Cache SelfDrop per context

Author: karreiro

lib/liquid/context.rb

@@ -208,7 +208,7 @@ def find_variable(key, raise_on_not_found: true)
 
       # `self` resolves to a SelfDrop (enabling `self['var']` lookups),
       # but only when it hasn't been explicitly assigned as a local variable.
-      return SelfDrop.new(self) if key == Expression::SELF && !index
+      return @self_drop ||= SelfDrop.new(self) if key == Expression::SELF && !index
 
       variable = if index
         lookup_and_evaluate(@scopes[index], key, raise_on_not_found: raise_on_not_found)

test/integration/self_drop_context_test.rb

@@ -79,8 +79,12 @@ def test_self_drop_context_setter_is_undefined
 
   def test_self_drop_repeated_lookups_compare_equal_for_same_context
     context = Context.new
+    drop = context.find_variable("self")
+    cached_drop = context.find_variable("self")
 
-    assert_equal(context.find_variable("self"), context.find_variable("self"))
+    assert_same(drop, cached_drop)
+    assert_equal(drop.object_id, cached_drop.object_id)
+    assert_equal(drop, cached_drop)
   end
 
   def test_assigned_self_drop_compares_equal_to_itself