std: Rename Show/String to Debug/Display

This commit is an implementation of [RFC 565][rfc] which is a stabilization of
the `std::fmt` module and the implementations of various formatting traits.
Specifically, the following changes were performed:

[rfc]: https://github.com/rust-lang/rfcs/blob/master/text/0565-show-string-guidelines.md

* The `Show` trait is now deprecated, it was renamed to `Debug`
* The `String` trait is now deprecated, it was renamed to `Display`
* Many `Debug` and `Display` implementations were audited in accordance with the
  RFC and audited implementations now have the `#[stable]` attribute
  * Integers and floats no longer print a suffix
  * Smart pointers no longer print details that they are a smart pointer
  * Paths with `Debug` are now quoted and escape characters
* The `unwrap` methods on `Result` now require `Display` instead of `Debug`
* The `Error` trait no longer has a `detail` method and now requires that
  `Display` must be implemented. With the loss of `String`, this has moved into
  libcore.
* `impl<E: Error> FromError<E> for Box<Error>` now exists
* `derive(Show)` has been renamed to `derive(Debug)`. This is not currently
  warned about due to warnings being emitted on stage1+

While backwards compatibility is attempted to be maintained with a blanket
implementation of `Display` for the old `String` trait (and the same for
`Show`/`Debug`) this is still a breaking change due to primitives no longer
implementing `String` as well as modifications such as `unwrap` and the `Error`
trait. Most code is fairly straightforward to update with a rename or tweaks of
method calls.

[breaking-change]
Closes #21436

1 files changed, 4 insertions, 2 deletions

diff --git a/src/libstd/io/net/ip.rs b/src/libstd/io/net/ip.rs
index adc122ff447..e8e065533e5 100644
--- a/src/libstd/io/net/ip.rs
+++ b/src/libstd/io/net/ip.rs
@@ -38,7 +38,8 @@ pub enum IpAddr {
     Ipv6Addr(u16, u16, u16, u16, u16, u16, u16, u16)
 }
 
-impl fmt::String for IpAddr {
+#[stable]
+impl fmt::Display for IpAddr {
     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
         match *self {
             Ipv4Addr(a, b, c, d) =>
@@ -69,7 +70,8 @@ pub struct SocketAddr {
     pub port: Port,
 }
 
-impl fmt::String for SocketAddr {
+#[stable]
+impl fmt::Display for SocketAddr {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self.ip {
             Ipv4Addr(..) => write!(f, "{}:{}", self.ip, self.port),