When in your $GOPATH, make `go` autocomplete to packages. Add this to your .bashrc.

go-complete.sh

function _gocomplete_()
{
    # What do we want to autocomplete ?
    local word=${COMP_WORDS[COMP_CWORD]}
    # list packages that match in src/ subfolder, discarding warnings if no result
    COMPREPLY=($(go list ./src/"${word}"... 2>/dev/null))
}

# register autocomplete function for `go`
complete -F _gocomplete_ go