Auto merge of #123 - goffrie:raw-entry-no-build-hasher, r=Amanieu

Remove BuildHasher requirement from raw entry APIs.

This makes it possible to use HashMap with `S=()`, which forces the user to always supply hashes manually. This is an alternative to making the key type unhashable.

I'm not sure if this change is desirable but I'm putting it up for discussion anyway :)

Author: bors

src/map.rs

@@ -958,10 +958,7 @@ where
     }
 }
 
-impl<K, V, S> HashMap<K, V, S>
-where
-    S: BuildHasher,
-{
+impl<K, V, S> HashMap<K, V, S> {
     /// Creates a raw entry builder for the HashMap.
     ///
     /// Raw entries provide the lowest level of control for searching and
@@ -1047,7 +1044,6 @@ impl<K, V, S> Debug for HashMap<K, V, S>
 where
     K: Debug,
     V: Debug,
-    S: BuildHasher,
 {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.debug_map().entries(self.iter()).finish()
@@ -1056,7 +1052,7 @@ where
 
 impl<K, V, S> Default for HashMap<K, V, S>
 where
-    S: BuildHasher + Default,
+    S: Default,
 {
     /// Creates an empty `HashMap<K, V, S>`, with the `Default` value for the hasher.
     #[cfg_attr(feature = "inline-more", inline)]
@@ -1318,15 +1314,13 @@ pub struct RawEntryBuilder<'a, K, V, S> {
     map: &'a HashMap<K, V, S>,
 }
 
-impl<'a, K, V, S> RawEntryBuilderMut<'a, K, V, S>
-where
-    S: BuildHasher,
-{
+impl<'a, K, V, S> RawEntryBuilderMut<'a, K, V, S> {
     /// Creates a `RawEntryMut` from the given key.
     #[cfg_attr(feature = "inline-more", inline)]
     #[allow(clippy::wrong_self_convention)]
     pub fn from_key<Q: ?Sized>(self, k: &Q) -> RawEntryMut<'a, K, V, S>
     where
+        S: BuildHasher,
         K: Borrow<Q>,
         Q: Hash + Eq,
     {
@@ -1347,10 +1341,7 @@ where
     }
 }
 
-impl<'a, K, V, S> RawEntryBuilderMut<'a, K, V, S>
-where
-    S: BuildHasher,
-{
+impl<'a, K, V, S> RawEntryBuilderMut<'a, K, V, S> {
     /// Creates a `RawEntryMut` from the given hash.
     #[cfg_attr(feature = "inline-more", inline)]
     #[allow(clippy::wrong_self_convention)]
@@ -1379,15 +1370,13 @@ where
     }
 }
 
-impl<'a, K, V, S> RawEntryBuilder<'a, K, V, S>
-where
-    S: BuildHasher,
-{
+impl<'a, K, V, S> RawEntryBuilder<'a, K, V, S> {
     /// Access an entry by key.
     #[cfg_attr(feature = "inline-more", inline)]
     #[allow(clippy::wrong_self_convention)]
     pub fn from_key<Q: ?Sized>(self, k: &Q) -> Option<(&'a K, &'a V)>
     where
+        S: BuildHasher,
         K: Borrow<Q>,
         Q: Hash + Eq,
     {
@@ -1692,7 +1681,6 @@ impl<'a, K, V, S> RawVacantEntryMut<'a, K, V, S> {
         hasher: H,
     ) -> (&'a mut K, &'a mut V)
     where
-        S: BuildHasher,
         H: Fn(&K) -> u64,
     {
         unsafe {
@@ -3636,7 +3624,7 @@ mod test_map {
         #[derive(Debug)]
         struct IntWrapper(u64);
 
-        let mut m: HashMap<IntWrapper, ()> = HashMap::new();
+        let mut m: HashMap<IntWrapper, (), ()> = HashMap::default();
         {
             assert!(m.raw_entry().from_hash(0, |k| k.0 == 0).is_none());
         }