visit is just a func, and there's no formatting
verb for it, and it's on an internal-error path.
It has been thus many years, unchanged and unexecuted.

Change-Id: I4c2e2673ee9996218c24143bcc3be3eb4abdff25
Reviewed-on: https://go-review.googlesource.com/32970
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>