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add comment to Lift impls

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This commit is contained in:
lcnr 2022-02-11 13:20:38 +01:00
parent 758f4e7158
commit c909b6dc22
1 changed files with 5 additions and 1 deletions
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6
compiler/rustc_middle/src/ty/context.rs
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@ -1655,6 +1655,8 @@ macro_rules! nop_lift {
type Lifted = $lifted;
fn lift_to_tcx(self, tcx: TyCtxt<'tcx>) -> Option<Self::Lifted> {
if tcx.interners.$set.contains_pointer_to(&InternedInSet(self.0.0)) {
// SAFETY: `self` is interned and therefore valid
// for the entire lifetime of the `TyCtxt`.
Some(unsafe { mem::transmute(self) })
} else {
None
@ -1674,7 +1676,9 @@ impl<'a, 'tcx> Lift<'tcx> for &'a List<Ty<'a>> {
return Some(List::empty());
}
if tcx.interners.substs.contains_pointer_to(&InternedInSet(self.as_substs())) {
Some(unsafe { mem::transmute(self) })
// SAFETY: `self` is interned and therefore valid
// for the entire lifetime of the `TyCtxt`.
Some(unsafe { mem::transmute::<&'a List<Ty<'a>>, &'tcx List<Ty<'tcx>>>(self) })
} else {
None
}