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
This extends cfg-gating to attributes.
```rust
#[cfg_attr(<cfg pattern>, <attr>)]
```
will expand to
```rust
#[<attr>]
```
if the `<cfg pattern>` matches the current cfg environment, and nothing
if it does not. The grammar for the cfg pattern has a simple
recursive structure:
* `value` and `key = "value"` are cfg patterns,
* `not(<cfg pattern>)` is a cfg pattern and matches if `<cfg pattern>`
does not.
* `all(<cfg pattern>, ...)` is a cfg pattern and matches if all of the
`<cfg pattern>`s do.
* `any(<cfg pattern>, ...)` is a cfg pattern and matches if any of the
`<cfg pattern>`s do.
Examples:
```rust
// only derive Show for assert_eq! in tests
#[cfg_attr(test, deriving(Show))]
struct Foo { ... }
// only derive Show for assert_eq! in tests and debug builds
#[cfg_attr(any(test, not(ndebug)), deriving(Show))]
struct Foo { ... }
// ignore a test in certain cases
#[test]
#[cfg_attr(all(not(target_os = "linux"), target_endian = "big"), ignore)]
fn test_broken_thing() { ... }
// Avoid duplication when fixing staging issues in rustc
#[cfg_attr(not(stage0), lang="iter")]
pub trait Iterator<T> { ... }
```
