Don't cast directly from &[T; N] to *const T

src/librustc/ty/adjustment.rs

@@ -20,6 +20,9 @@ pub enum PointerCast {
  /// Go from a mut raw pointer to a const raw pointer.
  MutToConstPointer,
 
+ /// Go from `*const [T; N]` to `*const T`
+ ArrayToPointer,
+
  /// Unsize a pointer/reference value, e.g., `&[T; n]` to
  /// `&[T]`. Note that the source could be a thin or fat pointer.
  /// This will do things like convert thin pointers to fat

src/librustc_codegen_ssa/mir/rvalue.rs

@@ -269,6 +269,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
  }
  }
  mir::CastKind::Pointer(PointerCast::MutToConstPointer)
+ | mir::CastKind::Pointer(PointerCast::ArrayToPointer)
  | mir::CastKind::Misc => {
  assert!(bx.cx().is_backend_immediate(cast));
  let ll_t_out = bx.cx().immediate_backend_type(cast);

src/librustc_mir/borrow_check/nll/type_check/mod.rs

@@ -35,6 +35,7 @@ use rustc::traits::query::type_op::custom::CustomTypeOp;
 use rustc::traits::query::{Fallible, NoSolution};
 use rustc::traits::{self, ObligationCause, PredicateObligations};
 use rustc::ty::adjustment::{PointerCast};
+use rustc::ty::cast::CastTy;
 use rustc::ty::fold::TypeFoldable;
 use rustc::ty::subst::{Subst, SubstsRef, GenericArgKind, UserSubsts};
 use rustc::ty::{
@@ -2169,72 +2170,125 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
  ty_from,
  ty_to,
  terr
- )
+ );
  }
  }
 
- CastKind::Misc => {
- if let ty::Ref(_, mut ty_from, _) = op.ty(body, tcx).kind {
- let (mut ty_to, mutability) = if let ty::RawPtr(ty::TypeAndMut {
- ty: ty_to,
- mutbl,
- }) = ty.kind {
- (ty_to, mutbl)
- } else {
+ 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::MutImmutable, ty: array_ty }
+ ) => {
+ match array_ty.kind {
+ ty::Array(ty_elem, _) => Some(ty_elem),
+ _ => None,
+ }
+ }
+ _ => None,
+ };
+
+ let ty_elem = match opt_ty_elem {
+ Some(ty_elem) => ty_elem,
+ None => {
  span_mirbug!(
  self,
  rvalue,
- "invalid cast types {:?} -> {:?}",
- op.ty(body, tcx),
+ "ArrayToPointer cast from unexpected type {:?}",
+ ty_from,
+ );
+ return;
+ }
+ };
+
+ let ty_to = match ty.kind {
+ ty::RawPtr(
+ ty::TypeAndMut { mutbl: hir::MutImmutable, ty: ty_to }
+ ) => {
+ ty_to
+ }
+ _ => {
+ span_mirbug!(
+ self,
+ rvalue,
+ "ArrayToPointer cast to unexpected type {:?}",
  ty,
  );
  return;
- };
-
- // Handle the direct cast from `&[T; N]` to `*const T` by unwrapping
- // any array we find.
- while let ty::Array(ty_elem_from, _) = ty_from.kind {
- ty_from = ty_elem_from;
- if let ty::Array(ty_elem_to, _) = ty_to.kind {
- ty_to = ty_elem_to;
- } else {
- break;
- }
  }
+ };
 
- if let hir::MutMutable = mutability {
- if let Err(terr) = self.eq_types(
- ty_from,
- ty_to,
- location.to_locations(),
- ConstraintCategory::Cast,
- ) {
- span_mirbug!(
- self,
- rvalue,
- "equating {:?} with {:?} yields {:?}",
- ty_from,
- ty_to,
- terr
- )
- }
- } else {
- if let Err(terr) = self.sub_types(
- ty_from,
- ty_to,
- location.to_locations(),
- ConstraintCategory::Cast,
- ) {
- span_mirbug!(
- self,
- rvalue,
- "relating {:?} with {:?} yields {:?}",
- ty_from,
- ty_to,
- terr
- )
+ if let Err(terr) = self.sub_types(
+ ty_elem,
+ ty_to,
+ location.to_locations(),
+ ConstraintCategory::Cast,
+ ) {
+ span_mirbug!(
+ self,
+ rvalue,
+ "relating {:?} with {:?} yields {:?}",
+ ty_elem,
+ ty_to,
+ terr
+ )
+ }
+ }
+
+ CastKind::Misc => {
+ let ty_from = op.ty(body, tcx);
+ let cast_ty_from = CastTy::from_ty(ty_from);
+ let cast_ty_to = CastTy::from_ty(ty);
+ match (cast_ty_from, cast_ty_to) {
+ (Some(CastTy::RPtr(ref_tm)), Some(CastTy::Ptr(ptr_tm))) => {
+ if let hir::MutMutable = ptr_tm.mutbl {
+ if let Err(terr) = self.eq_types(
+ ref_tm.ty,
+ ptr_tm.ty,
+ location.to_locations(),
+ ConstraintCategory::Cast,
+ ) {
+ span_mirbug!(
+ self,
+ rvalue,
+ "equating {:?} with {:?} yields {:?}",
+ ref_tm.ty,
+ ptr_tm.ty,
+ terr
+ )
+ }
+ } else {
+ if let Err(terr) = self.sub_types(
+ ref_tm.ty,
+ ptr_tm.ty,
+ location.to_locations(),
+ ConstraintCategory::Cast,
+ ) {
+ span_mirbug!(
+ self,
+ rvalue,
+ "relating {:?} with {:?} yields {:?}",
+ ref_tm.ty,
+ ptr_tm.ty,
+ terr
+ )
+ }
  }
- }
+ },
+ (None, _)
+ | (_, None)
+ | (_, Some(CastTy::FnPtr))
+ | (Some(CastTy::Float), Some(CastTy::Ptr(_)))
+ | (Some(CastTy::Ptr(_)), Some(CastTy::Float))
+ | (Some(CastTy::FnPtr), Some(CastTy::Float)) => span_mirbug!(
+ self,
+ rvalue,
+ "Invalid cast {:?} -> {:?}",
+ ty_from,
+ ty,
+ ),
+ _ => (),
  }
  }
  }

src/librustc_mir/hair/cx/expr.rs

@@ -628,6 +628,11 @@ fn make_mirror_unadjusted<'a, 'tcx>(
  let cast = if cx.tables().is_coercion_cast(source.hir_id) {
  // Convert the lexpr to a vexpr.
  ExprKind::Use { source: source.to_ref() }
+ } else if cx.tables().expr_ty(source).is_region_ptr() {
+ // Special cased so that we can type check that the element
+ // type of the source matches the pointed to type of the
+ // destination.
+ ExprKind::Pointer { source: source.to_ref(), cast: PointerCast::ArrayToPointer }
  } else {
  // check whether this is casting an enum variant discriminant
  // to prevent cycles, we refer to the discriminant initializer

src/librustc_mir/interpret/cast.rs

@@ -26,7 +26,9 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
  self.unsize_into(src, dest)?;
  }
 
- Misc | Pointer(PointerCast::MutToConstPointer) => {
+ Misc
+ | Pointer(PointerCast::MutToConstPointer)
+ | Pointer(PointerCast::ArrayToPointer) => {
  let src = self.read_immediate(src)?;
  let res = self.cast_immediate(src, dest.layout)?;
  self.write_immediate(res, dest)?;

src/librustc_mir/transform/qualify_min_const_fn.rs

@@ -150,7 +150,8 @@ fn check_rvalue(
  _ => check_operand(tcx, operand, span, def_id, body),
  }
  }
- Rvalue::Cast(CastKind::Pointer(PointerCast::MutToConstPointer), operand, _) => {
+ Rvalue::Cast(CastKind::Pointer(PointerCast::MutToConstPointer), operand, _)
+ | Rvalue::Cast(CastKind::Pointer(PointerCast::ArrayToPointer), operand, _) => {
  check_operand(tcx, operand, span, def_id, body)
  }
  Rvalue::Cast(CastKind::Pointer(PointerCast::UnsafeFnPointer), _, _) |

src/librustc_typeck/check/cast.rs

@@ -639,6 +639,15 @@ impl<'a, 'tcx> CastCheck<'tcx> {
  // need to special-case obtaining a raw pointer
  // from a region pointer to a vector.
 
+ // Coerce to a raw pointer so that we generate AddressOf in MIR.
+ let array_ptr_type = fcx.tcx.mk_ptr(m_expr);
+ fcx.try_coerce(self.expr, self.expr_ty, array_ptr_type, AllowTwoPhase::No)
+ .unwrap_or_else(|_| bug!(
+ "could not cast from reference to array to pointer to array ({:?} to {:?})",
+ self.expr_ty,
+ array_ptr_type,
+ ));
+
  // this will report a type mismatch if needed
  fcx.demand_eqtype(self.span, ety, m_cast.ty);
  return Ok(CastKind::ArrayPtrCast);