Rollup merge of #104060 - ink-feather-org:const_hash, r=fee1-dead

Make `Hash`, `Hasher` and `BuildHasher` `#[const_trait]` and make `Sip` const `Hasher`

This PR enables using Hashes in const context.

r? ``@fee1-dead``

Author: Manishearth

library/core/src/hash/mod.rs

@@ -86,7 +86,8 @@
 #![stable(feature = "rust1", since = "1.0.0")]
 
 use crate::fmt;
-use crate::marker;
+use crate::intrinsics::const_eval_select;
+use crate::marker::{self, Destruct};
 
 #[stable(feature = "rust1", since = "1.0.0")]
 #[allow(deprecated)]
@@ -183,6 +184,7 @@ mod sip;
 /// [impl]: ../../std/primitive.str.html#impl-Hash-for-str
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_diagnostic_item = "Hash"]
+#[const_trait]
 pub trait Hash {
     /// Feeds this value into the given [`Hasher`].
     ///
@@ -234,13 +236,25 @@ pub trait Hash {
     /// [`hash`]: Hash::hash
     /// [`hash_slice`]: Hash::hash_slice
     #[stable(feature = "hash_slice", since = "1.3.0")]
-    fn hash_slice<H: Hasher>(data: &[Self], state: &mut H)
+    fn hash_slice<H: ~const Hasher>(data: &[Self], state: &mut H)
     where
         Self: Sized,
     {
-        for piece in data {
-            piece.hash(state);
+        //FIXME(const_trait_impl): revert to only a for loop
+        fn rt<T: Hash, H: Hasher>(data: &[T], state: &mut H) {
+            for piece in data {
+                piece.hash(state)
+            }
+        }
+        const fn ct<T: ~const Hash, H: ~const Hasher>(data: &[T], state: &mut H) {
+            let mut i = 0;
+            while i < data.len() {
+                data[i].hash(state);
+                i += 1;
+            }
         }
+        // SAFETY: same behavior, CT just uses while instead of for
+        unsafe { const_eval_select((data, state), ct, rt) };
     }
 }
 
@@ -313,6 +327,7 @@ pub use macros::Hash;
 /// [`write_u8`]: Hasher::write_u8
 /// [`write_u32`]: Hasher::write_u32
 #[stable(feature = "rust1", since = "1.0.0")]
+#[const_trait]
 pub trait Hasher {
     /// Returns the hash value for the values written so far.
     ///
@@ -558,7 +573,8 @@ pub trait Hasher {
 }
 
 #[stable(feature = "indirect_hasher_impl", since = "1.22.0")]
-impl<H: Hasher + ?Sized> Hasher for &mut H {
+#[rustc_const_unstable(feature = "const_hash", issue = "104061")]
+impl<H: ~const Hasher + ?Sized> const Hasher for &mut H {
     fn finish(&self) -> u64 {
         (**self).finish()
     }
@@ -638,6 +654,7 @@ impl<H: Hasher + ?Sized> Hasher for &mut H {
 /// [`build_hasher`]: BuildHasher::build_hasher
 /// [`HashMap`]: ../../std/collections/struct.HashMap.html
 #[stable(since = "1.7.0", feature = "build_hasher")]
+#[const_trait]
 pub trait BuildHasher {
     /// Type of the hasher that will be created.
     #[stable(since = "1.7.0", feature = "build_hasher")]
@@ -698,9 +715,10 @@ pub trait BuildHasher {
     /// );
     /// ```
     #[unstable(feature = "build_hasher_simple_hash_one", issue = "86161")]
-    fn hash_one<T: Hash>(&self, x: T) -> u64
+    fn hash_one<T: ~const Hash + ~const Destruct>(&self, x: T) -> u64
     where
         Self: Sized,
+        Self::Hasher: ~const Hasher + ~const Destruct,
     {
         let mut hasher = self.build_hasher();
         x.hash(&mut hasher);
@@ -764,7 +782,8 @@ impl<H> fmt::Debug for BuildHasherDefault<H> {
 }
 
 #[stable(since = "1.7.0", feature = "build_hasher")]
-impl<H: Default + Hasher> BuildHasher for BuildHasherDefault<H> {
+#[rustc_const_unstable(feature = "const_hash", issue = "104061")]
+impl<H: ~const Default + Hasher> const BuildHasher for BuildHasherDefault<H> {
     type Hasher = H;
 
     fn build_hasher(&self) -> H {
@@ -806,14 +825,15 @@ mod impls {
     macro_rules! impl_write {
         ($(($ty:ident, $meth:ident),)*) => {$(
             #[stable(feature = "rust1", since = "1.0.0")]
-            impl Hash for $ty {
+            #[rustc_const_unstable(feature = "const_hash", issue = "104061")]
+            impl const Hash for $ty {
                 #[inline]
-                fn hash<H: Hasher>(&self, state: &mut H) {
+                fn hash<H: ~const Hasher>(&self, state: &mut H) {
                     state.$meth(*self)
                 }
 
                 #[inline]
-                fn hash_slice<H: Hasher>(data: &[$ty], state: &mut H) {
+                fn hash_slice<H: ~const Hasher>(data: &[$ty], state: &mut H) {
                     let newlen = data.len() * mem::size_of::<$ty>();
                     let ptr = data.as_ptr() as *const u8;
                     // SAFETY: `ptr` is valid and aligned, as this macro is only used
@@ -842,54 +862,60 @@ mod impls {
     }
 
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl Hash for bool {
+    #[rustc_const_unstable(feature = "const_hash", issue = "104061")]
+    impl const Hash for bool {
         #[inline]
-        fn hash<H: Hasher>(&self, state: &mut H) {
+        fn hash<H: ~const Hasher>(&self, state: &mut H) {
             state.write_u8(*self as u8)
         }
     }
 
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl Hash for char {
+    #[rustc_const_unstable(feature = "const_hash", issue = "104061")]
+    impl const Hash for char {
         #[inline]
-        fn hash<H: Hasher>(&self, state: &mut H) {
+        fn hash<H: ~const Hasher>(&self, state: &mut H) {
             state.write_u32(*self as u32)
         }
     }
 
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl Hash for str {
+    #[rustc_const_unstable(feature = "const_hash", issue = "104061")]
+    impl const Hash for str {
         #[inline]
-        fn hash<H: Hasher>(&self, state: &mut H) {
+        fn hash<H: ~const Hasher>(&self, state: &mut H) {
             state.write_str(self);
         }
     }
 
     #[stable(feature = "never_hash", since = "1.29.0")]
-    impl Hash for ! {
+    #[rustc_const_unstable(feature = "const_hash", issue = "104061")]
+    impl const Hash for ! {
         #[inline]
-        fn hash<H: Hasher>(&self, _: &mut H) {
+        fn hash<H: ~const Hasher>(&self, _: &mut H) {
             *self
         }
     }
 
     macro_rules! impl_hash_tuple {
         () => (
             #[stable(feature = "rust1", since = "1.0.0")]
-            impl Hash for () {
+            #[rustc_const_unstable(feature = "const_hash", issue = "104061")]
+            impl const Hash for () {
                 #[inline]
-                fn hash<H: Hasher>(&self, _state: &mut H) {}
+                fn hash<H: ~const Hasher>(&self, _state: &mut H) {}
             }
         );
 
         ( $($name:ident)+) => (
             maybe_tuple_doc! {
                 $($name)+ @
                 #[stable(feature = "rust1", since = "1.0.0")]
-                impl<$($name: Hash),+> Hash for ($($name,)+) where last_type!($($name,)+): ?Sized {
+                #[rustc_const_unstable(feature = "const_hash", issue = "104061")]
+                impl<$($name: ~const Hash),+> const Hash for ($($name,)+) where last_type!($($name,)+): ?Sized {
                     #[allow(non_snake_case)]
                     #[inline]
-                    fn hash<S: Hasher>(&self, state: &mut S) {
+                    fn hash<S: ~const Hasher>(&self, state: &mut S) {
                         let ($(ref $name,)+) = *self;
                         $($name.hash(state);)+
                     }
@@ -932,24 +958,27 @@ mod impls {
     impl_hash_tuple! { T B C D E F G H I J K L }
 
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl<T: Hash> Hash for [T] {
+    #[rustc_const_unstable(feature = "const_hash", issue = "104061")]
+    impl<T: ~const Hash> const Hash for [T] {
         #[inline]
-        fn hash<H: Hasher>(&self, state: &mut H) {
+        fn hash<H: ~const Hasher>(&self, state: &mut H) {
             state.write_length_prefix(self.len());
             Hash::hash_slice(self, state)
         }
     }
 
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl<T: ?Sized + Hash> Hash for &T {
+    #[rustc_const_unstable(feature = "const_hash", issue = "104061")]
+    impl<T: ?Sized + ~const Hash> const Hash for &T {
         #[inline]
-        fn hash<H: Hasher>(&self, state: &mut H) {
+        fn hash<H: ~const Hasher>(&self, state: &mut H) {
             (**self).hash(state);
         }
     }
 
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl<T: ?Sized + Hash> Hash for &mut T {
+    #[rustc_const_unstable(feature = "const_hash", issue = "104061")]
+    impl<T: ?Sized + ~const Hash> const Hash for &mut T {
         #[inline]
         fn hash<H: Hasher>(&self, state: &mut H) {
             (**self).hash(state);

library/core/src/hash/sip.rs

@@ -118,7 +118,7 @@ macro_rules! load_int_le {
 /// Safety: this performs unchecked indexing of `buf` at `start..start+len`, so
 /// that must be in-bounds.
 #[inline]
-unsafe fn u8to64_le(buf: &[u8], start: usize, len: usize) -> u64 {
+const unsafe fn u8to64_le(buf: &[u8], start: usize, len: usize) -> u64 {
     debug_assert!(len < 8);
     let mut i = 0; // current byte index (from LSB) in the output u64
     let mut out = 0;
@@ -138,7 +138,8 @@ unsafe fn u8to64_le(buf: &[u8], start: usize, len: usize) -> u64 {
         out |= (unsafe { *buf.get_unchecked(start + i) } as u64) << (i * 8);
         i += 1;
     }
-    debug_assert_eq!(i, len);
+    //FIXME(fee1-dead): use debug_assert_eq
+    debug_assert!(i == len);
     out
 }
 
@@ -150,8 +151,9 @@ impl SipHasher {
         since = "1.13.0",
         note = "use `std::collections::hash_map::DefaultHasher` instead"
     )]
+    #[rustc_const_unstable(feature = "const_hash", issue = "104061")]
     #[must_use]
-    pub fn new() -> SipHasher {
+    pub const fn new() -> SipHasher {
         SipHasher::new_with_keys(0, 0)
     }
 
@@ -162,8 +164,9 @@ impl SipHasher {
         since = "1.13.0",
         note = "use `std::collections::hash_map::DefaultHasher` instead"
     )]
+    #[rustc_const_unstable(feature = "const_hash", issue = "104061")]
     #[must_use]
-    pub fn new_with_keys(key0: u64, key1: u64) -> SipHasher {
+    pub const fn new_with_keys(key0: u64, key1: u64) -> SipHasher {
         SipHasher(SipHasher24 { hasher: Hasher::new_with_keys(key0, key1) })
     }
 }
@@ -176,7 +179,8 @@ impl SipHasher13 {
         since = "1.13.0",
         note = "use `std::collections::hash_map::DefaultHasher` instead"
     )]
-    pub fn new() -> SipHasher13 {
+    #[rustc_const_unstable(feature = "const_hash", issue = "104061")]
+    pub const fn new() -> SipHasher13 {
         SipHasher13::new_with_keys(0, 0)
     }
 
@@ -187,14 +191,15 @@ impl SipHasher13 {
         since = "1.13.0",
         note = "use `std::collections::hash_map::DefaultHasher` instead"
     )]
-    pub fn new_with_keys(key0: u64, key1: u64) -> SipHasher13 {
+    #[rustc_const_unstable(feature = "const_hash", issue = "104061")]
+    pub const fn new_with_keys(key0: u64, key1: u64) -> SipHasher13 {
         SipHasher13 { hasher: Hasher::new_with_keys(key0, key1) }
     }
 }
 
 impl<S: Sip> Hasher<S> {
     #[inline]
-    fn new_with_keys(key0: u64, key1: u64) -> Hasher<S> {
+    const fn new_with_keys(key0: u64, key1: u64) -> Hasher<S> {
         let mut state = Hasher {
             k0: key0,
             k1: key1,
@@ -209,7 +214,7 @@ impl<S: Sip> Hasher<S> {
     }
 
     #[inline]
-    fn reset(&mut self) {
+    const fn reset(&mut self) {
         self.length = 0;
         self.state.v0 = self.k0 ^ 0x736f6d6570736575;
         self.state.v1 = self.k1 ^ 0x646f72616e646f6d;
@@ -220,7 +225,8 @@ impl<S: Sip> Hasher<S> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl super::Hasher for SipHasher {
+#[rustc_const_unstable(feature = "const_hash", issue = "104061")]
+impl const super::Hasher for SipHasher {
     #[inline]
     fn write(&mut self, msg: &[u8]) {
         self.0.hasher.write(msg)
@@ -238,7 +244,8 @@ impl super::Hasher for SipHasher {
 }
 
 #[unstable(feature = "hashmap_internals", issue = "none")]
-impl super::Hasher for SipHasher13 {
+#[rustc_const_unstable(feature = "const_hash", issue = "104061")]
+impl const super::Hasher for SipHasher13 {
     #[inline]
     fn write(&mut self, msg: &[u8]) {
         self.hasher.write(msg)
@@ -255,7 +262,7 @@ impl super::Hasher for SipHasher13 {
     }
 }
 
-impl<S: Sip> super::Hasher for Hasher<S> {
+impl<S: ~const Sip> const super::Hasher for Hasher<S> {
     // Note: no integer hashing methods (`write_u*`, `write_i*`) are defined
     // for this type. We could add them, copy the `short_write` implementation
     // in librustc_data_structures/sip128.rs, and add `write_u*`/`write_i*`
@@ -335,7 +342,7 @@ impl<S: Sip> super::Hasher for Hasher<S> {
     }
 }
 
-impl<S: Sip> Clone for Hasher<S> {
+impl<S: Sip> const Clone for Hasher<S> {
     #[inline]
     fn clone(&self) -> Hasher<S> {
         Hasher {
@@ -359,6 +366,7 @@ impl<S: Sip> Default for Hasher<S> {
 }
 
 #[doc(hidden)]
+#[const_trait]
 trait Sip {
     fn c_rounds(_: &mut State);
     fn d_rounds(_: &mut State);
@@ -367,7 +375,7 @@ trait Sip {
 #[derive(Debug, Clone, Default)]
 struct Sip13Rounds;
 
-impl Sip for Sip13Rounds {
+impl const Sip for Sip13Rounds {
     #[inline]
     fn c_rounds(state: &mut State) {
         compress!(state);
@@ -384,7 +392,7 @@ impl Sip for Sip13Rounds {
 #[derive(Debug, Clone, Default)]
 struct Sip24Rounds;
 
-impl Sip for Sip24Rounds {
+impl const Sip for Sip24Rounds {
     #[inline]
     fn c_rounds(state: &mut State) {
         compress!(state);

library/core/src/lib.rs

@@ -112,6 +112,7 @@
 #![feature(const_float_bits_conv)]
 #![feature(const_float_classify)]
 #![feature(const_fmt_arguments_new)]
+#![feature(const_hash)]
 #![feature(const_heap)]
 #![feature(const_convert)]
 #![feature(const_index_range_slice_index)]