From 6d4cffa000b575323cf7bbfdc3248d8d18e0db0a Mon Sep 17 00:00:00 2001
From: Albert Chu <albert.chu@shopify.com>
Date: Tue, 4 Mar 2025 17:08:23 -0700
Subject: [PATCH] Support for simple boolean comparisons and boolean
 assignments

---
 lib/liquid.rb                    |  1 +
 lib/liquid/boolean_expression.rb | 21 +++++++++++++++++++++
 lib/liquid/variable.rb           | 27 ++++++++++++++++++++-------
 3 files changed, 42 insertions(+), 7 deletions(-)
 create mode 100644 lib/liquid/boolean_expression.rb

diff --git a/lib/liquid.rb b/lib/liquid.rb
index 4d0a71a6..445dfbf7 100644
--- a/lib/liquid.rb
+++ b/lib/liquid.rb
@@ -89,3 +89,4 @@ require 'liquid/partial_cache'
 require 'liquid/usage'
 require 'liquid/registers'
 require 'liquid/template_factory'
+require 'liquid/boolean_expression'
diff --git a/lib/liquid/boolean_expression.rb b/lib/liquid/boolean_expression.rb
new file mode 100644
index 00000000..bccffea0
--- /dev/null
+++ b/lib/liquid/boolean_expression.rb
@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+module Liquid
+  class BooleanExpression
+    def self.parse(markup, ss = StringScanner.new(""), cache = nil)
+      # Split the markup by comparison operators
+      if (match = markup.match(/\A\s*(.+?)\s*(==|!=|<>|<=|>=|<|>|contains)\s*(.+)\s*\z/))
+        left = Expression.parse(match[1], ss, cache)
+        operator = match[2]
+        right = Expression.parse(match[3], ss, cache)
+
+        # Create a condition object to evaluate the expression
+        condition = Condition.new(left, operator, right)
+        return condition
+      end
+
+      # If no comparison operator is found, just parse as regular expression
+      Expression.parse(markup, ss, cache)
+    end
+  end
+end
diff --git a/lib/liquid/variable.rb b/lib/liquid/variable.rb
index 20957065..fffa7fa9 100644
--- a/lib/liquid/variable.rb
+++ b/lib/liquid/variable.rb
@@ -17,6 +17,7 @@ module Liquid
     FilterArgsRegex          = /(?:#{FilterArgumentSeparator}|#{ArgumentSeparator})\s*((?:\w+\s*\:\s*)?#{QuotedFragment})/o
     JustTagAttributes        = /\A#{TagAttributes}\z/o
     MarkupWithQuotedFragment = /(#{QuotedFragment})(.*)/om
+    ComparisonOperator       = /==|!=|<>|<=|>=|<|>|contains/o
 
     attr_accessor :filters, :name, :line_number
     attr_reader :parse_context
@@ -47,7 +48,14 @@ module Liquid
 
       name_markup   = Regexp.last_match(1)
       filter_markup = Regexp.last_match(2)
-      @name         = parse_context.parse_expression(name_markup)
+
+      # Check if name_markup contains a comparison operator
+      @name = if /\s*(#{ComparisonOperator})\s*/.match?(name_markup)
+        BooleanExpression.parse(name_markup)
+      else
+        parse_context.parse_expression(name_markup)
+      end
+
       if filter_markup =~ FilterMarkupRegex
         filters = Regexp.last_match(1).scan(FilterParser)
         filters.each do |f|
@@ -65,13 +73,18 @@ module Liquid
 
       return if p.look(:end_of_string)
 
-      @name = parse_context.parse_expression(p.expression)
-      while p.consume?(:pipe)
-        filtername = p.consume(:id)
-        filterargs = p.consume?(:colon) ? parse_filterargs(p) : Const::EMPTY_ARRAY
-        @filters << parse_filter_expressions(filtername, filterargs)
+      # Check if markup contains a comparison operator
+      if /\s*(#{ComparisonOperator})\s*/.match?(markup)
+        @name = BooleanExpression.parse(markup)
+      else
+        @name = parse_context.parse_expression(p.expression)
+        while p.consume?(:pipe)
+          filtername = p.consume(:id)
+          filterargs = p.consume?(:colon) ? parse_filterargs(p) : Const::EMPTY_ARRAY
+          @filters << parse_filter_expressions(filtername, filterargs)
+        end
+        p.consume(:end_of_string)
       end
-      p.consume(:end_of_string)
     end
 
     def parse_filterargs(p)