Allow empty to behave like an empty array (change needed in liquid-c)

lib/liquid/expression.rb

@@ -7,7 +7,7 @@ class Expression
       'true' => true,
       'false' => false,
       'blank' => '',
-      'empty' => ''
+      'empty' => [].freeze
     }.freeze
 
     INTEGERS_REGEX       = /\A(-?\d+)\z/

test/integration/tags/statements_test.rb

@@ -2,17 +2,27 @@
 
 require 'test_helper'
 
+class EmptyDrop < Liquid::Drop
+  def empty?
+    true
+  end
+end
+
 class StatementsTest < Minitest::Test
   include Liquid
 
   def test_true_eql_true
     text = ' {% if true == true %} true {% else %} false {% endif %} '
     assert_template_result('  true  ', text)
+    text = ' {% if var == true %} true {% else %} false {% endif %} '
+    assert_template_result('  true  ', text, 'var' => true)
   end
 
   def test_true_not_eql_true
     text = ' {% if true != true %} true {% else %} false {% endif %} '
     assert_template_result('  false  ', text)
+    text = ' {% if var != true %} true {% else %} false {% endif %} '
+    assert_template_result('  false  ', text, 'var' => true)
   end
 
   def test_true_lq_true
@@ -93,6 +103,30 @@ def test_is_collection_empty
   def test_is_not_collection_empty
     text = ' {% if array == empty %} true {% else %} false {% endif %} '
     assert_template_result('  false  ', text, 'array' => [1, 2, 3])
+
+    text = ' {% if array != empty %} true {% else %} false {% endif %} '
+    assert_template_result('  true  ', text, 'array' => [1, 2, 3])
+  end
+
+  def test_is_collection_empty_backward
+    text = ' {% if empty == array %} true {% else %} false {% endif %} '
+    assert_template_result('  true  ', text, 'array' => [])
+  end
+
+  def test_is_string_empty
+    text = ' {% if string == empty %} true {% else %} false {% endif %} '
+    assert_template_result('  true  ', text, 'string' => '')
+
+    text = ' {% if empty == string %} true {% else %} false {% endif %} '
+    assert_template_result('  true  ', text, 'string' => '')
+  end
+
+  def test_is_non_array_empty
+    text = ' {% if obj == empty %} true {% else %} false {% endif %} '
+    assert_template_result('  true  ', text, 'obj' => EmptyDrop.new)
+
+    text = ' {% if empty == obj %} true {% else %} false {% endif %} '
+    assert_template_result('  true  ', text, 'obj' => EmptyDrop.new)
   end
 
   def test_nil

test/integration/variable_test.rb

@@ -66,6 +66,31 @@ def test_using_blank_as_variable_name
   def test_using_empty_as_variable_name
     template = Template.parse("{% assign foo = empty %}{{ foo }}")
     assert_equal('', template.render!)
+    template = Template.parse("{% assign foo = empty %}{% if foo == ary %}Y{% else %}N{% endif %}")
+    assert_equal('Y', template.render!('ary' => []))
+    template = Template.parse("{% assign foo = empty %}{% if foo == foo %}Y{% else %}N{% endif %}")
+    assert_equal('Y', template.render!)
+  end
+
+  def test_using_empty_as_variable_name_with_filters
+    template = Template.parse("{% assign foo = empty %}{{ foo | sort | size }}")
+    assert_equal('0', template.render!)
+    template = Template.parse("{% assign foo = empty | sort %}{{ foo | size }}")
+    assert_equal('0', template.render!)
+  end
+
+  def test_using_empty_as_empty_array
+    template = Template.parse("{% for x in empty %}x{% endfor %}")
+    assert_equal('', template.render!)
+  end
+
+  def test_empty_can_be_filled
+    template = Template.parse("{% assign foo = empty %}{{ foo | concat: bar }}")
+    assert_equal('Y', template.render!('bar' => ['Y']))
+    template = Template.parse("{% assign foo = empty %}{{ foo | concat: bar | join: '--' }}")
+    assert_equal('A--B', template.render!('bar' => ['A', 'B']))
+    template = Template.parse("{% assign foo = empty %}{% assign tar = foo | concat: bar %}{{ tar | join: '--' }}{{ tar | size }}")
+    assert_equal('A--B2', template.render!('bar' => ['A', 'B']))
   end
 
   def test_hash_scoping