Per feedback from mdempsky from https://go-review.googlesource.com/22096.

Also fix emitted position info.

Change-Id: I7ff1967430867d922be8784832042c75d81df28b
Reviewed-on: https://go-review.googlesource.com/22198
Run-TryBot: Robert Griesemer <gri@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>