compiler/rustc_hir_analysis/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, DelayDm, 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::{self, Binder, Ty, TypeAndMut, TypeVisitable, VariantDef};
  45 use rustc_session::lint;
  46 use rustc_session::Session;
  47 use rustc_span::symbol::sym;
  48 use rustc_span::Span;
  49 use rustc_trait_selection::infer::InferCtxtExt;
  50 use rustc_trait_selection::traits::error_reporting::report_object_safety_error;
  51
  52 /// Reifies a cast check to be checked once we have full type information for
  53 /// a function context.
  54 #[derive(Debug)]
  55 pub struct CastCheck<'tcx> {
  56     /// The expression whose value is being casted
  57     expr: &'tcx hir::Expr<'tcx>,
  58     /// The source type for the cast expression
  59     expr_ty: Ty<'tcx>,
  60     expr_span: Span,
  61     /// The target type. That is, the type we are casting to.
  62     cast_ty: Ty<'tcx>,
  63     cast_span: Span,
  64     span: Span,
  65 }
  66
  67 /// The kind of pointer and associated metadata (thin, length or vtable) - we
  68 /// only allow casts between fat pointers if their metadata have the same
  69 /// kind.
  70 #[derive(Copy, Clone, PartialEq, Eq)]
  71 enum PointerKind<'tcx> {
  72     /// No metadata attached, ie pointer to sized type or foreign type
  73     Thin,
  74     /// A trait object
  75     VTable(Option<DefId>),
  76     /// Slice
  77     Length,
  78     /// The unsize info of this projection
  79     OfProjection(&'tcx ty::ProjectionTy<'tcx>),
  80     /// The unsize info of this opaque ty
  81     OfOpaque(DefId, SubstsRef<'tcx>),
  82     /// The unsize info of this parameter
  83     OfParam(&'tcx ty::ParamTy),
  84 }
  85
  86 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  87     /// Returns the kind of unsize information of t, or None
  88     /// if t is unknown.
  89     fn pointer_kind(
  90         &self,
  91         t: Ty<'tcx>,
  92         span: Span,
  93     ) -> Result<Option<PointerKind<'tcx>>, ErrorGuaranteed> {
  94         debug!("pointer_kind({:?}, {:?})", t, span);
  95
  96         let t = self.resolve_vars_if_possible(t);
  97
  98         if let Some(reported) = t.error_reported() {
  99             return Err(reported);
 100         }
 101
 102         if self.type_is_sized_modulo_regions(self.param_env, t, span) {
 103             return Ok(Some(PointerKind::Thin));
 104         }
 105
 106         Ok(match *t.kind() {
 107             ty::Slice(_) | ty::Str => Some(PointerKind::Length),
 108             ty::Dynamic(ref tty, _, ty::Dyn) => Some(PointerKind::VTable(tty.principal_def_id())),
 109             ty::Adt(def, substs) if def.is_struct() => match def.non_enum_variant().fields.last() {
 110                 None => Some(PointerKind::Thin),
 111                 Some(f) => {
 112                     let field_ty = self.field_ty(span, f, substs);
 113                     self.pointer_kind(field_ty, span)?
 114                 }
 115             },
 116             ty::Tuple(fields) => match fields.last() {
 117                 None => Some(PointerKind::Thin),
 118                 Some(&f) => self.pointer_kind(f, span)?,
 119             },
 120
 121             // Pointers to foreign types are thin, despite being unsized
 122             ty::Foreign(..) => Some(PointerKind::Thin),
 123             // We should really try to normalize here.
 124             ty::Projection(ref pi) => Some(PointerKind::OfProjection(pi)),
 125             ty::Opaque(def_id, substs) => Some(PointerKind::OfOpaque(def_id, substs)),
 126             ty::Param(ref p) => Some(PointerKind::OfParam(p)),
 127             // Insufficient type information.
 128             ty::Placeholder(..) | ty::Bound(..) | ty::Infer(_) => None,
 129
 130             ty::Bool
 131             | ty::Char
 132             | ty::Int(..)
 133             | ty::Uint(..)
 134             | ty::Float(_)
 135             | ty::Array(..)
 136             | ty::GeneratorWitness(..)
 137             | ty::RawPtr(_)
 138             | ty::Ref(..)
 139             | ty::FnDef(..)
 140             | ty::FnPtr(..)
 141             | ty::Closure(..)
 142             | ty::Generator(..)
 143             | ty::Adt(..)
 144             | ty::Never
 145             | ty::Dynamic(_, _, ty::DynStar)
 146             | ty::Error(_) => {
 147                 let reported = self
 148                     .tcx
 149                     .sess
 150                     .delay_span_bug(span, &format!("`{:?}` should be sized but is not?", t));
 151                 return Err(reported);
 152             }
 153         })
 154     }
 155 }
 156
 157 #[derive(Copy, Clone)]
 158 pub enum CastError {
 159     ErrorGuaranteed,
 160
 161     CastToBool,
 162     CastToChar,
 163     DifferingKinds,
 164     /// Cast of thin to fat raw ptr (e.g., `*const () as *const [u8]`).
 165     SizedUnsizedCast,
 166     IllegalCast,
 167     NeedDeref,
 168     NeedViaPtr,
 169     NeedViaThinPtr,
 170     NeedViaInt,
 171     NonScalar,
 172     UnknownExprPtrKind,
 173     UnknownCastPtrKind,
 174     /// Cast of int to (possibly) fat raw pointer.
 175     ///
 176     /// Argument is the specific name of the metadata in plain words, such as "a vtable"
 177     /// or "a length". If this argument is None, then the metadata is unknown, for example,
 178     /// when we're typechecking a type parameter with a ?Sized bound.
 179     IntToFatCast(Option<&'static str>),
 180     ForeignNonExhaustiveAdt,
 181 }
 182
 183 impl From<ErrorGuaranteed> for CastError {
 184     fn from(_: ErrorGuaranteed) -> Self {
 185         CastError::ErrorGuaranteed
 186     }
 187 }
 188
 189 fn make_invalid_casting_error<'a, 'tcx>(
 190     sess: &'a Session,
 191     span: Span,
 192     expr_ty: Ty<'tcx>,
 193     cast_ty: Ty<'tcx>,
 194     fcx: &FnCtxt<'a, 'tcx>,
 195 ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
 196     type_error_struct!(
 197         sess,
 198         span,
 199         expr_ty,
 200         E0606,
 201         "casting `{}` as `{}` is invalid",
 202         fcx.ty_to_string(expr_ty),
 203         fcx.ty_to_string(cast_ty)
 204     )
 205 }
 206
 207 pub enum CastCheckResult<'tcx> {
 208     Ok,
 209     Deferred(CastCheck<'tcx>),
 210     Err(ErrorGuaranteed),
 211 }
 212
 213 pub fn check_cast<'tcx>(
 214     fcx: &FnCtxt<'_, 'tcx>,
 215     expr: &'tcx hir::Expr<'tcx>,
 216     expr_ty: Ty<'tcx>,
 217     cast_ty: Ty<'tcx>,
 218     cast_span: Span,
 219     span: Span,
 220 ) -> CastCheckResult<'tcx> {
 221     if cast_ty.is_dyn_star() {
 222         check_dyn_star_cast(fcx, expr, expr_ty, cast_ty)
 223     } else {
 224         match CastCheck::new(fcx, expr, expr_ty, cast_ty, cast_span, span) {
 225             Ok(check) => CastCheckResult::Deferred(check),
 226             Err(e) => CastCheckResult::Err(e),
 227         }
 228     }
 229 }
 230
 231 fn check_dyn_star_cast<'tcx>(
 232     fcx: &FnCtxt<'_, 'tcx>,
 233     expr: &'tcx hir::Expr<'tcx>,
 234     expr_ty: Ty<'tcx>,
 235     cast_ty: Ty<'tcx>,
 236 ) -> CastCheckResult<'tcx> {
 237     // Find the bounds in the dyn*. For eaxmple, if we have
 238     //
 239     //    let x = 22_usize as dyn* (Clone + Debug + 'static)
 240     //
 241     // this would return `existential_predicates = [?Self: Clone, ?Self: Debug]` and `region = 'static`.
 242     let (existential_predicates, region) = match cast_ty.kind() {
 243         ty::Dynamic(predicates, region, ty::DynStar) => (predicates, region),
 244         _ => panic!("Invalid dyn* cast_ty"),
 245     };
 246
 247     let cause = ObligationCause::new(
 248         expr.span,
 249         fcx.body_id,
 250         // FIXME(dyn-star): Use a better obligation cause code
 251         ObligationCauseCode::MiscObligation,
 252     );
 253
 254     // For each existential predicate (e.g., `?Self: Clone`) substitute
 255     // the type of the expression (e.g., `usize` in our example above)
 256     // and then require that the resulting predicate (e.g., `usize: Clone`)
 257     // holds (it does).
 258     for existential_predicate in existential_predicates.iter() {
 259         let predicate = existential_predicate.with_self_ty(fcx.tcx, expr_ty);
 260         fcx.register_predicate(Obligation::new(cause.clone(), fcx.param_env, predicate));
 261     }
 262
 263     // Enforce the region bound `'static` (e.g., `usize: 'static`, in our example).
 264     fcx.register_predicate(Obligation::new(
 265         cause,
 266         fcx.param_env,
 267         fcx.tcx.mk_predicate(Binder::dummy(ty::PredicateKind::TypeOutlives(
 268             ty::OutlivesPredicate(expr_ty, *region),
 269         ))),
 270     ));
 271
 272     CastCheckResult::Ok
 273 }
 274
 275 impl<'a, 'tcx> CastCheck<'tcx> {
 276     fn new(
 277         fcx: &FnCtxt<'a, 'tcx>,
 278         expr: &'tcx hir::Expr<'tcx>,
 279         expr_ty: Ty<'tcx>,
 280         cast_ty: Ty<'tcx>,
 281         cast_span: Span,
 282         span: Span,
 283     ) -> Result<CastCheck<'tcx>, ErrorGuaranteed> {
 284         let expr_span = expr.span.find_ancestor_inside(span).unwrap_or(expr.span);
 285         let check = CastCheck { expr, expr_ty, expr_span, cast_ty, cast_span, span };
 286
 287         // For better error messages, check for some obviously unsized
 288         // cases now. We do a more thorough check at the end, once
 289         // inference is more completely known.
 290         match cast_ty.kind() {
 291             ty::Dynamic(_, _, ty::Dyn) | ty::Slice(..) => {
 292                 let reported = check.report_cast_to_unsized_type(fcx);
 293                 Err(reported)
 294             }
 295             _ => Ok(check),
 296         }
 297     }
 298
 299     fn report_cast_error(&self, fcx: &FnCtxt<'a, 'tcx>, e: CastError) {
 300         match e {
 301             CastError::ErrorGuaranteed => {
 302                 // an error has already been reported
 303             }
 304             CastError::NeedDeref => {
 305                 let error_span = self.span;
 306                 let mut err = make_invalid_casting_error(
 307                     fcx.tcx.sess,
 308                     self.span,
 309                     self.expr_ty,
 310                     self.cast_ty,
 311                     fcx,
 312                 );
 313                 let cast_ty = fcx.ty_to_string(self.cast_ty);
 314                 err.span_label(
 315                     error_span,
 316                     format!("cannot cast `{}` as `{}`", fcx.ty_to_string(self.expr_ty), cast_ty),
 317                 );
 318                 if let Ok(snippet) = fcx.sess().source_map().span_to_snippet(self.expr_span) {
 319                     err.span_suggestion(
 320                         self.expr_span,
 321                         "dereference the expression",
 322                         format!("*{}", snippet),
 323                         Applicability::MaybeIncorrect,
 324                     );
 325                 } else {
 326                     err.span_help(self.expr_span, "dereference the expression with `*`");
 327                 }
 328                 err.emit();
 329             }
 330             CastError::NeedViaThinPtr | CastError::NeedViaPtr => {
 331                 let mut err = make_invalid_casting_error(
 332                     fcx.tcx.sess,
 333                     self.span,
 334                     self.expr_ty,
 335                     self.cast_ty,
 336                     fcx,
 337                 );
 338                 if self.cast_ty.is_integral() {
 339                     err.help(&format!(
 340                         "cast through {} first",
 341                         match e {
 342                             CastError::NeedViaPtr => "a raw pointer",
 343                             CastError::NeedViaThinPtr => "a thin pointer",
 344                             _ => bug!(),
 345                         }
 346                     ));
 347                 }
 348                 err.emit();
 349             }
 350             CastError::NeedViaInt => {
 351                 make_invalid_casting_error(
 352                     fcx.tcx.sess,
 353                     self.span,
 354                     self.expr_ty,
 355                     self.cast_ty,
 356                     fcx,
 357                 )
 358                 .help(&format!(
 359                     "cast through {} first",
 360                     match e {
 361                         CastError::NeedViaInt => "an integer",
 362                         _ => bug!(),
 363                     }
 364                 ))
 365                 .emit();
 366             }
 367             CastError::IllegalCast => {
 368                 make_invalid_casting_error(
 369                     fcx.tcx.sess,
 370                     self.span,
 371                     self.expr_ty,
 372                     self.cast_ty,
 373                     fcx,
 374                 )
 375                 .emit();
 376             }
 377             CastError::DifferingKinds => {
 378                 make_invalid_casting_error(
 379                     fcx.tcx.sess,
 380                     self.span,
 381                     self.expr_ty,
 382                     self.cast_ty,
 383                     fcx,
 384                 )
 385                 .note("vtable kinds may not match")
 386                 .emit();
 387             }
 388             CastError::CastToBool => {
 389                 let mut err =
 390                     struct_span_err!(fcx.tcx.sess, self.span, E0054, "cannot cast as `bool`");
 391
 392                 if self.expr_ty.is_numeric() {
 393                     match fcx.tcx.sess.source_map().span_to_snippet(self.expr_span) {
 394                         Ok(snippet) => {
 395                             err.span_suggestion(
 396                                 self.span,
 397                                 "compare with zero instead",
 398                                 format!("{snippet} != 0"),
 399                                 Applicability::MachineApplicable,
 400                             );
 401                         }
 402                         Err(_) => {
 403                             err.span_help(self.span, "compare with zero instead");
 404                         }
 405                     }
 406                 } else {
 407                     err.span_label(self.span, "unsupported cast");
 408                 }
 409
 410                 err.emit();
 411             }
 412             CastError::CastToChar => {
 413                 let mut err = type_error_struct!(
 414                     fcx.tcx.sess,
 415                     self.span,
 416                     self.expr_ty,
 417                     E0604,
 418                     "only `u8` can be cast as `char`, not `{}`",
 419                     self.expr_ty
 420                 );
 421                 err.span_label(self.span, "invalid cast");
 422                 if self.expr_ty.is_numeric() {
 423                     if self.expr_ty == fcx.tcx.types.u32 {
 424                         match fcx.tcx.sess.source_map().span_to_snippet(self.expr.span) {
 425                             Ok(snippet) => err.span_suggestion(
 426                                 self.span,
 427                                 "try `char::from_u32` instead",
 428                                 format!("char::from_u32({snippet})"),
 429                                 Applicability::MachineApplicable,
 430                             ),
 431
 432                             Err(_) => err.span_help(self.span, "try `char::from_u32` instead"),
 433                         };
 434                     } else if self.expr_ty == fcx.tcx.types.i8 {
 435                         err.span_help(self.span, "try casting from `u8` instead");
 436                     } else {
 437                         err.span_help(self.span, "try `char::from_u32` instead (via a `u32`)");
 438                     };
 439                 }
 440                 err.emit();
 441             }
 442             CastError::NonScalar => {
 443                 let mut err = type_error_struct!(
 444                     fcx.tcx.sess,
 445                     self.span,
 446                     self.expr_ty,
 447                     E0605,
 448                     "non-primitive cast: `{}` as `{}`",
 449                     self.expr_ty,
 450                     fcx.ty_to_string(self.cast_ty)
 451                 );
 452                 let mut sugg = None;
 453                 let mut sugg_mutref = false;
 454                 if let ty::Ref(reg, cast_ty, mutbl) = *self.cast_ty.kind() {
 455                     if let ty::RawPtr(TypeAndMut { ty: expr_ty, .. }) = *self.expr_ty.kind()
 456                         && fcx
 457                             .try_coerce(
 458                                 self.expr,
 459                                 fcx.tcx.mk_ref(
 460                                     fcx.tcx.lifetimes.re_erased,
 461                                     TypeAndMut { ty: expr_ty, mutbl },
 462                                 ),
 463                                 self.cast_ty,
 464                                 AllowTwoPhase::No,
 465                                 None,
 466                             )
 467                             .is_ok()
 468                     {
 469                         sugg = Some((format!("&{}*", mutbl.prefix_str()), cast_ty == expr_ty));
 470                     } else if let ty::Ref(expr_reg, expr_ty, expr_mutbl) = *self.expr_ty.kind()
 471                         && expr_mutbl == Mutability::Not
 472                         && mutbl == Mutability::Mut
 473                         && fcx
 474                             .try_coerce(
 475                                 self.expr,
 476                                 fcx.tcx.mk_ref(
 477                                     expr_reg,
 478                                     TypeAndMut { ty: expr_ty, mutbl: Mutability::Mut },
 479                                 ),
 480                                 self.cast_ty,
 481                                 AllowTwoPhase::No,
 482                                 None,
 483                             )
 484                             .is_ok()
 485                     {
 486                         sugg_mutref = true;
 487                     }
 488
 489                     if !sugg_mutref
 490                         && sugg == None
 491                         && fcx
 492                             .try_coerce(
 493                                 self.expr,
 494                                 fcx.tcx.mk_ref(reg, TypeAndMut { ty: self.expr_ty, mutbl }),
 495                                 self.cast_ty,
 496                                 AllowTwoPhase::No,
 497                                 None,
 498                             )
 499                             .is_ok()
 500                     {
 501                         sugg = Some((format!("&{}", mutbl.prefix_str()), false));
 502                     }
 503                 } else if let ty::RawPtr(TypeAndMut { mutbl, .. }) = *self.cast_ty.kind()
 504                     && fcx
 505                         .try_coerce(
 506                             self.expr,
 507                             fcx.tcx.mk_ref(
 508                                 fcx.tcx.lifetimes.re_erased,
 509                                 TypeAndMut { ty: self.expr_ty, mutbl },
 510                             ),
 511                             self.cast_ty,
 512                             AllowTwoPhase::No,
 513                             None,
 514                         )
 515                         .is_ok()
 516                 {
 517                     sugg = Some((format!("&{}", mutbl.prefix_str()), false));
 518                 }
 519                 if sugg_mutref {
 520                     err.span_label(self.span, "invalid cast");
 521                     err.span_note(self.expr_span, "this reference is immutable");
 522                     err.span_note(self.cast_span, "trying to cast to a mutable reference type");
 523                 } else if let Some((sugg, remove_cast)) = sugg {
 524                     err.span_label(self.span, "invalid cast");
 525
 526                     let has_parens = fcx
 527                         .tcx
 528                         .sess
 529                         .source_map()
 530                         .span_to_snippet(self.expr_span)
 531                         .map_or(false, |snip| snip.starts_with('('));
 532
 533                     // Very crude check to see whether the expression must be wrapped
 534                     // in parentheses for the suggestion to work (issue #89497).
 535                     // Can/should be extended in the future.
 536                     let needs_parens =
 537                         !has_parens && matches!(self.expr.kind, hir::ExprKind::Cast(..));
 538
 539                     let mut suggestion = vec![(self.expr_span.shrink_to_lo(), sugg)];
 540                     if needs_parens {
 541                         suggestion[0].1 += "(";
 542                         suggestion.push((self.expr_span.shrink_to_hi(), ")".to_string()));
 543                     }
 544                     if remove_cast {
 545                         suggestion.push((
 546                             self.expr_span.shrink_to_hi().to(self.cast_span),
 547                             String::new(),
 548                         ));
 549                     }
 550
 551                     err.multipart_suggestion_verbose(
 552                         "consider borrowing the value",
 553                         suggestion,
 554                         Applicability::MachineApplicable,
 555                     );
 556                 } else if !matches!(
 557                     self.cast_ty.kind(),
 558                     ty::FnDef(..) | ty::FnPtr(..) | ty::Closure(..)
 559                 ) {
 560                     let mut label = true;
 561                     // Check `impl From<self.expr_ty> for self.cast_ty {}` for accurate suggestion:
 562                     if let Ok(snippet) = fcx.tcx.sess.source_map().span_to_snippet(self.expr_span)
 563                         && let Some(from_trait) = fcx.tcx.get_diagnostic_item(sym::From)
 564                     {
 565                         let ty = fcx.resolve_vars_if_possible(self.cast_ty);
 566                         // Erase regions to avoid panic in `prove_value` when calling
 567                         // `type_implements_trait`.
 568                         let ty = fcx.tcx.erase_regions(ty);
 569                         let expr_ty = fcx.resolve_vars_if_possible(self.expr_ty);
 570                         let expr_ty = fcx.tcx.erase_regions(expr_ty);
 571                         let ty_params = fcx.tcx.mk_substs_trait(expr_ty, &[]);
 572                         if fcx
 573                             .infcx
 574                             .type_implements_trait(from_trait, ty, ty_params, fcx.param_env)
 575                             .must_apply_modulo_regions()
 576                         {
 577                             label = false;
 578                             err.span_suggestion(
 579                                 self.span,
 580                                 "consider using the `From` trait instead",
 581                                 format!("{}::from({})", self.cast_ty, snippet),
 582                                 Applicability::MaybeIncorrect,
 583                             );
 584                         }
 585                     }
 586                     let msg = "an `as` expression can only be used to convert between primitive \
 587                                types or to coerce to a specific trait object";
 588                     if label {
 589                         err.span_label(self.span, msg);
 590                     } else {
 591                         err.note(msg);
 592                     }
 593                 } else {
 594                     err.span_label(self.span, "invalid cast");
 595                 }
 596                 err.emit();
 597             }
 598             CastError::SizedUnsizedCast => {
 599                 use crate::structured_errors::{SizedUnsizedCast, StructuredDiagnostic};
 600
 601                 SizedUnsizedCast {
 602                     sess: &fcx.tcx.sess,
 603                     span: self.span,
 604                     expr_ty: self.expr_ty,
 605                     cast_ty: fcx.ty_to_string(self.cast_ty),
 606                 }
 607                 .diagnostic()
 608                 .emit();
 609             }
 610             CastError::IntToFatCast(known_metadata) => {
 611                 let mut err = struct_span_err!(
 612                     fcx.tcx.sess,
 613                     self.cast_span,
 614                     E0606,
 615                     "cannot cast `{}` to a pointer that {} wide",
 616                     fcx.ty_to_string(self.expr_ty),
 617                     if known_metadata.is_some() { "is" } else { "may be" }
 618                 );
 619
 620                 err.span_label(
 621                     self.cast_span,
 622                     format!(
 623                         "creating a `{}` requires both an address and {}",
 624                         self.cast_ty,
 625                         known_metadata.unwrap_or("type-specific metadata"),
 626                     ),
 627                 );
 628
 629                 if fcx.tcx.sess.is_nightly_build() {
 630                     err.span_label(
 631                         self.expr_span,
 632                         "consider casting this expression to `*const ()`, \
 633                         then using `core::ptr::from_raw_parts`",
 634                     );
 635                 }
 636
 637                 err.emit();
 638             }
 639             CastError::UnknownCastPtrKind | CastError::UnknownExprPtrKind => {
 640                 let unknown_cast_to = match e {
 641                     CastError::UnknownCastPtrKind => true,
 642                     CastError::UnknownExprPtrKind => false,
 643                     _ => bug!(),
 644                 };
 645                 let mut err = struct_span_err!(
 646                     fcx.tcx.sess,
 647                     if unknown_cast_to { self.cast_span } else { self.span },
 648                     E0641,
 649                     "cannot cast {} a pointer of an unknown kind",
 650                     if unknown_cast_to { "to" } else { "from" }
 651                 );
 652                 if unknown_cast_to {
 653                     err.span_label(self.cast_span, "needs more type information");
 654                     err.note(
 655                         "the type information given here is insufficient to check whether \
 656                         the pointer cast is valid",
 657                     );
 658                 } else {
 659                     err.span_label(
 660                         self.span,
 661                         "the type information given here is insufficient to check whether \
 662                         the pointer cast is valid",
 663                     );
 664                 }
 665                 err.emit();
 666             }
 667             CastError::ForeignNonExhaustiveAdt => {
 668                 make_invalid_casting_error(
 669                     fcx.tcx.sess,
 670                     self.span,
 671                     self.expr_ty,
 672                     self.cast_ty,
 673                     fcx,
 674                 )
 675                 .note("cannot cast an enum with a non-exhaustive variant when it's defined in another crate")
 676                 .emit();
 677             }
 678         }
 679     }
 680
 681     fn report_cast_to_unsized_type(&self, fcx: &FnCtxt<'a, 'tcx>) -> ErrorGuaranteed {
 682         if let Some(reported) =
 683             self.cast_ty.error_reported().or_else(|| self.expr_ty.error_reported())
 684         {
 685             return reported;
 686         }
 687
 688         let tstr = fcx.ty_to_string(self.cast_ty);
 689         let mut err = type_error_struct!(
 690             fcx.tcx.sess,
 691             self.span,
 692             self.expr_ty,
 693             E0620,
 694             "cast to unsized type: `{}` as `{}`",
 695             fcx.resolve_vars_if_possible(self.expr_ty),
 696             tstr
 697         );
 698         match self.expr_ty.kind() {
 699             ty::Ref(_, _, mt) => {
 700                 let mtstr = mt.prefix_str();
 701                 if self.cast_ty.is_trait() {
 702                     match fcx.tcx.sess.source_map().span_to_snippet(self.cast_span) {
 703                         Ok(s) => {
 704                             err.span_suggestion(
 705                                 self.cast_span,
 706                                 "try casting to a reference instead",
 707                                 format!("&{}{}", mtstr, s),
 708                                 Applicability::MachineApplicable,
 709                             );
 710                         }
 711                         Err(_) => {
 712                             let msg = &format!("did you mean `&{}{}`?", mtstr, tstr);
 713                             err.span_help(self.cast_span, msg);
 714                         }
 715                     }
 716                 } else {
 717                     let msg =
 718                         &format!("consider using an implicit coercion to `&{mtstr}{tstr}` instead");
 719                     err.span_help(self.span, msg);
 720                 }
 721             }
 722             ty::Adt(def, ..) if def.is_box() => {
 723                 match fcx.tcx.sess.source_map().span_to_snippet(self.cast_span) {
 724                     Ok(s) => {
 725                         err.span_suggestion(
 726                             self.cast_span,
 727                             "you can cast to a `Box` instead",
 728                             format!("Box<{s}>"),
 729                             Applicability::MachineApplicable,
 730                         );
 731                     }
 732                     Err(_) => {
 733                         err.span_help(
 734                             self.cast_span,
 735                             &format!("you might have meant `Box<{tstr}>`"),
 736                         );
 737                     }
 738                 }
 739             }
 740             _ => {
 741                 err.span_help(self.expr_span, "consider using a box or reference as appropriate");
 742             }
 743         }
 744         err.emit()
 745     }
 746
 747     fn trivial_cast_lint(&self, fcx: &FnCtxt<'a, 'tcx>) {
 748         let t_cast = self.cast_ty;
 749         let t_expr = self.expr_ty;
 750         let type_asc_or =
 751             if fcx.tcx.features().type_ascription { "type ascription or " } else { "" };
 752         let (adjective, lint) = if t_cast.is_numeric() && t_expr.is_numeric() {
 753             ("numeric ", lint::builtin::TRIVIAL_NUMERIC_CASTS)
 754         } else {
 755             ("", lint::builtin::TRIVIAL_CASTS)
 756         };
 757         fcx.tcx.struct_span_lint_hir(
 758             lint,
 759             self.expr.hir_id,
 760             self.span,
 761             DelayDm(|| {
 762                 format!(
 763                     "trivial {}cast: `{}` as `{}`",
 764                     adjective,
 765                     fcx.ty_to_string(t_expr),
 766                     fcx.ty_to_string(t_cast)
 767                 )
 768             }),
 769             |lint| {
 770                 lint.help(format!(
 771                     "cast can be replaced by coercion; this might \
 772                      require {type_asc_or}a temporary variable"
 773                 ))
 774             },
 775         );
 776     }
 777
 778     #[instrument(skip(fcx), level = "debug")]
 779     pub fn check(mut self, fcx: &FnCtxt<'a, 'tcx>) {
 780         self.expr_ty = fcx.structurally_resolved_type(self.expr_span, self.expr_ty);
 781         self.cast_ty = fcx.structurally_resolved_type(self.cast_span, self.cast_ty);
 782
 783         debug!("check_cast({}, {:?} as {:?})", self.expr.hir_id, self.expr_ty, self.cast_ty);
 784
 785         if !fcx.type_is_sized_modulo_regions(fcx.param_env, self.cast_ty, self.span)
 786             && !self.cast_ty.has_infer_types()
 787         {
 788             self.report_cast_to_unsized_type(fcx);
 789         } else if self.expr_ty.references_error() || self.cast_ty.references_error() {
 790             // No sense in giving duplicate error messages
 791         } else {
 792             match self.try_coercion_cast(fcx) {
 793                 Ok(()) => {
 794                     self.trivial_cast_lint(fcx);
 795                     debug!(" -> CoercionCast");
 796                     fcx.typeck_results.borrow_mut().set_coercion_cast(self.expr.hir_id.local_id);
 797                 }
 798                 Err(ty::error::TypeError::ObjectUnsafeCoercion(did)) => {
 799                     self.report_object_unsafe_cast(&fcx, did);
 800                 }
 801                 Err(_) => {
 802                     match self.do_check(fcx) {
 803                         Ok(k) => {
 804                             debug!(" -> {:?}", k);
 805                         }
 806                         Err(e) => self.report_cast_error(fcx, e),
 807                     };
 808                 }
 809             };
 810         }
 811     }
 812
 813     fn report_object_unsafe_cast(&self, fcx: &FnCtxt<'a, 'tcx>, did: DefId) {
 814         let violations = fcx.tcx.object_safety_violations(did);
 815         let mut err = report_object_safety_error(fcx.tcx, self.cast_span, did, violations);
 816         err.note(&format!("required by cast to type '{}'", fcx.ty_to_string(self.cast_ty)));
 817         err.emit();
 818     }
 819
 820     /// Checks a cast, and report an error if one exists. In some cases, this
 821     /// can return Ok and create type errors in the fcx rather than returning
 822     /// directly. coercion-cast is handled in check instead of here.
 823     pub fn do_check(&self, fcx: &FnCtxt<'a, 'tcx>) -> Result<CastKind, CastError> {
 824         use rustc_middle::ty::cast::CastTy::*;
 825         use rustc_middle::ty::cast::IntTy::*;
 826
 827         let (t_from, t_cast) = match (CastTy::from_ty(self.expr_ty), CastTy::from_ty(self.cast_ty))
 828         {
 829             (Some(t_from), Some(t_cast)) => (t_from, t_cast),
 830             // Function item types may need to be reified before casts.
 831             (None, Some(t_cast)) => {
 832                 match *self.expr_ty.kind() {
 833                     ty::FnDef(..) => {
 834                         // Attempt a coercion to a fn pointer type.
 835                         let f = fcx.normalize_associated_types_in(
 836                             self.expr_span,
 837                             self.expr_ty.fn_sig(fcx.tcx),
 838                         );
 839                         let res = fcx.try_coerce(
 840                             self.expr,
 841                             self.expr_ty,
 842                             fcx.tcx.mk_fn_ptr(f),
 843                             AllowTwoPhase::No,
 844                             None,
 845                         );
 846                         if let Err(TypeError::IntrinsicCast) = res {
 847                             return Err(CastError::IllegalCast);
 848                         }
 849                         if res.is_err() {
 850                             return Err(CastError::NonScalar);
 851                         }
 852                         (FnPtr, t_cast)
 853                     }
 854                     // Special case some errors for references, and check for
 855                     // array-ptr-casts. `Ref` is not a CastTy because the cast
 856                     // is split into a coercion to a pointer type, followed by
 857                     // a cast.
 858                     ty::Ref(_, inner_ty, mutbl) => {
 859                         return match t_cast {
 860                             Int(_) | Float => match *inner_ty.kind() {
 861                                 ty::Int(_)
 862                                 | ty::Uint(_)
 863                                 | ty::Float(_)
 864                                 | ty::Infer(ty::InferTy::IntVar(_) | ty::InferTy::FloatVar(_)) => {
 865                                     Err(CastError::NeedDeref)
 866                                 }
 867                                 _ => Err(CastError::NeedViaPtr),
 868                             },
 869                             // array-ptr-cast
 870                             Ptr(mt) => {
 871                                 self.check_ref_cast(fcx, TypeAndMut { mutbl, ty: inner_ty }, mt)
 872                             }
 873                             _ => Err(CastError::NonScalar),
 874                         };
 875                     }
 876                     _ => return Err(CastError::NonScalar),
 877                 }
 878             }
 879             _ => return Err(CastError::NonScalar),
 880         };
 881
 882         if let ty::Adt(adt_def, _) = *self.expr_ty.kind() {
 883             if adt_def.did().krate != LOCAL_CRATE {
 884                 if adt_def.variants().iter().any(VariantDef::is_field_list_non_exhaustive) {
 885                     return Err(CastError::ForeignNonExhaustiveAdt);
 886                 }
 887             }
 888         }
 889
 890         match (t_from, t_cast) {
 891             // These types have invariants! can't cast into them.
 892             (_, Int(CEnum) | FnPtr) => Err(CastError::NonScalar),
 893
 894             // * -> Bool
 895             (_, Int(Bool)) => Err(CastError::CastToBool),
 896
 897             // * -> Char
 898             (Int(U(ty::UintTy::U8)), Int(Char)) => Ok(CastKind::U8CharCast), // u8-char-cast
 899             (_, Int(Char)) => Err(CastError::CastToChar),
 900
 901             // prim -> float,ptr
 902             (Int(Bool) | Int(CEnum) | Int(Char), Float) => Err(CastError::NeedViaInt),
 903
 904             (Int(Bool) | Int(CEnum) | Int(Char) | Float, Ptr(_)) | (Ptr(_) | FnPtr, Float) => {
 905                 Err(CastError::IllegalCast)
 906             }
 907
 908             // ptr -> *
 909             (Ptr(m_e), Ptr(m_c)) => self.check_ptr_ptr_cast(fcx, m_e, m_c), // ptr-ptr-cast
 910
 911             // ptr-addr-cast
 912             (Ptr(m_expr), Int(t_c)) => {
 913                 self.lossy_provenance_ptr2int_lint(fcx, t_c);
 914                 self.check_ptr_addr_cast(fcx, m_expr)
 915             }
 916             (FnPtr, Int(_)) => {
 917                 // FIXME(#95489): there should eventually be a lint for these casts
 918                 Ok(CastKind::FnPtrAddrCast)
 919             }
 920             // addr-ptr-cast
 921             (Int(_), Ptr(mt)) => {
 922                 self.fuzzy_provenance_int2ptr_lint(fcx);
 923                 self.check_addr_ptr_cast(fcx, mt)
 924             }
 925             // fn-ptr-cast
 926             (FnPtr, Ptr(mt)) => self.check_fptr_ptr_cast(fcx, mt),
 927
 928             // prim -> prim
 929             (Int(CEnum), Int(_)) => {
 930                 self.cenum_impl_drop_lint(fcx);
 931                 Ok(CastKind::EnumCast)
 932             }
 933             (Int(Char) | Int(Bool), Int(_)) => Ok(CastKind::PrimIntCast),
 934
 935             (Int(_) | Float, Int(_) | Float) => Ok(CastKind::NumericCast),
 936
 937             // FIXME(dyn-star): this needs more conditions...
 938             (_, DynStar) => Ok(CastKind::DynStarCast),
 939
 940             // FIXME(dyn-star): do we want to allow dyn* upcasting or other casts?
 941             (DynStar, _) => Err(CastError::IllegalCast),
 942         }
 943     }
 944
 945     fn check_ptr_ptr_cast(
 946         &self,
 947         fcx: &FnCtxt<'a, 'tcx>,
 948         m_expr: ty::TypeAndMut<'tcx>,
 949         m_cast: ty::TypeAndMut<'tcx>,
 950     ) -> Result<CastKind, CastError> {
 951         debug!("check_ptr_ptr_cast m_expr={:?} m_cast={:?}", m_expr, m_cast);
 952         // ptr-ptr cast. vtables must match.
 953
 954         let expr_kind = fcx.pointer_kind(m_expr.ty, self.span)?;
 955         let cast_kind = fcx.pointer_kind(m_cast.ty, self.span)?;
 956
 957         let Some(cast_kind) = cast_kind else {
 958             // We can't cast if target pointer kind is unknown
 959             return Err(CastError::UnknownCastPtrKind);
 960         };
 961
 962         // Cast to thin pointer is OK
 963         if cast_kind == PointerKind::Thin {
 964             return Ok(CastKind::PtrPtrCast);
 965         }
 966
 967         let Some(expr_kind) = expr_kind else {
 968             // We can't cast to fat pointer if source pointer kind is unknown
 969             return Err(CastError::UnknownExprPtrKind);
 970         };
 971
 972         // thin -> fat? report invalid cast (don't complain about vtable kinds)
 973         if expr_kind == PointerKind::Thin {
 974             return Err(CastError::SizedUnsizedCast);
 975         }
 976
 977         // vtable kinds must match
 978         if cast_kind == expr_kind {
 979             Ok(CastKind::PtrPtrCast)
 980         } else {
 981             Err(CastError::DifferingKinds)
 982         }
 983     }
 984
 985     fn check_fptr_ptr_cast(
 986         &self,
 987         fcx: &FnCtxt<'a, 'tcx>,
 988         m_cast: ty::TypeAndMut<'tcx>,
 989     ) -> Result<CastKind, CastError> {
 990         // fptr-ptr cast. must be to thin ptr
 991
 992         match fcx.pointer_kind(m_cast.ty, self.span)? {
 993             None => Err(CastError::UnknownCastPtrKind),
 994             Some(PointerKind::Thin) => Ok(CastKind::FnPtrPtrCast),
 995             _ => Err(CastError::IllegalCast),
 996         }
 997     }
 998
 999     fn check_ptr_addr_cast(
1000         &self,
1001         fcx: &FnCtxt<'a, 'tcx>,
1002         m_expr: ty::TypeAndMut<'tcx>,
1003     ) -> Result<CastKind, CastError> {
1004         // ptr-addr cast. must be from thin ptr
1005
1006         match fcx.pointer_kind(m_expr.ty, self.span)? {
1007             None => Err(CastError::UnknownExprPtrKind),
1008             Some(PointerKind::Thin) => Ok(CastKind::PtrAddrCast),
1009             _ => Err(CastError::NeedViaThinPtr),
1010         }
1011     }
1012
1013     fn check_ref_cast(
1014         &self,
1015         fcx: &FnCtxt<'a, 'tcx>,
1016         m_expr: ty::TypeAndMut<'tcx>,
1017         m_cast: ty::TypeAndMut<'tcx>,
1018     ) -> Result<CastKind, CastError> {
1019         // array-ptr-cast: allow mut-to-mut, mut-to-const, const-to-const
1020         if m_expr.mutbl == hir::Mutability::Mut || m_cast.mutbl == hir::Mutability::Not {
1021             if let ty::Array(ety, _) = m_expr.ty.kind() {
1022                 // Due to the limitations of LLVM global constants,
1023                 // region pointers end up pointing at copies of
1024                 // vector elements instead of the original values.
1025                 // To allow raw pointers to work correctly, we
1026                 // need to special-case obtaining a raw pointer
1027                 // from a region pointer to a vector.
1028
1029                 // Coerce to a raw pointer so that we generate AddressOf in MIR.
1030                 let array_ptr_type = fcx.tcx.mk_ptr(m_expr);
1031                 fcx.try_coerce(self.expr, self.expr_ty, array_ptr_type, AllowTwoPhase::No, None)
1032                     .unwrap_or_else(|_| {
1033                         bug!(
1034                         "could not cast from reference to array to pointer to array ({:?} to {:?})",
1035                         self.expr_ty,
1036                         array_ptr_type,
1037                     )
1038                     });
1039
1040                 // this will report a type mismatch if needed
1041                 fcx.demand_eqtype(self.span, *ety, m_cast.ty);
1042                 return Ok(CastKind::ArrayPtrCast);
1043             }
1044         }
1045
1046         Err(CastError::IllegalCast)
1047     }
1048
1049     fn check_addr_ptr_cast(
1050         &self,
1051         fcx: &FnCtxt<'a, 'tcx>,
1052         m_cast: TypeAndMut<'tcx>,
1053     ) -> Result<CastKind, CastError> {
1054         // ptr-addr cast. pointer must be thin.
1055         match fcx.pointer_kind(m_cast.ty, self.span)? {
1056             None => Err(CastError::UnknownCastPtrKind),
1057             Some(PointerKind::Thin) => Ok(CastKind::AddrPtrCast),
1058             Some(PointerKind::VTable(_)) => Err(CastError::IntToFatCast(Some("a vtable"))),
1059             Some(PointerKind::Length) => Err(CastError::IntToFatCast(Some("a length"))),
1060             Some(
1061                 PointerKind::OfProjection(_)
1062                 | PointerKind::OfOpaque(_, _)
1063                 | PointerKind::OfParam(_),
1064             ) => Err(CastError::IntToFatCast(None)),
1065         }
1066     }
1067
1068     fn try_coercion_cast(&self, fcx: &FnCtxt<'a, 'tcx>) -> Result<(), ty::error::TypeError<'tcx>> {
1069         match fcx.try_coerce(self.expr, self.expr_ty, self.cast_ty, AllowTwoPhase::No, None) {
1070             Ok(_) => Ok(()),
1071             Err(err) => Err(err),
1072         }
1073     }
1074
1075     fn cenum_impl_drop_lint(&self, fcx: &FnCtxt<'a, 'tcx>) {
1076         if let ty::Adt(d, _) = self.expr_ty.kind()
1077             && d.has_dtor(fcx.tcx)
1078         {
1079             fcx.tcx.struct_span_lint_hir(
1080                 lint::builtin::CENUM_IMPL_DROP_CAST,
1081                 self.expr.hir_id,
1082                 self.span,
1083                 DelayDm(|| format!(
1084                     "cannot cast enum `{}` into integer `{}` because it implements `Drop`",
1085                     self.expr_ty, self.cast_ty
1086                 )),
1087                 |lint| {
1088                     lint
1089                 },
1090             );
1091         }
1092     }
1093
1094     fn lossy_provenance_ptr2int_lint(&self, fcx: &FnCtxt<'a, 'tcx>, t_c: ty::cast::IntTy) {
1095         fcx.tcx.struct_span_lint_hir(
1096             lint::builtin::LOSSY_PROVENANCE_CASTS,
1097             self.expr.hir_id,
1098             self.span,
1099             DelayDm(|| format!(
1100                     "under strict provenance it is considered bad style to cast pointer `{}` to integer `{}`",
1101                     self.expr_ty, self.cast_ty
1102                 )),
1103             |lint| {
1104                 let msg = "use `.addr()` to obtain the address of a pointer";
1105
1106                 let expr_prec = self.expr.precedence().order();
1107                 let needs_parens = expr_prec < rustc_ast::util::parser::PREC_POSTFIX;
1108
1109                 let scalar_cast = match t_c {
1110                     ty::cast::IntTy::U(ty::UintTy::Usize) => String::new(),
1111                     _ => format!(" as {}", self.cast_ty),
1112                 };
1113
1114                 let cast_span = self.expr_span.shrink_to_hi().to(self.cast_span);
1115
1116                 if needs_parens {
1117                     let suggestions = vec![
1118                         (self.expr_span.shrink_to_lo(), String::from("(")),
1119                         (cast_span, format!(").addr(){scalar_cast}")),
1120                     ];
1121
1122                     lint.multipart_suggestion(msg, suggestions, Applicability::MaybeIncorrect);
1123                 } else {
1124                     lint.span_suggestion(
1125                         cast_span,
1126                         msg,
1127                         format!(".addr(){scalar_cast}"),
1128                         Applicability::MaybeIncorrect,
1129                     );
1130                 }
1131
1132                 lint.help(
1133                     "if you can't comply with strict provenance and need to expose the pointer \
1134                     provenance you can use `.expose_addr()` instead"
1135                 );
1136
1137                 lint
1138             },
1139         );
1140     }
1141
1142     fn fuzzy_provenance_int2ptr_lint(&self, fcx: &FnCtxt<'a, 'tcx>) {
1143         fcx.tcx.struct_span_lint_hir(
1144             lint::builtin::FUZZY_PROVENANCE_CASTS,
1145             self.expr.hir_id,
1146             self.span,
1147             DelayDm(|| format!(
1148                 "strict provenance disallows casting integer `{}` to pointer `{}`",
1149                 self.expr_ty, self.cast_ty
1150             )),
1151             |lint| {
1152                 let msg = "use `.with_addr()` to adjust a valid pointer in the same allocation, to this address";
1153                 let suggestions = vec![
1154                     (self.expr_span.shrink_to_lo(), String::from("(...).with_addr(")),
1155                     (self.expr_span.shrink_to_hi().to(self.cast_span), String::from(")")),
1156                 ];
1157
1158                 lint.multipart_suggestion(msg, suggestions, Applicability::MaybeIncorrect);
1159                 lint.help(
1160                     "if you can't comply with strict provenance and don't have a pointer with \
1161                     the correct provenance you can use `std::ptr::from_exposed_addr()` instead"
1162                  );
1163
1164                 lint
1165             },
1166         );
1167     }
1168 }