This is reapplying CL121995 after rolling back the change to the importing
methods. There is still a need for a flag to control tags.
The original CL decription:
The feature has been requested but, like build tags in general,
only works in a directory, not when files are specified explicitly.
Unlike the build tools, report when the feature is misused like this
to avoid confusion.
Fixesgolang/go#9449
Change-Id: I732627d5f2e6323367e3bdd5de746923868890a9
Reviewed-on: https://go-review.googlesource.com/122537
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
18f0b668f1