Rollup merge of #71677 - Mark-Simulacrum:hasher-docs, r=Amanieu

Add explicit references to the BuildHasher trait

Fixes #71652

src/libstd/collections/hash/map.rs

@@ -251,6 +251,9 @@ impl<K, V, S> HashMap<K, V, S> {
     /// cause many collisions and very poor performance. Setting it
     /// manually using this function can expose a DoS attack vector.
     ///
+    /// The `hash_builder` passed should implement the [`BuildHasher`] trait for
+    /// the HashMap to be useful, see its documentation for details.
+    ///
     /// # Examples
     ///
     /// ```
@@ -261,6 +264,8 @@ impl<K, V, S> HashMap<K, V, S> {
     /// let mut map = HashMap::with_hasher(s);
     /// map.insert(1, 2);
     /// ```
+    ///
+    /// [`BuildHasher`]: ../../std/hash/trait.BuildHasher.html
     #[inline]
     #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
     pub fn with_hasher(hash_builder: S) -> HashMap<K, V, S> {
@@ -278,6 +283,9 @@ impl<K, V, S> HashMap<K, V, S> {
     /// cause many collisions and very poor performance. Setting it
     /// manually using this function can expose a DoS attack vector.
     ///
+    /// The `hash_builder` passed should implement the [`BuildHasher`] trait for
+    /// the HashMap to be useful, see its documentation for details.
+    ///
     /// # Examples
     ///
     /// ```
@@ -288,6 +296,8 @@ impl<K, V, S> HashMap<K, V, S> {
     /// let mut map = HashMap::with_capacity_and_hasher(10, s);
     /// map.insert(1, 2);
     /// ```
+    ///
+    /// [`BuildHasher`]: ../../std/hash/trait.BuildHasher.html
     #[inline]
     #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
     pub fn with_capacity_and_hasher(capacity: usize, hash_builder: S) -> HashMap<K, V, S> {

src/libstd/collections/hash/set.rs

@@ -273,6 +273,9 @@ impl<T, S> HashSet<T, S> {
     /// cause many collisions and very poor performance. Setting it
     /// manually using this function can expose a DoS attack vector.
     ///
+    /// The `hash_builder` passed should implement the [`BuildHasher`] trait for
+    /// the HashMap to be useful, see its documentation for details.
+    ///
     /// # Examples
     ///
     /// ```
@@ -283,6 +286,8 @@ impl<T, S> HashSet<T, S> {
     /// let mut set = HashSet::with_hasher(s);
     /// set.insert(2);
     /// ```
+    ///
+    /// [`BuildHasher`]: ../../std/hash/trait.BuildHasher.html
     #[inline]
     #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
     pub fn with_hasher(hasher: S) -> HashSet<T, S> {
@@ -300,6 +305,9 @@ impl<T, S> HashSet<T, S> {
     /// cause many collisions and very poor performance. Setting it
     /// manually using this function can expose a DoS attack vector.
     ///
+    /// The `hash_builder` passed should implement the [`BuildHasher`] trait for
+    /// the HashMap to be useful, see its documentation for details.
+    ///
     /// # Examples
     ///
     /// ```
@@ -310,6 +318,8 @@ impl<T, S> HashSet<T, S> {
     /// let mut set = HashSet::with_capacity_and_hasher(10, s);
     /// set.insert(1);
     /// ```
+    ///
+    /// [`BuildHasher`]: ../../std/hash/trait.BuildHasher.html
     #[inline]
     #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
     pub fn with_capacity_and_hasher(capacity: usize, hasher: S) -> HashSet<T, S> {