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

3 files changed, 6 insertions, 4 deletions

diff --git a/src/libsyntax/ext/deriving/mod.rs b/src/libsyntax/ext/deriving/mod.rs
index 603c4478007..e52a2b513ce 100644
--- a/src/libsyntax/ext/deriving/mod.rs
+++ b/src/libsyntax/ext/deriving/mod.rs
@@ -99,7 +99,9 @@ pub fn expand_meta_derive(cx: &mut ExtCtxt,
 
                             "Rand" => expand!(rand::expand_deriving_rand),
 
+                            // NOTE(stage0): remove "Show"
                             "Show" => expand!(show::expand_deriving_show),
+                            "Debug" => expand!(show::expand_deriving_show),
 
                             "Default" => expand!(default::expand_deriving_default),
 
diff --git a/src/libsyntax/ext/deriving/show.rs b/src/libsyntax/ext/deriving/show.rs
index 48034ce50ab..f5b5d4dda19 100644
--- a/src/libsyntax/ext/deriving/show.rs
+++ b/src/libsyntax/ext/deriving/show.rs
@@ -35,7 +35,7 @@ pub fn expand_deriving_show<F>(cx: &mut ExtCtxt,
     let trait_def = TraitDef {
         span: span,
         attributes: Vec::new(),
-        path: Path::new(vec!("std", "fmt", "Show")),
+        path: Path::new(vec!("std", "fmt", "Debug")),
         additional_bounds: Vec::new(),
         generics: LifetimeBounds::empty(),
         methods: vec!(
@@ -67,7 +67,7 @@ fn show_substructure(cx: &mut ExtCtxt, span: Span,
         Struct(_) => substr.type_ident,
         EnumMatching(_, v, _) => v.node.name,
         EnumNonMatchingCollapsed(..) | StaticStruct(..) | StaticEnum(..) => {
-            cx.span_bug(span, "nonsensical .fields in `#[derive(Show)]`")
+            cx.span_bug(span, "nonsensical .fields in `#[derive(Debug)]`")
         }
     };
 
diff --git a/src/libsyntax/ext/format.rs b/src/libsyntax/ext/format.rs
index f512b33f024..84f2ef0678d 100644
--- a/src/libsyntax/ext/format.rs
+++ b/src/libsyntax/ext/format.rs
@@ -603,8 +603,8 @@ impl<'a, 'b> Context<'a, 'b> {
         let trait_ = match *ty {
             Known(ref tyname) => {
                 match &tyname[] {
-                    ""  => "String",
-                    "?" => "Show",
+                    ""  => "Display",
+                    "?" => "Debug",
                     "e" => "LowerExp",
                     "E" => "UpperExp",
                     "o" => "Octal",