compiler/rustc_typeck/src/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::type_error_struct;
  35 use hir::def_id::LOCAL_CRATE;
  36 use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder, ErrorGuaranteed};
  37 use rustc_hir as hir;
  38 use rustc_hir::lang_items::LangItem;
  39 use rustc_middle::mir::Mutability;
  40 use rustc_middle::ty::adjustment::AllowTwoPhase;
  41 use rustc_middle::ty::cast::{CastKind, CastTy};
  42 use rustc_middle::ty::error::TypeError;
  43 use rustc_middle::ty::subst::SubstsRef;
  44 use rustc_middle::ty::{self, Ty, TypeAndMut, TypeVisitable, VariantDef};
  45 use rustc_session::lint;
  46 use rustc_session::Session;
  47 use rustc_span::symbol::sym;
  48 use rustc_span::Span;
  49 use rustc_trait_selection::infer::InferCtxtExt;
  50 use rustc_trait_selection::traits;
  51 use rustc_trait_selection::traits::error_reporting::report_object_safety_error;
  52
  53 /// Reifies a cast check to be checked once we have full type information for
  54 /// a function context.
  55 #[derive(Debug)]
  56 pub struct CastCheck<'tcx> {
  57     expr: &'tcx hir::Expr<'tcx>,
  58     expr_ty: Ty<'tcx>,
  59     expr_span: Span,
  60     cast_ty: Ty<'tcx>,
  61     cast_span: Span,
  62     span: Span,
  63 }
  64
  65 /// The kind of pointer and associated metadata (thin, length or vtable) - we
  66 /// only allow casts between fat pointers if their metadata have the same
  67 /// kind.
  68 #[derive(Copy, Clone, PartialEq, Eq)]
  69 enum PointerKind<'tcx> {
  70     /// No metadata attached, ie pointer to sized type or foreign type
  71     Thin,
  72     /// A trait object
  73     VTable(Option<DefId>),
  74     /// Slice
  75     Length,
  76     /// The unsize info of this projection
  77     OfProjection(&'tcx ty::ProjectionTy<'tcx>),
  78     /// The unsize info of this opaque ty
  79     OfOpaque(DefId, SubstsRef<'tcx>),
  80     /// The unsize info of this parameter
  81     OfParam(&'tcx ty::ParamTy),
  82 }
  83
  84 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  85     /// Returns the kind of unsize information of t, or None
  86     /// if t is unknown.
  87     fn pointer_kind(
  88         &self,
  89         t: Ty<'tcx>,
  90         span: Span,
  91     ) -> Result<Option<PointerKind<'tcx>>, ErrorGuaranteed> {
  92         debug!("pointer_kind({:?}, {:?})", t, span);
  93
  94         let t = self.resolve_vars_if_possible(t);
  95
  96         if let Some(reported) = t.error_reported() {
  97             return Err(reported);
  98         }
  99
 100         if self.type_is_known_to_be_sized_modulo_regions(t, span) {
 101             return Ok(Some(PointerKind::Thin));
 102         }
 103
 104         Ok(match *t.kind() {
 105             ty::Slice(_) | ty::Str => Some(PointerKind::Length),
 106             ty::Dynamic(ref tty, ..) => Some(PointerKind::VTable(tty.principal_def_id())),
 107             ty::Adt(def, substs) if def.is_struct() => match def.non_enum_variant().fields.last() {
 108                 None => Some(PointerKind::Thin),
 109                 Some(f) => {
 110                     let field_ty = self.field_ty(span, f, substs);
 111                     self.pointer_kind(field_ty, span)?
 112                 }
 113             },
 114             ty::Tuple(fields) => match fields.last() {
 115                 None => Some(PointerKind::Thin),
 116                 Some(&f) => self.pointer_kind(f, span)?,
 117             },
 118
 119             // Pointers to foreign types are thin, despite being unsized
 120             ty::Foreign(..) => Some(PointerKind::Thin),
 121             // We should really try to normalize here.
 122             ty::Projection(ref pi) => Some(PointerKind::OfProjection(pi)),
 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                 let reported = self
 145                     .tcx
 146                     .sess
 147                     .delay_span_bug(span, &format!("`{:?}` should be sized but is not?", t));
 148                 return Err(reported);
 149             }
 150         })
 151     }
 152 }
 153
 154 #[derive(Copy, Clone)]
 155 pub enum CastError {
 156     ErrorGuaranteed,
 157
 158     CastToBool,
 159     CastToChar,
 160     DifferingKinds,
 161     /// Cast of thin to fat raw ptr (e.g., `*const () as *const [u8]`).
 162     SizedUnsizedCast,
 163     IllegalCast,
 164     NeedDeref,
 165     NeedViaPtr,
 166     NeedViaThinPtr,
 167     NeedViaInt,
 168     NonScalar,
 169     UnknownExprPtrKind,
 170     UnknownCastPtrKind,
 171     /// Cast of int to (possibly) fat raw pointer.
 172     ///
 173     /// Argument is the specific name of the metadata in plain words, such as "a vtable"
 174     /// or "a length". If this argument is None, then the metadata is unknown, for example,
 175     /// when we're typechecking a type parameter with a ?Sized bound.
 176     IntToFatCast(Option<&'static str>),
 177     ForeignNonExhaustiveAdt,
 178 }
 179
 180 impl From<ErrorGuaranteed> for CastError {
 181     fn from(_: ErrorGuaranteed) -> Self {
 182         CastError::ErrorGuaranteed
 183     }
 184 }
 185
 186 fn make_invalid_casting_error<'a, 'tcx>(
 187     sess: &'a Session,
 188     span: Span,
 189     expr_ty: Ty<'tcx>,
 190     cast_ty: Ty<'tcx>,
 191     fcx: &FnCtxt<'a, 'tcx>,
 192 ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
 193     type_error_struct!(
 194         sess,
 195         span,
 196         expr_ty,
 197         E0606,
 198         "casting `{}` as `{}` is invalid",
 199         fcx.ty_to_string(expr_ty),
 200         fcx.ty_to_string(cast_ty)
 201     )
 202 }
 203
 204 impl<'a, 'tcx> CastCheck<'tcx> {
 205     pub fn new(
 206         fcx: &FnCtxt<'a, 'tcx>,
 207         expr: &'tcx hir::Expr<'tcx>,
 208         expr_ty: Ty<'tcx>,
 209         cast_ty: Ty<'tcx>,
 210         cast_span: Span,
 211         span: Span,
 212     ) -> Result<CastCheck<'tcx>, ErrorGuaranteed> {
 213         let expr_span = expr.span.find_ancestor_inside(span).unwrap_or(expr.span);
 214         let check = CastCheck { expr, expr_ty, expr_span, cast_ty, cast_span, span };
 215
 216         // For better error messages, check for some obviously unsized
 217         // cases now. We do a more thorough check at the end, once
 218         // inference is more completely known.
 219         match cast_ty.kind() {
 220             ty::Dynamic(..) | ty::Slice(..) => {
 221                 let reported = check.report_cast_to_unsized_type(fcx);
 222                 Err(reported)
 223             }
 224             _ => Ok(check),
 225         }
 226     }
 227
 228     fn report_cast_error(&self, fcx: &FnCtxt<'a, 'tcx>, e: CastError) {
 229         match e {
 230             CastError::ErrorGuaranteed => {
 231                 // an error has already been reported
 232             }
 233             CastError::NeedDeref => {
 234                 let error_span = self.span;
 235                 let mut err = make_invalid_casting_error(
 236                     fcx.tcx.sess,
 237                     self.span,
 238                     self.expr_ty,
 239                     self.cast_ty,
 240                     fcx,
 241                 );
 242                 let cast_ty = fcx.ty_to_string(self.cast_ty);
 243                 err.span_label(
 244                     error_span,
 245                     format!("cannot cast `{}` as `{}`", fcx.ty_to_string(self.expr_ty), cast_ty),
 246                 );
 247                 if let Ok(snippet) = fcx.sess().source_map().span_to_snippet(self.expr_span) {
 248                     err.span_suggestion(
 249                         self.expr_span,
 250                         "dereference the expression",
 251                         format!("*{}", snippet),
 252                         Applicability::MaybeIncorrect,
 253                     );
 254                 } else {
 255                     err.span_help(self.expr_span, "dereference the expression with `*`");
 256                 }
 257                 err.emit();
 258             }
 259             CastError::NeedViaThinPtr | CastError::NeedViaPtr => {
 260                 let mut err = make_invalid_casting_error(
 261                     fcx.tcx.sess,
 262                     self.span,
 263                     self.expr_ty,
 264                     self.cast_ty,
 265                     fcx,
 266                 );
 267                 if self.cast_ty.is_integral() {
 268                     err.help(&format!(
 269                         "cast through {} first",
 270                         match e {
 271                             CastError::NeedViaPtr => "a raw pointer",
 272                             CastError::NeedViaThinPtr => "a thin pointer",
 273                             _ => bug!(),
 274                         }
 275                     ));
 276                 }
 277                 err.emit();
 278             }
 279             CastError::NeedViaInt => {
 280                 make_invalid_casting_error(
 281                     fcx.tcx.sess,
 282                     self.span,
 283                     self.expr_ty,
 284                     self.cast_ty,
 285                     fcx,
 286                 )
 287                 .help(&format!(
 288                     "cast through {} first",
 289                     match e {
 290                         CastError::NeedViaInt => "an integer",
 291                         _ => bug!(),
 292                     }
 293                 ))
 294                 .emit();
 295             }
 296             CastError::IllegalCast => {
 297                 make_invalid_casting_error(
 298                     fcx.tcx.sess,
 299                     self.span,
 300                     self.expr_ty,
 301                     self.cast_ty,
 302                     fcx,
 303                 )
 304                 .emit();
 305             }
 306             CastError::DifferingKinds => {
 307                 make_invalid_casting_error(
 308                     fcx.tcx.sess,
 309                     self.span,
 310                     self.expr_ty,
 311                     self.cast_ty,
 312                     fcx,
 313                 )
 314                 .note("vtable kinds may not match")
 315                 .emit();
 316             }
 317             CastError::CastToBool => {
 318                 let mut err =
 319                     struct_span_err!(fcx.tcx.sess, self.span, E0054, "cannot cast as `bool`");
 320
 321                 if self.expr_ty.is_numeric() {
 322                     match fcx.tcx.sess.source_map().span_to_snippet(self.expr_span) {
 323                         Ok(snippet) => {
 324                             err.span_suggestion(
 325                                 self.span,
 326                                 "compare with zero instead",
 327                                 format!("{snippet} != 0"),
 328                                 Applicability::MachineApplicable,
 329                             );
 330                         }
 331                         Err(_) => {
 332                             err.span_help(self.span, "compare with zero instead");
 333                         }
 334                     }
 335                 } else {
 336                     err.span_label(self.span, "unsupported cast");
 337                 }
 338
 339                 err.emit();
 340             }
 341             CastError::CastToChar => {
 342                 let mut err = type_error_struct!(
 343                     fcx.tcx.sess,
 344                     self.span,
 345                     self.expr_ty,
 346                     E0604,
 347                     "only `u8` can be cast as `char`, not `{}`",
 348                     self.expr_ty
 349                 );
 350                 err.span_label(self.span, "invalid cast");
 351                 if self.expr_ty.is_numeric() {
 352                     if self.expr_ty == fcx.tcx.types.u32 {
 353                         match fcx.tcx.sess.source_map().span_to_snippet(self.expr.span) {
 354                             Ok(snippet) => err.span_suggestion(
 355                                 self.span,
 356                                 "try `char::from_u32` instead",
 357                                 format!("char::from_u32({snippet})"),
 358                                 Applicability::MachineApplicable,
 359                             ),
 360
 361                             Err(_) => err.span_help(self.span, "try `char::from_u32` instead"),
 362                         };
 363                     } else if self.expr_ty == fcx.tcx.types.i8 {
 364                         err.span_help(self.span, "try casting from `u8` instead");
 365                     } else {
 366                         err.span_help(self.span, "try `char::from_u32` instead (via a `u32`)");
 367                     };
 368                 }
 369                 err.emit();
 370             }
 371             CastError::NonScalar => {
 372                 let mut err = type_error_struct!(
 373                     fcx.tcx.sess,
 374                     self.span,
 375                     self.expr_ty,
 376                     E0605,
 377                     "non-primitive cast: `{}` as `{}`",
 378                     self.expr_ty,
 379                     fcx.ty_to_string(self.cast_ty)
 380                 );
 381                 let mut sugg = None;
 382                 let mut sugg_mutref = false;
 383                 if let ty::Ref(reg, cast_ty, mutbl) = *self.cast_ty.kind() {
 384                     if let ty::RawPtr(TypeAndMut { ty: expr_ty, .. }) = *self.expr_ty.kind()
 385                         && fcx
 386                             .try_coerce(
 387                                 self.expr,
 388                                 fcx.tcx.mk_ref(
 389                                     fcx.tcx.lifetimes.re_erased,
 390                                     TypeAndMut { ty: expr_ty, mutbl },
 391                                 ),
 392                                 self.cast_ty,
 393                                 AllowTwoPhase::No,
 394                                 None,
 395                             )
 396                             .is_ok()
 397                     {
 398                         sugg = Some((format!("&{}*", mutbl.prefix_str()), cast_ty == expr_ty));
 399                     } else if let ty::Ref(expr_reg, expr_ty, expr_mutbl) = *self.expr_ty.kind()
 400                         && expr_mutbl == Mutability::Not
 401                         && mutbl == Mutability::Mut
 402                         && fcx
 403                             .try_coerce(
 404                                 self.expr,
 405                                 fcx.tcx.mk_ref(
 406                                     expr_reg,
 407                                     TypeAndMut { ty: expr_ty, mutbl: Mutability::Mut },
 408                                 ),
 409                                 self.cast_ty,
 410                                 AllowTwoPhase::No,
 411                                 None,
 412                             )
 413                             .is_ok()
 414                     {
 415                         sugg_mutref = true;
 416                     }
 417
 418                     if !sugg_mutref
 419                         && sugg == None
 420                         && fcx
 421                             .try_coerce(
 422                                 self.expr,
 423                                 fcx.tcx.mk_ref(reg, TypeAndMut { ty: self.expr_ty, mutbl }),
 424                                 self.cast_ty,
 425                                 AllowTwoPhase::No,
 426                                 None,
 427                             )
 428                             .is_ok()
 429                     {
 430                         sugg = Some((format!("&{}", mutbl.prefix_str()), false));
 431                     }
 432                 } else if let ty::RawPtr(TypeAndMut { mutbl, .. }) = *self.cast_ty.kind()
 433                     && fcx
 434                         .try_coerce(
 435                             self.expr,
 436                             fcx.tcx.mk_ref(
 437                                 fcx.tcx.lifetimes.re_erased,
 438                                 TypeAndMut { ty: self.expr_ty, mutbl },
 439                             ),
 440                             self.cast_ty,
 441                             AllowTwoPhase::No,
 442                             None,
 443                         )
 444                         .is_ok()
 445                 {
 446                     sugg = Some((format!("&{}", mutbl.prefix_str()), false));
 447                 }
 448                 if sugg_mutref {
 449                     err.span_label(self.span, "invalid cast");
 450                     err.span_note(self.expr_span, "this reference is immutable");
 451                     err.span_note(self.cast_span, "trying to cast to a mutable reference type");
 452                 } else if let Some((sugg, remove_cast)) = sugg {
 453                     err.span_label(self.span, "invalid cast");
 454
 455                     let has_parens = fcx
 456                         .tcx
 457                         .sess
 458                         .source_map()
 459                         .span_to_snippet(self.expr_span)
 460                         .map_or(false, |snip| snip.starts_with('('));
 461
 462                     // Very crude check to see whether the expression must be wrapped
 463                     // in parentheses for the suggestion to work (issue #89497).
 464                     // Can/should be extended in the future.
 465                     let needs_parens =
 466                         !has_parens && matches!(self.expr.kind, hir::ExprKind::Cast(..));
 467
 468                     let mut suggestion = vec![(self.expr_span.shrink_to_lo(), sugg)];
 469                     if needs_parens {
 470                         suggestion[0].1 += "(";
 471                         suggestion.push((self.expr_span.shrink_to_hi(), ")".to_string()));
 472                     }
 473                     if remove_cast {
 474                         suggestion.push((
 475                             self.expr_span.shrink_to_hi().to(self.cast_span),
 476                             String::new(),
 477                         ));
 478                     }
 479
 480                     err.multipart_suggestion_verbose(
 481                         "consider borrowing the value",
 482                         suggestion,
 483                         Applicability::MachineApplicable,
 484                     );
 485                 } else if !matches!(
 486                     self.cast_ty.kind(),
 487                     ty::FnDef(..) | ty::FnPtr(..) | ty::Closure(..)
 488                 ) {
 489                     let mut label = true;
 490                     // Check `impl From<self.expr_ty> for self.cast_ty {}` for accurate suggestion:
 491                     if let Ok(snippet) = fcx.tcx.sess.source_map().span_to_snippet(self.expr_span)
 492                         && let Some(from_trait) = fcx.tcx.get_diagnostic_item(sym::From)
 493                     {
 494                         let ty = fcx.resolve_vars_if_possible(self.cast_ty);
 495                         // Erase regions to avoid panic in `prove_value` when calling
 496                         // `type_implements_trait`.
 497                         let ty = fcx.tcx.erase_regions(ty);
 498                         let expr_ty = fcx.resolve_vars_if_possible(self.expr_ty);
 499                         let expr_ty = fcx.tcx.erase_regions(expr_ty);
 500                         let ty_params = fcx.tcx.mk_substs_trait(expr_ty, &[]);
 501                         if fcx
 502                             .infcx
 503                             .type_implements_trait(from_trait, ty, ty_params, fcx.param_env)
 504                             .must_apply_modulo_regions()
 505                         {
 506                             label = false;
 507                             err.span_suggestion(
 508                                 self.span,
 509                                 "consider using the `From` trait instead",
 510                                 format!("{}::from({})", self.cast_ty, snippet),
 511                                 Applicability::MaybeIncorrect,
 512                             );
 513                         }
 514                     }
 515                     let msg = "an `as` expression can only be used to convert between primitive \
 516                                types or to coerce to a specific trait object";
 517                     if label {
 518                         err.span_label(self.span, msg);
 519                     } else {
 520                         err.note(msg);
 521                     }
 522                 } else {
 523                     err.span_label(self.span, "invalid cast");
 524                 }
 525                 err.emit();
 526             }
 527             CastError::SizedUnsizedCast => {
 528                 use crate::structured_errors::{SizedUnsizedCast, StructuredDiagnostic};
 529
 530                 SizedUnsizedCast {
 531                     sess: &fcx.tcx.sess,
 532                     span: self.span,
 533                     expr_ty: self.expr_ty,
 534                     cast_ty: fcx.ty_to_string(self.cast_ty),
 535                 }
 536                 .diagnostic()
 537                 .emit();
 538             }
 539             CastError::IntToFatCast(known_metadata) => {
 540                 let mut err = struct_span_err!(
 541                     fcx.tcx.sess,
 542                     self.cast_span,
 543                     E0606,
 544                     "cannot cast `{}` to a pointer that {} wide",
 545                     fcx.ty_to_string(self.expr_ty),
 546                     if known_metadata.is_some() { "is" } else { "may be" }
 547                 );
 548
 549                 err.span_label(
 550                     self.cast_span,
 551                     format!(
 552                         "creating a `{}` requires both an address and {}",
 553                         self.cast_ty,
 554                         known_metadata.unwrap_or("type-specific metadata"),
 555                     ),
 556                 );
 557
 558                 if fcx.tcx.sess.is_nightly_build() {
 559                     err.span_label(
 560                         self.expr_span,
 561                         "consider casting this expression to `*const ()`, \
 562                         then using `core::ptr::from_raw_parts`",
 563                     );
 564                 }
 565
 566                 err.emit();
 567             }
 568             CastError::UnknownCastPtrKind | CastError::UnknownExprPtrKind => {
 569                 let unknown_cast_to = match e {
 570                     CastError::UnknownCastPtrKind => true,
 571                     CastError::UnknownExprPtrKind => false,
 572                     _ => bug!(),
 573                 };
 574                 let mut err = struct_span_err!(
 575                     fcx.tcx.sess,
 576                     if unknown_cast_to { self.cast_span } else { self.span },
 577                     E0641,
 578                     "cannot cast {} a pointer of an unknown kind",
 579                     if unknown_cast_to { "to" } else { "from" }
 580                 );
 581                 if unknown_cast_to {
 582                     err.span_label(self.cast_span, "needs more type information");
 583                     err.note(
 584                         "the type information given here is insufficient to check whether \
 585                         the pointer cast is valid",
 586                     );
 587                 } else {
 588                     err.span_label(
 589                         self.span,
 590                         "the type information given here is insufficient to check whether \
 591                         the pointer cast is valid",
 592                     );
 593                 }
 594                 err.emit();
 595             }
 596             CastError::ForeignNonExhaustiveAdt => {
 597                 make_invalid_casting_error(
 598                     fcx.tcx.sess,
 599                     self.span,
 600                     self.expr_ty,
 601                     self.cast_ty,
 602                     fcx,
 603                 )
 604                 .note("cannot cast an enum with a non-exhaustive variant when it's defined in another crate")
 605                 .emit();
 606             }
 607         }
 608     }
 609
 610     fn report_cast_to_unsized_type(&self, fcx: &FnCtxt<'a, 'tcx>) -> ErrorGuaranteed {
 611         if let Some(reported) =
 612             self.cast_ty.error_reported().or_else(|| self.expr_ty.error_reported())
 613         {
 614             return reported;
 615         }
 616
 617         let tstr = fcx.ty_to_string(self.cast_ty);
 618         let mut err = type_error_struct!(
 619             fcx.tcx.sess,
 620             self.span,
 621             self.expr_ty,
 622             E0620,
 623             "cast to unsized type: `{}` as `{}`",
 624             fcx.resolve_vars_if_possible(self.expr_ty),
 625             tstr
 626         );
 627         match self.expr_ty.kind() {
 628             ty::Ref(_, _, mt) => {
 629                 let mtstr = mt.prefix_str();
 630                 if self.cast_ty.is_trait() {
 631                     match fcx.tcx.sess.source_map().span_to_snippet(self.cast_span) {
 632                         Ok(s) => {
 633                             err.span_suggestion(
 634                                 self.cast_span,
 635                                 "try casting to a reference instead",
 636                                 format!("&{}{}", mtstr, s),
 637                                 Applicability::MachineApplicable,
 638                             );
 639                         }
 640                         Err(_) => {
 641                             let msg = &format!("did you mean `&{}{}`?", mtstr, tstr);
 642                             err.span_help(self.cast_span, msg);
 643                         }
 644                     }
 645                 } else {
 646                     let msg =
 647                         &format!("consider using an implicit coercion to `&{mtstr}{tstr}` instead");
 648                     err.span_help(self.span, msg);
 649                 }
 650             }
 651             ty::Adt(def, ..) if def.is_box() => {
 652                 match fcx.tcx.sess.source_map().span_to_snippet(self.cast_span) {
 653                     Ok(s) => {
 654                         err.span_suggestion(
 655                             self.cast_span,
 656                             "you can cast to a `Box` instead",
 657                             format!("Box<{s}>"),
 658                             Applicability::MachineApplicable,
 659                         );
 660                     }
 661                     Err(_) => {
 662                         err.span_help(
 663                             self.cast_span,
 664                             &format!("you might have meant `Box<{tstr}>`"),
 665                         );
 666                     }
 667                 }
 668             }
 669             _ => {
 670                 err.span_help(self.expr_span, "consider using a box or reference as appropriate");
 671             }
 672         }
 673         err.emit()
 674     }
 675
 676     fn trivial_cast_lint(&self, fcx: &FnCtxt<'a, 'tcx>) {
 677         let t_cast = self.cast_ty;
 678         let t_expr = self.expr_ty;
 679         let type_asc_or =
 680             if fcx.tcx.features().type_ascription { "type ascription or " } else { "" };
 681         let (adjective, lint) = if t_cast.is_numeric() && t_expr.is_numeric() {
 682             ("numeric ", lint::builtin::TRIVIAL_NUMERIC_CASTS)
 683         } else {
 684             ("", lint::builtin::TRIVIAL_CASTS)
 685         };
 686         fcx.tcx.struct_span_lint_hir(lint, self.expr.hir_id, self.span, |err| {
 687             err.build(&format!(
 688                 "trivial {}cast: `{}` as `{}`",
 689                 adjective,
 690                 fcx.ty_to_string(t_expr),
 691                 fcx.ty_to_string(t_cast)
 692             ))
 693             .help(&format!(
 694                 "cast can be replaced by coercion; this might \
 695                                    require {type_asc_or}a temporary variable"
 696             ))
 697             .emit();
 698         });
 699     }
 700
 701     #[instrument(skip(fcx), level = "debug")]
 702     pub fn check(mut self, fcx: &FnCtxt<'a, 'tcx>) {
 703         self.expr_ty = fcx.structurally_resolved_type(self.expr_span, self.expr_ty);
 704         self.cast_ty = fcx.structurally_resolved_type(self.cast_span, self.cast_ty);
 705
 706         debug!("check_cast({}, {:?} as {:?})", self.expr.hir_id, self.expr_ty, self.cast_ty);
 707
 708         if !fcx.type_is_known_to_be_sized_modulo_regions(self.cast_ty, self.span)
 709             && !self.cast_ty.has_infer_types()
 710         {
 711             self.report_cast_to_unsized_type(fcx);
 712         } else if self.expr_ty.references_error() || self.cast_ty.references_error() {
 713             // No sense in giving duplicate error messages
 714         } else {
 715             match self.try_coercion_cast(fcx) {
 716                 Ok(()) => {
 717                     self.trivial_cast_lint(fcx);
 718                     debug!(" -> CoercionCast");
 719                     fcx.typeck_results.borrow_mut().set_coercion_cast(self.expr.hir_id.local_id);
 720                 }
 721                 Err(ty::error::TypeError::ObjectUnsafeCoercion(did)) => {
 722                     self.report_object_unsafe_cast(&fcx, did);
 723                 }
 724                 Err(_) => {
 725                     match self.do_check(fcx) {
 726                         Ok(k) => {
 727                             debug!(" -> {:?}", k);
 728                         }
 729                         Err(e) => self.report_cast_error(fcx, e),
 730                     };
 731                 }
 732             };
 733         }
 734     }
 735
 736     fn report_object_unsafe_cast(&self, fcx: &FnCtxt<'a, 'tcx>, did: DefId) {
 737         let violations = fcx.tcx.object_safety_violations(did);
 738         let mut err = report_object_safety_error(fcx.tcx, self.cast_span, did, violations);
 739         err.note(&format!("required by cast to type '{}'", fcx.ty_to_string(self.cast_ty)));
 740         err.emit();
 741     }
 742
 743     /// Checks a cast, and report an error if one exists. In some cases, this
 744     /// can return Ok and create type errors in the fcx rather than returning
 745     /// directly. coercion-cast is handled in check instead of here.
 746     pub fn do_check(&self, fcx: &FnCtxt<'a, 'tcx>) -> Result<CastKind, CastError> {
 747         use rustc_middle::ty::cast::CastTy::*;
 748         use rustc_middle::ty::cast::IntTy::*;
 749
 750         let (t_from, t_cast) = match (CastTy::from_ty(self.expr_ty), CastTy::from_ty(self.cast_ty))
 751         {
 752             (Some(t_from), Some(t_cast)) => (t_from, t_cast),
 753             // Function item types may need to be reified before casts.
 754             (None, Some(t_cast)) => {
 755                 match *self.expr_ty.kind() {
 756                     ty::FnDef(..) => {
 757                         // Attempt a coercion to a fn pointer type.
 758                         let f = fcx.normalize_associated_types_in(
 759                             self.expr_span,
 760                             self.expr_ty.fn_sig(fcx.tcx),
 761                         );
 762                         let res = fcx.try_coerce(
 763                             self.expr,
 764                             self.expr_ty,
 765                             fcx.tcx.mk_fn_ptr(f),
 766                             AllowTwoPhase::No,
 767                             None,
 768                         );
 769                         if let Err(TypeError::IntrinsicCast) = res {
 770                             return Err(CastError::IllegalCast);
 771                         }
 772                         if res.is_err() {
 773                             return Err(CastError::NonScalar);
 774                         }
 775                         (FnPtr, t_cast)
 776                     }
 777                     // Special case some errors for references, and check for
 778                     // array-ptr-casts. `Ref` is not a CastTy because the cast
 779                     // is split into a coercion to a pointer type, followed by
 780                     // a cast.
 781                     ty::Ref(_, inner_ty, mutbl) => {
 782                         return match t_cast {
 783                             Int(_) | Float => match *inner_ty.kind() {
 784                                 ty::Int(_)
 785                                 | ty::Uint(_)
 786                                 | ty::Float(_)
 787                                 | ty::Infer(ty::InferTy::IntVar(_) | ty::InferTy::FloatVar(_)) => {
 788                                     Err(CastError::NeedDeref)
 789                                 }
 790                                 _ => Err(CastError::NeedViaPtr),
 791                             },
 792                             // array-ptr-cast
 793                             Ptr(mt) => {
 794                                 self.check_ref_cast(fcx, TypeAndMut { mutbl, ty: inner_ty }, mt)
 795                             }
 796                             _ => Err(CastError::NonScalar),
 797                         };
 798                     }
 799                     _ => return Err(CastError::NonScalar),
 800                 }
 801             }
 802             _ => return Err(CastError::NonScalar),
 803         };
 804
 805         if let ty::Adt(adt_def, _) = *self.expr_ty.kind() {
 806             if adt_def.did().krate != LOCAL_CRATE {
 807                 if adt_def.variants().iter().any(VariantDef::is_field_list_non_exhaustive) {
 808                     return Err(CastError::ForeignNonExhaustiveAdt);
 809                 }
 810             }
 811         }
 812
 813         match (t_from, t_cast) {
 814             // These types have invariants! can't cast into them.
 815             (_, Int(CEnum) | FnPtr) => Err(CastError::NonScalar),
 816
 817             // * -> Bool
 818             (_, Int(Bool)) => Err(CastError::CastToBool),
 819
 820             // * -> Char
 821             (Int(U(ty::UintTy::U8)), Int(Char)) => Ok(CastKind::U8CharCast), // u8-char-cast
 822             (_, Int(Char)) => Err(CastError::CastToChar),
 823
 824             // prim -> float,ptr
 825             (Int(Bool) | Int(CEnum) | Int(Char), Float) => Err(CastError::NeedViaInt),
 826
 827             (Int(Bool) | Int(CEnum) | Int(Char) | Float, Ptr(_)) | (Ptr(_) | FnPtr, Float) => {
 828                 Err(CastError::IllegalCast)
 829             }
 830
 831             // ptr -> *
 832             (Ptr(m_e), Ptr(m_c)) => self.check_ptr_ptr_cast(fcx, m_e, m_c), // ptr-ptr-cast
 833
 834             // ptr-addr-cast
 835             (Ptr(m_expr), Int(t_c)) => {
 836                 self.lossy_provenance_ptr2int_lint(fcx, t_c);
 837                 self.check_ptr_addr_cast(fcx, m_expr)
 838             }
 839             (FnPtr, Int(_)) => {
 840                 // FIXME(#95489): there should eventually be a lint for these casts
 841                 Ok(CastKind::FnPtrAddrCast)
 842             }
 843             // addr-ptr-cast
 844             (Int(_), Ptr(mt)) => {
 845                 self.fuzzy_provenance_int2ptr_lint(fcx);
 846                 self.check_addr_ptr_cast(fcx, mt)
 847             }
 848             // fn-ptr-cast
 849             (FnPtr, Ptr(mt)) => self.check_fptr_ptr_cast(fcx, mt),
 850
 851             // prim -> prim
 852             (Int(CEnum), Int(_)) => {
 853                 self.cenum_impl_drop_lint(fcx);
 854                 Ok(CastKind::EnumCast)
 855             }
 856             (Int(Char) | Int(Bool), Int(_)) => Ok(CastKind::PrimIntCast),
 857
 858             (Int(_) | Float, Int(_) | Float) => Ok(CastKind::NumericCast),
 859         }
 860     }
 861
 862     fn check_ptr_ptr_cast(
 863         &self,
 864         fcx: &FnCtxt<'a, 'tcx>,
 865         m_expr: ty::TypeAndMut<'tcx>,
 866         m_cast: ty::TypeAndMut<'tcx>,
 867     ) -> Result<CastKind, CastError> {
 868         debug!("check_ptr_ptr_cast m_expr={:?} m_cast={:?}", m_expr, m_cast);
 869         // ptr-ptr cast. vtables must match.
 870
 871         let expr_kind = fcx.pointer_kind(m_expr.ty, self.span)?;
 872         let cast_kind = fcx.pointer_kind(m_cast.ty, self.span)?;
 873
 874         let Some(cast_kind) = cast_kind else {
 875             // We can't cast if target pointer kind is unknown
 876             return Err(CastError::UnknownCastPtrKind);
 877         };
 878
 879         // Cast to thin pointer is OK
 880         if cast_kind == PointerKind::Thin {
 881             return Ok(CastKind::PtrPtrCast);
 882         }
 883
 884         let Some(expr_kind) = expr_kind else {
 885             // We can't cast to fat pointer if source pointer kind is unknown
 886             return Err(CastError::UnknownExprPtrKind);
 887         };
 888
 889         // thin -> fat? report invalid cast (don't complain about vtable kinds)
 890         if expr_kind == PointerKind::Thin {
 891             return Err(CastError::SizedUnsizedCast);
 892         }
 893
 894         // vtable kinds must match
 895         if cast_kind == expr_kind {
 896             Ok(CastKind::PtrPtrCast)
 897         } else {
 898             Err(CastError::DifferingKinds)
 899         }
 900     }
 901
 902     fn check_fptr_ptr_cast(
 903         &self,
 904         fcx: &FnCtxt<'a, 'tcx>,
 905         m_cast: ty::TypeAndMut<'tcx>,
 906     ) -> Result<CastKind, CastError> {
 907         // fptr-ptr cast. must be to thin ptr
 908
 909         match fcx.pointer_kind(m_cast.ty, self.span)? {
 910             None => Err(CastError::UnknownCastPtrKind),
 911             Some(PointerKind::Thin) => Ok(CastKind::FnPtrPtrCast),
 912             _ => Err(CastError::IllegalCast),
 913         }
 914     }
 915
 916     fn check_ptr_addr_cast(
 917         &self,
 918         fcx: &FnCtxt<'a, 'tcx>,
 919         m_expr: ty::TypeAndMut<'tcx>,
 920     ) -> Result<CastKind, CastError> {
 921         // ptr-addr cast. must be from thin ptr
 922
 923         match fcx.pointer_kind(m_expr.ty, self.span)? {
 924             None => Err(CastError::UnknownExprPtrKind),
 925             Some(PointerKind::Thin) => Ok(CastKind::PtrAddrCast),
 926             _ => Err(CastError::NeedViaThinPtr),
 927         }
 928     }
 929
 930     fn check_ref_cast(
 931         &self,
 932         fcx: &FnCtxt<'a, 'tcx>,
 933         m_expr: ty::TypeAndMut<'tcx>,
 934         m_cast: ty::TypeAndMut<'tcx>,
 935     ) -> Result<CastKind, CastError> {
 936         // array-ptr-cast: allow mut-to-mut, mut-to-const, const-to-const
 937         if m_expr.mutbl == hir::Mutability::Mut || m_cast.mutbl == hir::Mutability::Not {
 938             if let ty::Array(ety, _) = m_expr.ty.kind() {
 939                 // Due to the limitations of LLVM global constants,
 940                 // region pointers end up pointing at copies of
 941                 // vector elements instead of the original values.
 942                 // To allow raw pointers to work correctly, we
 943                 // need to special-case obtaining a raw pointer
 944                 // from a region pointer to a vector.
 945
 946                 // Coerce to a raw pointer so that we generate AddressOf in MIR.
 947                 let array_ptr_type = fcx.tcx.mk_ptr(m_expr);
 948                 fcx.try_coerce(self.expr, self.expr_ty, array_ptr_type, AllowTwoPhase::No, None)
 949                     .unwrap_or_else(|_| {
 950                         bug!(
 951                         "could not cast from reference to array to pointer to array ({:?} to {:?})",
 952                         self.expr_ty,
 953                         array_ptr_type,
 954                     )
 955                     });
 956
 957                 // this will report a type mismatch if needed
 958                 fcx.demand_eqtype(self.span, *ety, m_cast.ty);
 959                 return Ok(CastKind::ArrayPtrCast);
 960             }
 961         }
 962
 963         Err(CastError::IllegalCast)
 964     }
 965
 966     fn check_addr_ptr_cast(
 967         &self,
 968         fcx: &FnCtxt<'a, 'tcx>,
 969         m_cast: TypeAndMut<'tcx>,
 970     ) -> Result<CastKind, CastError> {
 971         // ptr-addr cast. pointer must be thin.
 972         match fcx.pointer_kind(m_cast.ty, self.span)? {
 973             None => Err(CastError::UnknownCastPtrKind),
 974             Some(PointerKind::Thin) => Ok(CastKind::AddrPtrCast),
 975             Some(PointerKind::VTable(_)) => Err(CastError::IntToFatCast(Some("a vtable"))),
 976             Some(PointerKind::Length) => Err(CastError::IntToFatCast(Some("a length"))),
 977             Some(
 978                 PointerKind::OfProjection(_)
 979                 | PointerKind::OfOpaque(_, _)
 980                 | PointerKind::OfParam(_),
 981             ) => Err(CastError::IntToFatCast(None)),
 982         }
 983     }
 984
 985     fn try_coercion_cast(&self, fcx: &FnCtxt<'a, 'tcx>) -> Result<(), ty::error::TypeError<'tcx>> {
 986         match fcx.try_coerce(self.expr, self.expr_ty, self.cast_ty, AllowTwoPhase::No, None) {
 987             Ok(_) => Ok(()),
 988             Err(err) => Err(err),
 989         }
 990     }
 991
 992     fn cenum_impl_drop_lint(&self, fcx: &FnCtxt<'a, 'tcx>) {
 993         if let ty::Adt(d, _) = self.expr_ty.kind()
 994             && d.has_dtor(fcx.tcx)
 995         {
 996             fcx.tcx.struct_span_lint_hir(
 997                 lint::builtin::CENUM_IMPL_DROP_CAST,
 998                 self.expr.hir_id,
 999                 self.span,
1000                 |err| {
1001                     err.build(&format!(
1002                         "cannot cast enum `{}` into integer `{}` because it implements `Drop`",
1003                         self.expr_ty, self.cast_ty
1004                     ))
1005                     .emit();
1006                 },
1007             );
1008         }
1009     }
1010
1011     fn lossy_provenance_ptr2int_lint(&self, fcx: &FnCtxt<'a, 'tcx>, t_c: ty::cast::IntTy) {
1012         fcx.tcx.struct_span_lint_hir(
1013             lint::builtin::LOSSY_PROVENANCE_CASTS,
1014             self.expr.hir_id,
1015             self.span,
1016             |err| {
1017                 let mut err = err.build(&format!(
1018                     "under strict provenance it is considered bad style to cast pointer `{}` to integer `{}`",
1019                     self.expr_ty, self.cast_ty
1020                 ));
1021
1022                 let msg = "use `.addr()` to obtain the address of a pointer";
1023
1024                 let expr_prec = self.expr.precedence().order();
1025                 let needs_parens = expr_prec < rustc_ast::util::parser::PREC_POSTFIX;
1026
1027                 let scalar_cast = match t_c {
1028                     ty::cast::IntTy::U(ty::UintTy::Usize) => String::new(),
1029                     _ => format!(" as {}", self.cast_ty),
1030                 };
1031
1032                 let cast_span = self.expr_span.shrink_to_hi().to(self.cast_span);
1033
1034                 if needs_parens {
1035                     let suggestions = vec![
1036                         (self.expr_span.shrink_to_lo(), String::from("(")),
1037                         (cast_span, format!(").addr(){scalar_cast}")),
1038                     ];
1039
1040                     err.multipart_suggestion(msg, suggestions, Applicability::MaybeIncorrect);
1041                 } else {
1042                     err.span_suggestion(
1043                         cast_span,
1044                         msg,
1045                         format!(".addr(){scalar_cast}"),
1046                         Applicability::MaybeIncorrect,
1047                     );
1048                 }
1049
1050                 err.help(
1051                     "if you can't comply with strict provenance and need to expose the pointer \
1052                     provenance you can use `.expose_addr()` instead"
1053                 );
1054
1055                 err.emit();
1056             },
1057         );
1058     }
1059
1060     fn fuzzy_provenance_int2ptr_lint(&self, fcx: &FnCtxt<'a, 'tcx>) {
1061         fcx.tcx.struct_span_lint_hir(
1062             lint::builtin::FUZZY_PROVENANCE_CASTS,
1063             self.expr.hir_id,
1064             self.span,
1065             |err| {
1066                 let mut err = err.build(&format!(
1067                     "strict provenance disallows casting integer `{}` to pointer `{}`",
1068                     self.expr_ty, self.cast_ty
1069                 ));
1070                 let msg = "use `.with_addr()` to adjust a valid pointer in the same allocation, to this address";
1071                 let suggestions = vec![
1072                     (self.expr_span.shrink_to_lo(), String::from("(...).with_addr(")),
1073                     (self.expr_span.shrink_to_hi().to(self.cast_span), String::from(")")),
1074                 ];
1075
1076                 err.multipart_suggestion(msg, suggestions, Applicability::MaybeIncorrect);
1077                 err.help(
1078                     "if you can't comply with strict provenance and don't have a pointer with \
1079                     the correct provenance you can use `std::ptr::from_exposed_addr()` instead"
1080                  );
1081
1082                 err.emit();
1083             },
1084         );
1085     }
1086 }
1087
1088 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
1089     fn type_is_known_to_be_sized_modulo_regions(&self, ty: Ty<'tcx>, span: Span) -> bool {
1090         let lang_item = self.tcx.require_lang_item(LangItem::Sized, None);
1091         traits::type_known_to_meet_bound_modulo_regions(self, self.param_env, ty, lang_item, span)
1092     }
1093 }