From 0b890904f052ac11cdd53423f35dc87a34c71af8 Mon Sep 17 00:00:00 2001
From: "Charles-P. Clermont" <charles@cpclermont.com>
Date: Wed, 3 Dec 2025 15:03:42 -0500
Subject: [PATCH] Make Parser.expression parse equality expressions

---
 lib/liquid/lexer.rb           |  6 +++---
 lib/liquid/parser.rb          | 14 ++++++++++++--
 lib/liquid/tags/if.rb         |  2 +-
 test/unit/lexer_unit_test.rb  | 13 ++++++++++---
 test/unit/parser_unit_test.rb | 25 +++++++++++++++++++++++++
 5 files changed, 51 insertions(+), 9 deletions(-)

diff --git a/lib/liquid/lexer.rb b/lib/liquid/lexer.rb
index f1740dba..c0a6463b 100644
--- a/lib/liquid/lexer.rb
+++ b/lib/liquid/lexer.rb
@@ -6,14 +6,14 @@ module Liquid
     CLOSE_SQUARE = [:close_square, "]"].freeze
     COLON = [:colon, ":"].freeze
     COMMA = [:comma, ","].freeze
-    COMPARISION_NOT_EQUAL = [:comparison, "!="].freeze
+    COMPARISION_NOT_EQUAL = [:equality, "!="].freeze
     COMPARISON_CONTAINS = [:comparison, "contains"].freeze
-    COMPARISON_EQUAL = [:comparison, "=="].freeze
+    COMPARISON_EQUAL = [:equality, "=="].freeze
     COMPARISON_GREATER_THAN = [:comparison, ">"].freeze
     COMPARISON_GREATER_THAN_OR_EQUAL = [:comparison, ">="].freeze
     COMPARISON_LESS_THAN = [:comparison, "<"].freeze
     COMPARISON_LESS_THAN_OR_EQUAL = [:comparison, "<="].freeze
-    COMPARISON_NOT_EQUAL_ALT = [:comparison, "<>"].freeze
+    COMPARISON_NOT_EQUAL_ALT = [:equality, "<>"].freeze
     DASH = [:dash, "-"].freeze
     DOT = [:dot, "."].freeze
     DOTDOT = [:dotdot, ".."].freeze
diff --git a/lib/liquid/parser.rb b/lib/liquid/parser.rb
index 66d7c423..8d5151e7 100644
--- a/lib/liquid/parser.rb
+++ b/lib/liquid/parser.rb
@@ -47,11 +47,21 @@ module Liquid
       tok[0] == type
     end
 
-    # expression := comparison
+    # expression := equality
+    # equality   := comparison (("==" | "!=" | "<>") comparison)*
     # comparison := primary ((">=" | ">" | "<" | "<=" | ... ) primary)*
     # primary    := string | number | variable_lookup | range | boolean
     def expression
-      comparison
+      equality
+    end
+
+    def equality
+      expr = comparison
+      while look(:equality)
+        operator = consume
+        expr = BinaryExpression.new(expr, operator, comparison)
+      end
+      expr
     end
 
     # comparison := primary ((">=" | ">" | "<" | "<=" | ... ) primary)*
diff --git a/lib/liquid/tags/if.rb b/lib/liquid/tags/if.rb
index 2081c788..3471f677 100644
--- a/lib/liquid/tags/if.rb
+++ b/lib/liquid/tags/if.rb
@@ -97,7 +97,7 @@ module Liquid
 
     def parse_comparison(p)
       a = parse_expression(p)
-      if (op = p.consume?(:comparison))
+      if (op = p.consume?(:comparison) || p.consume?(:equality))
         b = parse_expression(p)
         Condition.new(a, op, b)
       else
diff --git a/test/unit/lexer_unit_test.rb b/test/unit/lexer_unit_test.rb
index 73eeb739..494769b8 100644
--- a/test/unit/lexer_unit_test.rb
+++ b/test/unit/lexer_unit_test.rb
@@ -26,10 +26,17 @@ class LexerUnitTest < Minitest::Test
     )
   end
 
+  def test_equality
+    assert_equal(
+      [[:equality, '=='], [:equality, '<>'], [:equality, '!='], [:end_of_string]],
+      tokenize('== <> != '),
+    )
+  end
+
   def test_comparison
     assert_equal(
-      [[:comparison, '=='], [:comparison, '<>'], [:comparison, 'contains'], [:end_of_string]],
-      tokenize('== <> contains '),
+      [[:comparison, '>'], [:comparison, '>='], [:comparison, '<'], [:comparison, '<='], [:comparison, 'contains'], [:end_of_string]],
+      tokenize('> >= < <= contains'),
     )
   end
 
@@ -81,7 +88,7 @@ class LexerUnitTest < Minitest::Test
 
   def test_whitespace
     assert_equal(
-      [[:id, 'five'], [:pipe, '|'], [:comparison, '=='], [:end_of_string]],
+      [[:id, 'five'], [:pipe, '|'], [:equality, '=='], [:end_of_string]],
       tokenize("five|\n\t =="),
     )
   end
diff --git a/test/unit/parser_unit_test.rb b/test/unit/parser_unit_test.rb
index a4d52d65..dccee43f 100644
--- a/test/unit/parser_unit_test.rb
+++ b/test/unit/parser_unit_test.rb
@@ -77,6 +77,31 @@ class ParserUnitTest < Minitest::Test
     assert_equal(0..5, p.expression)
   end
 
+  def test_equality
+    p = new_parser("a == b")
+    expr = p.expression
+    assert(expr.is_a?(BinaryExpression))
+    assert_equal('==', expr.operator)
+    assert_equal('a', expr.left.name)
+    assert_equal('b', expr.right.name)
+
+    # BinaryExpression(==)
+    #   left: BinaryExpression(<)
+    #     left: 0
+    #     right: 5
+    #   right: BinaryExpression(>)
+    #     left: 6
+    #     right: 1
+    p = new_parser("0 < 5 == 6 > 1")
+    expr = p.expression
+    assert(expr.is_a?(BinaryExpression))
+    assert_equal('==', expr.operator)
+    assert_equal(0, expr.left.left)
+    assert_equal(5, expr.left.right)
+    assert_equal(6, expr.right.left)
+    assert_equal(1, expr.right.right)
+  end
+
   def test_comparison
     p = new_parser("a > b")
     expr = p.expression