--- a/mercurial/vfs.py	Sat Dec 15 13:41:34 2018 -0500
+++ b/mercurial/vfs.py	Sat Dec 15 13:54:37 2018 -0500
@@ -518,7 +518,8 @@
         return delattr(self._origfh, attr)
 
     def __enter__(self):
-        return self._origfh.__enter__()
+        self._origfh.__enter__()
+        return self
 
     def __exit__(self, exc_type, exc_value, exc_tb):
         raise NotImplementedError('attempted instantiating ' + str(type(self)))