fixes #4177

tests/usingstmt/tthis.nim

@@ -0,0 +1,15 @@
+
+# bug #4177
+
+type
+  Parent = object of RootObj
+    parentField: int
+  Child = object of Parent
+    childField: int
+
+{.this: self.}
+proc sumFields(self: Child): int =
+  result = parentField + childField # Error: undeclared identifier: 'parentField'
+
+proc sumFieldsWorks(self: Child): int =
+  result = self.parentField + childField