Discussion in #527 resulted in gps getting moved to an internal path. I'd like to discuss moving out a stable subset of it to a public API that other projects can import.

One concrete use case to kick things off:

I work on a tool called retool which vendors executables. Right now, it can be pretty slow because it doesn't have any cache; invocations of retool have to do full git clones (via go get in a managed GOPATH), then git checkout the proper revision, then call go get again to lean on the go tool's ability to pull in dependencies at that particular revision.

Retool would be improved a lot by using some of the tools in gps.

For one thing, gps provides access to the local cache of packages, including their git metadata, which would speed up most of retool's operations.

A second (less crucial, to me) benefit would be gps's ability to compute the appropriate set of dependencies of a package, instead of relying on go get.