bjoernager/rust
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Allow casting mut array ref to mut ptr

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We now allow two new casts:

- mut array reference to mut ptr. Example:

      let mut x: [usize; 2] = [0, 0];
      let p = &mut x as *mut usize;

  We allow casting const array references to const pointers so not
  allowing mut references to mut pointers was inconsistent.

- mut array reference to const ptr. Example:

      let mut x: [usize; 2] = [0, 0];
      let p = &mut x as *const usize;

  This was similarly inconsistent as we allow casting mut references to
  const pointers.

Existing test 'vector-cast-weirdness' updated to test both cases.

Fixes #24151
This commit is contained in:
Ömer Sinan Ağacan 2021-01-28 20:22:33 +03:00
parent 6523b721c3
commit d64b749f2c
4 changed files with 55 additions and 25 deletions
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39
compiler/rustc_mir/src/borrow_check/type_check/mod.rs
View file

@ -2191,19 +2191,18 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
CastKind::Pointer(PointerCast::ArrayToPointer) => {
let ty_from = op.ty(body, tcx);
let opt_ty_elem = match ty_from.kind() {
ty::RawPtr(ty::TypeAndMut {
mutbl: hir::Mutability::Not,
ty: array_ty,
}) => match array_ty.kind() {
ty::Array(ty_elem, _) => Some(ty_elem),
_ => None,
},
let opt_ty_elem_mut = match ty_from.kind() {
ty::RawPtr(ty::TypeAndMut { mutbl: array_mut, ty: array_ty }) => {
match array_ty.kind() {
ty::Array(ty_elem, _) => Some((ty_elem, *array_mut)),
_ => None,
}
}
_ => None,
};
let ty_elem = match opt_ty_elem {
Some(ty_elem) => ty_elem,
let (ty_elem, ty_mut) = match opt_ty_elem_mut {
Some(ty_elem_mut) => ty_elem_mut,
None => {
span_mirbug!(
self,
@ -2215,11 +2214,10 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
}
};
let ty_to = match ty.kind() {
ty::RawPtr(ty::TypeAndMut {
mutbl: hir::Mutability::Not,
ty: ty_to,
}) => ty_to,
let (ty_to, ty_to_mut) = match ty.kind() {
ty::RawPtr(ty::TypeAndMut { mutbl: ty_to_mut, ty: ty_to }) => {
(ty_to, *ty_to_mut)
}
_ => {
span_mirbug!(
self,
@ -2231,6 +2229,17 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
}
};
if ty_to_mut == Mutability::Mut && ty_mut == Mutability::Not {
span_mirbug!(
self,
rvalue,
"ArrayToPointer cast from const {:?} to mut {:?}",
ty,
ty_to
);
return;
}
if let Err(terr) = self.sub_types(
ty_elem,
ty_to,