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