+        @from.render(context)
+      else
+        context.stack(@to => nil) { @from.render(context) }
+      end
+      context.resource_limits.increment_assign_score(Assign.assign_score_of(value))
+      context.set_local(@to, value)
+      output
+    end
+
+    def blank?
+      true
+    end
+
+    class ParseTreeVisitor < Liquid::ParseTreeVisitor
+      def children
+        [@node.from]
+      end
+    end
+  end
+end

lib/liquid/tags/table_row.rb

@@ -24,6 +24,7 @@ module Liquid
   # @liquid_optional_param offset: [number] The 1-based index to start iterating at.
   # @liquid_optional_param range [untyped] A custom numeric range to iterate over.
   class TableRow < Block
+    Syntax = /(\w+)\s+in\s+(#{QuotedFragment}+)/o
     ALLOWED_ATTRIBUTES = ['cols', 'limit', 'offset', 'range'].freeze
 
     attr_reader :variable_name, :collection_name, :attributes
@@ -33,7 +34,14 @@ module Liquid
       parse_with_selected_parser(markup)
     end
 
-    def parse_markup(markup)
+    def parse(tokens)
+      parse_context.with_lexical_scope do
+        super
+        @has_local_declarations = parse_context.local_declarations?
+      end
+    end
+
+    def strict2_parse(markup)
       p = @parse_context.new_parser(markup)
 
       @variable_name = p.consume(:id)
@@ -61,6 +69,23 @@ module Liquid
       p.consume(:end_of_string)
     end
 
+    def strict_parse(markup)
+      lax_parse(markup)
+    end
+
+    def lax_parse(markup)
+      if markup =~ Syntax
+        @variable_name   = Regexp.last_match(1)
+        @collection_name = parse_expression(Regexp.last_match(2))
+        @attributes      = {}
+        markup.scan(TagAttributes) do |key, value|
+          @attributes[key] = parse_expression(value)
+        end
+      else
+        raise SyntaxError, options[:locale].t("errors.syntax.table_row")
+      end
+    end
+
     def render_to_output_buffer(context, output)
       (collection = context.evaluate(@collection_name)) || (return '')
 
@@ -81,7 +106,11 @@ module Liquid
           context[@variable_name] = item
 
           output << "<td class=\"col#{tablerowloop.col}\">"
-          super
+          if @has_local_declarations
+            context.stack { super }
+          else
+            super
+          end
           output << '</td>'
 
           # Handle any interrupts if they exist.

lib/liquid/template.rb

@@ -16,11 +16,25 @@ module Liquid
   #
   class Template
     attr_accessor :root, :name
-    attr_reader :resource_limits
+    attr_reader :resource_limits, :warnings
 
     attr_reader :profiler
 
     class << self
+      # Sets how strict the parser should be.
+      # :lax acts like liquid 2.5 and silently ignores malformed tags in most cases.
+      # :warn is the default and will give deprecation warnings when invalid syntax is used.
+      # :strict enforces correct syntax for most tags
+      # :strict2 enforces correct syntax for all tags
+      def error_mode=(mode)
+        Deprecations.warn("Template.error_mode=", "Environment#error_mode=")
+        Environment.default.error_mode = mode
+      end
+
+      def error_mode
+        Environment.default.error_mode
+      end
+
       def default_exception_renderer=(renderer)
         Deprecations.warn("Template.default_exception_renderer=", "Environment#exception_renderer=")
         Environment.default.exception_renderer = renderer
@@ -137,8 +151,10 @@ module Liquid
 
         c
       when Liquid::Drop
-        drop         = args.shift
-        drop.context = Context.new([drop, assigns], instance_assigns, registers, @rethrow_errors, @resource_limits, {}, @environment)
+        drop = args.shift
+        c    = Context.new([drop, assigns], instance_assigns, registers, @rethrow_errors, @resource_limits, {}, @environment)
+        drop.context = c if drop.respond_to?(:context=)
+        c
       when Hash
         Context.new([args.shift, assigns], instance_assigns, registers, @rethrow_errors, @resource_limits, {}, @environment)
       when nil
@@ -173,12 +189,20 @@ module Liquid
 
       context.template_name ||= name
 
+      previous_error_mode = context.registers.static[:template_error_mode]
+      context.registers.static[:template_error_mode] = @error_mode
+
       begin
         # render the nodelist.
         @root.render_to_output_buffer(context, output || +'')
       rescue Liquid::MemoryError => e
         context.handle_error(e)
       ensure
+        if previous_error_mode
+          context.registers.static[:template_error_mode] = previous_error_mode
+        else
+          context.registers.static.delete(:template_error_mode)
+        end
         @errors = context.errors
       end
     end
@@ -209,6 +233,8 @@ module Liquid
         ParseContext.new(opts)
       end
 
+      @warnings = parse_context.warnings
+      @error_mode = parse_context.error_mode
       parse_context
     end
 

lib/liquid/variable.rb

@@ -25,33 +25,79 @@ module Liquid
     include ParserSwitching
 
     def initialize(markup, parse_context)
-      @markup        = markup
+      @markup        = markup.is_a?(Parser) ? markup.remaining_markup : markup
       @name          = nil
       @parse_context = parse_context
       @line_number   = parse_context.line_number
 
-      parse_with_selected_parser(markup)
+      strict_parse_with_error_mode_fallback(markup)
     end
 
     def raw
       @markup
     end
 
+    def ==(other)
+      self.class == other.class && name == other.name && filters == other.filters
+    end
+
     def markup_context(markup)
+      markup = @markup if markup.is_a?(Parser)
       "in \"{{#{markup}}}\""
     end
 
-    def parse_markup(markup)
+    def lax_parse(markup)
+      @filters = []
+      return unless markup =~ MarkupWithQuotedFragment
+
+      name_markup   = Regexp.last_match(1)
+      filter_markup = Regexp.last_match(2)
+      @name         = parse_context.parse_expression(name_markup)
+      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(FilterArgsRegex).flatten
+          @filters << lax_parse_filter_expressions(filtername, filterargs)
+        end
+      end
+    end
+
+    def strict_parse(markup)
       @filters = []
       p = @parse_context.new_parser(markup)
 
       return if p.look(:end_of_string)
 
       @name = parse_context.safe_parse_expression(p)
-      @filters << parse_filter_expressions(p) while p.consume?(:pipe)
+      while p.consume?(:pipe)
+        filtername = p.consume(:id)
+        filterargs = p.consume?(:colon) ? parse_filterargs(p) : Const::EMPTY_ARRAY
+        @filters << lax_parse_filter_expressions(filtername, filterargs)
+      end
       p.consume(:end_of_string)
     end
 
+    def strict2_parse(markup)
+      @filters = []
+      p = markup.is_a?(Parser) ? markup : @parse_context.new_parser(markup)
+
+      return if p.look(:end_of_string)
+
+      @name = parse_context.safe_parse_expression(p)
+      @filters << strict2_parse_filter_expressions(p) while p.consume?(:pipe)
+      p.consume(:end_of_string)
+    end
+
+    def parse_filterargs(p)
+      # first argument
+      filterargs = [p.argument]
+      # followed by comma separated others
+      filterargs << p.argument while p.consume?(:comma)
+      filterargs
+    end
+
     def render(context)
       obj = context.evaluate(@name)
 
@@ -64,6 +110,10 @@ module Liquid
     end
 
     def render_to_output_buffer(context, output)
+      if @name.is_a?(CallExpression) && @filters.empty? && context.global_filter.nil?
+        return @name.render_to_output_buffer(context, output)
+      end
+
       obj = render(context)
       render_obj_to_output(obj, output)
       output
@@ -92,6 +142,22 @@ module Liquid
 
     private
 
+    def lax_parse_filter_expressions(filter_name, unparsed_args)
+      filter_args  = []
+      keyword_args = nil
+      unparsed_args.each do |a|
+        if (matches = a.match(JustTagAttributes))
+          keyword_args           ||= {}
+          keyword_args[matches[1]] = parse_context.parse_expression(matches[2])
+        else
+          filter_args << parse_context.parse_expression(a)
+        end
+      end
+      result = [filter_name, filter_args]
+      result << keyword_args if keyword_args
+      result
+    end
+
     # Surprisingly, positional and keyword arguments can be mixed.
     #
     # filter = filtername [":" filterargs?]
@@ -99,7 +165,7 @@ module Liquid
     # argument = (positional_argument | keyword_argument)
     # positional_argument = expression
     # keyword_argument = id ":" expression
-    def parse_filter_expressions(p)
+    def strict2_parse_filter_expressions(p)
       filtername = p.consume(:id)
       filter_args = []
       keyword_args = {}
@@ -146,7 +212,7 @@ module Liquid
 
     class ParseTreeVisitor < Liquid::ParseTreeVisitor
       def children
-        [@node.name] + @node.filters.flatten
+        [@node.name] + @node.filters.flatten.flat_map { |value| value.is_a?(Hash) ? value.values : value }
       end
     end
   end

lib/liquid/variable_lookup.rb

@@ -40,6 +40,12 @@ module Liquid
       end
     end
 
+    # @api private
+    def add_lookup(key, command: false)
+      @command_flags |= 1 << @lookups.length if command && COMMAND_METHODS.include?(key)
+      @lookups << key
+    end
+
     def lookup_command?(lookup_index)
       @command_flags & (1 << lookup_index) != 0
     end

lib/liquid/version.rb

@@ -2,5 +2,5 @@
 # frozen_string_literal: true
 
 module Liquid
-  VERSION = "5.11.0"
+  VERSION = "5.13.0"
 end

performance/benchmark.rb

@@ -4,6 +4,7 @@ require 'benchmark/ips'
 require_relative 'theme_runner'
 
 RubyVM::YJIT.enable if defined?(RubyVM::YJIT)
+Liquid::Environment.default.error_mode = ARGV.first.to_sym if ARGV.first
 
 profiler = ThemeRunner.new
 

performance/memory_profile.rb

@@ -53,6 +53,8 @@ class Profiler
   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 }

performance/profile.rb

@@ -3,6 +3,7 @@
 require 'stackprof'
 require_relative 'theme_runner'
 
+Liquid::Template.error_mode = ARGV.first.to_sym if ARGV.first
 profiler = ThemeRunner.new
 profiler.run
 

spec/ruby_liquid.rb

@@ -6,14 +6,24 @@
 
 $LOAD_PATH.unshift(File.expand_path('../lib', __dir__))
 require 'liquid'
+require_relative 'support/liquid_spec_adapter_helper'
 
 LiquidSpec.configure do |config|
-  # Run core Liquid specs
-  config.features = [:core]
+  config.missing_features = [
+    :activesupport,
+    :lax_parsing,
+    :shopify_filters,
+    :shopify_includes,
+    :shopify_blank,
+    :shopify_error_handling,
+    :shopify_error_format,
+    :shopify_string_access,
+  ]
 end
 
 # Compile a template string into a Liquid::Template
 LiquidSpec.compile do |ctx, source, options|
+  options[:error_mode] ||= :strict
   ctx[:template] = Liquid::Template.parse(source, **options)
 end
 
@@ -28,9 +38,12 @@ LiquidSpec.render do |ctx, assigns, options|
     static_environments: assigns,
     registers: registers,
     rethrow_errors: options[:strict_errors],
+    resource_limits: LiquidSpecAdapterHelper.resource_limits(options),
   )
 
   context.exception_renderer = options[:exception_renderer] if options[:exception_renderer]
 
-  ctx[:template].render(context)
+  LiquidSpecAdapterHelper.with_frozen_time do
+    ctx[:template].render(context)
+  end
 end

spec/ruby_liquid_lax.rb

@@ -0,0 +1,46 @@
+# frozen_string_literal: true
+
+# Liquid Spec Adapter for Shopify/liquid with lax parsing mode
+#
+# Run with: bundle exec liquid-spec run spec/ruby_liquid_lax.rb
+
+$LOAD_PATH.unshift(File.expand_path('../lib', __dir__))
+require 'liquid'
+require_relative 'support/liquid_spec_adapter_helper'
+
+LiquidSpec.configure do |config|
+  config.missing_features = [
+    :activesupport,
+    :shopify_filters,
+    :shopify_includes,
+    :shopify_blank,
+    :shopify_error_handling,
+    :shopify_error_format,
+    :shopify_string_access,
+  ]
+end
+
+# Compile a template string into a Liquid::Template
+LiquidSpec.compile do |ctx, source, options|
+  # Default to lax mode while still honoring specs that explicitly set error_mode.
+  options = { error_mode: :lax }.merge(options)
+  ctx[:template] = Liquid::Template.parse(source, **options)
+end
+
+# Render a compiled template with the given context
+LiquidSpec.render do |ctx, assigns, options|
+  registers = Liquid::Registers.new(options[:registers] || {})
+
+  context = Liquid::Context.build(
+    static_environments: assigns,
+    registers: registers,
+    rethrow_errors: options[:strict_errors],
+    resource_limits: LiquidSpecAdapterHelper.resource_limits(options),
+  )
+
+  context.exception_renderer = options[:exception_renderer] if options[:exception_renderer]
+
+  LiquidSpecAdapterHelper.with_frozen_time do
+    ctx[:template].render(context)
+  end
+end

spec/ruby_liquid_with_active_support.rb

@@ -7,14 +7,23 @@
 $LOAD_PATH.unshift(File.expand_path('../lib', __dir__))
 require 'active_support/all'
 require 'liquid'
+require_relative 'support/liquid_spec_adapter_helper'
 
 LiquidSpec.configure do |config|
-  # Run core Liquid specs plus ActiveSupport SafeBuffer tests
-  config.features = [:core, :activesupport]
+  config.missing_features = [
+    :lax_parsing,
+    :shopify_filters,
+    :shopify_includes,
+    :shopify_blank,
+    :shopify_error_handling,
+    :shopify_error_format,
+    :shopify_string_access,
+  ]
 end
 
 # Compile a template string into a Liquid::Template
 LiquidSpec.compile do |ctx, source, options|
+  options[:error_mode] ||= :strict
   ctx[:template] = Liquid::Template.parse(source, **options)
 end
 
@@ -29,9 +38,12 @@ LiquidSpec.render do |ctx, assigns, options|
     static_environments: assigns,
     registers: registers,
     rethrow_errors: options[:strict_errors],
+    resource_limits: LiquidSpecAdapterHelper.resource_limits(options),
   )
 
   context.exception_renderer = options[:exception_renderer] if options[:exception_renderer]
 
-  ctx[:template].render(context)
+  LiquidSpecAdapterHelper.with_frozen_time do
+    ctx[:template].render(context)
+  end
 end

spec/ruby_liquid_yjit.rb

@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-# Liquid Spec Adapter for Shopify/liquid with YJIT + ActiveSupport
+# Liquid Spec Adapter for Shopify/liquid with YJIT + strict mode + ActiveSupport
 #
 # Run with: bundle exec liquid-spec run spec/ruby_liquid_yjit.rb
 
@@ -13,13 +13,24 @@ end
 
 require 'active_support/all'
 require 'liquid'
+require_relative 'support/liquid_spec_adapter_helper'
 
 LiquidSpec.configure do |config|
-  config.features = [:core, :activesupport]
+  config.missing_features = [
+    :lax_parsing,
+    :shopify_filters,
+    :shopify_includes,
+    :shopify_blank,
+    :shopify_error_handling,
+    :shopify_error_format,
+    :shopify_string_access,
+  ]
 end
 
 # Compile a template string into a Liquid::Template
 LiquidSpec.compile do |ctx, source, options|
+  # Force strict mode
+  options = { error_mode: :strict }.merge(options)
   ctx[:template] = Liquid::Template.parse(source, **options)
 end
 
@@ -31,9 +42,12 @@ LiquidSpec.render do |ctx, assigns, options|
     static_environments: assigns,
     registers: registers,
     rethrow_errors: options[:strict_errors],
+    resource_limits: LiquidSpecAdapterHelper.resource_limits(options),
   )
 
   context.exception_renderer = options[:exception_renderer] if options[:exception_renderer]
 
-  ctx[:template].render(context)
+  LiquidSpecAdapterHelper.with_frozen_time do
+    ctx[:template].render(context)
+  end
 end

spec/support/liquid_spec_adapter_helper.rb

@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+
+module LiquidSpecAdapterHelper
+  extend self
+
+  def resource_limits(render_options)
+    return unless render_options[:resource_limits]
+
+    Liquid::ResourceLimits.new({}).tap do |limits|
+      render_options[:resource_limits].each do |key, value|
+        limits.public_send(:"#{key}=", value)
+      end
+    end
+  end
+
+  def with_frozen_time(&block)
+    original_tz = ENV['TZ']
+    ENV['TZ'] = 'UTC'
+
+    Liquid::Spec::TimeFreezer.freeze(Liquid::Spec::AdapterRunner::TEST_TIME, &block)
+  ensure
+    ENV['TZ'] = original_tz
+  end
+end

test/integration/assign_test.rb

@@ -39,11 +39,13 @@ class AssignTest < Minitest::Test
     assert_match_syntax_error(/assign/, '{% assign foo not values %}.')
   end
 
-  def test_assign_throws_on_unsupported_syntax
+  def test_assign_uses_error_mode
     assert_match_syntax_error(
-      "Expected dotdot but found pipe",
+      "Expected dotdot but found pipe in ",
       "{% assign foo = ('X' | downcase) %}",
+      error_mode: :strict,
     )
+    assert_template_result("", "{% assign foo = ('X' | downcase) %}", error_mode: :lax)
   end
 
   def test_expression_with_whitespace_in_square_brackets
@@ -95,6 +97,46 @@ class AssignTest < Minitest::Test
     assert_equal(12, assign_score_of('int' => 123, 'str' => 'abcd'))
   end
 
+  def test_assign_with_valid_identifier_in_strict2
+    assert_template_result("hello", "{% assign my_var = 'hello' %}{{ my_var }}", error_mode: :strict2)
+  end
+
+  def test_assign_with_hyphen_in_strict2
+    assert_template_result("hello", "{% assign my-var = 'hello' %}{{ my-var }}", error_mode: :strict2)
+  end
+
+  def test_assign_rejects_parentheses_in_variable_name_in_strict2
+    assert_raises(Liquid::SyntaxError) do
+      Liquid::Template.parse("{% assign (a(b(c) = 1234 %}", error_mode: :strict2)
+    end
+  end
+
+  def test_assign_rejects_brackets_in_variable_name_in_strict2
+    assert_raises(Liquid::SyntaxError) do
+      Liquid::Template.parse("{% assign [x.y] = 'hello' %}", error_mode: :strict2)
+    end
+  end
+
+  def test_assign_rejects_dot_in_variable_name_in_strict2
+    assert_raises(Liquid::SyntaxError) do
+      Liquid::Template.parse("{% assign a.b = 'hello' %}", error_mode: :strict2)
+    end
+  end
+
+  def test_assign_rejects_numeric_variable_name_in_strict2
+    assert_raises(Liquid::SyntaxError) do
+      Liquid::Template.parse("{% assign 1abc = 'hello' %}", error_mode: :strict2)
+    end
+  end
+
+  def test_assign_allows_invalid_names_in_lax
+    assert_template_result("1234", "{% assign (a(b(c) = 1234 %}{{ self['(a(b(c)'] }}", error_mode: :lax)
+  end
+
+  def test_assign_with_filter_in_strict2
+    assert_template_result("HELLO", "{% assign my_var = 'hello' | upcase %}{{ my_var }}", error_mode: :strict2)
+  end
+
   private
 
   class ObjectWrapperDrop < Liquid::Drop

test/integration/blank_body_error_handling_test.rb

@@ -0,0 +1,85 @@
+# frozen_string_literal: true
+
+require 'test_helper'
+
+class BlankBodyErrorHandlingTest < Minitest::Test
+  COMPARISON_ERROR = 'Liquid error (line 1): comparison of Integer with String failed'
+  INVALID_INTEGER_ERROR = 'Liquid error (line 1): invalid integer'
+
+  def render_inline(source, error_mode:, assigns: {})
+    Liquid::Template.parse(source, line_numbers: true, error_mode: error_mode).render(assigns, render_errors: true)
+  end
+
+  def assert_render_raises(source, error_mode:, assigns: {}, message: nil)
+    error = assert_raises(Liquid::ArgumentError) do
+      Liquid::Template.parse(source, line_numbers: true, error_mode: error_mode).render!(assigns)
+    end
+    assert_includes(error.message, message) if message
+  end
+
+  def test_blank_if_body_suppresses_inline_error_text_in_lax_and_strict
+    [:lax, :strict].each do |mode|
+      assert_equal('', render_inline('{% if 5 > "x" %}{% endif %}', error_mode: mode))
+    end
+  end
+
+  def test_blank_unless_body_suppresses_inline_error_text_in_lax_and_strict
+    [:lax, :strict].each do |mode|
+      assert_equal('', render_inline('{% unless 5 > "x" %} {% endunless %}', error_mode: mode))
+    end
+  end
+
+  def test_blank_for_body_suppresses_inline_error_text_in_lax_and_strict
+    [:lax, :strict].each do |mode|
+      assert_equal('', render_inline('{% for i in (1..3) offset: xs %}{% endfor %}', error_mode: mode, assigns: { 'xs' => 'bad' }))
+    end
+  end
+
+  def test_strict2_blank_if_body_shows_inline_error_text
+    assert_equal(COMPARISON_ERROR, render_inline('{% if 5 > "x" %}{% endif %}', error_mode: :strict2))
+  end
+
+  def test_strict2_whitespace_if_body_shows_inline_error_text
+    assert_equal(COMPARISON_ERROR, render_inline('{% if 5 > "x" %}   {% endif %}', error_mode: :strict2))
+  end
+
+  def test_strict2_assign_if_body_shows_inline_error_text
+    assert_equal(COMPARISON_ERROR, render_inline('{% if 5 > "x" %}{% assign a = 1 %}{% endif %}', error_mode: :strict2))
+  end
+
+  def test_strict2_comment_if_body_shows_inline_error_text
+    assert_equal(COMPARISON_ERROR, render_inline('{% if 5 > "x" %}{% comment %}c{% endcomment %}{% endif %}', error_mode: :strict2))
+  end
+
+  def test_strict2_capture_if_body_shows_inline_error_text
+    assert_equal(COMPARISON_ERROR, render_inline('{% if 5 > "x" %}{% capture c %}text{% endcapture %}{% endif %}', error_mode: :strict2))
+  end
+
+  def test_strict2_blank_unless_body_shows_inline_error_text
+    assert_equal(COMPARISON_ERROR, render_inline('{% unless 5 > "x" %} {% endunless %}', error_mode: :strict2))
+  end
+
+  def test_strict2_blank_for_body_shows_inline_error_text
+    assert_equal(INVALID_INTEGER_ERROR, render_inline('{% for i in (1..3) offset: xs %}{% endfor %}', error_mode: :strict2, assigns: { 'xs' => 'bad' }))
+  end
+
+  def test_nonblank_bodies_show_inline_error_text_in_all_modes
+    [:lax, :strict, :strict2].each do |mode|
+      assert_equal(COMPARISON_ERROR, render_inline('{% if 5 > "x" %}{% echo 1 %}{% endif %}', error_mode: mode))
+      assert_equal(COMPARISON_ERROR, render_inline('{% if 5 > "x" %}{{ "" }}{% endif %}', error_mode: mode))
+      assert_equal(COMPARISON_ERROR, render_inline('{% if 5 > "x" %}{% else %}E{% endif %}', error_mode: mode))
+    end
+  end
+
+  def test_raised_errors_are_not_swallowed_by_blank_if_body
+    [:lax, :strict, :strict2].each do |mode|
+      assert_render_raises('{% if 5 > "x" %}{% endif %}', error_mode: mode, message: 'comparison of Integer with String failed')
+    end
+  end
+
+  def test_raised_errors_are_not_swallowed_by_blank_for_body
+    [:lax, :strict, :strict2].each do |mode|
+      assert_render_raises('{% for i in (1..3) offset: xs %}{% endfor %}', error_mode: mode, assigns: { 'xs' => 'bad' }, message: 'invalid integer')
+    end
+  end
+end

test/integration/capture_test.rb

@@ -6,7 +6,11 @@ class CaptureTest < Minitest::Test
   include Liquid
 
   def test_captures_block_content_in_variable
-    assert_template_result("test string", "{% capture 'var' %}test string{% endcapture %}{{var}}", {})
+    assert_template_result("test string", "{% capture var %}test string{% endcapture %}{{var}}", {})
+  end
+
+  def test_captures_block_content_in_quoted_variable_in_lax
+    assert_template_result("test string", "{% capture 'var' %}test string{% endcapture %}{{var}}", {}, error_mode: :lax)
   end
 
   def test_capture_with_hyphen_in_variable_name
@@ -49,4 +53,35 @@ class CaptureTest < Minitest::Test
     t.render!
     assert_equal(9, t.resource_limits.assign_score)
   end
+
+  def test_capture_with_valid_identifier_in_strict2
+    assert_template_result("hello", "{% capture my_var %}hello{% endcapture %}{{ my_var }}", error_mode: :strict2)
+  end
+
+  def test_capture_with_hyphen_in_strict2
+    assert_template_result("hello", "{% capture my-var %}hello{% endcapture %}{{ my-var }}", error_mode: :strict2)
+  end
+
+  def test_capture_rejects_parentheses_in_variable_name_in_strict2
+    assert_raises(Liquid::SyntaxError) do
+      Liquid::Template.parse("{% capture (x[y %}hello{% endcapture %}", error_mode: :strict2)
+    end
+  end
+
+  def test_capture_rejects_dot_in_variable_name_in_strict2
+    assert_raises(Liquid::SyntaxError) do
+      Liquid::Template.parse("{% capture a.b %}hello{% endcapture %}", error_mode: :strict2)
+    end
+  end
+
+  def test_capture_rejects_numeric_variable_name_in_strict2
+    assert_raises(Liquid::SyntaxError) do
+      Liquid::Template.parse("{% capture 1abc %}hello{% endcapture %}", error_mode: :strict2)
+    end
+  end
+
+  def test_capture_allows_invalid_names_in_lax
+    t = Liquid::Template.parse("{% capture (x[y %}hello{% endcapture %}", error_mode: :lax)
+    assert_equal("(x[y", t.root.nodelist.first.to)
+  end
 end

test/integration/context_test.rb

@@ -296,8 +296,8 @@ class ContextTest < Minitest::Test
   end
 
   def test_access_variable_with_hash_notation
-    assert_template_result('baz', '{{ ["foo"] }}', { "foo" => "baz" })
-    assert_template_result('baz', '{{ [bar] }}', { 'foo' => 'baz', 'bar' => 'foo' })
+    assert_template_result('baz', '{{ foo }}', { "foo" => "baz" })
+    assert_template_result('baz', '{{ self[bar] }}', { 'foo' => 'baz', 'bar' => 'foo' })
   end
 
   def test_access_hashes_with_hash_access_variables
@@ -632,9 +632,11 @@ class ContextTest < Minitest::Test
   end
 
   def test_has_key_will_not_add_an_error_for_missing_keys
-    context = Context.new
-    context.key?('unknown')
-    assert_empty(context.errors)
+    with_error_modes(:strict) do
+      context = Context.new
+      context.key?('unknown')
+      assert_empty(context.errors)
+    end
   end
 
   def test_key_lookup_will_raise_for_missing_keys_when_strict_variables_is_enabled

test/integration/error_handling_test.rb

@@ -67,11 +67,20 @@ class ErrorHandlingTest < Minitest::Test
   end
 
   def test_unrecognized_operator
-    assert_raises(SyntaxError) do
-      Liquid::Template.parse(' {% if 1 =! 2 %}ok{% endif %} ')
+    with_error_modes(:strict) do
+      assert_raises(SyntaxError) do
+        Liquid::Template.parse(' {% if 1 =! 2 %}ok{% endif %} ')
+      end
     end
   end
 
+  def test_lax_unrecognized_operator
+    template = Liquid::Template.parse(' {% if 1 =! 2 %}ok{% endif %} ', error_mode: :lax)
+    assert_equal(' Liquid error: Unknown operator =! ', template.render)
+    assert_equal(1, template.errors.size)
+    assert_equal(Liquid::ArgumentError, template.errors.first.class)
+  end
+
   def test_with_line_numbers_adds_numbers_to_parser_errors
     source = <<~LIQUID
       foobar
@@ -95,6 +104,25 @@ class ErrorHandlingTest < Minitest::Test
     assert_match_syntax_error(/Liquid syntax error \(line 3\)/, source)
   end
 
+  def test_parsing_warn_with_line_numbers_adds_numbers_to_lexer_errors
+    template = Liquid::Template.parse(
+      '
+        foobar
+
+        {% if 1 =! 2 %}ok{% endif %}
+
+        bla
+            ',
+      error_mode: :warn,
+      line_numbers: true,
+    )
+
+    assert_equal(
+      ['Liquid syntax error (line 4): Unexpected character = in "1 =! 2"'],
+      template.warnings.map(&:message),
+    )
+  end
+
   def test_parsing_strict_with_line_numbers_adds_numbers_to_lexer_errors
     err = assert_raises(SyntaxError) do
       Liquid::Template.parse(
@@ -105,6 +133,7 @@ class ErrorHandlingTest < Minitest::Test
 
           bla
                 ',
+        error_mode: :strict,
         line_numbers: true,
       )
     end
@@ -128,16 +157,34 @@ class ErrorHandlingTest < Minitest::Test
 
   def test_strict_error_messages
     err = assert_raises(SyntaxError) do
-      Liquid::Template.parse(' {% if 1 =! 2 %}ok{% endif %} ')
+      Liquid::Template.parse(' {% if 1 =! 2 %}ok{% endif %} ', error_mode: :strict)
     end
     assert_equal('Liquid syntax error: Unexpected character = in "1 =! 2"', err.message)
 
     err = assert_raises(SyntaxError) do
-      Liquid::Template.parse('{{%%%}}')
+      Liquid::Template.parse('{{%%%}}', error_mode: :strict)
     end
     assert_equal('Liquid syntax error: Unexpected character % in "{{%%%}}"', err.message)
   end
 
+  def test_warnings
+    template = Liquid::Template.parse('{% if ~~~ %}{{%%%}}{% else %}{{ hello. }}{% endif %}', error_mode: :warn)
+    assert_equal(3, template.warnings.size)
+    assert_equal('Unexpected character ~ in "~~~"', template.warnings[0].to_s(false))
+    assert_equal('Unexpected character % in "{{%%%}}"', template.warnings[1].to_s(false))
+    assert_equal('Expected id but found end_of_string in "{{ hello. }}"', template.warnings[2].to_s(false))
+    assert_equal('', template.render)
+  end
+
+  def test_warning_line_numbers
+    template = Liquid::Template.parse("{% if ~~~ %}\n{{%%%}}{% else %}\n{{ hello. }}{% endif %}", error_mode: :warn, line_numbers: true)
+    assert_equal('Liquid syntax error (line 1): Unexpected character ~ in "~~~"', template.warnings[0].message)
+    assert_equal('Liquid syntax error (line 2): Unexpected character % in "{{%%%}}"', template.warnings[1].message)
+    assert_equal('Liquid syntax error (line 3): Expected id but found end_of_string in "{{ hello. }}"', template.warnings[2].message)
+    assert_equal(3, template.warnings.size)
+    assert_equal([1, 2, 3], template.warnings.map(&:line_number))
+  end
+
   # Liquid should not catch Exceptions that are not subclasses of StandardError, like Interrupt and NoMemoryError
   def test_exceptions_propagate
     assert_raises(Exception) do
@@ -221,8 +268,11 @@ class ErrorHandlingTest < Minitest::Test
     output = Liquid::Template.parse("{% assign x = 0 %}{% if 1 < '2' %}not blank{% assign x = 3 %}{% endif %}{{ x }}").render
     assert_equal("Liquid error: comparison of Integer with String failed0", output)
 
-    output = Liquid::Template.parse("{% assign x = 0 %}{% if 1 < '2' %}{% assign x = 3 %}{% endif %}{{ x }}").render
-    assert_equal("0", output)
+    source = "{% assign x = 0 %}{% if 1 < '2' %}{% assign x = 3 %}{% endif %}{{ x }}"
+    [:lax, :warn, :strict].each do |mode|
+      assert_equal("0", Liquid::Template.parse(source, error_mode: mode).render)
+    end
+    assert_equal("Liquid error: comparison of Integer with String failed0", Liquid::Template.parse(source, error_mode: :strict2).render)
   end
 
   def test_syntax_error_is_raised_with_template_name

test/integration/expression_test.rb

@@ -27,6 +27,11 @@ class ExpressionTest < Minitest::Test
     assert_template_result("-17.42", "{{ -17.42 }}")
     assert_template_result("2.5", "{{ 2.5 }}")
 
+    with_error_modes(:lax) do
+      assert_expression_result(0.0, "0.....5")
+      assert_expression_result(0.0, "-0..1")
+    end
+
     assert_expression_result(1.5, "1.5")
 
     # this is a unfortunate quirky behavior of Liquid
@@ -51,6 +56,19 @@ class ExpressionTest < Minitest::Test
     )
   end
 
+  def test_quirky_negative_sign_expression_markup
+    result = Expression.parse("-", nil)
+    assert(result.is_a?(VariableLookup))
+    assert_equal("-", result.name)
+
+    # for this template, the expression markup is "-"
+    assert_template_result(
+      "",
+      "{{ - 'theme.css' - }}",
+      error_mode: :lax,
+    )
+  end
+
   def test_expression_cache
     skip("Liquid-C does not support Expression caching") if defined?(Liquid::C) && Liquid::C.enabled
 

test/integration/let_closure_test.rb

@@ -0,0 +1,547 @@
+# frozen_string_literal: true
+
+require 'test_helper'
+
+class LetClosureTest < Minitest::Test
+  def test_value_binding_and_filtered_initializer
+    assert_render('HELLO:3', "{% let title = product.title | upcase %}{{ title }}:{% let n = 1 | plus: 2 %}{{ n }}", 'product' => { 'title' => 'hello' })
+  end
+
+  def test_initializer_reads_parent_before_installing_shadow
+    assert_render('231', '{% let n = 1 %}{% let title(step) %}{% let n = n | plus: step %}{{ n }}{% endlet %}{{ title(1) }}{{ title(2) }}{{ n }}')
+  end
+
+  def test_empty_and_parameterless_bodies
+    assert_render('ok', '{% let empty %}{% endlet %}{% let title() %}ok{% endlet %}{{ empty() }}{{ title() }}')
+  end
+
+  def test_parameters_are_writable_and_fresh
+    assert_render('23', '{% let title(n,) %}{% set n = n | plus: 1 %}{{ n }}{% endlet %}{{ title(1,) }}{{ title(2) }}')
+  end
+
+  def test_live_captures
+    assert_render('12', '{% let n = 1 %}{% let title %}{{ n }}{% endlet %}{{ title() }}{% set n = 2 %}{{ title() }}')
+  end
+
+  def test_captured_environments_fall_through_nil_values
+    context = Liquid::Context.build(environments: [{ 'n' => nil }, { 'n' => 'fallback' }])
+    source = '{{ n }}/{% let show %}{{ n }}{% endlet %}{{ show() }}'
+    assert_equal('fallback/fallback', parse(source).render!(context))
+  end
+
+  def test_captured_environments_keep_false_values
+    context = Liquid::Context.build(environments: [{ 'n' => false }, { 'n' => 'fallback' }])
+    source = '{{ n }}/{% let show %}{{ n }}{% endlet %}{{ show() }}'
+    assert_equal('false/false', parse(source).render!(context))
+  end
+
+  def test_captured_environments_use_hash_defaults
+    context = Liquid::Context.build(environments: Hash.new('fallback'))
+    source = '{{ n }}/{% let show %}{{ n }}{% endlet %}{{ show() }}'
+    assert_equal('fallback/fallback', parse(source).render!(context))
+  end
+
+  def test_captured_environments_fall_through_drops
+    context = Liquid::Context.build(environments: [Liquid::Drop.new, { 'n' => 'fallback' }])
+    source = '{{ n }}/{% let outer %}{% let inner %}{{ n }}{% endlet %}{{ inner() }}{% endlet %}{{ outer() }}'
+    assert_equal('fallback/fallback', parse(source).render!(context))
+  end
+
+  def test_captured_static_environments_preserve_fallthrough_and_defaults
+    context = Liquid::Context.build(environments: [], static_environments: [{ 'n' => nil }, Hash.new('fallback')])
+    source = '{{ n }}/{% let show %}{{ n }}{% endlet %}{{ show() }}'
+    assert_equal('fallback/fallback', parse(source).render!(context))
+  end
+
+  def test_captured_local_nil_shadows_environment_values
+    context = Liquid::Context.build(environments: { 'n' => 'dynamic' }, static_environments: { 'n' => 'static' })
+    source = '{% let n = nil %}{{ n }}/{% let outer %}{% let inner %}{{ n }}{% endlet %}{{ inner() }}{% endlet %}{{ outer() }}'
+    assert_equal('/', parse(source).render!(context))
+  end
+
+  def test_captured_local_self_nil_does_not_become_a_self_drop
+    source = '{% let self = nil %}{% let show %}{% if self == nil %}nil{% endif %}{% endlet %}{{ show() }}'
+    assert_render('nil', source)
+  end
+
+  def test_captured_environments_remain_live_and_read_only
+    values = { 'n' => 1 }
+    source = '{% let show %}{{ n }}{% set n = n | plus: 10 %}{{ n }}{% endlet %}{{ show() }}{% increment n %}{{ show() }}'
+    assert_render('1111212', source, values)
+    assert_equal(2, values['n'])
+  end
+
+  def test_strict_captured_environments_stop_at_nil
+    context = Liquid::Context.build(environments: [{ 'n' => nil }, { 'n' => 'fallback' }])
+    source = '{{ n }}/{% let show %}{{ n }}{% endlet %}{{ show() }}'
+    assert_equal('/', parse(source).render!(context, strict_variables: true))
+  end
+
+  def test_strict_captured_environments_reject_missing_keys_before_fallback
+    source = '{% let outer %}{% let inner %}{{ n }}{% endlet %}{{ inner() }}{% endlet %}{{ outer() }}'
+    context = Liquid::Context.build(environments: [{}, { 'n' => 'fallback' }])
+    assert_raises(Liquid::UndefinedVariable) { parse(source).render!(context, strict_variables: true) }
+  end
+
+  def test_strict_captured_environments_reject_hash_defaults
+    context = Liquid::Context.build(environments: Hash.new('fallback'))
+    source = '{% let show %}{{ n }}{% endlet %}{{ show() }}'
+    assert_raises(Liquid::UndefinedVariable) { parse(source).render!(context, strict_variables: true) }
+  end
+
+  def test_strict_captured_self_lookup_can_fall_back_to_self_drop
+    source = '{% let show %}{{ self["n"] }}{% endlet %}{{ show() }}'
+    assert_equal('value', parse(source).render!({ 'n' => 'value' }, strict_variables: true))
+  end
+
+  def test_render_in_closures_inherits_only_static_globals
+    file_system = StubFileSystem.new('snippet' => '{{ g }}/{{ dynamic }}/{{ local }};')
+    environment = Liquid::Environment.build(file_system: file_system)
+    context = Liquid::Context.build(environment: environment, environments: { 'dynamic' => 'D' }, static_environments: { 'g' => 'G' })
+    source = '{% let local = "L" %}{% render "snippet" %}{% let show %}{% render "snippet" %}{% render "snippet", dynamic: dynamic, local: local %}{% endlet %}{{ show() }}'
+    assert_equal('G//;G//;G/D/L;', parse(source, environment: environment).render!(context))
+  end
+
+  def test_render_in_closures_uses_globals_despite_local_shadows
+    file_system = StubFileSystem.new('snippet' => '{{ g }}')
+    environment = Liquid::Environment.build(file_system: file_system)
+    context = Liquid::Context.build(environment: environment, static_environments: { 'g' => 'G' })
+    source = '{% render "snippet" %}/{% let g = nil %}{% let outer %}{% let inner %}{{ g }}{% render "snippet" %}{% endlet %}{{ inner() }}{% endlet %}{{ outer() }}'
+    assert_equal('G/G', parse(source, environment: environment).render!(context))
+  end
+
+  def test_capture_shadows_are_fresh_and_read_only
+    assert_render('221', '{% let n = 1 %}{% let title %}{% set n = n | plus: 1 %}{{ n }}{% endlet %}{{ title() }}{{ title() }}{{ n }}')
+  end
+
+  def test_set_creates_missing_binding_at_invocation_root
+    source = '{% let title %}{% for i in (1..2) %}{% set n = n | plus: i %}{% endfor %}{{ n }}{% endlet %}{{ title() }}{{ title() }}'
+    assert_equal('33', parse(source).render!({}, strict_variables: true))
+  end
+
+  def test_set_searches_owned_control_flow_scopes
+    source = '{% let title(n) %}{% for i in (1..2) %}{% set n = n | plus: i %}{% set i = i | plus: 10 %}{{ i }},{% endfor %}{{ n }}{% endlet %}{{ title(1) }}'
+    assert_render('11,12,4', source)
+  end
+
+  def test_set_shadows_capture_at_root_from_inside_loop
+    source = '{% let n = 1 %}{% let title %}{% for i in (1..2) %}{% set n = n | plus: i %}{% endfor %}{{ n }}{% endlet %}{{ title() }}{{ n }}'
+    assert_render('41', source)
+  end
+
+  def test_let_shadows_in_loop_and_can_execute_repeatedly
+    source = '{% let n = 10 %}{% for i in (1..3) %}{% let n = i %}{% set n = n | plus: 1 %}{{ n }}{% endfor %}{{ n }}'
+    assert_render('23410', source)
+  end
+
+  def test_each_iteration_initializer_reads_outer_binding
+    source = '{% let n = 10 %}{% for i in (1..2) %}{% let n = n | plus: 1 %}{{ n }},{% endfor %}{{ n }}'
+    assert_render('11,11,10', source)
+  end
+
+  def test_retained_callbacks_capture_iteration_local_bindings
+    source = '{% let n = 10 %}{% let first = nil %}{% let second = nil %}{% for i in (1..2) %}{% let n = n | plus: i %}{% let title %}{{ n }}{% endlet %}{% if i == 1 %}{% set first = title %}{% else %}{% set second = title %}{% endif %}{% endfor %}{{ first() }}/{{ second() }}:{{ n }}'
+    assert_render('11/12:10', source)
+  end
+
+  def test_set_traverses_fresh_iteration_frames_and_persists_at_root
+    source = '{% let captured = 5 %}{% let title(n) %}{% for i in (1..2) %}{% let step = i %}{% set n = n | plus: step %}{% set missing = missing | plus: step %}{% set captured = captured | plus: step %}{% endfor %}{{ n }}/{{ missing }}/{{ captured }};{% endlet %}{{ title(1) }}{{ title(1) }}{{ captured }}'
+    assert_equal('4/3/8;4/3/8;5', parse(source).render!({}, strict_variables: true))
+  end
+
+  def test_each_table_row_initializer_reads_outer_binding
+    source = '{% let n = 10 %}{% tablerow i in (1..2) %}{% let n = n | plus: 1 %}{{ n }}{% endtablerow %}{{ n }}'
+    assert_render("<tr class=\"row1\">\n<td class=\"col1\">11</td><td class=\"col2\">11</td></tr>\n10", source)
+  end
+
+  def test_table_row_callbacks_retain_iteration_local_bindings
+    source = '{% let first = nil %}{% let second = nil %}{% tablerow i in (1..2) %}{% let n = i %}{% let title %}{{ n }}{% endlet %}{% if i == 1 %}{% set first = title %}{% else %}{% set second = title %}{% endif %}{% endtablerow %}{{ first() }}/{{ second() }}'
+    assert_render("<tr class=\"row1\">\n<td class=\"col1\"></td><td class=\"col2\"></td></tr>\n1/2", source)
+  end
+
+  def test_set_traverses_table_row_frames_to_invocation_root
+    source = '{% let title(n) %}{% tablerow i in (1..2) %}{% let step = i %}{% set n = n | plus: step %}{% set missing = missing | plus: step %}{% endtablerow %}{{ n }}/{{ missing }}{% endlet %}{{ title(1) }}'
+    assert_render("<tr class=\"row1\">\n<td class=\"col1\"></td><td class=\"col2\"></td></tr>\n4/3", source)
+  end
+
+  def test_empty_loop_branch_has_its_own_let_scope
+    source = '{% let n = 1 %}{% for i in missing %}{% else %}{% let n = 2 %}{{ n }}{% endfor %}{{ n }}'
+    assert_render('21', source)
+  end
+
+  def test_table_row_scope_can_shadow_outer_let
+    source = '{% let n = 10 %}{% tablerow i in (1..2) %}{% let n = i %}{{ n }}{% endtablerow %}{{ n }}'
+    assert_render("<tr class=\"row1\">\n<td class=\"col1\">1</td><td class=\"col2\">2</td></tr>\n10", source)
+  end
+
+  def test_body_declaration_can_execute_on_every_iteration
+    assert_render('123', '{% for i in (1..3) %}{% let title %}{{ i }}{% endlet %}{{ title() }}{% endfor %}')
+  end
+
+  def test_set_updates_nearest_owned_let
+    source = '{% let title(n) %}{% for i in (1..2) %}{% let n = i %}{% set n = n | plus: 10 %}{{ n }},{% endfor %}{{ n }}{% endlet %}{{ title(5) }}'
+    assert_render('11,12,5', source)
+  end
+
+  def test_nested_closures_have_live_read_only_captures
+    source = '{% let outer(n) %}{% let inner %}{% set n = n | plus: 10 %}{{ n }}{% endlet %}{% set n = n | plus: 1 %}{{ inner() }}{{ n }}{% endlet %}{{ outer(1) }}{{ outer(2) }}'
+    assert_render('122133', source)
+  end
+
+  def test_captures_search_all_parents_with_strict_variables
+    source = '{% let outer %}{% let inner %}{{ title }}{% endlet %}{{ inner() }}{% endlet %}{{ outer() }}'
+    assert_equal('hello', parse(source).render!({ 'title' => 'hello' }, strict_variables: true))
+  end
+
+  def test_repeated_renders_start_with_fresh_bindings
+    template = parse('{% set n = n | plus: 1 %}{% let title %}{% set n = n | plus: 1 %}{{ n }}{% endlet %}{{ title() }}{{ n }}')
+    2.times { assert_equal('21', template.render!) }
+  end
+
+  def test_repeated_renders_use_current_inputs
+    template = parse('{% let title = title | upcase %}{% let render_title %}{{ title }}{% endlet %}{{ render_title() }}')
+    assert_equal('FIRST', template.render!('title' => 'first'))
+    assert_equal('SECOND', template.render!('title' => 'second'))
+  end
+
+  def test_nil_and_false_bindings_are_owned
+    source = '{% let title %}{% let n = nil %}{% set n = n | default: 3 %}{% let flag = false %}{% set flag = true %}{{ n }}{{ flag }}{% endlet %}{{ title() }}'
+    assert_render('3true', source)
+  end
+
+  def test_nested_call_arguments_and_filters
+    source = '{% let title(text) %}[{{ text }}]{% endlet %}{{ title(title("hello")) | upcase }}'
+    assert_render('[[HELLO]]', source)
+  end
+
+  def test_calls_in_filter_arguments_conditions_and_dynamic_lookups
+    source = '{% let key %}title{% endlet %}{% if key() == "title" %}{{ product[key()] | append: key() }}{% endif %}'
+    assert_render('hellotitle', source, 'product' => { 'title' => 'hello' })
+  end
+
+  def test_calls_in_ranges
+    assert_render('123', '{% let finish %}3{% endlet %}{% for i in (1..finish()) %}{{ i }}{% endfor %}')
+  end
+
+  def test_callable_ranges_share_loop_continuation
+    source = '{% let finish %}3{% endlet %}{% for i in (1..finish()) limit: 1 %}{{ i }}{% endfor %}{% for i in ( 1 .. finish( ) ) limit: 1 offset: continue %}{{ i }}{% endfor %}'
+    assert_render('12', source)
+  end
+
+  def test_callable_dynamic_lookups_share_loop_continuation
+    source = '{% let key %}items{% endlet %}{% for i in groups[key()] limit: 1 %}{{ i }}{% endfor %}{% for i in groups[ key( ) ] limit: 1 offset: continue %}{{ i }}{% endfor %}'
+    assert_render('12', source, 'groups' => { 'items' => [1, 2, 3] })
+  end
+
+  def test_callable_collection_loop_names_preserve_syntax
+    source = '{% let identity(value) %}{{ value }}{% endlet %}{% let key %}items{% endlet %}{% for i in identity("a b") %}{{ forloop.name }}{% endfor %}/{% for i in groups[key()] limit: 1 %}{{ forloop.name }}{% endfor %}/{% for i in (1..identity(3)) limit: 1 %}{{ forloop.name }}{% endfor %}'
+    assert_render('i-identity("a b")/i-groups[key()]/i-(1..identity(3))', source, 'groups' => { 'items' => [1, 2, 3] })
+  end
+
+  def test_distinct_callable_arguments_have_separate_loop_continuations
+    source = '{% let finish(value) %}{{ value }}{% endlet %}{% for i in (1..finish(2)) limit: 1 %}{{ i }}{% endfor %}{% for i in (1..finish(3)) limit: 1 offset: continue %}{{ i }}{% endfor %}'
+    assert_render('11', source)
+  end
+
+  def test_callable_value_can_be_passed_through_let
+    assert_render('hello', '{% let title %}hello{% endlet %}{% let alias = title %}{{ alias() }}')
+  end
+
+  def test_multiline_liquid
+    source = <<~LIQUID
+      {% liquid
+        let n = 1
+        let title(step)
+          set n = n | plus: step
+          echo n
+        endlet
+        echo title(2)
+        echo n
+      %}
+    LIQUID
+    assert_render("31\n", source)
+  end
+
+  def test_same_scope_redeclarations_are_parse_errors
+    [
+      '{% let n = 1 %}{% let n = 2 %}',
+      '{% let n %}{% endlet %}{% let n = 2 %}',
+      '{% let title(n) %}{% let n = 1 %}{% endlet %}',
+      '{% let title %}{% let n = 1 %}{% if false %}{% let n = 2 %}{% endif %}{% endlet %}',
+    ].each do |source|
+      assert_raises(Liquid::SyntaxError, source) { parse(source) }
+    end
+  end
+
+  def test_invalid_headers_and_complete_input_validation
+    [
+      '{% let %}',
+      '{% let 1 = 2 %}',
+      '{% let a.b = 2 %}',
+      '{% let a == 2 %}',
+      '{% let a = %}',
+      '{% let a = 1 junk %}',
+      '{% let a = 1 | %}',
+      '{% let a(x) = 2 %}',
+      '{% let a(x,x) %}{% endlet %}',
+      '{% let a(,x) %}{% endlet %}',
+      '{% let a(x,,) %}{% endlet %}',
+      '{% let a(x) junk %}{% endlet %}',
+      '{% let a %}',
+      '{% set %}',
+      '{% set a.b = 1 %}',
+      '{% set a == 1 %}',
+      '{% set a = %}',
+      '{% set a = 1 junk %}',
+      '{{ title(,1) }}',
+      '{{ title(1,,) }}',
+      '{{ title(1) junk }}',
+      '{{ title(1 }}',
+    ].each do |source|
+      assert_raises(Liquid::SyntaxError, source) { parse(source) }
+    end
+  end
+
+  def test_assign_is_rejected_through_nested_control_flow
+    [
+      '{% assign x = 1 %}',
+      '{% if false %}{% assign x = 1 %}{% endif %}',
+      '{% for i in (1..2) %}{% unless false %}{% assign x = 1 %}{% endunless %}{% endfor %}',
+      '{% case n %}{% when 1 %}{% assign x = 1 %}{% endcase %}',
+      "{% liquid\nif false\nassign x = 1\nendif\n%}",
+    ].each do |body|
+      error = assert_raises(Liquid::SyntaxError) { parse("{% let title %}#{body}{% endlet %}") }
+      assert_match('assign is not allowed', error.message)
+    end
+  end
+
+  def test_assign_still_works_outside_closures
+    assert_render('12', '{% assign n = 1 %}{% let title %}{{ n }}{% endlet %}{{ title() }}{% assign n = 2 %}{{ title() }}')
+  end
+
+  def test_capture_tag_does_not_mutate_parent_bindings
+    assert_render('localparent', '{% let n = "parent" %}{% let title %}{% capture n %}local{% endcapture %}{{ n }}{% endlet %}{{ title() }}{{ n }}')
+  end
+
+  def test_counters_in_closures_have_fresh_shadows
+    source = '{% let n = 5 %}{% let title %}{% increment n %}{{ n }}{% decrement n %}{{ n }}{% endlet %}{{ title() }}{{ title() }}{{ n }}'
+    assert_render('565556555', source)
+  end
+
+  def test_tags_are_unavailable_in_every_other_mode
+    [:lax, :warn, :strict, :rigid].each do |mode|
+      ['{% let n = 1 %}', '{% let title %}{% endlet %}', '{% set n = 1 %}'].each do |source|
+        assert_raises(Liquid::SyntaxError, "#{mode}: #{source}") { Liquid::Template.parse(source, error_mode: mode) }
+      end
+    end
+  end
+
+  def test_calls_preserve_legacy_parsing_behavior
+    [:lax, :warn].each do |mode|
+      template = Liquid::Template.parse('{{ title(1) }}', error_mode: mode)
+      assert_equal('', template.render!('title' => 'value'))
+    end
+    [:strict, :rigid].each do |mode|
+      assert_raises(Liquid::SyntaxError) { Liquid::Template.parse('{{ title(1) }}', error_mode: mode) }
+    end
+  end
+
+  def test_effective_template_mode_overrides_environment
+    environment = Liquid::Environment.build(error_mode: :strict)
+    assert_equal('1', parse('{% let n = 1 %}{{ n }}', environment: environment).render!)
+    environment = Liquid::Environment.build(error_mode: :strict2)
+    assert_raises(Liquid::SyntaxError) { Liquid::Template.parse('{% let n = 1 %}', environment: environment, error_mode: :strict) }
+  end
+
+  def test_effective_partial_mode_enables_feature
+    environment = Liquid::Environment.build(error_mode: :strict2, file_system: StubFileSystem.new('snippet' => '{% let title %}ok{% endlet %}{{ title() }}'))
+    template = Liquid::Template.parse('{% render "snippet" %}', environment: environment, error_mode: :strict, include_options_blacklist: [:error_mode])
+    assert_equal('ok', template.render!)
+  end
+
+  def test_effective_partial_mode_disables_feature
+    [:lax, :warn, :strict, :rigid].each do |mode|
+      environment = Liquid::Environment.build(error_mode: mode, file_system: StubFileSystem.new('snippet' => '{% let n = 1 %}'))
+      template = parse('{% render "snippet" %}', environment: environment, include_options_blacklist: [:error_mode])
+      assert_raises(Liquid::SyntaxError) { template.render! }
+    end
+  end
+
+  def test_callable_security
+    callable = Object.new
+    def callable.to_liquid
+      self
+    end
+
+    def callable.call(*)
+      raise 'must not call arbitrary Ruby objects'
+    end
+    [callable, Liquid::Drop.new, 'text', 1, nil].each do |value|
+      assert_raises(Liquid::ArgumentError) { parse('{{ title(1) }}').render!('title' => value) }
+    end
+  end
+
+  def test_proc_lookup_is_unchanged_and_receives_no_callable_arguments
+    values = { 'title' => -> { 'resolved' } }
+    template = parse('{{ title(1) }}')
+    assert_raises(Liquid::ArgumentError) { template.render!(values) }
+    assert_equal('resolved', values['title'])
+    assert_equal('resolved', parse('{{ title }}').render!(values))
+  end
+
+  def test_proc_captures_keep_existing_lookup_and_memoization
+    values = { 'title' => -> { 'resolved' } }
+    assert_render('resolvedresolved', '{% let show %}{{ title }}{% endlet %}{{ show() }}{{ show() }}', values)
+    assert_equal('resolved', values['title'])
+  end
+
+  def test_nil_proc_captures_are_memoized_before_environment_fallback
+    values = { 'n' => -> { nil } }
+    context = Liquid::Context.build(environments: [values, { 'n' => 'fallback' }])
+    source = '{% let show %}{{ n }}{% endlet %}{{ show() }}/{{ show() }}'
+    assert_equal('fallback/fallback', parse(source).render!(context))
+    assert_nil(values['n'])
+  end
+
+  def test_nested_proc_captures_receive_the_current_invocation_context
+    values = { 'n' => ->(context) { context['argument'] } }
+    source = '{% let outer %}{% let inner(argument) %}{{ n }}{% endlet %}{{ inner("value") }}{% endlet %}{{ outer() }}'
+    assert_render('value', source, values)
+    assert_equal('value', values['n'])
+  end
+
+  def test_argument_count_is_validated
+    ['title()', 'title(1,2)'].each do |call|
+      assert_raises(Liquid::ArgumentError) { parse("{% let title(n) %}{{ n }}{% endlet %}{{ #{call} }}").render! }
+    end
+  end
+
+  def test_recursion_uses_liquid_runtime_depth_limit
+    template = parse('{% let title %}{{ title() }}{% endlet %}{{ title() }}')
+    assert_raises(Liquid::StackLevelError) { template.render! }
+  end
+
+  def test_output_buffer_and_output_limit
+    template = parse('{% let title %}hello{% endlet %}{{ title() }}{{ title() }}')
+    output = +'prefix:'
+    assert_same(output, template.render!({}, output: output))
+    assert_equal('prefix:hellohello', output)
+    template.resource_limits.render_length_limit = 9
+    assert_raises(Liquid::MemoryError) { template.render! }
+  end
+
+  def test_assignment_limits_include_let_set_and_callable_initializers
+    ['{% let n = "hello" %}', '{% set n = "hello" %}', '{% let title %}hello{% endlet %}{% let n = title() %}'].each do |source|
+      template = parse(source)
+      template.resource_limits.assign_score_limit = 4
+      assert_raises(Liquid::MemoryError) { template.render! }
+    end
+  end
+
+  def test_render_score_limit_includes_callable_body
+    template = parse('{% let title %}hello{% endlet %}{{ title() }}{{ title() }}')
+    template.resource_limits.render_score_limit = 4
+    assert_raises(Liquid::MemoryError) { template.render! }
+  end
+
+  def test_visitor_sees_initializers_arguments_and_bodies_without_captures
+    template = parse('{% let n = source | plus: step %}{% let title(x) %}{% set n = other %}{{ x }}{% endlet %}{{ title(product.name) }}')
+    visitor = Liquid::ParseTreeVisitor.for(template.root).add_callback_for(Liquid::VariableLookup) { |node| node.name } # rubocop:disable Style/SymbolProc
+    expected = ['source', 'step', 'other', 'x', 'title', 'product']
+    assert_equal(expected, visitor.visit.flatten.compact)
+    template.render!('source' => 1, 'step' => 2, 'other' => 3, 'product' => { 'name' => 'hello' })
+    assert_equal(expected, visitor.visit.flatten.compact)
+  end
+
+  def test_visitor_includes_initializer_filter_keyword_arguments
+    template = parse('{% let n = source | default: fallback, allow_false: flag %}')
+    visitor = Liquid::ParseTreeVisitor.for(template.root).add_callback_for(Liquid::VariableLookup) { |node| node.name } # rubocop:disable Style/SymbolProc
+    assert_equal(['source', 'fallback', 'flag'], visitor.visit.flatten.compact)
+  end
+
+  def test_custom_closure_body_parameters_are_writable_and_fresh
+    with_custom_tag('parameterized', ParameterizedBody) do
+      source = '{% let value = 10 %}{% parameterized %}{% set value = value | plus: 1 %}{{ value }}{% endparameterized %}{{ value }}'
+      assert_render('2310', source)
+    end
+  end
+
+  def test_custom_closure_body_exports_only_direct_child_body_declarations
+    source = '{% let n = 1 %}{% compose %}{% set n = n | plus: 1 %}{% let value = "hidden" %}{% if true %}{% let nested %}hidden{% endlet %}{% endif %}{% let item(text) %}{{ n }}:{{ text }}{% endlet %}{% endcompose %}{{ n }}'
+    with_custom_tag('compose', Compose) do
+      template = parse(source)
+      assert_equal('2:a|2:a|1', template.render!)
+      assert_equal('2:a|2:a|1', template.render!)
+    end
+  end
+
+  def test_custom_closure_bodies_can_nest
+    source = '{% compose %}{% let item(text) %}{% compose %}{% let item(inner) %}{{ text }}{{ inner }}{% endlet %}{% endcompose %}{% endlet %}{% endcompose %}'
+    with_custom_tag('compose', Compose) { assert_render('aa|aa||aa|aa||', source) }
+  end
+
+  def test_multiline_liquid_declarations_are_direct_child_exports
+    source = "{% compose %}{% liquid\nlet item(text)\necho text\nendlet\n%}{% endcompose %}"
+    with_custom_tag('compose', Compose) { assert_render('a|a|', source) }
+  end
+
+  def test_custom_closure_body_api_requires_strict2
+    with_custom_tag('compose', Compose) do
+      [:lax, :warn, :strict, :rigid].each do |mode|
+        assert_raises(Liquid::SyntaxError) { Liquid::Template.parse('{% compose %}{% endcompose %}', error_mode: mode) }
+      end
+    end
+  end
+
+  def test_custom_closure_body_rejects_nested_assign
+    with_custom_tag('compose', Compose) do
+      assert_raises(Liquid::SyntaxError) { parse('{% compose %}{% if false %}{% assign n = 1 %}{% endif %}{% endcompose %}') }
+    end
+  end
+
+  private
+
+  def parse(source, **options)
+    Liquid::Template.parse(source, **options, error_mode: :strict2)
+  end
+
+  def assert_render(expected, source, values = {})
+    assert_equal(expected, parse(source).render!(values))
+  end
+
+  class ParameterizedBody < Liquid::Block
+    def parse(tokens)
+      @closure_body = parse_closure_body(tokens, parameters: ['value'])
+    end
+
+    def render_to_output_buffer(context, output)
+      body = @closure_body.bind(context)
+      body.render_to_output_buffer(context, output, [1])
+      body.render_to_output_buffer(context, output, [2])
+    end
+  end
+
+  class Compose < Liquid::Block
+    def initialize(tag_name, markup, parse_context)
+      super
+      @component = Liquid::Template.parse("{{ item('a') }}|", environment: parse_context.environment, error_mode: :strict2)
+    end
+
+    def parse(tokens)
+      @closure_body = parse_closure_body(tokens)
+    end
+
+    def render_to_output_buffer(context, output)
+      body = @closure_body.bind(context)
+      2.times do
+        exports = body.invoke(context, output: output)
+        raise Liquid::ArgumentError, 'Unexpected exports' unless exports.keys == ['item']
+
+        inner = context.new_isolated_subcontext
+        inner.merge(exports)
+        @component.root.render_to_output_buffer(inner, output)
+      end
+      output
+    end
+  end
+end

test/integration/parsing_quirks_test.rb

@@ -31,25 +31,58 @@ class ParsingQuirksTest < Minitest::Test
   def test_error_on_empty_filter
     assert(Template.parse("{{test}}"))
 
-    assert_raises(Liquid::SyntaxError) { Template.parse("{{|test}}") }
-    assert_raises(Liquid::SyntaxError) { Template.parse("{{test |a|b|}}") }
+    with_error_modes(:lax) do
+      assert(Template.parse("{{|test}}"))
+    end
+
+    with_error_modes(:strict) do
+      assert_raises(SyntaxError) { Template.parse("{{|test}}") }
+      assert_raises(SyntaxError) { Template.parse("{{test |a|b|}}") }
+    end
   end
 
   def test_meaningless_parens_error
-    assert_raises(SyntaxError) do
-      markup = "a == 'foo' or (b == 'bar' and c == 'baz') or false"
-      Template.parse("{% if #{markup} %} YES {% endif %}")
+    with_error_modes(:strict) do
+      assert_raises(SyntaxError) do
+        markup = "a == 'foo' or (b == 'bar' and c == 'baz') or false"
+        Template.parse("{% if #{markup} %} YES {% endif %}")
+      end
     end
   end
 
   def test_unexpected_characters_syntax_error
-    assert_raises(SyntaxError) do
-      markup = "true && false"
-      Template.parse("{% if #{markup} %} YES {% endif %}")
+    with_error_modes(:strict) do
+      assert_raises(SyntaxError) do
+        markup = "true && false"
+        Template.parse("{% if #{markup} %} YES {% endif %}")
+      end
+      assert_raises(SyntaxError) do
+        markup = "false || true"
+        Template.parse("{% if #{markup} %} YES {% endif %}")
+      end
     end
-    assert_raises(SyntaxError) do
+  end
+
+  def test_no_error_on_lax_empty_filter
+    assert(Template.parse("{{test |a|b|}}", error_mode: :lax))
+    assert(Template.parse("{{test}}", error_mode: :lax))
+    assert(Template.parse("{{|test|}}", error_mode: :lax))
+  end
+
+  def test_meaningless_parens_lax
+    with_error_modes(:lax) do
+      assigns = { 'b' => 'bar', 'c' => 'baz' }
+      markup  = "a == 'foo' or (b == 'bar' and c == 'baz') or false"
+      assert_template_result(' YES ', "{% if #{markup} %} YES {% endif %}", assigns)
+    end
+  end
+
+  def test_unexpected_characters_silently_eat_logic_lax
+    with_error_modes(:lax) do
+      markup = "true && false"
+      assert_template_result(' YES ', "{% if #{markup} %} YES {% endif %}")
       markup = "false || true"
-      Template.parse("{% if #{markup} %} YES {% endif %}")
+      assert_template_result('', "{% if #{markup} %} YES {% endif %}")
     end
   end
 
@@ -59,6 +92,32 @@ class ParsingQuirksTest < Minitest::Test
     end
   end
 
+  def test_unanchored_filter_arguments
+    with_error_modes(:lax) do
+      assert_template_result('hi', "{{ 'hi there' | split$$$:' ' | first }}")
+
+      assert_template_result('x', "{{ 'X' | downcase) }}")
+
+      # 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}}")
+    end
+  end
+
+  def test_invalid_variables_work
+    with_error_modes(:lax) do
+      assert_template_result('bar', "{% assign 123foo = 'bar' %}{{ 123foo }}")
+      assert_template_result('123', "{% assign 123 = 'bar' %}{{ 123 }}")
+    end
+  end
+
+  def test_extra_dots_in_ranges
+    with_error_modes(:lax) do
+      assert_template_result('12345', "{% for i in (1...5) %}{{ i }}{% endfor %}")
+    end
+  end
+
   def test_blank_variable_markup
     assert_template_result('', "{{}}")
   end
@@ -72,4 +131,24 @@ class ParsingQuirksTest < Minitest::Test
   def test_contains_in_id
     assert_template_result(' YES ', '{% if containsallshipments == true %} YES {% endif %}', { 'containsallshipments' => true })
   end
+
+  def test_incomplete_expression
+    with_error_modes(:lax) do
+      assert_template_result("false", "{{ false - }}")
+      assert_template_result("false", "{{ false > }}")
+      assert_template_result("false", "{{ false < }}")
+      assert_template_result("false", "{{ false = }}")
+      assert_template_result("false", "{{ false ! }}")
+      assert_template_result("false", "{{ false 1 }}")
+      assert_template_result("false", "{{ false a }}")
+
+      assert_template_result("false", "{% liquid assign foo = false -\n%}{{ foo }}")
+      assert_template_result("false", "{% liquid assign foo = false >\n%}{{ foo }}")
+      assert_template_result("false", "{% liquid assign foo = false <\n%}{{ foo }}")
+      assert_template_result("false", "{% liquid assign foo = false =\n%}{{ foo }}")
+      assert_template_result("false", "{% liquid assign foo = false !\n%}{{ foo }}")
+      assert_template_result("false", "{% liquid assign foo = false 1\n%}{{ foo }}")
+      assert_template_result("false", "{% liquid assign foo = false a\n%}{{ foo }}")
+    end
+  end
 end # ParsingQuirksTest

test/integration/security_test.rb

@@ -44,32 +44,39 @@ class SecurityTest < Minitest::Test
   end
 
   def test_does_not_permanently_add_filters_to_symbol_table
-    current_symbols = Symbol.all_symbols
+    assert_no_new_symbols do
+      # MRI imprecisely marks objects found on the C stack, which can result
+      # in uninitialized memory being marked. This can even result in the test failing
+      # deterministically for a given compilation of ruby. Using a separate thread will
+      # keep these writes of the symbol pointer on a separate stack that will be garbage
+      # collected after Thread#join.
+      Thread.new do
+        test = %( {{ "some_string" | a_bad_filter }} )
+        Template.parse(test).render!
+        nil
+      end.join
 
-    # MRI imprecisely marks objects found on the C stack, which can result
-    # in uninitialized memory being marked. This can even result in the test failing
-    # deterministically for a given compilation of ruby. Using a separate thread will
-    # keep these writes of the symbol pointer on a separate stack that will be garbage
-    # collected after Thread#join.
-    Thread.new do
-      test = %( {{ "some_string" | a_bad_filter }} )
-      Template.parse(test).render!
-      nil
-    end.join
-
-    GC.start
-
-    assert_equal([], Symbol.all_symbols - current_symbols)
+      GC.start
+    end
   end
 
   def test_does_not_add_drop_methods_to_symbol_table
+    assert_no_new_symbols do
+      assigns = { 'drop' => Drop.new }
+      assert_equal("", Template.parse("{{ drop.custom_method_1 }}", assigns).render!)
+      assert_equal("", Template.parse("{{ drop.custom_method_2 }}", assigns).render!)
+      assert_equal("", Template.parse("{{ drop.custom_method_3 }}", assigns).render!)
+    end
+  end
+
+  def assert_no_new_symbols
+    # Run once to trigger any first-time initialization which might create some symbols,
+    # for example autoload or lazy method parsing might create symbols on first execution.
+    yield
+
+    # Ensure no new symbols for further runs, i.e. the code does not leak symbols
     current_symbols = Symbol.all_symbols
-
-    assigns = { 'drop' => Drop.new }
-    assert_equal("", Template.parse("{{ drop.custom_method_1 }}", assigns).render!)
-    assert_equal("", Template.parse("{{ drop.custom_method_2 }}", assigns).render!)
-    assert_equal("", Template.parse("{{ drop.custom_method_3 }}", assigns).render!)
-
+    yield
     assert_equal([], Symbol.all_symbols - current_symbols)
   end
 

test/integration/self_drop_context_test.rb

@@ -0,0 +1,120 @@
+# frozen_string_literal: true
+
+require 'test_helper'
+
+class SelfDropContextTest < Minitest::Test
+  include Liquid
+
+  def test_self_drop_passed_as_render_param_preserves_original_scope
+    source = <<~LIQUID
+      {%- assign var = 42 -%}
+      {%- assign s = self -%}
+      {%- render "snippet1", other_self: s -%}
+    LIQUID
+
+    partials = {
+      'snippet1' => <<~LIQUID,
+        {%- assign var = 43 -%}
+        {{- other_self.var }}|{{ self.var -}}
+      LIQUID
+    }
+
+    assert_template_result('42|43', source, partials: partials)
+  end
+
+  def test_self_drop_in_render_without_passing_resolves_inner_scope
+    source = <<~LIQUID
+      {%- assign var = 42 -%}
+      {%- render "snippet1" -%}
+    LIQUID
+
+    partials = {
+      'snippet1' => <<~LIQUID,
+        {%- assign var = 99 -%}
+        {{- self.var -}}
+      LIQUID
+    }
+
+    assert_template_result('99', source, partials: partials)
+  end
+
+  def test_self_drop_passed_to_nested_renders_preserves_each_level
+    source = <<~LIQUID
+      {%- assign a = 1 -%}
+      {%- assign s1 = self -%}
+      {%- render "snippet1", outer: s1 -%}
+    LIQUID
+
+    partials = {
+      'snippet1' => <<~LIQUID,
+        {%- assign a = 2 -%}
+        {%- assign s2 = self -%}
+        {%- render "snippet2", outer: outer, middle: s2 -%}
+      LIQUID
+      'snippet2' => <<~LIQUID,
+        {%- assign a = 3 -%}
+        {{- outer.a }}|{{ middle.a }}|{{ self.a -}}
+      LIQUID
+    }
+
+    assert_template_result('1|2|3', source, partials: partials)
+  end
+
+  def test_self_drop_reflects_variables_assigned_after_creation
+    source = <<~LIQUID
+      {%- assign s = self -%}
+      {%- assign x = 42 %}{{ s.x -}}
+    LIQUID
+
+    assert_template_result('42', source)
+  end
+
+  def test_self_drop_context_setter_is_undefined
+    context = Context.new
+    drop = SelfDrop.new(context)
+    refute(drop.respond_to?(:context=))
+
+    assert_template_result('42', '{{ self.x }}', { 'x' => 42 })
+  end
+
+  def test_self_drop_repeated_lookups_compare_equal_for_same_context
+    context = Context.new
+    drop = context.find_variable("self")
+    cached_drop = context.find_variable("self")
+
+    assert_same(drop, cached_drop)
+    assert_equal(drop.object_id, cached_drop.object_id)
+    assert_equal(drop, cached_drop)
+  end
+
+  def test_assigned_self_drop_compares_equal_to_itself
+    assert_template_result('T', '{% assign s = self %}{% if s == s %}T{% else %}F{% endif %}')
+  end
+
+  def test_distinct_self_assignments_compare_equal_for_same_context
+    assert_template_result('T', '{% assign a = self %}{% assign b = self %}{% if a == b %}T{% else %}F{% endif %}')
+  end
+
+  def test_bare_self_compares_equal_to_bare_self
+    assert_template_result('T', '{% if self == self %}T{% else %}F{% endif %}')
+  end
+
+  def test_self_drop_with_strict_variables_does_not_raise_for_defined_var
+    t = Template.parse('{{ self.x }}')
+    result = t.render({ 'x' => 42 }, strict_variables: true)
+    assert_equal('42', result)
+  end
+
+  def test_self_drop_with_strict_variables_returns_nil_for_undefined_var
+    t = Template.parse('{{ self.x }}')
+    result = t.render({}, strict_variables: true)
+    assert_equal('', result)
+  end
+
+  def test_self_drop_can_be_passed_as_bare_drop_to_render
+    t = Template.parse('{{ self.x }}')
+    drop = SelfDrop.new(Context.new({ 'x' => 42 }))
+    result = t.render(drop)
+    assert_equal('42', result)
+  end
+end

test/integration/standard_filter_test.rb

@@ -164,6 +164,13 @@ class StandardFiltersTest < Minitest::Test
     assert_equal(['A', 'Z'], @filters.split('A1Z', 1))
   end
 
+  def test_squish_filter
+    assert_equal("foo bar boo", Liquid::Template.parse(%({{ " foo   bar
+\t   boo   " | squish }})).render)
+    assert_equal("", Liquid::Template.parse('{{ nil | squish }}').render)
+    assert_equal("", Liquid::Template.parse('{{ " " | squish }}').render)
+  end
+
   def test_escape
     assert_equal('&lt;strong&gt;', @filters.escape('<strong>'))
     assert_equal('1', @filters.escape(1))
@@ -1174,6 +1181,8 @@ class StandardFiltersTest < Minitest::Test
   end
 
   def test_all_filters_never_raise_non_liquid_exception
+    skip("too slow on non-CRuby due to many exceptions") unless RUBY_ENGINE == 'ruby'
+
     test_drop = TestDrop.new(value: "test")
     test_drop.context = Context.new
     test_enum = TestEnumerable.new

test/integration/tags/cycle_tag_test.rb

@@ -91,21 +91,26 @@ class CycleTagTest < Minitest::Test
     assert_match(/Syntax Error in 'cycle' - Valid syntax: cycle \[name :\] var/, error.message)
   end
 
-  def test_cycle_tag_unsupported_legacy_quirk
+  def test_cycle_tag_with_error_mode
     # QuotedFragment is more permissive than what Parser#expression allows.
     template1 = "{% assign 5 = 'b' %}{% cycle .5, .4 %}"
     template2 = "{% cycle .5: 'a', 'b' %}"
 
-    error1 = assert_raises(Liquid::SyntaxError) { Template.parse(template1) }
-    error2 = assert_raises(Liquid::SyntaxError) { Template.parse(template2) }
+    with_error_modes(:lax, :strict) do
+      assert_template_result("b", template1)
+      assert_template_result("a", template2)
+    end
 
-    expected_error = /Liquid syntax error: \[:dot, "."\] is not a valid expression/
+    with_error_modes(:strict2) do
+      error1 = assert_raises(Liquid::SyntaxError) { Template.parse(template1) }
+      error2 = assert_raises(Liquid::SyntaxError) { Template.parse(template2) }
 
-    assert_match(expected_error, error1.message)
-    assert_match(expected_error, error2.message)
+      assert_match(/Liquid syntax error:/, error1.message)
+      assert_match(/Liquid syntax error: \[:dot, "."\] is not a valid expression/, error2.message)
+    end
   end
 
-  def test_cycle_with_trailing_elements_legacy_syntax
+  def test_cycle_with_trailing_elements
     assignments = "{% assign a = 'A' %}{% assign n = 'N' %}"
 
     template1 = "#{assignments}{% cycle       'a'  'b', 'c' %}"
@@ -114,19 +119,29 @@ class CycleTagTest < Minitest::Test
     template4 = "#{assignments}{% cycle n  e: 'a', 'b', 'c' %}"
     template5 = "#{assignments}{% cycle n  e  'a', 'b', 'c' %}"
 
-    error1 = assert_raises(Liquid::SyntaxError) { Template.parse(template1) }
-    error2 = assert_raises(Liquid::SyntaxError) { Template.parse(template2) }
-    error3 = assert_raises(Liquid::SyntaxError) { Template.parse(template3) }
-    error4 = assert_raises(Liquid::SyntaxError) { Template.parse(template4) }
-    error5 = assert_raises(Liquid::SyntaxError) { Template.parse(template5) }
+    with_error_modes(:lax, :strict) do
+      assert_template_result("a", template1)
+      assert_template_result("a", template2)
+      assert_template_result("a", template3)
+      assert_template_result("N", template4)
+      assert_template_result("N", template5)
+    end
 
-    expected_error = /Expected end_of_string but found/
+    with_error_modes(:strict2) do
+      error1 = assert_raises(Liquid::SyntaxError) { Template.parse(template1) }
+      error2 = assert_raises(Liquid::SyntaxError) { Template.parse(template2) }
+      error3 = assert_raises(Liquid::SyntaxError) { Template.parse(template3) }
+      error4 = assert_raises(Liquid::SyntaxError) { Template.parse(template4) }
+      error5 = assert_raises(Liquid::SyntaxError) { Template.parse(template5) }
 
-    assert_match(expected_error, error1.message)
-    assert_match(expected_error, error2.message)
-    assert_match(expected_error, error3.message)
-    assert_match(expected_error, error4.message)
-    assert_match(expected_error, error5.message)
+      expected_error = /Expected end_of_string but found/
+
+      assert_match(expected_error, error1.message)
+      assert_match(expected_error, error2.message)
+      assert_match(expected_error, error3.message)
+      assert_match(expected_error, error4.message)
+      assert_match(expected_error, error5.message)
+    end
   end
 
   def test_cycle_name_with_invalid_expression
@@ -136,8 +151,14 @@ class CycleTagTest < Minitest::Test
       {% endfor %}
     LIQUID
 
-    error = assert_raises(Liquid::SyntaxError) { Template.parse(template) }
-    assert_match(/Unexpected character =/, error.message)
+    with_error_modes(:lax, :strict) do
+      refute_nil(Template.parse(template))
+    end
+
+    with_error_modes(:strict2) do
+      error = assert_raises(Liquid::SyntaxError) { Template.parse(template) }
+      assert_match(/Unexpected character =/, error.message)
+    end
   end
 
   def test_cycle_variable_with_invalid_expression
@@ -147,7 +168,13 @@ class CycleTagTest < Minitest::Test
       {% endfor %}
     LIQUID
 
-    error = assert_raises(Liquid::SyntaxError) { Template.parse(template) }
-    assert_match(/Unexpected character =/, error.message)
+    with_error_modes(:lax, :strict) do
+      refute_nil(Template.parse(template))
+    end
+
+    with_error_modes(:strict2) do
+      error = assert_raises(Liquid::SyntaxError) { Template.parse(template) }
+      assert_match(/Unexpected character =/, error.message)
+    end
   end
 end

test/integration/tags/include_tag_test.rb

@@ -204,13 +204,23 @@ class IncludeTagTest < Minitest::Test
     )
   end
 
-  def test_parsing_errors_for_legacy_quirk
-    assert_syntax_error(
-      '{% include "snippet" !!! arg1: "value1" ~~~ arg2: "value2" %}',
-    )
-    assert_syntax_error(
-      '{% include "snippet" | filter %}',
-    )
+  def test_strict2_parsing_errors
+    with_error_modes(:lax, :strict) do
+      assert_template_result(
+        'hello value1 value2',
+        '{% include "snippet" !!! arg1: "value1" ~~~ arg2: "value2" %}',
+        partials: { 'snippet' => 'hello {{ arg1 }} {{ arg2 }}' },
+      )
+    end
+
+    with_error_modes(:strict2) do
+      assert_syntax_error(
+        '{% include "snippet" !!! arg1: "value1" ~~~ arg2: "value2" %}',
+      )
+      assert_syntax_error(
+        '{% include "snippet" | filter %}',
+      )
+    end
   end
 
   def test_optional_commas
@@ -291,10 +301,16 @@ class IncludeTagTest < Minitest::Test
     env = Liquid::Environment.build(file_system: TestFileSystem.new)
 
     assert_raises(Liquid::SyntaxError) do
-      Template.parse("{% include template %}", environment: env).render!("template" => '{{ "X" || downcase }}')
+      Template.parse("{% include template %}", error_mode: :strict, environment: env).render!("template" => '{{ "X" || downcase }}')
+    end
+    with_error_modes(:lax) do
+      assert_equal('x', Template.parse("{% include template %}", error_mode: :strict, include_options_blacklist: true, environment: env).render!("template" => '{{ "X" || downcase }}'))
     end
     assert_raises(Liquid::SyntaxError) do
-      Template.parse("{% include template %}", include_options_blacklist: [:locale], environment: env).render!("template" => '{{ "X" || downcase }}')
+      Template.parse("{% include template %}", error_mode: :strict, include_options_blacklist: [:locale], environment: env).render!("template" => '{{ "X" || downcase }}')
+    end
+    with_error_modes(:lax) do
+      assert_equal('x', Template.parse("{% include template %}", error_mode: :strict, include_options_blacklist: [:error_mode], environment: env).render!("template" => '{{ "X" || downcase }}'))
     end
   end
 
@@ -349,7 +365,7 @@ class IncludeTagTest < Minitest::Test
       file_system: StubFileSystem.new('simple' => 'simple'),
     )
 
-    template = Liquid::Template.parse("{% include 'simple' %}", environment: env)
+    template = Liquid::Template.parse("{% include 'simple' %}", error_mode: :warn, environment: env)
     template.render(nil, strict_variables: true)
 
     assert_equal([], template.errors)
@@ -388,21 +404,84 @@ class IncludeTagTest < Minitest::Test
   def test_include_template_with_invalid_expression
     template = "{% include foo=>bar %}"
 
-    error = assert_raises(Liquid::SyntaxError) { Template.parse(template) }
-    assert_match(/Unexpected character =/, error.message)
+    with_error_modes(:lax, :strict) do
+      refute_nil(Template.parse(template))
+    end
+
+    with_error_modes(:strict2) do
+      error = assert_raises(Liquid::SyntaxError) { Template.parse(template) }
+      assert_match(/Unexpected character =/, error.message)
+    end
   end
 
   def test_include_with_invalid_expression
     template = '{% include "snippet" with foo=>bar %}'
 
-    error = assert_raises(Liquid::SyntaxError) { Template.parse(template) }
-    assert_match(/Unexpected character =/, error.message)
+    with_error_modes(:lax, :strict) do
+      refute_nil(Template.parse(template))
+    end
+
+    with_error_modes(:strict2) do
+      error = assert_raises(Liquid::SyntaxError) { Template.parse(template) }
+      assert_match(/Unexpected character =/, error.message)
+    end
   end
 
   def test_include_attribute_with_invalid_expression
     template = '{% include "snippet", key: foo=>bar %}'
 
-    error = assert_raises(Liquid::SyntaxError) { Template.parse(template) }
-    assert_match(/Unexpected character =/, error.message)
+    with_error_modes(:lax, :strict) do
+      refute_nil(Template.parse(template))
+    end
+
+    with_error_modes(:strict2) do
+      error = assert_raises(Liquid::SyntaxError) { Template.parse(template) }
+      assert_match(/Unexpected character =/, error.message)
+    end
+  end
+
+  def test_include_for_loop_true_with_for_keyword
+    with_error_modes(:lax, :strict, :strict2) do
+      template = Template.parse("{% include 'product' for products %}")
+      include_node = template.root.nodelist.first
+
+      assert(include_node.for_loop?, "Expected for_loop? to be true for 'for' keyword")
+    end
+  end
+
+  def test_include_for_loop_false_with_with_keyword
+    with_error_modes(:lax, :strict, :strict2) do
+      template = Template.parse("{% include 'product' with product %}")
+      include_node = template.root.nodelist.first
+
+      refute(include_node.for_loop?, "Expected for_loop? to be false for 'with' keyword")
+    end
+  end
+
+  def test_include_for_loop_false_without_keyword
+    with_error_modes(:lax, :strict, :strict2) do
+      template = Template.parse("{% include 'header' %}")
+      include_node = template.root.nodelist.first
+
+      refute(include_node.for_loop?, "Expected for_loop? to be false when no keyword")
+    end
+  end
+
+  def test_include_for_loop_with_alias
+    with_error_modes(:lax, :strict, :strict2) do
+      template = Template.parse("{% include 'product' for products as item %}")
+      include_node = template.root.nodelist.first
+
+      assert(include_node.for_loop?, "Expected for_loop? to be true for 'for' with alias")
+    end
+  end
+
+  def test_include_with_keyword_and_alias
+    with_error_modes(:lax, :strict, :strict2) do
+      template = Template.parse("{% include 'product' with products[0] as item %}")
+      include_node = template.root.nodelist.first
+
+      refute(include_node.for_loop?, "Expected for_loop? to be false for 'with' with alias")
+    end
   end
 end # IncludeTagTest

test/integration/tags/increment_tag_test.rb

@@ -27,4 +27,50 @@ class IncrementTagTest < Minitest::Test
       '{%decrement starboard %}',
     )
   end
+
+  def test_increment_strict2_rejects_invalid_variable_name
+    assert_raises(Liquid::SyntaxError) do
+      Template.parse('{% increment foo bar %}', error_mode: :strict2)
+    end
+  end
+
+  def test_increment_strict2_rejects_variable_starting_with_number
+    assert_raises(Liquid::SyntaxError) do
+      Template.parse('{% increment 11aa %}', error_mode: :strict2)
+    end
+  end
+
+  def test_increment_strict2_accepts_valid_variable_name
+    template = Template.parse('{% increment my-var %}', error_mode: :strict2)
+    assert_equal('0', template.render)
+  end
+
+  def test_decrement_strict2_rejects_invalid_variable_name
+    assert_raises(Liquid::SyntaxError) do
+      Template.parse('{% decrement foo bar %}', error_mode: :strict2)
+    end
+  end
+
+  def test_decrement_strict2_rejects_variable_starting_with_number
+    assert_raises(Liquid::SyntaxError) do
+      Template.parse('{% decrement 11aa %}', error_mode: :strict2)
+    end
+  end
+
+  def test_decrement_strict2_accepts_valid_variable_name
+    template = Template.parse('{% decrement my-var %}', error_mode: :strict2)
+    assert_equal('-1', template.render)
+  end
+
+  def test_increment_strict2_rejects_empty_variable_name
+    assert_raises(Liquid::SyntaxError) do
+      Template.parse('{% increment %}', error_mode: :strict2)
+    end
+  end
+
+  def test_decrement_strict2_rejects_empty_variable_name
+    assert_raises(Liquid::SyntaxError) do
+      Template.parse('{% decrement %}', error_mode: :strict2)
+    end
+  end
 end

test/integration/tags/render_tag_test.rb

@@ -105,13 +105,23 @@ class RenderTagTest < Minitest::Test
     assert_syntax_error("{% assign name = 'snippet' %}{% render name %}")
   end
 
-  def test_parsing_errors_legacy_syntax
-    assert_syntax_error(
-      '{% render "snippet" !!! arg1: "value1" ~~~ arg2: "value2" %}',
-    )
-    assert_syntax_error(
-      '{% render "snippet" | filter %}',
-    )
+  def test_strict2_parsing_errors
+    with_error_modes(:lax, :strict) do
+      assert_template_result(
+        'hello value1 value2',
+        '{% render "snippet" !!! arg1: "value1" ~~~ arg2: "value2" %}',
+        partials: { 'snippet' => 'hello {{ arg1 }} {{ arg2 }}' },
+      )
+    end
+
+    with_error_modes(:strict2) do
+      assert_syntax_error(
+        '{% render "snippet" !!! arg1: "value1" ~~~ arg2: "value2" %}',
+      )
+      assert_syntax_error(
+        '{% render "snippet" | filter %}',
+      )
+    end
   end
 
   def test_optional_commas
@@ -164,16 +174,16 @@ class RenderTagTest < Minitest::Test
   def test_increment_is_isolated_between_renders
     assert_template_result(
       '010',
-      '{% increment %}{% increment %}{% render "incr" %}',
-      partials: { 'incr' => '{% increment %}' },
+      '{% increment port %}{% increment port %}{% render "incr" %}',
+      partials: { 'incr' => '{% increment port %}' },
     )
   end
 
   def test_decrement_is_isolated_between_renders
     assert_template_result(
       '-1-2-1',
-      '{% decrement %}{% decrement %}{% render "decr" %}',
-      partials: { 'decr' => '{% decrement %}' },
+      '{% decrement port %}{% decrement port %}{% render "decr" %}',
+      partials: { 'decr' => '{% decrement port %}' },
     )
   end
 
@@ -307,13 +317,27 @@ class RenderTagTest < Minitest::Test
 
   def test_render_with_invalid_expression
     template = '{% render "snippet" with foo=>bar %}'
-    error = assert_raises(Liquid::SyntaxError) { Template.parse(template) }
-    assert_match(/Unexpected character =/, error.message)
+
+    with_error_modes(:lax, :strict) do
+      refute_nil(Template.parse(template))
+    end
+
+    with_error_modes(:strict2) do
+      error = assert_raises(Liquid::SyntaxError) { Template.parse(template) }
+      assert_match(/Unexpected character =/, error.message)
+    end
   end
 
   def test_render_attribute_with_invalid_expression
     template = '{% render "snippet", key: foo=>bar %}'
-    error = assert_raises(Liquid::SyntaxError) { Template.parse(template) }
-    assert_match(/Unexpected character =/, error.message)
+
+    with_error_modes(:lax, :strict) do
+      refute_nil(Template.parse(template))
+    end
+
+    with_error_modes(:strict2) do
+      error = assert_raises(Liquid::SyntaxError) { Template.parse(template) }
+      assert_match(/Unexpected character =/, error.message)
+    end
   end
 end

test/integration/tags/table_row_test.rb

@@ -188,6 +188,29 @@ class TableRowTest < Minitest::Test
     assert_template_result(expected_output, template)
   end
 
+  def test_table_row_renders_correct_error_message_for_invalid_parameters
+    assert_template_result(
+      "Liquid error (line 1): invalid integer",
+      '{% tablerow n in (1...10) limit:true %} {{n}} {% endtablerow %}',
+      error_mode: :warn,
+      render_errors: true,
+    )
+
+    assert_template_result(
+      "Liquid error (line 1): invalid integer",
+      '{% tablerow n in (1...10) offset:true %} {{n}} {% endtablerow %}',
+      error_mode: :warn,
+      render_errors: true,
+    )
+
+    assert_template_result(
+      "Liquid error (line 1): invalid integer",
+      '{% tablerow n in (1...10) cols:true %} {{n}} {% endtablerow %}',
+      render_errors: true,
+      error_mode: :warn,
+    )
+  end
+
   def test_table_row_handles_interrupts
     assert_template_result(
       "<tr class=\"row1\">\n<td class=\"col1\"> 1 </td></tr>\n",
@@ -236,7 +259,7 @@ class TableRowTest < Minitest::Test
     )
   end
 
-  def test_tablerow_with_cols_attribute
+  def test_tablerow_with_cols_attribute_in_strict2_mode
     template = <<~LIQUID.chomp
       {% tablerow i in (1..6) cols: 3 %}{{ i }}{% endtablerow %}
     LIQUID
@@ -247,10 +270,12 @@ class TableRowTest < Minitest::Test
       <tr class="row2"><td class="col1">4</td><td class="col2">5</td><td class="col3">6</td></tr>
     OUTPUT
 
-    assert_template_result(expected, template)
+    with_error_modes(:strict2) do
+      assert_template_result(expected, template)
+    end
   end
 
-  def test_tablerow_with_limit_attribute
+  def test_tablerow_with_limit_attribute_in_strict2_mode
     template = <<~LIQUID.chomp
       {% tablerow i in (1..10) limit: 3 %}{{ i }}{% endtablerow %}
     LIQUID
@@ -260,10 +285,12 @@ class TableRowTest < Minitest::Test
       <td class="col1">1</td><td class="col2">2</td><td class="col3">3</td></tr>
     OUTPUT
 
-    assert_template_result(expected, template)
+    with_error_modes(:strict2) do
+      assert_template_result(expected, template)
+    end
   end
 
-  def test_tablerow_with_offset_attribute
+  def test_tablerow_with_offset_attribute_in_strict2_mode
     template = <<~LIQUID.chomp
       {% tablerow i in (1..5) offset: 2 %}{{ i }}{% endtablerow %}
     LIQUID
@@ -273,10 +300,12 @@ class TableRowTest < Minitest::Test
       <td class="col1">3</td><td class="col2">4</td><td class="col3">5</td></tr>
     OUTPUT
 
-    assert_template_result(expected, template)
+    with_error_modes(:strict2) do
+      assert_template_result(expected, template)
+    end
   end
 
-  def test_tablerow_with_range_attribute
+  def test_tablerow_with_range_attribute_in_strict2_mode
     template = <<~LIQUID.chomp
       {% tablerow i in (1..3) range: (1..10) %}{{ i }}{% endtablerow %}
     LIQUID
@@ -286,10 +315,12 @@ class TableRowTest < Minitest::Test
       <td class="col1">1</td><td class="col2">2</td><td class="col3">3</td></tr>
     OUTPUT
 
-    assert_template_result(expected, template)
+    with_error_modes(:strict2) do
+      assert_template_result(expected, template)
+    end
   end
 
-  def test_tablerow_with_multiple_attributes
+  def test_tablerow_with_multiple_attributes_in_strict2_mode
     template = <<~LIQUID.chomp
       {% tablerow i in (1..10) cols: 2, limit: 4, offset: 1 %}{{ i }}{% endtablerow %}
     LIQUID
@@ -300,10 +331,12 @@ class TableRowTest < Minitest::Test
       <tr class="row2"><td class="col1">4</td><td class="col2">5</td></tr>
     OUTPUT
 
-    assert_template_result(expected, template)
+    with_error_modes(:strict2) do
+      assert_template_result(expected, template)
+    end
   end
 
-  def test_tablerow_with_variable_collection
+  def test_tablerow_with_variable_collection_in_strict2_mode
     template = <<~LIQUID.chomp
       {% tablerow n in numbers cols: 2 %}{{ n }}{% endtablerow %}
     LIQUID
@@ -314,10 +347,12 @@ class TableRowTest < Minitest::Test
       <tr class="row2"><td class="col1">3</td><td class="col2">4</td></tr>
     OUTPUT
 
-    assert_template_result(expected, template, { 'numbers' => [1, 2, 3, 4] })
+    with_error_modes(:strict2) do
+      assert_template_result(expected, template, { 'numbers' => [1, 2, 3, 4] })
+    end
   end
 
-  def test_tablerow_with_dotted_access
+  def test_tablerow_with_dotted_access_in_strict2_mode
     template = <<~LIQUID.chomp
       {% tablerow n in obj.numbers cols: 2 %}{{ n }}{% endtablerow %}
     LIQUID
@@ -328,10 +363,12 @@ class TableRowTest < Minitest::Test
       <tr class="row2"><td class="col1">3</td><td class="col2">4</td></tr>
     OUTPUT
 
-    assert_template_result(expected, template, { 'obj' => { 'numbers' => [1, 2, 3, 4] } })
+    with_error_modes(:strict2) do
+      assert_template_result(expected, template, { 'obj' => { 'numbers' => [1, 2, 3, 4] } })
+    end
   end
 
-  def test_tablerow_with_bracketed_access
+  def test_tablerow_with_bracketed_access_in_strict2_mode
     template = <<~LIQUID.chomp
       {% tablerow n in obj["numbers"] cols: 2 %}{{ n }}{% endtablerow %}
     LIQUID
@@ -341,10 +378,12 @@ class TableRowTest < Minitest::Test
       <td class="col1">10</td><td class="col2">20</td></tr>
     OUTPUT
 
-    assert_template_result(expected, template, { 'obj' => { 'numbers' => [10, 20] } })
+    with_error_modes(:strict2) do
+      assert_template_result(expected, template, { 'obj' => { 'numbers' => [10, 20] } })
+    end
   end
 
-  def test_tablerow_without_attributes
+  def test_tablerow_without_attributes_in_strict2_mode
     template = <<~LIQUID.chomp
       {% tablerow i in (1..3) %}{{ i }}{% endtablerow %}
     LIQUID
@@ -354,24 +393,30 @@ class TableRowTest < Minitest::Test
       <td class="col1">1</td><td class="col2">2</td><td class="col3">3</td></tr>
     OUTPUT
 
-    assert_template_result(expected, template)
+    with_error_modes(:strict2) do
+      assert_template_result(expected, template)
+    end
   end
 
-  def test_tablerow_without_in_keyword
+  def test_tablerow_without_in_keyword_in_strict2_mode
     template = '{% tablerow i (1..10) %}{{ i }}{% endtablerow %}'
 
-    error = assert_raises(SyntaxError) { Template.parse(template) }
-    assert_equal("Liquid syntax error: For loops require an 'in' clause in \"i (1..10)\"", error.message)
+    with_error_modes(:strict2) do
+      error = assert_raises(SyntaxError) { Template.parse(template) }
+      assert_equal("Liquid syntax error: For loops require an 'in' clause in \"i (1..10)\"", error.message)
+    end
   end
 
-  def test_tablerow_with_multiple_invalid_attributes_reports_first
+  def test_tablerow_with_multiple_invalid_attributes_reports_first_in_strict2_mode
     template = '{% tablerow i in (1..10) invalid1: 5, invalid2: 10 %}{{ i }}{% endtablerow %}'
 
-    error = assert_raises(SyntaxError) { Template.parse(template) }
-    assert_equal("Liquid syntax error: Invalid attribute 'invalid1' in tablerow loop. Valid attributes are cols, limit, offset, and range in \"i in (1..10) invalid1: 5, invalid2: 10\"", error.message)
+    with_error_modes(:strict2) do
+      error = assert_raises(SyntaxError) { Template.parse(template) }
+      assert_equal("Liquid syntax error: Invalid attribute 'invalid1' in tablerow loop. Valid attributes are cols, limit, offset, and range in \"i in (1..10) invalid1: 5, invalid2: 10\"", error.message)
+    end
   end
 
-  def test_tablerow_with_empty_collection
+  def test_tablerow_with_empty_collection_in_strict2_mode
     template = <<~LIQUID.chomp
       {% tablerow i in empty_array cols: 2 %}{{ i }}{% endtablerow %}
     LIQUID
@@ -381,18 +426,43 @@ class TableRowTest < Minitest::Test
       </tr>
     OUTPUT
 
-    assert_template_result(expected, template, { 'empty_array' => [] })
+    with_error_modes(:strict2) do
+      assert_template_result(expected, template, { 'empty_array' => [] })
+    end
   end
 
-  def test_tablerow_with_invalid_attribute
+  def test_tablerow_with_invalid_attribute_strict_vs_strict2
     template = '{% tablerow i in (1..5) invalid_attr: 10 %}{{ i }}{% endtablerow %}'
-    error = assert_raises(SyntaxError) { Template.parse(template) }
-    assert_match(/Invalid attribute 'invalid_attr'/, error.message)
+
+    expected = <<~OUTPUT
+      <tr class="row1">
+      <td class="col1">1</td><td class="col2">2</td><td class="col3">3</td><td class="col4">4</td><td class="col5">5</td></tr>
+    OUTPUT
+
+    with_error_modes(:lax, :strict) do
+      assert_template_result(expected, template)
+    end
+
+    with_error_modes(:strict2) do
+      error = assert_raises(SyntaxError) { Template.parse(template) }
+      assert_match(/Invalid attribute 'invalid_attr'/, error.message)
+    end
   end
 
-  def test_tablerow_with_invalid_expression
+  def test_tablerow_with_invalid_expression_strict_vs_strict2
     template = '{% tablerow i in (1..5) limit: foo=>bar %}{{ i }}{% endtablerow %}'
-    error = assert_raises(SyntaxError) { Template.parse(template) }
-    assert_match(/Unexpected character =/, error.message)
+
+    with_error_modes(:lax, :strict) do
+      expected = <<~OUTPUT
+        <tr class="row1">
+        </tr>
+      OUTPUT
+      assert_template_result(expected, template)
+    end
+
+    with_error_modes(:strict2) do
+      error = assert_raises(SyntaxError) { Template.parse(template) }
+      assert_match(/Unexpected character =/, error.message)
+    end
   end
 end

test/integration/template_test.rb

@@ -44,6 +44,16 @@ class TemplateTest < Minitest::Test
     assert_equal('from instance assigns', t.parse("{{ foo }}").render!)
   end
 
+  def test_warnings_is_not_exponential_time
+    str = "false"
+    100.times do
+      str = "{% if true %}true{% else %}#{str}{% endif %}"
+    end
+
+    t = Template.parse(str)
+    assert_equal([], Timeout.timeout(1) { t.warnings })
+  end
+
   def test_instance_assigns_persist_on_same_template_parsing_between_renders
     t = Template.new.parse("{{ foo }}{% assign foo = 'foo' %}{{ foo }}")
     assert_equal('foo', t.render!)
@@ -169,6 +179,86 @@ class TemplateTest < Minitest::Test
     assert_equal("すごい", t.render)
   end
 
+  def test_cumulative_render_score_limit_across_render_tags
+    file_system = StubFileSystem.new(
+      'loop' => '{% for a in (1..10) %} foo {% endfor %}',
+    )
+    environment = Liquid::Environment.build(file_system: file_system)
+
+    # Without cumulative limit, all 5 partials render successfully
+    t = Template.parse(
+      '{% render "loop" %}{% render "loop" %}{% render "loop" %}{% render "loop" %}{% render "loop" %}',
+      environment: environment,
+    )
+    unlimited_output = t.render!
+    total_cumulative = t.resource_limits.cumulative_render_score
+
+    # With cumulative limit set below the total, rendering stops early
+    t2 = Template.parse(
+      '{% render "loop" %}{% render "loop" %}{% render "loop" %}{% render "loop" %}{% render "loop" %}',
+      environment: environment,
+    )
+    t2.resource_limits.cumulative_render_score_limit = total_cumulative / 2
+    limited_output = t2.render
+    assert(t2.resource_limits.reached?)
+    assert_operator(limited_output.length, :<, unlimited_output.length)
+  end
+
+  def test_cumulative_render_score_limit_raises_on_render_bang
+    file_system = StubFileSystem.new(
+      'loop' => '{% for a in (1..10) %} foo {% endfor %}',
+    )
+    environment = Liquid::Environment.build(file_system: file_system)
+    t = Template.parse(
+      '{% render "loop" %}{% render "loop" %}{% render "loop" %}{% render "loop" %}{% render "loop" %}',
+      environment: environment,
+    )
+    t.resource_limits.cumulative_render_score_limit = 20
+    assert_raises(Liquid::MemoryError) do
+      t.render!
+    end
+  end
+
+  def test_cumulative_assign_score_limit_across_include_tags
+    file_system = StubFileSystem.new(
+      'assign_partial' => '{% assign x = "a long string value here" %}',
+    )
+    environment = Liquid::Environment.build(file_system: file_system)
+
+    # Without cumulative limit, all 5 partials render
+    t = Template.parse(
+      '{% include "assign_partial" %}{% include "assign_partial" %}{% include "assign_partial" %}{% include "assign_partial" %}{% include "assign_partial" %}',
+      environment: environment,
+    )
+    t.render!
+    total_cumulative = t.resource_limits.cumulative_assign_score
+
+    # With cumulative limit set below the total, rendering stops early
+    t2 = Template.parse(
+      '{% include "assign_partial" %}{% include "assign_partial" %}{% include "assign_partial" %}{% include "assign_partial" %}{% include "assign_partial" %}',
+      environment: environment,
+    )
+    t2.resource_limits.cumulative_assign_score_limit = total_cumulative / 2
+    t2.render
+    assert(t2.resource_limits.reached?)
+  end
+
+  def test_cumulative_render_score_tracks_across_partials_without_limit
+    file_system = StubFileSystem.new(
+      'loop' => '{% for a in (1..10) %} foo {% endfor %}',
+    )
+    environment = Liquid::Environment.build(file_system: file_system)
+    t = Template.parse(
+      '{% render "loop" %}{% render "loop" %}{% render "loop" %}',
+      environment: environment,
+    )
+    t.render!
+    assert(
+      t.resource_limits.cumulative_render_score > t.resource_limits.render_score,
+      "cumulative should exceed per-template score after multiple partials",
+    )
+  end
+
   def test_default_resource_limits_unaffected_by_render_with_context
     context = Context.new
     t = Template.parse("{% for a in (1..100) %}x{% assign foo = 1 %} {% endfor %}")
@@ -249,7 +339,7 @@ class TemplateTest < Minitest::Test
   end
 
   def test_nil_value_does_not_raise
-    t      = Template.parse("some{{x}}thing")
+    t      = Template.parse("some{{x}}thing", error_mode: :strict)
     result = t.render!({ 'x' => nil }, strict_variables: true)
 
     assert_equal(0, t.errors.count)

test/integration/variable_test.rb

@@ -55,7 +55,7 @@ class VariableTest < Minitest::Test
 
   def test_expression_with_whitespace_in_square_brackets
     assert_template_result('result', "{{ a[ 'b' ] }}", { 'a' => { 'b' => 'result' } })
-    assert_template_result('result', "{{ a[ [ 'b' ] ] }}", { 'b' => 'c', 'a' => { 'c' => 'result' } })
+    assert_template_result('result', "{{ a[ self[ 'b' ] ] }}", { 'b' => 'c', 'a' => { 'c' => 'result' } })
   end
 
   def test_ignore_unknown
@@ -135,17 +135,17 @@ class VariableTest < Minitest::Test
   end
 
   def test_dynamic_find_var
-    assert_template_result('bar', '{{ [key] }}', { 'key' => 'foo', 'foo' => 'bar' })
+    assert_template_result('bar', '{{ self[key] }}', { 'key' => 'foo', 'foo' => 'bar' })
   end
 
   def test_raw_value_variable
-    assert_template_result('bar', '{{ [key] }}', { 'key' => 'foo', 'foo' => 'bar' })
+    assert_template_result('bar', '{{ self[key] }}', { 'key' => 'foo', 'foo' => 'bar' })
   end
 
   def test_dynamic_find_var_with_drop
     assert_template_result(
       'bar',
-      '{{ [list[settings.zero]] }}',
+      '{{ self[list[settings.zero]] }}',
       {
         'list' => ['foo'],
         'settings' => SettingsDrop.new("zero" => 0),
@@ -155,7 +155,7 @@ class VariableTest < Minitest::Test
 
     assert_template_result(
       'foo',
-      '{{ [list[settings.zero]["foo"]] }}',
+      '{{ self[list[settings.zero]["foo"]] }}',
       {
         'list' => [{ 'foo' => 'bar' }],
         'settings' => SettingsDrop.new("zero" => 0),
@@ -176,33 +176,102 @@ class VariableTest < Minitest::Test
     )
   end
 
+  def test_variable_lookup_should_not_hang_with_invalid_syntax
+    Timeout.timeout(1) do
+      assert_template_result(
+        'bar',
+        "{{['foo'}}",
+        {
+          'foo' => 'bar',
+        },
+        error_mode: :lax,
+      )
+    end
+
+    very_long_key = "1234567890" * 100
+
+    template_list = [
+      "{{['#{very_long_key}']}}", # valid
+      "{{['#{very_long_key}'}}", # missing closing bracket
+      "{{[['#{very_long_key}']}}", # extra open bracket
+    ]
+
+    template_list.each do |template|
+      Timeout.timeout(1) do
+        assert_template_result(
+          'bar',
+          template,
+          {
+            very_long_key => 'bar',
+          },
+          error_mode: :lax,
+        )
+      end
+    end
+  end
+
   def test_filter_with_single_trailing_comma
     template = '{{ "hello" | append: "world", }}'
 
-    assert_template_result('helloworld', template)
+    with_error_modes(:strict) do
+      error = assert_raises(Liquid::SyntaxError) { Template.parse(template) }
+      assert_match(/is not a valid expression/, error.message)
+    end
+
+    with_error_modes(:strict2) do
+      assert_template_result('helloworld', template)
+    end
   end
 
   def test_multiple_filters_with_trailing_commas
     template = '{{ "hello" | append: "1", | append: "2", }}'
 
-    assert_template_result('hello12', template)
+    with_error_modes(:strict) do
+      error = assert_raises(Liquid::SyntaxError) { Template.parse(template) }
+      assert_match(/is not a valid expression/, error.message)
+    end
+
+    with_error_modes(:strict2) do
+      assert_template_result('hello12', template)
+    end
   end
 
   def test_filter_with_colon_but_no_arguments
     template = '{{ "test" | upcase: }}'
 
-    assert_template_result('TEST', template)
+    with_error_modes(:strict) do
+      error = assert_raises(Liquid::SyntaxError) { Template.parse(template) }
+      assert_match(/is not a valid expression/, error.message)
+    end
+
+    with_error_modes(:strict2) do
+      assert_template_result('TEST', template)
+    end
   end
 
   def test_filter_chain_with_colon_no_args
     template = '{{ "test" | append: "x" | upcase: }}'
 
-    assert_template_result('TESTX', template)
+    with_error_modes(:strict) do
+      error = assert_raises(Liquid::SyntaxError) { Template.parse(template) }
+      assert_match(/is not a valid expression/, error.message)
+    end
+
+    with_error_modes(:strict2) do
+      assert_template_result('TESTX', template)
+    end
   end
 
   def test_combining_trailing_comma_and_empty_args
     template = '{{ "test" | append: "x", | upcase: }}'
 
-    assert_template_result('TESTX', template)
+    with_error_modes(:strict) do
+      error = assert_raises(Liquid::SyntaxError) { Template.parse(template) }
+      assert_match(/is not a valid expression/, error.message)
+    end
+
+    with_error_modes(:strict2) do
+      assert_template_result('TESTX', template)
+    end
   end
 end

test/test_helper.rb

@@ -8,6 +8,13 @@ $LOAD_PATH.unshift(File.join(File.expand_path(__dir__), '..', 'lib'))
 require 'liquid.rb'
 require 'liquid/profiler'
 
+mode = :strict
+if (env_mode = ENV['LIQUID_PARSER_MODE'])
+  puts "-- #{env_mode.upcase} ERROR MODE"
+  mode = env_mode.to_sym
+end
+Liquid::Environment.default.error_mode = mode
+
 if Minitest.const_defined?('Test')
   # We're on Minitest 5+. Nothing to do here.
 else
@@ -27,27 +34,27 @@ module Minitest
 
     def assert_template_result(
       expected, template, assigns = {},
-      message: nil, partials: nil, render_errors: false,
+      message: nil, partials: nil, error_mode: Liquid::Environment.default.error_mode, render_errors: false,
       template_factory: nil
     )
       file_system = StubFileSystem.new(partials || {})
       environment = Liquid::Environment.build(file_system: file_system)
-      template = Liquid::Template.parse(template, line_numbers: true, environment: environment)
+      template = Liquid::Template.parse(template, line_numbers: true, error_mode: error_mode&.to_sym, environment: environment)
       registers = Liquid::Registers.new(file_system: file_system, template_factory: template_factory)
       context = Liquid::Context.build(static_environments: assigns, rethrow_errors: !render_errors, registers: registers, environment: environment)
       output = template.render(context)
       assert_equal(expected, output, message)
     end
 
-    def assert_match_syntax_error(match, template)
+    def assert_match_syntax_error(match, template, error_mode: nil)
       exception = assert_raises(Liquid::SyntaxError) do
-        Template.parse(template, line_numbers: true).render
+        Template.parse(template, line_numbers: true, error_mode: error_mode&.to_sym).render
       end
       assert_match(match, exception.message)
     end
 
-    def assert_syntax_error(template)
-      assert_match_syntax_error("", template)
+    def assert_syntax_error(template, error_mode: nil)
+      assert_match_syntax_error("", template, error_mode: error_mode)
     end
 
     def assert_usage_increment(name, times: 1)
@@ -75,6 +82,16 @@ module Minitest
       Environment.dangerously_override(environment, &blk)
     end
 
+    def with_error_modes(*modes)
+      old_mode = Liquid::Environment.default.error_mode
+      modes.each do |mode|
+        Liquid::Environment.default.error_mode = mode
+        yield
+      end
+    ensure
+      Liquid::Environment.default.error_mode = old_mode
+    end
+
     def with_custom_tag(tag_name, tag_class, &block)
       environment = Liquid::Environment.default.dup
       environment.register_tag(tag_name, tag_class)

test/unit/condition_unit_test.rb

@@ -166,25 +166,35 @@ class ConditionUnitTest < Minitest::Test
     assert_includes(err.lines.map(&:strip), expected)
   end
 
-  def test_parse_expression_with_safe_true
-    environment = Environment.build
+  def test_parse_expression_in_strict_mode
+    environment = Environment.build(error_mode: :strict)
     parse_context = ParseContext.new(environment: environment)
-    result = Condition.parse_expression(parse_context, 'product.title', safe: true)
+    result = Condition.parse_expression(parse_context, 'product.title')
 
     assert_instance_of(VariableLookup, result)
     assert_equal('product', result.name)
     assert_equal(['title'], result.lookups)
   end
 
-  def test_parse_expression_raises_internal_error_if_not_safe
-    environment = Environment.build
+  def test_parse_expression_in_strict2_mode_raises_internal_error
+    environment = Environment.build(error_mode: :strict2)
     parse_context = ParseContext.new(environment: environment)
 
     error = assert_raises(Liquid::InternalError) do
       Condition.parse_expression(parse_context, 'product.title')
     end
 
-    assert_match(/unsafe parse_expression cannot be used/, error.message)
+    assert_match(/unsafe parse_expression cannot be used in strict2 mode/, error.message)
+  end
+
+  def test_parse_expression_with_safe_true_in_strict2_mode
+    environment = Environment.build(error_mode: :strict2)
+    parse_context = ParseContext.new(environment: environment)
+    result = Condition.parse_expression(parse_context, 'product.title', safe: true)
+
+    assert_instance_of(VariableLookup, result)
+    assert_equal('product', result.name)
+    assert_equal(['title'], result.lookups)
   end
 
   # Tests for blank? comparison without ActiveSupport

test/unit/lexer_unit_test.rb

@@ -26,6 +26,13 @@ class LexerUnitTest < Minitest::Test
     )
   end
 
+  def test_assignment_and_comparison_tokens
+    assert_equal(
+      [[:id, 'n'], [:assign, '='], [:number, '1'], [:comparison, '=='], [:number, '2'], [:end_of_string]],
+      tokenize('n=1==2'),
+    )
+  end
+
   def test_comparison
     assert_equal(
       [[:comparison, '=='], [:comparison, '<>'], [:comparison, 'contains'], [:end_of_string]],

test/unit/parse_context_unit_test.rb

@@ -6,81 +6,118 @@ class ParseContextUnitTest < Minitest::Test
   include Liquid
 
   def test_safe_parse_expression_with_variable_lookup
-    parser = parse_context.new_parser('product.title')
-    result = parse_context.safe_parse_expression(parser)
+    parser_strict = strict_parse_context.new_parser('product.title')
+    result_strict = strict_parse_context.safe_parse_expression(parser_strict)
 
-    assert_instance_of(VariableLookup, result)
-    assert_equal('product', result.name)
-    assert_equal(['title'], result.lookups)
+    parser_strict2 = strict2_parse_context.new_parser('product.title')
+    result_strict2 = strict2_parse_context.safe_parse_expression(parser_strict2)
+
+    assert_instance_of(VariableLookup, result_strict)
+    assert_equal('product', result_strict.name)
+    assert_equal(['title'], result_strict.lookups)
+
+    assert_instance_of(VariableLookup, result_strict2)
+    assert_equal('product', result_strict2.name)
+    assert_equal(['title'], result_strict2.lookups)
   end
 
   def test_safe_parse_expression_raises_syntax_error_for_invalid_expression
-    parser = parse_context.new_parser('')
+    parser_strict = strict_parse_context.new_parser('')
+    parser_strict2 = strict2_parse_context.new_parser('')
 
-    error = assert_raises(Liquid::SyntaxError) do
-      parse_context.safe_parse_expression(parser)
+    error_strict = assert_raises(Liquid::SyntaxError) do
+      strict_parse_context.safe_parse_expression(parser_strict)
+    end
+    assert_match(/is not a valid expression/, error_strict.message)
+
+    error_strict2 = assert_raises(Liquid::SyntaxError) do
+      strict2_parse_context.safe_parse_expression(parser_strict2)
     end
 
-    assert_match(/is not a valid expression/, error.message)
+    assert_match(/is not a valid expression/, error_strict2.message)
   end
 
   def test_parse_expression_with_variable_lookup
+    result_strict = strict_parse_context.parse_expression('product.title')
+
+    assert_instance_of(VariableLookup, result_strict)
+    assert_equal('product', result_strict.name)
+    assert_equal(['title'], result_strict.lookups)
+
     error = assert_raises(Liquid::InternalError) do
-      parse_context.parse_expression('product.title')
+      strict2_parse_context.parse_expression('product.title')
     end
 
-    assert_match(/unsafe parse_expression cannot be used/, error.message)
+    assert_match(/unsafe parse_expression cannot be used in strict2 mode/, error.message)
   end
 
   def test_parse_expression_with_safe_true
-    result = parse_context.parse_expression('product.title', safe: true)
+    result_strict = strict_parse_context.parse_expression('product.title', safe: true)
 
-    assert_instance_of(VariableLookup, result)
-    assert_equal('product', result.name)
-    assert_equal(['title'], result.lookups)
+    assert_instance_of(VariableLookup, result_strict)
+    assert_equal('product', result_strict.name)
+    assert_equal(['title'], result_strict.lookups)
+
+    result_strict2 = strict2_parse_context.parse_expression('product.title', safe: true)
+
+    assert_instance_of(VariableLookup, result_strict2)
+    assert_equal('product', result_strict2.name)
+    assert_equal(['title'], result_strict2.lookups)
   end
 
   def test_parse_expression_with_empty_string
+    result_strict = strict_parse_context.parse_expression('')
+    assert_nil(result_strict)
+
     error = assert_raises(Liquid::InternalError) do
-      parse_context.parse_expression('')
+      strict2_parse_context.parse_expression('')
     end
 
-    assert_match(/unsafe parse_expression cannot be used/, error.message)
+    assert_match(/unsafe parse_expression cannot be used in strict2 mode/, error.message)
   end
 
   def test_parse_expression_with_empty_string_and_safe_true
-    result = parse_context.parse_expression('', safe: true)
-    assert_nil(result)
+    result_strict = strict_parse_context.parse_expression('', safe: true)
+    assert_nil(result_strict)
+
+    result_strict2 = strict2_parse_context.parse_expression('', safe: true)
+    assert_nil(result_strict2)
   end
 
   def test_safe_parse_expression_advances_parser_pointer
-    parser = parse_context.new_parser('foo, bar')
+    parser = strict2_parse_context.new_parser('foo, bar')
 
     # safe_parse_expression consumes "foo"
-    first_result = parse_context.safe_parse_expression(parser)
+    first_result = strict2_parse_context.safe_parse_expression(parser)
     assert_instance_of(VariableLookup, first_result)
     assert_equal('foo', first_result.name)
 
     parser.consume(:comma)
 
     # safe_parse_expression consumes "bar"
-    second_result = parse_context.safe_parse_expression(parser)
+    second_result = strict2_parse_context.safe_parse_expression(parser)
     assert_instance_of(VariableLookup, second_result)
     assert_equal('bar', second_result.name)
 
     parser.consume(:end_of_string)
   end
 
-  def test_parse_expression_with_whitespace
-    result = parse_context.parse_expression('   ', safe: true)
+  def test_parse_expression_with_whitespace_in_strict2_mode
+    result = strict2_parse_context.parse_expression('   ', safe: true)
     assert_nil(result)
   end
 
   private
 
-  def parse_context
-    @parse_context ||= ParseContext.new(
-      environment: Environment.build,
+  def strict_parse_context
+    @strict_parse_context ||= ParseContext.new(
+      environment: Environment.build(error_mode: :strict),
+    )
+  end
+
+  def strict2_parse_context
+    @strict2_parse_context ||= ParseContext.new(
+      environment: Environment.build(error_mode: :strict2),
     )
   end
 end

test/unit/parser_unit_test.rb

@@ -82,6 +82,78 @@ class ParserUnitTest < Minitest::Test
     end
   end
 
+  def test_assignment_delimiter
+    parser = new_parser('title = product.title')
+    assert_equal('title', parser.consume(:id))
+    assert_equal('=', parser.consume(:assign))
+    assert_equal('product.title', parser.expression)
+    parser.consume(:end_of_string)
+  end
+
+  def test_callable_expression_consumes_only_its_arguments
+    context = ParseContext.new(error_mode: :strict2)
+    parser = context.new_parser('title(product, nested(1),), next')
+    expression = context.safe_parse_expression(parser)
+    assert_instance_of(CallExpression, expression)
+    assert_equal('title', expression.target.name)
+    assert_equal('product', expression.arguments.first.name)
+    assert_instance_of(CallExpression, expression.arguments.last)
+    assert_equal([1], expression.arguments.last.arguments)
+    parser.consume(:comma)
+    assert_equal('next', parser.consume(:id))
+    parser.consume(:end_of_string)
+  end
+
+  def test_expression_markup_preserves_callable_syntax_without_consuming_attributes
+    [
+      ['(1 .. finish( ))', '(1..finish())', RangeLookup],
+      ['groups[ key( ) ].items', 'groups[key()].items', VariableLookup],
+      ['identity( "a b", nested(1) )', 'identity("a b",nested(1))', CallExpression],
+    ].each do |source, expected_markup, expected_class|
+      parser = ParseContext.new(error_mode: :strict2).new_parser("#{source} limit: 1")
+      value, markup = parser.expression_with_markup
+      assert_instance_of(expected_class, value)
+      assert_equal(expected_markup, markup)
+      assert_equal('limit', parser.consume(:id))
+      parser.consume(:colon)
+      assert_equal('1', parser.consume(:number))
+      parser.consume(:end_of_string)
+    end
+  end
+
+  def test_expression_markup_preserves_non_callable_loop_names
+    ['items', 'groups[key].items', '(1..finish)', '"a b"'].each do |source|
+      value, markup = new_parser(source).expression_with_markup
+      assert_equal(source, value)
+      assert_equal(source, markup)
+    end
+  end
+
+  def test_parameters_consume_parentheses_and_optional_trailing_comma
+    parser = new_parser('(first, second,)')
+    assert_equal(['first', 'second'], parser.parameters)
+    parser.consume(:end_of_string)
+    assert_equal([], new_parser('()').parameters)
+  end
+
+  def test_callable_grammar_uses_effective_partial_mode
+    environment = Environment.build(error_mode: :strict)
+    context = ParseContext.new(environment: environment, error_mode: :strict2, include_options_blacklist: [:error_mode])
+    assert_instance_of(CallExpression, context.safe_parse_expression(context.new_parser('title()')))
+    context.partial = true
+    parser = context.new_parser('title()')
+    assert_equal('title', parser.expression)
+    assert_raises(SyntaxError) { parser.consume(:end_of_string) }
+  end
+
+  def test_callable_grammar_is_explicitly_disabled_in_other_modes
+    [:lax, :warn, :strict, :rigid].each do |mode|
+      parser = ParseContext.new(error_mode: mode).new_parser('title(1)')
+      assert_equal('title', parser.expression)
+      assert_raises(SyntaxError) { parser.consume(:end_of_string) }
+    end
+  end
+
   private
 
   def new_parser(str)

test/unit/partial_cache_unit_test.rb

@@ -175,7 +175,7 @@ class PartialCacheUnitTest < Minitest::Test
     assert_equal('some/path/my_partial', partial.name)
   end
 
-  def test_cache_key
+  def test_includes_error_mode_into_template_cache
     template_factory = StubTemplateFactory.new
     context = Liquid::Context.build(
       registers: {
@@ -184,14 +184,16 @@ class PartialCacheUnitTest < Minitest::Test
       },
     )
 
-    Liquid::PartialCache.load(
-      'my_partial',
-      context: context,
-      parse_context: Liquid::ParseContext.new,
-    )
+    [:lax, :warn, :strict, :strict2].each do |error_mode|
+      Liquid::PartialCache.load(
+        'my_partial',
+        context: context,
+        parse_context: Liquid::ParseContext.new(error_mode: error_mode),
+      )
+    end
 
     assert_equal(
-      ["my_partial"],
+      ["my_partial:lax", "my_partial:warn", "my_partial:strict", "my_partial:strict2"],
       context.registers[:cached_partials].keys,
     )
   end

test/unit/resource_limits_unit_test.rb

@@ -0,0 +1,91 @@
+# frozen_string_literal: true
+
+require 'test_helper'
+
+class ResourceLimitsUnitTest < Minitest::Test
+  def test_cumulative_scores_initialize_to_zero
+    limits = Liquid::ResourceLimits.new({})
+    assert_equal(0, limits.cumulative_render_score)
+    assert_equal(0, limits.cumulative_assign_score)
+  end
+
+  def test_cumulative_limits_default_to_nil
+    limits = Liquid::ResourceLimits.new({})
+    assert_nil(limits.cumulative_render_score_limit)
+    assert_nil(limits.cumulative_assign_score_limit)
+  end
+
+  def test_cumulative_limits_configurable_via_hash
+    limits = Liquid::ResourceLimits.new(
+      cumulative_render_score_limit: 500,
+      cumulative_assign_score_limit: 300,
+    )
+    assert_equal(500, limits.cumulative_render_score_limit)
+    assert_equal(300, limits.cumulative_assign_score_limit)
+  end
+
+  def test_cumulative_limits_configurable_via_accessor
+    limits = Liquid::ResourceLimits.new({})
+    limits.cumulative_render_score_limit = 500
+    assert_equal(500, limits.cumulative_render_score_limit)
+  end
+
+  def test_cumulative_scores_survive_reset
+    limits = Liquid::ResourceLimits.new({})
+    limits.increment_render_score(10)
+    limits.increment_assign_score(5)
+
+    limits.reset
+
+    assert_equal(0, limits.render_score)
+    assert_equal(0, limits.assign_score)
+    assert_equal(10, limits.cumulative_render_score)
+    assert_equal(5, limits.cumulative_assign_score)
+  end
+
+  def test_cumulative_scores_accumulate_across_resets
+    limits = Liquid::ResourceLimits.new({})
+    limits.increment_render_score(10)
+    limits.reset
+    limits.increment_render_score(20)
+    limits.reset
+    limits.increment_render_score(30)
+
+    assert_equal(30, limits.render_score)
+    assert_equal(60, limits.cumulative_render_score)
+  end
+
+  def test_cumulative_render_score_limit_raises
+    limits = Liquid::ResourceLimits.new(cumulative_render_score_limit: 25)
+    limits.increment_render_score(10)
+    limits.reset
+    limits.increment_render_score(10)
+    limits.reset
+
+    assert_raises(Liquid::MemoryError) do
+      limits.increment_render_score(10)
+    end
+    assert(limits.reached?)
+  end
+
+  def test_cumulative_assign_score_limit_raises
+    limits = Liquid::ResourceLimits.new(cumulative_assign_score_limit: 15)
+    limits.increment_assign_score(8)
+    limits.reset
+
+    assert_raises(Liquid::MemoryError) do
+      limits.increment_assign_score(8)
+    end
+    assert(limits.reached?)
+  end
+
+  def test_per_template_limits_still_work_with_cumulative
+    limits = Liquid::ResourceLimits.new(
+      render_score_limit: 50,
+      cumulative_render_score_limit: 1000,
+    )
+    assert_raises(Liquid::MemoryError) do
+      limits.increment_render_score(51)
+    end
+  end
+end

test/unit/tags/case_tag_unit_test.rb

@@ -20,9 +20,15 @@ class CaseTagUnitTest < Minitest::Test
       {%- endcase -%}
     LIQUID
 
-    error = assert_raises(Liquid::SyntaxError) { Template.parse(template) }
+    with_error_modes(:lax, :strict) do
+      assert_template_result("one", template)
+    end
 
-    assert_match(/Expected end_of_string but found/, error.message)
+    with_error_modes(:strict2) do
+      error = assert_raises(Liquid::SyntaxError) { Template.parse(template) }
+
+      assert_match(/Expected end_of_string but found/, error.message)
+    end
   end
 
   def test_case_when_with_trailing_element
@@ -35,9 +41,15 @@ class CaseTagUnitTest < Minitest::Test
       {%- endcase -%}
     LIQUID
 
-    error = assert_raises(Liquid::SyntaxError) { Template.parse(template) }
+    with_error_modes(:lax, :strict) do
+      assert_template_result("one", template)
+    end
 
-    assert_match(/Expected end_of_string but found/, error.message)
+    with_error_modes(:strict2) do
+      error = assert_raises(Liquid::SyntaxError) { Template.parse(template) }
+
+      assert_match(/Expected end_of_string but found/, error.message)
+    end
   end
 
   def test_case_when_with_comma
@@ -50,7 +62,9 @@ class CaseTagUnitTest < Minitest::Test
       {%- endcase -%}
     LIQUID
 
-    assert_template_result("one", template)
+    with_error_modes(:lax, :strict, :strict2) do
+      assert_template_result("one", template)
+    end
   end
 
   def test_case_when_with_or
@@ -63,7 +77,9 @@ class CaseTagUnitTest < Minitest::Test
       {%- endcase -%}
     LIQUID
 
-    assert_template_result("one", template)
+    with_error_modes(:lax, :strict, :strict2) do
+      assert_template_result("one", template)
+    end
   end
 
   def test_case_when_empty
@@ -76,12 +92,14 @@ class CaseTagUnitTest < Minitest::Test
       {%- endcase -%}
     LIQUID
 
-    assert_template_result("2 or empty", template, { 'x' => 2 })
-    assert_template_result("2 or empty", template, { 'x' => {} })
-    assert_template_result("2 or empty", template, { 'x' => [] })
-    assert_template_result("not 2 or empty", template, { 'x' => { 'a' => 'b' } })
-    assert_template_result("not 2 or empty", template, { 'x' => ['a'] })
-    assert_template_result("not 2 or empty", template, { 'x' => 4 })
+    with_error_modes(:lax, :strict, :strict2) do
+      assert_template_result("2 or empty", template, { 'x' => 2 })
+      assert_template_result("2 or empty", template, { 'x' => {} })
+      assert_template_result("2 or empty", template, { 'x' => [] })
+      assert_template_result("not 2 or empty", template, { 'x' => { 'a' => 'b' } })
+      assert_template_result("not 2 or empty", template, { 'x' => ['a'] })
+      assert_template_result("not 2 or empty", template, { 'x' => 4 })
+    end
   end
 
   def test_case_with_invalid_expression
@@ -95,9 +113,15 @@ class CaseTagUnitTest < Minitest::Test
     LIQUID
     assigns = { 'foo' => { 'bar' => 'baz' } }
 
-    error = assert_raises(Liquid::SyntaxError) { Template.parse(template, assigns) }
+    with_error_modes(:lax, :strict) do
+      assert_template_result("one", template, assigns)
+    end
 
-    assert_match(/Unexpected character =/, error.message)
+    with_error_modes(:strict2) do
+      error = assert_raises(Liquid::SyntaxError) { Template.parse(template) }
+
+      assert_match(/Unexpected character =/, error.message)
+    end
   end
 
   def test_case_when_with_invalid_expression
@@ -111,8 +135,14 @@ class CaseTagUnitTest < Minitest::Test
     LIQUID
     assigns = { 'foo' => { 'bar' => 'baz' } }
 
-    error = assert_raises(Liquid::SyntaxError) { Template.parse(template, assigns) }
+    with_error_modes(:lax, :strict) do
+      assert_template_result("one", template, assigns)
+    end
 
-    assert_match(/Unexpected character =/, error.message)
+    with_error_modes(:strict2) do
+      error = assert_raises(Liquid::SyntaxError) { Template.parse(template) }
+
+      assert_match(/Unexpected character =/, error.message)
+    end
   end
 end

test/unit/variable_unit_test.rb

@@ -72,6 +72,12 @@ class VariableUnitTest < Minitest::Test
     assert_equal([['replace', ['foo', 'bar']], ['textileze', []]], var.filters)
   end
 
+  def test_symbol
+    var = create_variable("http://disney.com/logo.gif | image: 'med' ", error_mode: :lax)
+    assert_equal(VariableLookup.new('http://disney.com/logo.gif'), var.name)
+    assert_equal([['image', ['med']]], var.filters)
+  end
+
   def test_string_to_filter
     var = create_variable("'http://disney.com/logo.gif' | image: 'med' ")
     assert_equal('http://disney.com/logo.gif', var.name)
@@ -102,9 +108,11 @@ class VariableUnitTest < Minitest::Test
     assert_equal(VariableLookup.new('foo-bar'), create_variable('foo-bar').name)
     assert_equal(VariableLookup.new('foo-bar-2'), create_variable('foo-bar-2').name)
 
-    assert_raises(Liquid::SyntaxError) { create_variable('foo - bar') }
-    assert_raises(Liquid::SyntaxError) { create_variable('-foo') }
-    assert_raises(Liquid::SyntaxError) { create_variable('2foo') }
+    with_error_modes(:strict) do
+      assert_raises(Liquid::SyntaxError) { create_variable('foo - bar') }
+      assert_raises(Liquid::SyntaxError) { create_variable('-foo') }
+      assert_raises(Liquid::SyntaxError) { create_variable('2foo') }
+    end
   end
 
   def test_string_with_special_chars
@@ -123,38 +131,70 @@ class VariableUnitTest < Minitest::Test
     assert_equal([['things', [], { 'greeting' => 'world', 'farewell' => 'goodbye' }]], var.filters)
   end
 
-  def test_filter_argument_parsing
-    # optional colon
-    var = create_variable(%(n | f1 | f2:))
-    assert_equal([['f1', []], ['f2', []]], var.filters)
+  def test_lax_filter_argument_parsing
+    var = create_variable(%( number_of_comments | pluralize: 'comment': 'comments' ), error_mode: :lax)
+    assert_equal(VariableLookup.new('number_of_comments'), var.name)
+    assert_equal([['pluralize', ['comment', 'comments']]], var.filters)
 
-    # missing argument throws error
-    assert_raises(SyntaxError) { create_variable(%(n | f1: ,)) }
-    assert_raises(SyntaxError) { create_variable(%(n | f1: ,| f2)) }
+    # missing does not throws error
+    create_variable(%(n | f1: ,), error_mode: :lax)
+    create_variable(%(n | f1: ,| f2), error_mode: :lax)
 
-    # arg requires colon
-    assert_raises(SyntaxError) { create_variable(%(n | f1 1)) }
-
-    # trailing comma doesn't throw
-    create_variable(%(n | f1: 1, 2, 3, | f2:))
-
-    # missing comma throws error
-    assert_raises(SyntaxError) { create_variable(%(n | filter: 1 2, 3)) }
+    # arg does not require colon, but ignores args :O, also ignores first kwarg since it splits on ':'
+    var = create_variable(%(n | f1 1 | f2 k1: v1), error_mode: :lax)
+    assert_equal([['f1', []], ['f2', [VariableLookup.new('v1')]]], var.filters)
 
     # positional and kwargs parsing
-    var = create_variable(%(n | filter: 1, 2, 3 | filter2: k1: 1, k2: 2))
+    var = create_variable(%(n | filter: 1, 2, 3 | filter2: k1: 1, k2: 2), error_mode: :lax)
     assert_equal([['filter', [1, 2, 3]], ['filter2', [], { "k1" => 1, "k2" => 2 }]], var.filters)
 
-    # positional and kwargs mixed
-    var = create_variable(%(n | filter: 'a', 'b', key1: 1, key2: 2, 'c'))
-    assert_equal([["filter", ["a", "b", "c"], { "key1" => 1, "key2" => 2 }]], var.filters)
-
     # positional and kwargs intermixed (pos1, key1: val1, pos2)
-    var = create_variable(%(n | link_to: class: "black", "https://example.com", title: "title"))
+    var = create_variable(%(n | link_to: class: "black", "https://example.com", title: "title"), error_mode: :lax)
     assert_equal([['link_to', ["https://example.com"], { "class" => "black", "title" => "title" }]], var.filters)
+  end
 
-    # string key throws
-    assert_raises(SyntaxError) { create_variable(%(n | pluralize: 'comment': 'comments')) }
+  def test_strict_filter_argument_parsing
+    with_error_modes(:strict) do
+      assert_raises(SyntaxError) do
+        create_variable(%( number_of_comments | pluralize: 'comment': 'comments' ))
+      end
+    end
+  end
+
+  def test_strict2_filter_argument_parsing
+    with_error_modes(:strict2) do
+      # optional colon
+      var = create_variable(%(n | f1 | f2:))
+      assert_equal([['f1', []], ['f2', []]], var.filters)
+
+      # missing argument throws error
+      assert_raises(SyntaxError) { create_variable(%(n | f1: ,)) }
+      assert_raises(SyntaxError) { create_variable(%(n | f1: ,| f2)) }
+
+      # arg requires colon
+      assert_raises(SyntaxError) { create_variable(%(n | f1 1)) }
+
+      # trailing comma doesn't throw
+      create_variable(%(n | f1: 1, 2, 3, | f2:))
+
+      # missing comma throws error
+      assert_raises(SyntaxError) { create_variable(%(n | filter: 1 2, 3)) }
+
+      # positional and kwargs parsing
+      var = create_variable(%(n | filter: 1, 2, 3 | filter2: k1: 1, k2: 2))
+      assert_equal([['filter', [1, 2, 3]], ['filter2', [], { "k1" => 1, "k2" => 2 }]], var.filters)
+
+      # positional and kwargs mixed
+      var = create_variable(%(n | filter: 'a', 'b', key1: 1, key2: 2, 'c'))
+      assert_equal([["filter", ["a", "b", "c"], { "key1" => 1, "key2" => 2 }]], var.filters)
+
+      # positional and kwargs intermixed (pos1, key1: val1, pos2)
+      var = create_variable(%(n | link_to: class: "black", "https://example.com", title: "title"))
+      assert_equal([['link_to', ["https://example.com"], { "class" => "black", "title" => "title" }]], var.filters)
+
+      # string key throws
+      assert_raises(SyntaxError) { create_variable(%(n | pluralize: 'comment': 'comments')) }
+    end
   end
 
   def test_output_raw_source_of_variable