1 //! "Object safety" refers to the ability for a trait to be converted
2 //! to an object. In general, traits may only be converted to an
3 //! object if all of their methods meet certain criteria. In particular,
6 //! - have a suitable receiver from which we can extract a vtable and coerce to a "thin" version
7 //! that doesn't contain the vtable;
8 //! - not reference the erased type `Self` except for in this receiver;
9 //! - not have generic type parameters.
11 use super::elaborate_predicates;
13 use crate::traits::{self, Obligation, ObligationCause};
14 use crate::ty::subst::{InternalSubsts, Subst};
15 use crate::ty::{self, Predicate, ToPredicate, Ty, TyCtxt, TypeFoldable};
17 use rustc_hir::def_id::DefId;
18 use rustc_session::lint::builtin::WHERE_CLAUSES_OBJECT_SAFETY;
19 use rustc_span::symbol::Symbol;
20 use rustc_span::{Span, DUMMY_SP};
24 use std::iter::{self};
26 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
27 pub enum ObjectSafetyViolation {
28 /// `Self: Sized` declared on the trait.
31 /// Supertrait reference references `Self` an in illegal location
32 /// (e.g., `trait Foo : Bar<Self>`).
35 /// Method has something illegal.
36 Method(ast::Name, MethodViolationCode, Span),
39 AssocConst(ast::Name, Span),
42 impl ObjectSafetyViolation {
43 pub fn error_msg(&self) -> Cow<'static, str> {
45 ObjectSafetyViolation::SizedSelf => {
46 "the trait cannot require that `Self : Sized`".into()
48 ObjectSafetyViolation::SupertraitSelf => {
49 "the trait cannot use `Self` as a type parameter \
50 in the supertraits or where-clauses"
53 ObjectSafetyViolation::Method(name, MethodViolationCode::StaticMethod, _) => {
54 format!("associated function `{}` has no `self` parameter", name).into()
56 ObjectSafetyViolation::Method(name, MethodViolationCode::ReferencesSelf, _) => format!(
57 "method `{}` references the `Self` type in its parameters or return type",
61 ObjectSafetyViolation::Method(
63 MethodViolationCode::WhereClauseReferencesSelf,
65 ) => format!("method `{}` references the `Self` type in where clauses", name).into(),
66 ObjectSafetyViolation::Method(name, MethodViolationCode::Generic, _) => {
67 format!("method `{}` has generic type parameters", name).into()
69 ObjectSafetyViolation::Method(name, MethodViolationCode::UndispatchableReceiver, _) => {
70 format!("method `{}`'s `self` parameter cannot be dispatched on", name).into()
72 ObjectSafetyViolation::AssocConst(name, _) => {
73 format!("the trait cannot contain associated consts like `{}`", name).into()
78 pub fn span(&self) -> Option<Span> {
79 // When `span` comes from a separate crate, it'll be `DUMMY_SP`. Treat it as `None` so
80 // diagnostics use a `note` instead of a `span_label`.
82 ObjectSafetyViolation::AssocConst(_, span)
83 | ObjectSafetyViolation::Method(_, _, span)
84 if span != DUMMY_SP =>
93 /// Reasons a method might not be object-safe.
94 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
95 pub enum MethodViolationCode {
99 /// e.g., `fn foo(&self, x: Self)` or `fn foo(&self) -> Self`
102 /// e.g., `fn foo(&self) where Self: Clone`
103 WhereClauseReferencesSelf,
105 /// e.g., `fn foo<A>()`
108 /// the method's receiver (`self` argument) can't be dispatched on
109 UndispatchableReceiver,
112 /// Returns the object safety violations that affect
113 /// astconv -- currently, `Self` in supertraits. This is needed
114 /// because `object_safety_violations` can't be used during
116 pub fn astconv_object_safety_violations(
119 ) -> Vec<ObjectSafetyViolation> {
120 debug_assert!(tcx.generics_of(trait_def_id).has_self);
121 let violations = traits::supertrait_def_ids(tcx, trait_def_id)
122 .filter(|&def_id| predicates_reference_self(tcx, def_id, true))
123 .map(|_| ObjectSafetyViolation::SupertraitSelf)
126 debug!("astconv_object_safety_violations(trait_def_id={:?}) = {:?}", trait_def_id, violations);
131 pub fn object_safety_violations(
134 ) -> Vec<ObjectSafetyViolation> {
135 debug_assert!(tcx.generics_of(trait_def_id).has_self);
136 debug!("object_safety_violations: {:?}", trait_def_id);
138 traits::supertrait_def_ids(tcx, trait_def_id)
139 .flat_map(|def_id| object_safety_violations_for_trait(tcx, def_id))
143 /// We say a method is *vtable safe* if it can be invoked on a trait
144 /// object. Note that object-safe traits can have some
145 /// non-vtable-safe methods, so long as they require `Self: Sized` or
146 /// otherwise ensure that they cannot be used when `Self = Trait`.
147 pub fn is_vtable_safe_method(tcx: TyCtxt<'_>, trait_def_id: DefId, method: &ty::AssocItem) -> bool {
148 debug_assert!(tcx.generics_of(trait_def_id).has_self);
149 debug!("is_vtable_safe_method({:?}, {:?})", trait_def_id, method);
150 // Any method that has a `Self: Sized` bound cannot be called.
151 if generics_require_sized_self(tcx, method.def_id) {
155 match virtual_call_violation_for_method(tcx, trait_def_id, method) {
156 None | Some(MethodViolationCode::WhereClauseReferencesSelf) => true,
161 fn object_safety_violations_for_trait(
164 ) -> Vec<ObjectSafetyViolation> {
165 // Check methods for violations.
166 let mut violations: Vec<_> = tcx
167 .associated_items(trait_def_id)
168 .filter(|item| item.kind == ty::AssocKind::Method)
170 object_safety_violation_for_method(tcx, trait_def_id, &item)
171 .map(|code| ObjectSafetyViolation::Method(item.ident.name, code, item.ident.span))
173 .filter(|violation| {
174 if let ObjectSafetyViolation::Method(
176 MethodViolationCode::WhereClauseReferencesSelf,
180 // Using `CRATE_NODE_ID` is wrong, but it's hard to get a more precise id.
181 // It's also hard to get a use site span, so we use the method definition span.
182 tcx.struct_span_lint_hir(
183 WHERE_CLAUSES_OBJECT_SAFETY,
187 "the trait `{}` cannot be made into an object",
188 tcx.def_path_str(trait_def_id)
191 .note(&violation.error_msg())
200 // Check the trait itself.
201 if trait_has_sized_self(tcx, trait_def_id) {
202 violations.push(ObjectSafetyViolation::SizedSelf);
204 if predicates_reference_self(tcx, trait_def_id, false) {
205 violations.push(ObjectSafetyViolation::SupertraitSelf);
209 tcx.associated_items(trait_def_id)
210 .filter(|item| item.kind == ty::AssocKind::Const)
211 .map(|item| ObjectSafetyViolation::AssocConst(item.ident.name, item.ident.span)),
215 "object_safety_violations_for_trait(trait_def_id={:?}) = {:?}",
216 trait_def_id, violations
222 fn predicates_reference_self(tcx: TyCtxt<'_>, trait_def_id: DefId, supertraits_only: bool) -> bool {
223 let trait_ref = ty::Binder::dummy(ty::TraitRef::identity(tcx, trait_def_id));
224 let predicates = if supertraits_only {
225 tcx.super_predicates_of(trait_def_id)
227 tcx.predicates_of(trait_def_id)
229 let self_ty = tcx.types.self_param;
230 let has_self_ty = |t: Ty<'_>| t.walk().any(|t| t == self_ty);
234 .map(|(predicate, _)| predicate.subst_supertrait(tcx, &trait_ref))
237 ty::Predicate::Trait(ref data, _) => {
238 // In the case of a trait predicate, we can skip the "self" type.
239 data.skip_binder().input_types().skip(1).any(has_self_ty)
241 ty::Predicate::Projection(ref data) => {
242 // And similarly for projections. This should be redundant with
243 // the previous check because any projection should have a
244 // matching `Trait` predicate with the same inputs, but we do
245 // the check to be safe.
247 // Note that we *do* allow projection *outputs* to contain
248 // `self` (i.e., `trait Foo: Bar<Output=Self::Result> { type Result; }`),
249 // we just require the user to specify *both* outputs
250 // in the object type (i.e., `dyn Foo<Output=(), Result=()>`).
252 // This is ALT2 in issue #56288, see that for discussion of the
253 // possible alternatives.
261 ty::Predicate::WellFormed(..)
262 | ty::Predicate::ObjectSafe(..)
263 | ty::Predicate::TypeOutlives(..)
264 | ty::Predicate::RegionOutlives(..)
265 | ty::Predicate::ClosureKind(..)
266 | ty::Predicate::Subtype(..)
267 | ty::Predicate::ConstEvaluatable(..) => false,
272 fn trait_has_sized_self(tcx: TyCtxt<'_>, trait_def_id: DefId) -> bool {
273 generics_require_sized_self(tcx, trait_def_id)
276 fn generics_require_sized_self(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
277 let sized_def_id = match tcx.lang_items().sized_trait() {
278 Some(def_id) => def_id,
280 return false; /* No Sized trait, can't require it! */
284 // Search for a predicate like `Self : Sized` amongst the trait bounds.
285 let predicates = tcx.predicates_of(def_id);
286 let predicates = predicates.instantiate_identity(tcx).predicates;
287 elaborate_predicates(tcx, predicates).any(|predicate| match predicate {
288 ty::Predicate::Trait(ref trait_pred, _) => {
289 trait_pred.def_id() == sized_def_id && trait_pred.skip_binder().self_ty().is_param(0)
291 ty::Predicate::Projection(..)
292 | ty::Predicate::Subtype(..)
293 | ty::Predicate::RegionOutlives(..)
294 | ty::Predicate::WellFormed(..)
295 | ty::Predicate::ObjectSafe(..)
296 | ty::Predicate::ClosureKind(..)
297 | ty::Predicate::TypeOutlives(..)
298 | ty::Predicate::ConstEvaluatable(..) => false,
302 /// Returns `Some(_)` if this method makes the containing trait not object safe.
303 fn object_safety_violation_for_method(
306 method: &ty::AssocItem,
307 ) -> Option<MethodViolationCode> {
308 debug!("object_safety_violation_for_method({:?}, {:?})", trait_def_id, method);
309 // Any method that has a `Self : Sized` requisite is otherwise
310 // exempt from the regulations.
311 if generics_require_sized_self(tcx, method.def_id) {
315 virtual_call_violation_for_method(tcx, trait_def_id, method)
318 /// Returns `Some(_)` if this method cannot be called on a trait
319 /// object; this does not necessarily imply that the enclosing trait
320 /// is not object safe, because the method might have a where clause
322 fn virtual_call_violation_for_method<'tcx>(
325 method: &ty::AssocItem,
326 ) -> Option<MethodViolationCode> {
327 // The method's first parameter must be named `self`
328 if !method.method_has_self_argument {
329 return Some(MethodViolationCode::StaticMethod);
332 let sig = tcx.fn_sig(method.def_id);
334 for input_ty in &sig.skip_binder().inputs()[1..] {
335 if contains_illegal_self_type_reference(tcx, trait_def_id, input_ty) {
336 return Some(MethodViolationCode::ReferencesSelf);
339 if contains_illegal_self_type_reference(tcx, trait_def_id, sig.output().skip_binder()) {
340 return Some(MethodViolationCode::ReferencesSelf);
343 // We can't monomorphize things like `fn foo<A>(...)`.
344 let own_counts = tcx.generics_of(method.def_id).own_counts();
345 if own_counts.types + own_counts.consts != 0 {
346 return Some(MethodViolationCode::Generic);
350 .predicates_of(method.def_id)
353 // A trait object can't claim to live more than the concrete type,
354 // so outlives predicates will always hold.
356 .filter(|(p, _)| p.to_opt_type_outlives().is_none())
358 // Do a shallow visit so that `contains_illegal_self_type_reference`
359 // may apply it's custom visiting.
360 .visit_tys_shallow(|t| contains_illegal_self_type_reference(tcx, trait_def_id, t))
362 return Some(MethodViolationCode::WhereClauseReferencesSelf);
366 tcx.liberate_late_bound_regions(method.def_id, &sig.map_bound(|sig| sig.inputs()[0]));
368 // Until `unsized_locals` is fully implemented, `self: Self` can't be dispatched on.
369 // However, this is already considered object-safe. We allow it as a special case here.
370 // FIXME(mikeyhew) get rid of this `if` statement once `receiver_is_dispatchable` allows
371 // `Receiver: Unsize<Receiver[Self => dyn Trait]>`.
372 if receiver_ty != tcx.types.self_param {
373 if !receiver_is_dispatchable(tcx, method, receiver_ty) {
374 return Some(MethodViolationCode::UndispatchableReceiver);
376 // Do sanity check to make sure the receiver actually has the layout of a pointer.
378 use crate::ty::layout::Abi;
380 let param_env = tcx.param_env(method.def_id);
382 let abi_of_ty = |ty: Ty<'tcx>| -> &Abi {
383 match tcx.layout_of(param_env.and(ty)) {
384 Ok(layout) => &layout.abi,
385 Err(err) => bug!("error: {}\n while computing layout for type {:?}", err, ty),
390 let unit_receiver_ty =
391 receiver_for_self_ty(tcx, receiver_ty, tcx.mk_unit(), method.def_id);
393 match abi_of_ty(unit_receiver_ty) {
394 &Abi::Scalar(..) => (),
396 tcx.sess.delay_span_bug(
397 tcx.def_span(method.def_id),
399 "receiver when `Self = ()` should have a Scalar ABI; found {:?}",
406 let trait_object_ty =
407 object_ty_for_trait(tcx, trait_def_id, tcx.mk_region(ty::ReStatic));
409 // e.g., `Rc<dyn Trait>`
410 let trait_object_receiver =
411 receiver_for_self_ty(tcx, receiver_ty, trait_object_ty, method.def_id);
413 match abi_of_ty(trait_object_receiver) {
414 &Abi::ScalarPair(..) => (),
416 tcx.sess.delay_span_bug(
417 tcx.def_span(method.def_id),
419 "receiver when `Self = {}` should have a ScalarPair ABI; \
432 /// Performs a type substitution to produce the version of `receiver_ty` when `Self = self_ty`.
433 /// For example, for `receiver_ty = Rc<Self>` and `self_ty = Foo`, returns `Rc<Foo>`.
434 fn receiver_for_self_ty<'tcx>(
436 receiver_ty: Ty<'tcx>,
438 method_def_id: DefId,
440 debug!("receiver_for_self_ty({:?}, {:?}, {:?})", receiver_ty, self_ty, method_def_id);
441 let substs = InternalSubsts::for_item(tcx, method_def_id, |param, _| {
442 if param.index == 0 { self_ty.into() } else { tcx.mk_param_from_def(param) }
445 let result = receiver_ty.subst(tcx, substs);
447 "receiver_for_self_ty({:?}, {:?}, {:?}) = {:?}",
448 receiver_ty, self_ty, method_def_id, result
453 /// Creates the object type for the current trait. For example,
454 /// if the current trait is `Deref`, then this will be
455 /// `dyn Deref<Target = Self::Target> + 'static`.
456 fn object_ty_for_trait<'tcx>(
459 lifetime: ty::Region<'tcx>,
461 debug!("object_ty_for_trait: trait_def_id={:?}", trait_def_id);
463 let trait_ref = ty::TraitRef::identity(tcx, trait_def_id);
465 let trait_predicate =
466 ty::ExistentialPredicate::Trait(ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref));
468 let mut associated_types = traits::supertraits(tcx, ty::Binder::dummy(trait_ref))
469 .flat_map(|super_trait_ref| {
470 tcx.associated_items(super_trait_ref.def_id()).map(move |item| (super_trait_ref, item))
472 .filter(|(_, item)| item.kind == ty::AssocKind::Type)
473 .collect::<Vec<_>>();
475 // existential predicates need to be in a specific order
476 associated_types.sort_by_cached_key(|(_, item)| tcx.def_path_hash(item.def_id));
478 let projection_predicates = associated_types.into_iter().map(|(super_trait_ref, item)| {
479 // We *can* get bound lifetimes here in cases like
480 // `trait MyTrait: for<'s> OtherTrait<&'s T, Output=bool>`.
482 // binder moved to (*)...
483 let super_trait_ref = super_trait_ref.skip_binder();
484 ty::ExistentialPredicate::Projection(ty::ExistentialProjection {
485 ty: tcx.mk_projection(item.def_id, super_trait_ref.substs),
486 item_def_id: item.def_id,
487 substs: super_trait_ref.substs,
491 let existential_predicates =
492 tcx.mk_existential_predicates(iter::once(trait_predicate).chain(projection_predicates));
494 let object_ty = tcx.mk_dynamic(
495 // (*) ... binder re-introduced here
496 ty::Binder::bind(existential_predicates),
500 debug!("object_ty_for_trait: object_ty=`{}`", object_ty);
505 /// Checks the method's receiver (the `self` argument) can be dispatched on when `Self` is a
506 /// trait object. We require that `DispatchableFromDyn` be implemented for the receiver type
507 /// in the following way:
508 /// - let `Receiver` be the type of the `self` argument, i.e `Self`, `&Self`, `Rc<Self>`,
509 /// - require the following bound:
512 /// Receiver[Self => T]: DispatchFromDyn<Receiver[Self => dyn Trait]>
515 /// where `Foo[X => Y]` means "the same type as `Foo`, but with `X` replaced with `Y`"
516 /// (substitution notation).
518 /// Some examples of receiver types and their required obligation:
519 /// - `&'a mut self` requires `&'a mut Self: DispatchFromDyn<&'a mut dyn Trait>`,
520 /// - `self: Rc<Self>` requires `Rc<Self>: DispatchFromDyn<Rc<dyn Trait>>`,
521 /// - `self: Pin<Box<Self>>` requires `Pin<Box<Self>>: DispatchFromDyn<Pin<Box<dyn Trait>>>`.
523 /// The only case where the receiver is not dispatchable, but is still a valid receiver
524 /// type (just not object-safe), is when there is more than one level of pointer indirection.
525 /// E.g., `self: &&Self`, `self: &Rc<Self>`, `self: Box<Box<Self>>`. In these cases, there
526 /// is no way, or at least no inexpensive way, to coerce the receiver from the version where
527 /// `Self = dyn Trait` to the version where `Self = T`, where `T` is the unknown erased type
528 /// contained by the trait object, because the object that needs to be coerced is behind
531 /// In practice, we cannot use `dyn Trait` explicitly in the obligation because it would result
532 /// in a new check that `Trait` is object safe, creating a cycle (until object_safe_for_dispatch
533 /// is stabilized, see tracking issue https://github.com/rust-lang/rust/issues/43561).
534 /// Instead, we fudge a little by introducing a new type parameter `U` such that
535 /// `Self: Unsize<U>` and `U: Trait + ?Sized`, and use `U` in place of `dyn Trait`.
536 /// Written as a chalk-style query:
538 /// forall (U: Trait + ?Sized) {
539 /// if (Self: Unsize<U>) {
540 /// Receiver: DispatchFromDyn<Receiver[Self => U]>
544 /// for `self: &'a mut Self`, this means `&'a mut Self: DispatchFromDyn<&'a mut U>`
545 /// for `self: Rc<Self>`, this means `Rc<Self>: DispatchFromDyn<Rc<U>>`
546 /// for `self: Pin<Box<Self>>`, this means `Pin<Box<Self>>: DispatchFromDyn<Pin<Box<U>>>`
548 // FIXME(mikeyhew) when unsized receivers are implemented as part of unsized rvalues, add this
549 // fallback query: `Receiver: Unsize<Receiver[Self => U]>` to support receivers like
550 // `self: Wrapper<Self>`.
552 fn receiver_is_dispatchable<'tcx>(
554 method: &ty::AssocItem,
555 receiver_ty: Ty<'tcx>,
557 debug!("receiver_is_dispatchable: method = {:?}, receiver_ty = {:?}", method, receiver_ty);
559 let traits = (tcx.lang_items().unsize_trait(), tcx.lang_items().dispatch_from_dyn_trait());
560 let (unsize_did, dispatch_from_dyn_did) = if let (Some(u), Some(cu)) = traits {
563 debug!("receiver_is_dispatchable: Missing Unsize or DispatchFromDyn traits");
567 // the type `U` in the query
568 // use a bogus type parameter to mimick a forall(U) query using u32::MAX for now.
569 // FIXME(mikeyhew) this is a total hack. Once object_safe_for_dispatch is stabilized, we can
570 // replace this with `dyn Trait`
571 let unsized_self_ty: Ty<'tcx> =
572 tcx.mk_ty_param(::std::u32::MAX, Symbol::intern("RustaceansAreAwesome"));
574 // `Receiver[Self => U]`
575 let unsized_receiver_ty =
576 receiver_for_self_ty(tcx, receiver_ty, unsized_self_ty, method.def_id);
578 // create a modified param env, with `Self: Unsize<U>` and `U: Trait` added to caller bounds
579 // `U: ?Sized` is already implied here
581 let mut param_env = tcx.param_env(method.def_id);
584 let unsize_predicate = ty::TraitRef {
586 substs: tcx.mk_substs_trait(tcx.types.self_param, &[unsized_self_ty.into()]),
590 // U: Trait<Arg1, ..., ArgN>
591 let trait_predicate = {
593 InternalSubsts::for_item(tcx, method.container.assert_trait(), |param, _| {
594 if param.index == 0 {
595 unsized_self_ty.into()
597 tcx.mk_param_from_def(param)
601 ty::TraitRef { def_id: unsize_did, substs }.to_predicate()
604 let caller_bounds: Vec<Predicate<'tcx>> = param_env
608 .chain(iter::once(unsize_predicate))
609 .chain(iter::once(trait_predicate))
612 param_env.caller_bounds = tcx.intern_predicates(&caller_bounds);
617 // Receiver: DispatchFromDyn<Receiver[Self => U]>
619 let predicate = ty::TraitRef {
620 def_id: dispatch_from_dyn_did,
621 substs: tcx.mk_substs_trait(receiver_ty, &[unsized_receiver_ty.into()]),
625 Obligation::new(ObligationCause::dummy(), param_env, predicate)
628 tcx.infer_ctxt().enter(|ref infcx| {
629 // the receiver is dispatchable iff the obligation holds
630 infcx.predicate_must_hold_modulo_regions(&obligation)
634 fn contains_illegal_self_type_reference<'tcx>(
639 // This is somewhat subtle. In general, we want to forbid
640 // references to `Self` in the argument and return types,
641 // since the value of `Self` is erased. However, there is one
642 // exception: it is ok to reference `Self` in order to access
643 // an associated type of the current trait, since we retain
644 // the value of those associated types in the object type
648 // trait SuperTrait {
652 // trait Trait : SuperTrait {
654 // fn foo(&self, x: Self) // bad
655 // fn foo(&self) -> Self // bad
656 // fn foo(&self) -> Option<Self> // bad
657 // fn foo(&self) -> Self::Y // OK, desugars to next example
658 // fn foo(&self) -> <Self as Trait>::Y // OK
659 // fn foo(&self) -> Self::X // OK, desugars to next example
660 // fn foo(&self) -> <Self as SuperTrait>::X // OK
664 // However, it is not as simple as allowing `Self` in a projected
665 // type, because there are illegal ways to use `Self` as well:
668 // trait Trait : SuperTrait {
670 // fn foo(&self) -> <Self as SomeOtherTrait>::X;
674 // Here we will not have the type of `X` recorded in the
675 // object type, and we cannot resolve `Self as SomeOtherTrait`
676 // without knowing what `Self` is.
678 let mut supertraits: Option<Vec<ty::PolyTraitRef<'tcx>>> = None;
679 let mut error = false;
680 let self_ty = tcx.types.self_param;
688 false // no contained types to walk
691 ty::Projection(ref data) => {
692 // This is a projected type `<Foo as SomeTrait>::X`.
694 // Compute supertraits of current trait lazily.
695 if supertraits.is_none() {
696 let trait_ref = ty::Binder::bind(ty::TraitRef::identity(tcx, trait_def_id));
697 supertraits = Some(traits::supertraits(tcx, trait_ref).collect());
700 // Determine whether the trait reference `Foo as
701 // SomeTrait` is in fact a supertrait of the
702 // current trait. In that case, this type is
703 // legal, because the type `X` will be specified
704 // in the object type. Note that we can just use
705 // direct equality here because all of these types
706 // are part of the formal parameter listing, and
707 // hence there should be no inference variables.
708 let projection_trait_ref = ty::Binder::bind(data.trait_ref(tcx));
709 let is_supertrait_of_current_trait =
710 supertraits.as_ref().unwrap().contains(&projection_trait_ref);
712 if is_supertrait_of_current_trait {
713 false // do not walk contained types, do not report error, do collect $200
715 true // DO walk contained types, POSSIBLY reporting an error
719 _ => true, // walk contained types, if any
726 pub(super) fn is_object_safe_provider(tcx: TyCtxt<'_>, trait_def_id: DefId) -> bool {
727 object_safety_violations(tcx, trait_def_id).is_empty()