Add strict2_parse to increment and decrement tags

Both tags previously accepted any string as a variable name via
`markup.strip`. Now they use `parse_with_selected_parser` and validate
the variable name with `p.consume(:id)` in strict2 mode.

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

.github/workflows/liquid.yml

@@ -22,7 +22,6 @@ 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 }

lib/liquid.rb

@@ -52,7 +52,6 @@ end
 require "liquid/version"
 require "liquid/deprecations"
 require "liquid/const"
-require "liquid/byte_tables"
 require 'liquid/standardfilters'
 require 'liquid/file_system'
 require 'liquid/parser_switching'
@@ -66,6 +65,7 @@ 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_body.rb

@@ -130,21 +130,16 @@ module Liquid
         case
         when token.start_with?(TAGSTART)
           whitespace_handler(token, parse_context)
-          # rubocop:disable Metrics/BlockNesting
-          fast = try_parse_tag_token(token)
-          if fast
-            tag_name, markup, newlines = fast
-          elsif token =~ FullToken
-            tag_name = Regexp.last_match(2)
-            markup   = Regexp.last_match(4)
-            newlines = parse_context.line_number ? Regexp.last_match(1).count("\n") + Regexp.last_match(3).count("\n") : 0
-          else
+          unless token =~ FullToken
             return handle_invalid_tag_token(token, parse_context, &block)
           end
-          # rubocop:enable Metrics/BlockNesting
+          tag_name = Regexp.last_match(2)
+          markup   = Regexp.last_match(4)
 
-          if parse_context.line_number && newlines > 0
-            parse_context.line_number += newlines
+          if parse_context.line_number
+            # newlines inside the tag should increase the line number,
+            # particularly important for multiline {% liquid %} tags
+            parse_context.line_number += Regexp.last_match(1).count("\n") + Regexp.last_match(3).count("\n")
           end
 
           if tag_name == 'liquid'
@@ -265,77 +260,6 @@ module Liquid
       BlockBody.raise_missing_variable_terminator(token, parse_context)
     end
 
-    # Fast path for parsing "{%[-] tag_name markup [-]%}" tag tokens.
-    # Returns [tag_name, markup, newline_count] or nil.
-    #
-    # Accepts tokens where:
-    #   - Tag name is '#' or starts with [a-zA-Z_] followed by \w chars
-    #     (matching TagName = /#|\w+/ exactly — no hyphens, no '?' suffix)
-    #   - Whitespace is spaces, tabs, newlines, \r, \f, \v
-    #   - Whitespace control dashes are at positions 2 and len-3
-    # Rejects (returns nil → caller falls back to FullToken regex):
-    #   - Tokens shorter than "{%x%}" (4 bytes)
-    #   - Tag names starting with a digit (valid in FullToken but rare)
-    #   - Any structure the byte-walk can't confidently parse
-    # Fallback: nil return triggers the original `token =~ FullToken` regex
-    #   match in parse_for_document, preserving identical behavior for any
-    #   input the fast path doesn't handle.
-    def try_parse_tag_token(token)
-      len = token.bytesize
-      pos = 2 # skip "{%"
-      return if pos >= len
-
-      pos += 1 if token.getbyte(pos) == ByteTables::DASH
-      newline_count = 0
-
-      # Skip whitespace before tag name, count newlines
-      while pos < len
-        b = token.getbyte(pos)
-        if b == ByteTables::NEWLINE
-          pos += 1
-          newline_count += 1
-        elsif ByteTables::WHITESPACE[b]
-          pos += 1
-        else
-          break
-        end
-      end
-      return if pos >= len
-
-      # Scan tag name: '#' or \w+ (matching TagName = /#|\w+/)
-      name_start = pos
-      b = token.getbyte(pos)
-      if b == ByteTables::HASH
-        pos += 1
-      elsif ByteTables::IDENT_START[b]
-        pos += 1
-        pos += 1 while pos < len && ByteTables::WORD[token.getbyte(pos)]
-      else
-        return
-      end
-      tag_name = token.byteslice(name_start, pos - name_start)
-
-      # Skip whitespace after tag name, count newlines
-      while pos < len
-        b = token.getbyte(pos)
-        if b == ByteTables::NEWLINE
-          pos += 1
-          newline_count += 1
-        elsif ByteTables::WHITESPACE[b]
-          pos += 1
-        else
-          break
-        end
-      end
-
-      # Markup: everything up to optional '-' before '%}'
-      markup_end = len - 2 # skip '%}'
-      markup_end -= 1 if markup_end > pos && token.getbyte(markup_end - 1) == ByteTables::DASH
-      markup = pos >= markup_end ? "" : token.byteslice(pos, markup_end - pos)
-
-      [tag_name, markup, newline_count]
-    end
-
     # @deprecated Use {.raise_missing_tag_terminator} instead
     def raise_missing_tag_terminator(token, parse_context)
       BlockBody.raise_missing_tag_terminator(token, parse_context)

lib/liquid/byte_tables.rb

@@ -1,48 +0,0 @@
-# frozen_string_literal: true
-
-module Liquid
-  # Pre-computed 256-entry boolean lookup tables for byte classification.
-  # Built once at load time; used as TABLE[byte] — a single array index
-  # instead of 3-5 comparison operators per check.
-  module ByteTables
-    # [a-zA-Z_] — valid first byte of an identifier
-    IDENT_START = Array.new(256, false).tap do |t|
-      (97..122).each { |b| t[b] = true }  # a-z
-      (65..90).each  { |b| t[b] = true }  # A-Z
-      t[95] = true # _
-    end.freeze
-
-    # [a-zA-Z0-9_-] — valid continuation byte of an identifier
-    IDENT_CONT = Array.new(256, false).tap do |t|
-      (97..122).each { |b| t[b] = true }  # a-z
-      (65..90).each  { |b| t[b] = true }  # A-Z
-      (48..57).each  { |b| t[b] = true }  # 0-9
-      t[95] = true                          # _
-      t[45] = true                          # -
-    end.freeze
-
-    # [a-zA-Z0-9_] — \w equivalent (no hyphen), for tag name scanning
-    WORD = Array.new(256, false).tap do |t|
-      (97..122).each { |b| t[b] = true }  # a-z
-      (65..90).each  { |b| t[b] = true }  # A-Z
-      (48..57).each  { |b| t[b] = true }  # 0-9
-      t[95] = true # _
-    end.freeze
-
-    # [0-9] — ASCII digit
-    DIGIT = Array.new(256, false).tap do |t|
-      (48..57).each { |b| t[b] = true }
-    end.freeze
-
-    # Matches bytes removed by Ruby's String#strip: \x00, \t, \n, \v, \f, \r, space
-    WHITESPACE = Array.new(256, false).tap do |t|
-      [0, 9, 10, 11, 12, 13, 32].each { |b| t[b] = true }
-    end.freeze
-
-    # Byte constants for delimiters and punctuation
-    NEWLINE = 10
-    DASH    = 45  # '-'
-    DOT     = 46  # '.'
-    HASH    = 35  # '#'
-  end
-end

lib/liquid/context.rb

@@ -187,6 +187,15 @@ 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
@@ -197,6 +206,10 @@ module Liquid
       # path and find_index() is optimized in MRI to reduce object allocation
       index = @scopes.find_index { |s| s.key?(key) }
 
+      # `self` resolves to a SelfDrop (enabling `self['var']` lookups),
+      # but only when it hasn't been explicitly assigned as a local variable.
+      return SelfDrop.new(self) if key == Expression::SELF && !index
+
       variable = if index
         lookup_and_evaluate(@scopes[index], key, raise_on_not_found: raise_on_not_found)
       else

lib/liquid/expression.rb

@@ -2,6 +2,8 @@
 
 module Liquid
   class Expression
+    SELF = 'self'
+
     LITERALS = {
       nil => nil,
       'nil' => nil,
@@ -16,9 +18,16 @@ module Liquid
       '-' => VariableLookup.parse("-", nil).freeze,
     }.freeze
 
+    DOT = ".".ord
+    ZERO = "0".ord
+    NINE = "9".ord
+    DASH = "-".ord
+
     # Use an atomic group (?>...) to avoid pathological backtracing from
     # malicious input as described in https://github.com/Shopify/liquid/issues/1357
     RANGES_REGEX = /\A\(\s*(?>(\S+)\s*\.\.)\s*(\S+)\s*\)\z/
+    INTEGER_REGEX = /\A(-?\d+)\z/
+    FLOAT_REGEX = /\A(-?\d+)\.\d+\z/
 
     class << self
       def safe_parse(parser, ss = StringScanner.new(""), cache = nil)
@@ -28,15 +37,7 @@ module Liquid
       def parse(markup, ss = StringScanner.new(""), cache = nil)
         return unless markup
 
-        # Guard: only call .strip when the first or last byte is whitespace.
-        # String#strip always allocates a new String, even when there's nothing
-        # to strip. ByteTables::WHITESPACE matches the same bytes that strip
-        # removes (space, \t, \n, \v, \f, \r, \x00). When neither end has
-        # whitespace, we skip the call and avoid ~4,464 allocations per compile.
-        first = markup.getbyte(0)
-        if first && (ByteTables::WHITESPACE[first] || ByteTables::WHITESPACE[markup.getbyte(markup.bytesize - 1)])
-          markup = markup.strip
-        end
+        markup = markup.strip # markup can be a frozen string
 
         if (markup.start_with?('"') && markup.end_with?('"')) ||
           (markup.start_with?("'") && markup.end_with?("'"))
@@ -72,74 +73,56 @@ module Liquid
         end
       end
 
-      # Fast path for number parsing. Accepts:
-      #   - Simple integers: "42", "-7"
-      #   - Simple floats: "3.14", "-0.5"
-      #   - Multi-dot floats (truncated at second dot): "1.2.3" → 1.2
-      #   - Trailing-dot floats: "123." → 123.0
-      # Rejects (returns nil → caller treats as VariableLookup):
-      #   - Non-numeric input: "hello", ""
-      #   - Inputs with non-digit/non-dot bytes after the number: "1.2.3a"
-      # Fallback: nil return causes caller to fall through to VariableLookup.parse,
-      #   which is the same path the old regex-based code took on non-match.
-      def parse_number(markup, _ss = nil)
-        len = markup.bytesize
-        return if len == 0
-
-        pos = 0
-        first = markup.getbyte(pos)
-
-        if first == ByteTables::DASH
-          pos += 1
-          return if pos >= len
-          return unless ByteTables::DIGIT[markup.getbyte(pos)]
-
-          pos += 1
-        elsif ByteTables::DIGIT[first]
-          pos += 1
-        else
-          return
+      def parse_number(markup, ss)
+        # check if the markup is simple integer or float
+        case markup
+        when INTEGER_REGEX
+          return Integer(markup, 10)
+        when FLOAT_REGEX
+          return markup.to_f
         end
 
-        # Scan digits
-        pos += 1 while pos < len && ByteTables::DIGIT[markup.getbyte(pos)]
+        ss.string = markup
+        # the first byte must be a digit or  a dash
+        byte = ss.scan_byte
 
-        # Consumed everything = simple integer
-        return Integer(markup, 10) if pos == len
+        return false if byte != DASH && (byte < ZERO || byte > NINE)
 
-        # Check for dot — three float cases:
-        #   1. Simple float:   "123.456"   → markup.to_f
-        #   2. Multi-dot:      "1.2.3.4"   → truncate at second dot → 1.2
-        #   3. Trailing dot:   "123."      → truncate before dot → 123.0
-        return unless markup.getbyte(pos) == ByteTables::DOT
+        if byte == DASH
+          peek_byte = ss.peek_byte
 
-        dot_pos = pos
-        pos += 1
-        digit_start = pos
-        pos += 1 while pos < len && ByteTables::DIGIT[markup.getbyte(pos)]
+          # if it starts with a dash, the next byte must be a digit
+          return false if peek_byte.nil? || !(peek_byte >= ZERO && peek_byte <= NINE)
+        end
 
-        if pos > digit_start && pos == len
-          # Case 1: simple float like "123.456"
-          markup.to_f
-        elsif pos > digit_start
-          # Case 2: multi-dot like "1.2.3.4" — find where the numeric
-          # portion ends. Reject if any non-digit, non-dot byte is found
-          # (e.g. "1.2.3a" → nil, matching the old regex-based behavior).
-          num_end = nil
-          check = pos
-          while check < len
-            b = markup.getbyte(check)
-            if b == ByteTables::DOT
-              num_end ||= check
-            elsif !ByteTables::DIGIT[b]
-              return
+        # The markup could be a float with multiple dots
+        first_dot_pos = nil
+        num_end_pos = nil
+
+        while (byte = ss.scan_byte)
+          return false if byte != DOT && (byte < ZERO || byte > NINE)
+
+          # we found our number and now we are just scanning the rest of the string
+          next if num_end_pos
+
+          if byte == DOT
+            if first_dot_pos.nil?
+              first_dot_pos = ss.pos
+            else
+              # we found another dot, so we know that the number ends here
+              num_end_pos = ss.pos - 1
             end
-            check += 1
           end
-          markup.byteslice(0, num_end || len).to_f
+        end
+
+        num_end_pos = markup.length if ss.eos?
+
+        if num_end_pos
+          # number ends with a number "123.123"
+          markup.byteslice(0, num_end_pos).to_f
         else
-          # Case 3: trailing dot like "123."
-          markup.byteslice(0, dot_pos).to_f
+          # number ends with a dot "123."
+          markup.byteslice(0, first_dot_pos).to_f
         end
       end
     end

lib/liquid/parse_context.rb

@@ -38,7 +38,7 @@ 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)
     end
 
     def new_tokenizer(source, start_line_number: nil, for_liquid_tag: false)

lib/liquid/parser.rb

@@ -2,10 +2,11 @@
 
 module Liquid
   class Parser
-    def initialize(input)
+    def initialize(input, reject_bare_brackets: 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
     end
 
     def jump(point)
@@ -53,6 +54,9 @@ module Liquid
         str = consume
         str << variable_lookups
       when :open_square
+        if @reject_bare_brackets
+          raise SyntaxError, "Bare bracket access is not allowed in strict2 mode. Use #{Expression::SELF}['...'] instead"
+        end
         str = consume.dup
         str << expression
         str << consume(:close_square)

lib/liquid/self_drop.rb

@@ -0,0 +1,38 @@
+# 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(context)
+      super()
+      @context = context
+    end
+
+    def [](key)
+      @context.find_variable(key)
+    rescue UndefinedVariable
+      nil
+    end
+
+    def key?(key)
+      @context.variable_defined?(key)
+    end
+
+    def to_liquid
+      self
+    end
+  end
+end

lib/liquid/standardfilters.rb

@@ -8,19 +8,10 @@ module Liquid
     MAX_I32 = (1 << 31) - 1
     private_constant :MAX_I32
 
-    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
+    MIN_I64 = -(1 << 63)
+    MAX_I64 = (1 << 63) - 1
+    I64_RANGE = MIN_I64..MAX_I64
+    private_constant :MIN_I64, :MAX_I64, :I64_RANGE
 
     HTML_ESCAPE = {
       '&' => '&amp;',
@@ -223,11 +214,11 @@ module Liquid
           Utils.to_s(input).slice(offset, length) || ''
         end
       rescue RangeError
-        if INDEX_RANGE.cover?(length) && INDEX_RANGE.cover?(offset)
+        if I64_RANGE.cover?(length) && I64_RANGE.cover?(offset)
           raise # unexpected error
         end
-        offset = offset.clamp(INDEX_RANGE)
-        length = length.clamp(INDEX_RANGE)
+        offset = offset.clamp(I64_RANGE)
+        length = length.clamp(I64_RANGE)
         retry
       end
     end

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 +31,10 @@ module Liquid
 
     def initialize(tag_name, markup, parse_context)
       super
+      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)
@@ -37,6 +43,25 @@ 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

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/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/include.rb

@@ -20,7 +20,8 @@ module Liquid
   class Include < Tag
     prepend Tag::Disableable
 
-    SYNTAX = /(#{QuotedFragment}+)(\s+(?:with|for)\s+(#{QuotedFragment}+))?(\s+(?:as)\s+(#{VariableSegment}+))?/o
+    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
@@ -84,12 +85,18 @@ module Liquid
     alias_method :parse_context, :options
     private :parse_context
 
+    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)
 
@@ -111,11 +118,13 @@ module Liquid
     def lax_parse(markup)
       if markup =~ SYNTAX
         template_name = Regexp.last_match(1)
-        variable_name = Regexp.last_match(3)
+        with_or_for   = Regexp.last_match(3)
+        variable_name = Regexp.last_match(4)
 
-        @alias_name         = Regexp.last_match(5)
+        @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|

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/variable.rb

@@ -37,6 +37,10 @@ module Liquid
       @markup
     end
 
+    def ==(other)
+      self.class == other.class && name == other.name && filters == other.filters
+    end
+
     def markup_context(markup)
       "in \"{{#{markup}}}\""
     end

lib/liquid/variable_lookup.rb

@@ -4,25 +4,6 @@ module Liquid
   class VariableLookup
     COMMAND_METHODS = ['size', 'first', 'last'].freeze
 
-    # Matches simple identifier chains: name(.name)* with no brackets/quotes
-    SIMPLE_LOOKUP_RE = /\A[\w-]+\??(?:\.[\w-]+\??)*\z/
-
-    # Returns true when markup is a simple dotted identifier chain that the
-    # fast path in initialize can handle. Accepts:
-    #   - Single names: "product", "item"
-    #   - Dotted chains: "product.title", "cart.items.first"
-    #   - Question-mark suffixes: "product.available?"
-    #   - Hyphens in names: "my-var.some-field"
-    # Rejects (falls through to VariableParser regex):
-    #   - Bracket lookups: "product[0]", "hash['key']"
-    #   - Quoted strings, empty input, leading/trailing dots
-    # Fallback: when this returns false, initialize uses the original
-    #   markup.scan(VariableParser) path — behavior is identical to
-    #   the pre-optimization code for any input the fast path rejects.
-    def self.simple_lookup?(markup)
-      markup.bytesize > 0 && markup.match?(SIMPLE_LOOKUP_RE)
-    end
-
     attr_reader :name, :lookups
 
     def self.parse(markup, string_scanner = StringScanner.new(""), cache = nil)
@@ -30,31 +11,6 @@ module Liquid
     end
 
     def initialize(markup, string_scanner = StringScanner.new(""), cache = nil)
-      if self.class.simple_lookup?(markup)
-        dot_pos = markup.index('.')
-        if dot_pos.nil?
-          @name = markup
-          @lookups = Const::EMPTY_ARRAY
-          @command_flags = 0
-          return
-        end
-
-        @name = markup.byteslice(0, dot_pos)
-        @lookups = []
-        @command_flags = 0
-        pos = dot_pos + 1
-        len = markup.bytesize
-        while pos < len
-          seg_start = pos
-          pos += 1 while pos < len && markup.getbyte(pos) != ByteTables::DOT
-          seg = markup.byteslice(seg_start, pos - seg_start)
-          @command_flags |= 1 << @lookups.length if COMMAND_METHODS.include?(seg)
-          @lookups << seg
-          pos += 1 # skip dot
-        end
-        return
-      end
-
       lookups = markup.scan(VariableParser)
 
       name = lookups.shift

performance/bench_quick.rb

@@ -1,62 +0,0 @@
-# frozen_string_literal: true
-
-# Quick benchmark: measures parse µs, render µs, and object allocations
-# Outputs machine-readable metrics to stdout
-
-require_relative 'theme_runner'
-
-RubyVM::YJIT.enable if defined?(RubyVM::YJIT)
-
-runner = ThemeRunner.new
-
-# Warmup — enough iterations for YJIT to fully optimize hot paths
-20.times { runner.compile }
-20.times { runner.render }
-
-GC.start
-GC.compact if GC.respond_to?(:compact)
-
-# Measure parse
-parse_times = []
-10.times do
-  GC.disable
-  t0 = Process.clock_gettime(Process::CLOCK_MONOTONIC)
-  runner.compile
-  t1 = Process.clock_gettime(Process::CLOCK_MONOTONIC)
-  GC.enable
-  GC.start
-  parse_times << (t1 - t0) * 1_000_000 # µs
-end
-
-# Measure render
-render_times = []
-10.times do
-  GC.disable
-  t0 = Process.clock_gettime(Process::CLOCK_MONOTONIC)
-  runner.render
-  t1 = Process.clock_gettime(Process::CLOCK_MONOTONIC)
-  GC.enable
-  GC.start
-  render_times << (t1 - t0) * 1_000_000 # µs
-end
-
-# Measure object allocations for one parse+render cycle
-require 'objspace'
-GC.start
-GC.disable
-before = ObjectSpace.count_objects.values_at(:TOTAL).first - ObjectSpace.count_objects.values_at(:FREE).first
-runner.compile
-runner.render
-after = ObjectSpace.count_objects.values_at(:TOTAL).first - ObjectSpace.count_objects.values_at(:FREE).first
-GC.enable
-allocations = after - before
-
-parse_us = parse_times.min.round(0)
-render_us = render_times.min.round(0)
-combined_us = parse_us + render_us
-
-puts "RESULTS"
-puts "parse_us=#{parse_us}"
-puts "render_us=#{render_us}"
-puts "combined_us=#{combined_us}"
-puts "allocations=#{allocations}"

test/integration/assign_test.rb

@@ -97,6 +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/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

test/integration/security_test.rb

@@ -44,39 +44,32 @@ class SecurityTest < Minitest::Test
   end
 
   def test_does_not_permanently_add_filters_to_symbol_table
-    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
+    current_symbols = Symbol.all_symbols
 
-      GC.start
-    end
+    # 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)
   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
-    yield
+
+    assigns = { 'drop' => Drop.new }
+    assert_equal("", Template.parse("{{ drop.custom_method_1 }}", assigns).render!)
+    assert_equal("", Template.parse("{{ drop.custom_method_2 }}", assigns).render!)
+    assert_equal("", Template.parse("{{ drop.custom_method_3 }}", assigns).render!)
+
     assert_equal([], Symbol.all_symbols - current_symbols)
   end
 

test/integration/standard_filter_test.rb

@@ -1181,8 +1181,6 @@ 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

@@ -105,10 +105,8 @@ class CycleTagTest < Minitest::Test
       error1 = assert_raises(Liquid::SyntaxError) { Template.parse(template1) }
       error2 = assert_raises(Liquid::SyntaxError) { Template.parse(template2) }
 
-      expected_error = /Liquid syntax error: \[:dot, "."\] is not a valid expression/
-
-      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
 

test/integration/tags/include_tag_test.rb

@@ -439,4 +439,49 @@ class IncludeTagTest < Minitest::Test
       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

@@ -174,16 +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
 

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),

test/unit/fast_path_unit_test.rb

@@ -1,256 +0,0 @@
-# frozen_string_literal: true
-
-require 'test_helper'
-
-# Tests for the byte-walking fast paths introduced in the ByteTables optimization.
-# Each fast path is tested for equivalence with the original regex-based code path
-# it replaces, covering accepted inputs, rejected inputs, and boundary cases.
-class FastPathUnitTest < Minitest::Test
-  # ── Expression.parse_number ────────────────────────────────────────
-  # Fast path: byte-walk with ByteTables::DIGIT
-  # Replaces: INTEGER_REGEX, FLOAT_REGEX, StringScanner loop
-
-  def test_parse_number_simple_integers
-    assert_equal(42, Liquid::Expression.parse_number("42"))
-    assert_equal(0, Liquid::Expression.parse_number("0"))
-    assert_equal(999, Liquid::Expression.parse_number("999"))
-  end
-
-  def test_parse_number_negative_integers
-    assert_equal(-7, Liquid::Expression.parse_number("-7"))
-    assert_equal(-0, Liquid::Expression.parse_number("-0"))
-    assert_equal(-123, Liquid::Expression.parse_number("-123"))
-  end
-
-  def test_parse_number_simple_floats
-    assert_equal(3.14, Liquid::Expression.parse_number("3.14"))
-    assert_equal(0.5, Liquid::Expression.parse_number("0.5"))
-    assert_equal(-0.5, Liquid::Expression.parse_number("-0.5"))
-    assert_equal(100.0, Liquid::Expression.parse_number("100.0"))
-  end
-
-  def test_parse_number_trailing_dot
-    # "123." → 123.0 (truncate before dot)
-    assert_equal(123.0, Liquid::Expression.parse_number("123."))
-    assert_equal(0.0, Liquid::Expression.parse_number("0."))
-  end
-
-  def test_parse_number_multi_dot_floats
-    # "1.2.3" → 1.2 (truncate at second dot)
-    assert_equal(1.2, Liquid::Expression.parse_number("1.2.3"))
-    assert_equal(1.2, Liquid::Expression.parse_number("1.2.3.4"))
-    assert_equal(0.0, Liquid::Expression.parse_number("0.0.0"))
-  end
-
-  def test_parse_number_rejects_non_numeric
-    assert_nil(Liquid::Expression.parse_number("hello"))
-    assert_nil(Liquid::Expression.parse_number(""))
-    assert_nil(Liquid::Expression.parse_number("abc123"))
-    assert_nil(Liquid::Expression.parse_number(".5"))
-    assert_nil(Liquid::Expression.parse_number("-.5"))
-  end
-
-  def test_parse_number_rejects_trailing_alpha_after_multi_dot
-    # "1.2.3a" must be nil, not 1.2 — these are not valid numbers
-    assert_nil(Liquid::Expression.parse_number("1.2.3a"))
-    assert_nil(Liquid::Expression.parse_number("1.2.3.4a"))
-    assert_nil(Liquid::Expression.parse_number("1.2.34a"))
-    assert_nil(Liquid::Expression.parse_number("-1.2.3a"))
-  end
-
-  def test_parse_number_rejects_bare_dash
-    assert_nil(Liquid::Expression.parse_number("-"))
-    assert_nil(Liquid::Expression.parse_number("-a"))
-  end
-
-  # ── Expression.parse strip guard ───────────────────────────────────
-  # Fast path: skip String#strip when no leading/trailing whitespace
-  # Must produce identical results to unconditional .strip
-
-  def test_parse_strips_leading_whitespace
-    assert_equal(42, Liquid::Expression.parse("  42"))
-    assert_equal(42, Liquid::Expression.parse("\t42"))
-    assert_equal(42, Liquid::Expression.parse("\n42"))
-  end
-
-  def test_parse_strips_trailing_whitespace
-    assert_equal(42, Liquid::Expression.parse("42  "))
-    assert_equal(42, Liquid::Expression.parse("42\t"))
-    assert_equal(42, Liquid::Expression.parse("42\n"))
-  end
-
-  def test_parse_strips_both_sides
-    assert_equal(42, Liquid::Expression.parse("  42  "))
-    assert_equal("hello", Liquid::Expression.parse("  'hello'  "))
-  end
-
-  def test_parse_no_strip_needed
-    assert_equal(42, Liquid::Expression.parse("42"))
-    assert_equal("hello", Liquid::Expression.parse("'hello'"))
-    assert_equal(true, Liquid::Expression.parse("true"))
-  end
-
-  def test_parse_strips_null_bytes
-    # String#strip removes \x00 — the WHITESPACE table must match
-    assert_equal(true, Liquid::Expression.parse("\x00true"))
-    assert_equal(true, Liquid::Expression.parse("true\x00"))
-  end
-
-  # ── VariableLookup.simple_lookup? ──────────────────────────────────
-  # Fast path: regex gate for simple a.b.c chains
-  # Must accept only inputs the byte-walk can handle correctly
-
-  def test_simple_lookup_accepts_single_names
-    assert(Liquid::VariableLookup.simple_lookup?("product"))
-    assert(Liquid::VariableLookup.simple_lookup?("x"))
-    assert(Liquid::VariableLookup.simple_lookup?("_private"))
-  end
-
-  def test_simple_lookup_accepts_dotted_chains
-    assert(Liquid::VariableLookup.simple_lookup?("product.title"))
-    assert(Liquid::VariableLookup.simple_lookup?("a.b.c.d"))
-  end
-
-  def test_simple_lookup_accepts_question_marks
-    assert(Liquid::VariableLookup.simple_lookup?("product.available?"))
-    assert(Liquid::VariableLookup.simple_lookup?("empty?"))
-  end
-
-  def test_simple_lookup_accepts_hyphens
-    assert(Liquid::VariableLookup.simple_lookup?("my-var"))
-    assert(Liquid::VariableLookup.simple_lookup?("my-var.some-field"))
-  end
-
-  def test_simple_lookup_rejects_brackets
-    refute(Liquid::VariableLookup.simple_lookup?("product[0]"))
-    refute(Liquid::VariableLookup.simple_lookup?("hash['key']"))
-    refute(Liquid::VariableLookup.simple_lookup?("[0]"))
-  end
-
-  def test_simple_lookup_rejects_empty_and_malformed
-    refute(Liquid::VariableLookup.simple_lookup?(""))
-    refute(Liquid::VariableLookup.simple_lookup?(".leading"))
-    refute(Liquid::VariableLookup.simple_lookup?("trailing."))
-    refute(Liquid::VariableLookup.simple_lookup?("a..b"))
-  end
-
-  # ── VariableLookup fast path equivalence ───────────────────────────
-  # The fast path must produce identical name, lookups, and command_flags
-  # to the original VariableParser regex path
-
-  def test_fast_path_simple_name
-    vl = Liquid::VariableLookup.new("product")
-    assert_equal("product", vl.name)
-    assert_equal([], vl.lookups)
-  end
-
-  def test_fast_path_dotted_chain
-    vl = Liquid::VariableLookup.new("product.title")
-    assert_equal("product", vl.name)
-    assert_equal(["title"], vl.lookups)
-  end
-
-  def test_fast_path_deep_chain
-    vl = Liquid::VariableLookup.new("a.b.c.d")
-    assert_equal("a", vl.name)
-    assert_equal(["b", "c", "d"], vl.lookups)
-  end
-
-  def test_fast_path_command_methods
-    vl = Liquid::VariableLookup.new("items.size")
-    assert_equal("items", vl.name)
-    assert_equal(["size"], vl.lookups)
-    assert(vl.lookup_command?(0))
-
-    vl2 = Liquid::VariableLookup.new("items.first")
-    assert(vl2.lookup_command?(0))
-
-    vl3 = Liquid::VariableLookup.new("items.last")
-    assert(vl3.lookup_command?(0))
-  end
-
-  def test_fast_path_non_command_lookups
-    vl = Liquid::VariableLookup.new("product.title")
-    refute(vl.lookup_command?(0))
-  end
-
-  def test_fast_path_question_mark
-    vl = Liquid::VariableLookup.new("product.available?")
-    assert_equal("product", vl.name)
-    assert_equal(["available?"], vl.lookups)
-  end
-
-  def test_bracket_lookup_falls_to_regex_path
-    vl = Liquid::VariableLookup.new("product[0]")
-    assert_equal("product", vl.name)
-    assert_equal([0], vl.lookups)
-  end
-
-  # ── BlockBody.try_parse_tag_token ──────────────────────────────────
-  # Fast path: byte-walk tag tokens instead of FullToken regex
-  # Must produce identical [tag_name, markup, newline_count] or nil
-
-  def test_tag_token_simple
-    body = Liquid::BlockBody.new
-    result = body.send(:try_parse_tag_token, "{% if x %}")
-    assert_equal(["if", "x ", 0], result)
-  end
-
-  def test_tag_token_whitespace_control_leading
-    body = Liquid::BlockBody.new
-    result = body.send(:try_parse_tag_token, "{%- if x %}")
-    assert_equal(["if", "x ", 0], result)
-  end
-
-  def test_tag_token_whitespace_control_trailing
-    body = Liquid::BlockBody.new
-    result = body.send(:try_parse_tag_token, "{% if x -%}")
-    assert_equal(["if", "x ", 0], result)
-  end
-
-  def test_tag_token_whitespace_control_both
-    body = Liquid::BlockBody.new
-    result = body.send(:try_parse_tag_token, "{%- if x -%}")
-    assert_equal(["if", "x ", 0], result)
-  end
-
-  def test_tag_token_no_markup
-    body = Liquid::BlockBody.new
-    result = body.send(:try_parse_tag_token, "{% endif %}")
-    assert_equal(["endif", "", 0], result)
-  end
-
-  def test_tag_token_hash_comment
-    body = Liquid::BlockBody.new
-    result = body.send(:try_parse_tag_token, "{% # this is a comment %}")
-    assert_equal(["#", "this is a comment ", 0], result)
-  end
-
-  def test_tag_token_with_newlines
-    body = Liquid::BlockBody.new
-    result = body.send(:try_parse_tag_token, "{% \n if \n x %}")
-    assert_equal(["if", "x ", 2], result)
-  end
-
-  def test_tag_token_hyphenated_name_stops_at_hyphen
-    # TagName = /\w+/ does not include hyphens
-    body = Liquid::BlockBody.new
-    result = body.send(:try_parse_tag_token, "{% my-tag markup %}")
-    assert_equal("my", result[0])
-  end
-
-  def test_tag_token_complex_markup
-    body = Liquid::BlockBody.new
-    result = body.send(:try_parse_tag_token, "{% for item in collection reversed %}")
-    assert_equal("for", result[0])
-    assert_equal("item in collection reversed ", result[1])
-  end
-
-  def test_tag_token_malformed_returns_nil
-    body = Liquid::BlockBody.new
-    # Token too short
-    assert_nil(body.send(:try_parse_tag_token, "{%"))
-    # No valid tag name start (digit)
-    assert_nil(body.send(:try_parse_tag_token, "{% 123 %}"))
-  end
-end