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