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use std::mem::Discriminant;
pub use turbo_tasks_macros::DeterministicHash;
macro_rules! deterministic_hash_number {
($(($ty:ident, $meth:ident),)*) => {$(
impl DeterministicHash for $ty {
fn deterministic_hash<H: DeterministicHasher>(&self, state: &mut H) {
state.$meth(*self);
}
}
)*}
}
macro_rules! impl_write_number {
($(($ty:ident, $meth:ident),)*) => {$(
/// Writes a single `$ty` to this hasher
#[inline]
fn $meth(&mut self, i: $ty) {
// Apple silicon and Intel chips both use little endian, so this should be fast.
let little_endian = i.to_le_bytes();
self.write_bytes(&little_endian);
}
)*}
}
/// Signals the implementor can safely be hashed in a replicatable way across platforms and process
/// runs.
///
/// Note that the default [`std::hash::Hash`] trait used by Rust allows for hashing that differs
/// across process runs, so it is not suitable for persistent caching with turbo-tasks.
///
/// It's very important that `Vc`s never implement this, since they cannot be deterministic. The
/// value that they wrap, however, can implement the trait.
pub trait DeterministicHash {
/// Adds `self`'s bytes to the [`DeterministicHasher`]'s state, in a way that is replicatable on
/// any platform or process run.
fn deterministic_hash<H: DeterministicHasher>(&self, state: &mut H);
}
/// Signals the implementor can safely hash in a replicatable way across platforms and process runs.
///
/// Note that the default [`std::hash::Hash`] trait used by Rust allows for hashing that differs
/// across process runs, so it is not suitable for persistent caching with turbo-tasks.
pub trait DeterministicHasher {
fn finish(&self) -> u64;
fn write_bytes(&mut self, bytes: &[u8]);
/// Writes a single `u8` to this hasher
#[inline]
fn write_u8(&mut self, i: u8) {
self.write_bytes(&[i]);
}
/// Writes a single `usize` to this hasher
#[inline]
fn write_usize(&mut self, i: usize) {
// usize can be 4 or 8 bytes, standardize on the larger.
// As long as the original value is smaller than 4 bytes, the two will hash
// equivalently.
self.write_u64(i as u64);
}
/// Writes a single `isize` to this hasher
#[inline]
fn write_isize(&mut self, i: isize) {
// isize can be 4 or 8 bytes, standardize on the larger.
// As long as the original value is smaller than 4 bytes, the two will hash
// equivalently.
self.write_i64(i as i64);
}
impl_write_number! {
(u16, write_u16),
(u32, write_u32),
(u64, write_u64),
(i8, write_i8),
(i16, write_i16),
(i32, write_i32),
(i64, write_i64),
(u128, write_u128),
(i128, write_i128),
}
}
deterministic_hash_number! {
(u8, write_u8),
(u16, write_u16),
(u32, write_u32),
(u64, write_u64),
(usize, write_usize),
(i8, write_i8),
(i16, write_i16),
(i32, write_i32),
(i64, write_i64),
(isize, write_isize),
(u128, write_u128),
(i128, write_i128),
}
impl<T: ?Sized + DeterministicHash> DeterministicHash for &T {
fn deterministic_hash<H: DeterministicHasher>(&self, state: &mut H) {
(**self).deterministic_hash(state);
}
}
impl DeterministicHash for [u8] {
fn deterministic_hash<H: DeterministicHasher>(&self, state: &mut H) {
state.write_usize(self.len());
state.write_bytes(self);
}
}
impl DeterministicHash for String {
fn deterministic_hash<H: DeterministicHasher>(&self, state: &mut H) {
state.write_usize(self.len());
state.write_bytes(self.as_bytes());
}
}
impl DeterministicHash for &str {
fn deterministic_hash<H: DeterministicHasher>(&self, state: &mut H) {
state.write_usize(self.len());
state.write_bytes(self.as_bytes());
}
}
impl DeterministicHash for bool {
fn deterministic_hash<H: DeterministicHasher>(&self, state: &mut H) {
state.write_u8(*self as u8);
}
}
impl<T: DeterministicHash> DeterministicHash for Option<T> {
fn deterministic_hash<H: DeterministicHasher>(&self, state: &mut H) {
match self {
None => state.write_u8(0),
Some(v) => {
state.write_u8(1);
v.deterministic_hash(state);
}
}
}
}
impl<T: DeterministicHash> DeterministicHash for Vec<T> {
fn deterministic_hash<H: DeterministicHasher>(&self, state: &mut H) {
state.write_usize(self.len());
for v in self {
v.deterministic_hash(state);
}
}
}
macro_rules! tuple_impls {
( $( $name:ident )+ ) => {
impl<$($name: DeterministicHash),+> DeterministicHash for ($($name,)+)
{
#[allow(non_snake_case)]
fn deterministic_hash<Hasher: DeterministicHasher>(&self, state: &mut Hasher) {
let ($(ref $name,)+) = *self;
$($name.deterministic_hash(state);)+
}
}
};
}
// Implement `DeterministicHash` for all tuples of 1 to 12 elements.
tuple_impls! { A }
tuple_impls! { A B }
tuple_impls! { A B C }
tuple_impls! { A B C D }
tuple_impls! { A B C D E }
tuple_impls! { A B C D E F }
tuple_impls! { A B C D E F G }
tuple_impls! { A B C D E F G H }
tuple_impls! { A B C D E F G H I }
tuple_impls! { A B C D E F G H I J }
tuple_impls! { A B C D E F G H I J K }
tuple_impls! { A B C D E F G H I J K L }
/// HasherWrapper allows the DeterministicHasher to be used as a Hasher, for
/// standard types that do not allow us to directly access their internals.
struct HasherWrapper<'a, D: DeterministicHasher>(&'a mut D);
impl<D: DeterministicHasher> std::hash::Hasher for HasherWrapper<'_, D> {
fn write(&mut self, bytes: &[u8]) {
self.0.write_bytes(bytes);
}
fn finish(&self) -> u64 {
unimplemented!();
}
}
impl<T> DeterministicHash for Discriminant<T> {
fn deterministic_hash<H: DeterministicHasher>(&self, state: &mut H) {
// The Discriminant does not allow us to access its internal state, but does
// allow us to Hash it.
let mut wrapper = HasherWrapper(state);
std::hash::Hash::hash(self, &mut wrapper);
}
}
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