+ fn from_box_ty<'tcx>(
+ ty: Ty<'tcx>,
+ kind: RetagKind,
+ cx: &crate::MiriInterpCx<'_, 'tcx>,
+ ) -> Self {
+ // `ty` is not the `Box` but the field of the Box with this pointer (due to allocator handling).
+ let pointee = ty.builtin_deref(true).unwrap().ty;
+ if pointee.is_unpin(*cx.tcx, cx.param_env()) {
+ // A regular box. On `FnEntry` this is `noalias`, but not `dereferenceable` (hence only
+ // a weak protector).
+ NewPermission::Uniform {
+ perm: Permission::Unique,
+ access: Some(AccessKind::Write),
+ protector: (kind == RetagKind::FnEntry)
+ .then_some(ProtectorKind::WeakProtector),
+ }
+ } else {
+ // `!Unpin` boxes do not get `noalias` nor `dereferenceable`.
+ NewPermission::Uniform {
+ perm: Permission::SharedReadWrite,
+ access: None,
+ protector: None,
+ }
+ }
+ }
+