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 use rustc_trait_selection::traits::error_reporting::report_object_safety_error;
  50
  51 /// Reifies a cast check to be checked once we have full type information for
  52 /// a function context.
  53 #[derive(Debug)]
  54 pub struct CastCheck<'tcx> {
  55     /// The expression whose value is being casted
  56     expr: &'tcx hir::Expr<'tcx>,
  57     /// The source type for the cast expression
  58     expr_ty: Ty<'tcx>,
  59     expr_span: Span,
  60     /// The target type. That is, the type we are casting to.
  61     cast_ty: Ty<'tcx>,
  62     cast_span: Span,
  63     span: Span,
  64     /// whether the cast is made in a const context or not.
  65     pub constness: hir::Constness,
  66 }
  67
  68 /// The kind of pointer and associated metadata (thin, length or vtable) - we
  69 /// only allow casts between fat pointers if their metadata have the same
  70 /// kind.
  71 #[derive(Debug, Copy, Clone, PartialEq, Eq, TypeVisitable, TypeFoldable)]
  72 enum PointerKind<'tcx> {
  73     /// No metadata attached, ie pointer to sized type or foreign type
  74     Thin,
  75     /// A trait object
  76     VTable(Option<DefId>),
  77     /// Slice
  78     Length,
  79     /// The unsize info of this projection
  80     OfProjection(ty::ProjectionTy<'tcx>),
  81     /// The unsize info of this opaque ty
  82     OfOpaque(DefId, SubstsRef<'tcx>),
  83     /// The unsize info of this parameter
  84     OfParam(ty::ParamTy),
  85 }
  86
  87 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  88     /// Returns the kind of unsize information of t, or None
  89     /// if t is unknown.
  90     fn pointer_kind(
  91         &self,
  92         t: Ty<'tcx>,
  93         span: Span,
  94     ) -> Result<Option<PointerKind<'tcx>>, ErrorGuaranteed> {
  95         debug!("pointer_kind({:?}, {:?})", t, span);
  96
  97         let t = self.resolve_vars_if_possible(t);
  98         t.error_reported()?;
  99
 100         if self.type_is_sized_modulo_regions(self.param_env, t, span) {
 101             return Ok(Some(PointerKind::Thin));
 102         }
 103
 104         Ok(match *t.kind() {
 105             ty::Slice(_) | ty::Str => Some(PointerKind::Length),
 106             ty::Dynamic(ref tty, _, ty::Dyn) => Some(PointerKind::VTable(tty.principal_def_id())),
 107             ty::Adt(def, substs) if def.is_struct() => match def.non_enum_variant().fields.last() {
 108                 None => Some(PointerKind::Thin),
 109                 Some(f) => {
 110                     let field_ty = self.field_ty(span, f, substs);
 111                     self.pointer_kind(field_ty, span)?
 112                 }
 113             },
 114             ty::Tuple(fields) => match fields.last() {
 115                 None => Some(PointerKind::Thin),
 116                 Some(&f) => self.pointer_kind(f, span)?,
 117             },
 118
 119             // Pointers to foreign types are thin, despite being unsized
 120             ty::Foreign(..) => Some(PointerKind::Thin),
 121             // We should really try to normalize here.
 122             ty::Projection(pi) => Some(PointerKind::OfProjection(pi)),
 123             ty::Opaque(def_id, substs) => Some(PointerKind::OfOpaque(def_id, substs)),
 124             ty::Param(p) => Some(PointerKind::OfParam(p)),
 125             // Insufficient type information.
 126             ty::Placeholder(..) | ty::Bound(..) | ty::Infer(_) => None,
 127
 128             ty::Bool
 129             | ty::Char
 130             | ty::Int(..)
 131             | ty::Uint(..)
 132             | ty::Float(_)
 133             | ty::Array(..)
 134             | ty::GeneratorWitness(..)
 135             | ty::RawPtr(_)
 136             | ty::Ref(..)
 137             | ty::FnDef(..)
 138             | ty::FnPtr(..)
 139             | ty::Closure(..)
 140             | ty::Generator(..)
 141             | ty::Adt(..)
 142             | ty::Never
 143             | ty::Dynamic(_, _, ty::DynStar)
 144             | ty::Error(_) => {
 145                 let reported = self
 146                     .tcx
 147                     .sess
 148                     .delay_span_bug(span, &format!("`{:?}` should be sized but is not?", t));
 149                 return Err(reported);
 150             }
 151         })
 152     }
 153 }
 154
 155 #[derive(Copy, Clone)]
 156 pub enum CastError {
 157     ErrorGuaranteed,
 158
 159     CastToBool,
 160     CastToChar,
 161     DifferingKinds,
 162     /// Cast of thin to fat raw ptr (e.g., `*const () as *const [u8]`).
 163     SizedUnsizedCast,
 164     IllegalCast,
 165     NeedDeref,
 166     NeedViaPtr,
 167     NeedViaThinPtr,
 168     NeedViaInt,
 169     NonScalar,
 170     UnknownExprPtrKind,
 171     UnknownCastPtrKind,
 172     /// Cast of int to (possibly) fat raw pointer.
 173     ///
 174     /// Argument is the specific name of the metadata in plain words, such as "a vtable"
 175     /// or "a length". If this argument is None, then the metadata is unknown, for example,
 176     /// when we're typechecking a type parameter with a ?Sized bound.
 177     IntToFatCast(Option<&'static str>),
 178     ForeignNonExhaustiveAdt,
 179 }
 180
 181 impl From<ErrorGuaranteed> for CastError {
 182     fn from(_: ErrorGuaranteed) -> Self {
 183         CastError::ErrorGuaranteed
 184     }
 185 }
 186
 187 fn make_invalid_casting_error<'a, 'tcx>(
 188     sess: &'a Session,
 189     span: Span,
 190     expr_ty: Ty<'tcx>,
 191     cast_ty: Ty<'tcx>,
 192     fcx: &FnCtxt<'a, 'tcx>,
 193 ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
 194     type_error_struct!(
 195         sess,
 196         span,
 197         expr_ty,
 198         E0606,
 199         "casting `{}` as `{}` is invalid",
 200         fcx.ty_to_string(expr_ty),
 201         fcx.ty_to_string(cast_ty)
 202     )
 203 }
 204
 205 impl<'a, 'tcx> CastCheck<'tcx> {
 206     pub fn new(
 207         fcx: &FnCtxt<'a, 'tcx>,
 208         expr: &'tcx hir::Expr<'tcx>,
 209         expr_ty: Ty<'tcx>,
 210         cast_ty: Ty<'tcx>,
 211         cast_span: Span,
 212         span: Span,
 213         constness: hir::Constness,
 214     ) -> Result<CastCheck<'tcx>, ErrorGuaranteed> {
 215         let expr_span = expr.span.find_ancestor_inside(span).unwrap_or(expr.span);
 216         let check = CastCheck { expr, expr_ty, expr_span, cast_ty, cast_span, span, constness };
 217
 218         // For better error messages, check for some obviously unsized
 219         // cases now. We do a more thorough check at the end, once
 220         // inference is more completely known.
 221         match cast_ty.kind() {
 222             ty::Dynamic(_, _, ty::Dyn) | ty::Slice(..) => {
 223                 Err(check.report_cast_to_unsized_type(fcx))
 224             }
 225             _ => Ok(check),
 226         }
 227     }
 228
 229     fn report_cast_error(&self, fcx: &FnCtxt<'a, 'tcx>, e: CastError) {
 230         match e {
 231             CastError::ErrorGuaranteed => {
 232                 // an error has already been reported
 233             }
 234             CastError::NeedDeref => {
 235                 let error_span = self.span;
 236                 let mut err = make_invalid_casting_error(
 237                     fcx.tcx.sess,
 238                     self.span,
 239                     self.expr_ty,
 240                     self.cast_ty,
 241                     fcx,
 242                 );
 243                 let cast_ty = fcx.ty_to_string(self.cast_ty);
 244                 err.span_label(
 245                     error_span,
 246                     format!("cannot cast `{}` as `{}`", fcx.ty_to_string(self.expr_ty), cast_ty),
 247                 );
 248                 if let Ok(snippet) = fcx.sess().source_map().span_to_snippet(self.expr_span) {
 249                     err.span_suggestion(
 250                         self.expr_span,
 251                         "dereference the expression",
 252                         format!("*{}", snippet),
 253                         Applicability::MaybeIncorrect,
 254                     );
 255                 } else {
 256                     err.span_help(self.expr_span, "dereference the expression with `*`");
 257                 }
 258                 err.emit();
 259             }
 260             CastError::NeedViaThinPtr | CastError::NeedViaPtr => {
 261                 let mut err = make_invalid_casting_error(
 262                     fcx.tcx.sess,
 263                     self.span,
 264                     self.expr_ty,
 265                     self.cast_ty,
 266                     fcx,
 267                 );
 268                 if self.cast_ty.is_integral() {
 269                     err.help(&format!(
 270                         "cast through {} first",
 271                         match e {
 272                             CastError::NeedViaPtr => "a raw pointer",
 273                             CastError::NeedViaThinPtr => "a thin pointer",
 274                             _ => bug!(),
 275                         }
 276                     ));
 277                 }
 278                 err.emit();
 279             }
 280             CastError::NeedViaInt => {
 281                 make_invalid_casting_error(
 282                     fcx.tcx.sess,
 283                     self.span,
 284                     self.expr_ty,
 285                     self.cast_ty,
 286                     fcx,
 287                 )
 288                 .help(&format!(
 289                     "cast through {} first",
 290                     match e {
 291                         CastError::NeedViaInt => "an integer",
 292                         _ => bug!(),
 293                     }
 294                 ))
 295                 .emit();
 296             }
 297             CastError::IllegalCast => {
 298                 make_invalid_casting_error(
 299                     fcx.tcx.sess,
 300                     self.span,
 301                     self.expr_ty,
 302                     self.cast_ty,
 303                     fcx,
 304                 )
 305                 .emit();
 306             }
 307             CastError::DifferingKinds => {
 308                 make_invalid_casting_error(
 309                     fcx.tcx.sess,
 310                     self.span,
 311                     self.expr_ty,
 312                     self.cast_ty,
 313                     fcx,
 314                 )
 315                 .note("vtable kinds may not match")
 316                 .emit();
 317             }
 318             CastError::CastToBool => {
 319                 let mut err =
 320                     struct_span_err!(fcx.tcx.sess, self.span, E0054, "cannot cast as `bool`");
 321
 322                 if self.expr_ty.is_numeric() {
 323                     match fcx.tcx.sess.source_map().span_to_snippet(self.expr_span) {
 324                         Ok(snippet) => {
 325                             err.span_suggestion(
 326                                 self.span,
 327                                 "compare with zero instead",
 328                                 format!("{snippet} != 0"),
 329                                 Applicability::MachineApplicable,
 330                             );
 331                         }
 332                         Err(_) => {
 333                             err.span_help(self.span, "compare with zero instead");
 334                         }
 335                     }
 336                 } else {
 337                     err.span_label(self.span, "unsupported cast");
 338                 }
 339
 340                 err.emit();
 341             }
 342             CastError::CastToChar => {
 343                 let mut err = type_error_struct!(
 344                     fcx.tcx.sess,
 345                     self.span,
 346                     self.expr_ty,
 347                     E0604,
 348                     "only `u8` can be cast as `char`, not `{}`",
 349                     self.expr_ty
 350                 );
 351                 err.span_label(self.span, "invalid cast");
 352                 if self.expr_ty.is_numeric() {
 353                     if self.expr_ty == fcx.tcx.types.u32 {
 354                         match fcx.tcx.sess.source_map().span_to_snippet(self.expr.span) {
 355                             Ok(snippet) => err.span_suggestion(
 356                                 self.span,
 357                                 "try `char::from_u32` instead",
 358                                 format!("char::from_u32({snippet})"),
 359                                 Applicability::MachineApplicable,
 360                             ),
 361
 362                             Err(_) => err.span_help(self.span, "try `char::from_u32` instead"),
 363                         };
 364                     } else if self.expr_ty == fcx.tcx.types.i8 {
 365                         err.span_help(self.span, "try casting from `u8` instead");
 366                     } else {
 367                         err.span_help(self.span, "try `char::from_u32` instead (via a `u32`)");
 368                     };
 369                 }
 370                 err.emit();
 371             }
 372             CastError::NonScalar => {
 373                 let mut err = type_error_struct!(
 374                     fcx.tcx.sess,
 375                     self.span,
 376                     self.expr_ty,
 377                     E0605,
 378                     "non-primitive cast: `{}` as `{}`",
 379                     self.expr_ty,
 380                     fcx.ty_to_string(self.cast_ty)
 381                 );
 382                 let mut sugg = None;
 383                 let mut sugg_mutref = false;
 384                 if let ty::Ref(reg, cast_ty, mutbl) = *self.cast_ty.kind() {
 385                     if let ty::RawPtr(TypeAndMut { ty: expr_ty, .. }) = *self.expr_ty.kind()
 386                         && fcx
 387                             .try_coerce(
 388                                 self.expr,
 389                                 fcx.tcx.mk_ref(
 390                                     fcx.tcx.lifetimes.re_erased,
 391                                     TypeAndMut { ty: expr_ty, mutbl },
 392                                 ),
 393                                 self.cast_ty,
 394                                 AllowTwoPhase::No,
 395                                 None,
 396                             )
 397                             .is_ok()
 398                     {
 399                         sugg = Some((format!("&{}*", mutbl.prefix_str()), cast_ty == expr_ty));
 400                     } else if let ty::Ref(expr_reg, expr_ty, expr_mutbl) = *self.expr_ty.kind()
 401                         && expr_mutbl == Mutability::Not
 402                         && mutbl == Mutability::Mut
 403                         && fcx
 404                             .try_coerce(
 405                                 self.expr,
 406                                 fcx.tcx.mk_ref(
 407                                     expr_reg,
 408                                     TypeAndMut { ty: expr_ty, mutbl: Mutability::Mut },
 409                                 ),
 410                                 self.cast_ty,
 411                                 AllowTwoPhase::No,
 412                                 None,
 413                             )
 414                             .is_ok()
 415                     {
 416                         sugg_mutref = true;
 417                     }
 418
 419                     if !sugg_mutref
 420                         && sugg == None
 421                         && fcx
 422                             .try_coerce(
 423                                 self.expr,
 424                                 fcx.tcx.mk_ref(reg, TypeAndMut { ty: self.expr_ty, mutbl }),
 425                                 self.cast_ty,
 426                                 AllowTwoPhase::No,
 427                                 None,
 428                             )
 429                             .is_ok()
 430                     {
 431                         sugg = Some((format!("&{}", mutbl.prefix_str()), false));
 432                     }
 433                 } else if let ty::RawPtr(TypeAndMut { mutbl, .. }) = *self.cast_ty.kind()
 434                     && fcx
 435                         .try_coerce(
 436                             self.expr,
 437                             fcx.tcx.mk_ref(
 438                                 fcx.tcx.lifetimes.re_erased,
 439                                 TypeAndMut { ty: self.expr_ty, mutbl },
 440                             ),
 441                             self.cast_ty,
 442                             AllowTwoPhase::No,
 443                             None,
 444                         )
 445                         .is_ok()
 446                 {
 447                     sugg = Some((format!("&{}", mutbl.prefix_str()), false));
 448                 }
 449                 if sugg_mutref {
 450                     err.span_label(self.span, "invalid cast");
 451                     err.span_note(self.expr_span, "this reference is immutable");
 452                     err.span_note(self.cast_span, "trying to cast to a mutable reference type");
 453                 } else if let Some((sugg, remove_cast)) = sugg {
 454                     err.span_label(self.span, "invalid cast");
 455
 456                     let has_parens = fcx
 457                         .tcx
 458                         .sess
 459                         .source_map()
 460                         .span_to_snippet(self.expr_span)
 461                         .map_or(false, |snip| snip.starts_with('('));
 462
 463                     // Very crude check to see whether the expression must be wrapped
 464                     // in parentheses for the suggestion to work (issue #89497).
 465                     // Can/should be extended in the future.
 466                     let needs_parens =
 467                         !has_parens && matches!(self.expr.kind, hir::ExprKind::Cast(..));
 468
 469                     let mut suggestion = vec![(self.expr_span.shrink_to_lo(), sugg)];
 470                     if needs_parens {
 471                         suggestion[0].1 += "(";
 472                         suggestion.push((self.expr_span.shrink_to_hi(), ")".to_string()));
 473                     }
 474                     if remove_cast {
 475                         suggestion.push((
 476                             self.expr_span.shrink_to_hi().to(self.cast_span),
 477                             String::new(),
 478                         ));
 479                     }
 480
 481                     err.multipart_suggestion_verbose(
 482                         "consider borrowing the value",
 483                         suggestion,
 484                         Applicability::MachineApplicable,
 485                     );
 486                 } else if !matches!(
 487                     self.cast_ty.kind(),
 488                     ty::FnDef(..) | ty::FnPtr(..) | ty::Closure(..)
 489                 ) {
 490                     let mut label = true;
 491                     // Check `impl From<self.expr_ty> for self.cast_ty {}` for accurate suggestion:
 492                     if let Ok(snippet) = fcx.tcx.sess.source_map().span_to_snippet(self.expr_span)
 493                         && let Some(from_trait) = fcx.tcx.get_diagnostic_item(sym::From)
 494                     {
 495                         let ty = fcx.resolve_vars_if_possible(self.cast_ty);
 496                         // Erase regions to avoid panic in `prove_value` when calling
 497                         // `type_implements_trait`.
 498                         let ty = fcx.tcx.erase_regions(ty);
 499                         let expr_ty = fcx.resolve_vars_if_possible(self.expr_ty);
 500                         let expr_ty = fcx.tcx.erase_regions(expr_ty);
 501                         let ty_params = fcx.tcx.mk_substs_trait(expr_ty, &[]);
 502                         if fcx
 503                             .infcx
 504                             .type_implements_trait(from_trait, ty, ty_params, fcx.param_env)
 505                             .must_apply_modulo_regions()
 506                         {
 507                             label = false;
 508                             err.span_suggestion(
 509                                 self.span,
 510                                 "consider using the `From` trait instead",
 511                                 format!("{}::from({})", self.cast_ty, snippet),
 512                                 Applicability::MaybeIncorrect,
 513                             );
 514                         }
 515                     }
 516                     let msg = "an `as` expression can only be used to convert between primitive \
 517                                types or to coerce to a specific trait object";
 518                     if label {
 519                         err.span_label(self.span, msg);
 520                     } else {
 521                         err.note(msg);
 522                     }
 523                 } else {
 524                     err.span_label(self.span, "invalid cast");
 525                 }
 526                 err.emit();
 527             }
 528             CastError::SizedUnsizedCast => {
 529                 use rustc_hir_analysis::structured_errors::{
 530                     SizedUnsizedCast, StructuredDiagnostic,
 531                 };
 532
 533                 SizedUnsizedCast {
 534                     sess: &fcx.tcx.sess,
 535                     span: self.span,
 536                     expr_ty: self.expr_ty,
 537                     cast_ty: fcx.ty_to_string(self.cast_ty),
 538                 }
 539                 .diagnostic()
 540                 .emit();
 541             }
 542             CastError::IntToFatCast(known_metadata) => {
 543                 let mut err = struct_span_err!(
 544                     fcx.tcx.sess,
 545                     self.cast_span,
 546                     E0606,
 547                     "cannot cast `{}` to a pointer that {} wide",
 548                     fcx.ty_to_string(self.expr_ty),
 549                     if known_metadata.is_some() { "is" } else { "may be" }
 550                 );
 551
 552                 err.span_label(
 553                     self.cast_span,
 554                     format!(
 555                         "creating a `{}` requires both an address and {}",
 556                         self.cast_ty,
 557                         known_metadata.unwrap_or("type-specific metadata"),
 558                     ),
 559                 );
 560
 561                 if fcx.tcx.sess.is_nightly_build() {
 562                     err.span_label(
 563                         self.expr_span,
 564                         "consider casting this expression to `*const ()`, \
 565                         then using `core::ptr::from_raw_parts`",
 566                     );
 567                 }
 568
 569                 err.emit();
 570             }
 571             CastError::UnknownCastPtrKind | CastError::UnknownExprPtrKind => {
 572                 let unknown_cast_to = match e {
 573                     CastError::UnknownCastPtrKind => true,
 574                     CastError::UnknownExprPtrKind => false,
 575                     _ => bug!(),
 576                 };
 577                 let mut err = struct_span_err!(
 578                     fcx.tcx.sess,
 579                     if unknown_cast_to { self.cast_span } else { self.span },
 580                     E0641,
 581                     "cannot cast {} a pointer of an unknown kind",
 582                     if unknown_cast_to { "to" } else { "from" }
 583                 );
 584                 if unknown_cast_to {
 585                     err.span_label(self.cast_span, "needs more type information");
 586                     err.note(
 587                         "the type information given here is insufficient to check whether \
 588                         the pointer cast is valid",
 589                     );
 590                 } else {
 591                     err.span_label(
 592                         self.span,
 593                         "the type information given here is insufficient to check whether \
 594                         the pointer cast is valid",
 595                     );
 596                 }
 597                 err.emit();
 598             }
 599             CastError::ForeignNonExhaustiveAdt => {
 600                 make_invalid_casting_error(
 601                     fcx.tcx.sess,
 602                     self.span,
 603                     self.expr_ty,
 604                     self.cast_ty,
 605                     fcx,
 606                 )
 607                 .note("cannot cast an enum with a non-exhaustive variant when it's defined in another crate")
 608                 .emit();
 609             }
 610         }
 611     }
 612
 613     fn report_cast_to_unsized_type(&self, fcx: &FnCtxt<'a, 'tcx>) -> ErrorGuaranteed {
 614         if let Err(err) = self.cast_ty.error_reported() {
 615             return err;
 616         }
 617         if let Err(err) = self.expr_ty.error_reported() {
 618             return err;
 619         }
 620
 621         let tstr = fcx.ty_to_string(self.cast_ty);
 622         let mut err = type_error_struct!(
 623             fcx.tcx.sess,
 624             self.span,
 625             self.expr_ty,
 626             E0620,
 627             "cast to unsized type: `{}` as `{}`",
 628             fcx.resolve_vars_if_possible(self.expr_ty),
 629             tstr
 630         );
 631         match self.expr_ty.kind() {
 632             ty::Ref(_, _, mt) => {
 633                 let mtstr = mt.prefix_str();
 634                 if self.cast_ty.is_trait() {
 635                     match fcx.tcx.sess.source_map().span_to_snippet(self.cast_span) {
 636                         Ok(s) => {
 637                             err.span_suggestion(
 638                                 self.cast_span,
 639                                 "try casting to a reference instead",
 640                                 format!("&{}{}", mtstr, s),
 641                                 Applicability::MachineApplicable,
 642                             );
 643                         }
 644                         Err(_) => {
 645                             let msg = &format!("did you mean `&{}{}`?", mtstr, tstr);
 646                             err.span_help(self.cast_span, msg);
 647                         }
 648                     }
 649                 } else {
 650                     let msg =
 651                         &format!("consider using an implicit coercion to `&{mtstr}{tstr}` instead");
 652                     err.span_help(self.span, msg);
 653                 }
 654             }
 655             ty::Adt(def, ..) if def.is_box() => {
 656                 match fcx.tcx.sess.source_map().span_to_snippet(self.cast_span) {
 657                     Ok(s) => {
 658                         err.span_suggestion(
 659                             self.cast_span,
 660                             "you can cast to a `Box` instead",
 661                             format!("Box<{s}>"),
 662                             Applicability::MachineApplicable,
 663                         );
 664                     }
 665                     Err(_) => {
 666                         err.span_help(
 667                             self.cast_span,
 668                             &format!("you might have meant `Box<{tstr}>`"),
 669                         );
 670                     }
 671                 }
 672             }
 673             _ => {
 674                 err.span_help(self.expr_span, "consider using a box or reference as appropriate");
 675             }
 676         }
 677         err.emit()
 678     }
 679
 680     fn trivial_cast_lint(&self, fcx: &FnCtxt<'a, 'tcx>) {
 681         let t_cast = self.cast_ty;
 682         let t_expr = self.expr_ty;
 683         let type_asc_or =
 684             if fcx.tcx.features().type_ascription { "type ascription or " } else { "" };
 685         let (adjective, lint) = if t_cast.is_numeric() && t_expr.is_numeric() {
 686             ("numeric ", lint::builtin::TRIVIAL_NUMERIC_CASTS)
 687         } else {
 688             ("", lint::builtin::TRIVIAL_CASTS)
 689         };
 690         fcx.tcx.struct_span_lint_hir(
 691             lint,
 692             self.expr.hir_id,
 693             self.span,
 694             DelayDm(|| {
 695                 format!(
 696                     "trivial {}cast: `{}` as `{}`",
 697                     adjective,
 698                     fcx.ty_to_string(t_expr),
 699                     fcx.ty_to_string(t_cast)
 700                 )
 701             }),
 702             |lint| {
 703                 lint.help(format!(
 704                     "cast can be replaced by coercion; this might \
 705                      require {type_asc_or}a temporary variable"
 706                 ))
 707             },
 708         );
 709     }
 710
 711     #[instrument(skip(fcx), level = "debug")]
 712     pub fn check(mut self, fcx: &FnCtxt<'a, 'tcx>) {
 713         self.expr_ty = fcx.structurally_resolved_type(self.expr_span, self.expr_ty);
 714         self.cast_ty = fcx.structurally_resolved_type(self.cast_span, self.cast_ty);
 715
 716         debug!("check_cast({}, {:?} as {:?})", self.expr.hir_id, self.expr_ty, self.cast_ty);
 717
 718         if !fcx.type_is_sized_modulo_regions(fcx.param_env, self.cast_ty, self.span)
 719             && !self.cast_ty.has_infer_types()
 720         {
 721             self.report_cast_to_unsized_type(fcx);
 722         } else if self.expr_ty.references_error() || self.cast_ty.references_error() {
 723             // No sense in giving duplicate error messages
 724         } else {
 725             match self.try_coercion_cast(fcx) {
 726                 Ok(()) => {
 727                     self.trivial_cast_lint(fcx);
 728                     debug!(" -> CoercionCast");
 729                     fcx.typeck_results.borrow_mut().set_coercion_cast(self.expr.hir_id.local_id);
 730                 }
 731                 Err(ty::error::TypeError::ObjectUnsafeCoercion(did)) => {
 732                     self.report_object_unsafe_cast(&fcx, did);
 733                 }
 734                 Err(_) => {
 735                     match self.do_check(fcx) {
 736                         Ok(k) => {
 737                             debug!(" -> {:?}", k);
 738                         }
 739                         Err(e) => self.report_cast_error(fcx, e),
 740                     };
 741                 }
 742             };
 743         }
 744     }
 745
 746     fn report_object_unsafe_cast(&self, fcx: &FnCtxt<'a, 'tcx>, did: DefId) {
 747         let violations = fcx.tcx.object_safety_violations(did);
 748         let mut err = report_object_safety_error(fcx.tcx, self.cast_span, did, violations);
 749         err.note(&format!("required by cast to type '{}'", fcx.ty_to_string(self.cast_ty)));
 750         err.emit();
 751     }
 752
 753     /// Checks a cast, and report an error if one exists. In some cases, this
 754     /// can return Ok and create type errors in the fcx rather than returning
 755     /// directly. coercion-cast is handled in check instead of here.
 756     pub fn do_check(&self, fcx: &FnCtxt<'a, 'tcx>) -> Result<CastKind, CastError> {
 757         use rustc_middle::ty::cast::CastTy::*;
 758         use rustc_middle::ty::cast::IntTy::*;
 759
 760         let (t_from, t_cast) = match (CastTy::from_ty(self.expr_ty), CastTy::from_ty(self.cast_ty))
 761         {
 762             (Some(t_from), Some(t_cast)) => (t_from, t_cast),
 763             // Function item types may need to be reified before casts.
 764             (None, Some(t_cast)) => {
 765                 match *self.expr_ty.kind() {
 766                     ty::FnDef(..) => {
 767                         // Attempt a coercion to a fn pointer type.
 768                         let f = fcx.normalize_associated_types_in(
 769                             self.expr_span,
 770                             self.expr_ty.fn_sig(fcx.tcx),
 771                         );
 772                         let res = fcx.try_coerce(
 773                             self.expr,
 774                             self.expr_ty,
 775                             fcx.tcx.mk_fn_ptr(f),
 776                             AllowTwoPhase::No,
 777                             None,
 778                         );
 779                         if let Err(TypeError::IntrinsicCast) = res {
 780                             return Err(CastError::IllegalCast);
 781                         }
 782                         if res.is_err() {
 783                             return Err(CastError::NonScalar);
 784                         }
 785                         (FnPtr, t_cast)
 786                     }
 787                     // Special case some errors for references, and check for
 788                     // array-ptr-casts. `Ref` is not a CastTy because the cast
 789                     // is split into a coercion to a pointer type, followed by
 790                     // a cast.
 791                     ty::Ref(_, inner_ty, mutbl) => {
 792                         return match t_cast {
 793                             Int(_) | Float => match *inner_ty.kind() {
 794                                 ty::Int(_)
 795                                 | ty::Uint(_)
 796                                 | ty::Float(_)
 797                                 | ty::Infer(ty::InferTy::IntVar(_) | ty::InferTy::FloatVar(_)) => {
 798                                     Err(CastError::NeedDeref)
 799                                 }
 800                                 _ => Err(CastError::NeedViaPtr),
 801                             },
 802                             // array-ptr-cast
 803                             Ptr(mt) => {
 804                                 self.check_ref_cast(fcx, TypeAndMut { mutbl, ty: inner_ty }, mt)
 805                             }
 806                             _ => Err(CastError::NonScalar),
 807                         };
 808                     }
 809                     _ => return Err(CastError::NonScalar),
 810                 }
 811             }
 812             _ => return Err(CastError::NonScalar),
 813         };
 814
 815         if let ty::Adt(adt_def, _) = *self.expr_ty.kind() {
 816             if adt_def.did().krate != LOCAL_CRATE {
 817                 if adt_def.variants().iter().any(VariantDef::is_field_list_non_exhaustive) {
 818                     return Err(CastError::ForeignNonExhaustiveAdt);
 819                 }
 820             }
 821         }
 822
 823         match (t_from, t_cast) {
 824             // These types have invariants! can't cast into them.
 825             (_, Int(CEnum) | FnPtr) => Err(CastError::NonScalar),
 826
 827             // * -> Bool
 828             (_, Int(Bool)) => Err(CastError::CastToBool),
 829
 830             // * -> Char
 831             (Int(U(ty::UintTy::U8)), Int(Char)) => Ok(CastKind::U8CharCast), // u8-char-cast
 832             (_, Int(Char)) => Err(CastError::CastToChar),
 833
 834             // prim -> float,ptr
 835             (Int(Bool) | Int(CEnum) | Int(Char), Float) => Err(CastError::NeedViaInt),
 836
 837             (Int(Bool) | Int(CEnum) | Int(Char) | Float, Ptr(_)) | (Ptr(_) | FnPtr, Float) => {
 838                 Err(CastError::IllegalCast)
 839             }
 840
 841             // ptr -> *
 842             (Ptr(m_e), Ptr(m_c)) => self.check_ptr_ptr_cast(fcx, m_e, m_c), // ptr-ptr-cast
 843
 844             // ptr-addr-cast
 845             (Ptr(m_expr), Int(t_c)) => {
 846                 self.lossy_provenance_ptr2int_lint(fcx, t_c);
 847                 self.check_ptr_addr_cast(fcx, m_expr)
 848             }
 849             (FnPtr, Int(_)) => {
 850                 // FIXME(#95489): there should eventually be a lint for these casts
 851                 Ok(CastKind::FnPtrAddrCast)
 852             }
 853             // addr-ptr-cast
 854             (Int(_), Ptr(mt)) => {
 855                 self.fuzzy_provenance_int2ptr_lint(fcx);
 856                 self.check_addr_ptr_cast(fcx, mt)
 857             }
 858             // fn-ptr-cast
 859             (FnPtr, Ptr(mt)) => self.check_fptr_ptr_cast(fcx, mt),
 860
 861             // prim -> prim
 862             (Int(CEnum), Int(_)) => {
 863                 self.cenum_impl_drop_lint(fcx);
 864                 Ok(CastKind::EnumCast)
 865             }
 866             (Int(Char) | Int(Bool), Int(_)) => Ok(CastKind::PrimIntCast),
 867
 868             (Int(_) | Float, Int(_) | Float) => Ok(CastKind::NumericCast),
 869
 870             (_, DynStar) | (DynStar, _) => {
 871                 if fcx.tcx.features().dyn_star {
 872                     bug!("should be handled by `try_coerce`")
 873                 } else {
 874                     Err(CastError::IllegalCast)
 875                 }
 876             }
 877         }
 878     }
 879
 880     fn check_ptr_ptr_cast(
 881         &self,
 882         fcx: &FnCtxt<'a, 'tcx>,
 883         m_expr: ty::TypeAndMut<'tcx>,
 884         m_cast: ty::TypeAndMut<'tcx>,
 885     ) -> Result<CastKind, CastError> {
 886         debug!("check_ptr_ptr_cast m_expr={:?} m_cast={:?}", m_expr, m_cast);
 887         // ptr-ptr cast. vtables must match.
 888
 889         let expr_kind = fcx.pointer_kind(m_expr.ty, self.span)?;
 890         let cast_kind = fcx.pointer_kind(m_cast.ty, self.span)?;
 891
 892         let Some(cast_kind) = cast_kind else {
 893             // We can't cast if target pointer kind is unknown
 894             return Err(CastError::UnknownCastPtrKind);
 895         };
 896
 897         // Cast to thin pointer is OK
 898         if cast_kind == PointerKind::Thin {
 899             return Ok(CastKind::PtrPtrCast);
 900         }
 901
 902         let Some(expr_kind) = expr_kind else {
 903             // We can't cast to fat pointer if source pointer kind is unknown
 904             return Err(CastError::UnknownExprPtrKind);
 905         };
 906
 907         // thin -> fat? report invalid cast (don't complain about vtable kinds)
 908         if expr_kind == PointerKind::Thin {
 909             return Err(CastError::SizedUnsizedCast);
 910         }
 911
 912         // vtable kinds must match
 913         if fcx.tcx.erase_regions(cast_kind) == fcx.tcx.erase_regions(expr_kind) {
 914             Ok(CastKind::PtrPtrCast)
 915         } else {
 916             Err(CastError::DifferingKinds)
 917         }
 918     }
 919
 920     fn check_fptr_ptr_cast(
 921         &self,
 922         fcx: &FnCtxt<'a, 'tcx>,
 923         m_cast: ty::TypeAndMut<'tcx>,
 924     ) -> Result<CastKind, CastError> {
 925         // fptr-ptr cast. must be to thin ptr
 926
 927         match fcx.pointer_kind(m_cast.ty, self.span)? {
 928             None => Err(CastError::UnknownCastPtrKind),
 929             Some(PointerKind::Thin) => Ok(CastKind::FnPtrPtrCast),
 930             _ => Err(CastError::IllegalCast),
 931         }
 932     }
 933
 934     fn check_ptr_addr_cast(
 935         &self,
 936         fcx: &FnCtxt<'a, 'tcx>,
 937         m_expr: ty::TypeAndMut<'tcx>,
 938     ) -> Result<CastKind, CastError> {
 939         // ptr-addr cast. must be from thin ptr
 940
 941         match fcx.pointer_kind(m_expr.ty, self.span)? {
 942             None => Err(CastError::UnknownExprPtrKind),
 943             Some(PointerKind::Thin) => Ok(CastKind::PtrAddrCast),
 944             _ => Err(CastError::NeedViaThinPtr),
 945         }
 946     }
 947
 948     fn check_ref_cast(
 949         &self,
 950         fcx: &FnCtxt<'a, 'tcx>,
 951         m_expr: ty::TypeAndMut<'tcx>,
 952         m_cast: ty::TypeAndMut<'tcx>,
 953     ) -> Result<CastKind, CastError> {
 954         // array-ptr-cast: allow mut-to-mut, mut-to-const, const-to-const
 955         if m_expr.mutbl == hir::Mutability::Mut || m_cast.mutbl == hir::Mutability::Not {
 956             if let ty::Array(ety, _) = m_expr.ty.kind() {
 957                 // Due to the limitations of LLVM global constants,
 958                 // region pointers end up pointing at copies of
 959                 // vector elements instead of the original values.
 960                 // To allow raw pointers to work correctly, we
 961                 // need to special-case obtaining a raw pointer
 962                 // from a region pointer to a vector.
 963
 964                 // Coerce to a raw pointer so that we generate AddressOf in MIR.
 965                 let array_ptr_type = fcx.tcx.mk_ptr(m_expr);
 966                 fcx.try_coerce(self.expr, self.expr_ty, array_ptr_type, AllowTwoPhase::No, None)
 967                     .unwrap_or_else(|_| {
 968                         bug!(
 969                         "could not cast from reference to array to pointer to array ({:?} to {:?})",
 970                         self.expr_ty,
 971                         array_ptr_type,
 972                     )
 973                     });
 974
 975                 // this will report a type mismatch if needed
 976                 fcx.demand_eqtype(self.span, *ety, m_cast.ty);
 977                 return Ok(CastKind::ArrayPtrCast);
 978             }
 979         }
 980
 981         Err(CastError::IllegalCast)
 982     }
 983
 984     fn check_addr_ptr_cast(
 985         &self,
 986         fcx: &FnCtxt<'a, 'tcx>,
 987         m_cast: TypeAndMut<'tcx>,
 988     ) -> Result<CastKind, CastError> {
 989         // ptr-addr cast. pointer must be thin.
 990         match fcx.pointer_kind(m_cast.ty, self.span)? {
 991             None => Err(CastError::UnknownCastPtrKind),
 992             Some(PointerKind::Thin) => Ok(CastKind::AddrPtrCast),
 993             Some(PointerKind::VTable(_)) => Err(CastError::IntToFatCast(Some("a vtable"))),
 994             Some(PointerKind::Length) => Err(CastError::IntToFatCast(Some("a length"))),
 995             Some(
 996                 PointerKind::OfProjection(_)
 997                 | PointerKind::OfOpaque(_, _)
 998                 | PointerKind::OfParam(_),
 999             ) => Err(CastError::IntToFatCast(None)),
1000         }
1001     }
1002
1003     fn try_coercion_cast(&self, fcx: &FnCtxt<'a, 'tcx>) -> Result<(), ty::error::TypeError<'tcx>> {
1004         match fcx.try_coerce(self.expr, self.expr_ty, self.cast_ty, AllowTwoPhase::No, None) {
1005             Ok(_) => Ok(()),
1006             Err(err) => Err(err),
1007         }
1008     }
1009
1010     fn cenum_impl_drop_lint(&self, fcx: &FnCtxt<'a, 'tcx>) {
1011         if let ty::Adt(d, _) = self.expr_ty.kind()
1012             && d.has_dtor(fcx.tcx)
1013         {
1014             fcx.tcx.struct_span_lint_hir(
1015                 lint::builtin::CENUM_IMPL_DROP_CAST,
1016                 self.expr.hir_id,
1017                 self.span,
1018                 DelayDm(|| format!(
1019                     "cannot cast enum `{}` into integer `{}` because it implements `Drop`",
1020                     self.expr_ty, self.cast_ty
1021                 )),
1022                 |lint| {
1023                     lint
1024                 },
1025             );
1026         }
1027     }
1028
1029     fn lossy_provenance_ptr2int_lint(&self, fcx: &FnCtxt<'a, 'tcx>, t_c: ty::cast::IntTy) {
1030         fcx.tcx.struct_span_lint_hir(
1031             lint::builtin::LOSSY_PROVENANCE_CASTS,
1032             self.expr.hir_id,
1033             self.span,
1034             DelayDm(|| format!(
1035                     "under strict provenance it is considered bad style to cast pointer `{}` to integer `{}`",
1036                     self.expr_ty, self.cast_ty
1037                 )),
1038             |lint| {
1039                 let msg = "use `.addr()` to obtain the address of a pointer";
1040
1041                 let expr_prec = self.expr.precedence().order();
1042                 let needs_parens = expr_prec < rustc_ast::util::parser::PREC_POSTFIX;
1043
1044                 let scalar_cast = match t_c {
1045                     ty::cast::IntTy::U(ty::UintTy::Usize) => String::new(),
1046                     _ => format!(" as {}", self.cast_ty),
1047                 };
1048
1049                 let cast_span = self.expr_span.shrink_to_hi().to(self.cast_span);
1050
1051                 if needs_parens {
1052                     let suggestions = vec![
1053                         (self.expr_span.shrink_to_lo(), String::from("(")),
1054                         (cast_span, format!(").addr(){scalar_cast}")),
1055                     ];
1056
1057                     lint.multipart_suggestion(msg, suggestions, Applicability::MaybeIncorrect);
1058                 } else {
1059                     lint.span_suggestion(
1060                         cast_span,
1061                         msg,
1062                         format!(".addr(){scalar_cast}"),
1063                         Applicability::MaybeIncorrect,
1064                     );
1065                 }
1066
1067                 lint.help(
1068                     "if you can't comply with strict provenance and need to expose the pointer \
1069                     provenance you can use `.expose_addr()` instead"
1070                 );
1071
1072                 lint
1073             },
1074         );
1075     }
1076
1077     fn fuzzy_provenance_int2ptr_lint(&self, fcx: &FnCtxt<'a, 'tcx>) {
1078         fcx.tcx.struct_span_lint_hir(
1079             lint::builtin::FUZZY_PROVENANCE_CASTS,
1080             self.expr.hir_id,
1081             self.span,
1082             DelayDm(|| format!(
1083                 "strict provenance disallows casting integer `{}` to pointer `{}`",
1084                 self.expr_ty, self.cast_ty
1085             )),
1086             |lint| {
1087                 let msg = "use `.with_addr()` to adjust a valid pointer in the same allocation, to this address";
1088                 let suggestions = vec![
1089                     (self.expr_span.shrink_to_lo(), String::from("(...).with_addr(")),
1090                     (self.expr_span.shrink_to_hi().to(self.cast_span), String::from(")")),
1091                 ];
1092
1093                 lint.multipart_suggestion(msg, suggestions, Applicability::MaybeIncorrect);
1094                 lint.help(
1095                     "if you can't comply with strict provenance and don't have a pointer with \
1096                     the correct provenance you can use `std::ptr::from_exposed_addr()` instead"
1097                  );
1098
1099                 lint
1100             },
1101         );
1102     }
1103 }