Added more non-parity unit tests

* Evaluate expressions as truthy/falsy to unlock scenarios, such as `<div class="{{ disabled and "modal--disabled" }}">`
* Add additional scenarios to the expression test suite
* Simplify `LogicalExpression`

Gemfile

@@ -25,6 +25,8 @@ group :development do
 end
 
 group :test do
+  gem 'ruby-lsp'
+  gem 'debug'
   gem 'rubocop', '~> 1.61.0'
   gem 'rubocop-shopify', '~> 2.12.0', require: false
   gem 'rubocop-performance', require: false

lib/liquid.rb

@@ -80,6 +80,8 @@ require 'liquid/variable_lookup'
 require 'liquid/range_lookup'
 require 'liquid/resource_limits'
 require 'liquid/expression'
+require 'liquid/expression/comparison_expression'
+require 'liquid/expression/logical_expression'
 require 'liquid/template'
 require 'liquid/condition'
 require 'liquid/utils'

lib/liquid/condition.rb

@@ -52,6 +52,10 @@ module Liquid
       @@method_literals[markup] || parse_context.parse_expression(markup)
     end
 
+    def self.parse(markup, ss, cache)
+      @@method_literals[markup] || Expression.parse(markup, ss, cache)
+    end
+
     attr_reader :attachment, :child_condition
     attr_accessor :left, :operator, :right
 
@@ -112,11 +116,15 @@ module Liquid
     private
 
     def equal_variables(left, right)
+      if left.is_a?(MethodLiteral) && right.is_a?(MethodLiteral)
+        return left.to_s == right.to_s
+      end
+
       if left.is_a?(MethodLiteral)
         if right.respond_to?(left.method_name)
           return right.send(left.method_name)
         else
-          return nil
+          return left.to_s == right
         end
       end
 
@@ -124,7 +132,7 @@ module Liquid
         if left.respond_to?(right.method_name)
           return left.send(right.method_name)
         else
-          return nil
+          return right.to_s == left
         end
       end
 

lib/liquid/expression.rb

@@ -26,6 +26,7 @@ module Liquid
     RANGES_REGEX = /\A\(\s*(?>(\S+)\s*\.\.)\s*(\S+)\s*\)\z/
     INTEGER_REGEX = /\A(-?\d+)\z/
     FLOAT_REGEX = /\A(-?\d+)\.\d+\z/
+    QUOTED_STRING = /\A#{QuotedString}\z/
 
     class << self
       def parse(markup, ss = StringScanner.new(""), cache = nil)
@@ -33,12 +34,9 @@ module Liquid
 
         markup = markup.strip # markup can be a frozen string
 
-        if (markup.start_with?('"') && markup.end_with?('"')) ||
-          (markup.start_with?("'") && markup.end_with?("'"))
-          return markup[1..-2]
-        elsif LITERALS.key?(markup)
-          return LITERALS[markup]
-        end
+        return markup[1..-2] if QUOTED_STRING.match?(markup)
+
+        return LITERALS[markup] if LITERALS.key?(markup)
 
         # Cache only exists during parsing
         if cache
@@ -51,6 +49,9 @@ module Liquid
       end
 
       def inner_parse(markup, ss, cache)
+        return LogicalExpression.parse(markup, ss, cache)    if LogicalExpression.logical?(markup)
+        return ComparisonExpression.parse(markup, ss, cache) if ComparisonExpression.comparison?(markup)
+
         if (markup.start_with?("(") && markup.end_with?(")")) && markup =~ RANGES_REGEX
           return RangeLookup.parse(
             Regexp.last_match(1),

lib/liquid/expression/comparison_expression.rb

@@ -0,0 +1,31 @@
+# frozen_string_literal: true
+
+module Liquid
+  class Expression
+    class ComparisonExpression
+      # We can improve the resiliency of lax parsing by not expecting whitespace
+      # surrounding the operator (ie \s+ => \s*).
+      # However this is not in parity with existing lax parsing behavior.
+      COMPARISON_REGEX = /\A\s*(.+?)\s+(==|!=|<>|<=|>=|<|>|contains)\s+(.+)\s*\z/
+
+      class << self
+        def comparison?(markup)
+          markup.match(COMPARISON_REGEX)
+        end
+
+        def parse(markup, ss, cache)
+          match = comparison?(markup)
+
+          if match
+            left = Condition.parse(match[1].strip, ss, cache)
+            operator = match[2].strip
+            right = Condition.parse(match[3].strip, ss, cache)
+            return Condition.new(left, operator, right)
+          end
+
+          Condition.new(parse(markup, ss, cache), nil, nil)
+        end
+      end
+    end
+  end
+end

lib/liquid/expression/logical_expression.rb

@@ -0,0 +1,59 @@
+# frozen_string_literal: true
+
+module Liquid
+  class Expression
+    class LogicalExpression
+      LOGICAL_REGEX = /\A\s*(.+?)\s+(and|or)\s+(.+)\s*\z/i
+      EXPRESSIONS_AND_OPERATORS = /(?:\b(?:\s?and\s?|\s?or\s?)\b|(?:\s*(?!\b(?:\s?and\s?|\s?or\s?)\b)(?:#{QuotedFragment}|\S+)\s*)+)/o
+      BOOLEAN_OPERATORS = ['and', 'or'].freeze
+
+      class << self
+        def logical?(markup)
+          markup.match(LOGICAL_REGEX)
+        end
+
+        def boolean_operator?(markup)
+          BOOLEAN_OPERATORS.include?(markup)
+        end
+
+        def parse(markup, ss, cache)
+          expressions = markup.scan(EXPRESSIONS_AND_OPERATORS)
+
+          expression = expressions.pop
+          condition  = parse_condition(expression, ss, cache)
+
+          until expressions.empty?
+            operator = expressions.pop.to_s.strip
+
+            next unless boolean_operator?(operator)
+
+            expression    = expressions.pop.to_s.strip
+            new_condition = parse_condition(expression, ss, cache)
+
+            case operator
+            when 'and' then new_condition.and(condition)
+            when 'or'  then new_condition.or(condition)
+            end
+
+            condition = new_condition
+          end
+
+          condition
+        end
+
+        private
+
+        def parse_condition(expr, ss, cache)
+          return ComparisonExpression.parse(expr, ss, cache) if comparison?(expr)
+          return LogicalExpression.parse(expr, ss, cache)    if logical?(expr)
+
+          Condition.new(Expression.parse(expr, ss, cache), nil, nil)
+        end
+
+        def comparison?(...)
+          ComparisonExpression.comparison?(...)
+        end
+      end
+    end
+  end
+end

lib/liquid/lexer.rb

@@ -14,6 +14,8 @@ module Liquid
     COMPARISON_LESS_THAN = [:comparison, "<"].freeze
     COMPARISON_LESS_THAN_OR_EQUAL = [:comparison, "<="].freeze
     COMPARISON_NOT_EQUAL_ALT = [:comparison, "<>"].freeze
+    BOOLEAN_AND = [:boolean_operator, "and"].freeze
+    BOOLEAN_OR = [:boolean_operator, "or"].freeze
     DASH = [:dash, "-"].freeze
     DOT = [:dot, "."].freeze
     DOTDOT = [:dotdot, ".."].freeze
@@ -151,6 +153,10 @@ module Liquid
               # Special case for "contains"
               output << if type == :id && t == "contains" && output.last&.first != :dot
                 COMPARISON_CONTAINS
+              elsif type == :id && t == "and" && output.last&.first != :dot
+                BOOLEAN_AND
+              elsif type == :id && t == "or" && output.last&.first != :dot
+                BOOLEAN_OR
               else
                 [type, t]
               end

lib/liquid/parser.rb

@@ -48,7 +48,7 @@ module Liquid
 
     def expression
       token = @tokens[@p]
-      case token[0]
+      expr = case token[0]
       when :id
         str = consume
         str << variable_lookups
@@ -69,6 +69,21 @@ module Liquid
       else
         raise SyntaxError, "#{token} is not a valid expression"
       end
+      if look(:comparison)
+        operator = consume(:comparison)
+        left     = expr
+        right    = expression
+
+        "#{left} #{operator} #{right}"
+      elsif look(:boolean_operator)
+        operator = consume(:boolean_operator)
+        left     = expr
+        right    = expression
+
+        "#{left} #{operator} #{right}"
+      else
+        expr
+      end
     end
 
     def argument

test/unit/boolean_unit_test.rb

@@ -0,0 +1,546 @@
+# frozen_string_literal: true
+
+require 'test_helper'
+
+class BooleanUnitTest < Minitest::Test
+  include Liquid
+  def test_simple_boolean_comparison
+    assert_parity("1 > 0", "true")
+    assert_parity("1 < 0", "false")
+  end
+
+  def test_boolean_and_operator
+    assert_parity("true and true", "true")
+    assert_parity("true and false", "false")
+  end
+
+  def test_boolean_or_operator
+    assert_parity("true or false", "true")
+    assert_parity("false or false", "false")
+  end
+
+  def test_operator_precedence
+    assert_parity("false and false or true", "false")
+  end
+
+  def test_complex_boolean_expressions
+    assert_parity("true and true and true", "true")
+    assert_parity("true and false and true", "false")
+    assert_parity("false or false or true", "true")
+  end
+
+  def test_boolean_with_variables
+    assert_parity("a and b", "true", { "a" => true, "b" => true })
+    assert_parity("a and b", "false", { "a" => true, "b" => false })
+    assert_parity("a or b", "true", { "a" => false, "b" => true })
+    assert_parity("a or b", "false", { "a" => false, "b" => false })
+  end
+
+  def test_nil_equals_nil
+    assert_parity("nil == nil", "true")
+  end
+
+  def test_nil_not_equals_nil
+    assert_parity("nil != nil", "false")
+  end
+
+  def test_nil_not_equals_empty_string
+    assert_parity("nil == ''", "false")
+    assert_parity("nil != ''", "true")
+  end
+
+  def test_undefined_variable_in_comparisons
+    assert_parity("undefined_var == nil", "true")
+    assert_parity("undefined_var != nil", "false")
+  end
+
+  def test_undefined_variable_compared_to_empty_string
+    assert_parity("undefined_var == ''", "false")
+    assert_parity("undefined_var != ''", "true")
+  end
+
+  def test_boolean_variable_in_comparisons
+    assert_parity("t == true", "true", { "t" => true })
+    assert_parity("f == false", "true", { "f" => false })
+  end
+
+  def test_boolean_variable_compared_to_nil
+    assert_parity("t == nil", "false", { "t" => true })
+    assert_parity("f == nil", "false", { "f" => false })
+    assert_parity("f != nil", "true", { "f" => false })
+  end
+
+  def test_nil_and_undefined_variables_in_boolean_expressions
+    assert_parity("x == undefined_var", "true", { "x" => nil })
+    assert_parity("x != undefined_var", "false", { "x" => nil })
+  end
+
+  def test_nil_literal_in_or_expression
+    assert_parity("nil or true", "true")
+  end
+
+  def test_nil_variable_in_or_expression
+    assert_parity("x or false", "false", { "x" => nil })
+  end
+
+  def test_mixed_boolean_expressions
+    assert_parity("a > b and c < d", "true",  { "a" => 99, "b" => 0, "c" => 0,  "d" => 99 })
+    assert_parity("a > b and c < d", "false", { "a" => 99, "b" => 0, "c" => 99, "d" => 0  })
+  end
+
+  def test_boolean_assignment_shorthand
+    template = Liquid::Template.parse("{% assign lazy_load = media_position > 1 %}{{ lazy_load }}")
+    assert_equal("false", template.render("media_position" => 1))
+    assert_equal("true",  template.render("media_position" => 2))
+  end
+
+  def test_equality_operators_with_integer_literals
+    assert_expression("1", "1")
+    assert_expression("1 == 1", "true")
+    assert_expression("1 != 1", "false")
+    assert_expression("1 == 2", "false")
+    assert_expression("1 != 2", "true")
+  end
+
+  def test_equality_operators_with_stirng_literals
+    assert_expression("'hello'", "hello")
+    assert_expression("'hello' == 'hello'", "true")
+    assert_expression("'hello' != 'hello'", "false")
+    assert_expression("'hello' == 'world'", "false")
+    assert_expression("'hello' != 'world'", "true")
+  end
+
+  def test_equality_operators_with_float_literals
+    assert_expression("1.5", "1.5")
+    assert_expression("1.5 == 1.5", "true")
+    assert_expression("1.5 != 1.5", "false")
+    assert_expression("1.5 == 2.5", "false")
+    assert_expression("1.5 != 2.5", "true")
+  end
+
+  def test_equality_operators_with_nil_literals
+    assert_expression("nil", "")
+    assert_expression("nil == nil", "true")
+    assert_expression("nil != nil", "false")
+    assert_expression("null == nil", "true")
+    assert_expression("null != nil", "false")
+  end
+
+  def test_equality_operators_with_boolean_literals
+    assert_expression("true", "true")
+    assert_expression("false", "false")
+    assert_expression("true == true", "true")
+    assert_expression("true != true", "false")
+    assert_expression("false == false", "true")
+    assert_expression("false != false", "false")
+    assert_expression("true == false", "false")
+    assert_expression("true != false", "true")
+  end
+
+  def test_equality_operators_with_empty_literals
+    assert_expression("empty", "")
+    assert_expression("empty == ''", "true")
+    assert_expression("empty == empty", "true")
+    assert_expression("empty != empty", "false")
+    assert_expression("blank == blank", "true")
+    assert_expression("blank != blank", "false")
+    assert_expression("empty == blank", "true")
+    assert_expression("empty != blank", "false")
+  end
+
+  def test_nil_renders_as_empty_string
+    # No parity needed here. This is to ensure expressions rendered with {{ }}
+    # will still render as an empty string to preserve pre-existing behavior.
+    assert_expression("nil", "")
+    assert_expression("x", "", { "x" => nil })
+    assert_parity_scenario(:expression, "hello {{ x }}", "hello ", { "x" => nil })
+  end
+
+  def test_nil_comparison_with_blank
+    assert_parity("nil_value == blank", "false")
+    assert_parity("nil_value != blank", "true")
+    assert_parity("undefined != blank", "true")
+    assert_parity("undefined == blank", "false")
+  end
+
+  def test_if_with_variables
+    assert_parity("value", "true",  { "value" => true })
+    assert_parity("value", "false", { "value" => false })
+  end
+
+  def test_nil_variable_in_and_expression
+    assert_condition("x and true", "false", { "x" => nil })
+    assert_condition("true and x", "false", { "x" => nil })
+
+    assert_expression("x and true", "",     { "x" => nil })
+    assert_expression("true and x", "",     { "x" => nil })
+  end
+
+  def test_boolean_variable_in_and_expression
+    assert_parity("true and x", "false", { "x" => false })
+    assert_parity("x and true", "false", { "x" => false })
+
+    assert_parity("true and x", "true",  { "x" => true })
+    assert_parity("x and true", "true",  { "x" => true })
+
+    assert_parity("true or x", "true",   { "x" => false })
+    assert_parity("x or true", "true",   { "x" => false })
+
+    assert_parity("true or x", "true",   { "x" => true })
+    assert_parity("x or true", "true",   { "x" => true })
+  end
+
+  def test_multi_variable_boolean_nil_and_expression
+    assert_condition("x and y", "false", { "x" => nil, "y" => true })
+    assert_condition("y and x", "false", { "x" => true, "y" => nil })
+
+    assert_expression("x and y", "",     { "x" => nil, "y" => true })
+    assert_expression("y and x", "",     { "x" => true, "y" => nil })
+  end
+
+  def test_multi_truthy_variables_and_expressions
+    assert_condition("x or y", "true",   { "x" => nil, "y" => "hello" })
+    assert_condition("y or x", "true",   { "x" => "hello", "y" => nil })
+
+    assert_expression("x or y", "hello", { "x" => nil, "y" => "hello" })
+    assert_expression("y or x", "hello", { "x" => "hello", "y" => nil })
+  end
+
+  def test_multi_variable_boolean_nil_or_expression
+    assert_parity("x or y", "true", { "x" => nil, "y" => true })
+    assert_parity("y or x", "true", { "x" => true, "y" => nil })
+  end
+
+  def test_links_not_blank_with_drop_returns_true_for_all_cases
+    link = LinkDrop.new(
+      levels: 0,
+      links: [
+        LinkDrop.new(levels: 1, links: [], title: "About", type: "page_link", url: "/pages/about"),
+        LinkDrop.new(levels: 1, links: [], title: "Contact", type: "page_link", url: "/pages/contact"),
+      ],
+      title: "Main Menu",
+      type: "menu",
+      url: nil,
+    )
+
+    template = <<~LIQUID
+      {%- if link.links != blank -%}
+        true
+      {%- else -%}
+        false
+      {%- endif -%}
+    LIQUID
+
+    act_output = Liquid::Template.parse(template).render({ "link" => link })
+    assert_equal("true", act_output)
+
+    act_output = Liquid::Template.parse(template).render({ "link" => link.tap { |l| l.links = [] } })
+    assert_equal("true", act_output)
+
+    act_output = Liquid::Template.parse(template).render({ "link" => link.tap { |l| l.links = nil } })
+    assert_equal("true", act_output)
+
+    act_output = Liquid::Template.parse(template).render({ "link" => LinkDrop.new })
+    assert_equal("true", act_output)
+  end
+
+  def test_links_truthy_with_drop_returns_false_for_nil_and_empty_drop
+    link = LinkDrop.new(
+      levels: 0,
+      links: [
+        LinkDrop.new(levels: 1, links: [], title: "About", type: "page_link", url: "/pages/about"),
+        LinkDrop.new(levels: 1, links: [], title: "Contact", type: "page_link", url: "/pages/contact"),
+      ],
+      title: "Main Menu",
+      type: "menu",
+      url: nil,
+    )
+
+    template = <<~LIQUID
+      {%- if link.links -%}
+        true
+      {%- else -%}
+        false
+      {%- endif -%}
+    LIQUID
+
+    act_output = Liquid::Template.parse(template).render({ "link" => link })
+    assert_equal("true", act_output)
+
+    act_output = Liquid::Template.parse(template).render({ "link" => link.tap { |l| l.links = [] } })
+    assert_equal("true", act_output)
+
+    act_output = Liquid::Template.parse(template).render({ "link" => link.tap { |l| l.links = nil } })
+    assert_equal("false", act_output)
+
+    act_output = Liquid::Template.parse(template).render({ "link" => {} })
+    assert_equal("false", act_output)
+  end
+
+  def test_links_not_blank_with_hash_returns_true_for_all_cases
+    link = {
+      "levels" => 0,
+      "links" => [
+        {
+          "levels" => 1,
+          "links" => [],
+          "title" => { "text" => "About" },
+          "type" => "page_link",
+          "url" => "/pages/about",
+        },
+        {
+          "levels" => 1,
+          "links" => [],
+          "title" => { "text" => "Contact" },
+          "type" => "page_link",
+          "url" => "/pages/contact",
+        },
+      ],
+      "title" => { "text" => "Main Menu" },
+      "type" => "menu",
+      "url" => nil,
+    }
+
+    template = <<~LIQUID
+      {%- if link.links != blank -%}
+        true
+      {%- else -%}
+        false
+      {%- endif -%}
+    LIQUID
+
+    act_output = Liquid::Template.parse(template).render({ "link" => link })
+    assert_equal("true", act_output)
+
+    act_output = Liquid::Template.parse(template).render({ "link" => { **link, "links" => [] } })
+    assert_equal("true", act_output)
+
+    act_output = Liquid::Template.parse(template).render({ "link" => { **link, "links" => nil } })
+    assert_equal("true", act_output)
+
+    act_output = Liquid::Template.parse(template).render({ "link" => {} })
+    assert_equal("true", act_output)
+  end
+
+  def test_links_truthy_with_hash_returns_false_for_nil_and_empty_hash
+    link = {
+      "levels" => 0,
+      "links" => [
+        {
+          "levels" => 1,
+          "links" => [],
+          "title" => { "text" => "About" },
+          "type" => "page_link",
+          "url" => "/pages/about",
+        },
+        {
+          "levels" => 1,
+          "links" => [],
+          "title" => { "text" => "Contact" },
+          "type" => "page_link",
+          "url" => "/pages/contact",
+        },
+      ],
+      "title" => { "text" => "Main Menu" },
+      "type" => "menu",
+      "url" => nil,
+    }
+
+    template = <<~LIQUID
+      {%- if link.links -%}
+        true
+      {%- else -%}
+        false
+      {%- endif -%}
+    LIQUID
+
+    act_output = Liquid::Template.parse(template).render({ "link" => link })
+    assert_equal("true", act_output)
+
+    act_output = Liquid::Template.parse(template).render({ "link" => { **link, "links" => [] } })
+    assert_equal("true", act_output)
+
+    act_output = Liquid::Template.parse(template).render({ "link" => { **link, "links" => nil } })
+    assert_equal("false", act_output)
+
+    act_output = Liquid::Template.parse(template).render({ "link" => {} })
+    assert_equal("false", act_output)
+  end
+
+  def test_conditions_with_boolean_operators_without_whitespace_around_operator
+    template = <<~LIQUID
+      <option variant_id="{{ variant.id }}" {% if current_variant.id==variant.id %}selected{%- endif -%}>{{ variant.title }}</option>
+    LIQUID
+
+    context = {
+      "variant" => {
+        "id" => 420,
+        "title" => "Default Title",
+      },
+      "current_variant" => {
+        "id" => 420,
+      },
+    }
+
+    # Expected output
+    # Note: Ideally we would like the whitespace around the boolean operator to be optional.
+    # So the more correct expected output would be:
+    #
+    # <option variant_id="420" selected>Default Title</option>
+    #
+    # However, the existing behaviour in liquid-ruby is that the whitespace is required around the boolean operator.
+    expected_lax_output = <<~HTML
+      <option variant_id="420" >Default Title</option>
+    HTML
+
+    expected_strict_output = <<~HTML
+      <option variant_id="420" selected>Default Title</option>
+    HTML
+
+    # This bugged output only happens in lax mode.
+    assert_with_lax_parsing(template, expected_lax_output, context)
+
+    # Default test parsing mode (strict) works as properly expected
+    assert_equal(expected_strict_output.delete("\n"), actual_strict_output.delete("\n"))
+  end
+
+  # TESTING INCORRECT BEHAVIOUR OF LIQUID-RUBY
+  # If liquid-vm fails this test, we should change it.
+  def test_boolean_conditional_with_json_filter
+    # Define the Liquid template to test
+    template = <<~LIQUID
+      {{ template.name == 'index' | json }}
+    LIQUID
+
+    # Define the context for the template where the template name is 'index'
+    context = {
+      "template" => {
+        "name" => "product",
+      },
+    }
+
+    # Expected output
+    # Note: I dont know what is the correct output here but this is the liquid-ruby 'main' output.
+    #
+    # It feels incorrect but I dont know whats better
+    expected_output = "product"
+
+    # Render the template with the context
+    actual_parsed_template = Liquid::Template.parse(template)
+    actual_output = actual_parsed_template.render(context)
+
+    # Assert that the actual output matches the expected output
+    assert_equal(expected_output, actual_output.strip)
+  end
+
+  # TESTING INCORRECT BEHAVIOUR OF LIQUID-RUBY
+  # If liquid-vm fails this test, we should change it.
+  def test_chained_conditional_with_object_contains
+    # Define the Liquid template to test
+    template = <<~LIQUID
+      {{ settings.prefilter_status and template contains 'collection' }}
+    LIQUID
+
+    # Test with context containing 'collection'
+    context_with_collection = {
+      "template" => {
+        "name" => "collection",
+      },
+      "settings" => {
+        "prefilter_status" => true,
+      },
+    }
+    # NOTE: This is a bug that liquid-ruby `main` output returns the first value.
+    assert_with_lax_parsing(template, "true", context_with_collection)
+
+    # Test with context not containing 'collection'
+    context_without_collection = {
+      "template" => {
+        "name" => "not-collection",
+      },
+      "settings" => {
+        "prefilter_status" => true,
+      },
+    }
+    # NOTE: This is a bug that liquid-ruby `main` output returns the first value.
+    assert_with_lax_parsing(template, "true", context_without_collection)
+  end
+
+  # TESTING INCORRECT BEHAVIOUR OF LIQUID-RUBY
+  # If liquid-vm fails this test, we should change it.
+  def test_assign_boolean_expression_to_variable
+    template = <<~LIQUID
+      {%- liquid
+        assign is_preview_mode = content_for_header contains "foo" or content_for_header contains "bar"
+        echo is_preview_mode
+      -%}
+    LIQUID
+
+    context = { "content_for_header" => "Some content" }
+
+    # Expected output
+    # This value should be "false" but it is the value of the variable from the failed expression.
+    assert_template_result("Some content", template, context)
+
+    # This following validation should only be supported with our changes. It is the short-hand for the above template.
+    # The validation for it is the expected correct output.
+    template = Liquid::Template.parse("{% assign is_preview_mode = content_for_header contains 'foo' or content_for_header contains 'bar' %}{{ is_preview_mode }}")
+    assert_equal("false", template.render(context))
+  end
+
+  private
+
+  def assert_with_lax_parsing(template, expected_output, context = {})
+    prev_error_mode = Liquid::Environment.default.error_mode
+    Liquid::Environment.default.error_mode = :lax
+
+    begin
+      actual_output = Liquid::Template.parse(template).render(context)
+    rescue StandardError => e
+      actual_output = e.message
+    ensure
+      Liquid::Environment.default.error_mode = prev_error_mode
+    end
+
+    assert_equal(expected_output.strip, actual_output.strip)
+  end
+
+  def assert_parity(liquid_expression, expected_result, args = {})
+    assert_condition(liquid_expression, expected_result, args)
+    assert_expression(liquid_expression, expected_result, args)
+  end
+
+  def assert_expression(liquid_expression, expected_result, args = {})
+    assert_parity_scenario(:expression, "{{ #{liquid_expression} }}", expected_result, args)
+  end
+
+  def assert_condition(liquid_condition, expected_result, args = {})
+    assert_parity_scenario(:condition, "{% if #{liquid_condition} %}true{% else %}false{% endif %}", expected_result, args)
+  end
+
+  def assert_parity_scenario(kind, template, exp_output, args = {})
+    act_output = Liquid::Template.parse(template).render(args)
+
+    assert_equal(exp_output, act_output, <<~ERROR_MESSAGE)
+      #{kind.to_s.capitalize} template failure:
+      ---
+      #{template}
+      ---
+      args: #{args.inspect}
+    ERROR_MESSAGE
+  end
+
+  class LinkDrop < Liquid::Drop
+    attr_accessor :levels, :links, :title, :type, :url
+
+    def initialize(levels: nil, links: nil, title: nil, type: nil, url: nil)
+      super()
+
+      @levels = levels
+      @links = links
+      @title = title
+      @type = type
+      @url = url
+    end
+  end
+end

test/unit/lexer_unit_test.rb

@@ -141,6 +141,78 @@ class LexerUnitTest < Minitest::Test
     )
   end
 
+  def test_boolean_and_operator
+    exp = [
+      [:id, "true"],
+      [:boolean_operator, "and"],
+      [:id, "false"],
+      [:end_of_string],
+    ]
+    act = tokenize("true and false")
+    assert_equal(exp, act)
+  end
+
+  def test_boolean_or_operator
+    exp = [
+      [:id, "false"],
+      [:boolean_operator, "or"],
+      [:id, "true"],
+      [:end_of_string],
+    ]
+    act = tokenize("false or true")
+    assert_equal(exp, act)
+  end
+
+  def test_boolean_operators_in_complex_expressions
+    exp = [
+      [:id, "a"],
+      [:boolean_operator, "and"],
+      [:id, "b"],
+      [:boolean_operator, "or"],
+      [:id, "c"],
+      [:end_of_string],
+    ]
+    act = tokenize("a and b or c")
+    assert_equal(exp, act)
+  end
+
+  def test_boolean_operators_with_comparisons
+    exp = [
+      [:id, "a"],
+      [:comparison, ">"],
+      [:number, "5"],
+      [:boolean_operator, "and"],
+      [:id, "b"],
+      [:comparison, "<"],
+      [:number, "10"],
+      [:end_of_string],
+    ]
+    act = tokenize("a > 5 and b < 10")
+    assert_equal(exp, act)
+  end
+
+  def test_boolean_operators_as_property_names
+    exp = [
+      [:id, "obj"],
+      [:dot, "."],
+      [:id, "and"],
+      [:dot, "."],
+      [:id, "property"],
+      [:end_of_string],
+    ]
+    act = tokenize("obj.and.property")
+    assert_equal(exp, act)
+
+    exp = [
+      [:id, "obj"],
+      [:dot, "."],
+      [:id, "or"],
+      [:end_of_string],
+    ]
+    act = tokenize("obj.or")
+    assert_equal(exp, act)
+  end
+
   private
 
   def tokenize(input)