Fix SelfDrop equality

lib/liquid/self_drop.rb

@@ -35,6 +35,20 @@ module Liquid
       self
     end
 
+    def ==(other)
+      other.is_a?(SelfDrop) && other.self_context.equal?(@self_context)
+    end
+
+    alias_method :eql?, :==
+
+    def hash
+      @self_context.object_id.hash
+    end
+
+    protected
+
+    attr_reader :self_context
+
     undef context=
   end
 end

test/integration/self_drop_context_test.rb

@@ -77,6 +77,24 @@ class SelfDropContextTest < Minitest::Test
     assert_template_result('42', '{{ self.x }}', { 'x' => 42 })
   end
 
+  def test_self_drop_repeated_lookups_compare_equal_for_same_context
+    context = Context.new
+
+    assert_equal(context.find_variable("self"), context.find_variable("self"))
+  end
+
+  def test_assigned_self_drop_compares_equal_to_itself
+    assert_template_result('T', '{% assign s = self %}{% if s == s %}T{% else %}F{% endif %}')
+  end
+
+  def test_distinct_self_assignments_compare_equal_for_same_context
+    assert_template_result('T', '{% assign a = self %}{% assign b = self %}{% if a == b %}T{% else %}F{% endif %}')
+  end
+
+  def test_bare_self_compares_equal_to_bare_self
+    assert_template_result('T', '{% if self == self %}T{% else %}F{% endif %}')
+  end
+
   def test_self_drop_with_strict_variables_does_not_raise_for_defined_var
     t = Template.parse('{{ self.x }}')
     result = t.render({ 'x' => 42 }, strict_variables: true)