compiler/rustc_hir_typeck/src/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::type_error_struct;
  34 use rustc_errors::{struct_span_err, Applicability, DelayDm, DiagnosticBuilder, ErrorGuaranteed};
  35 use rustc_hir as hir;
  36 use rustc_macros::{TypeFoldable, TypeVisitable};
  37 use rustc_middle::mir::Mutability;
  38 use rustc_middle::ty::adjustment::AllowTwoPhase;
  39 use rustc_middle::ty::cast::{CastKind, CastTy};
  40 use rustc_middle::ty::error::TypeError;
  41 use rustc_middle::ty::subst::SubstsRef;
  42 use rustc_middle::ty::{self, Ty, TypeAndMut, TypeVisitable, VariantDef};
  43 use rustc_session::lint;
  44 use rustc_session::Session;
  45 use rustc_span::def_id::{DefId, LOCAL_CRATE};
  46 use rustc_span::symbol::sym;
  47 use rustc_span::Span;
  48 use rustc_trait_selection::infer::InferCtxtExt;
  49
  50 /// Reifies a cast check to be checked once we have full type information for
  51 /// a function context.
  52 #[derive(Debug)]
  53 pub struct CastCheck<'tcx> {
  54     /// The expression whose value is being casted
  55     expr: &'tcx hir::Expr<'tcx>,
  56     /// The source type for the cast expression
  57     expr_ty: Ty<'tcx>,
  58     expr_span: Span,
  59     /// The target type. That is, the type we are casting to.
  60     cast_ty: Ty<'tcx>,
  61     cast_span: Span,
  62     span: Span,
  63     /// whether the cast is made in a const context or not.
  64     pub constness: hir::Constness,
  65 }
  66
  67 /// The kind of pointer and associated metadata (thin, length or vtable) - we
  68 /// only allow casts between fat pointers if their metadata have the same
  69 /// kind.
  70 #[derive(Debug, Copy, Clone, PartialEq, Eq, TypeVisitable, TypeFoldable)]
  71 enum PointerKind<'tcx> {
  72     /// No metadata attached, ie pointer to sized type or foreign type
  73     Thin,
  74     /// A trait object
  75     VTable(Option<DefId>),
  76     /// Slice
  77     Length,
  78     /// The unsize info of this projection
  79     OfProjection(ty::ProjectionTy<'tcx>),
  80     /// The unsize info of this opaque ty
  81     OfOpaque(DefId, SubstsRef<'tcx>),
  82     /// The unsize info of this parameter
  83     OfParam(ty::ParamTy),
  84 }
  85
  86 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  87     /// Returns the kind of unsize information of t, or None
  88     /// if t is unknown.
  89     fn pointer_kind(
  90         &self,
  91         t: Ty<'tcx>,
  92         span: Span,
  93     ) -> Result<Option<PointerKind<'tcx>>, ErrorGuaranteed> {
  94         debug!("pointer_kind({:?}, {:?})", t, span);
  95
  96         let t = self.resolve_vars_if_possible(t);
  97         t.error_reported()?;
  98
  99         if self.type_is_sized_modulo_regions(self.param_env, 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, _, ty::Dyn) => 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, 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(pi) => Some(PointerKind::OfProjection(pi)),
 122             ty::Opaque(def_id, substs) => Some(PointerKind::OfOpaque(def_id, substs)),
 123             ty::Param(p) => Some(PointerKind::OfParam(p)),
 124             // Insufficient type information.
 125             ty::Placeholder(..) | ty::Bound(..) | ty::Infer(_) => None,
 126
 127             ty::Bool
 128             | ty::Char
 129             | ty::Int(..)
 130             | ty::Uint(..)
 131             | ty::Float(_)
 132             | ty::Array(..)
 133             | ty::GeneratorWitness(..)
 134             | ty::RawPtr(_)
 135             | ty::Ref(..)
 136             | ty::FnDef(..)
 137             | ty::FnPtr(..)
 138             | ty::Closure(..)
 139             | ty::Generator(..)
 140             | ty::Adt(..)
 141             | ty::Never
 142             | ty::Dynamic(_, _, ty::DynStar)
 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         constness: hir::Constness,
 213     ) -> Result<CastCheck<'tcx>, ErrorGuaranteed> {
 214         let expr_span = expr.span.find_ancestor_inside(span).unwrap_or(expr.span);
 215         let check = CastCheck { expr, expr_ty, expr_span, cast_ty, cast_span, span, constness };
 216
 217         // For better error messages, check for some obviously unsized
 218         // cases now. We do a more thorough check at the end, once
 219         // inference is more completely known.
 220         match cast_ty.kind() {
 221             ty::Dynamic(_, _, ty::Dyn) | ty::Slice(..) => {
 222                 Err(check.report_cast_to_unsized_type(fcx))
 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                         if fcx
 501                             .infcx
 502                             .type_implements_trait(from_trait, [ty, expr_ty], fcx.param_env)
 503                             .must_apply_modulo_regions()
 504                         {
 505                             label = false;
 506                             err.span_suggestion(
 507                                 self.span,
 508                                 "consider using the `From` trait instead",
 509                                 format!("{}::from({})", self.cast_ty, snippet),
 510                                 Applicability::MaybeIncorrect,
 511                             );
 512                         }
 513                     }
 514                     let msg = "an `as` expression can only be used to convert between primitive \
 515                                types or to coerce to a specific trait object";
 516                     if label {
 517                         err.span_label(self.span, msg);
 518                     } else {
 519                         err.note(msg);
 520                     }
 521                 } else {
 522                     err.span_label(self.span, "invalid cast");
 523                 }
 524                 err.emit();
 525             }
 526             CastError::SizedUnsizedCast => {
 527                 use rustc_hir_analysis::structured_errors::{
 528                     SizedUnsizedCast, StructuredDiagnostic,
 529                 };
 530
 531                 SizedUnsizedCast {
 532                     sess: &fcx.tcx.sess,
 533                     span: self.span,
 534                     expr_ty: self.expr_ty,
 535                     cast_ty: fcx.ty_to_string(self.cast_ty),
 536                 }
 537                 .diagnostic()
 538                 .emit();
 539             }
 540             CastError::IntToFatCast(known_metadata) => {
 541                 let mut err = struct_span_err!(
 542                     fcx.tcx.sess,
 543                     self.cast_span,
 544                     E0606,
 545                     "cannot cast `{}` to a pointer that {} wide",
 546                     fcx.ty_to_string(self.expr_ty),
 547                     if known_metadata.is_some() { "is" } else { "may be" }
 548                 );
 549
 550                 err.span_label(
 551                     self.cast_span,
 552                     format!(
 553                         "creating a `{}` requires both an address and {}",
 554                         self.cast_ty,
 555                         known_metadata.unwrap_or("type-specific metadata"),
 556                     ),
 557                 );
 558
 559                 if fcx.tcx.sess.is_nightly_build() {
 560                     err.span_label(
 561                         self.expr_span,
 562                         "consider casting this expression to `*const ()`, \
 563                         then using `core::ptr::from_raw_parts`",
 564                     );
 565                 }
 566
 567                 err.emit();
 568             }
 569             CastError::UnknownCastPtrKind | CastError::UnknownExprPtrKind => {
 570                 let unknown_cast_to = match e {
 571                     CastError::UnknownCastPtrKind => true,
 572                     CastError::UnknownExprPtrKind => false,
 573                     _ => bug!(),
 574                 };
 575                 let mut err = struct_span_err!(
 576                     fcx.tcx.sess,
 577                     if unknown_cast_to { self.cast_span } else { self.span },
 578                     E0641,
 579                     "cannot cast {} a pointer of an unknown kind",
 580                     if unknown_cast_to { "to" } else { "from" }
 581                 );
 582                 if unknown_cast_to {
 583                     err.span_label(self.cast_span, "needs more type information");
 584                     err.note(
 585                         "the type information given here is insufficient to check whether \
 586                         the pointer cast is valid",
 587                     );
 588                 } else {
 589                     err.span_label(
 590                         self.span,
 591                         "the type information given here is insufficient to check whether \
 592                         the pointer cast is valid",
 593                     );
 594                 }
 595                 err.emit();
 596             }
 597             CastError::ForeignNonExhaustiveAdt => {
 598                 make_invalid_casting_error(
 599                     fcx.tcx.sess,
 600                     self.span,
 601                     self.expr_ty,
 602                     self.cast_ty,
 603                     fcx,
 604                 )
 605                 .note("cannot cast an enum with a non-exhaustive variant when it's defined in another crate")
 606                 .emit();
 607             }
 608         }
 609     }
 610
 611     fn report_cast_to_unsized_type(&self, fcx: &FnCtxt<'a, 'tcx>) -> ErrorGuaranteed {
 612         if let Err(err) = self.cast_ty.error_reported() {
 613             return err;
 614         }
 615         if let Err(err) = self.expr_ty.error_reported() {
 616             return err;
 617         }
 618
 619         let tstr = fcx.ty_to_string(self.cast_ty);
 620         let mut err = type_error_struct!(
 621             fcx.tcx.sess,
 622             self.span,
 623             self.expr_ty,
 624             E0620,
 625             "cast to unsized type: `{}` as `{}`",
 626             fcx.resolve_vars_if_possible(self.expr_ty),
 627             tstr
 628         );
 629         match self.expr_ty.kind() {
 630             ty::Ref(_, _, mt) => {
 631                 let mtstr = mt.prefix_str();
 632                 if self.cast_ty.is_trait() {
 633                     match fcx.tcx.sess.source_map().span_to_snippet(self.cast_span) {
 634                         Ok(s) => {
 635                             err.span_suggestion(
 636                                 self.cast_span,
 637                                 "try casting to a reference instead",
 638                                 format!("&{}{}", mtstr, s),
 639                                 Applicability::MachineApplicable,
 640                             );
 641                         }
 642                         Err(_) => {
 643                             let msg = &format!("did you mean `&{}{}`?", mtstr, tstr);
 644                             err.span_help(self.cast_span, msg);
 645                         }
 646                     }
 647                 } else {
 648                     let msg =
 649                         &format!("consider using an implicit coercion to `&{mtstr}{tstr}` instead");
 650                     err.span_help(self.span, msg);
 651                 }
 652             }
 653             ty::Adt(def, ..) if def.is_box() => {
 654                 match fcx.tcx.sess.source_map().span_to_snippet(self.cast_span) {
 655                     Ok(s) => {
 656                         err.span_suggestion(
 657                             self.cast_span,
 658                             "you can cast to a `Box` instead",
 659                             format!("Box<{s}>"),
 660                             Applicability::MachineApplicable,
 661                         );
 662                     }
 663                     Err(_) => {
 664                         err.span_help(
 665                             self.cast_span,
 666                             &format!("you might have meant `Box<{tstr}>`"),
 667                         );
 668                     }
 669                 }
 670             }
 671             _ => {
 672                 err.span_help(self.expr_span, "consider using a box or reference as appropriate");
 673             }
 674         }
 675         err.emit()
 676     }
 677
 678     fn trivial_cast_lint(&self, fcx: &FnCtxt<'a, 'tcx>) {
 679         let t_cast = self.cast_ty;
 680         let t_expr = self.expr_ty;
 681         let type_asc_or =
 682             if fcx.tcx.features().type_ascription { "type ascription or " } else { "" };
 683         let (adjective, lint) = if t_cast.is_numeric() && t_expr.is_numeric() {
 684             ("numeric ", lint::builtin::TRIVIAL_NUMERIC_CASTS)
 685         } else {
 686             ("", lint::builtin::TRIVIAL_CASTS)
 687         };
 688         fcx.tcx.struct_span_lint_hir(
 689             lint,
 690             self.expr.hir_id,
 691             self.span,
 692             DelayDm(|| {
 693                 format!(
 694                     "trivial {}cast: `{}` as `{}`",
 695                     adjective,
 696                     fcx.ty_to_string(t_expr),
 697                     fcx.ty_to_string(t_cast)
 698                 )
 699             }),
 700             |lint| {
 701                 lint.help(format!(
 702                     "cast can be replaced by coercion; this might \
 703                      require {type_asc_or}a temporary variable"
 704                 ))
 705             },
 706         );
 707     }
 708
 709     #[instrument(skip(fcx), level = "debug")]
 710     pub fn check(mut self, fcx: &FnCtxt<'a, 'tcx>) {
 711         self.expr_ty = fcx.structurally_resolved_type(self.expr_span, self.expr_ty);
 712         self.cast_ty = fcx.structurally_resolved_type(self.cast_span, self.cast_ty);
 713
 714         debug!("check_cast({}, {:?} as {:?})", self.expr.hir_id, self.expr_ty, self.cast_ty);
 715
 716         if !fcx.type_is_sized_modulo_regions(fcx.param_env, self.cast_ty, self.span)
 717             && !self.cast_ty.has_infer_types()
 718         {
 719             self.report_cast_to_unsized_type(fcx);
 720         } else if self.expr_ty.references_error() || self.cast_ty.references_error() {
 721             // No sense in giving duplicate error messages
 722         } else {
 723             match self.try_coercion_cast(fcx) {
 724                 Ok(()) => {
 725                     self.trivial_cast_lint(fcx);
 726                     debug!(" -> CoercionCast");
 727                     fcx.typeck_results.borrow_mut().set_coercion_cast(self.expr.hir_id.local_id);
 728                 }
 729                 Err(_) => {
 730                     match self.do_check(fcx) {
 731                         Ok(k) => {
 732                             debug!(" -> {:?}", k);
 733                         }
 734                         Err(e) => self.report_cast_error(fcx, e),
 735                     };
 736                 }
 737             };
 738         }
 739     }
 740     /// Checks a cast, and report an error if one exists. In some cases, this
 741     /// can return Ok and create type errors in the fcx rather than returning
 742     /// directly. coercion-cast is handled in check instead of here.
 743     pub fn do_check(&self, fcx: &FnCtxt<'a, 'tcx>) -> Result<CastKind, CastError> {
 744         use rustc_middle::ty::cast::CastTy::*;
 745         use rustc_middle::ty::cast::IntTy::*;
 746
 747         let (t_from, t_cast) = match (CastTy::from_ty(self.expr_ty), CastTy::from_ty(self.cast_ty))
 748         {
 749             (Some(t_from), Some(t_cast)) => (t_from, t_cast),
 750             // Function item types may need to be reified before casts.
 751             (None, Some(t_cast)) => {
 752                 match *self.expr_ty.kind() {
 753                     ty::FnDef(..) => {
 754                         // Attempt a coercion to a fn pointer type.
 755                         let f = fcx.normalize(self.expr_span, self.expr_ty.fn_sig(fcx.tcx));
 756                         let res = fcx.try_coerce(
 757                             self.expr,
 758                             self.expr_ty,
 759                             fcx.tcx.mk_fn_ptr(f),
 760                             AllowTwoPhase::No,
 761                             None,
 762                         );
 763                         if let Err(TypeError::IntrinsicCast) = res {
 764                             return Err(CastError::IllegalCast);
 765                         }
 766                         if res.is_err() {
 767                             return Err(CastError::NonScalar);
 768                         }
 769                         (FnPtr, t_cast)
 770                     }
 771                     // Special case some errors for references, and check for
 772                     // array-ptr-casts. `Ref` is not a CastTy because the cast
 773                     // is split into a coercion to a pointer type, followed by
 774                     // a cast.
 775                     ty::Ref(_, inner_ty, mutbl) => {
 776                         return match t_cast {
 777                             Int(_) | Float => match *inner_ty.kind() {
 778                                 ty::Int(_)
 779                                 | ty::Uint(_)
 780                                 | ty::Float(_)
 781                                 | ty::Infer(ty::InferTy::IntVar(_) | ty::InferTy::FloatVar(_)) => {
 782                                     Err(CastError::NeedDeref)
 783                                 }
 784                                 _ => Err(CastError::NeedViaPtr),
 785                             },
 786                             // array-ptr-cast
 787                             Ptr(mt) => {
 788                                 self.check_ref_cast(fcx, TypeAndMut { mutbl, ty: inner_ty }, mt)
 789                             }
 790                             _ => Err(CastError::NonScalar),
 791                         };
 792                     }
 793                     _ => return Err(CastError::NonScalar),
 794                 }
 795             }
 796             _ => return Err(CastError::NonScalar),
 797         };
 798
 799         if let ty::Adt(adt_def, _) = *self.expr_ty.kind() {
 800             if adt_def.did().krate != LOCAL_CRATE {
 801                 if adt_def.variants().iter().any(VariantDef::is_field_list_non_exhaustive) {
 802                     return Err(CastError::ForeignNonExhaustiveAdt);
 803                 }
 804             }
 805         }
 806
 807         match (t_from, t_cast) {
 808             // These types have invariants! can't cast into them.
 809             (_, Int(CEnum) | FnPtr) => Err(CastError::NonScalar),
 810
 811             // * -> Bool
 812             (_, Int(Bool)) => Err(CastError::CastToBool),
 813
 814             // * -> Char
 815             (Int(U(ty::UintTy::U8)), Int(Char)) => Ok(CastKind::U8CharCast), // u8-char-cast
 816             (_, Int(Char)) => Err(CastError::CastToChar),
 817
 818             // prim -> float,ptr
 819             (Int(Bool) | Int(CEnum) | Int(Char), Float) => Err(CastError::NeedViaInt),
 820
 821             (Int(Bool) | Int(CEnum) | Int(Char) | Float, Ptr(_)) | (Ptr(_) | FnPtr, Float) => {
 822                 Err(CastError::IllegalCast)
 823             }
 824
 825             // ptr -> *
 826             (Ptr(m_e), Ptr(m_c)) => self.check_ptr_ptr_cast(fcx, m_e, m_c), // ptr-ptr-cast
 827
 828             // ptr-addr-cast
 829             (Ptr(m_expr), Int(t_c)) => {
 830                 self.lossy_provenance_ptr2int_lint(fcx, t_c);
 831                 self.check_ptr_addr_cast(fcx, m_expr)
 832             }
 833             (FnPtr, Int(_)) => {
 834                 // FIXME(#95489): there should eventually be a lint for these casts
 835                 Ok(CastKind::FnPtrAddrCast)
 836             }
 837             // addr-ptr-cast
 838             (Int(_), Ptr(mt)) => {
 839                 self.fuzzy_provenance_int2ptr_lint(fcx);
 840                 self.check_addr_ptr_cast(fcx, mt)
 841             }
 842             // fn-ptr-cast
 843             (FnPtr, Ptr(mt)) => self.check_fptr_ptr_cast(fcx, mt),
 844
 845             // prim -> prim
 846             (Int(CEnum), Int(_)) => {
 847                 self.cenum_impl_drop_lint(fcx);
 848                 Ok(CastKind::EnumCast)
 849             }
 850             (Int(Char) | Int(Bool), Int(_)) => Ok(CastKind::PrimIntCast),
 851
 852             (Int(_) | Float, Int(_) | Float) => Ok(CastKind::NumericCast),
 853
 854             (_, DynStar) | (DynStar, _) => {
 855                 if fcx.tcx.features().dyn_star {
 856                     bug!("should be handled by `try_coerce`")
 857                 } else {
 858                     Err(CastError::IllegalCast)
 859                 }
 860             }
 861         }
 862     }
 863
 864     fn check_ptr_ptr_cast(
 865         &self,
 866         fcx: &FnCtxt<'a, 'tcx>,
 867         m_expr: ty::TypeAndMut<'tcx>,
 868         m_cast: ty::TypeAndMut<'tcx>,
 869     ) -> Result<CastKind, CastError> {
 870         debug!("check_ptr_ptr_cast m_expr={:?} m_cast={:?}", m_expr, m_cast);
 871         // ptr-ptr cast. vtables must match.
 872
 873         let expr_kind = fcx.pointer_kind(m_expr.ty, self.span)?;
 874         let cast_kind = fcx.pointer_kind(m_cast.ty, self.span)?;
 875
 876         let Some(cast_kind) = cast_kind else {
 877             // We can't cast if target pointer kind is unknown
 878             return Err(CastError::UnknownCastPtrKind);
 879         };
 880
 881         // Cast to thin pointer is OK
 882         if cast_kind == PointerKind::Thin {
 883             return Ok(CastKind::PtrPtrCast);
 884         }
 885
 886         let Some(expr_kind) = expr_kind else {
 887             // We can't cast to fat pointer if source pointer kind is unknown
 888             return Err(CastError::UnknownExprPtrKind);
 889         };
 890
 891         // thin -> fat? report invalid cast (don't complain about vtable kinds)
 892         if expr_kind == PointerKind::Thin {
 893             return Err(CastError::SizedUnsizedCast);
 894         }
 895
 896         // vtable kinds must match
 897         if fcx.tcx.erase_regions(cast_kind) == fcx.tcx.erase_regions(expr_kind) {
 898             Ok(CastKind::PtrPtrCast)
 899         } else {
 900             Err(CastError::DifferingKinds)
 901         }
 902     }
 903
 904     fn check_fptr_ptr_cast(
 905         &self,
 906         fcx: &FnCtxt<'a, 'tcx>,
 907         m_cast: ty::TypeAndMut<'tcx>,
 908     ) -> Result<CastKind, CastError> {
 909         // fptr-ptr cast. must be to thin ptr
 910
 911         match fcx.pointer_kind(m_cast.ty, self.span)? {
 912             None => Err(CastError::UnknownCastPtrKind),
 913             Some(PointerKind::Thin) => Ok(CastKind::FnPtrPtrCast),
 914             _ => Err(CastError::IllegalCast),
 915         }
 916     }
 917
 918     fn check_ptr_addr_cast(
 919         &self,
 920         fcx: &FnCtxt<'a, 'tcx>,
 921         m_expr: ty::TypeAndMut<'tcx>,
 922     ) -> Result<CastKind, CastError> {
 923         // ptr-addr cast. must be from thin ptr
 924
 925         match fcx.pointer_kind(m_expr.ty, self.span)? {
 926             None => Err(CastError::UnknownExprPtrKind),
 927             Some(PointerKind::Thin) => Ok(CastKind::PtrAddrCast),
 928             _ => Err(CastError::NeedViaThinPtr),
 929         }
 930     }
 931
 932     fn check_ref_cast(
 933         &self,
 934         fcx: &FnCtxt<'a, 'tcx>,
 935         m_expr: ty::TypeAndMut<'tcx>,
 936         m_cast: ty::TypeAndMut<'tcx>,
 937     ) -> Result<CastKind, CastError> {
 938         // array-ptr-cast: allow mut-to-mut, mut-to-const, const-to-const
 939         if m_expr.mutbl >= m_cast.mutbl {
 940             if let ty::Array(ety, _) = m_expr.ty.kind() {
 941                 // Due to the limitations of LLVM global constants,
 942                 // region pointers end up pointing at copies of
 943                 // vector elements instead of the original values.
 944                 // To allow raw pointers to work correctly, we
 945                 // need to special-case obtaining a raw pointer
 946                 // from a region pointer to a vector.
 947
 948                 // Coerce to a raw pointer so that we generate AddressOf in MIR.
 949                 let array_ptr_type = fcx.tcx.mk_ptr(m_expr);
 950                 fcx.try_coerce(self.expr, self.expr_ty, array_ptr_type, AllowTwoPhase::No, None)
 951                     .unwrap_or_else(|_| {
 952                         bug!(
 953                         "could not cast from reference to array to pointer to array ({:?} to {:?})",
 954                         self.expr_ty,
 955                         array_ptr_type,
 956                     )
 957                     });
 958
 959                 // this will report a type mismatch if needed
 960                 fcx.demand_eqtype(self.span, *ety, m_cast.ty);
 961                 return Ok(CastKind::ArrayPtrCast);
 962             }
 963         }
 964
 965         Err(CastError::IllegalCast)
 966     }
 967
 968     fn check_addr_ptr_cast(
 969         &self,
 970         fcx: &FnCtxt<'a, 'tcx>,
 971         m_cast: TypeAndMut<'tcx>,
 972     ) -> Result<CastKind, CastError> {
 973         // ptr-addr cast. pointer must be thin.
 974         match fcx.pointer_kind(m_cast.ty, self.span)? {
 975             None => Err(CastError::UnknownCastPtrKind),
 976             Some(PointerKind::Thin) => Ok(CastKind::AddrPtrCast),
 977             Some(PointerKind::VTable(_)) => Err(CastError::IntToFatCast(Some("a vtable"))),
 978             Some(PointerKind::Length) => Err(CastError::IntToFatCast(Some("a length"))),
 979             Some(
 980                 PointerKind::OfProjection(_)
 981                 | PointerKind::OfOpaque(_, _)
 982                 | PointerKind::OfParam(_),
 983             ) => Err(CastError::IntToFatCast(None)),
 984         }
 985     }
 986
 987     fn try_coercion_cast(&self, fcx: &FnCtxt<'a, 'tcx>) -> Result<(), ty::error::TypeError<'tcx>> {
 988         match fcx.try_coerce(self.expr, self.expr_ty, self.cast_ty, AllowTwoPhase::No, None) {
 989             Ok(_) => Ok(()),
 990             Err(err) => Err(err),
 991         }
 992     }
 993
 994     fn cenum_impl_drop_lint(&self, fcx: &FnCtxt<'a, 'tcx>) {
 995         if let ty::Adt(d, _) = self.expr_ty.kind()
 996             && d.has_dtor(fcx.tcx)
 997         {
 998             fcx.tcx.struct_span_lint_hir(
 999                 lint::builtin::CENUM_IMPL_DROP_CAST,
1000                 self.expr.hir_id,
1001                 self.span,
1002                 DelayDm(|| format!(
1003                     "cannot cast enum `{}` into integer `{}` because it implements `Drop`",
1004                     self.expr_ty, self.cast_ty
1005                 )),
1006                 |lint| {
1007                     lint
1008                 },
1009             );
1010         }
1011     }
1012
1013     fn lossy_provenance_ptr2int_lint(&self, fcx: &FnCtxt<'a, 'tcx>, t_c: ty::cast::IntTy) {
1014         fcx.tcx.struct_span_lint_hir(
1015             lint::builtin::LOSSY_PROVENANCE_CASTS,
1016             self.expr.hir_id,
1017             self.span,
1018             DelayDm(|| format!(
1019                     "under strict provenance it is considered bad style to cast pointer `{}` to integer `{}`",
1020                     self.expr_ty, self.cast_ty
1021                 )),
1022             |lint| {
1023                 let msg = "use `.addr()` to obtain the address of a pointer";
1024
1025                 let expr_prec = self.expr.precedence().order();
1026                 let needs_parens = expr_prec < rustc_ast::util::parser::PREC_POSTFIX;
1027
1028                 let scalar_cast = match t_c {
1029                     ty::cast::IntTy::U(ty::UintTy::Usize) => String::new(),
1030                     _ => format!(" as {}", self.cast_ty),
1031                 };
1032
1033                 let cast_span = self.expr_span.shrink_to_hi().to(self.cast_span);
1034
1035                 if needs_parens {
1036                     let suggestions = vec![
1037                         (self.expr_span.shrink_to_lo(), String::from("(")),
1038                         (cast_span, format!(").addr(){scalar_cast}")),
1039                     ];
1040
1041                     lint.multipart_suggestion(msg, suggestions, Applicability::MaybeIncorrect);
1042                 } else {
1043                     lint.span_suggestion(
1044                         cast_span,
1045                         msg,
1046                         format!(".addr(){scalar_cast}"),
1047                         Applicability::MaybeIncorrect,
1048                     );
1049                 }
1050
1051                 lint.help(
1052                     "if you can't comply with strict provenance and need to expose the pointer \
1053                     provenance you can use `.expose_addr()` instead"
1054                 );
1055
1056                 lint
1057             },
1058         );
1059     }
1060
1061     fn fuzzy_provenance_int2ptr_lint(&self, fcx: &FnCtxt<'a, 'tcx>) {
1062         fcx.tcx.struct_span_lint_hir(
1063             lint::builtin::FUZZY_PROVENANCE_CASTS,
1064             self.expr.hir_id,
1065             self.span,
1066             DelayDm(|| format!(
1067                 "strict provenance disallows casting integer `{}` to pointer `{}`",
1068                 self.expr_ty, self.cast_ty
1069             )),
1070             |lint| {
1071                 let msg = "use `.with_addr()` to adjust a valid pointer in the same allocation, to this address";
1072                 let suggestions = vec![
1073                     (self.expr_span.shrink_to_lo(), String::from("(...).with_addr(")),
1074                     (self.expr_span.shrink_to_hi().to(self.cast_span), String::from(")")),
1075                 ];
1076
1077                 lint.multipart_suggestion(msg, suggestions, Applicability::MaybeIncorrect);
1078                 lint.help(
1079                     "if you can't comply with strict provenance and don't have a pointer with \
1080                     the correct provenance you can use `std::ptr::from_exposed_addr()` instead"
1081                  );
1082
1083                 lint
1084             },
1085         );
1086     }
1087 }