compiler/rustc_hir_typeck/src/cast.rs

   1 //! Code for type-checking cast expressions.
   2 //!
   3 //! A cast `e as U` is valid if one of the following holds:
   4 //! * `e` has type `T` and `T` coerces to `U`; *coercion-cast*
   5 //! * `e` has type `*T`, `U` is `*U_0`, and either `U_0: Sized` or
   6 //!    pointer_kind(`T`) = pointer_kind(`U_0`); *ptr-ptr-cast*
   7 //! * `e` has type `*T` and `U` is a numeric type, while `T: Sized`; *ptr-addr-cast*
   8 //! * `e` is an integer and `U` is `*U_0`, while `U_0: Sized`; *addr-ptr-cast*
   9 //! * `e` has type `T` and `T` and `U` are any numeric types; *numeric-cast*
  10 //! * `e` is a C-like enum and `U` is an integer type; *enum-cast*
  11 //! * `e` has type `bool` or `char` and `U` is an integer; *prim-int-cast*
  12 //! * `e` has type `u8` and `U` is `char`; *u8-char-cast*
  13 //! * `e` has type `&[T; n]` and `U` is `*const T`; *array-ptr-cast*
  14 //! * `e` is a function pointer type and `U` has type `*T`,
  15 //!   while `T: Sized`; *fptr-ptr-cast*
  16 //! * `e` is a function pointer type and `U` is an integer; *fptr-addr-cast*
  17 //!
  18 //! where `&.T` and `*T` are references of either mutability,
  19 //! and where pointer_kind(`T`) is the kind of the unsize info
  20 //! in `T` - the vtable for a trait definition (e.g., `fmt::Display` or
  21 //! `Iterator`, not `Iterator<Item=u8>`) or a length (or `()` if `T: Sized`).
  22 //!
  23 //! Note that lengths are not adjusted when casting raw slices -
  24 //! `T: *const [u16] as *const [u8]` creates a slice that only includes
  25 //! half of the original memory.
  26 //!
  27 //! Casting is not transitive, that is, even if `e as U1 as U2` is a valid
  28 //! expression, `e as U2` is not necessarily so (in fact it will only be valid if
  29 //! `U1` coerces to `U2`).
  30
  31 use super::FnCtxt;
  32
  33 use crate::type_error_struct;
  34 use rustc_errors::{struct_span_err, Applicability, DelayDm, DiagnosticBuilder, ErrorGuaranteed};
  35 use rustc_hir as hir;
  36 use rustc_macros::{TypeFoldable, TypeVisitable};
  37 use rustc_middle::mir::Mutability;
  38 use rustc_middle::ty::adjustment::AllowTwoPhase;
  39 use rustc_middle::ty::cast::{CastKind, CastTy};
  40 use rustc_middle::ty::error::TypeError;
  41 use rustc_middle::ty::{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
  49 /// Reifies a cast check to be checked once we have full type information for
  50 /// a function context.
  51 #[derive(Debug)]
  52 pub struct CastCheck<'tcx> {
  53     /// The expression whose value is being casted
  54     expr: &'tcx hir::Expr<'tcx>,
  55     /// The source type for the cast expression
  56     expr_ty: Ty<'tcx>,
  57     expr_span: Span,
  58     /// The target type. That is, the type we are casting to.
  59     cast_ty: Ty<'tcx>,
  60     cast_span: Span,
  61     span: Span,
  62     /// whether the cast is made in a const context or not.
  63     pub constness: hir::Constness,
  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(Debug, Copy, Clone, PartialEq, Eq, TypeVisitable, TypeFoldable)]
  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 or opaque type
  78     OfAlias(ty::AliasTy<'tcx>),
  79     /// The unsize info of this parameter
  80     OfParam(ty::ParamTy),
  81 }
  82
  83 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  84     /// Returns the kind of unsize information of t, or None
  85     /// if t is unknown.
  86     fn pointer_kind(
  87         &self,
  88         t: Ty<'tcx>,
  89         span: Span,
  90     ) -> Result<Option<PointerKind<'tcx>>, ErrorGuaranteed> {
  91         debug!("pointer_kind({:?}, {:?})", t, span);
  92
  93         let t = self.resolve_vars_if_possible(t);
  94         t.error_reported()?;
  95
  96         if self.type_is_sized_modulo_regions(self.param_env, t, span) {
  97             return Ok(Some(PointerKind::Thin));
  98         }
  99
 100         Ok(match *t.kind() {
 101             ty::Slice(_) | ty::Str => Some(PointerKind::Length),
 102             ty::Dynamic(ref tty, _, ty::Dyn) => Some(PointerKind::VTable(tty.principal_def_id())),
 103             ty::Adt(def, substs) if def.is_struct() => match def.non_enum_variant().fields.last() {
 104                 None => Some(PointerKind::Thin),
 105                 Some(f) => {
 106                     let field_ty = self.field_ty(span, f, substs);
 107                     self.pointer_kind(field_ty, span)?
 108                 }
 109             },
 110             ty::Tuple(fields) => match fields.last() {
 111                 None => Some(PointerKind::Thin),
 112                 Some(&f) => self.pointer_kind(f, span)?,
 113             },
 114
 115             // Pointers to foreign types are thin, despite being unsized
 116             ty::Foreign(..) => Some(PointerKind::Thin),
 117             // We should really try to normalize here.
 118             ty::Alias(_, pi) => Some(PointerKind::OfAlias(pi)),
 119             ty::Param(p) => Some(PointerKind::OfParam(p)),
 120             // Insufficient type information.
 121             ty::Placeholder(..) | ty::Bound(..) | ty::Infer(_) => None,
 122
 123             ty::Bool
 124             | ty::Char
 125             | ty::Int(..)
 126             | ty::Uint(..)
 127             | ty::Float(_)
 128             | ty::Array(..)
 129             | ty::GeneratorWitness(..)
 130             | ty::RawPtr(_)
 131             | ty::Ref(..)
 132             | ty::FnDef(..)
 133             | ty::FnPtr(..)
 134             | ty::Closure(..)
 135             | ty::Generator(..)
 136             | ty::Adt(..)
 137             | ty::Never
 138             | ty::Dynamic(_, _, ty::DynStar)
 139             | ty::Error(_) => {
 140                 let reported = self
 141                     .tcx
 142                     .sess
 143                     .delay_span_bug(span, &format!("`{:?}` should be sized but is not?", t));
 144                 return Err(reported);
 145             }
 146         })
 147     }
 148 }
 149
 150 #[derive(Copy, Clone)]
 151 pub enum CastError {
 152     ErrorGuaranteed,
 153
 154     CastToBool,
 155     CastToChar,
 156     DifferingKinds,
 157     /// Cast of thin to fat raw ptr (e.g., `*const () as *const [u8]`).
 158     SizedUnsizedCast,
 159     IllegalCast,
 160     NeedDeref,
 161     NeedViaPtr,
 162     NeedViaThinPtr,
 163     NeedViaInt,
 164     NonScalar,
 165     UnknownExprPtrKind,
 166     UnknownCastPtrKind,
 167     /// Cast of int to (possibly) fat raw pointer.
 168     ///
 169     /// Argument is the specific name of the metadata in plain words, such as "a vtable"
 170     /// or "a length". If this argument is None, then the metadata is unknown, for example,
 171     /// when we're typechecking a type parameter with a ?Sized bound.
 172     IntToFatCast(Option<&'static str>),
 173     ForeignNonExhaustiveAdt,
 174 }
 175
 176 impl From<ErrorGuaranteed> for CastError {
 177     fn from(_: ErrorGuaranteed) -> Self {
 178         CastError::ErrorGuaranteed
 179     }
 180 }
 181
 182 fn make_invalid_casting_error<'a, 'tcx>(
 183     sess: &'a Session,
 184     span: Span,
 185     expr_ty: Ty<'tcx>,
 186     cast_ty: Ty<'tcx>,
 187     fcx: &FnCtxt<'a, 'tcx>,
 188 ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
 189     type_error_struct!(
 190         sess,
 191         span,
 192         expr_ty,
 193         E0606,
 194         "casting `{}` as `{}` is invalid",
 195         fcx.ty_to_string(expr_ty),
 196         fcx.ty_to_string(cast_ty)
 197     )
 198 }
 199
 200 impl<'a, 'tcx> CastCheck<'tcx> {
 201     pub fn new(
 202         fcx: &FnCtxt<'a, 'tcx>,
 203         expr: &'tcx hir::Expr<'tcx>,
 204         expr_ty: Ty<'tcx>,
 205         cast_ty: Ty<'tcx>,
 206         cast_span: Span,
 207         span: Span,
 208         constness: hir::Constness,
 209     ) -> Result<CastCheck<'tcx>, ErrorGuaranteed> {
 210         let expr_span = expr.span.find_ancestor_inside(span).unwrap_or(expr.span);
 211         let check = CastCheck { expr, expr_ty, expr_span, cast_ty, cast_span, span, constness };
 212
 213         // For better error messages, check for some obviously unsized
 214         // cases now. We do a more thorough check at the end, once
 215         // inference is more completely known.
 216         match cast_ty.kind() {
 217             ty::Dynamic(_, _, ty::Dyn) | ty::Slice(..) => {
 218                 Err(check.report_cast_to_unsized_type(fcx))
 219             }
 220             _ => Ok(check),
 221         }
 222     }
 223
 224     fn report_cast_error(&self, fcx: &FnCtxt<'a, 'tcx>, e: CastError) {
 225         match e {
 226             CastError::ErrorGuaranteed => {
 227                 // an error has already been reported
 228             }
 229             CastError::NeedDeref => {
 230                 let error_span = self.span;
 231                 let mut err = make_invalid_casting_error(
 232                     fcx.tcx.sess,
 233                     self.span,
 234                     self.expr_ty,
 235                     self.cast_ty,
 236                     fcx,
 237                 );
 238                 let cast_ty = fcx.ty_to_string(self.cast_ty);
 239                 err.span_label(
 240                     error_span,
 241                     format!("cannot cast `{}` as `{}`", fcx.ty_to_string(self.expr_ty), cast_ty),
 242                 );
 243                 if let Ok(snippet) = fcx.sess().source_map().span_to_snippet(self.expr_span) {
 244                     err.span_suggestion(
 245                         self.expr_span,
 246                         "dereference the expression",
 247                         format!("*{}", snippet),
 248                         Applicability::MaybeIncorrect,
 249                     );
 250                 } else {
 251                     err.span_help(self.expr_span, "dereference the expression with `*`");
 252                 }
 253                 err.emit();
 254             }
 255             CastError::NeedViaThinPtr | CastError::NeedViaPtr => {
 256                 let mut err = make_invalid_casting_error(
 257                     fcx.tcx.sess,
 258                     self.span,
 259                     self.expr_ty,
 260                     self.cast_ty,
 261                     fcx,
 262                 );
 263                 if self.cast_ty.is_integral() {
 264                     err.help(&format!(
 265                         "cast through {} first",
 266                         match e {
 267                             CastError::NeedViaPtr => "a raw pointer",
 268                             CastError::NeedViaThinPtr => "a thin pointer",
 269                             _ => bug!(),
 270                         }
 271                     ));
 272                 }
 273                 err.emit();
 274             }
 275             CastError::NeedViaInt => {
 276                 make_invalid_casting_error(
 277                     fcx.tcx.sess,
 278                     self.span,
 279                     self.expr_ty,
 280                     self.cast_ty,
 281                     fcx,
 282                 )
 283                 .help(&format!(
 284                     "cast through {} first",
 285                     match e {
 286                         CastError::NeedViaInt => "an integer",
 287                         _ => bug!(),
 288                     }
 289                 ))
 290                 .emit();
 291             }
 292             CastError::IllegalCast => {
 293                 make_invalid_casting_error(
 294                     fcx.tcx.sess,
 295                     self.span,
 296                     self.expr_ty,
 297                     self.cast_ty,
 298                     fcx,
 299                 )
 300                 .emit();
 301             }
 302             CastError::DifferingKinds => {
 303                 make_invalid_casting_error(
 304                     fcx.tcx.sess,
 305                     self.span,
 306                     self.expr_ty,
 307                     self.cast_ty,
 308                     fcx,
 309                 )
 310                 .note("vtable kinds may not match")
 311                 .emit();
 312             }
 313             CastError::CastToBool => {
 314                 let mut err =
 315                     struct_span_err!(fcx.tcx.sess, self.span, E0054, "cannot cast as `bool`");
 316
 317                 if self.expr_ty.is_numeric() {
 318                     match fcx.tcx.sess.source_map().span_to_snippet(self.expr_span) {
 319                         Ok(snippet) => {
 320                             err.span_suggestion(
 321                                 self.span,
 322                                 "compare with zero instead",
 323                                 format!("{snippet} != 0"),
 324                                 Applicability::MachineApplicable,
 325                             );
 326                         }
 327                         Err(_) => {
 328                             err.span_help(self.span, "compare with zero instead");
 329                         }
 330                     }
 331                 } else {
 332                     err.span_label(self.span, "unsupported cast");
 333                 }
 334
 335                 err.emit();
 336             }
 337             CastError::CastToChar => {
 338                 let mut err = type_error_struct!(
 339                     fcx.tcx.sess,
 340                     self.span,
 341                     self.expr_ty,
 342                     E0604,
 343                     "only `u8` can be cast as `char`, not `{}`",
 344                     self.expr_ty
 345                 );
 346                 err.span_label(self.span, "invalid cast");
 347                 if self.expr_ty.is_numeric() {
 348                     if self.expr_ty == fcx.tcx.types.u32 {
 349                         match fcx.tcx.sess.source_map().span_to_snippet(self.expr.span) {
 350                             Ok(snippet) => err.span_suggestion(
 351                                 self.span,
 352                                 "try `char::from_u32` instead",
 353                                 format!("char::from_u32({snippet})"),
 354                                 Applicability::MachineApplicable,
 355                             ),
 356
 357                             Err(_) => err.span_help(self.span, "try `char::from_u32` instead"),
 358                         };
 359                     } else if self.expr_ty == fcx.tcx.types.i8 {
 360                         err.span_help(self.span, "try casting from `u8` instead");
 361                     } else {
 362                         err.span_help(self.span, "try `char::from_u32` instead (via a `u32`)");
 363                     };
 364                 }
 365                 err.emit();
 366             }
 367             CastError::NonScalar => {
 368                 let mut err = type_error_struct!(
 369                     fcx.tcx.sess,
 370                     self.span,
 371                     self.expr_ty,
 372                     E0605,
 373                     "non-primitive cast: `{}` as `{}`",
 374                     self.expr_ty,
 375                     fcx.ty_to_string(self.cast_ty)
 376                 );
 377                 let mut sugg = None;
 378                 let mut sugg_mutref = false;
 379                 if let ty::Ref(reg, cast_ty, mutbl) = *self.cast_ty.kind() {
 380                     if let ty::RawPtr(TypeAndMut { ty: expr_ty, .. }) = *self.expr_ty.kind()
 381                         && fcx
 382                             .try_coerce(
 383                                 self.expr,
 384                                 fcx.tcx.mk_ref(
 385                                     fcx.tcx.lifetimes.re_erased,
 386                                     TypeAndMut { ty: expr_ty, mutbl },
 387                                 ),
 388                                 self.cast_ty,
 389                                 AllowTwoPhase::No,
 390                                 None,
 391                             )
 392                             .is_ok()
 393                     {
 394                         sugg = Some((format!("&{}*", mutbl.prefix_str()), cast_ty == expr_ty));
 395                     } else if let ty::Ref(expr_reg, expr_ty, expr_mutbl) = *self.expr_ty.kind()
 396                         && expr_mutbl == Mutability::Not
 397                         && mutbl == Mutability::Mut
 398                         && fcx
 399                             .try_coerce(
 400                                 self.expr,
 401                                 fcx.tcx.mk_ref(
 402                                     expr_reg,
 403                                     TypeAndMut { ty: expr_ty, mutbl: Mutability::Mut },
 404                                 ),
 405                                 self.cast_ty,
 406                                 AllowTwoPhase::No,
 407                                 None,
 408                             )
 409                             .is_ok()
 410                     {
 411                         sugg_mutref = true;
 412                     }
 413
 414                     if !sugg_mutref
 415                         && sugg == None
 416                         && fcx
 417                             .try_coerce(
 418                                 self.expr,
 419                                 fcx.tcx.mk_ref(reg, TypeAndMut { ty: self.expr_ty, mutbl }),
 420                                 self.cast_ty,
 421                                 AllowTwoPhase::No,
 422                                 None,
 423                             )
 424                             .is_ok()
 425                     {
 426                         sugg = Some((format!("&{}", mutbl.prefix_str()), false));
 427                     }
 428                 } else if let ty::RawPtr(TypeAndMut { mutbl, .. }) = *self.cast_ty.kind()
 429                     && fcx
 430                         .try_coerce(
 431                             self.expr,
 432                             fcx.tcx.mk_ref(
 433                                 fcx.tcx.lifetimes.re_erased,
 434                                 TypeAndMut { ty: self.expr_ty, mutbl },
 435                             ),
 436                             self.cast_ty,
 437                             AllowTwoPhase::No,
 438                             None,
 439                         )
 440                         .is_ok()
 441                 {
 442                     sugg = Some((format!("&{}", mutbl.prefix_str()), false));
 443                 }
 444                 if sugg_mutref {
 445                     err.span_label(self.span, "invalid cast");
 446                     err.span_note(self.expr_span, "this reference is immutable");
 447                     err.span_note(self.cast_span, "trying to cast to a mutable reference type");
 448                 } else if let Some((sugg, remove_cast)) = sugg {
 449                     err.span_label(self.span, "invalid cast");
 450
 451                     let has_parens = fcx
 452                         .tcx
 453                         .sess
 454                         .source_map()
 455                         .span_to_snippet(self.expr_span)
 456                         .map_or(false, |snip| snip.starts_with('('));
 457
 458                     // Very crude check to see whether the expression must be wrapped
 459                     // in parentheses for the suggestion to work (issue #89497).
 460                     // Can/should be extended in the future.
 461                     let needs_parens =
 462                         !has_parens && matches!(self.expr.kind, hir::ExprKind::Cast(..));
 463
 464                     let mut suggestion = vec![(self.expr_span.shrink_to_lo(), sugg)];
 465                     if needs_parens {
 466                         suggestion[0].1 += "(";
 467                         suggestion.push((self.expr_span.shrink_to_hi(), ")".to_string()));
 468                     }
 469                     if remove_cast {
 470                         suggestion.push((
 471                             self.expr_span.shrink_to_hi().to(self.cast_span),
 472                             String::new(),
 473                         ));
 474                     }
 475
 476                     err.multipart_suggestion_verbose(
 477                         "consider borrowing the value",
 478                         suggestion,
 479                         Applicability::MachineApplicable,
 480                     );
 481                 } else if !matches!(
 482                     self.cast_ty.kind(),
 483                     ty::FnDef(..) | ty::FnPtr(..) | ty::Closure(..)
 484                 ) {
 485                     let mut label = true;
 486                     // Check `impl From<self.expr_ty> for self.cast_ty {}` for accurate suggestion:
 487                     if let Ok(snippet) = fcx.tcx.sess.source_map().span_to_snippet(self.expr_span)
 488                         && let Some(from_trait) = fcx.tcx.get_diagnostic_item(sym::From)
 489                     {
 490                         let ty = fcx.resolve_vars_if_possible(self.cast_ty);
 491                         // Erase regions to avoid panic in `prove_value` when calling
 492                         // `type_implements_trait`.
 493                         let ty = fcx.tcx.erase_regions(ty);
 494                         let expr_ty = fcx.resolve_vars_if_possible(self.expr_ty);
 495                         let expr_ty = fcx.tcx.erase_regions(expr_ty);
 496                         if fcx
 497                             .infcx
 498                             .type_implements_trait(from_trait, [ty, expr_ty], fcx.param_env)
 499                             .must_apply_modulo_regions()
 500                         {
 501                             label = false;
 502                             err.span_suggestion(
 503                                 self.span,
 504                                 "consider using the `From` trait instead",
 505                                 format!("{}::from({})", self.cast_ty, snippet),
 506                                 Applicability::MaybeIncorrect,
 507                             );
 508                         }
 509                     }
 510                     let msg = "an `as` expression can only be used to convert between primitive \
 511                                types or to coerce to a specific trait object";
 512                     if label {
 513                         err.span_label(self.span, msg);
 514                     } else {
 515                         err.note(msg);
 516                     }
 517                 } else {
 518                     err.span_label(self.span, "invalid cast");
 519                 }
 520                 err.emit();
 521             }
 522             CastError::SizedUnsizedCast => {
 523                 use rustc_hir_analysis::structured_errors::{
 524                     SizedUnsizedCast, StructuredDiagnostic,
 525                 };
 526
 527                 SizedUnsizedCast {
 528                     sess: &fcx.tcx.sess,
 529                     span: self.span,
 530                     expr_ty: self.expr_ty,
 531                     cast_ty: fcx.ty_to_string(self.cast_ty),
 532                 }
 533                 .diagnostic()
 534                 .emit();
 535             }
 536             CastError::IntToFatCast(known_metadata) => {
 537                 let mut err = struct_span_err!(
 538                     fcx.tcx.sess,
 539                     self.cast_span,
 540                     E0606,
 541                     "cannot cast `{}` to a pointer that {} wide",
 542                     fcx.ty_to_string(self.expr_ty),
 543                     if known_metadata.is_some() { "is" } else { "may be" }
 544                 );
 545
 546                 err.span_label(
 547                     self.cast_span,
 548                     format!(
 549                         "creating a `{}` requires both an address and {}",
 550                         self.cast_ty,
 551                         known_metadata.unwrap_or("type-specific metadata"),
 552                     ),
 553                 );
 554
 555                 if fcx.tcx.sess.is_nightly_build() {
 556                     err.span_label(
 557                         self.expr_span,
 558                         "consider casting this expression to `*const ()`, \
 559                         then using `core::ptr::from_raw_parts`",
 560                     );
 561                 }
 562
 563                 err.emit();
 564             }
 565             CastError::UnknownCastPtrKind | CastError::UnknownExprPtrKind => {
 566                 let unknown_cast_to = match e {
 567                     CastError::UnknownCastPtrKind => true,
 568                     CastError::UnknownExprPtrKind => false,
 569                     _ => bug!(),
 570                 };
 571                 let mut err = struct_span_err!(
 572                     fcx.tcx.sess,
 573                     if unknown_cast_to { self.cast_span } else { self.span },
 574                     E0641,
 575                     "cannot cast {} a pointer of an unknown kind",
 576                     if unknown_cast_to { "to" } else { "from" }
 577                 );
 578                 if unknown_cast_to {
 579                     err.span_label(self.cast_span, "needs more type information");
 580                     err.note(
 581                         "the type information given here is insufficient to check whether \
 582                         the pointer cast is valid",
 583                     );
 584                 } else {
 585                     err.span_label(
 586                         self.span,
 587                         "the type information given here is insufficient to check whether \
 588                         the pointer cast is valid",
 589                     );
 590                 }
 591                 err.emit();
 592             }
 593             CastError::ForeignNonExhaustiveAdt => {
 594                 make_invalid_casting_error(
 595                     fcx.tcx.sess,
 596                     self.span,
 597                     self.expr_ty,
 598                     self.cast_ty,
 599                     fcx,
 600                 )
 601                 .note("cannot cast an enum with a non-exhaustive variant when it's defined in another crate")
 602                 .emit();
 603             }
 604         }
 605     }
 606
 607     fn report_cast_to_unsized_type(&self, fcx: &FnCtxt<'a, 'tcx>) -> ErrorGuaranteed {
 608         if let Err(err) = self.cast_ty.error_reported() {
 609             return err;
 610         }
 611         if let Err(err) = self.expr_ty.error_reported() {
 612             return err;
 613         }
 614
 615         let tstr = fcx.ty_to_string(self.cast_ty);
 616         let mut err = type_error_struct!(
 617             fcx.tcx.sess,
 618             self.span,
 619             self.expr_ty,
 620             E0620,
 621             "cast to unsized type: `{}` as `{}`",
 622             fcx.resolve_vars_if_possible(self.expr_ty),
 623             tstr
 624         );
 625         match self.expr_ty.kind() {
 626             ty::Ref(_, _, mt) => {
 627                 let mtstr = mt.prefix_str();
 628                 if self.cast_ty.is_trait() {
 629                     match fcx.tcx.sess.source_map().span_to_snippet(self.cast_span) {
 630                         Ok(s) => {
 631                             err.span_suggestion(
 632                                 self.cast_span,
 633                                 "try casting to a reference instead",
 634                                 format!("&{}{}", mtstr, s),
 635                                 Applicability::MachineApplicable,
 636                             );
 637                         }
 638                         Err(_) => {
 639                             let msg = &format!("did you mean `&{}{}`?", mtstr, tstr);
 640                             err.span_help(self.cast_span, msg);
 641                         }
 642                     }
 643                 } else {
 644                     let msg =
 645                         &format!("consider using an implicit coercion to `&{mtstr}{tstr}` instead");
 646                     err.span_help(self.span, msg);
 647                 }
 648             }
 649             ty::Adt(def, ..) if def.is_box() => {
 650                 match fcx.tcx.sess.source_map().span_to_snippet(self.cast_span) {
 651                     Ok(s) => {
 652                         err.span_suggestion(
 653                             self.cast_span,
 654                             "you can cast to a `Box` instead",
 655                             format!("Box<{s}>"),
 656                             Applicability::MachineApplicable,
 657                         );
 658                     }
 659                     Err(_) => {
 660                         err.span_help(
 661                             self.cast_span,
 662                             &format!("you might have meant `Box<{tstr}>`"),
 663                         );
 664                     }
 665                 }
 666             }
 667             _ => {
 668                 err.span_help(self.expr_span, "consider using a box or reference as appropriate");
 669             }
 670         }
 671         err.emit()
 672     }
 673
 674     fn trivial_cast_lint(&self, fcx: &FnCtxt<'a, 'tcx>) {
 675         let t_cast = self.cast_ty;
 676         let t_expr = self.expr_ty;
 677         let type_asc_or =
 678             if fcx.tcx.features().type_ascription { "type ascription or " } else { "" };
 679         let (adjective, lint) = if t_cast.is_numeric() && t_expr.is_numeric() {
 680             ("numeric ", lint::builtin::TRIVIAL_NUMERIC_CASTS)
 681         } else {
 682             ("", lint::builtin::TRIVIAL_CASTS)
 683         };
 684         fcx.tcx.struct_span_lint_hir(
 685             lint,
 686             self.expr.hir_id,
 687             self.span,
 688             DelayDm(|| {
 689                 format!(
 690                     "trivial {}cast: `{}` as `{}`",
 691                     adjective,
 692                     fcx.ty_to_string(t_expr),
 693                     fcx.ty_to_string(t_cast)
 694                 )
 695             }),
 696             |lint| {
 697                 lint.help(format!(
 698                     "cast can be replaced by coercion; this might \
 699                      require {type_asc_or}a temporary variable"
 700                 ))
 701             },
 702         );
 703     }
 704
 705     #[instrument(skip(fcx), level = "debug")]
 706     pub fn check(mut self, fcx: &FnCtxt<'a, 'tcx>) {
 707         self.expr_ty = fcx.structurally_resolved_type(self.expr_span, self.expr_ty);
 708         self.cast_ty = fcx.structurally_resolved_type(self.cast_span, self.cast_ty);
 709
 710         debug!("check_cast({}, {:?} as {:?})", self.expr.hir_id, self.expr_ty, self.cast_ty);
 711
 712         if !fcx.type_is_sized_modulo_regions(fcx.param_env, self.cast_ty, self.span)
 713             && !self.cast_ty.has_infer_types()
 714         {
 715             self.report_cast_to_unsized_type(fcx);
 716         } else if self.expr_ty.references_error() || self.cast_ty.references_error() {
 717             // No sense in giving duplicate error messages
 718         } else {
 719             match self.try_coercion_cast(fcx) {
 720                 Ok(()) => {
 721                     self.trivial_cast_lint(fcx);
 722                     debug!(" -> CoercionCast");
 723                     fcx.typeck_results.borrow_mut().set_coercion_cast(self.expr.hir_id.local_id);
 724                 }
 725                 Err(_) => {
 726                     match self.do_check(fcx) {
 727                         Ok(k) => {
 728                             debug!(" -> {:?}", k);
 729                         }
 730                         Err(e) => self.report_cast_error(fcx, e),
 731                     };
 732                 }
 733             };
 734         }
 735     }
 736     /// Checks a cast, and report an error if one exists. In some cases, this
 737     /// can return Ok and create type errors in the fcx rather than returning
 738     /// directly. coercion-cast is handled in check instead of here.
 739     pub fn do_check(&self, fcx: &FnCtxt<'a, 'tcx>) -> Result<CastKind, CastError> {
 740         use rustc_middle::ty::cast::CastTy::*;
 741         use rustc_middle::ty::cast::IntTy::*;
 742
 743         let (t_from, t_cast) = match (CastTy::from_ty(self.expr_ty), CastTy::from_ty(self.cast_ty))
 744         {
 745             (Some(t_from), Some(t_cast)) => (t_from, t_cast),
 746             // Function item types may need to be reified before casts.
 747             (None, Some(t_cast)) => {
 748                 match *self.expr_ty.kind() {
 749                     ty::FnDef(..) => {
 750                         // Attempt a coercion to a fn pointer type.
 751                         let f = fcx.normalize(self.expr_span, self.expr_ty.fn_sig(fcx.tcx));
 752                         let res = fcx.try_coerce(
 753                             self.expr,
 754                             self.expr_ty,
 755                             fcx.tcx.mk_fn_ptr(f),
 756                             AllowTwoPhase::No,
 757                             None,
 758                         );
 759                         if let Err(TypeError::IntrinsicCast) = res {
 760                             return Err(CastError::IllegalCast);
 761                         }
 762                         if res.is_err() {
 763                             return Err(CastError::NonScalar);
 764                         }
 765                         (FnPtr, t_cast)
 766                     }
 767                     // Special case some errors for references, and check for
 768                     // array-ptr-casts. `Ref` is not a CastTy because the cast
 769                     // is split into a coercion to a pointer type, followed by
 770                     // a cast.
 771                     ty::Ref(_, inner_ty, mutbl) => {
 772                         return match t_cast {
 773                             Int(_) | Float => match *inner_ty.kind() {
 774                                 ty::Int(_)
 775                                 | ty::Uint(_)
 776                                 | ty::Float(_)
 777                                 | ty::Infer(ty::InferTy::IntVar(_) | ty::InferTy::FloatVar(_)) => {
 778                                     Err(CastError::NeedDeref)
 779                                 }
 780                                 _ => Err(CastError::NeedViaPtr),
 781                             },
 782                             // array-ptr-cast
 783                             Ptr(mt) => {
 784                                 self.check_ref_cast(fcx, TypeAndMut { mutbl, ty: inner_ty }, mt)
 785                             }
 786                             _ => Err(CastError::NonScalar),
 787                         };
 788                     }
 789                     _ => return Err(CastError::NonScalar),
 790                 }
 791             }
 792             _ => return Err(CastError::NonScalar),
 793         };
 794
 795         if let ty::Adt(adt_def, _) = *self.expr_ty.kind() {
 796             if adt_def.did().krate != LOCAL_CRATE {
 797                 if adt_def.variants().iter().any(VariantDef::is_field_list_non_exhaustive) {
 798                     return Err(CastError::ForeignNonExhaustiveAdt);
 799                 }
 800             }
 801         }
 802
 803         match (t_from, t_cast) {
 804             // These types have invariants! can't cast into them.
 805             (_, Int(CEnum) | FnPtr) => Err(CastError::NonScalar),
 806
 807             // * -> Bool
 808             (_, Int(Bool)) => Err(CastError::CastToBool),
 809
 810             // * -> Char
 811             (Int(U(ty::UintTy::U8)), Int(Char)) => Ok(CastKind::U8CharCast), // u8-char-cast
 812             (_, Int(Char)) => Err(CastError::CastToChar),
 813
 814             // prim -> float,ptr
 815             (Int(Bool) | Int(CEnum) | Int(Char), Float) => Err(CastError::NeedViaInt),
 816
 817             (Int(Bool) | Int(CEnum) | Int(Char) | Float, Ptr(_)) | (Ptr(_) | FnPtr, Float) => {
 818                 Err(CastError::IllegalCast)
 819             }
 820
 821             // ptr -> *
 822             (Ptr(m_e), Ptr(m_c)) => self.check_ptr_ptr_cast(fcx, m_e, m_c), // ptr-ptr-cast
 823
 824             // ptr-addr-cast
 825             (Ptr(m_expr), Int(t_c)) => {
 826                 self.lossy_provenance_ptr2int_lint(fcx, t_c);
 827                 self.check_ptr_addr_cast(fcx, m_expr)
 828             }
 829             (FnPtr, Int(_)) => {
 830                 // FIXME(#95489): there should eventually be a lint for these casts
 831                 Ok(CastKind::FnPtrAddrCast)
 832             }
 833             // addr-ptr-cast
 834             (Int(_), Ptr(mt)) => {
 835                 self.fuzzy_provenance_int2ptr_lint(fcx);
 836                 self.check_addr_ptr_cast(fcx, mt)
 837             }
 838             // fn-ptr-cast
 839             (FnPtr, Ptr(mt)) => self.check_fptr_ptr_cast(fcx, mt),
 840
 841             // prim -> prim
 842             (Int(CEnum), Int(_)) => {
 843                 self.cenum_impl_drop_lint(fcx);
 844                 Ok(CastKind::EnumCast)
 845             }
 846             (Int(Char) | Int(Bool), Int(_)) => Ok(CastKind::PrimIntCast),
 847
 848             (Int(_) | Float, Int(_) | Float) => Ok(CastKind::NumericCast),
 849
 850             (_, DynStar) | (DynStar, _) => {
 851                 if fcx.tcx.features().dyn_star {
 852                     bug!("should be handled by `try_coerce`")
 853                 } else {
 854                     Err(CastError::IllegalCast)
 855                 }
 856             }
 857         }
 858     }
 859
 860     fn check_ptr_ptr_cast(
 861         &self,
 862         fcx: &FnCtxt<'a, 'tcx>,
 863         m_expr: ty::TypeAndMut<'tcx>,
 864         m_cast: ty::TypeAndMut<'tcx>,
 865     ) -> Result<CastKind, CastError> {
 866         debug!("check_ptr_ptr_cast m_expr={:?} m_cast={:?}", m_expr, m_cast);
 867         // ptr-ptr cast. vtables must match.
 868
 869         let expr_kind = fcx.pointer_kind(m_expr.ty, self.span)?;
 870         let cast_kind = fcx.pointer_kind(m_cast.ty, self.span)?;
 871
 872         let Some(cast_kind) = cast_kind else {
 873             // We can't cast if target pointer kind is unknown
 874             return Err(CastError::UnknownCastPtrKind);
 875         };
 876
 877         // Cast to thin pointer is OK
 878         if cast_kind == PointerKind::Thin {
 879             return Ok(CastKind::PtrPtrCast);
 880         }
 881
 882         let Some(expr_kind) = expr_kind else {
 883             // We can't cast to fat pointer if source pointer kind is unknown
 884             return Err(CastError::UnknownExprPtrKind);
 885         };
 886
 887         // thin -> fat? report invalid cast (don't complain about vtable kinds)
 888         if expr_kind == PointerKind::Thin {
 889             return Err(CastError::SizedUnsizedCast);
 890         }
 891
 892         // vtable kinds must match
 893         if fcx.tcx.erase_regions(cast_kind) == fcx.tcx.erase_regions(expr_kind) {
 894             Ok(CastKind::PtrPtrCast)
 895         } else {
 896             Err(CastError::DifferingKinds)
 897         }
 898     }
 899
 900     fn check_fptr_ptr_cast(
 901         &self,
 902         fcx: &FnCtxt<'a, 'tcx>,
 903         m_cast: ty::TypeAndMut<'tcx>,
 904     ) -> Result<CastKind, CastError> {
 905         // fptr-ptr cast. must be to thin ptr
 906
 907         match fcx.pointer_kind(m_cast.ty, self.span)? {
 908             None => Err(CastError::UnknownCastPtrKind),
 909             Some(PointerKind::Thin) => Ok(CastKind::FnPtrPtrCast),
 910             _ => Err(CastError::IllegalCast),
 911         }
 912     }
 913
 914     fn check_ptr_addr_cast(
 915         &self,
 916         fcx: &FnCtxt<'a, 'tcx>,
 917         m_expr: ty::TypeAndMut<'tcx>,
 918     ) -> Result<CastKind, CastError> {
 919         // ptr-addr cast. must be from thin ptr
 920
 921         match fcx.pointer_kind(m_expr.ty, self.span)? {
 922             None => Err(CastError::UnknownExprPtrKind),
 923             Some(PointerKind::Thin) => Ok(CastKind::PtrAddrCast),
 924             _ => Err(CastError::NeedViaThinPtr),
 925         }
 926     }
 927
 928     fn check_ref_cast(
 929         &self,
 930         fcx: &FnCtxt<'a, 'tcx>,
 931         m_expr: ty::TypeAndMut<'tcx>,
 932         m_cast: ty::TypeAndMut<'tcx>,
 933     ) -> Result<CastKind, CastError> {
 934         // array-ptr-cast: allow mut-to-mut, mut-to-const, const-to-const
 935         if m_expr.mutbl >= m_cast.mutbl {
 936             if let ty::Array(ety, _) = m_expr.ty.kind() {
 937                 // Due to the limitations of LLVM global constants,
 938                 // region pointers end up pointing at copies of
 939                 // vector elements instead of the original values.
 940                 // To allow raw pointers to work correctly, we
 941                 // need to special-case obtaining a raw pointer
 942                 // from a region pointer to a vector.
 943
 944                 // Coerce to a raw pointer so that we generate AddressOf in MIR.
 945                 let array_ptr_type = fcx.tcx.mk_ptr(m_expr);
 946                 fcx.try_coerce(self.expr, self.expr_ty, array_ptr_type, AllowTwoPhase::No, None)
 947                     .unwrap_or_else(|_| {
 948                         bug!(
 949                         "could not cast from reference to array to pointer to array ({:?} to {:?})",
 950                         self.expr_ty,
 951                         array_ptr_type,
 952                     )
 953                     });
 954
 955                 // this will report a type mismatch if needed
 956                 fcx.demand_eqtype(self.span, *ety, m_cast.ty);
 957                 return Ok(CastKind::ArrayPtrCast);
 958             }
 959         }
 960
 961         Err(CastError::IllegalCast)
 962     }
 963
 964     fn check_addr_ptr_cast(
 965         &self,
 966         fcx: &FnCtxt<'a, 'tcx>,
 967         m_cast: TypeAndMut<'tcx>,
 968     ) -> Result<CastKind, CastError> {
 969         // ptr-addr cast. pointer must be thin.
 970         match fcx.pointer_kind(m_cast.ty, self.span)? {
 971             None => Err(CastError::UnknownCastPtrKind),
 972             Some(PointerKind::Thin) => Ok(CastKind::AddrPtrCast),
 973             Some(PointerKind::VTable(_)) => Err(CastError::IntToFatCast(Some("a vtable"))),
 974             Some(PointerKind::Length) => Err(CastError::IntToFatCast(Some("a length"))),
 975             Some(PointerKind::OfAlias(_) | PointerKind::OfParam(_)) => {
 976                 Err(CastError::IntToFatCast(None))
 977             }
 978         }
 979     }
 980
 981     fn try_coercion_cast(&self, fcx: &FnCtxt<'a, 'tcx>) -> Result<(), ty::error::TypeError<'tcx>> {
 982         match fcx.try_coerce(self.expr, self.expr_ty, self.cast_ty, AllowTwoPhase::No, None) {
 983             Ok(_) => Ok(()),
 984             Err(err) => Err(err),
 985         }
 986     }
 987
 988     fn cenum_impl_drop_lint(&self, fcx: &FnCtxt<'a, 'tcx>) {
 989         if let ty::Adt(d, _) = self.expr_ty.kind()
 990             && d.has_dtor(fcx.tcx)
 991         {
 992             fcx.tcx.struct_span_lint_hir(
 993                 lint::builtin::CENUM_IMPL_DROP_CAST,
 994                 self.expr.hir_id,
 995                 self.span,
 996                 DelayDm(|| format!(
 997                     "cannot cast enum `{}` into integer `{}` because it implements `Drop`",
 998                     self.expr_ty, self.cast_ty
 999                 )),
1000                 |lint| {
1001                     lint
1002                 },
1003             );
1004         }
1005     }
1006
1007     fn lossy_provenance_ptr2int_lint(&self, fcx: &FnCtxt<'a, 'tcx>, t_c: ty::cast::IntTy) {
1008         fcx.tcx.struct_span_lint_hir(
1009             lint::builtin::LOSSY_PROVENANCE_CASTS,
1010             self.expr.hir_id,
1011             self.span,
1012             DelayDm(|| format!(
1013                     "under strict provenance it is considered bad style to cast pointer `{}` to integer `{}`",
1014                     self.expr_ty, self.cast_ty
1015                 )),
1016             |lint| {
1017                 let msg = "use `.addr()` to obtain the address of a pointer";
1018
1019                 let expr_prec = self.expr.precedence().order();
1020                 let needs_parens = expr_prec < rustc_ast::util::parser::PREC_POSTFIX;
1021
1022                 let scalar_cast = match t_c {
1023                     ty::cast::IntTy::U(ty::UintTy::Usize) => String::new(),
1024                     _ => format!(" as {}", self.cast_ty),
1025                 };
1026
1027                 let cast_span = self.expr_span.shrink_to_hi().to(self.cast_span);
1028
1029                 if needs_parens {
1030                     let suggestions = vec![
1031                         (self.expr_span.shrink_to_lo(), String::from("(")),
1032                         (cast_span, format!(").addr(){scalar_cast}")),
1033                     ];
1034
1035                     lint.multipart_suggestion(msg, suggestions, Applicability::MaybeIncorrect);
1036                 } else {
1037                     lint.span_suggestion(
1038                         cast_span,
1039                         msg,
1040                         format!(".addr(){scalar_cast}"),
1041                         Applicability::MaybeIncorrect,
1042                     );
1043                 }
1044
1045                 lint.help(
1046                     "if you can't comply with strict provenance and need to expose the pointer \
1047                     provenance you can use `.expose_addr()` instead"
1048                 );
1049
1050                 lint
1051             },
1052         );
1053     }
1054
1055     fn fuzzy_provenance_int2ptr_lint(&self, fcx: &FnCtxt<'a, 'tcx>) {
1056         fcx.tcx.struct_span_lint_hir(
1057             lint::builtin::FUZZY_PROVENANCE_CASTS,
1058             self.expr.hir_id,
1059             self.span,
1060             DelayDm(|| format!(
1061                 "strict provenance disallows casting integer `{}` to pointer `{}`",
1062                 self.expr_ty, self.cast_ty
1063             )),
1064             |lint| {
1065                 let msg = "use `.with_addr()` to adjust a valid pointer in the same allocation, to this address";
1066                 let suggestions = vec![
1067                     (self.expr_span.shrink_to_lo(), String::from("(...).with_addr(")),
1068                     (self.expr_span.shrink_to_hi().to(self.cast_span), String::from(")")),
1069                 ];
1070
1071                 lint.multipart_suggestion(msg, suggestions, Applicability::MaybeIncorrect);
1072                 lint.help(
1073                     "if you can't comply with strict provenance and don't have a pointer with \
1074                     the correct provenance you can use `std::ptr::from_exposed_addr()` instead"
1075                  );
1076
1077                 lint
1078             },
1079         );
1080     }
1081 }