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