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]

1 files changed, 28 insertions, 1 deletions

diff --git a/src/libstd/sys/common/wtf8.rs b/src/libstd/sys/common/wtf8.rs
index b610f6c370b..c4f2de7fb45 100644
--- a/src/libstd/sys/common/wtf8.rs
+++ b/src/libstd/sys/common/wtf8.rs
@@ -31,7 +31,8 @@ use ascii::*;
 use borrow::Cow;
 use cmp;
 use fmt;
-use hash::{Hash, Writer, Hasher};
+use hash::{Hash, Hasher};
+#[cfg(stage0)] use hash::Writer;
 use iter::FromIterator;
 use mem;
 use num::Int;
@@ -794,13 +795,22 @@ impl<'a> Iterator for EncodeWide<'a> {
     }
 }
 
+#[cfg(stage0)]
 impl<S: Writer + Hasher> Hash<S> for CodePoint {
     #[inline]
     fn hash(&self, state: &mut S) {
         self.value.hash(state)
     }
 }
+#[cfg(not(stage0))]
+impl Hash for CodePoint {
+    #[inline]
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        self.value.hash(state)
+    }
+}
 
+#[cfg(stage0)]
 impl<S: Writer + Hasher> Hash<S> for Wtf8Buf {
     #[inline]
     fn hash(&self, state: &mut S) {
@@ -808,7 +818,16 @@ impl<S: Writer + Hasher> Hash<S> for Wtf8Buf {
         0xfeu8.hash(state)
     }
 }
+#[cfg(not(stage0))]
+impl Hash for Wtf8Buf {
+    #[inline]
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        state.write(&self.bytes);
+        0xfeu8.hash(state)
+    }
+}
 
+#[cfg(stage0)]
 impl<'a, S: Writer + Hasher> Hash<S> for Wtf8 {
     #[inline]
     fn hash(&self, state: &mut S) {
@@ -816,6 +835,14 @@ impl<'a, S: Writer + Hasher> Hash<S> for Wtf8 {
         0xfeu8.hash(state)
     }
 }
+#[cfg(not(stage0))]
+impl Hash for Wtf8 {
+    #[inline]
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        state.write(&self.bytes);
+        0xfeu8.hash(state)
+    }
+}
 
 impl AsciiExt for Wtf8 {
     type Owned = Wtf8Buf;