src/librustc_typeck/check/cast.rs

   1 //! Code for type-checking cast expressions.
   2 //!
   3 //! A cast `e as U` is valid if one of the following holds:
   4 //! * `e` has type `T` and `T` coerces to `U`; *coercion-cast*
   5 //! * `e` has type `*T`, `U` is `*U_0`, and either `U_0: Sized` or
   6 //!    pointer_kind(`T`) = pointer_kind(`U_0`); *ptr-ptr-cast*
   7 //! * `e` has type `*T` and `U` is a numeric type, while `T: Sized`; *ptr-addr-cast*
   8 //! * `e` is an integer and `U` is `*U_0`, while `U_0: Sized`; *addr-ptr-cast*
   9 //! * `e` has type `T` and `T` and `U` are any numeric types; *numeric-cast*
  10 //! * `e` is a C-like enum and `U` is an integer type; *enum-cast*
  11 //! * `e` has type `bool` or `char` and `U` is an integer; *prim-int-cast*
  12 //! * `e` has type `u8` and `U` is `char`; *u8-char-cast*
  13 //! * `e` has type `&[T; n]` and `U` is `*const T`; *array-ptr-cast*
  14 //! * `e` is a function pointer type and `U` has type `*T`,
  15 //!   while `T: Sized`; *fptr-ptr-cast*
  16 //! * `e` is a function pointer type and `U` is an integer; *fptr-addr-cast*
  17 //!
  18 //! where `&.T` and `*T` are references of either mutability,
  19 //! and where pointer_kind(`T`) is the kind of the unsize info
  20 //! in `T` - the vtable for a trait definition (e.g., `fmt::Display` or
  21 //! `Iterator`, not `Iterator<Item=u8>`) or a length (or `()` if `T: Sized`).
  22 //!
  23 //! Note that lengths are not adjusted when casting raw slices -
  24 //! `T: *const [u16] as *const [u8]` creates a slice that only includes
  25 //! half of the original memory.
  26 //!
  27 //! Casting is not transitive, that is, even if `e as U1 as U2` is a valid
  28 //! expression, `e as U2` is not necessarily so (in fact it will only be valid if
  29 //! `U1` coerces to `U2`).
  30
  31 use super::FnCtxt;
  32
  33 use errors::{DiagnosticBuilder,Applicability};
  34 use crate::hir::def_id::DefId;
  35 use crate::lint;
  36 use rustc::hir;
  37 use rustc::session::Session;
  38 use rustc::traits;
  39 use rustc::ty::{self, Ty, TypeFoldable, TypeAndMut};
  40 use rustc::ty::subst::SubstsRef;
  41 use rustc::ty::adjustment::AllowTwoPhase;
  42 use rustc::ty::cast::{CastKind, CastTy};
  43 use rustc::ty::error::TypeError;
  44 use rustc::middle::lang_items;
  45 use syntax::ast;
  46 use syntax_pos::Span;
  47 use crate::util::common::ErrorReported;
  48
  49 /// Reifies a cast check to be checked once we have full type information for
  50 /// a function context.
  51 pub struct CastCheck<'tcx> {
  52     expr: &'tcx hir::Expr,
  53     expr_ty: Ty<'tcx>,
  54     cast_ty: Ty<'tcx>,
  55     cast_span: Span,
  56     span: Span,
  57 }
  58
  59 /// The kind of pointer and associated metadata (thin, length or vtable) - we
  60 /// only allow casts between fat pointers if their metadata have the same
  61 /// kind.
  62 #[derive(Copy, Clone, PartialEq, Eq)]
  63 enum PointerKind<'tcx> {
  64     /// No metadata attached, ie pointer to sized type or foreign type
  65     Thin,
  66     /// A trait object
  67     Vtable(Option<DefId>),
  68     /// Slice
  69     Length,
  70     /// The unsize info of this projection
  71     OfProjection(&'tcx ty::ProjectionTy<'tcx>),
  72     /// The unsize info of this opaque ty
  73     OfOpaque(DefId, SubstsRef<'tcx>),
  74     /// The unsize info of this parameter
  75     OfParam(&'tcx ty::ParamTy),
  76 }
  77
  78 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  79     /// Returns the kind of unsize information of t, or None
  80     /// if t is unknown.
  81     fn pointer_kind(&self, t: Ty<'tcx>, span: Span) ->
  82         Result<Option<PointerKind<'tcx>>, ErrorReported>
  83     {
  84         debug!("pointer_kind({:?}, {:?})", t, span);
  85
  86         let t = self.resolve_vars_if_possible(&t);
  87
  88         if t.references_error() {
  89             return Err(ErrorReported);
  90         }
  91
  92         if self.type_is_known_to_be_sized_modulo_regions(t, span) {
  93             return Ok(Some(PointerKind::Thin));
  94         }
  95
  96         Ok(match t.sty {
  97             ty::Slice(_) | ty::Str => Some(PointerKind::Length),
  98             ty::Dynamic(ref tty, ..) =>
  99                 Some(PointerKind::Vtable(tty.principal_def_id())),
 100             ty::Adt(def, substs) if def.is_struct() => {
 101                 match def.non_enum_variant().fields.last() {
 102                     None => Some(PointerKind::Thin),
 103                     Some(f) => {
 104                         let field_ty = self.field_ty(span, f, substs);
 105                         self.pointer_kind(field_ty, span)?
 106                     }
 107                 }
 108             }
 109             ty::Tuple(fields) => match fields.last() {
 110                 None => Some(PointerKind::Thin),
 111                 Some(f) => self.pointer_kind(f.expect_ty(), span)?
 112             },
 113
 114             // Pointers to foreign types are thin, despite being unsized
 115             ty::Foreign(..) => Some(PointerKind::Thin),
 116             // We should really try to normalize here.
 117             ty::Projection(ref pi) => Some(PointerKind::OfProjection(pi)),
 118             ty::UnnormalizedProjection(..) => bug!("only used with chalk-engine"),
 119             ty::Opaque(def_id, substs) => Some(PointerKind::OfOpaque(def_id, substs)),
 120             ty::Param(ref p) => Some(PointerKind::OfParam(p)),
 121             // Insufficient type information.
 122             ty::Placeholder(..) | ty::Bound(..) | ty::Infer(_) => None,
 123
 124             ty::Bool | ty::Char | ty::Int(..) | ty::Uint(..) |
 125             ty::Float(_) | ty::Array(..) | ty::GeneratorWitness(..) |
 126             ty::RawPtr(_) | ty::Ref(..) | ty::FnDef(..) |
 127             ty::FnPtr(..) | ty::Closure(..) | ty::Generator(..) |
 128             ty::Adt(..) | ty::Never | ty::Error => {
 129                 self.tcx.sess.delay_span_bug(
 130                     span, &format!("`{:?}` should be sized but is not?", t));
 131                 return Err(ErrorReported);
 132             }
 133         })
 134     }
 135 }
 136
 137 #[derive(Copy, Clone)]
 138 enum CastError {
 139     ErrorReported,
 140
 141     CastToBool,
 142     CastToChar,
 143     DifferingKinds,
 144     /// Cast of thin to fat raw ptr (e.g., `*const () as *const [u8]`).
 145     SizedUnsizedCast,
 146     IllegalCast,
 147     NeedDeref,
 148     NeedViaPtr,
 149     NeedViaThinPtr,
 150     NeedViaInt,
 151     NonScalar,
 152     UnknownExprPtrKind,
 153     UnknownCastPtrKind,
 154 }
 155
 156 impl From<ErrorReported> for CastError {
 157     fn from(ErrorReported: ErrorReported) -> Self {
 158         CastError::ErrorReported
 159     }
 160 }
 161
 162 fn make_invalid_casting_error<'a, 'tcx>(
 163     sess: &'a Session,
 164     span: Span,
 165     expr_ty: Ty<'tcx>,
 166     cast_ty: Ty<'tcx>,
 167     fcx: &FnCtxt<'a, 'tcx>,
 168 ) -> DiagnosticBuilder<'a> {
 169     type_error_struct!(sess, span, expr_ty, E0606,
 170                        "casting `{}` as `{}` is invalid",
 171                        fcx.ty_to_string(expr_ty),
 172                        fcx.ty_to_string(cast_ty))
 173 }
 174
 175 impl<'a, 'tcx> CastCheck<'tcx> {
 176     pub fn new(
 177         fcx: &FnCtxt<'a, 'tcx>,
 178         expr: &'tcx hir::Expr,
 179         expr_ty: Ty<'tcx>,
 180         cast_ty: Ty<'tcx>,
 181         cast_span: Span,
 182         span: Span,
 183     ) -> Result<CastCheck<'tcx>, ErrorReported> {
 184         let check = CastCheck {
 185             expr,
 186             expr_ty,
 187             cast_ty,
 188             cast_span,
 189             span,
 190         };
 191
 192         // For better error messages, check for some obviously unsized
 193         // cases now. We do a more thorough check at the end, once
 194         // inference is more completely known.
 195         match cast_ty.sty {
 196             ty::Dynamic(..) | ty::Slice(..) => {
 197                 check.report_cast_to_unsized_type(fcx);
 198                 Err(ErrorReported)
 199             }
 200             _ => Ok(check),
 201         }
 202     }
 203
 204     fn report_cast_error(&self, fcx: &FnCtxt<'a, 'tcx>, e: CastError) {
 205         match e {
 206             CastError::ErrorReported => {
 207                 // an error has already been reported
 208             }
 209             CastError::NeedDeref => {
 210                 let error_span = self.span;
 211                 let mut err = make_invalid_casting_error(fcx.tcx.sess, self.span, self.expr_ty,
 212                                                          self.cast_ty, fcx);
 213                 let cast_ty = fcx.ty_to_string(self.cast_ty);
 214                 err.span_label(error_span,
 215                                format!("cannot cast `{}` as `{}`",
 216                                        fcx.ty_to_string(self.expr_ty),
 217                                        cast_ty));
 218                 if let Ok(snippet) = fcx.sess().source_map().span_to_snippet(self.expr.span) {
 219                     err.span_suggestion(
 220                         self.expr.span,
 221                         "dereference the expression",
 222                         format!("*{}", snippet),
 223                         Applicability::MaybeIncorrect,
 224                     );
 225                 } else {
 226                     err.span_help(self.expr.span, "dereference the expression with `*`");
 227                 }
 228                 err.emit();
 229             }
 230             CastError::NeedViaThinPtr |
 231             CastError::NeedViaPtr => {
 232                 let mut err = make_invalid_casting_error(fcx.tcx.sess, self.span, self.expr_ty,
 233                                                          self.cast_ty, fcx);
 234                 if self.cast_ty.is_integral() {
 235                     err.help(&format!("cast through {} first",
 236                                       match e {
 237                                           CastError::NeedViaPtr => "a raw pointer",
 238                                           CastError::NeedViaThinPtr => "a thin pointer",
 239                                           _ => bug!(),
 240                                       }));
 241                 }
 242                 err.emit();
 243             }
 244             CastError::NeedViaInt => {
 245                 make_invalid_casting_error(fcx.tcx.sess, self.span, self.expr_ty, self.cast_ty, fcx)
 246                    .help(&format!("cast through {} first",
 247                                   match e {
 248                                       CastError::NeedViaInt => "an integer",
 249                                       _ => bug!(),
 250                                   }))
 251                    .emit();
 252             }
 253             CastError::IllegalCast => {
 254                 make_invalid_casting_error(fcx.tcx.sess, self.span, self.expr_ty, self.cast_ty, fcx)
 255                     .emit();
 256             }
 257             CastError::DifferingKinds => {
 258                 make_invalid_casting_error(fcx.tcx.sess, self.span, self.expr_ty, self.cast_ty, fcx)
 259                     .note("vtable kinds may not match")
 260                     .emit();
 261             }
 262             CastError::CastToBool => {
 263                 let mut err =
 264                     struct_span_err!(fcx.tcx.sess, self.span, E0054, "cannot cast as `bool`");
 265
 266                 if self.expr_ty.is_numeric() {
 267                     match fcx.tcx.sess.source_map().span_to_snippet(self.expr.span) {
 268                         Ok(snippet) => {
 269                             err.span_suggestion(
 270                                 self.span,
 271                                 "compare with zero instead",
 272                                 format!("{} != 0", snippet),
 273                                 Applicability::MachineApplicable,
 274                             );
 275                         }
 276                         Err(_) => {
 277                             err.span_help(self.span, "compare with zero instead");
 278                         }
 279                     }
 280                 } else {
 281                     err.span_label(self.span, "unsupported cast");
 282                 }
 283
 284                 err.emit();
 285             }
 286             CastError::CastToChar => {
 287                 type_error_struct!(fcx.tcx.sess, self.span, self.expr_ty, E0604,
 288                     "only `u8` can be cast as `char`, not `{}`", self.expr_ty).emit();
 289             }
 290             CastError::NonScalar => {
 291                 type_error_struct!(fcx.tcx.sess, self.span, self.expr_ty, E0605,
 292                                    "non-primitive cast: `{}` as `{}`",
 293                                    self.expr_ty,
 294                                    fcx.ty_to_string(self.cast_ty))
 295                                   .note("an `as` expression can only be used to convert between \
 296                                          primitive types. Consider using the `From` trait")
 297                                   .emit();
 298             }
 299             CastError::SizedUnsizedCast => {
 300                 use crate::structured_errors::{SizedUnsizedCastError, StructuredDiagnostic};
 301                 SizedUnsizedCastError::new(&fcx.tcx.sess,
 302                                            self.span,
 303                                            self.expr_ty,
 304                                            fcx.ty_to_string(self.cast_ty))
 305                     .diagnostic().emit();
 306             }
 307             CastError::UnknownCastPtrKind |
 308             CastError::UnknownExprPtrKind => {
 309                 let unknown_cast_to = match e {
 310                     CastError::UnknownCastPtrKind => true,
 311                     CastError::UnknownExprPtrKind => false,
 312                     _ => bug!(),
 313                 };
 314                 let mut err = struct_span_err!(fcx.tcx.sess, self.span, E0641,
 315                                                "cannot cast {} a pointer of an unknown kind",
 316                                                if unknown_cast_to { "to" } else { "from" });
 317                 err.note("The type information given here is insufficient to check whether \
 318                           the pointer cast is valid");
 319                 if unknown_cast_to {
 320                     err.span_suggestion_short(
 321                         self.cast_span,
 322                         "consider giving more type information",
 323                         String::new(),
 324                         Applicability::Unspecified,
 325                     );
 326                 }
 327                 err.emit();
 328             }
 329         }
 330     }
 331
 332     fn report_cast_to_unsized_type(&self, fcx: &FnCtxt<'a, 'tcx>) {
 333         if self.cast_ty.references_error() || self.expr_ty.references_error() {
 334             return;
 335         }
 336
 337         let tstr = fcx.ty_to_string(self.cast_ty);
 338         let mut err = type_error_struct!(fcx.tcx.sess, self.span, self.expr_ty, E0620,
 339                                          "cast to unsized type: `{}` as `{}`",
 340                                          fcx.resolve_vars_if_possible(&self.expr_ty),
 341                                          tstr);
 342         match self.expr_ty.sty {
 343             ty::Ref(_, _, mt) => {
 344                 let mtstr = match mt {
 345                     hir::MutMutable => "mut ",
 346                     hir::MutImmutable => "",
 347                 };
 348                 if self.cast_ty.is_trait() {
 349                     match fcx.tcx.sess.source_map().span_to_snippet(self.cast_span) {
 350                         Ok(s) => {
 351                             err.span_suggestion(
 352                                 self.cast_span,
 353                                 "try casting to a reference instead",
 354                                 format!("&{}{}", mtstr, s),
 355                                 Applicability::MachineApplicable,
 356                             );
 357                         }
 358                         Err(_) => {
 359                             span_help!(err, self.cast_span, "did you mean `&{}{}`?", mtstr, tstr)
 360                         }
 361                     }
 362                 } else {
 363                     span_help!(err,
 364                                self.span,
 365                                "consider using an implicit coercion to `&{}{}` instead",
 366                                mtstr,
 367                                tstr);
 368                 }
 369             }
 370             ty::Adt(def, ..) if def.is_box() => {
 371                 match fcx.tcx.sess.source_map().span_to_snippet(self.cast_span) {
 372                     Ok(s) => {
 373                         err.span_suggestion(
 374                             self.cast_span,
 375                             "try casting to a `Box` instead",
 376                             format!("Box<{}>", s),
 377                             Applicability::MachineApplicable,
 378                         );
 379                     }
 380                     Err(_) => span_help!(err, self.cast_span, "did you mean `Box<{}>`?", tstr),
 381                 }
 382             }
 383             _ => {
 384                 span_help!(err,
 385                            self.expr.span,
 386                            "consider using a box or reference as appropriate");
 387             }
 388         }
 389         err.emit();
 390     }
 391
 392     fn trivial_cast_lint(&self, fcx: &FnCtxt<'a, 'tcx>) {
 393         let t_cast = self.cast_ty;
 394         let t_expr = self.expr_ty;
 395         let type_asc_or = if fcx.tcx.features().type_ascription {
 396             "type ascription or "
 397         } else {
 398             ""
 399         };
 400         let (adjective, lint) = if t_cast.is_numeric() && t_expr.is_numeric() {
 401             ("numeric ", lint::builtin::TRIVIAL_NUMERIC_CASTS)
 402         } else {
 403             ("", lint::builtin::TRIVIAL_CASTS)
 404         };
 405         let mut err = fcx.tcx.struct_span_lint_hir(
 406             lint,
 407             self.expr.hir_id,
 408             self.span,
 409             &format!("trivial {}cast: `{}` as `{}`",
 410                      adjective,
 411                      fcx.ty_to_string(t_expr),
 412                      fcx.ty_to_string(t_cast)));
 413         err.help(&format!("cast can be replaced by coercion; this might \
 414                            require {}a temporary variable", type_asc_or));
 415         err.emit();
 416     }
 417
 418     pub fn check(mut self, fcx: &FnCtxt<'a, 'tcx>) {
 419         self.expr_ty = fcx.structurally_resolved_type(self.span, self.expr_ty);
 420         self.cast_ty = fcx.structurally_resolved_type(self.span, self.cast_ty);
 421
 422         debug!("check_cast({}, {:?} as {:?})",
 423                self.expr.hir_id,
 424                self.expr_ty,
 425                self.cast_ty);
 426
 427         if !fcx.type_is_known_to_be_sized_modulo_regions(self.cast_ty, self.span) {
 428             self.report_cast_to_unsized_type(fcx);
 429         } else if self.expr_ty.references_error() || self.cast_ty.references_error() {
 430             // No sense in giving duplicate error messages
 431         } else if self.try_coercion_cast(fcx) {
 432             self.trivial_cast_lint(fcx);
 433             debug!(" -> CoercionCast");
 434             fcx.tables.borrow_mut().set_coercion_cast(self.expr.hir_id.local_id);
 435
 436         } else {
 437             match self.do_check(fcx) {
 438                 Ok(k) => {
 439                     debug!(" -> {:?}", k);
 440                 }
 441                 Err(e) => self.report_cast_error(fcx, e),
 442             };
 443         }
 444     }
 445
 446     /// Checks a cast, and report an error if one exists. In some cases, this
 447     /// can return Ok and create type errors in the fcx rather than returning
 448     /// directly. coercion-cast is handled in check instead of here.
 449     fn do_check(&self, fcx: &FnCtxt<'a, 'tcx>) -> Result<CastKind, CastError> {
 450         use rustc::ty::cast::IntTy::*;
 451         use rustc::ty::cast::CastTy::*;
 452
 453         let (t_from, t_cast) = match (CastTy::from_ty(self.expr_ty),
 454                                       CastTy::from_ty(self.cast_ty)) {
 455             (Some(t_from), Some(t_cast)) => (t_from, t_cast),
 456             // Function item types may need to be reified before casts.
 457             (None, Some(t_cast)) => {
 458                 if let ty::FnDef(..) = self.expr_ty.sty {
 459                     // Attempt a coercion to a fn pointer type.
 460                     let f = self.expr_ty.fn_sig(fcx.tcx);
 461                     let res = fcx.try_coerce(self.expr,
 462                                              self.expr_ty,
 463                                              fcx.tcx.mk_fn_ptr(f),
 464                                              AllowTwoPhase::No);
 465                     if let Err(TypeError::IntrinsicCast) = res {
 466                         return Err(CastError::IllegalCast);
 467                     }
 468                     if res.is_err() {
 469                         return Err(CastError::NonScalar);
 470                     }
 471                     (FnPtr, t_cast)
 472                 } else {
 473                     return Err(CastError::NonScalar);
 474                 }
 475             }
 476             _ => return Err(CastError::NonScalar),
 477         };
 478
 479         match (t_from, t_cast) {
 480             // These types have invariants! can't cast into them.
 481             (_, RPtr(_)) | (_, Int(CEnum)) | (_, FnPtr) => Err(CastError::NonScalar),
 482
 483             // * -> Bool
 484             (_, Int(Bool)) => Err(CastError::CastToBool),
 485
 486             // * -> Char
 487             (Int(U(ast::UintTy::U8)), Int(Char)) => Ok(CastKind::U8CharCast), // u8-char-cast
 488             (_, Int(Char)) => Err(CastError::CastToChar),
 489
 490             // prim -> float,ptr
 491             (Int(Bool), Float) |
 492             (Int(CEnum), Float) |
 493             (Int(Char), Float) => Err(CastError::NeedViaInt),
 494
 495             (Int(Bool), Ptr(_)) |
 496             (Int(CEnum), Ptr(_)) |
 497             (Int(Char), Ptr(_)) |
 498             (Ptr(_), Float) |
 499             (FnPtr, Float) |
 500             (Float, Ptr(_)) => Err(CastError::IllegalCast),
 501
 502             // ptr -> *
 503             (Ptr(m_e), Ptr(m_c)) => self.check_ptr_ptr_cast(fcx, m_e, m_c), // ptr-ptr-cast
 504             (Ptr(m_expr), Int(_)) => self.check_ptr_addr_cast(fcx, m_expr), // ptr-addr-cast
 505             (FnPtr, Int(_)) => Ok(CastKind::FnPtrAddrCast),
 506             (RPtr(p), Int(_)) |
 507             (RPtr(p), Float) => {
 508                 match p.ty.sty {
 509                     ty::Int(_) |
 510                     ty::Uint(_) |
 511                     ty::Float(_) => {
 512                         Err(CastError::NeedDeref)
 513                     }
 514                     ty::Infer(t) => {
 515                         match t {
 516                             ty::InferTy::IntVar(_) |
 517                             ty::InferTy::FloatVar(_) => Err(CastError::NeedDeref),
 518                             _ => Err(CastError::NeedViaPtr),
 519                         }
 520                     }
 521                     _ => Err(CastError::NeedViaPtr),
 522                 }
 523             }
 524             // * -> ptr
 525             (Int(_), Ptr(mt)) => self.check_addr_ptr_cast(fcx, mt), // addr-ptr-cast
 526             (FnPtr, Ptr(mt)) => self.check_fptr_ptr_cast(fcx, mt),
 527             (RPtr(rmt), Ptr(mt)) => self.check_ref_cast(fcx, rmt, mt), // array-ptr-cast
 528
 529             // prim -> prim
 530             (Int(CEnum), Int(_)) => Ok(CastKind::EnumCast),
 531             (Int(Char), Int(_)) |
 532             (Int(Bool), Int(_)) => Ok(CastKind::PrimIntCast),
 533
 534             (Int(_), Int(_)) | (Int(_), Float) | (Float, Int(_)) | (Float, Float) => {
 535                 Ok(CastKind::NumericCast)
 536             }
 537         }
 538     }
 539
 540     fn check_ptr_ptr_cast(
 541         &self,
 542         fcx: &FnCtxt<'a, 'tcx>,
 543         m_expr: ty::TypeAndMut<'tcx>,
 544         m_cast: ty::TypeAndMut<'tcx>,
 545     ) -> Result<CastKind, CastError> {
 546         debug!("check_ptr_ptr_cast m_expr={:?} m_cast={:?}", m_expr, m_cast);
 547         // ptr-ptr cast. vtables must match.
 548
 549         let expr_kind = fcx.pointer_kind(m_expr.ty, self.span)?;
 550         let cast_kind = fcx.pointer_kind(m_cast.ty, self.span)?;
 551
 552         let cast_kind = match cast_kind {
 553             // We can't cast if target pointer kind is unknown
 554             None => return Err(CastError::UnknownCastPtrKind),
 555             Some(cast_kind) => cast_kind,
 556         };
 557
 558         // Cast to thin pointer is OK
 559         if cast_kind == PointerKind::Thin {
 560             return Ok(CastKind::PtrPtrCast);
 561         }
 562
 563         let expr_kind = match expr_kind {
 564             // We can't cast to fat pointer if source pointer kind is unknown
 565             None => return Err(CastError::UnknownExprPtrKind),
 566             Some(expr_kind) => expr_kind,
 567         };
 568
 569         // thin -> fat? report invalid cast (don't complain about vtable kinds)
 570         if expr_kind == PointerKind::Thin {
 571             return Err(CastError::SizedUnsizedCast);
 572         }
 573
 574         // vtable kinds must match
 575         if cast_kind == expr_kind {
 576             Ok(CastKind::PtrPtrCast)
 577         } else {
 578             Err(CastError::DifferingKinds)
 579         }
 580     }
 581
 582     fn check_fptr_ptr_cast(
 583         &self,
 584         fcx: &FnCtxt<'a, 'tcx>,
 585         m_cast: ty::TypeAndMut<'tcx>,
 586     ) -> Result<CastKind, CastError> {
 587         // fptr-ptr cast. must be to thin ptr
 588
 589         match fcx.pointer_kind(m_cast.ty, self.span)? {
 590             None => Err(CastError::UnknownCastPtrKind),
 591             Some(PointerKind::Thin) => Ok(CastKind::FnPtrPtrCast),
 592             _ => Err(CastError::IllegalCast),
 593         }
 594     }
 595
 596     fn check_ptr_addr_cast(
 597         &self,
 598         fcx: &FnCtxt<'a, 'tcx>,
 599         m_expr: ty::TypeAndMut<'tcx>,
 600     ) -> Result<CastKind, CastError> {
 601         // ptr-addr cast. must be from thin ptr
 602
 603         match fcx.pointer_kind(m_expr.ty, self.span)? {
 604             None => Err(CastError::UnknownExprPtrKind),
 605             Some(PointerKind::Thin) => Ok(CastKind::PtrAddrCast),
 606             _ => Err(CastError::NeedViaThinPtr),
 607         }
 608     }
 609
 610     fn check_ref_cast(
 611         &self,
 612         fcx: &FnCtxt<'a, 'tcx>,
 613         m_expr: ty::TypeAndMut<'tcx>,
 614         m_cast: ty::TypeAndMut<'tcx>,
 615     ) -> Result<CastKind, CastError> {
 616         // array-ptr-cast.
 617
 618         if m_expr.mutbl == hir::MutImmutable && m_cast.mutbl == hir::MutImmutable {
 619             if let ty::Array(ety, _) = m_expr.ty.sty {
 620                 // Due to the limitations of LLVM global constants,
 621                 // region pointers end up pointing at copies of
 622                 // vector elements instead of the original values.
 623                 // To allow raw pointers to work correctly, we
 624                 // need to special-case obtaining a raw pointer
 625                 // from a region pointer to a vector.
 626
 627                 // this will report a type mismatch if needed
 628                 fcx.demand_eqtype(self.span, ety, m_cast.ty);
 629                 return Ok(CastKind::ArrayPtrCast);
 630             }
 631         }
 632
 633         Err(CastError::IllegalCast)
 634     }
 635
 636     fn check_addr_ptr_cast(
 637         &self,
 638         fcx: &FnCtxt<'a, 'tcx>,
 639         m_cast: TypeAndMut<'tcx>,
 640     ) -> Result<CastKind, CastError> {
 641         // ptr-addr cast. pointer must be thin.
 642         match fcx.pointer_kind(m_cast.ty, self.span)? {
 643             None => Err(CastError::UnknownCastPtrKind),
 644             Some(PointerKind::Thin) => Ok(CastKind::AddrPtrCast),
 645             _ => Err(CastError::IllegalCast),
 646         }
 647     }
 648
 649     fn try_coercion_cast(&self, fcx: &FnCtxt<'a, 'tcx>) -> bool {
 650         fcx.try_coerce(self.expr, self.expr_ty, self.cast_ty, AllowTwoPhase::No).is_ok()
 651     }
 652 }
 653
 654 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 655     fn type_is_known_to_be_sized_modulo_regions(&self, ty: Ty<'tcx>, span: Span) -> bool {
 656         let lang_item = self.tcx.require_lang_item(lang_items::SizedTraitLangItem, None);
 657         traits::type_known_to_meet_bound_modulo_regions(self, self.param_env, ty, lang_item, span)
 658     }
 659 }