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

src/libserialize/json.rs

@@ -235,7 +235,7 @@ pub struct AsJson<'a, T: 'a> { inner: &'a T }
 pub struct AsPrettyJson<'a, T: 'a> { inner: &'a T, indent: Option<uint> }
 
 /// The errors that can arise while parsing a JSON stream.
-#[derive(Clone, Copy, PartialEq)]
+#[derive(Clone, Copy, PartialEq, Show)]
 pub enum ErrorCode {
     InvalidSyntax,
     InvalidNumber,
@@ -325,7 +325,7 @@ pub fn encode<T: ::Encodable>(object: &T) -> string::String {
     s
 }
 
-impl fmt::Show for ErrorCode {
+impl fmt::Display for ErrorCode {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         error_str(*self).fmt(f)
     }
@@ -335,14 +335,33 @@ fn io_error_to_error(io: io::IoError) -> ParserError {
     IoError(io.kind, io.desc)
 }
 
+impl fmt::Display for ParserError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        // FIXME this should be a nicer error
+        fmt::Debug::fmt(self, f)
+    }
+}
+
+impl fmt::Display for DecoderError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        // FIXME this should be a nicer error
+        fmt::Debug::fmt(self, f)
+    }
+}
+
 impl std::error::Error for DecoderError {
     fn description(&self) -> &str { "decoder error" }
-    fn detail(&self) -> Option<std::string::String> { Some(format!("{:?}", self)) }
+}
+
+impl fmt::Display for EncoderError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        // FIXME this should be a nicer error
+        fmt::Debug::fmt(self, f)
+    }
 }
 
 impl std::error::Error for EncoderError {
     fn description(&self) -> &str { "encoder error" }
-    fn detail(&self) -> Option<std::string::String> { Some(format!("{:?}", self)) }
 }
 
 impl std::error::FromError<fmt::Error> for EncoderError {
@@ -2519,7 +2538,7 @@ impl<'a, 'b> fmt::Writer for FormatShim<'a, 'b> {
     }
 }
 
-impl fmt::String for Json {
+impl fmt::Display for Json {
     /// Encodes a json value into a string
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         let mut shim = FormatShim { inner: f };
@@ -2531,7 +2550,7 @@ impl fmt::String for Json {
     }
 }
 
-impl<'a> fmt::String for PrettyJson<'a> {
+impl<'a> fmt::Display for PrettyJson<'a> {
     /// Encodes a json value into a string
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         let mut shim = FormatShim { inner: f };
@@ -2543,7 +2562,7 @@ impl<'a> fmt::String for PrettyJson<'a> {
     }
 }
 
-impl<'a, T: Encodable> fmt::String for AsJson<'a, T> {
+impl<'a, T: Encodable> fmt::Display for AsJson<'a, T> {
     /// Encodes a json value into a string
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         let mut shim = FormatShim { inner: f };
@@ -2563,7 +2582,7 @@ impl<'a, T> AsPrettyJson<'a, T> {
     }
 }
 
-impl<'a, T: Encodable> fmt::String for AsPrettyJson<'a, T> {
+impl<'a, T: Encodable> fmt::Display for AsPrettyJson<'a, T> {
     /// Encodes a json value into a string
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         let mut shim = FormatShim { inner: f };
@@ -3920,7 +3939,7 @@ mod tests {
         let mut mem_buf = Vec::new();
         let mut encoder = Encoder::new(&mut mem_buf as &mut fmt::Writer);
         let result = hm.encode(&mut encoder);
-        match result.unwrap_err() {
+        match result.err().unwrap() {
             EncoderError::BadHashmapKey => (),
             _ => panic!("expected bad hash map key")
         }