std: Stabilize the `hash` module

This commit is an implementation of [RFC 823][rfc] which is another pass over
the `std::hash` module for stabilization. The contents of the module were not
entirely marked stable, but some portions which remained quite similar to the
previous incarnation are now marked `#[stable]`. Specifically:

[rfc]: https://github.com/rust-lang/rfcs/blob/master/text/0823-hash-simplification.md

* `std::hash` is now stable (the name)
* `Hash` is now stable
* `Hash::hash` is now stable
* `Hasher` is now stable
* `SipHasher` is now stable
* `SipHasher::new` and `new_with_keys` are now stable
* `Hasher for SipHasher` is now stable
* Many `Hash` implementations are now stable

All other portions of the `hash` module remain `#[unstable]` as they are less
commonly used and were recently redesigned.

This commit is a breaking change due to the modifications to the `std::hash` API
and more details can be found on the [RFC][rfc].

Closes #22467
[breaking-change]

4 files changed, 35 insertions, 11 deletions

diff --git a/src/liballoc/arc.rs b/src/liballoc/arc.rs
index 3830d7fe295..343ede4e2cf 100644
--- a/src/liballoc/arc.rs
+++ b/src/liballoc/arc.rs
@@ -605,11 +605,19 @@ impl<T: Default + Sync + Send> Default for Arc<T> {
     fn default() -> Arc<T> { Arc::new(Default::default()) }
 }
 
+#[cfg(stage0)]
 impl<H: Hasher, T: Hash<H>> Hash<H> for Arc<T> {
     fn hash(&self, state: &mut H) {
         (**self).hash(state)
     }
 }
+#[cfg(not(stage0))]
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: Hash> Hash for Arc<T> {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        (**self).hash(state)
+    }
+}
 
 #[cfg(test)]
 mod tests {
diff --git a/src/liballoc/boxed.rs b/src/liballoc/boxed.rs
index 340a8d59612..a3516bd667b 100644
--- a/src/liballoc/boxed.rs
+++ b/src/liballoc/boxed.rs
@@ -10,13 +10,14 @@
 
 //! A pointer type for heap allocation.
 //!
-//! `Box<T>`, casually referred to as a 'box', provides the simplest form of heap allocation in
-//! Rust. Boxes provide ownership for this allocation, and drop their contents when they go out of
-//! scope.
+//! `Box<T>`, casually referred to as a 'box', provides the simplest form of
+//! heap allocation in Rust. Boxes provide ownership for this allocation, and
+//! drop their contents when they go out of scope.
 //!
-//! Boxes are useful in two situations: recursive data structures, and occasionally when returning
-//! data. [The Pointer chapter of the Book](../../../book/pointers.html#best-practices-1) explains
-//! these cases in detail.
+//! Boxes are useful in two situations: recursive data structures, and
+//! occasionally when returning data. [The Pointer chapter of the
+//! Book](../../../book/pointers.html#best-practices-1) explains these cases in
+//! detail.
 //!
 //! # Examples
 //!
@@ -58,8 +59,8 @@ use core::ops::{Deref, DerefMut};
 use core::ptr::Unique;
 use core::raw::TraitObject;
 
-/// A value that represents the heap. This is the default place that the `box` keyword allocates
-/// into when no place is supplied.
+/// A value that represents the heap. This is the default place that the `box`
+/// keyword allocates into when no place is supplied.
 ///
 /// The following two examples are equivalent:
 ///
@@ -219,12 +220,20 @@ impl<T: ?Sized + Ord> Ord for Box<T> {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: ?Sized + Eq> Eq for Box<T> {}
 
+#[cfg(stage0)]
 impl<S: hash::Hasher, T: ?Sized + Hash<S>> Hash<S> for Box<T> {
     #[inline]
     fn hash(&self, state: &mut S) {
         (**self).hash(state);
     }
 }
+#[cfg(not(stage0))]
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized + Hash> Hash for Box<T> {
+    fn hash<H: hash::Hasher>(&self, state: &mut H) {
+        (**self).hash(state);
+    }
+}
 
 /// Extension methods for an owning `Any` trait object.
 #[unstable(feature = "alloc",
diff --git a/src/liballoc/lib.rs b/src/liballoc/lib.rs
index b3c2638f3ae..bc349ebebde 100644
--- a/src/liballoc/lib.rs
+++ b/src/liballoc/lib.rs
@@ -73,7 +73,6 @@
 #![feature(unboxed_closures)]
 #![feature(unsafe_no_drop_flag)]
 #![feature(core)]
-#![feature(hash)]
 #![cfg_attr(all(not(feature = "external_funcs"), not(feature = "external_crate")),
             feature(libc))]
 
diff --git a/src/liballoc/rc.rs b/src/liballoc/rc.rs
index f361c36ec8f..65513465dd2 100644
--- a/src/liballoc/rc.rs
+++ b/src/liballoc/rc.rs
@@ -150,7 +150,7 @@ use core::clone::Clone;
 use core::cmp::{PartialEq, PartialOrd, Eq, Ord, Ordering};
 use core::default::Default;
 use core::fmt;
-use core::hash::{self, Hash};
+use core::hash::{Hasher, Hash};
 use core::marker;
 use core::mem::{transmute, min_align_of, size_of, forget};
 use core::nonzero::NonZero;
@@ -599,12 +599,20 @@ impl<T: Ord> Ord for Rc<T> {
 }
 
 // FIXME (#18248) Make `T` `Sized?`
-impl<S: hash::Hasher, T: Hash<S>> Hash<S> for Rc<T> {
+#[cfg(stage0)]
+impl<S: Hasher, T: Hash<S>> Hash<S> for Rc<T> {
     #[inline]
     fn hash(&self, state: &mut S) {
         (**self).hash(state);
     }
 }
+#[cfg(not(stage0))]
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: Hash> Hash for Rc<T> {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        (**self).hash(state);
+    }
+}
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: fmt::Display> fmt::Display for Rc<T> {