std: Stabilize custom hasher support in HashMap

This commit implements the stabilization of the custom hasher support intended
for 1.7 but left out due to some last-minute questions that needed some
decisions. A summary of the actions done in this PR are:

Stable

* `std::hash::BuildHasher`
* `BuildHasher::Hasher`
* `BuildHasher::build_hasher`
* `std::hash::BuildHasherDefault`
* `HashMap::with_hasher`
* `HashMap::with_capacity_and_hasher`
* `HashSet::with_hasher`
* `HashSet::with_capacity_and_hasher`
* `std::collections::hash_map::RandomState`
* `RandomState::new`

Deprecated

* `std::collections::hash_state`
* `std::collections::hash_state::HashState` - this trait was also moved into
  `std::hash` with a reexport here to ensure that we can have a blanket impl to
  prevent immediate breakage on nightly. Note that this is unstable in both
  location.
* `HashMap::with_hash_state` - renamed
* `HashMap::with_capacity_and_hash_state` - renamed
* `HashSet::with_hash_state` - renamed
* `HashSet::with_capacity_and_hash_state` - renamed

Closes rust-lang#27713

Author: alexcrichton

src/libcore/hash/mod.rs

@@ -73,6 +73,7 @@
 
 use prelude::v1::*;
 
+use marker;
 use mem;
 
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -190,6 +191,77 @@ pub trait Hasher {
     }
 }
 
+/// A `BuildHasher` is typically used as a factory for instances of `Hasher`
+/// which a `HashMap` can then use to hash keys independently.
+///
+/// Note that for each instance of `BuildHasher` the create hashers should be
+/// identical. That is if the same stream of bytes is fed into each hasher the
+/// same output will also be generated.
+#[stable(since = "1.7.0", feature = "build_hasher")]
+pub trait BuildHasher {
+    /// Type of the hasher that will be created.
+    #[stable(since = "1.7.0", feature = "build_hasher")]
+    type Hasher: Hasher;
+
+    /// Creates a new hasher.
+    #[stable(since = "1.7.0", feature = "build_hasher")]
+    fn build_hasher(&self) -> Self::Hasher;
+}
+
+/// A structure which implements `BuildHasher` for all `Hasher` types which also
+/// implement `Default`.
+///
+/// This struct is 0-sized and does not need construction.
+#[stable(since = "1.7.0", feature = "build_hasher")]
+pub struct BuildHasherDefault<H>(marker::PhantomData<H>);
+
+#[stable(since = "1.7.0", feature = "build_hasher")]
+impl<H: Default + Hasher> BuildHasher for BuildHasherDefault<H> {
+    type Hasher = H;
+
+    fn build_hasher(&self) -> H {
+        H::default()
+    }
+}
+
+#[stable(since = "1.7.0", feature = "build_hasher")]
+impl<H> Clone for BuildHasherDefault<H> {
+    fn clone(&self) -> BuildHasherDefault<H> {
+        BuildHasherDefault(marker::PhantomData)
+    }
+}
+
+#[stable(since = "1.7.0", feature = "build_hasher")]
+impl<H> Default for BuildHasherDefault<H> {
+    fn default() -> BuildHasherDefault<H> {
+        BuildHasherDefault(marker::PhantomData)
+    }
+}
+
+// The HashState trait is super deprecated, but it's here to have the blanket
+// impl that goes from HashState -> BuildHasher
+
+/// Deprecated, renamed to `BuildHasher`
+#[unstable(feature = "hashmap_hasher", reason = "hasher stuff is unclear",
+           issue = "27713")]
+#[rustc_deprecated(since = "1.7.0", reason = "support moved to std::hash and \
+                                              renamed to BuildHasher")]
+pub trait HashState {
+    /// Type of the hasher that will be created.
+    type Hasher: Hasher;
+
+    /// Creates a new hasher based on the given state of this object.
+    fn hasher(&self) -> Self::Hasher;
+}
+
+#[unstable(feature = "hashmap_hasher", reason = "hasher stuff is unclear",
+           issue = "27713")]
+#[allow(deprecated)]
+impl<T: HashState> BuildHasher for T {
+    type Hasher = T::Hasher;
+    fn build_hasher(&self) -> T::Hasher { self.hasher() }
+}
+
 //////////////////////////////////////////////////////////////////////////////
 
 mod impls {

src/librustc/lib.rs

@@ -29,7 +29,6 @@
 #![feature(collections)]
 #![feature(const_fn)]
 #![feature(enumset)]
-#![feature(hashmap_hasher)]
 #![feature(iter_arith)]
 #![feature(libc)]
 #![feature(nonzero)]

src/librustc/util/common.rs

@@ -12,10 +12,9 @@
 
 use std::cell::{RefCell, Cell};
 use std::collections::HashMap;
-use std::collections::hash_state::HashState;
 use std::ffi::CString;
 use std::fmt::Debug;
-use std::hash::Hash;
+use std::hash::{Hash, BuildHasher};
 use std::iter::repeat;
 use std::path::Path;
 use std::time::Instant;
@@ -217,7 +216,7 @@ pub trait MemoizationMap {
 }
 
 impl<K, V, S> MemoizationMap for RefCell<HashMap<K,V,S>>
-    where K: Hash+Eq+Clone, V: Clone, S: HashState
+    where K: Hash+Eq+Clone, V: Clone, S: BuildHasher
 {
     type Key = K;
     type Value = V;

src/librustc_data_structures/fnv.rs

@@ -9,21 +9,20 @@
 // except according to those terms.
 
 use std::collections::{HashMap, HashSet};
-use std::collections::hash_state::DefaultState;
 use std::default::Default;
-use std::hash::{Hasher, Hash};
+use std::hash::{Hasher, Hash, BuildHasherDefault};
 
-pub type FnvHashMap<K, V> = HashMap<K, V, DefaultState<FnvHasher>>;
-pub type FnvHashSet<V> = HashSet<V, DefaultState<FnvHasher>>;
+pub type FnvHashMap<K, V> = HashMap<K, V, BuildHasherDefault<FnvHasher>>;
+pub type FnvHashSet<V> = HashSet<V, BuildHasherDefault<FnvHasher>>;
 
 #[allow(non_snake_case)]
 pub fn FnvHashMap<K: Hash + Eq, V>() -> FnvHashMap<K, V> {
-    Default::default()
+    HashMap::default()
 }
 
 #[allow(non_snake_case)]
 pub fn FnvHashSet<V: Hash + Eq>() -> FnvHashSet<V> {
-    Default::default()
+    HashSet::default()
 }
 
 /// A speedy hash algorithm for node ids and def ids. The hashmap in

src/librustc_data_structures/lib.rs

@@ -24,7 +24,6 @@
       html_favicon_url = "https://www.rust-lang.org/favicon.ico",
       html_root_url = "https://doc.rust-lang.org/nightly/")]
 
-#![feature(hashmap_hasher)]
 #![feature(nonzero)]
 #![feature(rustc_private)]
 #![feature(staged_api)]

src/libserialize/collection_impls.rs

@@ -10,8 +10,7 @@
 
 //! Implementations of serialization for structures found in libcollections
 
-use std::hash::Hash;
-use std::collections::hash_state::HashState;
+use std::hash::{Hash, BuildHasher};
 use std::mem;
 
 use {Decodable, Encodable, Decoder, Encoder};
@@ -159,7 +158,7 @@ impl<
 impl<K, V, S> Encodable for HashMap<K, V, S>
     where K: Encodable + Hash + Eq,
           V: Encodable,
-          S: HashState,
+          S: BuildHasher,
 {
     fn encode<E: Encoder>(&self, e: &mut E) -> Result<(), E::Error> {
         e.emit_map(self.len(), |e| {
@@ -177,12 +176,12 @@ impl<K, V, S> Encodable for HashMap<K, V, S>
 impl<K, V, S> Decodable for HashMap<K, V, S>
     where K: Decodable + Hash + Eq,
           V: Decodable,
-          S: HashState + Default,
+          S: BuildHasher + Default,
 {
     fn decode<D: Decoder>(d: &mut D) -> Result<HashMap<K, V, S>, D::Error> {
         d.read_map(|d, len| {
             let state = Default::default();
-            let mut map = HashMap::with_capacity_and_hash_state(len, state);
+            let mut map = HashMap::with_capacity_and_hasher(len, state);
             for i in 0..len {
                 let key = try!(d.read_map_elt_key(i, |d| Decodable::decode(d)));
                 let val = try!(d.read_map_elt_val(i, |d| Decodable::decode(d)));
@@ -195,7 +194,7 @@ impl<K, V, S> Decodable for HashMap<K, V, S>
 
 impl<T, S> Encodable for HashSet<T, S>
     where T: Encodable + Hash + Eq,
-          S: HashState,
+          S: BuildHasher,
 {
     fn encode<E: Encoder>(&self, s: &mut E) -> Result<(), E::Error> {
         s.emit_seq(self.len(), |s| {
@@ -211,12 +210,12 @@ impl<T, S> Encodable for HashSet<T, S>
 
 impl<T, S> Decodable for HashSet<T, S>
     where T: Decodable + Hash + Eq,
-          S: HashState + Default,
+          S: BuildHasher + Default,
 {
     fn decode<D: Decoder>(d: &mut D) -> Result<HashSet<T, S>, D::Error> {
         d.read_seq(|d, len| {
             let state = Default::default();
-            let mut set = HashSet::with_capacity_and_hash_state(len, state);
+            let mut set = HashSet::with_capacity_and_hasher(len, state);
             for i in 0..len {
                 set.insert(try!(d.read_seq_elt(i, |d| Decodable::decode(d))));
             }

src/libserialize/lib.rs

@@ -29,7 +29,6 @@ Core encoding and decoding interfaces.
 #![feature(box_syntax)]
 #![feature(collections)]
 #![feature(enumset)]
-#![feature(hashmap_hasher)]
 #![feature(rustc_private)]
 #![feature(staged_api)]
 #![feature(str_char)]