Dep should ignore packages only imported in files with tools build tag

[johanbrandhorst]

Hi!

I recently tried migrating one of my repositories to go modules (sorry!). I had some tool dependencies and the current go modules way of declaring such are through a tools.go file with a tools build tag.

This works fine until you have someone using dep depending on a package that contains your tools.go file. It seems dep, when resolving the transitive dependencies of such a dependency, concludes that these tool dependencies are also part of the graph. I think this is incorrect behaviour.

I propose that dep should ignore files that use the build tag tools.

Related issue: #463.
My repo with the problematic transative import behaviour: johanbrandhorst/certify#48.

[johanbrandhorst]

I made a mistake in the original post, I thought ignore was the build tag used, but it is not. The tag used is tools. I realize this greatly weakens the argument.

[kevinburke]

Thanks for the report! I think we are going to pass on this one.