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, 8 insertions, 1 deletions

diff --git a/src/libstd/ffi/c_str.rs b/src/libstd/ffi/c_str.rs
index d7f8eb2e415..b7f4b070591 100644
--- a/src/libstd/ffi/c_str.rs
+++ b/src/libstd/ffi/c_str.rs
@@ -119,7 +119,8 @@ impl Deref for CString {
     }
 }
 
-impl fmt::Show for CString {
+#[stable]
+impl fmt::Debug for CString {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         String::from_utf8_lossy(self.as_bytes()).fmt(f)
     }
@@ -215,4 +216,10 @@ mod tests {
             assert_eq!(s.as_bytes(), b"\0");
         }
     }
+
+    #[test]
+    fn formatted() {
+        let s = CString::from_slice(b"12");
+        assert_eq!(format!("{:?}", s), "\"12\"");
+    }
 }