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Allow casting mut array ref to mut ptr 

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,

5
compiler/rustc_typeck/src/check/cast.rs
View File

@ -765,9 +765,8 @@ impl<'a, 'tcx> CastCheck<'tcx> {
m_expr: ty::TypeAndMut<'tcx>,
m_cast: ty::TypeAndMut<'tcx>,
) -> Result<CastKind, CastError> {
// array-ptr-cast.
if m_expr.mutbl == hir::Mutability::Not && m_cast.mutbl == hir::Mutability::Not {
// array-ptr-cast: allow mut-to-mut, mut-to-const, const-to-const
if m_expr.mutbl == hir::Mutability::Mut || m_cast.mutbl == hir::Mutability::Not {
if let ty::Array(ety, _) = m_expr.ty.kind() {
// Due to the limitations of LLVM global constants,
// region pointers end up pointing at copies of

14
src/test/ui/array-slice-vec/vector-cast-weirdness.rs
View File

@ -1,7 +1,11 @@
// Issue #14893. Tests that casts from vectors don't behave strangely in the
// presence of the `_` type shorthand notation.
//
// Update: after a change to the way casts are done, we have more type information
// around and so the errors here are no longer exactly the same.
//
// Update: With PR #81479 some of the previously rejected cases are now allowed.
// New test cases added.
struct X {
y: [u8; 2],
@ -12,13 +16,19 @@ fn main() {
// No longer a type mismatch - the `_` can be fully resolved by type inference.
let p1: *const u8 = &x1.y as *const _;
let p1: *mut u8 = &x1.y as *mut _;
//~^ ERROR: casting `&[u8; 2]` as `*mut u8` is invalid
let t1: *const [u8; 2] = &x1.y as *const _;
let t1: *mut [u8; 2] = &x1.y as *mut _;
//~^ ERROR: casting `&[u8; 2]` as `*mut [u8; 2]` is invalid
let h1: *const [u8; 2] = &x1.y as *const [u8; 2];
let t1: *mut [u8; 2] = &x1.y as *mut [u8; 2];
//~^ ERROR: casting `&[u8; 2]` as `*mut [u8; 2]` is invalid
let mut x1 = X { y: [0, 0] };
// This is still an error since we don't allow casts from &mut [T; n] to *mut T.
let p1: *mut u8 = &mut x1.y as *mut _; //~ ERROR casting
let p1: *mut u8 = &mut x1.y as *mut _;
let p2: *const u8 = &mut x1.y as *const _;
let t1: *mut [u8; 2] = &mut x1.y as *mut _;
let h1: *mut [u8; 2] = &mut x1.y as *mut [u8; 2];
}

22
src/test/ui/array-slice-vec/vector-cast-weirdness.stderr
View File

@ -1,9 +1,21 @@
error[E0606]: casting `&mut [u8; 2]` as `*mut u8` is invalid
--> $DIR/vector-cast-weirdness.rs:21:23
error[E0606]: casting `&[u8; 2]` as `*mut u8` is invalid
--> $DIR/vector-cast-weirdness.rs:19:23
|
LL | let p1: *mut u8 = &mut x1.y as *mut _;
| ^^^^^^^^^^^^^^^^^^^
LL | let p1: *mut u8 = &x1.y as *mut _;
| ^^^^^^^^^^^^^^^
error: aborting due to previous error
error[E0606]: casting `&[u8; 2]` as `*mut [u8; 2]` is invalid
--> $DIR/vector-cast-weirdness.rs:22:28
|
LL | let t1: *mut [u8; 2] = &x1.y as *mut _;
| ^^^^^^^^^^^^^^^
error[E0606]: casting `&[u8; 2]` as `*mut [u8; 2]` is invalid
--> $DIR/vector-cast-weirdness.rs:25:28
|
LL | let t1: *mut [u8; 2] = &x1.y as *mut [u8; 2];
| ^^^^^^^^^^^^^^^^^^^^^
error: aborting due to 3 previous errors
For more information about this error, try `rustc --explain E0606`.