扩展包导入路径

Is there a Go standard library function to expand package import paths?

For example, I'd like a function Expand with the following behavior:

Expand("path/filepath")   => "/usr/local/go/src/path/filepath"
Expand("go/types")        => "/usr/local/go/src/go/types"
Expand("my/package/path") => "/Users/kvu/go/src/my/package/path"

Perhaps something like:

path.Join(os.Getenv("GOPATH"), "/my/package/path")