Removes dead code, tightens idioms, adds clarifying comments

Dead code removed:
  cursor.rb:     parse_for_markup + attr_reader :for_var/collection/reversed
                 (zero callers in lib/; method also incomplete -- no limit/offset)
  for.rb:        Syntax regex, REVERSED_BYTES constant (both unreferenced by
                 lax_parse and strict_parse)
  block_body.rb: BLANK_STRING_REGEX (exact duplicate of WhitespaceOrNothing)

Idioms:
  expression.rb:    parse_number returns nil on failure, not false
                    (Ruby convention for 'no result'; callers use if (num = parse_number))
  block_body.rb:    freeze (idempotent by spec); whitespace_handler marked private;
                    render_node gets rationale comment; redundant comments collapsed
  variable_lookup.rb: COMMAND_METHODS -> %w[]; initialize loop uses each_with_index;
                    removes redundant &. on second clause of &&
  for.rb:           strict2_parse -> alias_method; nil-guard if/else -> ternary;
                    render_else -> ternary; include? checks unconsumed rest only
  condition.rb:     loop/break chain -> while condition.child_relation
  utils.rb:         tightens slice_collection_using_each loop

Comments:
  variable.rb:         backward pipe-walk algorithm; SPACE-only whitespace asymmetry
  cursor.rb:           COMPARISON_OPS identity-map exists for frozen string interning
  if.rb:               include? pre-check is both correctness guard and perf gate
  for.rb:              cursor->regex fallback for limit:/offset: attributes
  strainer_template.rb: __LINE__+1 limitation in module_eval loop

lib/liquid/condition.rb

@@ -71,14 +71,12 @@ module Liquid
       return result unless @child_relation
 
       condition = self
-      loop do
+      while condition.child_relation
         case condition.child_relation
         when :or
           break if Liquid::Utils.to_liquid_value(result)
         when :and
           break unless Liquid::Utils.to_liquid_value(result)
-        else
-          break
         end
         condition = condition.child_condition
         result = interpret_condition(condition.left, condition.right, condition.operator, context)

lib/liquid/cursor.rb

@@ -189,6 +189,10 @@ module Liquid
     end
 
     # ── Comparison operators ────────────────────────────────────────
+    # Identity map used for frozen string interning: StringScanner#scan returns a
+    # new unfrozen String on every call. Indexing into this hash returns the frozen
+    # literal stored here, avoiding a separate allocation and enabling faster
+    # equality checks downstream (frozen strings can be compared by identity).
     COMPARISON_OPS = {
       '==' => '==',
       '!=' => '!=',
@@ -313,50 +317,6 @@ module Liquid
 
       true
     end
-    # ── For tag parser ────────────────────────────────────────────────
-    # Results from parse_for_markup
-    attr_reader :for_var, :for_collection, :for_reversed
 
-    # Parse "var in collection [reversed] [limit:N] [offset:N]"
-    # Returns true on success, nil on failure.
-    def parse_for_markup
-      skip_ws
-      @for_var = scan_id
-      return unless @for_var
-
-      skip_ws
-      # expect "in"
-      return unless scan_id == "in"
-
-      skip_ws
-      # Collection: parenthesized range or fragment
-      if peek_byte == LPAREN
-        start = @ss.pos
-        depth = 1
-        @ss.scan_byte
-        while !@ss.eos? && depth > 0
-          b = @ss.scan_byte
-          depth += 1 if b == LPAREN
-          depth -= 1 if b == RPAREN
-        end
-        @for_collection = @source.byteslice(start, @ss.pos - start)
-      else
-        @for_collection = scan_fragment
-        return unless @for_collection
-      end
-
-      skip_ws
-      # Check for 'reversed'
-      saved = @ss.pos
-      word = scan_id
-      if word == "reversed"
-        @for_reversed = true
-      else
-        @for_reversed = false
-        @ss.pos = saved if word # rewind if we consumed a non-'reversed' word
-      end
-
-      true
-    end
   end
 end

lib/liquid/expression.rb

@@ -72,23 +72,23 @@ module Liquid
 
       def parse_number(markup, _ss = nil)
         len = markup.bytesize
-        return false if len == 0
+        return if len == 0
 
         # Quick reject: first byte must be digit or dash
         pos = 0
         first = markup.getbyte(pos)
         if first == Cursor::DASH
           pos += 1
-          return false if pos >= len
+          return if pos >= len
 
           b = markup.getbyte(pos)
-          return false unless ByteTables::DIGIT[b]
+          return unless ByteTables::DIGIT[b]
 
           pos += 1
         elsif ByteTables::DIGIT[first]
           pos += 1
         else
-          return false
+          return
         end
 
         # Scan digits
@@ -121,19 +121,9 @@ module Liquid
             # Simple float like "123.456"
             return markup.to_f
           elsif pos > digit_after_dot
-            # Float followed by more dots or other chars: "1.2.3.4"
-            # Return the float portion up to second dot
-            while pos < len
-              b = markup.getbyte(pos)
-              if b == Cursor::DOT
-                return markup.byteslice(0, pos).to_f
-              elsif !ByteTables::DIGIT[b]
-                return false
-              end
-
-              pos += 1
-            end
-            return markup.byteslice(0, pos).to_f
+            # Float followed by more content: "1.2.3.4" — scan to find where the
+            # numeric portion ends (stop at next dot or non-digit).
+            return scan_float_with_trailing(markup, pos, len)
           else
             # dot at end: "123."
             return markup.byteslice(0, dot_pos).to_f
@@ -141,7 +131,24 @@ module Liquid
         end
 
         # Not a number (has non-digit, non-dot characters)
-        false
+        nil
+      end
+
+      private
+
+      # Scans forward from `pos` through digits, returning the float up to the
+      # next dot or the end of string. Returns nil when a non-digit, non-dot
+      # byte is found (not a valid number). Used by parse_number for inputs
+      # like "1.2.3.4" where the float literal ends at the second dot.
+      def scan_float_with_trailing(markup, pos, len)
+        while pos < len
+          b = markup.getbyte(pos)
+          return markup.byteslice(0, pos).to_f if b == Cursor::DOT
+          return unless ByteTables::DIGIT[b]
+
+          pos += 1
+        end
+        markup.byteslice(0, pos).to_f
       end
     end
   end

lib/liquid/tags/for.rb

@@ -25,8 +25,6 @@ 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)
@@ -73,8 +71,6 @@ module Liquid
     protected
 
     # Fast byte-level parser for "var in collection [reversed] [limit:N] [offset:N]"
-    REVERSED_BYTES = "reversed".bytes.freeze
-
     def lax_parse(markup)
       c = @parse_context.cursor
       c.reset(markup)
@@ -114,9 +110,9 @@ module Liquid
       @reversed = c.expect_id("reversed")
       c.skip_ws
 
-      # Parse limit:/offset: if present
-      if !c.eos? && markup.include?(':')
-        rest = c.slice(c.pos, markup.bytesize - c.pos)
+      # Parse limit:/offset: if present.
+      # Cursor doesn't handle key:value attributes — delegate to regex for limit:/offset:.
+      if !c.eos? && (rest = c.slice(c.pos, markup.bytesize - c.pos)).include?(':')
         rest.scan(TagAttributes) do |key, value|
           set_attribute(key, value)
         end
@@ -147,9 +143,7 @@ module Liquid
 
     private
 
-    def strict2_parse(markup)
-      strict_parse(markup)
-    end
+    alias_method :strict2_parse, :strict_parse
 
     def collection_segment(context)
       offsets = context.registers[:for] ||= {}
@@ -158,22 +152,14 @@ module Liquid
         offsets[@name].to_i
       else
         from_value = context.evaluate(@from)
-        if from_value.nil?
-          0
-        else
-          Utils.to_integer(from_value)
-        end
+        from_value.nil? ? 0 : Utils.to_integer(from_value)
       end
 
       collection = context.evaluate(@collection_name)
       collection = collection.to_a if collection.is_a?(Range)
 
       limit_value = context.evaluate(@limit)
-      to = if limit_value.nil?
-        nil
-      else
-        Utils.to_integer(limit_value) + from
-      end
+      to = limit_value && (Utils.to_integer(limit_value) + from)
 
       segment = Utils.slice_collection(collection, from, to)
       segment.reverse! if @reversed
@@ -228,11 +214,7 @@ module Liquid
     end
 
     def render_else(context, output)
-      if @else_block
-        @else_block.render_to_output_buffer(context, output)
-      else
-        output
-      end
+      @else_block ? @else_block.render_to_output_buffer(context, output) : output
     end
 
     class ParseTreeVisitor < Liquid::ParseTreeVisitor

lib/liquid/tags/if.rb

@@ -94,7 +94,10 @@ module Liquid
         return Condition.new(parse_expression(simple))
       end
 
-      # Fast path: simple condition without and/or — use Cursor
+      # Fast path: simple condition without and/or — use Cursor.
+      # The include? pre-checks are both a correctness guard (parse_simple_condition
+      # only handles a single comparison) and a perf gate (avoids cursor allocation
+      # for the compound-condition case that will always fall through to lax_parse).
       if !markup.include?(' and ') && !markup.include?(' or ')
         cursor = @parse_context.cursor
         cursor.reset(markup)

lib/liquid/utils.rb

@@ -18,23 +18,17 @@ module Liquid
 
     def self.slice_collection_using_each(collection, from, to)
       segments = []
-      index    = 0
 
-      # Maintains Ruby 1.8.7 String#each behaviour on 1.9
+      # String is Enumerable but #each is not defined; handle it as a single-element collection
       if collection.is_a?(String)
         return collection.empty? ? [] : [collection]
       end
       return [] unless collection.respond_to?(:each)
 
+      index = 0
       collection.each do |item|
-        if to && to <= index
-          break
-        end
-
-        if from <= index
-          segments << item
-        end
-
+        break if to && to <= index
+        segments << item if from <= index
         index += 1
       end
 
@@ -103,7 +97,7 @@ module Liquid
     def self.to_s(obj, seen = nil)
       case obj
       when Integer
-        return (obj >= 0 && obj < 1000) ? SMALL_INT_STRINGS[obj] : obj.to_s
+        obj >= 0 && obj < 1000 ? SMALL_INT_STRINGS[obj] : obj.to_s
       when BigDecimal
         obj.to_s("F")
       when Hash

lib/liquid/variable_lookup.rb

@@ -33,11 +33,8 @@ module Liquid
           pos += 1
           while pos < len && depth > 0
             b = markup.getbyte(pos)
-            if b == 91 # rubocop:disable Metrics/BlockNesting
-              depth += 1
-            elsif b == 93 # rubocop:disable Metrics/BlockNesting
-              depth -= 1
-            end
+            depth += 1 if b == 91
+            depth -= 1 if b == 93
             pos += 1
           end
           if depth == 0