| use rustc_data_structures::fx::FxHashSet; |
| use rustc_hir as hir; |
| use rustc_hir::LangItem; |
| use rustc_hir::def::DefKind; |
| use rustc_index::bit_set::BitSet; |
| use rustc_middle::bug; |
| use rustc_middle::query::Providers; |
| use rustc_middle::ty::{ |
| self, EarlyBinder, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, TypeVisitableExt, |
| TypeVisitor, Upcast, |
| }; |
| use rustc_span::DUMMY_SP; |
| use rustc_span::def_id::{CRATE_DEF_ID, DefId, LocalDefId}; |
| use rustc_trait_selection::traits; |
| use tracing::{debug, instrument}; |
| |
| #[instrument(level = "debug", skip(tcx), ret)] |
| fn sized_constraint_for_ty<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'tcx>> { |
| use rustc_type_ir::TyKind::*; |
| |
| match ty.kind() { |
| // these are always sized |
| Bool |
| | Char |
| | Int(..) |
| | Uint(..) |
| | Float(..) |
| | RawPtr(..) |
| | Ref(..) |
| | FnDef(..) |
| | FnPtr(..) |
| | Array(..) |
| | Closure(..) |
| | CoroutineClosure(..) |
| | Coroutine(..) |
| | CoroutineWitness(..) |
| | Never |
| | Dynamic(_, _, ty::DynStar) => None, |
| |
| // these are never sized |
| Str | Slice(..) | Dynamic(_, _, ty::Dyn) | Foreign(..) => Some(ty), |
| |
| Pat(ty, _) => sized_constraint_for_ty(tcx, *ty), |
| |
| Tuple(tys) => tys.last().and_then(|&ty| sized_constraint_for_ty(tcx, ty)), |
| |
| // recursive case |
| Adt(adt, args) => adt.sized_constraint(tcx).and_then(|intermediate| { |
| let ty = intermediate.instantiate(tcx, args); |
| sized_constraint_for_ty(tcx, ty) |
| }), |
| |
| // these can be sized or unsized |
| Param(..) | Alias(..) | Error(_) => Some(ty), |
| |
| Placeholder(..) | Bound(..) | Infer(..) => { |
| bug!("unexpected type `{ty:?}` in sized_constraint_for_ty") |
| } |
| } |
| } |
| |
| fn defaultness(tcx: TyCtxt<'_>, def_id: LocalDefId) -> hir::Defaultness { |
| match tcx.hir_node_by_def_id(def_id) { |
| hir::Node::Item(hir::Item { kind: hir::ItemKind::Impl(impl_), .. }) => impl_.defaultness, |
| hir::Node::ImplItem(hir::ImplItem { defaultness, .. }) |
| | hir::Node::TraitItem(hir::TraitItem { defaultness, .. }) => *defaultness, |
| node => { |
| bug!("`defaultness` called on {:?}", node); |
| } |
| } |
| } |
| |
| /// Calculates the `Sized` constraint. |
| /// |
| /// In fact, there are only a few options for the types in the constraint: |
| /// - an obviously-unsized type |
| /// - a type parameter or projection whose sizedness can't be known |
| #[instrument(level = "debug", skip(tcx), ret)] |
| fn adt_sized_constraint<'tcx>( |
| tcx: TyCtxt<'tcx>, |
| def_id: DefId, |
| ) -> Option<ty::EarlyBinder<'tcx, Ty<'tcx>>> { |
| if let Some(def_id) = def_id.as_local() { |
| if let ty::Representability::Infinite(_) = tcx.representability(def_id) { |
| return None; |
| } |
| } |
| let def = tcx.adt_def(def_id); |
| |
| if !def.is_struct() { |
| bug!("`adt_sized_constraint` called on non-struct type: {def:?}"); |
| } |
| |
| let tail_def = def.non_enum_variant().tail_opt()?; |
| let tail_ty = tcx.type_of(tail_def.did).instantiate_identity(); |
| |
| let constraint_ty = sized_constraint_for_ty(tcx, tail_ty)?; |
| if let Err(guar) = constraint_ty.error_reported() { |
| return Some(ty::EarlyBinder::bind(Ty::new_error(tcx, guar))); |
| } |
| |
| // perf hack: if there is a `constraint_ty: Sized` bound, then we know |
| // that the type is sized and do not need to check it on the impl. |
| let sized_trait_def_id = tcx.require_lang_item(LangItem::Sized, None); |
| let predicates = tcx.predicates_of(def.did()).predicates; |
| if predicates.iter().any(|(p, _)| { |
| p.as_trait_clause().is_some_and(|trait_pred| { |
| trait_pred.def_id() == sized_trait_def_id |
| && trait_pred.self_ty().skip_binder() == constraint_ty |
| }) |
| }) { |
| return None; |
| } |
| |
| Some(ty::EarlyBinder::bind(constraint_ty)) |
| } |
| |
| /// See `ParamEnv` struct definition for details. |
| fn param_env(tcx: TyCtxt<'_>, def_id: DefId) -> ty::ParamEnv<'_> { |
| // Compute the bounds on Self and the type parameters. |
| let ty::InstantiatedPredicates { mut predicates, .. } = |
| tcx.predicates_of(def_id).instantiate_identity(tcx); |
| |
| // Finally, we have to normalize the bounds in the environment, in |
| // case they contain any associated type projections. This process |
| // can yield errors if the put in illegal associated types, like |
| // `<i32 as Foo>::Bar` where `i32` does not implement `Foo`. We |
| // report these errors right here; this doesn't actually feel |
| // right to me, because constructing the environment feels like a |
| // kind of an "idempotent" action, but I'm not sure where would be |
| // a better place. In practice, we construct environments for |
| // every fn once during type checking, and we'll abort if there |
| // are any errors at that point, so outside of type inference you can be |
| // sure that this will succeed without errors anyway. |
| |
| if tcx.def_kind(def_id) == DefKind::AssocFn |
| && let assoc_item = tcx.associated_item(def_id) |
| && assoc_item.container == ty::AssocItemContainer::TraitContainer |
| && assoc_item.defaultness(tcx).has_value() |
| { |
| let sig = tcx.fn_sig(def_id).instantiate_identity(); |
| // We accounted for the binder of the fn sig, so skip the binder. |
| sig.skip_binder().visit_with(&mut ImplTraitInTraitFinder { |
| tcx, |
| fn_def_id: def_id, |
| bound_vars: sig.bound_vars(), |
| predicates: &mut predicates, |
| seen: FxHashSet::default(), |
| depth: ty::INNERMOST, |
| }); |
| } |
| |
| // We extend the param-env of our item with the const conditions of the item, |
| // since we're allowed to assume `~const` bounds hold within the item itself. |
| if tcx.is_conditionally_const(def_id) { |
| predicates.extend( |
| tcx.const_conditions(def_id).instantiate_identity(tcx).into_iter().map( |
| |(trait_ref, _)| trait_ref.to_host_effect_clause(tcx, ty::BoundConstness::Maybe), |
| ), |
| ); |
| } |
| |
| let local_did = def_id.as_local(); |
| |
| let unnormalized_env = |
| ty::ParamEnv::new(tcx.mk_clauses(&predicates), traits::Reveal::UserFacing); |
| |
| let body_id = local_did.unwrap_or(CRATE_DEF_ID); |
| let cause = traits::ObligationCause::misc(tcx.def_span(def_id), body_id); |
| traits::normalize_param_env_or_error(tcx, unnormalized_env, cause) |
| } |
| |
| /// Walk through a function type, gathering all RPITITs and installing a |
| /// `NormalizesTo(Projection(RPITIT) -> Opaque(RPITIT))` predicate into the |
| /// predicates list. This allows us to observe that an RPITIT projects to |
| /// its corresponding opaque within the body of a default-body trait method. |
| struct ImplTraitInTraitFinder<'a, 'tcx> { |
| tcx: TyCtxt<'tcx>, |
| predicates: &'a mut Vec<ty::Clause<'tcx>>, |
| fn_def_id: DefId, |
| bound_vars: &'tcx ty::List<ty::BoundVariableKind>, |
| seen: FxHashSet<DefId>, |
| depth: ty::DebruijnIndex, |
| } |
| |
| impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for ImplTraitInTraitFinder<'_, 'tcx> { |
| fn visit_binder<T: TypeVisitable<TyCtxt<'tcx>>>(&mut self, binder: &ty::Binder<'tcx, T>) { |
| self.depth.shift_in(1); |
| binder.super_visit_with(self); |
| self.depth.shift_out(1); |
| } |
| |
| fn visit_ty(&mut self, ty: Ty<'tcx>) { |
| if let ty::Alias(ty::Projection, unshifted_alias_ty) = *ty.kind() |
| && let Some( |
| ty::ImplTraitInTraitData::Trait { fn_def_id, .. } |
| | ty::ImplTraitInTraitData::Impl { fn_def_id, .. }, |
| ) = self.tcx.opt_rpitit_info(unshifted_alias_ty.def_id) |
| && fn_def_id == self.fn_def_id |
| && self.seen.insert(unshifted_alias_ty.def_id) |
| { |
| // We have entered some binders as we've walked into the |
| // bounds of the RPITIT. Shift these binders back out when |
| // constructing the top-level projection predicate. |
| let shifted_alias_ty = self.tcx.fold_regions(unshifted_alias_ty, |re, depth| { |
| if let ty::ReBound(index, bv) = re.kind() { |
| if depth != ty::INNERMOST { |
| return ty::Region::new_error_with_message( |
| self.tcx, |
| DUMMY_SP, |
| "we shouldn't walk non-predicate binders with `impl Trait`...", |
| ); |
| } |
| ty::Region::new_bound(self.tcx, index.shifted_out_to_binder(self.depth), bv) |
| } else { |
| re |
| } |
| }); |
| |
| // If we're lowering to associated item, install the opaque type which is just |
| // the `type_of` of the trait's associated item. If we're using the old lowering |
| // strategy, then just reinterpret the associated type like an opaque :^) |
| let default_ty = self |
| .tcx |
| .type_of(shifted_alias_ty.def_id) |
| .instantiate(self.tcx, shifted_alias_ty.args); |
| |
| self.predicates.push( |
| ty::Binder::bind_with_vars( |
| ty::ProjectionPredicate { |
| projection_term: shifted_alias_ty.into(), |
| term: default_ty.into(), |
| }, |
| self.bound_vars, |
| ) |
| .upcast(self.tcx), |
| ); |
| |
| // We walk the *un-shifted* alias ty, because we're tracking the de bruijn |
| // binder depth, and if we were to walk `shifted_alias_ty` instead, we'd |
| // have to reset `self.depth` back to `ty::INNERMOST` or something. It's |
| // easier to just do this. |
| for bound in self |
| .tcx |
| .item_bounds(unshifted_alias_ty.def_id) |
| .iter_instantiated(self.tcx, unshifted_alias_ty.args) |
| { |
| bound.visit_with(self); |
| } |
| } |
| |
| ty.super_visit_with(self) |
| } |
| } |
| |
| fn param_env_reveal_all_normalized(tcx: TyCtxt<'_>, def_id: DefId) -> ty::ParamEnv<'_> { |
| tcx.param_env(def_id).with_reveal_all_normalized(tcx) |
| } |
| |
| /// If the given trait impl enables exploiting the former order dependence of trait objects, |
| /// returns its self type; otherwise, returns `None`. |
| /// |
| /// See [`ty::ImplOverlapKind::FutureCompatOrderDepTraitObjects`] for more details. |
| #[instrument(level = "debug", skip(tcx))] |
| fn self_ty_of_trait_impl_enabling_order_dep_trait_object_hack( |
| tcx: TyCtxt<'_>, |
| def_id: DefId, |
| ) -> Option<EarlyBinder<'_, Ty<'_>>> { |
| let impl_ = |
| tcx.impl_trait_header(def_id).unwrap_or_else(|| bug!("called on inherent impl {def_id:?}")); |
| |
| let trait_ref = impl_.trait_ref.skip_binder(); |
| debug!(?trait_ref); |
| |
| let is_marker_like = impl_.polarity == ty::ImplPolarity::Positive |
| && tcx.associated_item_def_ids(trait_ref.def_id).is_empty(); |
| |
| // Check whether these impls would be ok for a marker trait. |
| if !is_marker_like { |
| debug!("not marker-like!"); |
| return None; |
| } |
| |
| // impl must be `impl Trait for dyn Marker1 + Marker2 + ...` |
| if trait_ref.args.len() != 1 { |
| debug!("impl has args!"); |
| return None; |
| } |
| |
| let predicates = tcx.predicates_of(def_id); |
| if predicates.parent.is_some() || !predicates.predicates.is_empty() { |
| debug!(?predicates, "impl has predicates!"); |
| return None; |
| } |
| |
| let self_ty = trait_ref.self_ty(); |
| let self_ty_matches = match self_ty.kind() { |
| ty::Dynamic(data, re, _) if re.is_static() => data.principal().is_none(), |
| _ => false, |
| }; |
| |
| if self_ty_matches { |
| debug!("MATCHES!"); |
| Some(EarlyBinder::bind(self_ty)) |
| } else { |
| debug!("non-matching self type"); |
| None |
| } |
| } |
| |
| /// Check if a function is async. |
| fn asyncness(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Asyncness { |
| let node = tcx.hir_node_by_def_id(def_id); |
| node.fn_sig().map_or(ty::Asyncness::No, |sig| match sig.header.asyncness { |
| hir::IsAsync::Async(_) => ty::Asyncness::Yes, |
| hir::IsAsync::NotAsync => ty::Asyncness::No, |
| }) |
| } |
| |
| fn unsizing_params_for_adt<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> BitSet<u32> { |
| let def = tcx.adt_def(def_id); |
| let num_params = tcx.generics_of(def_id).count(); |
| |
| let maybe_unsizing_param_idx = |arg: ty::GenericArg<'tcx>| match arg.unpack() { |
| ty::GenericArgKind::Type(ty) => match ty.kind() { |
| ty::Param(p) => Some(p.index), |
| _ => None, |
| }, |
| |
| // We can't unsize a lifetime |
| ty::GenericArgKind::Lifetime(_) => None, |
| |
| ty::GenericArgKind::Const(ct) => match ct.kind() { |
| ty::ConstKind::Param(p) => Some(p.index), |
| _ => None, |
| }, |
| }; |
| |
| // The last field of the structure has to exist and contain type/const parameters. |
| let Some((tail_field, prefix_fields)) = def.non_enum_variant().fields.raw.split_last() else { |
| return BitSet::new_empty(num_params); |
| }; |
| |
| let mut unsizing_params = BitSet::new_empty(num_params); |
| for arg in tcx.type_of(tail_field.did).instantiate_identity().walk() { |
| if let Some(i) = maybe_unsizing_param_idx(arg) { |
| unsizing_params.insert(i); |
| } |
| } |
| |
| // Ensure none of the other fields mention the parameters used |
| // in unsizing. |
| for field in prefix_fields { |
| for arg in tcx.type_of(field.did).instantiate_identity().walk() { |
| if let Some(i) = maybe_unsizing_param_idx(arg) { |
| unsizing_params.remove(i); |
| } |
| } |
| } |
| |
| unsizing_params |
| } |
| |
| pub(crate) fn provide(providers: &mut Providers) { |
| *providers = Providers { |
| asyncness, |
| adt_sized_constraint, |
| param_env, |
| param_env_reveal_all_normalized, |
| self_ty_of_trait_impl_enabling_order_dep_trait_object_hack, |
| defaultness, |
| unsizing_params_for_adt, |
| ..*providers |
| }; |
| } |
