Move RandomState and DefaultHasher into std::hash, but in a sneaky way

Author: clarfonthey

library/core/tests/hash/mod.rs

@@ -36,7 +36,8 @@ impl Hasher for MyHasher {
 #[test]
 fn test_writer_hasher() {
     // FIXME(#110395)
-    /* const */ fn hash<T: Hash>(t: &T) -> u64 {
+    /* const */
+    fn hash<T: Hash>(t: &T) -> u64 {
         let mut s = MyHasher { hash: 0 };
         t.hash(&mut s);
         s.finish()
@@ -141,7 +142,8 @@ impl Hash for Custom {
 #[test]
 fn test_custom_state() {
     // FIXME(#110395)
-    /* const */ fn hash<T: Hash>(t: &T) -> u64 {
+    /* const */
+    fn hash<T: Hash>(t: &T) -> u64 {
         let mut c = CustomHasher { output: 0 };
         t.hash(&mut c);
         c.finish()

library/std/src/collections/hash/map.rs

@@ -6,16 +6,14 @@ use self::Entry::*;
 use hashbrown::hash_map as base;
 
 use crate::borrow::Borrow;
-use crate::cell::Cell;
 use crate::collections::TryReserveError;
 use crate::collections::TryReserveErrorKind;
 use crate::error::Error;
 use crate::fmt::{self, Debug};
 #[allow(deprecated)]
-use crate::hash::{BuildHasher, Hash, Hasher, SipHasher13};
+use crate::hash::{BuildHasher, Hash, private::RandomState};
 use crate::iter::FusedIterator;
 use crate::ops::Index;
-use crate::sys;
 
 /// A [hash map] implemented with quadratic probing and SIMD lookup.
 ///
@@ -3072,152 +3070,6 @@ where
     }
 }
 
-/// `RandomState` is the default state for [`HashMap`] types.
-///
-/// A particular instance `RandomState` will create the same instances of
-/// [`Hasher`], but the hashers created by two different `RandomState`
-/// instances are unlikely to produce the same result for the same values.
-///
-/// # Examples
-///
-/// ```
-/// use std::collections::HashMap;
-/// use std::collections::hash_map::RandomState;
-///
-/// let s = RandomState::new();
-/// let mut map = HashMap::with_hasher(s);
-/// map.insert(1, 2);
-/// ```
-#[derive(Clone)]
-#[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
-pub struct RandomState {
-    k0: u64,
-    k1: u64,
-}
-
-impl RandomState {
-    /// Constructs a new `RandomState` that is initialized with random keys.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::collections::hash_map::RandomState;
-    ///
-    /// let s = RandomState::new();
-    /// ```
-    #[inline]
-    #[allow(deprecated)]
-    // rand
-    #[must_use]
-    #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
-    pub fn new() -> RandomState {
-        // Historically this function did not cache keys from the OS and instead
-        // simply always called `rand::thread_rng().gen()` twice. In #31356 it
-        // was discovered, however, that because we re-seed the thread-local RNG
-        // from the OS periodically that this can cause excessive slowdown when
-        // many hash maps are created on a thread. To solve this performance
-        // trap we cache the first set of randomly generated keys per-thread.
-        //
-        // Later in #36481 it was discovered that exposing a deterministic
-        // iteration order allows a form of DOS attack. To counter that we
-        // increment one of the seeds on every RandomState creation, giving
-        // every corresponding HashMap a different iteration order.
-        thread_local!(static KEYS: Cell<(u64, u64)> = {
-            Cell::new(sys::hashmap_random_keys())
-        });
-
-        KEYS.with(|keys| {
-            let (k0, k1) = keys.get();
-            keys.set((k0.wrapping_add(1), k1));
-            RandomState { k0, k1 }
-        })
-    }
-}
-
-#[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
-impl BuildHasher for RandomState {
-    type Hasher = DefaultHasher;
-    #[inline]
-    #[allow(deprecated)]
-    fn build_hasher(&self) -> DefaultHasher {
-        DefaultHasher(SipHasher13::new_with_keys(self.k0, self.k1))
-    }
-}
-
-/// The default [`Hasher`] used by [`RandomState`].
-///
-/// The internal algorithm is not specified, and so it and its hashes should
-/// not be relied upon over releases.
-#[stable(feature = "hashmap_default_hasher", since = "1.13.0")]
-#[allow(deprecated)]
-#[derive(Clone, Debug)]
-pub struct DefaultHasher(SipHasher13);
-
-impl DefaultHasher {
-    /// Creates a new `DefaultHasher`.
-    ///
-    /// This hasher is not guaranteed to be the same as all other
-    /// `DefaultHasher` instances, but is the same as all other `DefaultHasher`
-    /// instances created through `new` or `default`.
-    #[stable(feature = "hashmap_default_hasher", since = "1.13.0")]
-    #[inline]
-    #[allow(deprecated)]
-    #[rustc_const_unstable(feature = "const_hash", issue = "104061")]
-    #[must_use]
-    pub const fn new() -> DefaultHasher {
-        DefaultHasher(SipHasher13::new_with_keys(0, 0))
-    }
-}
-
-#[stable(feature = "hashmap_default_hasher", since = "1.13.0")]
-impl Default for DefaultHasher {
-    /// Creates a new `DefaultHasher` using [`new`].
-    /// See its documentation for more.
-    ///
-    /// [`new`]: DefaultHasher::new
-    #[inline]
-    fn default() -> DefaultHasher {
-        DefaultHasher::new()
-    }
-}
-
-#[stable(feature = "hashmap_default_hasher", since = "1.13.0")]
-impl Hasher for DefaultHasher {
-    // The underlying `SipHasher13` doesn't override the other
-    // `write_*` methods, so it's ok not to forward them here.
-
-    #[inline]
-    fn write(&mut self, msg: &[u8]) {
-        self.0.write(msg)
-    }
-
-    #[inline]
-    fn write_str(&mut self, s: &str) {
-        self.0.write_str(s);
-    }
-
-    #[inline]
-    fn finish(&self) -> u64 {
-        self.0.finish()
-    }
-}
-
-#[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
-impl Default for RandomState {
-    /// Constructs a new `RandomState`.
-    #[inline]
-    fn default() -> RandomState {
-        RandomState::new()
-    }
-}
-
-#[stable(feature = "std_debug", since = "1.16.0")]
-impl fmt::Debug for RandomState {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("RandomState").finish_non_exhaustive()
-    }
-}
-
 #[inline]
 fn map_entry<'a, K: 'a, V: 'a>(raw: base::RustcEntry<'a, K, V>) -> Entry<'a, K, V> {
     match raw {

library/std/src/collections/hash/map/tests.rs

@@ -1,8 +1,8 @@
 use super::Entry::{Occupied, Vacant};
 use super::HashMap;
-use super::RandomState;
 use crate::assert_matches::assert_matches;
 use crate::cell::RefCell;
+use crate::hash::private::RandomState;
 use crate::test_helpers::test_rng;
 use rand::Rng;
 use realstd::collections::TryReserveErrorKind::*;

library/std/src/collections/hash/set.rs

@@ -6,11 +6,11 @@ use hashbrown::hash_set as base;
 use crate::borrow::Borrow;
 use crate::collections::TryReserveError;
 use crate::fmt;
-use crate::hash::{BuildHasher, Hash};
+use crate::hash::{BuildHasher, Hash, private::RandomState};
 use crate::iter::{Chain, FusedIterator};
 use crate::ops::{BitAnd, BitOr, BitXor, Sub};
 
-use super::map::{map_try_reserve_error, RandomState};
+use super::map::map_try_reserve_error;
 
 /// A [hash set] implemented as a `HashMap` where the value is `()`.
 ///

library/std/src/collections/hash/set/tests.rs

@@ -1,6 +1,6 @@
-use super::super::map::RandomState;
 use super::HashSet;
 
+use crate::hash::private::RandomState;
 use crate::panic::{catch_unwind, AssertUnwindSafe};
 use crate::sync::atomic::{AtomicU32, Ordering};
 use crate::sync::Arc;

library/std/src/collections/mod.rs

@@ -439,6 +439,11 @@ pub mod hash_map {
     //! A hash map implemented with quadratic probing and SIMD lookup.
     #[stable(feature = "rust1", since = "1.0.0")]
     pub use super::hash::map::*;
+
+    #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
+    pub use crate::hash::private::DefaultHasher;
+    #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
+    pub use crate::hash::private::RandomState;
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]

library/std/src/hash/mod.rs

@@ -0,0 +1,90 @@
+//! Generic hashing support.
+//!
+//! This module provides a generic way to compute the [hash] of a value.
+//! Hashes are most commonly used with [`HashMap`] and [`HashSet`].
+//!
+//! [hash]: https://en.wikipedia.org/wiki/Hash_function
+//! [`HashMap`]: ../../std/collections/struct.HashMap.html
+//! [`HashSet`]: ../../std/collections/struct.HashSet.html
+//!
+//! The simplest way to make a type hashable is to use `#[derive(Hash)]`:
+//!
+//! # Examples
+//!
+//! ```rust
+//! use std::collections::hash_map::DefaultHasher;
+//! use std::hash::{Hash, Hasher};
+//!
+//! #[derive(Hash)]
+//! struct Person {
+//!     id: u32,
+//!     name: String,
+//!     phone: u64,
+//! }
+//!
+//! let person1 = Person {
+//!     id: 5,
+//!     name: "Janet".to_string(),
+//!     phone: 555_666_7777,
+//! };
+//! let person2 = Person {
+//!     id: 5,
+//!     name: "Bob".to_string(),
+//!     phone: 555_666_7777,
+//! };
+//!
+//! assert!(calculate_hash(&person1) != calculate_hash(&person2));
+//!
+//! fn calculate_hash<T: Hash>(t: &T) -> u64 {
+//!     let mut s = DefaultHasher::new();
+//!     t.hash(&mut s);
+//!     s.finish()
+//! }
+//! ```
+//!
+//! If you need more control over how a value is hashed, you need to implement
+//! the [`Hash`] trait:
+//!
+//! ```rust
+//! use std::collections::hash_map::DefaultHasher;
+//! use std::hash::{Hash, Hasher};
+//!
+//! struct Person {
+//!     id: u32,
+//!     # #[allow(dead_code)]
+//!     name: String,
+//!     phone: u64,
+//! }
+//!
+//! impl Hash for Person {
+//!     fn hash<H: Hasher>(&self, state: &mut H) {
+//!         self.id.hash(state);
+//!         self.phone.hash(state);
+//!     }
+//! }
+//!
+//! let person1 = Person {
+//!     id: 5,
+//!     name: "Janet".to_string(),
+//!     phone: 555_666_7777,
+//! };
+//! let person2 = Person {
+//!     id: 5,
+//!     name: "Bob".to_string(),
+//!     phone: 555_666_7777,
+//! };
+//!
+//! assert_eq!(calculate_hash(&person1), calculate_hash(&person2));
+//!
+//! fn calculate_hash<T: Hash>(t: &T) -> u64 {
+//!     let mut s = DefaultHasher::new();
+//!     t.hash(&mut s);
+//!     s.finish()
+//! }
+//! ```
+#![stable(feature = "rust1", since = "1.0.0")]
+
+pub(crate) mod private;
+
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use core::hash::*;