diff options
Diffstat (limited to 'compiler/rustc_hir_analysis/src/check/cast.rs')
| -rw-r--r-- | compiler/rustc_hir_analysis/src/check/cast.rs | 1163 |
1 files changed, 1163 insertions, 0 deletions
diff --git a/compiler/rustc_hir_analysis/src/check/cast.rs b/compiler/rustc_hir_analysis/src/check/cast.rs new file mode 100644 index 00000000000..81a979865ac --- /dev/null +++ b/compiler/rustc_hir_analysis/src/check/cast.rs @@ -0,0 +1,1163 @@ +//! Code for type-checking cast expressions. +//! +//! A cast `e as U` is valid if one of the following holds: +//! * `e` has type `T` and `T` coerces to `U`; *coercion-cast* +//! * `e` has type `*T`, `U` is `*U_0`, and either `U_0: Sized` or +//! pointer_kind(`T`) = pointer_kind(`U_0`); *ptr-ptr-cast* +//! * `e` has type `*T` and `U` is a numeric type, while `T: Sized`; *ptr-addr-cast* +//! * `e` is an integer and `U` is `*U_0`, while `U_0: Sized`; *addr-ptr-cast* +//! * `e` has type `T` and `T` and `U` are any numeric types; *numeric-cast* +//! * `e` is a C-like enum and `U` is an integer type; *enum-cast* +//! * `e` has type `bool` or `char` and `U` is an integer; *prim-int-cast* +//! * `e` has type `u8` and `U` is `char`; *u8-char-cast* +//! * `e` has type `&[T; n]` and `U` is `*const T`; *array-ptr-cast* +//! * `e` is a function pointer type and `U` has type `*T`, +//! while `T: Sized`; *fptr-ptr-cast* +//! * `e` is a function pointer type and `U` is an integer; *fptr-addr-cast* +//! +//! where `&.T` and `*T` are references of either mutability, +//! and where pointer_kind(`T`) is the kind of the unsize info +//! in `T` - the vtable for a trait definition (e.g., `fmt::Display` or +//! `Iterator`, not `Iterator<Item=u8>`) or a length (or `()` if `T: Sized`). +//! +//! Note that lengths are not adjusted when casting raw slices - +//! `T: *const [u16] as *const [u8]` creates a slice that only includes +//! half of the original memory. +//! +//! Casting is not transitive, that is, even if `e as U1 as U2` is a valid +//! expression, `e as U2` is not necessarily so (in fact it will only be valid if +//! `U1` coerces to `U2`). + +use super::FnCtxt; + +use crate::hir::def_id::DefId; +use crate::type_error_struct; +use hir::def_id::LOCAL_CRATE; +use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder, ErrorGuaranteed}; +use rustc_hir as hir; +use rustc_infer::traits::{Obligation, ObligationCause, ObligationCauseCode}; +use rustc_middle::mir::Mutability; +use rustc_middle::ty::adjustment::AllowTwoPhase; +use rustc_middle::ty::cast::{CastKind, CastTy}; +use rustc_middle::ty::error::TypeError; +use rustc_middle::ty::subst::SubstsRef; +use rustc_middle::ty::{self, Binder, Ty, TypeAndMut, TypeVisitable, VariantDef}; +use rustc_session::lint; +use rustc_session::Session; +use rustc_span::symbol::sym; +use rustc_span::Span; +use rustc_trait_selection::infer::InferCtxtExt; +use rustc_trait_selection::traits::error_reporting::report_object_safety_error; + +/// Reifies a cast check to be checked once we have full type information for +/// a function context. +#[derive(Debug)] +pub struct CastCheck<'tcx> { + /// The expression whose value is being casted + expr: &'tcx hir::Expr<'tcx>, + /// The source type for the cast expression + expr_ty: Ty<'tcx>, + expr_span: Span, + /// The target type. That is, the type we are casting to. + cast_ty: Ty<'tcx>, + cast_span: Span, + span: Span, +} + +/// The kind of pointer and associated metadata (thin, length or vtable) - we +/// only allow casts between fat pointers if their metadata have the same +/// kind. +#[derive(Copy, Clone, PartialEq, Eq)] +enum PointerKind<'tcx> { + /// No metadata attached, ie pointer to sized type or foreign type + Thin, + /// A trait object + VTable(Option<DefId>), + /// Slice + Length, + /// The unsize info of this projection + OfProjection(&'tcx ty::ProjectionTy<'tcx>), + /// The unsize info of this opaque ty + OfOpaque(DefId, SubstsRef<'tcx>), + /// The unsize info of this parameter + OfParam(&'tcx ty::ParamTy), +} + +impl<'a, 'tcx> FnCtxt<'a, 'tcx> { + /// Returns the kind of unsize information of t, or None + /// if t is unknown. + fn pointer_kind( + &self, + t: Ty<'tcx>, + span: Span, + ) -> Result<Option<PointerKind<'tcx>>, ErrorGuaranteed> { + debug!("pointer_kind({:?}, {:?})", t, span); + + let t = self.resolve_vars_if_possible(t); + + if let Some(reported) = t.error_reported() { + return Err(reported); + } + + if self.type_is_sized_modulo_regions(self.param_env, t, span) { + return Ok(Some(PointerKind::Thin)); + } + + Ok(match *t.kind() { + ty::Slice(_) | ty::Str => Some(PointerKind::Length), + ty::Dynamic(ref tty, _, ty::Dyn) => Some(PointerKind::VTable(tty.principal_def_id())), + ty::Adt(def, substs) if def.is_struct() => match def.non_enum_variant().fields.last() { + None => Some(PointerKind::Thin), + Some(f) => { + let field_ty = self.field_ty(span, f, substs); + self.pointer_kind(field_ty, span)? + } + }, + ty::Tuple(fields) => match fields.last() { + None => Some(PointerKind::Thin), + Some(&f) => self.pointer_kind(f, span)?, + }, + + // Pointers to foreign types are thin, despite being unsized + ty::Foreign(..) => Some(PointerKind::Thin), + // We should really try to normalize here. + ty::Projection(ref pi) => Some(PointerKind::OfProjection(pi)), + ty::Opaque(def_id, substs) => Some(PointerKind::OfOpaque(def_id, substs)), + ty::Param(ref p) => Some(PointerKind::OfParam(p)), + // Insufficient type information. + ty::Placeholder(..) | ty::Bound(..) | ty::Infer(_) => None, + + ty::Bool + | ty::Char + | ty::Int(..) + | ty::Uint(..) + | ty::Float(_) + | ty::Array(..) + | ty::GeneratorWitness(..) + | ty::RawPtr(_) + | ty::Ref(..) + | ty::FnDef(..) + | ty::FnPtr(..) + | ty::Closure(..) + | ty::Generator(..) + | ty::Adt(..) + | ty::Never + | ty::Dynamic(_, _, ty::DynStar) + | ty::Error(_) => { + let reported = self + .tcx + .sess + .delay_span_bug(span, &format!("`{:?}` should be sized but is not?", t)); + return Err(reported); + } + }) + } +} + +#[derive(Copy, Clone)] +pub enum CastError { + ErrorGuaranteed, + + CastToBool, + CastToChar, + DifferingKinds, + /// Cast of thin to fat raw ptr (e.g., `*const () as *const [u8]`). + SizedUnsizedCast, + IllegalCast, + NeedDeref, + NeedViaPtr, + NeedViaThinPtr, + NeedViaInt, + NonScalar, + UnknownExprPtrKind, + UnknownCastPtrKind, + /// Cast of int to (possibly) fat raw pointer. + /// + /// Argument is the specific name of the metadata in plain words, such as "a vtable" + /// or "a length". If this argument is None, then the metadata is unknown, for example, + /// when we're typechecking a type parameter with a ?Sized bound. + IntToFatCast(Option<&'static str>), + ForeignNonExhaustiveAdt, +} + +impl From<ErrorGuaranteed> for CastError { + fn from(_: ErrorGuaranteed) -> Self { + CastError::ErrorGuaranteed + } +} + +fn make_invalid_casting_error<'a, 'tcx>( + sess: &'a Session, + span: Span, + expr_ty: Ty<'tcx>, + cast_ty: Ty<'tcx>, + fcx: &FnCtxt<'a, 'tcx>, +) -> DiagnosticBuilder<'a, ErrorGuaranteed> { + type_error_struct!( + sess, + span, + expr_ty, + E0606, + "casting `{}` as `{}` is invalid", + fcx.ty_to_string(expr_ty), + fcx.ty_to_string(cast_ty) + ) +} + +pub enum CastCheckResult<'tcx> { + Ok, + Deferred(CastCheck<'tcx>), + Err(ErrorGuaranteed), +} + +pub fn check_cast<'tcx>( + fcx: &FnCtxt<'_, 'tcx>, + expr: &'tcx hir::Expr<'tcx>, + expr_ty: Ty<'tcx>, + cast_ty: Ty<'tcx>, + cast_span: Span, + span: Span, +) -> CastCheckResult<'tcx> { + if cast_ty.is_dyn_star() { + check_dyn_star_cast(fcx, expr, expr_ty, cast_ty) + } else { + match CastCheck::new(fcx, expr, expr_ty, cast_ty, cast_span, span) { + Ok(check) => CastCheckResult::Deferred(check), + Err(e) => CastCheckResult::Err(e), + } + } +} + +fn check_dyn_star_cast<'tcx>( + fcx: &FnCtxt<'_, 'tcx>, + expr: &'tcx hir::Expr<'tcx>, + expr_ty: Ty<'tcx>, + cast_ty: Ty<'tcx>, +) -> CastCheckResult<'tcx> { + // Find the bounds in the dyn*. For eaxmple, if we have + // + // let x = 22_usize as dyn* (Clone + Debug + 'static) + // + // this would return `existential_predicates = [?Self: Clone, ?Self: Debug]` and `region = 'static`. + let (existential_predicates, region) = match cast_ty.kind() { + ty::Dynamic(predicates, region, ty::DynStar) => (predicates, region), + _ => panic!("Invalid dyn* cast_ty"), + }; + + let cause = ObligationCause::new( + expr.span, + fcx.body_id, + // FIXME(dyn-star): Use a better obligation cause code + ObligationCauseCode::MiscObligation, + ); + + // For each existential predicate (e.g., `?Self: Clone`) substitute + // the type of the expression (e.g., `usize` in our example above) + // and then require that the resulting predicate (e.g., `usize: Clone`) + // holds (it does). + for existential_predicate in existential_predicates.iter() { + let predicate = existential_predicate.with_self_ty(fcx.tcx, expr_ty); + fcx.register_predicate(Obligation::new(cause.clone(), fcx.param_env, predicate)); + } + + // Enforce the region bound `'static` (e.g., `usize: 'static`, in our example). + fcx.register_predicate(Obligation::new( + cause, + fcx.param_env, + fcx.tcx.mk_predicate(Binder::dummy(ty::PredicateKind::TypeOutlives( + ty::OutlivesPredicate(expr_ty, *region), + ))), + )); + + CastCheckResult::Ok +} + +impl<'a, 'tcx> CastCheck<'tcx> { + fn new( + fcx: &FnCtxt<'a, 'tcx>, + expr: &'tcx hir::Expr<'tcx>, + expr_ty: Ty<'tcx>, + cast_ty: Ty<'tcx>, + cast_span: Span, + span: Span, + ) -> Result<CastCheck<'tcx>, ErrorGuaranteed> { + let expr_span = expr.span.find_ancestor_inside(span).unwrap_or(expr.span); + let check = CastCheck { expr, expr_ty, expr_span, cast_ty, cast_span, span }; + + // For better error messages, check for some obviously unsized + // cases now. We do a more thorough check at the end, once + // inference is more completely known. + match cast_ty.kind() { + ty::Dynamic(_, _, ty::Dyn) | ty::Slice(..) => { + let reported = check.report_cast_to_unsized_type(fcx); + Err(reported) + } + _ => Ok(check), + } + } + + fn report_cast_error(&self, fcx: &FnCtxt<'a, 'tcx>, e: CastError) { + match e { + CastError::ErrorGuaranteed => { + // an error has already been reported + } + CastError::NeedDeref => { + let error_span = self.span; + let mut err = make_invalid_casting_error( + fcx.tcx.sess, + self.span, + self.expr_ty, + self.cast_ty, + fcx, + ); + let cast_ty = fcx.ty_to_string(self.cast_ty); + err.span_label( + error_span, + format!("cannot cast `{}` as `{}`", fcx.ty_to_string(self.expr_ty), cast_ty), + ); + if let Ok(snippet) = fcx.sess().source_map().span_to_snippet(self.expr_span) { + err.span_suggestion( + self.expr_span, + "dereference the expression", + format!("*{}", snippet), + Applicability::MaybeIncorrect, + ); + } else { + err.span_help(self.expr_span, "dereference the expression with `*`"); + } + err.emit(); + } + CastError::NeedViaThinPtr | CastError::NeedViaPtr => { + let mut err = make_invalid_casting_error( + fcx.tcx.sess, + self.span, + self.expr_ty, + self.cast_ty, + fcx, + ); + if self.cast_ty.is_integral() { + err.help(&format!( + "cast through {} first", + match e { + CastError::NeedViaPtr => "a raw pointer", + CastError::NeedViaThinPtr => "a thin pointer", + _ => bug!(), + } + )); + } + err.emit(); + } + CastError::NeedViaInt => { + make_invalid_casting_error( + fcx.tcx.sess, + self.span, + self.expr_ty, + self.cast_ty, + fcx, + ) + .help(&format!( + "cast through {} first", + match e { + CastError::NeedViaInt => "an integer", + _ => bug!(), + } + )) + .emit(); + } + CastError::IllegalCast => { + make_invalid_casting_error( + fcx.tcx.sess, + self.span, + self.expr_ty, + self.cast_ty, + fcx, + ) + .emit(); + } + CastError::DifferingKinds => { + make_invalid_casting_error( + fcx.tcx.sess, + self.span, + self.expr_ty, + self.cast_ty, + fcx, + ) + .note("vtable kinds may not match") + .emit(); + } + CastError::CastToBool => { + let mut err = + struct_span_err!(fcx.tcx.sess, self.span, E0054, "cannot cast as `bool`"); + + if self.expr_ty.is_numeric() { + match fcx.tcx.sess.source_map().span_to_snippet(self.expr_span) { + Ok(snippet) => { + err.span_suggestion( + self.span, + "compare with zero instead", + format!("{snippet} != 0"), + Applicability::MachineApplicable, + ); + } + Err(_) => { + err.span_help(self.span, "compare with zero instead"); + } + } + } else { + err.span_label(self.span, "unsupported cast"); + } + + err.emit(); + } + CastError::CastToChar => { + let mut err = type_error_struct!( + fcx.tcx.sess, + self.span, + self.expr_ty, + E0604, + "only `u8` can be cast as `char`, not `{}`", + self.expr_ty + ); + err.span_label(self.span, "invalid cast"); + if self.expr_ty.is_numeric() { + if self.expr_ty == fcx.tcx.types.u32 { + match fcx.tcx.sess.source_map().span_to_snippet(self.expr.span) { + Ok(snippet) => err.span_suggestion( + self.span, + "try `char::from_u32` instead", + format!("char::from_u32({snippet})"), + Applicability::MachineApplicable, + ), + + Err(_) => err.span_help(self.span, "try `char::from_u32` instead"), + }; + } else if self.expr_ty == fcx.tcx.types.i8 { + err.span_help(self.span, "try casting from `u8` instead"); + } else { + err.span_help(self.span, "try `char::from_u32` instead (via a `u32`)"); + }; + } + err.emit(); + } + CastError::NonScalar => { + let mut err = type_error_struct!( + fcx.tcx.sess, + self.span, + self.expr_ty, + E0605, + "non-primitive cast: `{}` as `{}`", + self.expr_ty, + fcx.ty_to_string(self.cast_ty) + ); + let mut sugg = None; + let mut sugg_mutref = false; + if let ty::Ref(reg, cast_ty, mutbl) = *self.cast_ty.kind() { + if let ty::RawPtr(TypeAndMut { ty: expr_ty, .. }) = *self.expr_ty.kind() + && fcx + .try_coerce( + self.expr, + fcx.tcx.mk_ref( + fcx.tcx.lifetimes.re_erased, + TypeAndMut { ty: expr_ty, mutbl }, + ), + self.cast_ty, + AllowTwoPhase::No, + None, + ) + .is_ok() + { + sugg = Some((format!("&{}*", mutbl.prefix_str()), cast_ty == expr_ty)); + } else if let ty::Ref(expr_reg, expr_ty, expr_mutbl) = *self.expr_ty.kind() + && expr_mutbl == Mutability::Not + && mutbl == Mutability::Mut + && fcx + .try_coerce( + self.expr, + fcx.tcx.mk_ref( + expr_reg, + TypeAndMut { ty: expr_ty, mutbl: Mutability::Mut }, + ), + self.cast_ty, + AllowTwoPhase::No, + None, + ) + .is_ok() + { + sugg_mutref = true; + } + + if !sugg_mutref + && sugg == None + && fcx + .try_coerce( + self.expr, + fcx.tcx.mk_ref(reg, TypeAndMut { ty: self.expr_ty, mutbl }), + self.cast_ty, + AllowTwoPhase::No, + None, + ) + .is_ok() + { + sugg = Some((format!("&{}", mutbl.prefix_str()), false)); + } + } else if let ty::RawPtr(TypeAndMut { mutbl, .. }) = *self.cast_ty.kind() + && fcx + .try_coerce( + self.expr, + fcx.tcx.mk_ref( + fcx.tcx.lifetimes.re_erased, + TypeAndMut { ty: self.expr_ty, mutbl }, + ), + self.cast_ty, + AllowTwoPhase::No, + None, + ) + .is_ok() + { + sugg = Some((format!("&{}", mutbl.prefix_str()), false)); + } + if sugg_mutref { + err.span_label(self.span, "invalid cast"); + err.span_note(self.expr_span, "this reference is immutable"); + err.span_note(self.cast_span, "trying to cast to a mutable reference type"); + } else if let Some((sugg, remove_cast)) = sugg { + err.span_label(self.span, "invalid cast"); + + let has_parens = fcx + .tcx + .sess + .source_map() + .span_to_snippet(self.expr_span) + .map_or(false, |snip| snip.starts_with('(')); + + // Very crude check to see whether the expression must be wrapped + // in parentheses for the suggestion to work (issue #89497). + // Can/should be extended in the future. + let needs_parens = + !has_parens && matches!(self.expr.kind, hir::ExprKind::Cast(..)); + + let mut suggestion = vec![(self.expr_span.shrink_to_lo(), sugg)]; + if needs_parens { + suggestion[0].1 += "("; + suggestion.push((self.expr_span.shrink_to_hi(), ")".to_string())); + } + if remove_cast { + suggestion.push(( + self.expr_span.shrink_to_hi().to(self.cast_span), + String::new(), + )); + } + + err.multipart_suggestion_verbose( + "consider borrowing the value", + suggestion, + Applicability::MachineApplicable, + ); + } else if !matches!( + self.cast_ty.kind(), + ty::FnDef(..) | ty::FnPtr(..) | ty::Closure(..) + ) { + let mut label = true; + // Check `impl From<self.expr_ty> for self.cast_ty {}` for accurate suggestion: + if let Ok(snippet) = fcx.tcx.sess.source_map().span_to_snippet(self.expr_span) + && let Some(from_trait) = fcx.tcx.get_diagnostic_item(sym::From) + { + let ty = fcx.resolve_vars_if_possible(self.cast_ty); + // Erase regions to avoid panic in `prove_value` when calling + // `type_implements_trait`. + let ty = fcx.tcx.erase_regions(ty); + let expr_ty = fcx.resolve_vars_if_possible(self.expr_ty); + let expr_ty = fcx.tcx.erase_regions(expr_ty); + let ty_params = fcx.tcx.mk_substs_trait(expr_ty, &[]); + if fcx + .infcx + .type_implements_trait(from_trait, ty, ty_params, fcx.param_env) + .must_apply_modulo_regions() + { + label = false; + err.span_suggestion( + self.span, + "consider using the `From` trait instead", + format!("{}::from({})", self.cast_ty, snippet), + Applicability::MaybeIncorrect, + ); + } + } + let msg = "an `as` expression can only be used to convert between primitive \ + types or to coerce to a specific trait object"; + if label { + err.span_label(self.span, msg); + } else { + err.note(msg); + } + } else { + err.span_label(self.span, "invalid cast"); + } + err.emit(); + } + CastError::SizedUnsizedCast => { + use crate::structured_errors::{SizedUnsizedCast, StructuredDiagnostic}; + + SizedUnsizedCast { + sess: &fcx.tcx.sess, + span: self.span, + expr_ty: self.expr_ty, + cast_ty: fcx.ty_to_string(self.cast_ty), + } + .diagnostic() + .emit(); + } + CastError::IntToFatCast(known_metadata) => { + let mut err = struct_span_err!( + fcx.tcx.sess, + self.cast_span, + E0606, + "cannot cast `{}` to a pointer that {} wide", + fcx.ty_to_string(self.expr_ty), + if known_metadata.is_some() { "is" } else { "may be" } + ); + + err.span_label( + self.cast_span, + format!( + "creating a `{}` requires both an address and {}", + self.cast_ty, + known_metadata.unwrap_or("type-specific metadata"), + ), + ); + + if fcx.tcx.sess.is_nightly_build() { + err.span_label( + self.expr_span, + "consider casting this expression to `*const ()`, \ + then using `core::ptr::from_raw_parts`", + ); + } + + err.emit(); + } + CastError::UnknownCastPtrKind | CastError::UnknownExprPtrKind => { + let unknown_cast_to = match e { + CastError::UnknownCastPtrKind => true, + CastError::UnknownExprPtrKind => false, + _ => bug!(), + }; + let mut err = struct_span_err!( + fcx.tcx.sess, + if unknown_cast_to { self.cast_span } else { self.span }, + E0641, + "cannot cast {} a pointer of an unknown kind", + if unknown_cast_to { "to" } else { "from" } + ); + if unknown_cast_to { + err.span_label(self.cast_span, "needs more type information"); + err.note( + "the type information given here is insufficient to check whether \ + the pointer cast is valid", + ); + } else { + err.span_label( + self.span, + "the type information given here is insufficient to check whether \ + the pointer cast is valid", + ); + } + err.emit(); + } + CastError::ForeignNonExhaustiveAdt => { + make_invalid_casting_error( + fcx.tcx.sess, + self.span, + self.expr_ty, + self.cast_ty, + fcx, + ) + .note("cannot cast an enum with a non-exhaustive variant when it's defined in another crate") + .emit(); + } + } + } + + fn report_cast_to_unsized_type(&self, fcx: &FnCtxt<'a, 'tcx>) -> ErrorGuaranteed { + if let Some(reported) = + self.cast_ty.error_reported().or_else(|| self.expr_ty.error_reported()) + { + return reported; + } + + let tstr = fcx.ty_to_string(self.cast_ty); + let mut err = type_error_struct!( + fcx.tcx.sess, + self.span, + self.expr_ty, + E0620, + "cast to unsized type: `{}` as `{}`", + fcx.resolve_vars_if_possible(self.expr_ty), + tstr + ); + match self.expr_ty.kind() { + ty::Ref(_, _, mt) => { + let mtstr = mt.prefix_str(); + if self.cast_ty.is_trait() { + match fcx.tcx.sess.source_map().span_to_snippet(self.cast_span) { + Ok(s) => { + err.span_suggestion( + self.cast_span, + "try casting to a reference instead", + format!("&{}{}", mtstr, s), + Applicability::MachineApplicable, + ); + } + Err(_) => { + let msg = &format!("did you mean `&{}{}`?", mtstr, tstr); + err.span_help(self.cast_span, msg); + } + } + } else { + let msg = + &format!("consider using an implicit coercion to `&{mtstr}{tstr}` instead"); + err.span_help(self.span, msg); + } + } + ty::Adt(def, ..) if def.is_box() => { + match fcx.tcx.sess.source_map().span_to_snippet(self.cast_span) { + Ok(s) => { + err.span_suggestion( + self.cast_span, + "you can cast to a `Box` instead", + format!("Box<{s}>"), + Applicability::MachineApplicable, + ); + } + Err(_) => { + err.span_help( + self.cast_span, + &format!("you might have meant `Box<{tstr}>`"), + ); + } + } + } + _ => { + err.span_help(self.expr_span, "consider using a box or reference as appropriate"); + } + } + err.emit() + } + + fn trivial_cast_lint(&self, fcx: &FnCtxt<'a, 'tcx>) { + let t_cast = self.cast_ty; + let t_expr = self.expr_ty; + let type_asc_or = + if fcx.tcx.features().type_ascription { "type ascription or " } else { "" }; + let (adjective, lint) = if t_cast.is_numeric() && t_expr.is_numeric() { + ("numeric ", lint::builtin::TRIVIAL_NUMERIC_CASTS) + } else { + ("", lint::builtin::TRIVIAL_CASTS) + }; + fcx.tcx.struct_span_lint_hir(lint, self.expr.hir_id, self.span, |err| { + err.build(&format!( + "trivial {}cast: `{}` as `{}`", + adjective, + fcx.ty_to_string(t_expr), + fcx.ty_to_string(t_cast) + )) + .help(&format!( + "cast can be replaced by coercion; this might \ + require {type_asc_or}a temporary variable" + )) + .emit(); + }); + } + + #[instrument(skip(fcx), level = "debug")] + pub fn check(mut self, fcx: &FnCtxt<'a, 'tcx>) { + self.expr_ty = fcx.structurally_resolved_type(self.expr_span, self.expr_ty); + self.cast_ty = fcx.structurally_resolved_type(self.cast_span, self.cast_ty); + + debug!("check_cast({}, {:?} as {:?})", self.expr.hir_id, self.expr_ty, self.cast_ty); + + if !fcx.type_is_sized_modulo_regions(fcx.param_env, self.cast_ty, self.span) + && !self.cast_ty.has_infer_types() + { + self.report_cast_to_unsized_type(fcx); + } else if self.expr_ty.references_error() || self.cast_ty.references_error() { + // No sense in giving duplicate error messages + } else { + match self.try_coercion_cast(fcx) { + Ok(()) => { + self.trivial_cast_lint(fcx); + debug!(" -> CoercionCast"); + fcx.typeck_results.borrow_mut().set_coercion_cast(self.expr.hir_id.local_id); + } + Err(ty::error::TypeError::ObjectUnsafeCoercion(did)) => { + self.report_object_unsafe_cast(&fcx, did); + } + Err(_) => { + match self.do_check(fcx) { + Ok(k) => { + debug!(" -> {:?}", k); + } + Err(e) => self.report_cast_error(fcx, e), + }; + } + }; + } + } + + fn report_object_unsafe_cast(&self, fcx: &FnCtxt<'a, 'tcx>, did: DefId) { + let violations = fcx.tcx.object_safety_violations(did); + let mut err = report_object_safety_error(fcx.tcx, self.cast_span, did, violations); + err.note(&format!("required by cast to type '{}'", fcx.ty_to_string(self.cast_ty))); + err.emit(); + } + + /// Checks a cast, and report an error if one exists. In some cases, this + /// can return Ok and create type errors in the fcx rather than returning + /// directly. coercion-cast is handled in check instead of here. + pub fn do_check(&self, fcx: &FnCtxt<'a, 'tcx>) -> Result<CastKind, CastError> { + use rustc_middle::ty::cast::CastTy::*; + use rustc_middle::ty::cast::IntTy::*; + + let (t_from, t_cast) = match (CastTy::from_ty(self.expr_ty), CastTy::from_ty(self.cast_ty)) + { + (Some(t_from), Some(t_cast)) => (t_from, t_cast), + // Function item types may need to be reified before casts. + (None, Some(t_cast)) => { + match *self.expr_ty.kind() { + ty::FnDef(..) => { + // Attempt a coercion to a fn pointer type. + let f = fcx.normalize_associated_types_in( + self.expr_span, + self.expr_ty.fn_sig(fcx.tcx), + ); + let res = fcx.try_coerce( + self.expr, + self.expr_ty, + fcx.tcx.mk_fn_ptr(f), + AllowTwoPhase::No, + None, + ); + if let Err(TypeError::IntrinsicCast) = res { + return Err(CastError::IllegalCast); + } + if res.is_err() { + return Err(CastError::NonScalar); + } + (FnPtr, t_cast) + } + // Special case some errors for references, and check for + // array-ptr-casts. `Ref` is not a CastTy because the cast + // is split into a coercion to a pointer type, followed by + // a cast. + ty::Ref(_, inner_ty, mutbl) => { + return match t_cast { + Int(_) | Float => match *inner_ty.kind() { + ty::Int(_) + | ty::Uint(_) + | ty::Float(_) + | ty::Infer(ty::InferTy::IntVar(_) | ty::InferTy::FloatVar(_)) => { + Err(CastError::NeedDeref) + } + _ => Err(CastError::NeedViaPtr), + }, + // array-ptr-cast + Ptr(mt) => { + self.check_ref_cast(fcx, TypeAndMut { mutbl, ty: inner_ty }, mt) + } + _ => Err(CastError::NonScalar), + }; + } + _ => return Err(CastError::NonScalar), + } + } + _ => return Err(CastError::NonScalar), + }; + + if let ty::Adt(adt_def, _) = *self.expr_ty.kind() { + if adt_def.did().krate != LOCAL_CRATE { + if adt_def.variants().iter().any(VariantDef::is_field_list_non_exhaustive) { + return Err(CastError::ForeignNonExhaustiveAdt); + } + } + } + + match (t_from, t_cast) { + // These types have invariants! can't cast into them. + (_, Int(CEnum) | FnPtr) => Err(CastError::NonScalar), + + // * -> Bool + (_, Int(Bool)) => Err(CastError::CastToBool), + + // * -> Char + (Int(U(ty::UintTy::U8)), Int(Char)) => Ok(CastKind::U8CharCast), // u8-char-cast + (_, Int(Char)) => Err(CastError::CastToChar), + + // prim -> float,ptr + (Int(Bool) | Int(CEnum) | Int(Char), Float) => Err(CastError::NeedViaInt), + + (Int(Bool) | Int(CEnum) | Int(Char) | Float, Ptr(_)) | (Ptr(_) | FnPtr, Float) => { + Err(CastError::IllegalCast) + } + + // ptr -> * + (Ptr(m_e), Ptr(m_c)) => self.check_ptr_ptr_cast(fcx, m_e, m_c), // ptr-ptr-cast + + // ptr-addr-cast + (Ptr(m_expr), Int(t_c)) => { + self.lossy_provenance_ptr2int_lint(fcx, t_c); + self.check_ptr_addr_cast(fcx, m_expr) + } + (FnPtr, Int(_)) => { + // FIXME(#95489): there should eventually be a lint for these casts + Ok(CastKind::FnPtrAddrCast) + } + // addr-ptr-cast + (Int(_), Ptr(mt)) => { + self.fuzzy_provenance_int2ptr_lint(fcx); + self.check_addr_ptr_cast(fcx, mt) + } + // fn-ptr-cast + (FnPtr, Ptr(mt)) => self.check_fptr_ptr_cast(fcx, mt), + + // prim -> prim + (Int(CEnum), Int(_)) => { + self.cenum_impl_drop_lint(fcx); + Ok(CastKind::EnumCast) + } + (Int(Char) | Int(Bool), Int(_)) => Ok(CastKind::PrimIntCast), + + (Int(_) | Float, Int(_) | Float) => Ok(CastKind::NumericCast), + + // FIXME(dyn-star): this needs more conditions... + (_, DynStar) => Ok(CastKind::DynStarCast), + + // FIXME(dyn-star): do we want to allow dyn* upcasting or other casts? + (DynStar, _) => Err(CastError::IllegalCast), + } + } + + fn check_ptr_ptr_cast( + &self, + fcx: &FnCtxt<'a, 'tcx>, + m_expr: ty::TypeAndMut<'tcx>, + m_cast: ty::TypeAndMut<'tcx>, + ) -> Result<CastKind, CastError> { + debug!("check_ptr_ptr_cast m_expr={:?} m_cast={:?}", m_expr, m_cast); + // ptr-ptr cast. vtables must match. + + let expr_kind = fcx.pointer_kind(m_expr.ty, self.span)?; + let cast_kind = fcx.pointer_kind(m_cast.ty, self.span)?; + + let Some(cast_kind) = cast_kind else { + // We can't cast if target pointer kind is unknown + return Err(CastError::UnknownCastPtrKind); + }; + + // Cast to thin pointer is OK + if cast_kind == PointerKind::Thin { + return Ok(CastKind::PtrPtrCast); + } + + let Some(expr_kind) = expr_kind else { + // We can't cast to fat pointer if source pointer kind is unknown + return Err(CastError::UnknownExprPtrKind); + }; + + // thin -> fat? report invalid cast (don't complain about vtable kinds) + if expr_kind == PointerKind::Thin { + return Err(CastError::SizedUnsizedCast); + } + + // vtable kinds must match + if cast_kind == expr_kind { + Ok(CastKind::PtrPtrCast) + } else { + Err(CastError::DifferingKinds) + } + } + + fn check_fptr_ptr_cast( + &self, + fcx: &FnCtxt<'a, 'tcx>, + m_cast: ty::TypeAndMut<'tcx>, + ) -> Result<CastKind, CastError> { + // fptr-ptr cast. must be to thin ptr + + match fcx.pointer_kind(m_cast.ty, self.span)? { + None => Err(CastError::UnknownCastPtrKind), + Some(PointerKind::Thin) => Ok(CastKind::FnPtrPtrCast), + _ => Err(CastError::IllegalCast), + } + } + + fn check_ptr_addr_cast( + &self, + fcx: &FnCtxt<'a, 'tcx>, + m_expr: ty::TypeAndMut<'tcx>, + ) -> Result<CastKind, CastError> { + // ptr-addr cast. must be from thin ptr + + match fcx.pointer_kind(m_expr.ty, self.span)? { + None => Err(CastError::UnknownExprPtrKind), + Some(PointerKind::Thin) => Ok(CastKind::PtrAddrCast), + _ => Err(CastError::NeedViaThinPtr), + } + } + + fn check_ref_cast( + &self, + fcx: &FnCtxt<'a, 'tcx>, + m_expr: ty::TypeAndMut<'tcx>, + m_cast: ty::TypeAndMut<'tcx>, + ) -> Result<CastKind, CastError> { + // array-ptr-cast: allow mut-to-mut, mut-to-const, const-to-const + if m_expr.mutbl == hir::Mutability::Mut || m_cast.mutbl == hir::Mutability::Not { + if let ty::Array(ety, _) = m_expr.ty.kind() { + // Due to the limitations of LLVM global constants, + // region pointers end up pointing at copies of + // vector elements instead of the original values. + // To allow raw pointers to work correctly, we + // need to special-case obtaining a raw pointer + // from a region pointer to a vector. + + // Coerce to a raw pointer so that we generate AddressOf in MIR. + let array_ptr_type = fcx.tcx.mk_ptr(m_expr); + fcx.try_coerce(self.expr, self.expr_ty, array_ptr_type, AllowTwoPhase::No, None) + .unwrap_or_else(|_| { + bug!( + "could not cast from reference to array to pointer to array ({:?} to {:?})", + self.expr_ty, + array_ptr_type, + ) + }); + + // this will report a type mismatch if needed + fcx.demand_eqtype(self.span, *ety, m_cast.ty); + return Ok(CastKind::ArrayPtrCast); + } + } + + Err(CastError::IllegalCast) + } + + fn check_addr_ptr_cast( + &self, + fcx: &FnCtxt<'a, 'tcx>, + m_cast: TypeAndMut<'tcx>, + ) -> Result<CastKind, CastError> { + // ptr-addr cast. pointer must be thin. + match fcx.pointer_kind(m_cast.ty, self.span)? { + None => Err(CastError::UnknownCastPtrKind), + Some(PointerKind::Thin) => Ok(CastKind::AddrPtrCast), + Some(PointerKind::VTable(_)) => Err(CastError::IntToFatCast(Some("a vtable"))), + Some(PointerKind::Length) => Err(CastError::IntToFatCast(Some("a length"))), + Some( + PointerKind::OfProjection(_) + | PointerKind::OfOpaque(_, _) + | PointerKind::OfParam(_), + ) => Err(CastError::IntToFatCast(None)), + } + } + + fn try_coercion_cast(&self, fcx: &FnCtxt<'a, 'tcx>) -> Result<(), ty::error::TypeError<'tcx>> { + match fcx.try_coerce(self.expr, self.expr_ty, self.cast_ty, AllowTwoPhase::No, None) { + Ok(_) => Ok(()), + Err(err) => Err(err), + } + } + + fn cenum_impl_drop_lint(&self, fcx: &FnCtxt<'a, 'tcx>) { + if let ty::Adt(d, _) = self.expr_ty.kind() + && d.has_dtor(fcx.tcx) + { + fcx.tcx.struct_span_lint_hir( + lint::builtin::CENUM_IMPL_DROP_CAST, + self.expr.hir_id, + self.span, + |err| { + err.build(&format!( + "cannot cast enum `{}` into integer `{}` because it implements `Drop`", + self.expr_ty, self.cast_ty + )) + .emit(); + }, + ); + } + } + + fn lossy_provenance_ptr2int_lint(&self, fcx: &FnCtxt<'a, 'tcx>, t_c: ty::cast::IntTy) { + fcx.tcx.struct_span_lint_hir( + lint::builtin::LOSSY_PROVENANCE_CASTS, + self.expr.hir_id, + self.span, + |err| { + let mut err = err.build(&format!( + "under strict provenance it is considered bad style to cast pointer `{}` to integer `{}`", + self.expr_ty, self.cast_ty + )); + + let msg = "use `.addr()` to obtain the address of a pointer"; + + let expr_prec = self.expr.precedence().order(); + let needs_parens = expr_prec < rustc_ast::util::parser::PREC_POSTFIX; + + let scalar_cast = match t_c { + ty::cast::IntTy::U(ty::UintTy::Usize) => String::new(), + _ => format!(" as {}", self.cast_ty), + }; + + let cast_span = self.expr_span.shrink_to_hi().to(self.cast_span); + + if needs_parens { + let suggestions = vec![ + (self.expr_span.shrink_to_lo(), String::from("(")), + (cast_span, format!(").addr(){scalar_cast}")), + ]; + + err.multipart_suggestion(msg, suggestions, Applicability::MaybeIncorrect); + } else { + err.span_suggestion( + cast_span, + msg, + format!(".addr(){scalar_cast}"), + Applicability::MaybeIncorrect, + ); + } + + err.help( + "if you can't comply with strict provenance and need to expose the pointer \ + provenance you can use `.expose_addr()` instead" + ); + + err.emit(); + }, + ); + } + + fn fuzzy_provenance_int2ptr_lint(&self, fcx: &FnCtxt<'a, 'tcx>) { + fcx.tcx.struct_span_lint_hir( + lint::builtin::FUZZY_PROVENANCE_CASTS, + self.expr.hir_id, + self.span, + |err| { + let mut err = err.build(&format!( + "strict provenance disallows casting integer `{}` to pointer `{}`", + self.expr_ty, self.cast_ty + )); + let msg = "use `.with_addr()` to adjust a valid pointer in the same allocation, to this address"; + let suggestions = vec![ + (self.expr_span.shrink_to_lo(), String::from("(...).with_addr(")), + (self.expr_span.shrink_to_hi().to(self.cast_span), String::from(")")), + ]; + + err.multipart_suggestion(msg, suggestions, Applicability::MaybeIncorrect); + err.help( + "if you can't comply with strict provenance and don't have a pointer with \ + the correct provenance you can use `std::ptr::from_exposed_addr()` instead" + ); + + err.emit(); + }, + ); + } +} |