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