| //! "Object safety" refers to the ability for a trait to be converted |
| //! to an object. In general, traits may only be converted to an |
| //! object if all of their methods meet certain criteria. In particular, |
| //! they must: |
| //! |
| //! - have a suitable receiver from which we can extract a vtable and coerce to a "thin" version |
| //! that doesn't contain the vtable; |
| //! - not reference the erased type `Self` except for in this receiver; |
| //! - not have generic type parameters. |
| |
| use super::elaborate; |
| |
| use crate::infer::TyCtxtInferExt; |
| use crate::traits::query::evaluate_obligation::InferCtxtExt; |
| use crate::traits::{self, Obligation, ObligationCause}; |
| use rustc_errors::{DelayDm, FatalError, MultiSpan}; |
| use rustc_hir as hir; |
| use rustc_hir::def_id::DefId; |
| use rustc_middle::query::Providers; |
| use rustc_middle::ty::subst::{GenericArg, InternalSubsts}; |
| use rustc_middle::ty::{ |
| self, EarlyBinder, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, TypeVisitor, |
| }; |
| use rustc_middle::ty::{ToPredicate, TypeVisitableExt}; |
| use rustc_session::lint::builtin::WHERE_CLAUSES_OBJECT_SAFETY; |
| use rustc_span::symbol::Symbol; |
| use rustc_span::Span; |
| use smallvec::SmallVec; |
| |
| use std::iter; |
| use std::ops::ControlFlow; |
| |
| pub use crate::traits::{MethodViolationCode, ObjectSafetyViolation}; |
| |
| /// Returns the object safety violations that affect |
| /// astconv -- currently, `Self` in supertraits. This is needed |
| /// because `object_safety_violations` can't be used during |
| /// type collection. |
| pub fn astconv_object_safety_violations( |
| tcx: TyCtxt<'_>, |
| trait_def_id: DefId, |
| ) -> Vec<ObjectSafetyViolation> { |
| debug_assert!(tcx.generics_of(trait_def_id).has_self); |
| let violations = traits::supertrait_def_ids(tcx, trait_def_id) |
| .map(|def_id| predicates_reference_self(tcx, def_id, true)) |
| .filter(|spans| !spans.is_empty()) |
| .map(ObjectSafetyViolation::SupertraitSelf) |
| .collect(); |
| |
| debug!("astconv_object_safety_violations(trait_def_id={:?}) = {:?}", trait_def_id, violations); |
| |
| violations |
| } |
| |
| fn object_safety_violations(tcx: TyCtxt<'_>, trait_def_id: DefId) -> &'_ [ObjectSafetyViolation] { |
| debug_assert!(tcx.generics_of(trait_def_id).has_self); |
| debug!("object_safety_violations: {:?}", trait_def_id); |
| |
| tcx.arena.alloc_from_iter( |
| traits::supertrait_def_ids(tcx, trait_def_id) |
| .flat_map(|def_id| object_safety_violations_for_trait(tcx, def_id)), |
| ) |
| } |
| |
| fn check_is_object_safe(tcx: TyCtxt<'_>, trait_def_id: DefId) -> bool { |
| let violations = tcx.object_safety_violations(trait_def_id); |
| |
| if violations.is_empty() { |
| return true; |
| } |
| |
| // If the trait contains any other violations, then let the error reporting path |
| // report it instead of emitting a warning here. |
| if violations.iter().all(|violation| { |
| matches!( |
| violation, |
| ObjectSafetyViolation::Method(_, MethodViolationCode::WhereClauseReferencesSelf, _) |
| ) |
| }) { |
| for violation in violations { |
| if let ObjectSafetyViolation::Method( |
| _, |
| MethodViolationCode::WhereClauseReferencesSelf, |
| span, |
| ) = violation |
| { |
| lint_object_unsafe_trait(tcx, *span, trait_def_id, &violation); |
| } |
| } |
| return true; |
| } |
| |
| false |
| } |
| |
| /// We say a method is *vtable safe* if it can be invoked on a trait |
| /// object. Note that object-safe traits can have some |
| /// non-vtable-safe methods, so long as they require `Self: Sized` or |
| /// otherwise ensure that they cannot be used when `Self = Trait`. |
| pub fn is_vtable_safe_method(tcx: TyCtxt<'_>, trait_def_id: DefId, method: ty::AssocItem) -> bool { |
| debug_assert!(tcx.generics_of(trait_def_id).has_self); |
| debug!("is_vtable_safe_method({:?}, {:?})", trait_def_id, method); |
| // Any method that has a `Self: Sized` bound cannot be called. |
| if generics_require_sized_self(tcx, method.def_id) { |
| return false; |
| } |
| |
| match virtual_call_violation_for_method(tcx, trait_def_id, method) { |
| None | Some(MethodViolationCode::WhereClauseReferencesSelf) => true, |
| Some(_) => false, |
| } |
| } |
| |
| fn object_safety_violations_for_trait( |
| tcx: TyCtxt<'_>, |
| trait_def_id: DefId, |
| ) -> Vec<ObjectSafetyViolation> { |
| // Check methods for violations. |
| let mut violations: Vec<_> = tcx |
| .associated_items(trait_def_id) |
| .in_definition_order() |
| .filter(|item| item.kind == ty::AssocKind::Fn) |
| .filter_map(|&item| { |
| object_safety_violation_for_method(tcx, trait_def_id, item) |
| .map(|(code, span)| ObjectSafetyViolation::Method(item.name, code, span)) |
| }) |
| .collect(); |
| |
| // Check the trait itself. |
| if trait_has_sized_self(tcx, trait_def_id) { |
| // We don't want to include the requirement from `Sized` itself to be `Sized` in the list. |
| let spans = get_sized_bounds(tcx, trait_def_id); |
| violations.push(ObjectSafetyViolation::SizedSelf(spans)); |
| } |
| let spans = predicates_reference_self(tcx, trait_def_id, false); |
| if !spans.is_empty() { |
| violations.push(ObjectSafetyViolation::SupertraitSelf(spans)); |
| } |
| let spans = bounds_reference_self(tcx, trait_def_id); |
| if !spans.is_empty() { |
| violations.push(ObjectSafetyViolation::SupertraitSelf(spans)); |
| } |
| let spans = super_predicates_have_non_lifetime_binders(tcx, trait_def_id); |
| if !spans.is_empty() { |
| violations.push(ObjectSafetyViolation::SupertraitNonLifetimeBinder(spans)); |
| } |
| |
| violations.extend( |
| tcx.associated_items(trait_def_id) |
| .in_definition_order() |
| .filter(|item| item.kind == ty::AssocKind::Const) |
| .map(|item| { |
| let ident = item.ident(tcx); |
| ObjectSafetyViolation::AssocConst(ident.name, ident.span) |
| }), |
| ); |
| |
| if !tcx.features().generic_associated_types_extended { |
| violations.extend( |
| tcx.associated_items(trait_def_id) |
| .in_definition_order() |
| .filter(|item| item.kind == ty::AssocKind::Type) |
| .filter(|item| !tcx.generics_of(item.def_id).params.is_empty()) |
| .filter(|item| tcx.opt_rpitit_info(item.def_id).is_none()) |
| .map(|item| { |
| let ident = item.ident(tcx); |
| ObjectSafetyViolation::GAT(ident.name, ident.span) |
| }), |
| ); |
| } |
| |
| debug!( |
| "object_safety_violations_for_trait(trait_def_id={:?}) = {:?}", |
| trait_def_id, violations |
| ); |
| |
| violations |
| } |
| |
| /// Lint object-unsafe trait. |
| fn lint_object_unsafe_trait( |
| tcx: TyCtxt<'_>, |
| span: Span, |
| trait_def_id: DefId, |
| violation: &ObjectSafetyViolation, |
| ) { |
| // Using `CRATE_NODE_ID` is wrong, but it's hard to get a more precise id. |
| // It's also hard to get a use site span, so we use the method definition span. |
| tcx.struct_span_lint_hir( |
| WHERE_CLAUSES_OBJECT_SAFETY, |
| hir::CRATE_HIR_ID, |
| span, |
| DelayDm(|| format!("the trait `{}` cannot be made into an object", tcx.def_path_str(trait_def_id))), |
| |err| { |
| let node = tcx.hir().get_if_local(trait_def_id); |
| let mut spans = MultiSpan::from_span(span); |
| if let Some(hir::Node::Item(item)) = node { |
| spans.push_span_label( |
| item.ident.span, |
| "this trait cannot be made into an object...", |
| ); |
| spans.push_span_label(span, format!("...because {}", violation.error_msg())); |
| } else { |
| spans.push_span_label( |
| span, |
| format!( |
| "the trait cannot be made into an object because {}", |
| violation.error_msg() |
| ), |
| ); |
| }; |
| err.span_note( |
| spans, |
| "for a trait to be \"object safe\" it needs to allow building a vtable to allow the \ |
| call to be resolvable dynamically; for more information visit \ |
| <https://doc.rust-lang.org/reference/items/traits.html#object-safety>", |
| ); |
| if node.is_some() { |
| // Only provide the help if its a local trait, otherwise it's not |
| violation.solution(err); |
| } |
| err |
| }, |
| ); |
| } |
| |
| fn sized_trait_bound_spans<'tcx>( |
| tcx: TyCtxt<'tcx>, |
| bounds: hir::GenericBounds<'tcx>, |
| ) -> impl 'tcx + Iterator<Item = Span> { |
| bounds.iter().filter_map(move |b| match b { |
| hir::GenericBound::Trait(trait_ref, hir::TraitBoundModifier::None) |
| if trait_has_sized_self( |
| tcx, |
| trait_ref.trait_ref.trait_def_id().unwrap_or_else(|| FatalError.raise()), |
| ) => |
| { |
| // Fetch spans for supertraits that are `Sized`: `trait T: Super` |
| Some(trait_ref.span) |
| } |
| _ => None, |
| }) |
| } |
| |
| fn get_sized_bounds(tcx: TyCtxt<'_>, trait_def_id: DefId) -> SmallVec<[Span; 1]> { |
| tcx.hir() |
| .get_if_local(trait_def_id) |
| .and_then(|node| match node { |
| hir::Node::Item(hir::Item { |
| kind: hir::ItemKind::Trait(.., generics, bounds, _), |
| .. |
| }) => Some( |
| generics |
| .predicates |
| .iter() |
| .filter_map(|pred| { |
| match pred { |
| hir::WherePredicate::BoundPredicate(pred) |
| if pred.bounded_ty.hir_id.owner.to_def_id() == trait_def_id => |
| { |
| // Fetch spans for trait bounds that are Sized: |
| // `trait T where Self: Pred` |
| Some(sized_trait_bound_spans(tcx, pred.bounds)) |
| } |
| _ => None, |
| } |
| }) |
| .flatten() |
| // Fetch spans for supertraits that are `Sized`: `trait T: Super`. |
| .chain(sized_trait_bound_spans(tcx, bounds)) |
| .collect::<SmallVec<[Span; 1]>>(), |
| ), |
| _ => None, |
| }) |
| .unwrap_or_else(SmallVec::new) |
| } |
| |
| fn predicates_reference_self( |
| tcx: TyCtxt<'_>, |
| trait_def_id: DefId, |
| supertraits_only: bool, |
| ) -> SmallVec<[Span; 1]> { |
| let trait_ref = ty::Binder::dummy(ty::TraitRef::identity(tcx, trait_def_id)); |
| let predicates = if supertraits_only { |
| tcx.super_predicates_of(trait_def_id) |
| } else { |
| tcx.predicates_of(trait_def_id) |
| }; |
| predicates |
| .predicates |
| .iter() |
| .map(|&(predicate, sp)| (predicate.subst_supertrait(tcx, &trait_ref), sp)) |
| .filter_map(|predicate| predicate_references_self(tcx, predicate)) |
| .collect() |
| } |
| |
| fn bounds_reference_self(tcx: TyCtxt<'_>, trait_def_id: DefId) -> SmallVec<[Span; 1]> { |
| tcx.associated_items(trait_def_id) |
| .in_definition_order() |
| .filter(|item| item.kind == ty::AssocKind::Type) |
| .flat_map(|item| tcx.explicit_item_bounds(item.def_id).subst_identity_iter_copied()) |
| .filter_map(|pred_span| predicate_references_self(tcx, pred_span)) |
| .collect() |
| } |
| |
| fn predicate_references_self<'tcx>( |
| tcx: TyCtxt<'tcx>, |
| (predicate, sp): (ty::Predicate<'tcx>, Span), |
| ) -> Option<Span> { |
| let self_ty = tcx.types.self_param; |
| let has_self_ty = |arg: &GenericArg<'tcx>| arg.walk().any(|arg| arg == self_ty.into()); |
| match predicate.kind().skip_binder() { |
| ty::PredicateKind::Clause(ty::Clause::Trait(ref data)) => { |
| // In the case of a trait predicate, we can skip the "self" type. |
| data.trait_ref.substs[1..].iter().any(has_self_ty).then_some(sp) |
| } |
| ty::PredicateKind::Clause(ty::Clause::Projection(ref data)) => { |
| // And similarly for projections. This should be redundant with |
| // the previous check because any projection should have a |
| // matching `Trait` predicate with the same inputs, but we do |
| // the check to be safe. |
| // |
| // It's also won't be redundant if we allow type-generic associated |
| // types for trait objects. |
| // |
| // Note that we *do* allow projection *outputs* to contain |
| // `self` (i.e., `trait Foo: Bar<Output=Self::Result> { type Result; }`), |
| // we just require the user to specify *both* outputs |
| // in the object type (i.e., `dyn Foo<Output=(), Result=()>`). |
| // |
| // This is ALT2 in issue #56288, see that for discussion of the |
| // possible alternatives. |
| data.projection_ty.substs[1..].iter().any(has_self_ty).then_some(sp) |
| } |
| ty::PredicateKind::Clause(ty::Clause::ConstArgHasType(_ct, ty)) => { |
| has_self_ty(&ty.into()).then_some(sp) |
| } |
| |
| ty::PredicateKind::AliasRelate(..) => bug!("`AliasRelate` not allowed as assumption"), |
| |
| ty::PredicateKind::WellFormed(..) |
| | ty::PredicateKind::ObjectSafe(..) |
| | ty::PredicateKind::Clause(ty::Clause::TypeOutlives(..)) |
| | ty::PredicateKind::Clause(ty::Clause::RegionOutlives(..)) |
| | ty::PredicateKind::ClosureKind(..) |
| | ty::PredicateKind::Subtype(..) |
| | ty::PredicateKind::Coerce(..) |
| // FIXME(generic_const_exprs): this can mention `Self` |
| | ty::PredicateKind::ConstEvaluatable(..) |
| | ty::PredicateKind::ConstEquate(..) |
| | ty::PredicateKind::Ambiguous |
| | ty::PredicateKind::TypeWellFormedFromEnv(..) => None, |
| } |
| } |
| |
| fn super_predicates_have_non_lifetime_binders( |
| tcx: TyCtxt<'_>, |
| trait_def_id: DefId, |
| ) -> SmallVec<[Span; 1]> { |
| // If non_lifetime_binders is disabled, then exit early |
| if !tcx.features().non_lifetime_binders { |
| return SmallVec::new(); |
| } |
| tcx.super_predicates_of(trait_def_id) |
| .predicates |
| .iter() |
| .filter_map(|(pred, span)| pred.has_non_region_late_bound().then_some(*span)) |
| .collect() |
| } |
| |
| fn trait_has_sized_self(tcx: TyCtxt<'_>, trait_def_id: DefId) -> bool { |
| generics_require_sized_self(tcx, trait_def_id) |
| } |
| |
| fn generics_require_sized_self(tcx: TyCtxt<'_>, def_id: DefId) -> bool { |
| let Some(sized_def_id) = tcx.lang_items().sized_trait() else { |
| return false; /* No Sized trait, can't require it! */ |
| }; |
| |
| // Search for a predicate like `Self : Sized` amongst the trait bounds. |
| let predicates = tcx.predicates_of(def_id); |
| let predicates = predicates.instantiate_identity(tcx).predicates; |
| elaborate(tcx, predicates.into_iter()).any(|pred| match pred.kind().skip_binder() { |
| ty::PredicateKind::Clause(ty::Clause::Trait(ref trait_pred)) => { |
| trait_pred.def_id() == sized_def_id && trait_pred.self_ty().is_param(0) |
| } |
| ty::PredicateKind::Clause(ty::Clause::Projection(..)) |
| | ty::PredicateKind::Clause(ty::Clause::ConstArgHasType(..)) |
| | ty::PredicateKind::Subtype(..) |
| | ty::PredicateKind::Coerce(..) |
| | ty::PredicateKind::Clause(ty::Clause::RegionOutlives(..)) |
| | ty::PredicateKind::WellFormed(..) |
| | ty::PredicateKind::ObjectSafe(..) |
| | ty::PredicateKind::ClosureKind(..) |
| | ty::PredicateKind::Clause(ty::Clause::TypeOutlives(..)) |
| | ty::PredicateKind::ConstEvaluatable(..) |
| | ty::PredicateKind::ConstEquate(..) |
| | ty::PredicateKind::AliasRelate(..) |
| | ty::PredicateKind::Ambiguous |
| | ty::PredicateKind::TypeWellFormedFromEnv(..) => false, |
| }) |
| } |
| |
| /// Returns `Some(_)` if this method makes the containing trait not object safe. |
| fn object_safety_violation_for_method( |
| tcx: TyCtxt<'_>, |
| trait_def_id: DefId, |
| method: ty::AssocItem, |
| ) -> Option<(MethodViolationCode, Span)> { |
| debug!("object_safety_violation_for_method({:?}, {:?})", trait_def_id, method); |
| // Any method that has a `Self : Sized` requisite is otherwise |
| // exempt from the regulations. |
| if generics_require_sized_self(tcx, method.def_id) { |
| return None; |
| } |
| |
| let violation = virtual_call_violation_for_method(tcx, trait_def_id, method); |
| // Get an accurate span depending on the violation. |
| violation.map(|v| { |
| let node = tcx.hir().get_if_local(method.def_id); |
| let span = match (&v, node) { |
| (MethodViolationCode::ReferencesSelfInput(Some(span)), _) => *span, |
| (MethodViolationCode::UndispatchableReceiver(Some(span)), _) => *span, |
| (MethodViolationCode::ReferencesImplTraitInTrait(span), _) => *span, |
| (MethodViolationCode::ReferencesSelfOutput, Some(node)) => { |
| node.fn_decl().map_or(method.ident(tcx).span, |decl| decl.output.span()) |
| } |
| _ => method.ident(tcx).span, |
| }; |
| (v, span) |
| }) |
| } |
| |
| /// Returns `Some(_)` if this method cannot be called on a trait |
| /// object; this does not necessarily imply that the enclosing trait |
| /// is not object safe, because the method might have a where clause |
| /// `Self:Sized`. |
| fn virtual_call_violation_for_method<'tcx>( |
| tcx: TyCtxt<'tcx>, |
| trait_def_id: DefId, |
| method: ty::AssocItem, |
| ) -> Option<MethodViolationCode> { |
| let sig = tcx.fn_sig(method.def_id).subst_identity(); |
| |
| // The method's first parameter must be named `self` |
| if !method.fn_has_self_parameter { |
| let sugg = if let Some(hir::Node::TraitItem(hir::TraitItem { |
| generics, |
| kind: hir::TraitItemKind::Fn(sig, _), |
| .. |
| })) = tcx.hir().get_if_local(method.def_id).as_ref() |
| { |
| let sm = tcx.sess.source_map(); |
| Some(( |
| ( |
| format!("&self{}", if sig.decl.inputs.is_empty() { "" } else { ", " }), |
| sm.span_through_char(sig.span, '(').shrink_to_hi(), |
| ), |
| ( |
| format!("{} Self: Sized", generics.add_where_or_trailing_comma()), |
| generics.tail_span_for_predicate_suggestion(), |
| ), |
| )) |
| } else { |
| None |
| }; |
| return Some(MethodViolationCode::StaticMethod(sugg)); |
| } |
| |
| for (i, &input_ty) in sig.skip_binder().inputs().iter().enumerate().skip(1) { |
| if contains_illegal_self_type_reference(tcx, trait_def_id, sig.rebind(input_ty)) { |
| let span = if let Some(hir::Node::TraitItem(hir::TraitItem { |
| kind: hir::TraitItemKind::Fn(sig, _), |
| .. |
| })) = tcx.hir().get_if_local(method.def_id).as_ref() |
| { |
| Some(sig.decl.inputs[i].span) |
| } else { |
| None |
| }; |
| return Some(MethodViolationCode::ReferencesSelfInput(span)); |
| } |
| } |
| if contains_illegal_self_type_reference(tcx, trait_def_id, sig.output()) { |
| return Some(MethodViolationCode::ReferencesSelfOutput); |
| } |
| if let Some(code) = contains_illegal_impl_trait_in_trait(tcx, method.def_id, sig.output()) { |
| return Some(code); |
| } |
| |
| // We can't monomorphize things like `fn foo<A>(...)`. |
| let own_counts = tcx.generics_of(method.def_id).own_counts(); |
| if own_counts.types + own_counts.consts != 0 { |
| return Some(MethodViolationCode::Generic); |
| } |
| |
| let receiver_ty = tcx.liberate_late_bound_regions(method.def_id, sig.input(0)); |
| |
| // Until `unsized_locals` is fully implemented, `self: Self` can't be dispatched on. |
| // However, this is already considered object-safe. We allow it as a special case here. |
| // FIXME(mikeyhew) get rid of this `if` statement once `receiver_is_dispatchable` allows |
| // `Receiver: Unsize<Receiver[Self => dyn Trait]>`. |
| if receiver_ty != tcx.types.self_param { |
| if !receiver_is_dispatchable(tcx, method, receiver_ty) { |
| let span = if let Some(hir::Node::TraitItem(hir::TraitItem { |
| kind: hir::TraitItemKind::Fn(sig, _), |
| .. |
| })) = tcx.hir().get_if_local(method.def_id).as_ref() |
| { |
| Some(sig.decl.inputs[0].span) |
| } else { |
| None |
| }; |
| return Some(MethodViolationCode::UndispatchableReceiver(span)); |
| } else { |
| // Do sanity check to make sure the receiver actually has the layout of a pointer. |
| |
| use rustc_target::abi::Abi; |
| |
| let param_env = tcx.param_env(method.def_id); |
| |
| let abi_of_ty = |ty: Ty<'tcx>| -> Option<Abi> { |
| match tcx.layout_of(param_env.and(ty)) { |
| Ok(layout) => Some(layout.abi), |
| Err(err) => { |
| // #78372 |
| tcx.sess.delay_span_bug( |
| tcx.def_span(method.def_id), |
| format!("error: {}\n while computing layout for type {:?}", err, ty), |
| ); |
| None |
| } |
| } |
| }; |
| |
| // e.g., `Rc<()>` |
| let unit_receiver_ty = |
| receiver_for_self_ty(tcx, receiver_ty, tcx.mk_unit(), method.def_id); |
| |
| match abi_of_ty(unit_receiver_ty) { |
| Some(Abi::Scalar(..)) => (), |
| abi => { |
| tcx.sess.delay_span_bug( |
| tcx.def_span(method.def_id), |
| format!( |
| "receiver when `Self = ()` should have a Scalar ABI; found {:?}", |
| abi |
| ), |
| ); |
| } |
| } |
| |
| let trait_object_ty = object_ty_for_trait(tcx, trait_def_id, tcx.lifetimes.re_static); |
| |
| // e.g., `Rc<dyn Trait>` |
| let trait_object_receiver = |
| receiver_for_self_ty(tcx, receiver_ty, trait_object_ty, method.def_id); |
| |
| match abi_of_ty(trait_object_receiver) { |
| Some(Abi::ScalarPair(..)) => (), |
| abi => { |
| tcx.sess.delay_span_bug( |
| tcx.def_span(method.def_id), |
| format!( |
| "receiver when `Self = {}` should have a ScalarPair ABI; found {:?}", |
| trait_object_ty, abi |
| ), |
| ); |
| } |
| } |
| } |
| } |
| |
| // NOTE: This check happens last, because it results in a lint, and not a |
| // hard error. |
| if tcx.predicates_of(method.def_id).predicates.iter().any(|&(pred, span)| { |
| // dyn Trait is okay: |
| // |
| // trait Trait { |
| // fn f(&self) where Self: 'static; |
| // } |
| // |
| // because a trait object can't claim to live longer than the concrete |
| // type. If the lifetime bound holds on dyn Trait then it's guaranteed |
| // to hold as well on the concrete type. |
| if pred.to_opt_type_outlives().is_some() { |
| return false; |
| } |
| |
| // dyn Trait is okay: |
| // |
| // auto trait AutoTrait {} |
| // |
| // trait Trait { |
| // fn f(&self) where Self: AutoTrait; |
| // } |
| // |
| // because `impl AutoTrait for dyn Trait` is disallowed by coherence. |
| // Traits with a default impl are implemented for a trait object if and |
| // only if the autotrait is one of the trait object's trait bounds, like |
| // in `dyn Trait + AutoTrait`. This guarantees that trait objects only |
| // implement auto traits if the underlying type does as well. |
| if let ty::PredicateKind::Clause(ty::Clause::Trait(ty::TraitPredicate { |
| trait_ref: pred_trait_ref, |
| constness: ty::BoundConstness::NotConst, |
| polarity: ty::ImplPolarity::Positive, |
| })) = pred.kind().skip_binder() |
| && pred_trait_ref.self_ty() == tcx.types.self_param |
| && tcx.trait_is_auto(pred_trait_ref.def_id) |
| { |
| // Consider bounds like `Self: Bound<Self>`. Auto traits are not |
| // allowed to have generic parameters so `auto trait Bound<T> {}` |
| // would already have reported an error at the definition of the |
| // auto trait. |
| if pred_trait_ref.substs.len() != 1 { |
| tcx.sess.diagnostic().delay_span_bug( |
| span, |
| "auto traits cannot have generic parameters", |
| ); |
| } |
| return false; |
| } |
| |
| contains_illegal_self_type_reference(tcx, trait_def_id, pred) |
| }) { |
| return Some(MethodViolationCode::WhereClauseReferencesSelf); |
| } |
| |
| None |
| } |
| |
| /// Performs a type substitution to produce the version of `receiver_ty` when `Self = self_ty`. |
| /// For example, for `receiver_ty = Rc<Self>` and `self_ty = Foo`, returns `Rc<Foo>`. |
| fn receiver_for_self_ty<'tcx>( |
| tcx: TyCtxt<'tcx>, |
| receiver_ty: Ty<'tcx>, |
| self_ty: Ty<'tcx>, |
| method_def_id: DefId, |
| ) -> Ty<'tcx> { |
| debug!("receiver_for_self_ty({:?}, {:?}, {:?})", receiver_ty, self_ty, method_def_id); |
| let substs = InternalSubsts::for_item(tcx, method_def_id, |param, _| { |
| if param.index == 0 { self_ty.into() } else { tcx.mk_param_from_def(param) } |
| }); |
| |
| let result = EarlyBinder::new(receiver_ty).subst(tcx, substs); |
| debug!( |
| "receiver_for_self_ty({:?}, {:?}, {:?}) = {:?}", |
| receiver_ty, self_ty, method_def_id, result |
| ); |
| result |
| } |
| |
| /// Creates the object type for the current trait. For example, |
| /// if the current trait is `Deref`, then this will be |
| /// `dyn Deref<Target = Self::Target> + 'static`. |
| #[instrument(level = "trace", skip(tcx), ret)] |
| fn object_ty_for_trait<'tcx>( |
| tcx: TyCtxt<'tcx>, |
| trait_def_id: DefId, |
| lifetime: ty::Region<'tcx>, |
| ) -> Ty<'tcx> { |
| let trait_ref = ty::TraitRef::identity(tcx, trait_def_id); |
| debug!(?trait_ref); |
| |
| let trait_predicate = ty::Binder::dummy(ty::ExistentialPredicate::Trait( |
| ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref), |
| )); |
| debug!(?trait_predicate); |
| |
| let pred: ty::Predicate<'tcx> = trait_ref.to_predicate(tcx); |
| let mut elaborated_predicates: Vec<_> = elaborate(tcx, [pred]) |
| .filter_map(|pred| { |
| debug!(?pred); |
| let pred = pred.to_opt_poly_projection_pred()?; |
| Some(pred.map_bound(|p| { |
| ty::ExistentialPredicate::Projection(ty::ExistentialProjection::erase_self_ty( |
| tcx, p, |
| )) |
| })) |
| }) |
| .collect(); |
| // NOTE: Since #37965, the existential predicates list has depended on the |
| // list of predicates to be sorted. This is mostly to enforce that the primary |
| // predicate comes first. |
| elaborated_predicates.sort_by(|a, b| a.skip_binder().stable_cmp(tcx, &b.skip_binder())); |
| elaborated_predicates.dedup(); |
| |
| let existential_predicates = tcx.mk_poly_existential_predicates_from_iter( |
| iter::once(trait_predicate).chain(elaborated_predicates), |
| ); |
| debug!(?existential_predicates); |
| |
| tcx.mk_dynamic(existential_predicates, lifetime, ty::Dyn) |
| } |
| |
| /// Checks the method's receiver (the `self` argument) can be dispatched on when `Self` is a |
| /// trait object. We require that `DispatchableFromDyn` be implemented for the receiver type |
| /// in the following way: |
| /// - let `Receiver` be the type of the `self` argument, i.e `Self`, `&Self`, `Rc<Self>`, |
| /// - require the following bound: |
| /// |
| /// ```ignore (not-rust) |
| /// Receiver[Self => T]: DispatchFromDyn<Receiver[Self => dyn Trait]> |
| /// ``` |
| /// |
| /// where `Foo[X => Y]` means "the same type as `Foo`, but with `X` replaced with `Y`" |
| /// (substitution notation). |
| /// |
| /// Some examples of receiver types and their required obligation: |
| /// - `&'a mut self` requires `&'a mut Self: DispatchFromDyn<&'a mut dyn Trait>`, |
| /// - `self: Rc<Self>` requires `Rc<Self>: DispatchFromDyn<Rc<dyn Trait>>`, |
| /// - `self: Pin<Box<Self>>` requires `Pin<Box<Self>>: DispatchFromDyn<Pin<Box<dyn Trait>>>`. |
| /// |
| /// The only case where the receiver is not dispatchable, but is still a valid receiver |
| /// type (just not object-safe), is when there is more than one level of pointer indirection. |
| /// E.g., `self: &&Self`, `self: &Rc<Self>`, `self: Box<Box<Self>>`. In these cases, there |
| /// is no way, or at least no inexpensive way, to coerce the receiver from the version where |
| /// `Self = dyn Trait` to the version where `Self = T`, where `T` is the unknown erased type |
| /// contained by the trait object, because the object that needs to be coerced is behind |
| /// a pointer. |
| /// |
| /// In practice, we cannot use `dyn Trait` explicitly in the obligation because it would result |
| /// in a new check that `Trait` is object safe, creating a cycle (until object_safe_for_dispatch |
| /// is stabilized, see tracking issue <https://github.com/rust-lang/rust/issues/43561>). |
| /// Instead, we fudge a little by introducing a new type parameter `U` such that |
| /// `Self: Unsize<U>` and `U: Trait + ?Sized`, and use `U` in place of `dyn Trait`. |
| /// Written as a chalk-style query: |
| /// ```ignore (not-rust) |
| /// forall (U: Trait + ?Sized) { |
| /// if (Self: Unsize<U>) { |
| /// Receiver: DispatchFromDyn<Receiver[Self => U]> |
| /// } |
| /// } |
| /// ``` |
| /// for `self: &'a mut Self`, this means `&'a mut Self: DispatchFromDyn<&'a mut U>` |
| /// for `self: Rc<Self>`, this means `Rc<Self>: DispatchFromDyn<Rc<U>>` |
| /// for `self: Pin<Box<Self>>`, this means `Pin<Box<Self>>: DispatchFromDyn<Pin<Box<U>>>` |
| // |
| // FIXME(mikeyhew) when unsized receivers are implemented as part of unsized rvalues, add this |
| // fallback query: `Receiver: Unsize<Receiver[Self => U]>` to support receivers like |
| // `self: Wrapper<Self>`. |
| #[allow(dead_code)] |
| fn receiver_is_dispatchable<'tcx>( |
| tcx: TyCtxt<'tcx>, |
| method: ty::AssocItem, |
| receiver_ty: Ty<'tcx>, |
| ) -> bool { |
| debug!("receiver_is_dispatchable: method = {:?}, receiver_ty = {:?}", method, receiver_ty); |
| |
| let traits = (tcx.lang_items().unsize_trait(), tcx.lang_items().dispatch_from_dyn_trait()); |
| let (Some(unsize_did), Some(dispatch_from_dyn_did)) = traits else { |
| debug!("receiver_is_dispatchable: Missing Unsize or DispatchFromDyn traits"); |
| return false; |
| }; |
| |
| // the type `U` in the query |
| // use a bogus type parameter to mimic a forall(U) query using u32::MAX for now. |
| // FIXME(mikeyhew) this is a total hack. Once object_safe_for_dispatch is stabilized, we can |
| // replace this with `dyn Trait` |
| let unsized_self_ty: Ty<'tcx> = |
| tcx.mk_ty_param(u32::MAX, Symbol::intern("RustaceansAreAwesome")); |
| |
| // `Receiver[Self => U]` |
| let unsized_receiver_ty = |
| receiver_for_self_ty(tcx, receiver_ty, unsized_self_ty, method.def_id); |
| |
| // create a modified param env, with `Self: Unsize<U>` and `U: Trait` added to caller bounds |
| // `U: ?Sized` is already implied here |
| let param_env = { |
| let param_env = tcx.param_env(method.def_id); |
| |
| // Self: Unsize<U> |
| let unsize_predicate = |
| ty::TraitRef::new(tcx, unsize_did, [tcx.types.self_param, unsized_self_ty]) |
| .without_const() |
| .to_predicate(tcx); |
| |
| // U: Trait<Arg1, ..., ArgN> |
| let trait_predicate = { |
| let trait_def_id = method.trait_container(tcx).unwrap(); |
| let substs = InternalSubsts::for_item(tcx, trait_def_id, |param, _| { |
| if param.index == 0 { unsized_self_ty.into() } else { tcx.mk_param_from_def(param) } |
| }); |
| |
| ty::TraitRef::new(tcx, trait_def_id, substs).to_predicate(tcx) |
| }; |
| |
| let caller_bounds = |
| param_env.caller_bounds().iter().chain([unsize_predicate, trait_predicate]); |
| |
| ty::ParamEnv::new( |
| tcx.mk_predicates_from_iter(caller_bounds), |
| param_env.reveal(), |
| param_env.constness(), |
| ) |
| }; |
| |
| // Receiver: DispatchFromDyn<Receiver[Self => U]> |
| let obligation = { |
| let predicate = |
| ty::TraitRef::new(tcx, dispatch_from_dyn_did, [receiver_ty, unsized_receiver_ty]); |
| |
| Obligation::new(tcx, ObligationCause::dummy(), param_env, predicate) |
| }; |
| |
| let infcx = tcx.infer_ctxt().build(); |
| // the receiver is dispatchable iff the obligation holds |
| infcx.predicate_must_hold_modulo_regions(&obligation) |
| } |
| |
| fn contains_illegal_self_type_reference<'tcx, T: TypeVisitable<TyCtxt<'tcx>>>( |
| tcx: TyCtxt<'tcx>, |
| trait_def_id: DefId, |
| value: T, |
| ) -> bool { |
| // This is somewhat subtle. In general, we want to forbid |
| // references to `Self` in the argument and return types, |
| // since the value of `Self` is erased. However, there is one |
| // exception: it is ok to reference `Self` in order to access |
| // an associated type of the current trait, since we retain |
| // the value of those associated types in the object type |
| // itself. |
| // |
| // ```rust |
| // trait SuperTrait { |
| // type X; |
| // } |
| // |
| // trait Trait : SuperTrait { |
| // type Y; |
| // fn foo(&self, x: Self) // bad |
| // fn foo(&self) -> Self // bad |
| // fn foo(&self) -> Option<Self> // bad |
| // fn foo(&self) -> Self::Y // OK, desugars to next example |
| // fn foo(&self) -> <Self as Trait>::Y // OK |
| // fn foo(&self) -> Self::X // OK, desugars to next example |
| // fn foo(&self) -> <Self as SuperTrait>::X // OK |
| // } |
| // ``` |
| // |
| // However, it is not as simple as allowing `Self` in a projected |
| // type, because there are illegal ways to use `Self` as well: |
| // |
| // ```rust |
| // trait Trait : SuperTrait { |
| // ... |
| // fn foo(&self) -> <Self as SomeOtherTrait>::X; |
| // } |
| // ``` |
| // |
| // Here we will not have the type of `X` recorded in the |
| // object type, and we cannot resolve `Self as SomeOtherTrait` |
| // without knowing what `Self` is. |
| |
| struct IllegalSelfTypeVisitor<'tcx> { |
| tcx: TyCtxt<'tcx>, |
| trait_def_id: DefId, |
| supertraits: Option<Vec<DefId>>, |
| } |
| |
| impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for IllegalSelfTypeVisitor<'tcx> { |
| type BreakTy = (); |
| |
| fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> { |
| match t.kind() { |
| ty::Param(_) => { |
| if t == self.tcx.types.self_param { |
| ControlFlow::Break(()) |
| } else { |
| ControlFlow::Continue(()) |
| } |
| } |
| ty::Alias(ty::Projection, ref data) |
| if self.tcx.is_impl_trait_in_trait(data.def_id) => |
| { |
| // We'll deny these later in their own pass |
| ControlFlow::Continue(()) |
| } |
| ty::Alias(ty::Projection, ref data) => { |
| // This is a projected type `<Foo as SomeTrait>::X`. |
| |
| // Compute supertraits of current trait lazily. |
| if self.supertraits.is_none() { |
| let trait_ref = |
| ty::Binder::dummy(ty::TraitRef::identity(self.tcx, self.trait_def_id)); |
| self.supertraits = Some( |
| traits::supertraits(self.tcx, trait_ref).map(|t| t.def_id()).collect(), |
| ); |
| } |
| |
| // Determine whether the trait reference `Foo as |
| // SomeTrait` is in fact a supertrait of the |
| // current trait. In that case, this type is |
| // legal, because the type `X` will be specified |
| // in the object type. Note that we can just use |
| // direct equality here because all of these types |
| // are part of the formal parameter listing, and |
| // hence there should be no inference variables. |
| let is_supertrait_of_current_trait = self |
| .supertraits |
| .as_ref() |
| .unwrap() |
| .contains(&data.trait_ref(self.tcx).def_id); |
| |
| if is_supertrait_of_current_trait { |
| ControlFlow::Continue(()) // do not walk contained types, do not report error, do collect $200 |
| } else { |
| t.super_visit_with(self) // DO walk contained types, POSSIBLY reporting an error |
| } |
| } |
| _ => t.super_visit_with(self), // walk contained types, if any |
| } |
| } |
| |
| fn visit_const(&mut self, ct: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> { |
| // Constants can only influence object safety if they are generic and reference `Self`. |
| // This is only possible for unevaluated constants, so we walk these here. |
| self.tcx.expand_abstract_consts(ct).super_visit_with(self) |
| } |
| } |
| |
| value |
| .visit_with(&mut IllegalSelfTypeVisitor { tcx, trait_def_id, supertraits: None }) |
| .is_break() |
| } |
| |
| pub fn contains_illegal_impl_trait_in_trait<'tcx>( |
| tcx: TyCtxt<'tcx>, |
| fn_def_id: DefId, |
| ty: ty::Binder<'tcx, Ty<'tcx>>, |
| ) -> Option<MethodViolationCode> { |
| // This would be caught below, but rendering the error as a separate |
| // `async-specific` message is better. |
| if tcx.asyncness(fn_def_id).is_async() { |
| return Some(MethodViolationCode::AsyncFn); |
| } |
| |
| // FIXME(RPITIT): Perhaps we should use a visitor here? |
| ty.skip_binder().walk().find_map(|arg| { |
| if let ty::GenericArgKind::Type(ty) = arg.unpack() |
| && let ty::Alias(ty::Projection, proj) = ty.kind() |
| && tcx.is_impl_trait_in_trait(proj.def_id) |
| { |
| Some(MethodViolationCode::ReferencesImplTraitInTrait(tcx.def_span(proj.def_id))) |
| } else { |
| None |
| } |
| }) |
| } |
| |
| pub fn provide(providers: &mut Providers) { |
| *providers = Providers { object_safety_violations, check_is_object_safe, ..*providers }; |
| } |
