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_middle::mir::Mutability;
  37 use rustc_middle::ty::adjustment::AllowTwoPhase;
  38 use rustc_middle::ty::cast::{CastKind, CastTy};
  39 use rustc_middle::ty::error::TypeError;
  40 use rustc_middle::ty::subst::SubstsRef;
  41 use rustc_middle::ty::{self, Ty, TypeAndMut, TypeVisitable, VariantDef};
  42 use rustc_session::lint;
  43 use rustc_session::Session;
  44 use rustc_span::def_id::{DefId, LOCAL_CRATE};
  45 use rustc_span::symbol::sym;
  46 use rustc_span::Span;
  47 use rustc_trait_selection::infer::InferCtxtExt;
  48 use rustc_trait_selection::traits::error_reporting::report_object_safety_error;
  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(Copy, Clone, PartialEq, Eq)]
  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(&'tcx 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(&'tcx 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
  98         if let Some(reported) = t.error_reported() {
  99             return Err(reported);
 100         }
 101
 102         if self.type_is_sized_modulo_regions(self.param_env, t, span) {
 103             return Ok(Some(PointerKind::Thin));
 104         }
 105
 106         Ok(match *t.kind() {
 107             ty::Slice(_) | ty::Str => Some(PointerKind::Length),
 108             ty::Dynamic(ref tty, _, ty::Dyn) => Some(PointerKind::VTable(tty.principal_def_id())),
 109             ty::Adt(def, substs) if def.is_struct() => match def.non_enum_variant().fields.last() {
 110                 None => Some(PointerKind::Thin),
 111                 Some(f) => {
 112                     let field_ty = self.field_ty(span, f, substs);
 113                     self.pointer_kind(field_ty, span)?
 114                 }
 115             },
 116             ty::Tuple(fields) => match fields.last() {
 117                 None => Some(PointerKind::Thin),
 118                 Some(&f) => self.pointer_kind(f, span)?,
 119             },
 120
 121             // Pointers to foreign types are thin, despite being unsized
 122             ty::Foreign(..) => Some(PointerKind::Thin),
 123             // We should really try to normalize here.
 124             ty::Projection(ref pi) => Some(PointerKind::OfProjection(pi)),
 125             ty::Opaque(def_id, substs) => Some(PointerKind::OfOpaque(def_id, substs)),
 126             ty::Param(ref p) => Some(PointerKind::OfParam(p)),
 127             // Insufficient type information.
 128             ty::Placeholder(..) | ty::Bound(..) | ty::Infer(_) => None,
 129
 130             ty::Bool
 131             | ty::Char
 132             | ty::Int(..)
 133             | ty::Uint(..)
 134             | ty::Float(_)
 135             | ty::Array(..)
 136             | ty::GeneratorWitness(..)
 137             | ty::RawPtr(_)
 138             | ty::Ref(..)
 139             | ty::FnDef(..)
 140             | ty::FnPtr(..)
 141             | ty::Closure(..)
 142             | ty::Generator(..)
 143             | ty::Adt(..)
 144             | ty::Never
 145             | ty::Dynamic(_, _, ty::DynStar)
 146             | ty::Error(_) => {
 147                 let reported = self
 148                     .tcx
 149                     .sess
 150                     .delay_span_bug(span, &format!("`{:?}` should be sized but is not?", t));
 151                 return Err(reported);
 152             }
 153         })
 154     }
 155 }
 156
 157 #[derive(Copy, Clone)]
 158 pub enum CastError {
 159     ErrorGuaranteed,
 160
 161     CastToBool,
 162     CastToChar,
 163     DifferingKinds,
 164     /// Cast of thin to fat raw ptr (e.g., `*const () as *const [u8]`).
 165     SizedUnsizedCast,
 166     IllegalCast,
 167     NeedDeref,
 168     NeedViaPtr,
 169     NeedViaThinPtr,
 170     NeedViaInt,
 171     NonScalar,
 172     UnknownExprPtrKind,
 173     UnknownCastPtrKind,
 174     /// Cast of int to (possibly) fat raw pointer.
 175     ///
 176     /// Argument is the specific name of the metadata in plain words, such as "a vtable"
 177     /// or "a length". If this argument is None, then the metadata is unknown, for example,
 178     /// when we're typechecking a type parameter with a ?Sized bound.
 179     IntToFatCast(Option<&'static str>),
 180     ForeignNonExhaustiveAdt,
 181 }
 182
 183 impl From<ErrorGuaranteed> for CastError {
 184     fn from(_: ErrorGuaranteed) -> Self {
 185         CastError::ErrorGuaranteed
 186     }
 187 }
 188
 189 fn make_invalid_casting_error<'a, 'tcx>(
 190     sess: &'a Session,
 191     span: Span,
 192     expr_ty: Ty<'tcx>,
 193     cast_ty: Ty<'tcx>,
 194     fcx: &FnCtxt<'a, 'tcx>,
 195 ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
 196     type_error_struct!(
 197         sess,
 198         span,
 199         expr_ty,
 200         E0606,
 201         "casting `{}` as `{}` is invalid",
 202         fcx.ty_to_string(expr_ty),
 203         fcx.ty_to_string(cast_ty)
 204     )
 205 }
 206
 207 impl<'a, 'tcx> CastCheck<'tcx> {
 208     pub fn new(
 209         fcx: &FnCtxt<'a, 'tcx>,
 210         expr: &'tcx hir::Expr<'tcx>,
 211         expr_ty: Ty<'tcx>,
 212         cast_ty: Ty<'tcx>,
 213         cast_span: Span,
 214         span: Span,
 215         constness: hir::Constness,
 216     ) -> Result<CastCheck<'tcx>, ErrorGuaranteed> {
 217         let expr_span = expr.span.find_ancestor_inside(span).unwrap_or(expr.span);
 218         let check = CastCheck { expr, expr_ty, expr_span, cast_ty, cast_span, span, constness };
 219
 220         // For better error messages, check for some obviously unsized
 221         // cases now. We do a more thorough check at the end, once
 222         // inference is more completely known.
 223         match cast_ty.kind() {
 224             ty::Dynamic(_, _, ty::Dyn) | ty::Slice(..) => {
 225                 let reported = check.report_cast_to_unsized_type(fcx);
 226                 Err(reported)
 227             }
 228             _ => Ok(check),
 229         }
 230     }
 231
 232     fn report_cast_error(&self, fcx: &FnCtxt<'a, 'tcx>, e: CastError) {
 233         match e {
 234             CastError::ErrorGuaranteed => {
 235                 // an error has already been reported
 236             }
 237             CastError::NeedDeref => {
 238                 let error_span = self.span;
 239                 let mut err = make_invalid_casting_error(
 240                     fcx.tcx.sess,
 241                     self.span,
 242                     self.expr_ty,
 243                     self.cast_ty,
 244                     fcx,
 245                 );
 246                 let cast_ty = fcx.ty_to_string(self.cast_ty);
 247                 err.span_label(
 248                     error_span,
 249                     format!("cannot cast `{}` as `{}`", fcx.ty_to_string(self.expr_ty), cast_ty),
 250                 );
 251                 if let Ok(snippet) = fcx.sess().source_map().span_to_snippet(self.expr_span) {
 252                     err.span_suggestion(
 253                         self.expr_span,
 254                         "dereference the expression",
 255                         format!("*{}", snippet),
 256                         Applicability::MaybeIncorrect,
 257                     );
 258                 } else {
 259                     err.span_help(self.expr_span, "dereference the expression with `*`");
 260                 }
 261                 err.emit();
 262             }
 263             CastError::NeedViaThinPtr | CastError::NeedViaPtr => {
 264                 let mut err = make_invalid_casting_error(
 265                     fcx.tcx.sess,
 266                     self.span,
 267                     self.expr_ty,
 268                     self.cast_ty,
 269                     fcx,
 270                 );
 271                 if self.cast_ty.is_integral() {
 272                     err.help(&format!(
 273                         "cast through {} first",
 274                         match e {
 275                             CastError::NeedViaPtr => "a raw pointer",
 276                             CastError::NeedViaThinPtr => "a thin pointer",
 277                             _ => bug!(),
 278                         }
 279                     ));
 280                 }
 281                 err.emit();
 282             }
 283             CastError::NeedViaInt => {
 284                 make_invalid_casting_error(
 285                     fcx.tcx.sess,
 286                     self.span,
 287                     self.expr_ty,
 288                     self.cast_ty,
 289                     fcx,
 290                 )
 291                 .help(&format!(
 292                     "cast through {} first",
 293                     match e {
 294                         CastError::NeedViaInt => "an integer",
 295                         _ => bug!(),
 296                     }
 297                 ))
 298                 .emit();
 299             }
 300             CastError::IllegalCast => {
 301                 make_invalid_casting_error(
 302                     fcx.tcx.sess,
 303                     self.span,
 304                     self.expr_ty,
 305                     self.cast_ty,
 306                     fcx,
 307                 )
 308                 .emit();
 309             }
 310             CastError::DifferingKinds => {
 311                 make_invalid_casting_error(
 312                     fcx.tcx.sess,
 313                     self.span,
 314                     self.expr_ty,
 315                     self.cast_ty,
 316                     fcx,
 317                 )
 318                 .note("vtable kinds may not match")
 319                 .emit();
 320             }
 321             CastError::CastToBool => {
 322                 let mut err =
 323                     struct_span_err!(fcx.tcx.sess, self.span, E0054, "cannot cast as `bool`");
 324
 325                 if self.expr_ty.is_numeric() {
 326                     match fcx.tcx.sess.source_map().span_to_snippet(self.expr_span) {
 327                         Ok(snippet) => {
 328                             err.span_suggestion(
 329                                 self.span,
 330                                 "compare with zero instead",
 331                                 format!("{snippet} != 0"),
 332                                 Applicability::MachineApplicable,
 333                             );
 334                         }
 335                         Err(_) => {
 336                             err.span_help(self.span, "compare with zero instead");
 337                         }
 338                     }
 339                 } else {
 340                     err.span_label(self.span, "unsupported cast");
 341                 }
 342
 343                 err.emit();
 344             }
 345             CastError::CastToChar => {
 346                 let mut err = type_error_struct!(
 347                     fcx.tcx.sess,
 348                     self.span,
 349                     self.expr_ty,
 350                     E0604,
 351                     "only `u8` can be cast as `char`, not `{}`",
 352                     self.expr_ty
 353                 );
 354                 err.span_label(self.span, "invalid cast");
 355                 if self.expr_ty.is_numeric() {
 356                     if self.expr_ty == fcx.tcx.types.u32 {
 357                         match fcx.tcx.sess.source_map().span_to_snippet(self.expr.span) {
 358                             Ok(snippet) => err.span_suggestion(
 359                                 self.span,
 360                                 "try `char::from_u32` instead",
 361                                 format!("char::from_u32({snippet})"),
 362                                 Applicability::MachineApplicable,
 363                             ),
 364
 365                             Err(_) => err.span_help(self.span, "try `char::from_u32` instead"),
 366                         };
 367                     } else if self.expr_ty == fcx.tcx.types.i8 {
 368                         err.span_help(self.span, "try casting from `u8` instead");
 369                     } else {
 370                         err.span_help(self.span, "try `char::from_u32` instead (via a `u32`)");
 371                     };
 372                 }
 373                 err.emit();
 374             }
 375             CastError::NonScalar => {
 376                 let mut err = type_error_struct!(
 377                     fcx.tcx.sess,
 378                     self.span,
 379                     self.expr_ty,
 380                     E0605,
 381                     "non-primitive cast: `{}` as `{}`",
 382                     self.expr_ty,
 383                     fcx.ty_to_string(self.cast_ty)
 384                 );
 385                 let mut sugg = None;
 386                 let mut sugg_mutref = false;
 387                 if let ty::Ref(reg, cast_ty, mutbl) = *self.cast_ty.kind() {
 388                     if let ty::RawPtr(TypeAndMut { ty: expr_ty, .. }) = *self.expr_ty.kind()
 389                         && fcx
 390                             .try_coerce(
 391                                 self.expr,
 392                                 fcx.tcx.mk_ref(
 393                                     fcx.tcx.lifetimes.re_erased,
 394                                     TypeAndMut { ty: expr_ty, mutbl },
 395                                 ),
 396                                 self.cast_ty,
 397                                 AllowTwoPhase::No,
 398                                 None,
 399                             )
 400                             .is_ok()
 401                     {
 402                         sugg = Some((format!("&{}*", mutbl.prefix_str()), cast_ty == expr_ty));
 403                     } else if let ty::Ref(expr_reg, expr_ty, expr_mutbl) = *self.expr_ty.kind()
 404                         && expr_mutbl == Mutability::Not
 405                         && mutbl == Mutability::Mut
 406                         && fcx
 407                             .try_coerce(
 408                                 self.expr,
 409                                 fcx.tcx.mk_ref(
 410                                     expr_reg,
 411                                     TypeAndMut { ty: expr_ty, mutbl: Mutability::Mut },
 412                                 ),
 413                                 self.cast_ty,
 414                                 AllowTwoPhase::No,
 415                                 None,
 416                             )
 417                             .is_ok()
 418                     {
 419                         sugg_mutref = true;
 420                     }
 421
 422                     if !sugg_mutref
 423                         && sugg == None
 424                         && fcx
 425                             .try_coerce(
 426                                 self.expr,
 427                                 fcx.tcx.mk_ref(reg, TypeAndMut { ty: self.expr_ty, mutbl }),
 428                                 self.cast_ty,
 429                                 AllowTwoPhase::No,
 430                                 None,
 431                             )
 432                             .is_ok()
 433                     {
 434                         sugg = Some((format!("&{}", mutbl.prefix_str()), false));
 435                     }
 436                 } else if let ty::RawPtr(TypeAndMut { mutbl, .. }) = *self.cast_ty.kind()
 437                     && fcx
 438                         .try_coerce(
 439                             self.expr,
 440                             fcx.tcx.mk_ref(
 441                                 fcx.tcx.lifetimes.re_erased,
 442                                 TypeAndMut { ty: self.expr_ty, mutbl },
 443                             ),
 444                             self.cast_ty,
 445                             AllowTwoPhase::No,
 446                             None,
 447                         )
 448                         .is_ok()
 449                 {
 450                     sugg = Some((format!("&{}", mutbl.prefix_str()), false));
 451                 }
 452                 if sugg_mutref {
 453                     err.span_label(self.span, "invalid cast");
 454                     err.span_note(self.expr_span, "this reference is immutable");
 455                     err.span_note(self.cast_span, "trying to cast to a mutable reference type");
 456                 } else if let Some((sugg, remove_cast)) = sugg {
 457                     err.span_label(self.span, "invalid cast");
 458
 459                     let has_parens = fcx
 460                         .tcx
 461                         .sess
 462                         .source_map()
 463                         .span_to_snippet(self.expr_span)
 464                         .map_or(false, |snip| snip.starts_with('('));
 465
 466                     // Very crude check to see whether the expression must be wrapped
 467                     // in parentheses for the suggestion to work (issue #89497).
 468                     // Can/should be extended in the future.
 469                     let needs_parens =
 470                         !has_parens && matches!(self.expr.kind, hir::ExprKind::Cast(..));
 471
 472                     let mut suggestion = vec![(self.expr_span.shrink_to_lo(), sugg)];
 473                     if needs_parens {
 474                         suggestion[0].1 += "(";
 475                         suggestion.push((self.expr_span.shrink_to_hi(), ")".to_string()));
 476                     }
 477                     if remove_cast {
 478                         suggestion.push((
 479                             self.expr_span.shrink_to_hi().to(self.cast_span),
 480                             String::new(),
 481                         ));
 482                     }
 483
 484                     err.multipart_suggestion_verbose(
 485                         "consider borrowing the value",
 486                         suggestion,
 487                         Applicability::MachineApplicable,
 488                     );
 489                 } else if !matches!(
 490                     self.cast_ty.kind(),
 491                     ty::FnDef(..) | ty::FnPtr(..) | ty::Closure(..)
 492                 ) {
 493                     let mut label = true;
 494                     // Check `impl From<self.expr_ty> for self.cast_ty {}` for accurate suggestion:
 495                     if let Ok(snippet) = fcx.tcx.sess.source_map().span_to_snippet(self.expr_span)
 496                         && let Some(from_trait) = fcx.tcx.get_diagnostic_item(sym::From)
 497                     {
 498                         let ty = fcx.resolve_vars_if_possible(self.cast_ty);
 499                         // Erase regions to avoid panic in `prove_value` when calling
 500                         // `type_implements_trait`.
 501                         let ty = fcx.tcx.erase_regions(ty);
 502                         let expr_ty = fcx.resolve_vars_if_possible(self.expr_ty);
 503                         let expr_ty = fcx.tcx.erase_regions(expr_ty);
 504                         let ty_params = fcx.tcx.mk_substs_trait(expr_ty, &[]);
 505                         if fcx
 506                             .infcx
 507                             .type_implements_trait(from_trait, ty, ty_params, fcx.param_env)
 508                             .must_apply_modulo_regions()
 509                         {
 510                             label = false;
 511                             err.span_suggestion(
 512                                 self.span,
 513                                 "consider using the `From` trait instead",
 514                                 format!("{}::from({})", self.cast_ty, snippet),
 515                                 Applicability::MaybeIncorrect,
 516                             );
 517                         }
 518                     }
 519                     let msg = "an `as` expression can only be used to convert between primitive \
 520                                types or to coerce to a specific trait object";
 521                     if label {
 522                         err.span_label(self.span, msg);
 523                     } else {
 524                         err.note(msg);
 525                     }
 526                 } else {
 527                     err.span_label(self.span, "invalid cast");
 528                 }
 529                 err.emit();
 530             }
 531             CastError::SizedUnsizedCast => {
 532                 use rustc_hir_analysis::structured_errors::{
 533                     SizedUnsizedCast, StructuredDiagnostic,
 534                 };
 535
 536                 SizedUnsizedCast {
 537                     sess: &fcx.tcx.sess,
 538                     span: self.span,
 539                     expr_ty: self.expr_ty,
 540                     cast_ty: fcx.ty_to_string(self.cast_ty),
 541                 }
 542                 .diagnostic()
 543                 .emit();
 544             }
 545             CastError::IntToFatCast(known_metadata) => {
 546                 let mut err = struct_span_err!(
 547                     fcx.tcx.sess,
 548                     self.cast_span,
 549                     E0606,
 550                     "cannot cast `{}` to a pointer that {} wide",
 551                     fcx.ty_to_string(self.expr_ty),
 552                     if known_metadata.is_some() { "is" } else { "may be" }
 553                 );
 554
 555                 err.span_label(
 556                     self.cast_span,
 557                     format!(
 558                         "creating a `{}` requires both an address and {}",
 559                         self.cast_ty,
 560                         known_metadata.unwrap_or("type-specific metadata"),
 561                     ),
 562                 );
 563
 564                 if fcx.tcx.sess.is_nightly_build() {
 565                     err.span_label(
 566                         self.expr_span,
 567                         "consider casting this expression to `*const ()`, \
 568                         then using `core::ptr::from_raw_parts`",
 569                     );
 570                 }
 571
 572                 err.emit();
 573             }
 574             CastError::UnknownCastPtrKind | CastError::UnknownExprPtrKind => {
 575                 let unknown_cast_to = match e {
 576                     CastError::UnknownCastPtrKind => true,
 577                     CastError::UnknownExprPtrKind => false,
 578                     _ => bug!(),
 579                 };
 580                 let mut err = struct_span_err!(
 581                     fcx.tcx.sess,
 582                     if unknown_cast_to { self.cast_span } else { self.span },
 583                     E0641,
 584                     "cannot cast {} a pointer of an unknown kind",
 585                     if unknown_cast_to { "to" } else { "from" }
 586                 );
 587                 if unknown_cast_to {
 588                     err.span_label(self.cast_span, "needs more type information");
 589                     err.note(
 590                         "the type information given here is insufficient to check whether \
 591                         the pointer cast is valid",
 592                     );
 593                 } else {
 594                     err.span_label(
 595                         self.span,
 596                         "the type information given here is insufficient to check whether \
 597                         the pointer cast is valid",
 598                     );
 599                 }
 600                 err.emit();
 601             }
 602             CastError::ForeignNonExhaustiveAdt => {
 603                 make_invalid_casting_error(
 604                     fcx.tcx.sess,
 605                     self.span,
 606                     self.expr_ty,
 607                     self.cast_ty,
 608                     fcx,
 609                 )
 610                 .note("cannot cast an enum with a non-exhaustive variant when it's defined in another crate")
 611                 .emit();
 612             }
 613         }
 614     }
 615
 616     fn report_cast_to_unsized_type(&self, fcx: &FnCtxt<'a, 'tcx>) -> ErrorGuaranteed {
 617         if let Some(reported) =
 618             self.cast_ty.error_reported().or_else(|| self.expr_ty.error_reported())
 619         {
 620             return reported;
 621         }
 622
 623         let tstr = fcx.ty_to_string(self.cast_ty);
 624         let mut err = type_error_struct!(
 625             fcx.tcx.sess,
 626             self.span,
 627             self.expr_ty,
 628             E0620,
 629             "cast to unsized type: `{}` as `{}`",
 630             fcx.resolve_vars_if_possible(self.expr_ty),
 631             tstr
 632         );
 633         match self.expr_ty.kind() {
 634             ty::Ref(_, _, mt) => {
 635                 let mtstr = mt.prefix_str();
 636                 if self.cast_ty.is_trait() {
 637                     match fcx.tcx.sess.source_map().span_to_snippet(self.cast_span) {
 638                         Ok(s) => {
 639                             err.span_suggestion(
 640                                 self.cast_span,
 641                                 "try casting to a reference instead",
 642                                 format!("&{}{}", mtstr, s),
 643                                 Applicability::MachineApplicable,
 644                             );
 645                         }
 646                         Err(_) => {
 647                             let msg = &format!("did you mean `&{}{}`?", mtstr, tstr);
 648                             err.span_help(self.cast_span, msg);
 649                         }
 650                     }
 651                 } else {
 652                     let msg =
 653                         &format!("consider using an implicit coercion to `&{mtstr}{tstr}` instead");
 654                     err.span_help(self.span, msg);
 655                 }
 656             }
 657             ty::Adt(def, ..) if def.is_box() => {
 658                 match fcx.tcx.sess.source_map().span_to_snippet(self.cast_span) {
 659                     Ok(s) => {
 660                         err.span_suggestion(
 661                             self.cast_span,
 662                             "you can cast to a `Box` instead",
 663                             format!("Box<{s}>"),
 664                             Applicability::MachineApplicable,
 665                         );
 666                     }
 667                     Err(_) => {
 668                         err.span_help(
 669                             self.cast_span,
 670                             &format!("you might have meant `Box<{tstr}>`"),
 671                         );
 672                     }
 673                 }
 674             }
 675             _ => {
 676                 err.span_help(self.expr_span, "consider using a box or reference as appropriate");
 677             }
 678         }
 679         err.emit()
 680     }
 681
 682     fn trivial_cast_lint(&self, fcx: &FnCtxt<'a, 'tcx>) {
 683         let t_cast = self.cast_ty;
 684         let t_expr = self.expr_ty;
 685         let type_asc_or =
 686             if fcx.tcx.features().type_ascription { "type ascription or " } else { "" };
 687         let (adjective, lint) = if t_cast.is_numeric() && t_expr.is_numeric() {
 688             ("numeric ", lint::builtin::TRIVIAL_NUMERIC_CASTS)
 689         } else {
 690             ("", lint::builtin::TRIVIAL_CASTS)
 691         };
 692         fcx.tcx.struct_span_lint_hir(
 693             lint,
 694             self.expr.hir_id,
 695             self.span,
 696             DelayDm(|| {
 697                 format!(
 698                     "trivial {}cast: `{}` as `{}`",
 699                     adjective,
 700                     fcx.ty_to_string(t_expr),
 701                     fcx.ty_to_string(t_cast)
 702                 )
 703             }),
 704             |lint| {
 705                 lint.help(format!(
 706                     "cast can be replaced by coercion; this might \
 707                      require {type_asc_or}a temporary variable"
 708                 ))
 709             },
 710         );
 711     }
 712
 713     #[instrument(skip(fcx), level = "debug")]
 714     pub fn check(mut self, fcx: &FnCtxt<'a, 'tcx>) {
 715         self.expr_ty = fcx.structurally_resolved_type(self.expr_span, self.expr_ty);
 716         self.cast_ty = fcx.structurally_resolved_type(self.cast_span, self.cast_ty);
 717
 718         debug!("check_cast({}, {:?} as {:?})", self.expr.hir_id, self.expr_ty, self.cast_ty);
 719
 720         if !fcx.type_is_sized_modulo_regions(fcx.param_env, self.cast_ty, self.span)
 721             && !self.cast_ty.has_infer_types()
 722         {
 723             self.report_cast_to_unsized_type(fcx);
 724         } else if self.expr_ty.references_error() || self.cast_ty.references_error() {
 725             // No sense in giving duplicate error messages
 726         } else {
 727             match self.try_coercion_cast(fcx) {
 728                 Ok(()) => {
 729                     self.trivial_cast_lint(fcx);
 730                     debug!(" -> CoercionCast");
 731                     fcx.typeck_results.borrow_mut().set_coercion_cast(self.expr.hir_id.local_id);
 732                 }
 733                 Err(ty::error::TypeError::ObjectUnsafeCoercion(did)) => {
 734                     self.report_object_unsafe_cast(&fcx, did);
 735                 }
 736                 Err(_) => {
 737                     match self.do_check(fcx) {
 738                         Ok(k) => {
 739                             debug!(" -> {:?}", k);
 740                         }
 741                         Err(e) => self.report_cast_error(fcx, e),
 742                     };
 743                 }
 744             };
 745         }
 746     }
 747
 748     fn report_object_unsafe_cast(&self, fcx: &FnCtxt<'a, 'tcx>, did: DefId) {
 749         let violations = fcx.tcx.object_safety_violations(did);
 750         let mut err = report_object_safety_error(fcx.tcx, self.cast_span, did, violations);
 751         err.note(&format!("required by cast to type '{}'", fcx.ty_to_string(self.cast_ty)));
 752         err.emit();
 753     }
 754
 755     /// Checks a cast, and report an error if one exists. In some cases, this
 756     /// can return Ok and create type errors in the fcx rather than returning
 757     /// directly. coercion-cast is handled in check instead of here.
 758     pub fn do_check(&self, fcx: &FnCtxt<'a, 'tcx>) -> Result<CastKind, CastError> {
 759         use rustc_middle::ty::cast::CastTy::*;
 760         use rustc_middle::ty::cast::IntTy::*;
 761
 762         let (t_from, t_cast) = match (CastTy::from_ty(self.expr_ty), CastTy::from_ty(self.cast_ty))
 763         {
 764             (Some(t_from), Some(t_cast)) => (t_from, t_cast),
 765             // Function item types may need to be reified before casts.
 766             (None, Some(t_cast)) => {
 767                 match *self.expr_ty.kind() {
 768                     ty::FnDef(..) => {
 769                         // Attempt a coercion to a fn pointer type.
 770                         let f = fcx.normalize_associated_types_in(
 771                             self.expr_span,
 772                             self.expr_ty.fn_sig(fcx.tcx),
 773                         );
 774                         let res = fcx.try_coerce(
 775                             self.expr,
 776                             self.expr_ty,
 777                             fcx.tcx.mk_fn_ptr(f),
 778                             AllowTwoPhase::No,
 779                             None,
 780                         );
 781                         if let Err(TypeError::IntrinsicCast) = res {
 782                             return Err(CastError::IllegalCast);
 783                         }
 784                         if res.is_err() {
 785                             return Err(CastError::NonScalar);
 786                         }
 787                         (FnPtr, t_cast)
 788                     }
 789                     // Special case some errors for references, and check for
 790                     // array-ptr-casts. `Ref` is not a CastTy because the cast
 791                     // is split into a coercion to a pointer type, followed by
 792                     // a cast.
 793                     ty::Ref(_, inner_ty, mutbl) => {
 794                         return match t_cast {
 795                             Int(_) | Float => match *inner_ty.kind() {
 796                                 ty::Int(_)
 797                                 | ty::Uint(_)
 798                                 | ty::Float(_)
 799                                 | ty::Infer(ty::InferTy::IntVar(_) | ty::InferTy::FloatVar(_)) => {
 800                                     Err(CastError::NeedDeref)
 801                                 }
 802                                 _ => Err(CastError::NeedViaPtr),
 803                             },
 804                             // array-ptr-cast
 805                             Ptr(mt) => {
 806                                 self.check_ref_cast(fcx, TypeAndMut { mutbl, ty: inner_ty }, mt)
 807                             }
 808                             _ => Err(CastError::NonScalar),
 809                         };
 810                     }
 811                     _ => return Err(CastError::NonScalar),
 812                 }
 813             }
 814             _ => return Err(CastError::NonScalar),
 815         };
 816
 817         if let ty::Adt(adt_def, _) = *self.expr_ty.kind() {
 818             if adt_def.did().krate != LOCAL_CRATE {
 819                 if adt_def.variants().iter().any(VariantDef::is_field_list_non_exhaustive) {
 820                     return Err(CastError::ForeignNonExhaustiveAdt);
 821                 }
 822             }
 823         }
 824
 825         match (t_from, t_cast) {
 826             // These types have invariants! can't cast into them.
 827             (_, Int(CEnum) | FnPtr) => Err(CastError::NonScalar),
 828
 829             // * -> Bool
 830             (_, Int(Bool)) => Err(CastError::CastToBool),
 831
 832             // * -> Char
 833             (Int(U(ty::UintTy::U8)), Int(Char)) => Ok(CastKind::U8CharCast), // u8-char-cast
 834             (_, Int(Char)) => Err(CastError::CastToChar),
 835
 836             // prim -> float,ptr
 837             (Int(Bool) | Int(CEnum) | Int(Char), Float) => Err(CastError::NeedViaInt),
 838
 839             (Int(Bool) | Int(CEnum) | Int(Char) | Float, Ptr(_)) | (Ptr(_) | FnPtr, Float) => {
 840                 Err(CastError::IllegalCast)
 841             }
 842
 843             // ptr -> *
 844             (Ptr(m_e), Ptr(m_c)) => self.check_ptr_ptr_cast(fcx, m_e, m_c), // ptr-ptr-cast
 845
 846             // ptr-addr-cast
 847             (Ptr(m_expr), Int(t_c)) => {
 848                 self.lossy_provenance_ptr2int_lint(fcx, t_c);
 849                 self.check_ptr_addr_cast(fcx, m_expr)
 850             }
 851             (FnPtr, Int(_)) => {
 852                 // FIXME(#95489): there should eventually be a lint for these casts
 853                 Ok(CastKind::FnPtrAddrCast)
 854             }
 855             // addr-ptr-cast
 856             (Int(_), Ptr(mt)) => {
 857                 self.fuzzy_provenance_int2ptr_lint(fcx);
 858                 self.check_addr_ptr_cast(fcx, mt)
 859             }
 860             // fn-ptr-cast
 861             (FnPtr, Ptr(mt)) => self.check_fptr_ptr_cast(fcx, mt),
 862
 863             // prim -> prim
 864             (Int(CEnum), Int(_)) => {
 865                 self.cenum_impl_drop_lint(fcx);
 866                 Ok(CastKind::EnumCast)
 867             }
 868             (Int(Char) | Int(Bool), Int(_)) => Ok(CastKind::PrimIntCast),
 869
 870             (Int(_) | Float, Int(_) | Float) => Ok(CastKind::NumericCast),
 871
 872             (_, DynStar) | (DynStar, _) => {
 873                 if fcx.tcx.features().dyn_star {
 874                     bug!("should be handled by `try_coerce`")
 875                 } else {
 876                     Err(CastError::IllegalCast)
 877                 }
 878             }
 879         }
 880     }
 881
 882     fn check_ptr_ptr_cast(
 883         &self,
 884         fcx: &FnCtxt<'a, 'tcx>,
 885         m_expr: ty::TypeAndMut<'tcx>,
 886         m_cast: ty::TypeAndMut<'tcx>,
 887     ) -> Result<CastKind, CastError> {
 888         debug!("check_ptr_ptr_cast m_expr={:?} m_cast={:?}", m_expr, m_cast);
 889         // ptr-ptr cast. vtables must match.
 890
 891         let expr_kind = fcx.pointer_kind(m_expr.ty, self.span)?;
 892         let cast_kind = fcx.pointer_kind(m_cast.ty, self.span)?;
 893
 894         let Some(cast_kind) = cast_kind else {
 895             // We can't cast if target pointer kind is unknown
 896             return Err(CastError::UnknownCastPtrKind);
 897         };
 898
 899         // Cast to thin pointer is OK
 900         if cast_kind == PointerKind::Thin {
 901             return Ok(CastKind::PtrPtrCast);
 902         }
 903
 904         let Some(expr_kind) = expr_kind else {
 905             // We can't cast to fat pointer if source pointer kind is unknown
 906             return Err(CastError::UnknownExprPtrKind);
 907         };
 908
 909         // thin -> fat? report invalid cast (don't complain about vtable kinds)
 910         if expr_kind == PointerKind::Thin {
 911             return Err(CastError::SizedUnsizedCast);
 912         }
 913
 914         // vtable kinds must match
 915         if cast_kind == expr_kind {
 916             Ok(CastKind::PtrPtrCast)
 917         } else {
 918             Err(CastError::DifferingKinds)
 919         }
 920     }
 921
 922     fn check_fptr_ptr_cast(
 923         &self,
 924         fcx: &FnCtxt<'a, 'tcx>,
 925         m_cast: ty::TypeAndMut<'tcx>,
 926     ) -> Result<CastKind, CastError> {
 927         // fptr-ptr cast. must be to thin ptr
 928
 929         match fcx.pointer_kind(m_cast.ty, self.span)? {
 930             None => Err(CastError::UnknownCastPtrKind),
 931             Some(PointerKind::Thin) => Ok(CastKind::FnPtrPtrCast),
 932             _ => Err(CastError::IllegalCast),
 933         }
 934     }
 935
 936     fn check_ptr_addr_cast(
 937         &self,
 938         fcx: &FnCtxt<'a, 'tcx>,
 939         m_expr: ty::TypeAndMut<'tcx>,
 940     ) -> Result<CastKind, CastError> {
 941         // ptr-addr cast. must be from thin ptr
 942
 943         match fcx.pointer_kind(m_expr.ty, self.span)? {
 944             None => Err(CastError::UnknownExprPtrKind),
 945             Some(PointerKind::Thin) => Ok(CastKind::PtrAddrCast),
 946             _ => Err(CastError::NeedViaThinPtr),
 947         }
 948     }
 949
 950     fn check_ref_cast(
 951         &self,
 952         fcx: &FnCtxt<'a, 'tcx>,
 953         m_expr: ty::TypeAndMut<'tcx>,
 954         m_cast: ty::TypeAndMut<'tcx>,
 955     ) -> Result<CastKind, CastError> {
 956         // array-ptr-cast: allow mut-to-mut, mut-to-const, const-to-const
 957         if m_expr.mutbl == hir::Mutability::Mut || m_cast.mutbl == hir::Mutability::Not {
 958             if let ty::Array(ety, _) = m_expr.ty.kind() {
 959                 // Due to the limitations of LLVM global constants,
 960                 // region pointers end up pointing at copies of
 961                 // vector elements instead of the original values.
 962                 // To allow raw pointers to work correctly, we
 963                 // need to special-case obtaining a raw pointer
 964                 // from a region pointer to a vector.
 965
 966                 // Coerce to a raw pointer so that we generate AddressOf in MIR.
 967                 let array_ptr_type = fcx.tcx.mk_ptr(m_expr);
 968                 fcx.try_coerce(self.expr, self.expr_ty, array_ptr_type, AllowTwoPhase::No, None)
 969                     .unwrap_or_else(|_| {
 970                         bug!(
 971                         "could not cast from reference to array to pointer to array ({:?} to {:?})",
 972                         self.expr_ty,
 973                         array_ptr_type,
 974                     )
 975                     });
 976
 977                 // this will report a type mismatch if needed
 978                 fcx.demand_eqtype(self.span, *ety, m_cast.ty);
 979                 return Ok(CastKind::ArrayPtrCast);
 980             }
 981         }
 982
 983         Err(CastError::IllegalCast)
 984     }
 985
 986     fn check_addr_ptr_cast(
 987         &self,
 988         fcx: &FnCtxt<'a, 'tcx>,
 989         m_cast: TypeAndMut<'tcx>,
 990     ) -> Result<CastKind, CastError> {
 991         // ptr-addr cast. pointer must be thin.
 992         match fcx.pointer_kind(m_cast.ty, self.span)? {
 993             None => Err(CastError::UnknownCastPtrKind),
 994             Some(PointerKind::Thin) => Ok(CastKind::AddrPtrCast),
 995             Some(PointerKind::VTable(_)) => Err(CastError::IntToFatCast(Some("a vtable"))),
 996             Some(PointerKind::Length) => Err(CastError::IntToFatCast(Some("a length"))),
 997             Some(
 998                 PointerKind::OfProjection(_)
 999                 | PointerKind::OfOpaque(_, _)
1000                 | PointerKind::OfParam(_),
1001             ) => Err(CastError::IntToFatCast(None)),
1002         }
1003     }
1004
1005     fn try_coercion_cast(&self, fcx: &FnCtxt<'a, 'tcx>) -> Result<(), ty::error::TypeError<'tcx>> {
1006         match fcx.try_coerce(self.expr, self.expr_ty, self.cast_ty, AllowTwoPhase::No, None) {
1007             Ok(_) => Ok(()),
1008             Err(err) => Err(err),
1009         }
1010     }
1011
1012     fn cenum_impl_drop_lint(&self, fcx: &FnCtxt<'a, 'tcx>) {
1013         if let ty::Adt(d, _) = self.expr_ty.kind()
1014             && d.has_dtor(fcx.tcx)
1015         {
1016             fcx.tcx.struct_span_lint_hir(
1017                 lint::builtin::CENUM_IMPL_DROP_CAST,
1018                 self.expr.hir_id,
1019                 self.span,
1020                 DelayDm(|| format!(
1021                     "cannot cast enum `{}` into integer `{}` because it implements `Drop`",
1022                     self.expr_ty, self.cast_ty
1023                 )),
1024                 |lint| {
1025                     lint
1026                 },
1027             );
1028         }
1029     }
1030
1031     fn lossy_provenance_ptr2int_lint(&self, fcx: &FnCtxt<'a, 'tcx>, t_c: ty::cast::IntTy) {
1032         fcx.tcx.struct_span_lint_hir(
1033             lint::builtin::LOSSY_PROVENANCE_CASTS,
1034             self.expr.hir_id,
1035             self.span,
1036             DelayDm(|| format!(
1037                     "under strict provenance it is considered bad style to cast pointer `{}` to integer `{}`",
1038                     self.expr_ty, self.cast_ty
1039                 )),
1040             |lint| {
1041                 let msg = "use `.addr()` to obtain the address of a pointer";
1042
1043                 let expr_prec = self.expr.precedence().order();
1044                 let needs_parens = expr_prec < rustc_ast::util::parser::PREC_POSTFIX;
1045
1046                 let scalar_cast = match t_c {
1047                     ty::cast::IntTy::U(ty::UintTy::Usize) => String::new(),
1048                     _ => format!(" as {}", self.cast_ty),
1049                 };
1050
1051                 let cast_span = self.expr_span.shrink_to_hi().to(self.cast_span);
1052
1053                 if needs_parens {
1054                     let suggestions = vec![
1055                         (self.expr_span.shrink_to_lo(), String::from("(")),
1056                         (cast_span, format!(").addr(){scalar_cast}")),
1057                     ];
1058
1059                     lint.multipart_suggestion(msg, suggestions, Applicability::MaybeIncorrect);
1060                 } else {
1061                     lint.span_suggestion(
1062                         cast_span,
1063                         msg,
1064                         format!(".addr(){scalar_cast}"),
1065                         Applicability::MaybeIncorrect,
1066                     );
1067                 }
1068
1069                 lint.help(
1070                     "if you can't comply with strict provenance and need to expose the pointer \
1071                     provenance you can use `.expose_addr()` instead"
1072                 );
1073
1074                 lint
1075             },
1076         );
1077     }
1078
1079     fn fuzzy_provenance_int2ptr_lint(&self, fcx: &FnCtxt<'a, 'tcx>) {
1080         fcx.tcx.struct_span_lint_hir(
1081             lint::builtin::FUZZY_PROVENANCE_CASTS,
1082             self.expr.hir_id,
1083             self.span,
1084             DelayDm(|| format!(
1085                 "strict provenance disallows casting integer `{}` to pointer `{}`",
1086                 self.expr_ty, self.cast_ty
1087             )),
1088             |lint| {
1089                 let msg = "use `.with_addr()` to adjust a valid pointer in the same allocation, to this address";
1090                 let suggestions = vec![
1091                     (self.expr_span.shrink_to_lo(), String::from("(...).with_addr(")),
1092                     (self.expr_span.shrink_to_hi().to(self.cast_span), String::from(")")),
1093                 ];
1094
1095                 lint.multipart_suggestion(msg, suggestions, Applicability::MaybeIncorrect);
1096                 lint.help(
1097                     "if you can't comply with strict provenance and don't have a pointer with \
1098                     the correct provenance you can use `std::ptr::from_exposed_addr()` instead"
1099                  );
1100
1101                 lint
1102             },
1103         );
1104     }
1105 }