Extract goimports' logic for walking Go source directories into a
separate package, suitable for use in go/packages. No functional
changes. Added a convenience feature to fastwalk, allowing the user to
say that they're done with a directory and stop receiving callbacks for
it.
Testing is a little light; I expect goimports' tests to cover most
everything we care about.
Change-Id: If047ada4414f5f282637d11fd07e8342fadc9c33
Reviewed-on: https://go-review.googlesource.com/c/138877
Run-TryBot: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Matloob <matloob@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Heschi Kreinick