compiler/rustc_typeck/src/check/cast.rs

   1 //! Code for type-checking cast expressions.
   2 //!
   3 //! A cast `e as U` is valid if one of the following holds:
   4 //! * `e` has type `T` and `T` coerces to `U`; *coercion-cast*
   5 //! * `e` has type `*T`, `U` is `*U_0`, and either `U_0: Sized` or
   6 //!    pointer_kind(`T`) = pointer_kind(`U_0`); *ptr-ptr-cast*
   7 //! * `e` has type `*T` and `U` is a numeric type, while `T: Sized`; *ptr-addr-cast*
   8 //! * `e` is an integer and `U` is `*U_0`, while `U_0: Sized`; *addr-ptr-cast*
   9 //! * `e` has type `T` and `T` and `U` are any numeric types; *numeric-cast*
  10 //! * `e` is a C-like enum and `U` is an integer type; *enum-cast*
  11 //! * `e` has type `bool` or `char` and `U` is an integer; *prim-int-cast*
  12 //! * `e` has type `u8` and `U` is `char`; *u8-char-cast*
  13 //! * `e` has type `&[T; n]` and `U` is `*const T`; *array-ptr-cast*
  14 //! * `e` is a function pointer type and `U` has type `*T`,
  15 //!   while `T: Sized`; *fptr-ptr-cast*
  16 //! * `e` is a function pointer type and `U` is an integer; *fptr-addr-cast*
  17 //!
  18 //! where `&.T` and `*T` are references of either mutability,
  19 //! and where pointer_kind(`T`) is the kind of the unsize info
  20 //! in `T` - the vtable for a trait definition (e.g., `fmt::Display` or
  21 //! `Iterator`, not `Iterator<Item=u8>`) or a length (or `()` if `T: Sized`).
  22 //!
  23 //! Note that lengths are not adjusted when casting raw slices -
  24 //! `T: *const [u16] as *const [u8]` creates a slice that only includes
  25 //! half of the original memory.
  26 //!
  27 //! Casting is not transitive, that is, even if `e as U1 as U2` is a valid
  28 //! expression, `e as U2` is not necessarily so (in fact it will only be valid if
  29 //! `U1` coerces to `U2`).
  30
  31 use super::FnCtxt;
  32
  33 use crate::hir::def_id::DefId;
  34 use crate::type_error_struct;
  35 use hir::def_id::LOCAL_CRATE;
  36 use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder, ErrorGuaranteed};
  37 use rustc_hir as hir;
  38 use rustc_infer::traits::{Obligation, ObligationCause, ObligationCauseCode};
  39 use rustc_middle::mir::Mutability;
  40 use rustc_middle::ty::adjustment::AllowTwoPhase;
  41 use rustc_middle::ty::cast::{CastKind, CastTy};
  42 use rustc_middle::ty::error::TypeError;
  43 use rustc_middle::ty::subst::SubstsRef;
  44 use rustc_middle::ty::{
  45     self, Binder, TraitObjectRepresentation, Ty, TypeAndMut, TypeVisitable, VariantDef,
  46 };
  47 use rustc_session::lint;
  48 use rustc_session::Session;
  49 use rustc_span::symbol::sym;
  50 use rustc_span::Span;
  51 use rustc_trait_selection::infer::InferCtxtExt;
  52 use rustc_trait_selection::traits::error_reporting::report_object_safety_error;
  53
  54 /// Reifies a cast check to be checked once we have full type information for
  55 /// a function context.
  56 #[derive(Debug)]
  57 pub struct CastCheck<'tcx> {
  58     /// The expression whose value is being casted
  59     expr: &'tcx hir::Expr<'tcx>,
  60     /// The source type for the cast expression
  61     expr_ty: Ty<'tcx>,
  62     expr_span: Span,
  63     /// The target type. That is, the type we are casting to.
  64     cast_ty: Ty<'tcx>,
  65     cast_span: Span,
  66     span: Span,
  67 }
  68
  69 /// The kind of pointer and associated metadata (thin, length or vtable) - we
  70 /// only allow casts between fat pointers if their metadata have the same
  71 /// kind.
  72 #[derive(Copy, Clone, PartialEq, Eq)]
  73 enum PointerKind<'tcx> {
  74     /// No metadata attached, ie pointer to sized type or foreign type
  75     Thin,
  76     /// A trait object
  77     VTable(Option<DefId>),
  78     /// Slice
  79     Length,
  80     /// The unsize info of this projection
  81     OfProjection(&'tcx ty::ProjectionTy<'tcx>),
  82     /// The unsize info of this opaque ty
  83     OfOpaque(DefId, SubstsRef<'tcx>),
  84     /// The unsize info of this parameter
  85     OfParam(&'tcx ty::ParamTy),
  86 }
  87
  88 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  89     /// Returns the kind of unsize information of t, or None
  90     /// if t is unknown.
  91     fn pointer_kind(
  92         &self,
  93         t: Ty<'tcx>,
  94         span: Span,
  95     ) -> Result<Option<PointerKind<'tcx>>, ErrorGuaranteed> {
  96         debug!("pointer_kind({:?}, {:?})", t, span);
  97
  98         let t = self.resolve_vars_if_possible(t);
  99
 100         if let Some(reported) = t.error_reported() {
 101             return Err(reported);
 102         }
 103
 104         if self.type_is_sized_modulo_regions(self.param_env, t, span) {
 105             return Ok(Some(PointerKind::Thin));
 106         }
 107
 108         Ok(match *t.kind() {
 109             ty::Slice(_) | ty::Str => Some(PointerKind::Length),
 110             ty::Dynamic(ref tty, ..) => Some(PointerKind::VTable(tty.principal_def_id())),
 111             ty::Adt(def, substs) if def.is_struct() => match def.non_enum_variant().fields.last() {
 112                 None => Some(PointerKind::Thin),
 113                 Some(f) => {
 114                     let field_ty = self.field_ty(span, f, substs);
 115                     self.pointer_kind(field_ty, span)?
 116                 }
 117             },
 118             ty::Tuple(fields) => match fields.last() {
 119                 None => Some(PointerKind::Thin),
 120                 Some(&f) => self.pointer_kind(f, span)?,
 121             },
 122
 123             // Pointers to foreign types are thin, despite being unsized
 124             ty::Foreign(..) => Some(PointerKind::Thin),
 125             // We should really try to normalize here.
 126             ty::Projection(ref pi) => Some(PointerKind::OfProjection(pi)),
 127             ty::Opaque(def_id, substs) => Some(PointerKind::OfOpaque(def_id, substs)),
 128             ty::Param(ref p) => Some(PointerKind::OfParam(p)),
 129             // Insufficient type information.
 130             ty::Placeholder(..) | ty::Bound(..) | ty::Infer(_) => None,
 131
 132             ty::Bool
 133             | ty::Char
 134             | ty::Int(..)
 135             | ty::Uint(..)
 136             | ty::Float(_)
 137             | ty::Array(..)
 138             | ty::GeneratorWitness(..)
 139             | ty::RawPtr(_)
 140             | ty::Ref(..)
 141             | ty::FnDef(..)
 142             | ty::FnPtr(..)
 143             | ty::Closure(..)
 144             | ty::Generator(..)
 145             | ty::Adt(..)
 146             | ty::Never
 147             | ty::Error(_) => {
 148                 let reported = self
 149                     .tcx
 150                     .sess
 151                     .delay_span_bug(span, &format!("`{:?}` should be sized but is not?", t));
 152                 return Err(reported);
 153             }
 154         })
 155     }
 156 }
 157
 158 #[derive(Copy, Clone)]
 159 pub enum CastError {
 160     ErrorGuaranteed,
 161
 162     CastToBool,
 163     CastToChar,
 164     DifferingKinds,
 165     /// Cast of thin to fat raw ptr (e.g., `*const () as *const [u8]`).
 166     SizedUnsizedCast,
 167     IllegalCast,
 168     NeedDeref,
 169     NeedViaPtr,
 170     NeedViaThinPtr,
 171     NeedViaInt,
 172     NonScalar,
 173     UnknownExprPtrKind,
 174     UnknownCastPtrKind,
 175     /// Cast of int to (possibly) fat raw pointer.
 176     ///
 177     /// Argument is the specific name of the metadata in plain words, such as "a vtable"
 178     /// or "a length". If this argument is None, then the metadata is unknown, for example,
 179     /// when we're typechecking a type parameter with a ?Sized bound.
 180     IntToFatCast(Option<&'static str>),
 181     ForeignNonExhaustiveAdt,
 182 }
 183
 184 impl From<ErrorGuaranteed> for CastError {
 185     fn from(_: ErrorGuaranteed) -> Self {
 186         CastError::ErrorGuaranteed
 187     }
 188 }
 189
 190 fn make_invalid_casting_error<'a, 'tcx>(
 191     sess: &'a Session,
 192     span: Span,
 193     expr_ty: Ty<'tcx>,
 194     cast_ty: Ty<'tcx>,
 195     fcx: &FnCtxt<'a, 'tcx>,
 196 ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
 197     type_error_struct!(
 198         sess,
 199         span,
 200         expr_ty,
 201         E0606,
 202         "casting `{}` as `{}` is invalid",
 203         fcx.ty_to_string(expr_ty),
 204         fcx.ty_to_string(cast_ty)
 205     )
 206 }
 207
 208 pub enum CastCheckResult<'tcx> {
 209     Ok,
 210     Deferred(CastCheck<'tcx>),
 211     Err(ErrorGuaranteed),
 212 }
 213
 214 pub fn check_cast<'tcx>(
 215     fcx: &FnCtxt<'_, 'tcx>,
 216     expr: &'tcx hir::Expr<'tcx>,
 217     expr_ty: Ty<'tcx>,
 218     cast_ty: Ty<'tcx>,
 219     cast_span: Span,
 220     span: Span,
 221 ) -> CastCheckResult<'tcx> {
 222     if cast_ty.is_dyn_star() {
 223         check_dyn_star_cast(fcx, expr, expr_ty, cast_ty)
 224     } else {
 225         match CastCheck::new(fcx, expr, expr_ty, cast_ty, cast_span, span) {
 226             Ok(check) => CastCheckResult::Deferred(check),
 227             Err(e) => CastCheckResult::Err(e),
 228         }
 229     }
 230 }
 231
 232 fn check_dyn_star_cast<'tcx>(
 233     fcx: &FnCtxt<'_, 'tcx>,
 234     expr: &'tcx hir::Expr<'tcx>,
 235     expr_ty: Ty<'tcx>,
 236     cast_ty: Ty<'tcx>,
 237 ) -> CastCheckResult<'tcx> {
 238     // Find the bounds in the dyn*. For eaxmple, if we have
 239     //
 240     //    let x = 22_usize as dyn* (Clone + Debug + 'static)
 241     //
 242     // this would return `existential_predicates = [?Self: Clone, ?Self: Debug]` and `region = 'static`.
 243     let (existential_predicates, region) = match cast_ty.kind() {
 244         ty::Dynamic(predicates, region, TraitObjectRepresentation::Sized) => (predicates, region),
 245         _ => panic!("Invalid dyn* cast_ty"),
 246     };
 247
 248     let cause = ObligationCause::new(
 249         expr.span,
 250         fcx.body_id,
 251         // FIXME: Use a better obligation cause code
 252         ObligationCauseCode::MiscObligation,
 253     );
 254
 255     // For each existential predicate (e.g., `?Self: Clone`) substitute
 256     // the type of the expression (e.g., `usize` in our example above)
 257     // and then require that the resulting predicate (e.g., `usize: Clone`)
 258     // holds (it does).
 259     for existential_predicate in existential_predicates.iter() {
 260         let predicate = existential_predicate.with_self_ty(fcx.tcx, expr_ty);
 261         fcx.register_predicate(Obligation::new(cause.clone(), fcx.param_env, predicate));
 262     }
 263
 264     // Enforce the region bound `'static` (e.g., `usize: 'static`, in our example).
 265     fcx.register_predicate(Obligation::new(
 266         cause,
 267         fcx.param_env,
 268         fcx.tcx.mk_predicate(Binder::dummy(ty::PredicateKind::TypeOutlives(
 269             ty::OutlivesPredicate(expr_ty, *region),
 270         ))),
 271     ));
 272
 273     CastCheckResult::Ok
 274 }
 275
 276 impl<'a, 'tcx> CastCheck<'tcx> {
 277     fn new(
 278         fcx: &FnCtxt<'a, 'tcx>,
 279         expr: &'tcx hir::Expr<'tcx>,
 280         expr_ty: Ty<'tcx>,
 281         cast_ty: Ty<'tcx>,
 282         cast_span: Span,
 283         span: Span,
 284     ) -> Result<CastCheck<'tcx>, ErrorGuaranteed> {
 285         let expr_span = expr.span.find_ancestor_inside(span).unwrap_or(expr.span);
 286         let check = CastCheck { expr, expr_ty, expr_span, cast_ty, cast_span, span };
 287
 288         // For better error messages, check for some obviously unsized
 289         // cases now. We do a more thorough check at the end, once
 290         // inference is more completely known.
 291         match cast_ty.kind() {
 292             ty::Dynamic(_, _, TraitObjectRepresentation::Unsized) | ty::Slice(..) => {
 293                 let reported = check.report_cast_to_unsized_type(fcx);
 294                 Err(reported)
 295             }
 296             _ => Ok(check),
 297         }
 298     }
 299
 300     fn report_cast_error(&self, fcx: &FnCtxt<'a, 'tcx>, e: CastError) {
 301         match e {
 302             CastError::ErrorGuaranteed => {
 303                 // an error has already been reported
 304             }
 305             CastError::NeedDeref => {
 306                 let error_span = self.span;
 307                 let mut err = make_invalid_casting_error(
 308                     fcx.tcx.sess,
 309                     self.span,
 310                     self.expr_ty,
 311                     self.cast_ty,
 312                     fcx,
 313                 );
 314                 let cast_ty = fcx.ty_to_string(self.cast_ty);
 315                 err.span_label(
 316                     error_span,
 317                     format!("cannot cast `{}` as `{}`", fcx.ty_to_string(self.expr_ty), cast_ty),
 318                 );
 319                 if let Ok(snippet) = fcx.sess().source_map().span_to_snippet(self.expr_span) {
 320                     err.span_suggestion(
 321                         self.expr_span,
 322                         "dereference the expression",
 323                         format!("*{}", snippet),
 324                         Applicability::MaybeIncorrect,
 325                     );
 326                 } else {
 327                     err.span_help(self.expr_span, "dereference the expression with `*`");
 328                 }
 329                 err.emit();
 330             }
 331             CastError::NeedViaThinPtr | CastError::NeedViaPtr => {
 332                 let mut err = make_invalid_casting_error(
 333                     fcx.tcx.sess,
 334                     self.span,
 335                     self.expr_ty,
 336                     self.cast_ty,
 337                     fcx,
 338                 );
 339                 if self.cast_ty.is_integral() {
 340                     err.help(&format!(
 341                         "cast through {} first",
 342                         match e {
 343                             CastError::NeedViaPtr => "a raw pointer",
 344                             CastError::NeedViaThinPtr => "a thin pointer",
 345                             _ => bug!(),
 346                         }
 347                     ));
 348                 }
 349                 err.emit();
 350             }
 351             CastError::NeedViaInt => {
 352                 make_invalid_casting_error(
 353                     fcx.tcx.sess,
 354                     self.span,
 355                     self.expr_ty,
 356                     self.cast_ty,
 357                     fcx,
 358                 )
 359                 .help(&format!(
 360                     "cast through {} first",
 361                     match e {
 362                         CastError::NeedViaInt => "an integer",
 363                         _ => bug!(),
 364                     }
 365                 ))
 366                 .emit();
 367             }
 368             CastError::IllegalCast => {
 369                 make_invalid_casting_error(
 370                     fcx.tcx.sess,
 371                     self.span,
 372                     self.expr_ty,
 373                     self.cast_ty,
 374                     fcx,
 375                 )
 376                 .emit();
 377             }
 378             CastError::DifferingKinds => {
 379                 make_invalid_casting_error(
 380                     fcx.tcx.sess,
 381                     self.span,
 382                     self.expr_ty,
 383                     self.cast_ty,
 384                     fcx,
 385                 )
 386                 .note("vtable kinds may not match")
 387                 .emit();
 388             }
 389             CastError::CastToBool => {
 390                 let mut err =
 391                     struct_span_err!(fcx.tcx.sess, self.span, E0054, "cannot cast as `bool`");
 392
 393                 if self.expr_ty.is_numeric() {
 394                     match fcx.tcx.sess.source_map().span_to_snippet(self.expr_span) {
 395                         Ok(snippet) => {
 396                             err.span_suggestion(
 397                                 self.span,
 398                                 "compare with zero instead",
 399                                 format!("{snippet} != 0"),
 400                                 Applicability::MachineApplicable,
 401                             );
 402                         }
 403                         Err(_) => {
 404                             err.span_help(self.span, "compare with zero instead");
 405                         }
 406                     }
 407                 } else {
 408                     err.span_label(self.span, "unsupported cast");
 409                 }
 410
 411                 err.emit();
 412             }
 413             CastError::CastToChar => {
 414                 let mut err = type_error_struct!(
 415                     fcx.tcx.sess,
 416                     self.span,
 417                     self.expr_ty,
 418                     E0604,
 419                     "only `u8` can be cast as `char`, not `{}`",
 420                     self.expr_ty
 421                 );
 422                 err.span_label(self.span, "invalid cast");
 423                 if self.expr_ty.is_numeric() {
 424                     if self.expr_ty == fcx.tcx.types.u32 {
 425                         match fcx.tcx.sess.source_map().span_to_snippet(self.expr.span) {
 426                             Ok(snippet) => err.span_suggestion(
 427                                 self.span,
 428                                 "try `char::from_u32` instead",
 429                                 format!("char::from_u32({snippet})"),
 430                                 Applicability::MachineApplicable,
 431                             ),
 432
 433                             Err(_) => err.span_help(self.span, "try `char::from_u32` instead"),
 434                         };
 435                     } else if self.expr_ty == fcx.tcx.types.i8 {
 436                         err.span_help(self.span, "try casting from `u8` instead");
 437                     } else {
 438                         err.span_help(self.span, "try `char::from_u32` instead (via a `u32`)");
 439                     };
 440                 }
 441                 err.emit();
 442             }
 443             CastError::NonScalar => {
 444                 let mut err = type_error_struct!(
 445                     fcx.tcx.sess,
 446                     self.span,
 447                     self.expr_ty,
 448                     E0605,
 449                     "non-primitive cast: `{}` as `{}`",
 450                     self.expr_ty,
 451                     fcx.ty_to_string(self.cast_ty)
 452                 );
 453                 let mut sugg = None;
 454                 let mut sugg_mutref = false;
 455                 if let ty::Ref(reg, cast_ty, mutbl) = *self.cast_ty.kind() {
 456                     if let ty::RawPtr(TypeAndMut { ty: expr_ty, .. }) = *self.expr_ty.kind()
 457                         && fcx
 458                             .try_coerce(
 459                                 self.expr,
 460                                 fcx.tcx.mk_ref(
 461                                     fcx.tcx.lifetimes.re_erased,
 462                                     TypeAndMut { ty: expr_ty, mutbl },
 463                                 ),
 464                                 self.cast_ty,
 465                                 AllowTwoPhase::No,
 466                                 None,
 467                             )
 468                             .is_ok()
 469                     {
 470                         sugg = Some((format!("&{}*", mutbl.prefix_str()), cast_ty == expr_ty));
 471                     } else if let ty::Ref(expr_reg, expr_ty, expr_mutbl) = *self.expr_ty.kind()
 472                         && expr_mutbl == Mutability::Not
 473                         && mutbl == Mutability::Mut
 474                         && fcx
 475                             .try_coerce(
 476                                 self.expr,
 477                                 fcx.tcx.mk_ref(
 478                                     expr_reg,
 479                                     TypeAndMut { ty: expr_ty, mutbl: Mutability::Mut },
 480                                 ),
 481                                 self.cast_ty,
 482                                 AllowTwoPhase::No,
 483                                 None,
 484                             )
 485                             .is_ok()
 486                     {
 487                         sugg_mutref = true;
 488                     }
 489
 490                     if !sugg_mutref
 491                         && sugg == None
 492                         && fcx
 493                             .try_coerce(
 494                                 self.expr,
 495                                 fcx.tcx.mk_ref(reg, TypeAndMut { ty: self.expr_ty, mutbl }),
 496                                 self.cast_ty,
 497                                 AllowTwoPhase::No,
 498                                 None,
 499                             )
 500                             .is_ok()
 501                     {
 502                         sugg = Some((format!("&{}", mutbl.prefix_str()), false));
 503                     }
 504                 } else if let ty::RawPtr(TypeAndMut { mutbl, .. }) = *self.cast_ty.kind()
 505                     && fcx
 506                         .try_coerce(
 507                             self.expr,
 508                             fcx.tcx.mk_ref(
 509                                 fcx.tcx.lifetimes.re_erased,
 510                                 TypeAndMut { ty: self.expr_ty, mutbl },
 511                             ),
 512                             self.cast_ty,
 513                             AllowTwoPhase::No,
 514                             None,
 515                         )
 516                         .is_ok()
 517                 {
 518                     sugg = Some((format!("&{}", mutbl.prefix_str()), false));
 519                 }
 520                 if sugg_mutref {
 521                     err.span_label(self.span, "invalid cast");
 522                     err.span_note(self.expr_span, "this reference is immutable");
 523                     err.span_note(self.cast_span, "trying to cast to a mutable reference type");
 524                 } else if let Some((sugg, remove_cast)) = sugg {
 525                     err.span_label(self.span, "invalid cast");
 526
 527                     let has_parens = fcx
 528                         .tcx
 529                         .sess
 530                         .source_map()
 531                         .span_to_snippet(self.expr_span)
 532                         .map_or(false, |snip| snip.starts_with('('));
 533
 534                     // Very crude check to see whether the expression must be wrapped
 535                     // in parentheses for the suggestion to work (issue #89497).
 536                     // Can/should be extended in the future.
 537                     let needs_parens =
 538                         !has_parens && matches!(self.expr.kind, hir::ExprKind::Cast(..));
 539
 540                     let mut suggestion = vec![(self.expr_span.shrink_to_lo(), sugg)];
 541                     if needs_parens {
 542                         suggestion[0].1 += "(";
 543                         suggestion.push((self.expr_span.shrink_to_hi(), ")".to_string()));
 544                     }
 545                     if remove_cast {
 546                         suggestion.push((
 547                             self.expr_span.shrink_to_hi().to(self.cast_span),
 548                             String::new(),
 549                         ));
 550                     }
 551
 552                     err.multipart_suggestion_verbose(
 553                         "consider borrowing the value",
 554                         suggestion,
 555                         Applicability::MachineApplicable,
 556                     );
 557                 } else if !matches!(
 558                     self.cast_ty.kind(),
 559                     ty::FnDef(..) | ty::FnPtr(..) | ty::Closure(..)
 560                 ) {
 561                     let mut label = true;
 562                     // Check `impl From<self.expr_ty> for self.cast_ty {}` for accurate suggestion:
 563                     if let Ok(snippet) = fcx.tcx.sess.source_map().span_to_snippet(self.expr_span)
 564                         && let Some(from_trait) = fcx.tcx.get_diagnostic_item(sym::From)
 565                     {
 566                         let ty = fcx.resolve_vars_if_possible(self.cast_ty);
 567                         // Erase regions to avoid panic in `prove_value` when calling
 568                         // `type_implements_trait`.
 569                         let ty = fcx.tcx.erase_regions(ty);
 570                         let expr_ty = fcx.resolve_vars_if_possible(self.expr_ty);
 571                         let expr_ty = fcx.tcx.erase_regions(expr_ty);
 572                         let ty_params = fcx.tcx.mk_substs_trait(expr_ty, &[]);
 573                         if fcx
 574                             .infcx
 575                             .type_implements_trait(from_trait, ty, ty_params, fcx.param_env)
 576                             .must_apply_modulo_regions()
 577                         {
 578                             label = false;
 579                             err.span_suggestion(
 580                                 self.span,
 581                                 "consider using the `From` trait instead",
 582                                 format!("{}::from({})", self.cast_ty, snippet),
 583                                 Applicability::MaybeIncorrect,
 584                             );
 585                         }
 586                     }
 587                     let msg = "an `as` expression can only be used to convert between primitive \
 588                                types or to coerce to a specific trait object";
 589                     if label {
 590                         err.span_label(self.span, msg);
 591                     } else {
 592                         err.note(msg);
 593                     }
 594                 } else {
 595                     err.span_label(self.span, "invalid cast");
 596                 }
 597                 err.emit();
 598             }
 599             CastError::SizedUnsizedCast => {
 600                 use crate::structured_errors::{SizedUnsizedCast, StructuredDiagnostic};
 601
 602                 SizedUnsizedCast {
 603                     sess: &fcx.tcx.sess,
 604                     span: self.span,
 605                     expr_ty: self.expr_ty,
 606                     cast_ty: fcx.ty_to_string(self.cast_ty),
 607                 }
 608                 .diagnostic()
 609                 .emit();
 610             }
 611             CastError::IntToFatCast(known_metadata) => {
 612                 let mut err = struct_span_err!(
 613                     fcx.tcx.sess,
 614                     self.cast_span,
 615                     E0606,
 616                     "cannot cast `{}` to a pointer that {} wide",
 617                     fcx.ty_to_string(self.expr_ty),
 618                     if known_metadata.is_some() { "is" } else { "may be" }
 619                 );
 620
 621                 err.span_label(
 622                     self.cast_span,
 623                     format!(
 624                         "creating a `{}` requires both an address and {}",
 625                         self.cast_ty,
 626                         known_metadata.unwrap_or("type-specific metadata"),
 627                     ),
 628                 );
 629
 630                 if fcx.tcx.sess.is_nightly_build() {
 631                     err.span_label(
 632                         self.expr_span,
 633                         "consider casting this expression to `*const ()`, \
 634                         then using `core::ptr::from_raw_parts`",
 635                     );
 636                 }
 637
 638                 err.emit();
 639             }
 640             CastError::UnknownCastPtrKind | CastError::UnknownExprPtrKind => {
 641                 let unknown_cast_to = match e {
 642                     CastError::UnknownCastPtrKind => true,
 643                     CastError::UnknownExprPtrKind => false,
 644                     _ => bug!(),
 645                 };
 646                 let mut err = struct_span_err!(
 647                     fcx.tcx.sess,
 648                     if unknown_cast_to { self.cast_span } else { self.span },
 649                     E0641,
 650                     "cannot cast {} a pointer of an unknown kind",
 651                     if unknown_cast_to { "to" } else { "from" }
 652                 );
 653                 if unknown_cast_to {
 654                     err.span_label(self.cast_span, "needs more type information");
 655                     err.note(
 656                         "the type information given here is insufficient to check whether \
 657                         the pointer cast is valid",
 658                     );
 659                 } else {
 660                     err.span_label(
 661                         self.span,
 662                         "the type information given here is insufficient to check whether \
 663                         the pointer cast is valid",
 664                     );
 665                 }
 666                 err.emit();
 667             }
 668             CastError::ForeignNonExhaustiveAdt => {
 669                 make_invalid_casting_error(
 670                     fcx.tcx.sess,
 671                     self.span,
 672                     self.expr_ty,
 673                     self.cast_ty,
 674                     fcx,
 675                 )
 676                 .note("cannot cast an enum with a non-exhaustive variant when it's defined in another crate")
 677                 .emit();
 678             }
 679         }
 680     }
 681
 682     fn report_cast_to_unsized_type(&self, fcx: &FnCtxt<'a, 'tcx>) -> ErrorGuaranteed {
 683         if let Some(reported) =
 684             self.cast_ty.error_reported().or_else(|| self.expr_ty.error_reported())
 685         {
 686             return reported;
 687         }
 688
 689         let tstr = fcx.ty_to_string(self.cast_ty);
 690         let mut err = type_error_struct!(
 691             fcx.tcx.sess,
 692             self.span,
 693             self.expr_ty,
 694             E0620,
 695             "cast to unsized type: `{}` as `{}`",
 696             fcx.resolve_vars_if_possible(self.expr_ty),
 697             tstr
 698         );
 699         match self.expr_ty.kind() {
 700             ty::Ref(_, _, mt) => {
 701                 let mtstr = mt.prefix_str();
 702                 if self.cast_ty.is_trait() {
 703                     match fcx.tcx.sess.source_map().span_to_snippet(self.cast_span) {
 704                         Ok(s) => {
 705                             err.span_suggestion(
 706                                 self.cast_span,
 707                                 "try casting to a reference instead",
 708                                 format!("&{}{}", mtstr, s),
 709                                 Applicability::MachineApplicable,
 710                             );
 711                         }
 712                         Err(_) => {
 713                             let msg = &format!("did you mean `&{}{}`?", mtstr, tstr);
 714                             err.span_help(self.cast_span, msg);
 715                         }
 716                     }
 717                 } else {
 718                     let msg =
 719                         &format!("consider using an implicit coercion to `&{mtstr}{tstr}` instead");
 720                     err.span_help(self.span, msg);
 721                 }
 722             }
 723             ty::Adt(def, ..) if def.is_box() => {
 724                 match fcx.tcx.sess.source_map().span_to_snippet(self.cast_span) {
 725                     Ok(s) => {
 726                         err.span_suggestion(
 727                             self.cast_span,
 728                             "you can cast to a `Box` instead",
 729                             format!("Box<{s}>"),
 730                             Applicability::MachineApplicable,
 731                         );
 732                     }
 733                     Err(_) => {
 734                         err.span_help(
 735                             self.cast_span,
 736                             &format!("you might have meant `Box<{tstr}>`"),
 737                         );
 738                     }
 739                 }
 740             }
 741             _ => {
 742                 err.span_help(self.expr_span, "consider using a box or reference as appropriate");
 743             }
 744         }
 745         err.emit()
 746     }
 747
 748     fn trivial_cast_lint(&self, fcx: &FnCtxt<'a, 'tcx>) {
 749         let t_cast = self.cast_ty;
 750         let t_expr = self.expr_ty;
 751         let type_asc_or =
 752             if fcx.tcx.features().type_ascription { "type ascription or " } else { "" };
 753         let (adjective, lint) = if t_cast.is_numeric() && t_expr.is_numeric() {
 754             ("numeric ", lint::builtin::TRIVIAL_NUMERIC_CASTS)
 755         } else {
 756             ("", lint::builtin::TRIVIAL_CASTS)
 757         };
 758         fcx.tcx.struct_span_lint_hir(lint, self.expr.hir_id, self.span, |err| {
 759             err.build(&format!(
 760                 "trivial {}cast: `{}` as `{}`",
 761                 adjective,
 762                 fcx.ty_to_string(t_expr),
 763                 fcx.ty_to_string(t_cast)
 764             ))
 765             .help(&format!(
 766                 "cast can be replaced by coercion; this might \
 767                                    require {type_asc_or}a temporary variable"
 768             ))
 769             .emit();
 770         });
 771     }
 772
 773     #[instrument(skip(fcx), level = "debug")]
 774     pub fn check(mut self, fcx: &FnCtxt<'a, 'tcx>) {
 775         self.expr_ty = fcx.structurally_resolved_type(self.expr_span, self.expr_ty);
 776         self.cast_ty = fcx.structurally_resolved_type(self.cast_span, self.cast_ty);
 777
 778         debug!("check_cast({}, {:?} as {:?})", self.expr.hir_id, self.expr_ty, self.cast_ty);
 779
 780         if !fcx.type_is_sized_modulo_regions(fcx.param_env, self.cast_ty, self.span)
 781             && !self.cast_ty.has_infer_types()
 782         {
 783             self.report_cast_to_unsized_type(fcx);
 784         } else if self.expr_ty.references_error() || self.cast_ty.references_error() {
 785             // No sense in giving duplicate error messages
 786         } else {
 787             match self.try_coercion_cast(fcx) {
 788                 Ok(()) => {
 789                     self.trivial_cast_lint(fcx);
 790                     debug!(" -> CoercionCast");
 791                     fcx.typeck_results.borrow_mut().set_coercion_cast(self.expr.hir_id.local_id);
 792                 }
 793                 Err(ty::error::TypeError::ObjectUnsafeCoercion(did)) => {
 794                     self.report_object_unsafe_cast(&fcx, did);
 795                 }
 796                 Err(_) => {
 797                     match self.do_check(fcx) {
 798                         Ok(k) => {
 799                             debug!(" -> {:?}", k);
 800                         }
 801                         Err(e) => self.report_cast_error(fcx, e),
 802                     };
 803                 }
 804             };
 805         }
 806     }
 807
 808     fn report_object_unsafe_cast(&self, fcx: &FnCtxt<'a, 'tcx>, did: DefId) {
 809         let violations = fcx.tcx.object_safety_violations(did);
 810         let mut err = report_object_safety_error(fcx.tcx, self.cast_span, did, violations);
 811         err.note(&format!("required by cast to type '{}'", fcx.ty_to_string(self.cast_ty)));
 812         err.emit();
 813     }
 814
 815     /// Checks a cast, and report an error if one exists. In some cases, this
 816     /// can return Ok and create type errors in the fcx rather than returning
 817     /// directly. coercion-cast is handled in check instead of here.
 818     pub fn do_check(&self, fcx: &FnCtxt<'a, 'tcx>) -> Result<CastKind, CastError> {
 819         use rustc_middle::ty::cast::CastTy::*;
 820         use rustc_middle::ty::cast::IntTy::*;
 821
 822         let (t_from, t_cast) = match (CastTy::from_ty(self.expr_ty), CastTy::from_ty(self.cast_ty))
 823         {
 824             (Some(t_from), Some(t_cast)) => (t_from, t_cast),
 825             // Function item types may need to be reified before casts.
 826             (None, Some(t_cast)) => {
 827                 match *self.expr_ty.kind() {
 828                     ty::FnDef(..) => {
 829                         // Attempt a coercion to a fn pointer type.
 830                         let f = fcx.normalize_associated_types_in(
 831                             self.expr_span,
 832                             self.expr_ty.fn_sig(fcx.tcx),
 833                         );
 834                         let res = fcx.try_coerce(
 835                             self.expr,
 836                             self.expr_ty,
 837                             fcx.tcx.mk_fn_ptr(f),
 838                             AllowTwoPhase::No,
 839                             None,
 840                         );
 841                         if let Err(TypeError::IntrinsicCast) = res {
 842                             return Err(CastError::IllegalCast);
 843                         }
 844                         if res.is_err() {
 845                             return Err(CastError::NonScalar);
 846                         }
 847                         (FnPtr, t_cast)
 848                     }
 849                     // Special case some errors for references, and check for
 850                     // array-ptr-casts. `Ref` is not a CastTy because the cast
 851                     // is split into a coercion to a pointer type, followed by
 852                     // a cast.
 853                     ty::Ref(_, inner_ty, mutbl) => {
 854                         return match t_cast {
 855                             Int(_) | Float => match *inner_ty.kind() {
 856                                 ty::Int(_)
 857                                 | ty::Uint(_)
 858                                 | ty::Float(_)
 859                                 | ty::Infer(ty::InferTy::IntVar(_) | ty::InferTy::FloatVar(_)) => {
 860                                     Err(CastError::NeedDeref)
 861                                 }
 862                                 _ => Err(CastError::NeedViaPtr),
 863                             },
 864                             // array-ptr-cast
 865                             Ptr(mt) => {
 866                                 self.check_ref_cast(fcx, TypeAndMut { mutbl, ty: inner_ty }, mt)
 867                             }
 868                             _ => Err(CastError::NonScalar),
 869                         };
 870                     }
 871                     _ => return Err(CastError::NonScalar),
 872                 }
 873             }
 874             _ => return Err(CastError::NonScalar),
 875         };
 876
 877         if let ty::Adt(adt_def, _) = *self.expr_ty.kind() {
 878             if adt_def.did().krate != LOCAL_CRATE {
 879                 if adt_def.variants().iter().any(VariantDef::is_field_list_non_exhaustive) {
 880                     return Err(CastError::ForeignNonExhaustiveAdt);
 881                 }
 882             }
 883         }
 884
 885         match (t_from, t_cast) {
 886             // These types have invariants! can't cast into them.
 887             (_, Int(CEnum) | FnPtr) => Err(CastError::NonScalar),
 888
 889             // * -> Bool
 890             (_, Int(Bool)) => Err(CastError::CastToBool),
 891
 892             // * -> Char
 893             (Int(U(ty::UintTy::U8)), Int(Char)) => Ok(CastKind::U8CharCast), // u8-char-cast
 894             (_, Int(Char)) => Err(CastError::CastToChar),
 895
 896             // prim -> float,ptr
 897             (Int(Bool) | Int(CEnum) | Int(Char), Float) => Err(CastError::NeedViaInt),
 898
 899             (Int(Bool) | Int(CEnum) | Int(Char) | Float, Ptr(_)) | (Ptr(_) | FnPtr, Float) => {
 900                 Err(CastError::IllegalCast)
 901             }
 902
 903             // ptr -> *
 904             (Ptr(m_e), Ptr(m_c)) => self.check_ptr_ptr_cast(fcx, m_e, m_c), // ptr-ptr-cast
 905
 906             // ptr-addr-cast
 907             (Ptr(m_expr), Int(t_c)) => {
 908                 self.lossy_provenance_ptr2int_lint(fcx, t_c);
 909                 self.check_ptr_addr_cast(fcx, m_expr)
 910             }
 911             (FnPtr, Int(_)) => {
 912                 // FIXME(#95489): there should eventually be a lint for these casts
 913                 Ok(CastKind::FnPtrAddrCast)
 914             }
 915             // addr-ptr-cast
 916             (Int(_), Ptr(mt)) => {
 917                 self.fuzzy_provenance_int2ptr_lint(fcx);
 918                 self.check_addr_ptr_cast(fcx, mt)
 919             }
 920             // fn-ptr-cast
 921             (FnPtr, Ptr(mt)) => self.check_fptr_ptr_cast(fcx, mt),
 922
 923             // prim -> prim
 924             (Int(CEnum), Int(_)) => {
 925                 self.cenum_impl_drop_lint(fcx);
 926                 Ok(CastKind::EnumCast)
 927             }
 928             (Int(Char) | Int(Bool), Int(_)) => Ok(CastKind::PrimIntCast),
 929
 930             (Int(_) | Float, Int(_) | Float) => Ok(CastKind::NumericCast),
 931
 932             // FIXME: this needs more conditions...
 933             (_, DynStar) => Ok(CastKind::DynStarCast),
 934
 935             // FIXME: do we want to allow dyn* upcasting or other casts?
 936             (DynStar, _) => Err(CastError::IllegalCast),
 937         }
 938     }
 939
 940     fn check_ptr_ptr_cast(
 941         &self,
 942         fcx: &FnCtxt<'a, 'tcx>,
 943         m_expr: ty::TypeAndMut<'tcx>,
 944         m_cast: ty::TypeAndMut<'tcx>,
 945     ) -> Result<CastKind, CastError> {
 946         debug!("check_ptr_ptr_cast m_expr={:?} m_cast={:?}", m_expr, m_cast);
 947         // ptr-ptr cast. vtables must match.
 948
 949         let expr_kind = fcx.pointer_kind(m_expr.ty, self.span)?;
 950         let cast_kind = fcx.pointer_kind(m_cast.ty, self.span)?;
 951
 952         let Some(cast_kind) = cast_kind else {
 953             // We can't cast if target pointer kind is unknown
 954             return Err(CastError::UnknownCastPtrKind);
 955         };
 956
 957         // Cast to thin pointer is OK
 958         if cast_kind == PointerKind::Thin {
 959             return Ok(CastKind::PtrPtrCast);
 960         }
 961
 962         let Some(expr_kind) = expr_kind else {
 963             // We can't cast to fat pointer if source pointer kind is unknown
 964             return Err(CastError::UnknownExprPtrKind);
 965         };
 966
 967         // thin -> fat? report invalid cast (don't complain about vtable kinds)
 968         if expr_kind == PointerKind::Thin {
 969             return Err(CastError::SizedUnsizedCast);
 970         }
 971
 972         // vtable kinds must match
 973         if cast_kind == expr_kind {
 974             Ok(CastKind::PtrPtrCast)
 975         } else {
 976             Err(CastError::DifferingKinds)
 977         }
 978     }
 979
 980     fn check_fptr_ptr_cast(
 981         &self,
 982         fcx: &FnCtxt<'a, 'tcx>,
 983         m_cast: ty::TypeAndMut<'tcx>,
 984     ) -> Result<CastKind, CastError> {
 985         // fptr-ptr cast. must be to thin ptr
 986
 987         match fcx.pointer_kind(m_cast.ty, self.span)? {
 988             None => Err(CastError::UnknownCastPtrKind),
 989             Some(PointerKind::Thin) => Ok(CastKind::FnPtrPtrCast),
 990             _ => Err(CastError::IllegalCast),
 991         }
 992     }
 993
 994     fn check_ptr_addr_cast(
 995         &self,
 996         fcx: &FnCtxt<'a, 'tcx>,
 997         m_expr: ty::TypeAndMut<'tcx>,
 998     ) -> Result<CastKind, CastError> {
 999         // ptr-addr cast. must be from thin ptr
1000
1001         match fcx.pointer_kind(m_expr.ty, self.span)? {
1002             None => Err(CastError::UnknownExprPtrKind),
1003             Some(PointerKind::Thin) => Ok(CastKind::PtrAddrCast),
1004             _ => Err(CastError::NeedViaThinPtr),
1005         }
1006     }
1007
1008     fn check_ref_cast(
1009         &self,
1010         fcx: &FnCtxt<'a, 'tcx>,
1011         m_expr: ty::TypeAndMut<'tcx>,
1012         m_cast: ty::TypeAndMut<'tcx>,
1013     ) -> Result<CastKind, CastError> {
1014         // array-ptr-cast: allow mut-to-mut, mut-to-const, const-to-const
1015         if m_expr.mutbl == hir::Mutability::Mut || m_cast.mutbl == hir::Mutability::Not {
1016             if let ty::Array(ety, _) = m_expr.ty.kind() {
1017                 // Due to the limitations of LLVM global constants,
1018                 // region pointers end up pointing at copies of
1019                 // vector elements instead of the original values.
1020                 // To allow raw pointers to work correctly, we
1021                 // need to special-case obtaining a raw pointer
1022                 // from a region pointer to a vector.
1023
1024                 // Coerce to a raw pointer so that we generate AddressOf in MIR.
1025                 let array_ptr_type = fcx.tcx.mk_ptr(m_expr);
1026                 fcx.try_coerce(self.expr, self.expr_ty, array_ptr_type, AllowTwoPhase::No, None)
1027                     .unwrap_or_else(|_| {
1028                         bug!(
1029                         "could not cast from reference to array to pointer to array ({:?} to {:?})",
1030                         self.expr_ty,
1031                         array_ptr_type,
1032                     )
1033                     });
1034
1035                 // this will report a type mismatch if needed
1036                 fcx.demand_eqtype(self.span, *ety, m_cast.ty);
1037                 return Ok(CastKind::ArrayPtrCast);
1038             }
1039         }
1040
1041         Err(CastError::IllegalCast)
1042     }
1043
1044     fn check_addr_ptr_cast(
1045         &self,
1046         fcx: &FnCtxt<'a, 'tcx>,
1047         m_cast: TypeAndMut<'tcx>,
1048     ) -> Result<CastKind, CastError> {
1049         // ptr-addr cast. pointer must be thin.
1050         match fcx.pointer_kind(m_cast.ty, self.span)? {
1051             None => Err(CastError::UnknownCastPtrKind),
1052             Some(PointerKind::Thin) => Ok(CastKind::AddrPtrCast),
1053             Some(PointerKind::VTable(_)) => Err(CastError::IntToFatCast(Some("a vtable"))),
1054             Some(PointerKind::Length) => Err(CastError::IntToFatCast(Some("a length"))),
1055             Some(
1056                 PointerKind::OfProjection(_)
1057                 | PointerKind::OfOpaque(_, _)
1058                 | PointerKind::OfParam(_),
1059             ) => Err(CastError::IntToFatCast(None)),
1060         }
1061     }
1062
1063     fn try_coercion_cast(&self, fcx: &FnCtxt<'a, 'tcx>) -> Result<(), ty::error::TypeError<'tcx>> {
1064         match fcx.try_coerce(self.expr, self.expr_ty, self.cast_ty, AllowTwoPhase::No, None) {
1065             Ok(_) => Ok(()),
1066             Err(err) => Err(err),
1067         }
1068     }
1069
1070     fn cenum_impl_drop_lint(&self, fcx: &FnCtxt<'a, 'tcx>) {
1071         if let ty::Adt(d, _) = self.expr_ty.kind()
1072             && d.has_dtor(fcx.tcx)
1073         {
1074             fcx.tcx.struct_span_lint_hir(
1075                 lint::builtin::CENUM_IMPL_DROP_CAST,
1076                 self.expr.hir_id,
1077                 self.span,
1078                 |err| {
1079                     err.build(&format!(
1080                         "cannot cast enum `{}` into integer `{}` because it implements `Drop`",
1081                         self.expr_ty, self.cast_ty
1082                     ))
1083                     .emit();
1084                 },
1085             );
1086         }
1087     }
1088
1089     fn lossy_provenance_ptr2int_lint(&self, fcx: &FnCtxt<'a, 'tcx>, t_c: ty::cast::IntTy) {
1090         fcx.tcx.struct_span_lint_hir(
1091             lint::builtin::LOSSY_PROVENANCE_CASTS,
1092             self.expr.hir_id,
1093             self.span,
1094             |err| {
1095                 let mut err = err.build(&format!(
1096                     "under strict provenance it is considered bad style to cast pointer `{}` to integer `{}`",
1097                     self.expr_ty, self.cast_ty
1098                 ));
1099
1100                 let msg = "use `.addr()` to obtain the address of a pointer";
1101
1102                 let expr_prec = self.expr.precedence().order();
1103                 let needs_parens = expr_prec < rustc_ast::util::parser::PREC_POSTFIX;
1104
1105                 let scalar_cast = match t_c {
1106                     ty::cast::IntTy::U(ty::UintTy::Usize) => String::new(),
1107                     _ => format!(" as {}", self.cast_ty),
1108                 };
1109
1110                 let cast_span = self.expr_span.shrink_to_hi().to(self.cast_span);
1111
1112                 if needs_parens {
1113                     let suggestions = vec![
1114                         (self.expr_span.shrink_to_lo(), String::from("(")),
1115                         (cast_span, format!(").addr(){scalar_cast}")),
1116                     ];
1117
1118                     err.multipart_suggestion(msg, suggestions, Applicability::MaybeIncorrect);
1119                 } else {
1120                     err.span_suggestion(
1121                         cast_span,
1122                         msg,
1123                         format!(".addr(){scalar_cast}"),
1124                         Applicability::MaybeIncorrect,
1125                     );
1126                 }
1127
1128                 err.help(
1129                     "if you can't comply with strict provenance and need to expose the pointer \
1130                     provenance you can use `.expose_addr()` instead"
1131                 );
1132
1133                 err.emit();
1134             },
1135         );
1136     }
1137
1138     fn fuzzy_provenance_int2ptr_lint(&self, fcx: &FnCtxt<'a, 'tcx>) {
1139         fcx.tcx.struct_span_lint_hir(
1140             lint::builtin::FUZZY_PROVENANCE_CASTS,
1141             self.expr.hir_id,
1142             self.span,
1143             |err| {
1144                 let mut err = err.build(&format!(
1145                     "strict provenance disallows casting integer `{}` to pointer `{}`",
1146                     self.expr_ty, self.cast_ty
1147                 ));
1148                 let msg = "use `.with_addr()` to adjust a valid pointer in the same allocation, to this address";
1149                 let suggestions = vec![
1150                     (self.expr_span.shrink_to_lo(), String::from("(...).with_addr(")),
1151                     (self.expr_span.shrink_to_hi().to(self.cast_span), String::from(")")),
1152                 ];
1153
1154                 err.multipart_suggestion(msg, suggestions, Applicability::MaybeIncorrect);
1155                 err.help(
1156                     "if you can't comply with strict provenance and don't have a pointer with \
1157                     the correct provenance you can use `std::ptr::from_exposed_addr()` instead"
1158                  );
1159
1160                 err.emit();
1161             },
1162         );
1163     }
1164 }