From 6b66749e171e8a9c6718c0107f4ec2e3f47b28ed Mon Sep 17 00:00:00 2001
From: Lzu Tao <taolzu@gmail.com>
Date: Wed, 20 Jan 2021 01:33:38 +0000
Subject: [PATCH 1/2] Use slice::split_first instead of manuall slicing

---
 library/std/src/net/ip.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/library/std/src/net/ip.rs b/library/std/src/net/ip.rs
index d33b772633d..5c62ce43afb 100644
--- a/library/std/src/net/ip.rs
+++ b/library/std/src/net/ip.rs
@@ -1610,9 +1610,9 @@ impl fmt::Display for Ipv6Addr {
                 /// Write a colon-separated part of the address
                 #[inline]
                 fn fmt_subslice(f: &mut fmt::Formatter<'_>, chunk: &[u16]) -> fmt::Result {
-                    if let Some(first) = chunk.first() {
+                    if let Some((first, tail)) = chunk.split_first() {
                         fmt::LowerHex::fmt(first, f)?;
-                        for segment in &chunk[1..] {
+                        for segment in tail {
                             f.write_char(':')?;
                             fmt::LowerHex::fmt(segment, f)?;
                         }

From 116b66ad491b3f0a5a809e49a6377d2697d0ed1b Mon Sep 17 00:00:00 2001
From: Lzu Tao <taolzu@gmail.com>
Date: Wed, 20 Jan 2021 03:06:49 +0000
Subject: [PATCH 2/2] Dont prefix 0x when `dbg!(ipv6)`

---
 library/std/src/net/ip.rs       | 4 ++--
 library/std/src/net/ip/tests.rs | 3 +++
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/library/std/src/net/ip.rs b/library/std/src/net/ip.rs
index 5c62ce43afb..84449e48767 100644
--- a/library/std/src/net/ip.rs
+++ b/library/std/src/net/ip.rs
@@ -1611,10 +1611,10 @@ impl fmt::Display for Ipv6Addr {
                 #[inline]
                 fn fmt_subslice(f: &mut fmt::Formatter<'_>, chunk: &[u16]) -> fmt::Result {
                     if let Some((first, tail)) = chunk.split_first() {
-                        fmt::LowerHex::fmt(first, f)?;
+                        write!(f, "{:x}", first)?;
                         for segment in tail {
                             f.write_char(':')?;
-                            fmt::LowerHex::fmt(segment, f)?;
+                            write!(f, "{:x}", segment)?;
                         }
                     }
                     Ok(())
diff --git a/library/std/src/net/ip/tests.rs b/library/std/src/net/ip/tests.rs
index 44fb3adf070..ef0d4edc434 100644
--- a/library/std/src/net/ip/tests.rs
+++ b/library/std/src/net/ip/tests.rs
@@ -166,6 +166,9 @@ fn ipv6_addr_to_string() {
 
     // two runs of zeros, equal length
     assert_eq!("1::4:5:0:0:8", Ipv6Addr::new(1, 0, 0, 4, 5, 0, 0, 8).to_string());
+
+    // don't prefix `0x` to each segment in `dbg!`.
+    assert_eq!("1::4:5:0:0:8", &format!("{:#?}", Ipv6Addr::new(1, 0, 0, 4, 5, 0, 0, 8)));
 }
 
 #[test]