Goimport (i believe is the tool name, i use it for Vim) does just that. Also, because of the namespacing in Go, it actually works for non-standard library impor

Goimport (i believe is the tool name, i use it for Vim) does just that. Also, because of the namespacing in Go, it actually works for non-standard library imports as well. It runs along with Gofmt on every save for me. The only time in my experience that it has trouble is when there is a namespace conflict and it has to guess. Generally that's easy to avoid though, and uncommon.