In the following method:

func (w *Work) buildReleaseBinary() {

The golang.org/x/build/cmd/release binary is built explicitly in GOPATH mode, with a clean, deterministic GOPATH workspace.

releasebot should be updated to build release binary in module mode.

Making the change may result in different versions of its dependencies being used:

• cloud.google.com/go/storage
• golang.org/x/sync/errgroup
• google.golang.org/api/iterator

We should confirm that making this change won't influence a release negatively, and do the switch.

Building the release binary should continue to be reproducible and unaffected by user's local environment. This can be done by overriding environment variables from environment with explicit ones, as it was done when building in GOPATH mode:

r := w.runner(w.Dir, "GO111MODULE=off", "GOPATH="+gopath, "GOBIN="+filepath.Join(gopath, "bin"))
r.run("go", "get", "golang.org/x/build/cmd/release")