1 //! Code for type-checking cast expressions.
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*
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`).
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.
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`).
33 use crate::type_error_struct;
34 use rustc_errors::{struct_span_err, Applicability, DelayDm, DiagnosticBuilder, ErrorGuaranteed};
36 use rustc_macros::{TypeFoldable, TypeVisitable};
37 use rustc_middle::mir::Mutability;
38 use rustc_middle::ty::adjustment::AllowTwoPhase;
39 use rustc_middle::ty::cast::{CastKind, CastTy};
40 use rustc_middle::ty::error::TypeError;
41 use rustc_middle::ty::subst::SubstsRef;
42 use rustc_middle::ty::{self, Ty, TypeAndMut, TypeVisitable, VariantDef};
43 use rustc_session::lint;
44 use rustc_session::Session;
45 use rustc_span::def_id::{DefId, LOCAL_CRATE};
46 use rustc_span::symbol::sym;
48 use rustc_trait_selection::infer::InferCtxtExt;
49 use rustc_trait_selection::traits::error_reporting::report_object_safety_error;
51 /// Reifies a cast check to be checked once we have full type information for
52 /// a function context.
54 pub struct CastCheck<'tcx> {
55 /// The expression whose value is being casted
56 expr: &'tcx hir::Expr<'tcx>,
57 /// The source type for the cast expression
60 /// The target type. That is, the type we are casting to.
64 /// whether the cast is made in a const context or not.
65 pub constness: hir::Constness,
68 /// The kind of pointer and associated metadata (thin, length or vtable) - we
69 /// only allow casts between fat pointers if their metadata have the same
71 #[derive(Debug, Copy, Clone, PartialEq, Eq, TypeVisitable, TypeFoldable)]
72 enum PointerKind<'tcx> {
73 /// No metadata attached, ie pointer to sized type or foreign type
76 VTable(Option<DefId>),
79 /// The unsize info of this projection
80 OfProjection(ty::ProjectionTy<'tcx>),
81 /// The unsize info of this opaque ty
82 OfOpaque(DefId, SubstsRef<'tcx>),
83 /// The unsize info of this parameter
87 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
88 /// Returns the kind of unsize information of t, or None
94 ) -> Result<Option<PointerKind<'tcx>>, ErrorGuaranteed> {
95 debug!("pointer_kind({:?}, {:?})", t, span);
97 let t = self.resolve_vars_if_possible(t);
100 if self.type_is_sized_modulo_regions(self.param_env, t, span) {
101 return Ok(Some(PointerKind::Thin));
105 ty::Slice(_) | ty::Str => Some(PointerKind::Length),
106 ty::Dynamic(ref tty, _, ty::Dyn) => Some(PointerKind::VTable(tty.principal_def_id())),
107 ty::Adt(def, substs) if def.is_struct() => match def.non_enum_variant().fields.last() {
108 None => Some(PointerKind::Thin),
110 let field_ty = self.field_ty(span, f, substs);
111 self.pointer_kind(field_ty, span)?
114 ty::Tuple(fields) => match fields.last() {
115 None => Some(PointerKind::Thin),
116 Some(&f) => self.pointer_kind(f, span)?,
119 // Pointers to foreign types are thin, despite being unsized
120 ty::Foreign(..) => Some(PointerKind::Thin),
121 // We should really try to normalize here.
122 ty::Projection(pi) => Some(PointerKind::OfProjection(pi)),
123 ty::Opaque(def_id, substs) => Some(PointerKind::OfOpaque(def_id, substs)),
124 ty::Param(p) => Some(PointerKind::OfParam(p)),
125 // Insufficient type information.
126 ty::Placeholder(..) | ty::Bound(..) | ty::Infer(_) => None,
134 | ty::GeneratorWitness(..)
143 | ty::Dynamic(_, _, ty::DynStar)
148 .delay_span_bug(span, &format!("`{:?}` should be sized but is not?", t));
149 return Err(reported);
155 #[derive(Copy, Clone)]
162 /// Cast of thin to fat raw ptr (e.g., `*const () as *const [u8]`).
172 /// Cast of int to (possibly) fat raw pointer.
174 /// Argument is the specific name of the metadata in plain words, such as "a vtable"
175 /// or "a length". If this argument is None, then the metadata is unknown, for example,
176 /// when we're typechecking a type parameter with a ?Sized bound.
177 IntToFatCast(Option<&'static str>),
178 ForeignNonExhaustiveAdt,
181 impl From<ErrorGuaranteed> for CastError {
182 fn from(_: ErrorGuaranteed) -> Self {
183 CastError::ErrorGuaranteed
187 fn make_invalid_casting_error<'a, 'tcx>(
192 fcx: &FnCtxt<'a, 'tcx>,
193 ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
199 "casting `{}` as `{}` is invalid",
200 fcx.ty_to_string(expr_ty),
201 fcx.ty_to_string(cast_ty)
205 impl<'a, 'tcx> CastCheck<'tcx> {
207 fcx: &FnCtxt<'a, 'tcx>,
208 expr: &'tcx hir::Expr<'tcx>,
213 constness: hir::Constness,
214 ) -> Result<CastCheck<'tcx>, ErrorGuaranteed> {
215 let expr_span = expr.span.find_ancestor_inside(span).unwrap_or(expr.span);
216 let check = CastCheck { expr, expr_ty, expr_span, cast_ty, cast_span, span, constness };
218 // For better error messages, check for some obviously unsized
219 // cases now. We do a more thorough check at the end, once
220 // inference is more completely known.
221 match cast_ty.kind() {
222 ty::Dynamic(_, _, ty::Dyn) | ty::Slice(..) => {
223 Err(check.report_cast_to_unsized_type(fcx))
229 fn report_cast_error(&self, fcx: &FnCtxt<'a, 'tcx>, e: CastError) {
231 CastError::ErrorGuaranteed => {
232 // an error has already been reported
234 CastError::NeedDeref => {
235 let error_span = self.span;
236 let mut err = make_invalid_casting_error(
243 let cast_ty = fcx.ty_to_string(self.cast_ty);
246 format!("cannot cast `{}` as `{}`", fcx.ty_to_string(self.expr_ty), cast_ty),
248 if let Ok(snippet) = fcx.sess().source_map().span_to_snippet(self.expr_span) {
251 "dereference the expression",
252 format!("*{}", snippet),
253 Applicability::MaybeIncorrect,
256 err.span_help(self.expr_span, "dereference the expression with `*`");
260 CastError::NeedViaThinPtr | CastError::NeedViaPtr => {
261 let mut err = make_invalid_casting_error(
268 if self.cast_ty.is_integral() {
270 "cast through {} first",
272 CastError::NeedViaPtr => "a raw pointer",
273 CastError::NeedViaThinPtr => "a thin pointer",
280 CastError::NeedViaInt => {
281 make_invalid_casting_error(
289 "cast through {} first",
291 CastError::NeedViaInt => "an integer",
297 CastError::IllegalCast => {
298 make_invalid_casting_error(
307 CastError::DifferingKinds => {
308 make_invalid_casting_error(
315 .note("vtable kinds may not match")
318 CastError::CastToBool => {
320 struct_span_err!(fcx.tcx.sess, self.span, E0054, "cannot cast as `bool`");
322 if self.expr_ty.is_numeric() {
323 match fcx.tcx.sess.source_map().span_to_snippet(self.expr_span) {
327 "compare with zero instead",
328 format!("{snippet} != 0"),
329 Applicability::MachineApplicable,
333 err.span_help(self.span, "compare with zero instead");
337 err.span_label(self.span, "unsupported cast");
342 CastError::CastToChar => {
343 let mut err = type_error_struct!(
348 "only `u8` can be cast as `char`, not `{}`",
351 err.span_label(self.span, "invalid cast");
352 if self.expr_ty.is_numeric() {
353 if self.expr_ty == fcx.tcx.types.u32 {
354 match fcx.tcx.sess.source_map().span_to_snippet(self.expr.span) {
355 Ok(snippet) => err.span_suggestion(
357 "try `char::from_u32` instead",
358 format!("char::from_u32({snippet})"),
359 Applicability::MachineApplicable,
362 Err(_) => err.span_help(self.span, "try `char::from_u32` instead"),
364 } else if self.expr_ty == fcx.tcx.types.i8 {
365 err.span_help(self.span, "try casting from `u8` instead");
367 err.span_help(self.span, "try `char::from_u32` instead (via a `u32`)");
372 CastError::NonScalar => {
373 let mut err = type_error_struct!(
378 "non-primitive cast: `{}` as `{}`",
380 fcx.ty_to_string(self.cast_ty)
383 let mut sugg_mutref = false;
384 if let ty::Ref(reg, cast_ty, mutbl) = *self.cast_ty.kind() {
385 if let ty::RawPtr(TypeAndMut { ty: expr_ty, .. }) = *self.expr_ty.kind()
390 fcx.tcx.lifetimes.re_erased,
391 TypeAndMut { ty: expr_ty, mutbl },
399 sugg = Some((format!("&{}*", mutbl.prefix_str()), cast_ty == expr_ty));
400 } else if let ty::Ref(expr_reg, expr_ty, expr_mutbl) = *self.expr_ty.kind()
401 && expr_mutbl == Mutability::Not
402 && mutbl == Mutability::Mut
408 TypeAndMut { ty: expr_ty, mutbl: Mutability::Mut },
424 fcx.tcx.mk_ref(reg, TypeAndMut { ty: self.expr_ty, mutbl }),
431 sugg = Some((format!("&{}", mutbl.prefix_str()), false));
433 } else if let ty::RawPtr(TypeAndMut { mutbl, .. }) = *self.cast_ty.kind()
438 fcx.tcx.lifetimes.re_erased,
439 TypeAndMut { ty: self.expr_ty, mutbl },
447 sugg = Some((format!("&{}", mutbl.prefix_str()), false));
450 err.span_label(self.span, "invalid cast");
451 err.span_note(self.expr_span, "this reference is immutable");
452 err.span_note(self.cast_span, "trying to cast to a mutable reference type");
453 } else if let Some((sugg, remove_cast)) = sugg {
454 err.span_label(self.span, "invalid cast");
460 .span_to_snippet(self.expr_span)
461 .map_or(false, |snip| snip.starts_with('('));
463 // Very crude check to see whether the expression must be wrapped
464 // in parentheses for the suggestion to work (issue #89497).
465 // Can/should be extended in the future.
467 !has_parens && matches!(self.expr.kind, hir::ExprKind::Cast(..));
469 let mut suggestion = vec![(self.expr_span.shrink_to_lo(), sugg)];
471 suggestion[0].1 += "(";
472 suggestion.push((self.expr_span.shrink_to_hi(), ")".to_string()));
476 self.expr_span.shrink_to_hi().to(self.cast_span),
481 err.multipart_suggestion_verbose(
482 "consider borrowing the value",
484 Applicability::MachineApplicable,
488 ty::FnDef(..) | ty::FnPtr(..) | ty::Closure(..)
490 let mut label = true;
491 // Check `impl From<self.expr_ty> for self.cast_ty {}` for accurate suggestion:
492 if let Ok(snippet) = fcx.tcx.sess.source_map().span_to_snippet(self.expr_span)
493 && let Some(from_trait) = fcx.tcx.get_diagnostic_item(sym::From)
495 let ty = fcx.resolve_vars_if_possible(self.cast_ty);
496 // Erase regions to avoid panic in `prove_value` when calling
497 // `type_implements_trait`.
498 let ty = fcx.tcx.erase_regions(ty);
499 let expr_ty = fcx.resolve_vars_if_possible(self.expr_ty);
500 let expr_ty = fcx.tcx.erase_regions(expr_ty);
503 .type_implements_trait(from_trait, [ty, expr_ty], fcx.param_env)
504 .must_apply_modulo_regions()
509 "consider using the `From` trait instead",
510 format!("{}::from({})", self.cast_ty, snippet),
511 Applicability::MaybeIncorrect,
515 let msg = "an `as` expression can only be used to convert between primitive \
516 types or to coerce to a specific trait object";
518 err.span_label(self.span, msg);
523 err.span_label(self.span, "invalid cast");
527 CastError::SizedUnsizedCast => {
528 use rustc_hir_analysis::structured_errors::{
529 SizedUnsizedCast, StructuredDiagnostic,
535 expr_ty: self.expr_ty,
536 cast_ty: fcx.ty_to_string(self.cast_ty),
541 CastError::IntToFatCast(known_metadata) => {
542 let mut err = struct_span_err!(
546 "cannot cast `{}` to a pointer that {} wide",
547 fcx.ty_to_string(self.expr_ty),
548 if known_metadata.is_some() { "is" } else { "may be" }
554 "creating a `{}` requires both an address and {}",
556 known_metadata.unwrap_or("type-specific metadata"),
560 if fcx.tcx.sess.is_nightly_build() {
563 "consider casting this expression to `*const ()`, \
564 then using `core::ptr::from_raw_parts`",
570 CastError::UnknownCastPtrKind | CastError::UnknownExprPtrKind => {
571 let unknown_cast_to = match e {
572 CastError::UnknownCastPtrKind => true,
573 CastError::UnknownExprPtrKind => false,
576 let mut err = struct_span_err!(
578 if unknown_cast_to { self.cast_span } else { self.span },
580 "cannot cast {} a pointer of an unknown kind",
581 if unknown_cast_to { "to" } else { "from" }
584 err.span_label(self.cast_span, "needs more type information");
586 "the type information given here is insufficient to check whether \
587 the pointer cast is valid",
592 "the type information given here is insufficient to check whether \
593 the pointer cast is valid",
598 CastError::ForeignNonExhaustiveAdt => {
599 make_invalid_casting_error(
606 .note("cannot cast an enum with a non-exhaustive variant when it's defined in another crate")
612 fn report_cast_to_unsized_type(&self, fcx: &FnCtxt<'a, 'tcx>) -> ErrorGuaranteed {
613 if let Err(err) = self.cast_ty.error_reported() {
616 if let Err(err) = self.expr_ty.error_reported() {
620 let tstr = fcx.ty_to_string(self.cast_ty);
621 let mut err = type_error_struct!(
626 "cast to unsized type: `{}` as `{}`",
627 fcx.resolve_vars_if_possible(self.expr_ty),
630 match self.expr_ty.kind() {
631 ty::Ref(_, _, mt) => {
632 let mtstr = mt.prefix_str();
633 if self.cast_ty.is_trait() {
634 match fcx.tcx.sess.source_map().span_to_snippet(self.cast_span) {
638 "try casting to a reference instead",
639 format!("&{}{}", mtstr, s),
640 Applicability::MachineApplicable,
644 let msg = &format!("did you mean `&{}{}`?", mtstr, tstr);
645 err.span_help(self.cast_span, msg);
650 &format!("consider using an implicit coercion to `&{mtstr}{tstr}` instead");
651 err.span_help(self.span, msg);
654 ty::Adt(def, ..) if def.is_box() => {
655 match fcx.tcx.sess.source_map().span_to_snippet(self.cast_span) {
659 "you can cast to a `Box` instead",
661 Applicability::MachineApplicable,
667 &format!("you might have meant `Box<{tstr}>`"),
673 err.span_help(self.expr_span, "consider using a box or reference as appropriate");
679 fn trivial_cast_lint(&self, fcx: &FnCtxt<'a, 'tcx>) {
680 let t_cast = self.cast_ty;
681 let t_expr = self.expr_ty;
683 if fcx.tcx.features().type_ascription { "type ascription or " } else { "" };
684 let (adjective, lint) = if t_cast.is_numeric() && t_expr.is_numeric() {
685 ("numeric ", lint::builtin::TRIVIAL_NUMERIC_CASTS)
687 ("", lint::builtin::TRIVIAL_CASTS)
689 fcx.tcx.struct_span_lint_hir(
695 "trivial {}cast: `{}` as `{}`",
697 fcx.ty_to_string(t_expr),
698 fcx.ty_to_string(t_cast)
703 "cast can be replaced by coercion; this might \
704 require {type_asc_or}a temporary variable"
710 #[instrument(skip(fcx), level = "debug")]
711 pub fn check(mut self, fcx: &FnCtxt<'a, 'tcx>) {
712 self.expr_ty = fcx.structurally_resolved_type(self.expr_span, self.expr_ty);
713 self.cast_ty = fcx.structurally_resolved_type(self.cast_span, self.cast_ty);
715 debug!("check_cast({}, {:?} as {:?})", self.expr.hir_id, self.expr_ty, self.cast_ty);
717 if !fcx.type_is_sized_modulo_regions(fcx.param_env, self.cast_ty, self.span)
718 && !self.cast_ty.has_infer_types()
720 self.report_cast_to_unsized_type(fcx);
721 } else if self.expr_ty.references_error() || self.cast_ty.references_error() {
722 // No sense in giving duplicate error messages
724 match self.try_coercion_cast(fcx) {
726 self.trivial_cast_lint(fcx);
727 debug!(" -> CoercionCast");
728 fcx.typeck_results.borrow_mut().set_coercion_cast(self.expr.hir_id.local_id);
730 Err(ty::error::TypeError::ObjectUnsafeCoercion(did)) => {
731 self.report_object_unsafe_cast(&fcx, did);
734 match self.do_check(fcx) {
736 debug!(" -> {:?}", k);
738 Err(e) => self.report_cast_error(fcx, e),
745 fn report_object_unsafe_cast(&self, fcx: &FnCtxt<'a, 'tcx>, did: DefId) {
746 let violations = fcx.tcx.object_safety_violations(did);
747 let mut err = report_object_safety_error(fcx.tcx, self.cast_span, did, violations);
748 err.note(&format!("required by cast to type '{}'", fcx.ty_to_string(self.cast_ty)));
752 /// Checks a cast, and report an error if one exists. In some cases, this
753 /// can return Ok and create type errors in the fcx rather than returning
754 /// directly. coercion-cast is handled in check instead of here.
755 pub fn do_check(&self, fcx: &FnCtxt<'a, 'tcx>) -> Result<CastKind, CastError> {
756 use rustc_middle::ty::cast::CastTy::*;
757 use rustc_middle::ty::cast::IntTy::*;
759 let (t_from, t_cast) = match (CastTy::from_ty(self.expr_ty), CastTy::from_ty(self.cast_ty))
761 (Some(t_from), Some(t_cast)) => (t_from, t_cast),
762 // Function item types may need to be reified before casts.
763 (None, Some(t_cast)) => {
764 match *self.expr_ty.kind() {
766 // Attempt a coercion to a fn pointer type.
767 let f = fcx.normalize_associated_types_in(
769 self.expr_ty.fn_sig(fcx.tcx),
771 let res = fcx.try_coerce(
774 fcx.tcx.mk_fn_ptr(f),
778 if let Err(TypeError::IntrinsicCast) = res {
779 return Err(CastError::IllegalCast);
782 return Err(CastError::NonScalar);
786 // Special case some errors for references, and check for
787 // array-ptr-casts. `Ref` is not a CastTy because the cast
788 // is split into a coercion to a pointer type, followed by
790 ty::Ref(_, inner_ty, mutbl) => {
791 return match t_cast {
792 Int(_) | Float => match *inner_ty.kind() {
796 | ty::Infer(ty::InferTy::IntVar(_) | ty::InferTy::FloatVar(_)) => {
797 Err(CastError::NeedDeref)
799 _ => Err(CastError::NeedViaPtr),
803 self.check_ref_cast(fcx, TypeAndMut { mutbl, ty: inner_ty }, mt)
805 _ => Err(CastError::NonScalar),
808 _ => return Err(CastError::NonScalar),
811 _ => return Err(CastError::NonScalar),
814 if let ty::Adt(adt_def, _) = *self.expr_ty.kind() {
815 if adt_def.did().krate != LOCAL_CRATE {
816 if adt_def.variants().iter().any(VariantDef::is_field_list_non_exhaustive) {
817 return Err(CastError::ForeignNonExhaustiveAdt);
822 match (t_from, t_cast) {
823 // These types have invariants! can't cast into them.
824 (_, Int(CEnum) | FnPtr) => Err(CastError::NonScalar),
827 (_, Int(Bool)) => Err(CastError::CastToBool),
830 (Int(U(ty::UintTy::U8)), Int(Char)) => Ok(CastKind::U8CharCast), // u8-char-cast
831 (_, Int(Char)) => Err(CastError::CastToChar),
834 (Int(Bool) | Int(CEnum) | Int(Char), Float) => Err(CastError::NeedViaInt),
836 (Int(Bool) | Int(CEnum) | Int(Char) | Float, Ptr(_)) | (Ptr(_) | FnPtr, Float) => {
837 Err(CastError::IllegalCast)
841 (Ptr(m_e), Ptr(m_c)) => self.check_ptr_ptr_cast(fcx, m_e, m_c), // ptr-ptr-cast
844 (Ptr(m_expr), Int(t_c)) => {
845 self.lossy_provenance_ptr2int_lint(fcx, t_c);
846 self.check_ptr_addr_cast(fcx, m_expr)
849 // FIXME(#95489): there should eventually be a lint for these casts
850 Ok(CastKind::FnPtrAddrCast)
853 (Int(_), Ptr(mt)) => {
854 self.fuzzy_provenance_int2ptr_lint(fcx);
855 self.check_addr_ptr_cast(fcx, mt)
858 (FnPtr, Ptr(mt)) => self.check_fptr_ptr_cast(fcx, mt),
861 (Int(CEnum), Int(_)) => {
862 self.cenum_impl_drop_lint(fcx);
863 Ok(CastKind::EnumCast)
865 (Int(Char) | Int(Bool), Int(_)) => Ok(CastKind::PrimIntCast),
867 (Int(_) | Float, Int(_) | Float) => Ok(CastKind::NumericCast),
869 (_, DynStar) | (DynStar, _) => {
870 if fcx.tcx.features().dyn_star {
871 bug!("should be handled by `try_coerce`")
873 Err(CastError::IllegalCast)
879 fn check_ptr_ptr_cast(
881 fcx: &FnCtxt<'a, 'tcx>,
882 m_expr: ty::TypeAndMut<'tcx>,
883 m_cast: ty::TypeAndMut<'tcx>,
884 ) -> Result<CastKind, CastError> {
885 debug!("check_ptr_ptr_cast m_expr={:?} m_cast={:?}", m_expr, m_cast);
886 // ptr-ptr cast. vtables must match.
888 let expr_kind = fcx.pointer_kind(m_expr.ty, self.span)?;
889 let cast_kind = fcx.pointer_kind(m_cast.ty, self.span)?;
891 let Some(cast_kind) = cast_kind else {
892 // We can't cast if target pointer kind is unknown
893 return Err(CastError::UnknownCastPtrKind);
896 // Cast to thin pointer is OK
897 if cast_kind == PointerKind::Thin {
898 return Ok(CastKind::PtrPtrCast);
901 let Some(expr_kind) = expr_kind else {
902 // We can't cast to fat pointer if source pointer kind is unknown
903 return Err(CastError::UnknownExprPtrKind);
906 // thin -> fat? report invalid cast (don't complain about vtable kinds)
907 if expr_kind == PointerKind::Thin {
908 return Err(CastError::SizedUnsizedCast);
911 // vtable kinds must match
912 if fcx.tcx.erase_regions(cast_kind) == fcx.tcx.erase_regions(expr_kind) {
913 Ok(CastKind::PtrPtrCast)
915 Err(CastError::DifferingKinds)
919 fn check_fptr_ptr_cast(
921 fcx: &FnCtxt<'a, 'tcx>,
922 m_cast: ty::TypeAndMut<'tcx>,
923 ) -> Result<CastKind, CastError> {
924 // fptr-ptr cast. must be to thin ptr
926 match fcx.pointer_kind(m_cast.ty, self.span)? {
927 None => Err(CastError::UnknownCastPtrKind),
928 Some(PointerKind::Thin) => Ok(CastKind::FnPtrPtrCast),
929 _ => Err(CastError::IllegalCast),
933 fn check_ptr_addr_cast(
935 fcx: &FnCtxt<'a, 'tcx>,
936 m_expr: ty::TypeAndMut<'tcx>,
937 ) -> Result<CastKind, CastError> {
938 // ptr-addr cast. must be from thin ptr
940 match fcx.pointer_kind(m_expr.ty, self.span)? {
941 None => Err(CastError::UnknownExprPtrKind),
942 Some(PointerKind::Thin) => Ok(CastKind::PtrAddrCast),
943 _ => Err(CastError::NeedViaThinPtr),
949 fcx: &FnCtxt<'a, 'tcx>,
950 m_expr: ty::TypeAndMut<'tcx>,
951 m_cast: ty::TypeAndMut<'tcx>,
952 ) -> Result<CastKind, CastError> {
953 // array-ptr-cast: allow mut-to-mut, mut-to-const, const-to-const
954 if m_expr.mutbl >= m_cast.mutbl {
955 if let ty::Array(ety, _) = m_expr.ty.kind() {
956 // Due to the limitations of LLVM global constants,
957 // region pointers end up pointing at copies of
958 // vector elements instead of the original values.
959 // To allow raw pointers to work correctly, we
960 // need to special-case obtaining a raw pointer
961 // from a region pointer to a vector.
963 // Coerce to a raw pointer so that we generate AddressOf in MIR.
964 let array_ptr_type = fcx.tcx.mk_ptr(m_expr);
965 fcx.try_coerce(self.expr, self.expr_ty, array_ptr_type, AllowTwoPhase::No, None)
966 .unwrap_or_else(|_| {
968 "could not cast from reference to array to pointer to array ({:?} to {:?})",
974 // this will report a type mismatch if needed
975 fcx.demand_eqtype(self.span, *ety, m_cast.ty);
976 return Ok(CastKind::ArrayPtrCast);
980 Err(CastError::IllegalCast)
983 fn check_addr_ptr_cast(
985 fcx: &FnCtxt<'a, 'tcx>,
986 m_cast: TypeAndMut<'tcx>,
987 ) -> Result<CastKind, CastError> {
988 // ptr-addr cast. pointer must be thin.
989 match fcx.pointer_kind(m_cast.ty, self.span)? {
990 None => Err(CastError::UnknownCastPtrKind),
991 Some(PointerKind::Thin) => Ok(CastKind::AddrPtrCast),
992 Some(PointerKind::VTable(_)) => Err(CastError::IntToFatCast(Some("a vtable"))),
993 Some(PointerKind::Length) => Err(CastError::IntToFatCast(Some("a length"))),
995 PointerKind::OfProjection(_)
996 | PointerKind::OfOpaque(_, _)
997 | PointerKind::OfParam(_),
998 ) => Err(CastError::IntToFatCast(None)),
1002 fn try_coercion_cast(&self, fcx: &FnCtxt<'a, 'tcx>) -> Result<(), ty::error::TypeError<'tcx>> {
1003 match fcx.try_coerce(self.expr, self.expr_ty, self.cast_ty, AllowTwoPhase::No, None) {
1005 Err(err) => Err(err),
1009 fn cenum_impl_drop_lint(&self, fcx: &FnCtxt<'a, 'tcx>) {
1010 if let ty::Adt(d, _) = self.expr_ty.kind()
1011 && d.has_dtor(fcx.tcx)
1013 fcx.tcx.struct_span_lint_hir(
1014 lint::builtin::CENUM_IMPL_DROP_CAST,
1018 "cannot cast enum `{}` into integer `{}` because it implements `Drop`",
1019 self.expr_ty, self.cast_ty
1028 fn lossy_provenance_ptr2int_lint(&self, fcx: &FnCtxt<'a, 'tcx>, t_c: ty::cast::IntTy) {
1029 fcx.tcx.struct_span_lint_hir(
1030 lint::builtin::LOSSY_PROVENANCE_CASTS,
1034 "under strict provenance it is considered bad style to cast pointer `{}` to integer `{}`",
1035 self.expr_ty, self.cast_ty
1038 let msg = "use `.addr()` to obtain the address of a pointer";
1040 let expr_prec = self.expr.precedence().order();
1041 let needs_parens = expr_prec < rustc_ast::util::parser::PREC_POSTFIX;
1043 let scalar_cast = match t_c {
1044 ty::cast::IntTy::U(ty::UintTy::Usize) => String::new(),
1045 _ => format!(" as {}", self.cast_ty),
1048 let cast_span = self.expr_span.shrink_to_hi().to(self.cast_span);
1051 let suggestions = vec![
1052 (self.expr_span.shrink_to_lo(), String::from("(")),
1053 (cast_span, format!(").addr(){scalar_cast}")),
1056 lint.multipart_suggestion(msg, suggestions, Applicability::MaybeIncorrect);
1058 lint.span_suggestion(
1061 format!(".addr(){scalar_cast}"),
1062 Applicability::MaybeIncorrect,
1067 "if you can't comply with strict provenance and need to expose the pointer \
1068 provenance you can use `.expose_addr()` instead"
1076 fn fuzzy_provenance_int2ptr_lint(&self, fcx: &FnCtxt<'a, 'tcx>) {
1077 fcx.tcx.struct_span_lint_hir(
1078 lint::builtin::FUZZY_PROVENANCE_CASTS,
1082 "strict provenance disallows casting integer `{}` to pointer `{}`",
1083 self.expr_ty, self.cast_ty
1086 let msg = "use `.with_addr()` to adjust a valid pointer in the same allocation, to this address";
1087 let suggestions = vec![
1088 (self.expr_span.shrink_to_lo(), String::from("(...).with_addr(")),
1089 (self.expr_span.shrink_to_hi().to(self.cast_span), String::from(")")),
1092 lint.multipart_suggestion(msg, suggestions, Applicability::MaybeIncorrect);
1094 "if you can't comply with strict provenance and don't have a pointer with \
1095 the correct provenance you can use `std::ptr::from_exposed_addr()` instead"