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