net.ParseIP doesn't expand IPv4 addresses

[perpetual-hydrofoil]

package main

import (
    "fmt"
    "net"
)

func main() {
    ip := net.ParseIP("1.1") // this is nil
    if ip.To4() == nil {
        fmt.Printf("%v is not an IPv4 address", ip)
    }
}

See #36822 (comment) for more discussion.

It appears to be part of the POSIX specification, but not part of an RFC, but it still has a lot of uses (ping 127.1, https://1.1, etc) and is generally available in POSIX operating systems.

http://man7.org/linux/man-pages/man3/inet_addr.3.html

net being unable to expand IPv4's may also be the root cause behind #36822.

[ianlancetaylor]

I don't think we need two issues for this. Closing in favor of #36822. Please comment if you disagree.