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 #27713

2 files changed, 5 insertions, 7 deletions

diff --git a/src/librustc_data_structures/fnv.rs b/src/librustc_data_structures/fnv.rs
index 77baa84c023..6f4dc28e122 100644
--- a/src/librustc_data_structures/fnv.rs
+++ b/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
diff --git a/src/librustc_data_structures/lib.rs b/src/librustc_data_structures/lib.rs
index 1fbbdf17455..20caf7dd0cf 100644
--- a/src/librustc_data_structures/lib.rs
+++ b/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)]