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This commit is contained in:
lcnr 2022-02-18 12:31:12 +01:00
parent c909b6dc22
commit 80f56cdc2a
2 changed files with 10 additions and 1 deletions
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8
compiler/rustc_middle/src/ty/impls_ty.rs
View file

@ -70,12 +70,20 @@ impl<'a, 'tcx> HashStable<StableHashingContext<'a>> for ty::subst::GenericArgKin
// See `fn intern_type_list` for more details.
//
// We therefore hash types without adding a hash for their discriminant.
//
// In order to make it very unlikely for the sequence of bytes being hashed for
// a `GenericArgKind::Type` to be the same as the sequence of bytes being
// hashed for one of the other variants, we hash a `0xFF` byte before hashing
// their discriminant (since the discriminant of `TyKind` is unlikely to ever start
// with 0xFF).
ty::subst::GenericArgKind::Type(ty) => ty.hash_stable(hcx, hasher),
ty::subst::GenericArgKind::Const(ct) => {
0xFFu8.hash_stable(hcx, hasher);
mem::discriminant(self).hash_stable(hcx, hasher);
ct.hash_stable(hcx, hasher);
}
ty::subst::GenericArgKind::Lifetime(lt) => {
0xFFu8.hash_stable(hcx, hasher);
mem::discriminant(self).hash_stable(hcx, hasher);
lt.hash_stable(hcx, hasher);
}

3
compiler/rustc_middle/src/ty/subst.rs
View file

@ -51,7 +51,8 @@ pub enum GenericArgKind<'tcx> {
/// This function goes from `&'a [Ty<'tcx>]` to `&'a [GenericArg<'tcx>]`
///
/// This is sound as, for types, `GenericArg` is just
/// `NonZeroUsize::new_unchecked(ty as *const _ as usize)`.
/// `NonZeroUsize::new_unchecked(ty as *const _ as usize)` as
/// long as we use `0` for the `TYPE_TAG`.
pub fn ty_slice_as_generic_args<'a, 'tcx>(ts: &'a [Ty<'tcx>]) -> &'a [GenericArg<'tcx>] {
assert_eq!(TYPE_TAG, 0);
// SAFETY: the whole slice is valid and immutable.