Yes, I will send a followup CL for better consistency. FWIW, unfortunately the following snippet works w/ CGO_ENABLED=1 older versions or GODEBUG=netdns=cgo newer versions.

package main

import "net"

func main() {
    for _, arg := range []string{"127.0.0.1:+0", "127.0.0.1:-0"} {
        ln, err := net.Listen("tcp", arg)
        if err != nil {
            println(err.Error())
            continue
        }
        println(ln.Addr().String())
        ln.Close()
    }
}

Probably we should make consistent representation on transport service names and literal port numbers in ABNF for Dial/Listen APIs before Go 1.

Okay, if +n worked before, we don't need to do anything here. Still weird, but yay compatibility.