net: IPv6 network does not contain IPv4 to IPv6 translated addresses

[pixelbender]

What version of Go are you using (go version)?

1.14

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

All operating system and processor architectures

What did you do?

https://play.golang.org/p/IN-TOcROQnr

// "8.8.8.8" translated to IPv6, same as net.ParseIP("8.8.8.8")
ip := net.ParseIP("0:0:0:0:0:ffff:808:808")

_, ipv4, _ := net.ParseCIDR("0.0.0.0/0")
fmt.Println(ipv4.Contains(ip)) // true

_, ipv6, _ := net.ParseCIDR("::/0")
fmt.Println(ipv6.Contains(ip)) // why it says false?

_, translated, _ := net.ParseCIDR("::ffff:0:0/96")
fmt.Println(translated.Contains(ip)) // true

What did you expect to see?

true
true
true

What did you see instead?

true
false
true

[gopherbot]

Change https://golang.org/cl/221798 mentions this issue: net: IPv6 network does not contain IPv4 to IPv6 translated addresses

[dmitshur]

/cc @mikioh @bradfitz @ianlancetaylor per owners.