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 crate::hir::def_id::DefId;
  34 use crate::lint;
  35 use crate::type_error_struct;
  36 use crate::util::common::ErrorReported;
  37 use rustc::middle::lang_items;
  38 use rustc::session::Session;
  39 use rustc::traits;
  40 use rustc::traits::error_reporting::report_object_safety_error;
  41 use rustc::traits::object_safety_violations;
  42 use rustc::ty::adjustment::AllowTwoPhase;
  43 use rustc::ty::cast::{CastKind, CastTy};
  44 use rustc::ty::error::TypeError;
  45 use rustc::ty::subst::SubstsRef;
  46 use rustc::ty::{self, Ty, TypeAndMut, TypeFoldable};
  47 use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder};
  48 use rustc_hir as hir;
  49 use rustc_span::Span;
  50 use syntax::ast;
  51
  52 use rustc_error_codes::*;
  53
  54 /// Reifies a cast check to be checked once we have full type information for
  55 /// a function context.
  56 pub struct CastCheck<'tcx> {
  57     expr: &'tcx hir::Expr<'tcx>,
  58     expr_ty: Ty<'tcx>,
  59     cast_ty: Ty<'tcx>,
  60     cast_span: Span,
  61     span: Span,
  62 }
  63
  64 /// The kind of pointer and associated metadata (thin, length or vtable) - we
  65 /// only allow casts between fat pointers if their metadata have the same
  66 /// kind.
  67 #[derive(Copy, Clone, PartialEq, Eq)]
  68 enum PointerKind<'tcx> {
  69     /// No metadata attached, ie pointer to sized type or foreign type
  70     Thin,
  71     /// A trait object
  72     Vtable(Option<DefId>),
  73     /// Slice
  74     Length,
  75     /// The unsize info of this projection
  76     OfProjection(&'tcx ty::ProjectionTy<'tcx>),
  77     /// The unsize info of this opaque ty
  78     OfOpaque(DefId, SubstsRef<'tcx>),
  79     /// The unsize info of this parameter
  80     OfParam(&'tcx ty::ParamTy),
  81 }
  82
  83 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  84     /// Returns the kind of unsize information of t, or None
  85     /// if t is unknown.
  86     fn pointer_kind(
  87         &self,
  88         t: Ty<'tcx>,
  89         span: Span,
  90     ) -> Result<Option<PointerKind<'tcx>>, ErrorReported> {
  91         debug!("pointer_kind({:?}, {:?})", t, span);
  92
  93         let t = self.resolve_vars_if_possible(&t);
  94
  95         if t.references_error() {
  96             return Err(ErrorReported);
  97         }
  98
  99         if self.type_is_known_to_be_sized_modulo_regions(t, span) {
 100             return Ok(Some(PointerKind::Thin));
 101         }
 102
 103         Ok(match t.kind {
 104             ty::Slice(_) | ty::Str => Some(PointerKind::Length),
 105             ty::Dynamic(ref tty, ..) => Some(PointerKind::Vtable(tty.principal_def_id())),
 106             ty::Adt(def, substs) if def.is_struct() => match def.non_enum_variant().fields.last() {
 107                 None => Some(PointerKind::Thin),
 108                 Some(f) => {
 109                     let field_ty = self.field_ty(span, f, substs);
 110                     self.pointer_kind(field_ty, span)?
 111                 }
 112             },
 113             ty::Tuple(fields) => match fields.last() {
 114                 None => Some(PointerKind::Thin),
 115                 Some(f) => self.pointer_kind(f.expect_ty(), span)?,
 116             },
 117
 118             // Pointers to foreign types are thin, despite being unsized
 119             ty::Foreign(..) => Some(PointerKind::Thin),
 120             // We should really try to normalize here.
 121             ty::Projection(ref pi) => Some(PointerKind::OfProjection(pi)),
 122             ty::UnnormalizedProjection(..) => bug!("only used with chalk-engine"),
 123             ty::Opaque(def_id, substs) => Some(PointerKind::OfOpaque(def_id, substs)),
 124             ty::Param(ref p) => Some(PointerKind::OfParam(p)),
 125             // Insufficient type information.
 126             ty::Placeholder(..) | ty::Bound(..) | ty::Infer(_) => None,
 127
 128             ty::Bool
 129             | ty::Char
 130             | ty::Int(..)
 131             | ty::Uint(..)
 132             | ty::Float(_)
 133             | ty::Array(..)
 134             | ty::GeneratorWitness(..)
 135             | ty::RawPtr(_)
 136             | ty::Ref(..)
 137             | ty::FnDef(..)
 138             | ty::FnPtr(..)
 139             | ty::Closure(..)
 140             | ty::Generator(..)
 141             | ty::Adt(..)
 142             | ty::Never
 143             | ty::Error => {
 144                 self.tcx
 145                     .sess
 146                     .delay_span_bug(span, &format!("`{:?}` should be sized but is not?", t));
 147                 return Err(ErrorReported);
 148             }
 149         })
 150     }
 151 }
 152
 153 #[derive(Copy, Clone)]
 154 enum CastError {
 155     ErrorReported,
 156
 157     CastToBool,
 158     CastToChar,
 159     DifferingKinds,
 160     /// Cast of thin to fat raw ptr (e.g., `*const () as *const [u8]`).
 161     SizedUnsizedCast,
 162     IllegalCast,
 163     NeedDeref,
 164     NeedViaPtr,
 165     NeedViaThinPtr,
 166     NeedViaInt,
 167     NonScalar,
 168     UnknownExprPtrKind,
 169     UnknownCastPtrKind,
 170 }
 171
 172 impl From<ErrorReported> for CastError {
 173     fn from(ErrorReported: ErrorReported) -> Self {
 174         CastError::ErrorReported
 175     }
 176 }
 177
 178 fn make_invalid_casting_error<'a, 'tcx>(
 179     sess: &'a Session,
 180     span: Span,
 181     expr_ty: Ty<'tcx>,
 182     cast_ty: Ty<'tcx>,
 183     fcx: &FnCtxt<'a, 'tcx>,
 184 ) -> DiagnosticBuilder<'a> {
 185     type_error_struct!(
 186         sess,
 187         span,
 188         expr_ty,
 189         E0606,
 190         "casting `{}` as `{}` is invalid",
 191         fcx.ty_to_string(expr_ty),
 192         fcx.ty_to_string(cast_ty)
 193     )
 194 }
 195
 196 impl<'a, 'tcx> CastCheck<'tcx> {
 197     pub fn new(
 198         fcx: &FnCtxt<'a, 'tcx>,
 199         expr: &'tcx hir::Expr<'tcx>,
 200         expr_ty: Ty<'tcx>,
 201         cast_ty: Ty<'tcx>,
 202         cast_span: Span,
 203         span: Span,
 204     ) -> Result<CastCheck<'tcx>, ErrorReported> {
 205         let check = CastCheck { expr, expr_ty, cast_ty, cast_span, span };
 206
 207         // For better error messages, check for some obviously unsized
 208         // cases now. We do a more thorough check at the end, once
 209         // inference is more completely known.
 210         match cast_ty.kind {
 211             ty::Dynamic(..) | ty::Slice(..) => {
 212                 check.report_cast_to_unsized_type(fcx);
 213                 Err(ErrorReported)
 214             }
 215             _ => Ok(check),
 216         }
 217     }
 218
 219     fn report_cast_error(&self, fcx: &FnCtxt<'a, 'tcx>, e: CastError) {
 220         match e {
 221             CastError::ErrorReported => {
 222                 // an error has already been reported
 223             }
 224             CastError::NeedDeref => {
 225                 let error_span = self.span;
 226                 let mut err = make_invalid_casting_error(
 227                     fcx.tcx.sess,
 228                     self.span,
 229                     self.expr_ty,
 230                     self.cast_ty,
 231                     fcx,
 232                 );
 233                 let cast_ty = fcx.ty_to_string(self.cast_ty);
 234                 err.span_label(
 235                     error_span,
 236                     format!("cannot cast `{}` as `{}`", fcx.ty_to_string(self.expr_ty), cast_ty),
 237                 );
 238                 if let Ok(snippet) = fcx.sess().source_map().span_to_snippet(self.expr.span) {
 239                     err.span_suggestion(
 240                         self.expr.span,
 241                         "dereference the expression",
 242                         format!("*{}", snippet),
 243                         Applicability::MaybeIncorrect,
 244                     );
 245                 } else {
 246                     err.span_help(self.expr.span, "dereference the expression with `*`");
 247                 }
 248                 err.emit();
 249             }
 250             CastError::NeedViaThinPtr | CastError::NeedViaPtr => {
 251                 let mut err = make_invalid_casting_error(
 252                     fcx.tcx.sess,
 253                     self.span,
 254                     self.expr_ty,
 255                     self.cast_ty,
 256                     fcx,
 257                 );
 258                 if self.cast_ty.is_integral() {
 259                     err.help(&format!(
 260                         "cast through {} first",
 261                         match e {
 262                             CastError::NeedViaPtr => "a raw pointer",
 263                             CastError::NeedViaThinPtr => "a thin pointer",
 264                             _ => bug!(),
 265                         }
 266                     ));
 267                 }
 268                 err.emit();
 269             }
 270             CastError::NeedViaInt => {
 271                 make_invalid_casting_error(
 272                     fcx.tcx.sess,
 273                     self.span,
 274                     self.expr_ty,
 275                     self.cast_ty,
 276                     fcx,
 277                 )
 278                 .help(&format!(
 279                     "cast through {} first",
 280                     match e {
 281                         CastError::NeedViaInt => "an integer",
 282                         _ => bug!(),
 283                     }
 284                 ))
 285                 .emit();
 286             }
 287             CastError::IllegalCast => {
 288                 make_invalid_casting_error(
 289                     fcx.tcx.sess,
 290                     self.span,
 291                     self.expr_ty,
 292                     self.cast_ty,
 293                     fcx,
 294                 )
 295                 .emit();
 296             }
 297             CastError::DifferingKinds => {
 298                 make_invalid_casting_error(
 299                     fcx.tcx.sess,
 300                     self.span,
 301                     self.expr_ty,
 302                     self.cast_ty,
 303                     fcx,
 304                 )
 305                 .note("vtable kinds may not match")
 306                 .emit();
 307             }
 308             CastError::CastToBool => {
 309                 let mut err =
 310                     struct_span_err!(fcx.tcx.sess, self.span, E0054, "cannot cast as `bool`");
 311
 312                 if self.expr_ty.is_numeric() {
 313                     match fcx.tcx.sess.source_map().span_to_snippet(self.expr.span) {
 314                         Ok(snippet) => {
 315                             err.span_suggestion(
 316                                 self.span,
 317                                 "compare with zero instead",
 318                                 format!("{} != 0", snippet),
 319                                 Applicability::MachineApplicable,
 320                             );
 321                         }
 322                         Err(_) => {
 323                             err.span_help(self.span, "compare with zero instead");
 324                         }
 325                     }
 326                 } else {
 327                     err.span_label(self.span, "unsupported cast");
 328                 }
 329
 330                 err.emit();
 331             }
 332             CastError::CastToChar => {
 333                 type_error_struct!(
 334                     fcx.tcx.sess,
 335                     self.span,
 336                     self.expr_ty,
 337                     E0604,
 338                     "only `u8` can be cast as `char`, not `{}`",
 339                     self.expr_ty
 340                 )
 341                 .emit();
 342             }
 343             CastError::NonScalar => {
 344                 type_error_struct!(
 345                     fcx.tcx.sess,
 346                     self.span,
 347                     self.expr_ty,
 348                     E0605,
 349                     "non-primitive cast: `{}` as `{}`",
 350                     self.expr_ty,
 351                     fcx.ty_to_string(self.cast_ty)
 352                 )
 353                 .note(
 354                     "an `as` expression can only be used to convert between \
 355                                          primitive types. Consider using the `From` trait",
 356                 )
 357                 .emit();
 358             }
 359             CastError::SizedUnsizedCast => {
 360                 use crate::structured_errors::{SizedUnsizedCastError, StructuredDiagnostic};
 361                 SizedUnsizedCastError::new(
 362                     &fcx.tcx.sess,
 363                     self.span,
 364                     self.expr_ty,
 365                     fcx.ty_to_string(self.cast_ty),
 366                 )
 367                 .diagnostic()
 368                 .emit();
 369             }
 370             CastError::UnknownCastPtrKind | CastError::UnknownExprPtrKind => {
 371                 let unknown_cast_to = match e {
 372                     CastError::UnknownCastPtrKind => true,
 373                     CastError::UnknownExprPtrKind => false,
 374                     _ => bug!(),
 375                 };
 376                 let mut err = struct_span_err!(
 377                     fcx.tcx.sess,
 378                     self.span,
 379                     E0641,
 380                     "cannot cast {} a pointer of an unknown kind",
 381                     if unknown_cast_to { "to" } else { "from" }
 382                 );
 383                 err.note(
 384                     "The type information given here is insufficient to check whether \
 385                           the pointer cast is valid",
 386                 );
 387                 if unknown_cast_to {
 388                     err.span_suggestion_short(
 389                         self.cast_span,
 390                         "consider giving more type information",
 391                         String::new(),
 392                         Applicability::Unspecified,
 393                     );
 394                 }
 395                 err.emit();
 396             }
 397         }
 398     }
 399
 400     fn report_cast_to_unsized_type(&self, fcx: &FnCtxt<'a, 'tcx>) {
 401         if self.cast_ty.references_error() || self.expr_ty.references_error() {
 402             return;
 403         }
 404
 405         let tstr = fcx.ty_to_string(self.cast_ty);
 406         let mut err = type_error_struct!(
 407             fcx.tcx.sess,
 408             self.span,
 409             self.expr_ty,
 410             E0620,
 411             "cast to unsized type: `{}` as `{}`",
 412             fcx.resolve_vars_if_possible(&self.expr_ty),
 413             tstr
 414         );
 415         match self.expr_ty.kind {
 416             ty::Ref(_, _, mt) => {
 417                 let mtstr = mt.prefix_str();
 418                 if self.cast_ty.is_trait() {
 419                     match fcx.tcx.sess.source_map().span_to_snippet(self.cast_span) {
 420                         Ok(s) => {
 421                             err.span_suggestion(
 422                                 self.cast_span,
 423                                 "try casting to a reference instead",
 424                                 format!("&{}{}", mtstr, s),
 425                                 Applicability::MachineApplicable,
 426                             );
 427                         }
 428                         Err(_) => {
 429                             let msg = &format!("did you mean `&{}{}`?", mtstr, tstr);
 430                             err.span_help(self.cast_span, msg);
 431                         }
 432                     }
 433                 } else {
 434                     let msg = &format!(
 435                         "consider using an implicit coercion to `&{}{}` instead",
 436                         mtstr, tstr
 437                     );
 438                     err.span_help(self.span, msg);
 439                 }
 440             }
 441             ty::Adt(def, ..) if def.is_box() => {
 442                 match fcx.tcx.sess.source_map().span_to_snippet(self.cast_span) {
 443                     Ok(s) => {
 444                         err.span_suggestion(
 445                             self.cast_span,
 446                             "try casting to a `Box` instead",
 447                             format!("Box<{}>", s),
 448                             Applicability::MachineApplicable,
 449                         );
 450                     }
 451                     Err(_) => {
 452                         err.span_help(self.cast_span, &format!("did you mean `Box<{}>`?", tstr));
 453                     }
 454                 }
 455             }
 456             _ => {
 457                 err.span_help(self.expr.span, "consider using a box or reference as appropriate");
 458             }
 459         }
 460         err.emit();
 461     }
 462
 463     fn trivial_cast_lint(&self, fcx: &FnCtxt<'a, 'tcx>) {
 464         let t_cast = self.cast_ty;
 465         let t_expr = self.expr_ty;
 466         let type_asc_or =
 467             if fcx.tcx.features().type_ascription { "type ascription or " } else { "" };
 468         let (adjective, lint) = if t_cast.is_numeric() && t_expr.is_numeric() {
 469             ("numeric ", lint::builtin::TRIVIAL_NUMERIC_CASTS)
 470         } else {
 471             ("", lint::builtin::TRIVIAL_CASTS)
 472         };
 473         let mut err = fcx.tcx.struct_span_lint_hir(
 474             lint,
 475             self.expr.hir_id,
 476             self.span,
 477             &format!(
 478                 "trivial {}cast: `{}` as `{}`",
 479                 adjective,
 480                 fcx.ty_to_string(t_expr),
 481                 fcx.ty_to_string(t_cast)
 482             ),
 483         );
 484         err.help(&format!(
 485             "cast can be replaced by coercion; this might \
 486                            require {}a temporary variable",
 487             type_asc_or
 488         ));
 489         err.emit();
 490     }
 491
 492     pub fn check(mut self, fcx: &FnCtxt<'a, 'tcx>) {
 493         self.expr_ty = fcx.structurally_resolved_type(self.span, self.expr_ty);
 494         self.cast_ty = fcx.structurally_resolved_type(self.span, self.cast_ty);
 495
 496         debug!("check_cast({}, {:?} as {:?})", self.expr.hir_id, self.expr_ty, self.cast_ty);
 497
 498         if !fcx.type_is_known_to_be_sized_modulo_regions(self.cast_ty, self.span) {
 499             self.report_cast_to_unsized_type(fcx);
 500         } else if self.expr_ty.references_error() || self.cast_ty.references_error() {
 501             // No sense in giving duplicate error messages
 502         } else {
 503             match self.try_coercion_cast(fcx) {
 504                 Ok(()) => {
 505                     self.trivial_cast_lint(fcx);
 506                     debug!(" -> CoercionCast");
 507                     fcx.tables.borrow_mut().set_coercion_cast(self.expr.hir_id.local_id);
 508                 }
 509                 Err(ty::error::TypeError::ObjectUnsafeCoercion(did)) => {
 510                     self.report_object_unsafe_cast(&fcx, did);
 511                 }
 512                 Err(_) => {
 513                     match self.do_check(fcx) {
 514                         Ok(k) => {
 515                             debug!(" -> {:?}", k);
 516                         }
 517                         Err(e) => self.report_cast_error(fcx, e),
 518                     };
 519                 }
 520             };
 521         }
 522     }
 523
 524     fn report_object_unsafe_cast(&self, fcx: &FnCtxt<'a, 'tcx>, did: DefId) {
 525         let violations = object_safety_violations(fcx.tcx, did);
 526         let mut err = report_object_safety_error(fcx.tcx, self.cast_span, did, violations);
 527         err.note(&format!("required by cast to type '{}'", fcx.ty_to_string(self.cast_ty)));
 528         err.emit();
 529     }
 530
 531     /// Checks a cast, and report an error if one exists. In some cases, this
 532     /// can return Ok and create type errors in the fcx rather than returning
 533     /// directly. coercion-cast is handled in check instead of here.
 534     fn do_check(&self, fcx: &FnCtxt<'a, 'tcx>) -> Result<CastKind, CastError> {
 535         use rustc::ty::cast::CastTy::*;
 536         use rustc::ty::cast::IntTy::*;
 537
 538         let (t_from, t_cast) = match (CastTy::from_ty(self.expr_ty), CastTy::from_ty(self.cast_ty))
 539         {
 540             (Some(t_from), Some(t_cast)) => (t_from, t_cast),
 541             // Function item types may need to be reified before casts.
 542             (None, Some(t_cast)) => {
 543                 match self.expr_ty.kind {
 544                     ty::FnDef(..) => {
 545                         // Attempt a coercion to a fn pointer type.
 546                         let f = self.expr_ty.fn_sig(fcx.tcx);
 547                         let res = fcx.try_coerce(
 548                             self.expr,
 549                             self.expr_ty,
 550                             fcx.tcx.mk_fn_ptr(f),
 551                             AllowTwoPhase::No,
 552                         );
 553                         if let Err(TypeError::IntrinsicCast) = res {
 554                             return Err(CastError::IllegalCast);
 555                         }
 556                         if res.is_err() {
 557                             return Err(CastError::NonScalar);
 558                         }
 559                         (FnPtr, t_cast)
 560                     }
 561                     // Special case some errors for references, and check for
 562                     // array-ptr-casts. `Ref` is not a CastTy because the cast
 563                     // is split into a coercion to a pointer type, followed by
 564                     // a cast.
 565                     ty::Ref(_, inner_ty, mutbl) => {
 566                         return match t_cast {
 567                             Int(_) | Float => match inner_ty.kind {
 568                                 ty::Int(_)
 569                                 | ty::Uint(_)
 570                                 | ty::Float(_)
 571                                 | ty::Infer(ty::InferTy::IntVar(_))
 572                                 | ty::Infer(ty::InferTy::FloatVar(_)) => Err(CastError::NeedDeref),
 573                                 _ => Err(CastError::NeedViaPtr),
 574                             },
 575                             // array-ptr-cast
 576                             Ptr(mt) => {
 577                                 self.check_ref_cast(fcx, TypeAndMut { mutbl, ty: inner_ty }, mt)
 578                             }
 579                             _ => Err(CastError::NonScalar),
 580                         };
 581                     }
 582                     _ => return Err(CastError::NonScalar),
 583                 }
 584             }
 585             _ => return Err(CastError::NonScalar),
 586         };
 587
 588         match (t_from, t_cast) {
 589             // These types have invariants! can't cast into them.
 590             (_, Int(CEnum)) | (_, FnPtr) => Err(CastError::NonScalar),
 591
 592             // * -> Bool
 593             (_, Int(Bool)) => Err(CastError::CastToBool),
 594
 595             // * -> Char
 596             (Int(U(ast::UintTy::U8)), Int(Char)) => Ok(CastKind::U8CharCast), // u8-char-cast
 597             (_, Int(Char)) => Err(CastError::CastToChar),
 598
 599             // prim -> float,ptr
 600             (Int(Bool), Float) | (Int(CEnum), Float) | (Int(Char), Float) => {
 601                 Err(CastError::NeedViaInt)
 602             }
 603
 604             (Int(Bool), Ptr(_))
 605             | (Int(CEnum), Ptr(_))
 606             | (Int(Char), Ptr(_))
 607             | (Ptr(_), Float)
 608             | (FnPtr, Float)
 609             | (Float, Ptr(_)) => Err(CastError::IllegalCast),
 610
 611             // ptr -> *
 612             (Ptr(m_e), Ptr(m_c)) => self.check_ptr_ptr_cast(fcx, m_e, m_c), // ptr-ptr-cast
 613             (Ptr(m_expr), Int(_)) => self.check_ptr_addr_cast(fcx, m_expr), // ptr-addr-cast
 614             (FnPtr, Int(_)) => Ok(CastKind::FnPtrAddrCast),
 615
 616             // * -> ptr
 617             (Int(_), Ptr(mt)) => self.check_addr_ptr_cast(fcx, mt), // addr-ptr-cast
 618             (FnPtr, Ptr(mt)) => self.check_fptr_ptr_cast(fcx, mt),
 619
 620             // prim -> prim
 621             (Int(CEnum), Int(_)) => Ok(CastKind::EnumCast),
 622             (Int(Char), Int(_)) | (Int(Bool), Int(_)) => Ok(CastKind::PrimIntCast),
 623
 624             (Int(_), Int(_)) | (Int(_), Float) | (Float, Int(_)) | (Float, Float) => {
 625                 Ok(CastKind::NumericCast)
 626             }
 627         }
 628     }
 629
 630     fn check_ptr_ptr_cast(
 631         &self,
 632         fcx: &FnCtxt<'a, 'tcx>,
 633         m_expr: ty::TypeAndMut<'tcx>,
 634         m_cast: ty::TypeAndMut<'tcx>,
 635     ) -> Result<CastKind, CastError> {
 636         debug!("check_ptr_ptr_cast m_expr={:?} m_cast={:?}", m_expr, m_cast);
 637         // ptr-ptr cast. vtables must match.
 638
 639         let expr_kind = fcx.pointer_kind(m_expr.ty, self.span)?;
 640         let cast_kind = fcx.pointer_kind(m_cast.ty, self.span)?;
 641
 642         let cast_kind = match cast_kind {
 643             // We can't cast if target pointer kind is unknown
 644             None => return Err(CastError::UnknownCastPtrKind),
 645             Some(cast_kind) => cast_kind,
 646         };
 647
 648         // Cast to thin pointer is OK
 649         if cast_kind == PointerKind::Thin {
 650             return Ok(CastKind::PtrPtrCast);
 651         }
 652
 653         let expr_kind = match expr_kind {
 654             // We can't cast to fat pointer if source pointer kind is unknown
 655             None => return Err(CastError::UnknownExprPtrKind),
 656             Some(expr_kind) => expr_kind,
 657         };
 658
 659         // thin -> fat? report invalid cast (don't complain about vtable kinds)
 660         if expr_kind == PointerKind::Thin {
 661             return Err(CastError::SizedUnsizedCast);
 662         }
 663
 664         // vtable kinds must match
 665         if cast_kind == expr_kind {
 666             Ok(CastKind::PtrPtrCast)
 667         } else {
 668             Err(CastError::DifferingKinds)
 669         }
 670     }
 671
 672     fn check_fptr_ptr_cast(
 673         &self,
 674         fcx: &FnCtxt<'a, 'tcx>,
 675         m_cast: ty::TypeAndMut<'tcx>,
 676     ) -> Result<CastKind, CastError> {
 677         // fptr-ptr cast. must be to thin ptr
 678
 679         match fcx.pointer_kind(m_cast.ty, self.span)? {
 680             None => Err(CastError::UnknownCastPtrKind),
 681             Some(PointerKind::Thin) => Ok(CastKind::FnPtrPtrCast),
 682             _ => Err(CastError::IllegalCast),
 683         }
 684     }
 685
 686     fn check_ptr_addr_cast(
 687         &self,
 688         fcx: &FnCtxt<'a, 'tcx>,
 689         m_expr: ty::TypeAndMut<'tcx>,
 690     ) -> Result<CastKind, CastError> {
 691         // ptr-addr cast. must be from thin ptr
 692
 693         match fcx.pointer_kind(m_expr.ty, self.span)? {
 694             None => Err(CastError::UnknownExprPtrKind),
 695             Some(PointerKind::Thin) => Ok(CastKind::PtrAddrCast),
 696             _ => Err(CastError::NeedViaThinPtr),
 697         }
 698     }
 699
 700     fn check_ref_cast(
 701         &self,
 702         fcx: &FnCtxt<'a, 'tcx>,
 703         m_expr: ty::TypeAndMut<'tcx>,
 704         m_cast: ty::TypeAndMut<'tcx>,
 705     ) -> Result<CastKind, CastError> {
 706         // array-ptr-cast.
 707
 708         if m_expr.mutbl == hir::Mutability::Not && m_cast.mutbl == hir::Mutability::Not {
 709             if let ty::Array(ety, _) = m_expr.ty.kind {
 710                 // Due to the limitations of LLVM global constants,
 711                 // region pointers end up pointing at copies of
 712                 // vector elements instead of the original values.
 713                 // To allow raw pointers to work correctly, we
 714                 // need to special-case obtaining a raw pointer
 715                 // from a region pointer to a vector.
 716
 717                 // Coerce to a raw pointer so that we generate AddressOf in MIR.
 718                 let array_ptr_type = fcx.tcx.mk_ptr(m_expr);
 719                 fcx.try_coerce(self.expr, self.expr_ty, array_ptr_type, AllowTwoPhase::No)
 720                     .unwrap_or_else(|_| bug!(
 721                         "could not cast from reference to array to pointer to array ({:?} to {:?})",
 722                         self.expr_ty,
 723                         array_ptr_type,
 724                     ));
 725
 726                 // this will report a type mismatch if needed
 727                 fcx.demand_eqtype(self.span, ety, m_cast.ty);
 728                 return Ok(CastKind::ArrayPtrCast);
 729             }
 730         }
 731
 732         Err(CastError::IllegalCast)
 733     }
 734
 735     fn check_addr_ptr_cast(
 736         &self,
 737         fcx: &FnCtxt<'a, 'tcx>,
 738         m_cast: TypeAndMut<'tcx>,
 739     ) -> Result<CastKind, CastError> {
 740         // ptr-addr cast. pointer must be thin.
 741         match fcx.pointer_kind(m_cast.ty, self.span)? {
 742             None => Err(CastError::UnknownCastPtrKind),
 743             Some(PointerKind::Thin) => Ok(CastKind::AddrPtrCast),
 744             _ => Err(CastError::IllegalCast),
 745         }
 746     }
 747
 748     fn try_coercion_cast(&self, fcx: &FnCtxt<'a, 'tcx>) -> Result<(), ty::error::TypeError<'_>> {
 749         match fcx.try_coerce(self.expr, self.expr_ty, self.cast_ty, AllowTwoPhase::No) {
 750             Ok(_) => Ok(()),
 751             Err(err) => Err(err),
 752         }
 753     }
 754 }
 755
 756 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 757     fn type_is_known_to_be_sized_modulo_regions(&self, ty: Ty<'tcx>, span: Span) -> bool {
 758         let lang_item = self.tcx.require_lang_item(lang_items::SizedTraitLangItem, None);
 759         traits::type_known_to_meet_bound_modulo_regions(self, self.param_env, ty, lang_item, span)
 760     }
 761 }