| //! Confirmation. |
| //! |
| //! Confirmation unifies the output type parameters of the trait |
| //! with the values found in the obligation, possibly yielding a |
| //! type error. See the [rustc dev guide] for more details. |
| //! |
| //! [rustc dev guide]: |
| //! https://rustc-dev-guide.rust-lang.org/traits/resolution.html#confirmation |
| use rustc_data_structures::stack::ensure_sufficient_stack; |
| use rustc_hir::lang_items::LangItem; |
| use rustc_hir::Constness; |
| use rustc_index::bit_set::GrowableBitSet; |
| use rustc_infer::infer::InferOk; |
| use rustc_infer::infer::LateBoundRegionConversionTime::HigherRankedType; |
| use rustc_middle::ty::subst::{GenericArg, GenericArgKind, Subst, SubstsRef}; |
| use rustc_middle::ty::{self, Ty}; |
| use rustc_middle::ty::{ToPolyTraitRef, ToPredicate, WithConstness}; |
| use rustc_span::def_id::DefId; |
| |
| use crate::traits::project::{normalize_with_depth, normalize_with_depth_to}; |
| use crate::traits::select::TraitObligationExt; |
| use crate::traits::util; |
| use crate::traits::util::{closure_trait_ref_and_return_type, predicate_for_trait_def}; |
| use crate::traits::ImplSource; |
| use crate::traits::Normalized; |
| use crate::traits::OutputTypeParameterMismatch; |
| use crate::traits::Selection; |
| use crate::traits::TraitNotObjectSafe; |
| use crate::traits::{BuiltinDerivedObligation, ImplDerivedObligation}; |
| use crate::traits::{ |
| ImplSourceAutoImplData, ImplSourceBuiltinData, ImplSourceClosureData, |
| ImplSourceDiscriminantKindData, ImplSourceFnPointerData, ImplSourceGeneratorData, |
| ImplSourceObjectData, ImplSourceTraitAliasData, ImplSourceUserDefinedData, |
| }; |
| use crate::traits::{ObjectCastObligation, PredicateObligation, TraitObligation}; |
| use crate::traits::{Obligation, ObligationCause}; |
| use crate::traits::{SelectionError, Unimplemented}; |
| |
| use super::BuiltinImplConditions; |
| use super::SelectionCandidate::{self, *}; |
| use super::SelectionContext; |
| |
| use std::iter; |
| |
| impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> { |
| #[instrument(level = "debug", skip(self))] |
| pub(super) fn confirm_candidate( |
| &mut self, |
| obligation: &TraitObligation<'tcx>, |
| candidate: SelectionCandidate<'tcx>, |
| ) -> Result<Selection<'tcx>, SelectionError<'tcx>> { |
| match candidate { |
| BuiltinCandidate { has_nested } => { |
| let data = self.confirm_builtin_candidate(obligation, has_nested); |
| Ok(ImplSource::Builtin(data)) |
| } |
| |
| ParamCandidate(param) => { |
| let obligations = self.confirm_param_candidate(obligation, param.value); |
| Ok(ImplSource::Param(obligations, param.constness)) |
| } |
| |
| ImplCandidate(impl_def_id) => { |
| Ok(ImplSource::UserDefined(self.confirm_impl_candidate(obligation, impl_def_id))) |
| } |
| |
| AutoImplCandidate(trait_def_id) => { |
| let data = self.confirm_auto_impl_candidate(obligation, trait_def_id); |
| Ok(ImplSource::AutoImpl(data)) |
| } |
| |
| ProjectionCandidate(idx) => { |
| let obligations = self.confirm_projection_candidate(obligation, idx)?; |
| // FIXME(jschievink): constness |
| Ok(ImplSource::Param(obligations, Constness::NotConst)) |
| } |
| |
| ObjectCandidate(idx) => { |
| let data = self.confirm_object_candidate(obligation, idx)?; |
| Ok(ImplSource::Object(data)) |
| } |
| |
| ClosureCandidate => { |
| let vtable_closure = self.confirm_closure_candidate(obligation)?; |
| Ok(ImplSource::Closure(vtable_closure)) |
| } |
| |
| GeneratorCandidate => { |
| let vtable_generator = self.confirm_generator_candidate(obligation)?; |
| Ok(ImplSource::Generator(vtable_generator)) |
| } |
| |
| FnPointerCandidate => { |
| let data = self.confirm_fn_pointer_candidate(obligation)?; |
| Ok(ImplSource::FnPointer(data)) |
| } |
| |
| DiscriminantKindCandidate => { |
| Ok(ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData)) |
| } |
| |
| TraitAliasCandidate(alias_def_id) => { |
| let data = self.confirm_trait_alias_candidate(obligation, alias_def_id); |
| Ok(ImplSource::TraitAlias(data)) |
| } |
| |
| BuiltinObjectCandidate => { |
| // This indicates something like `Trait + Send: Send`. In this case, we know that |
| // this holds because that's what the object type is telling us, and there's really |
| // no additional obligations to prove and no types in particular to unify, etc. |
| Ok(ImplSource::Param(Vec::new(), Constness::NotConst)) |
| } |
| |
| BuiltinUnsizeCandidate => { |
| let data = self.confirm_builtin_unsize_candidate(obligation)?; |
| Ok(ImplSource::Builtin(data)) |
| } |
| } |
| } |
| |
| fn confirm_projection_candidate( |
| &mut self, |
| obligation: &TraitObligation<'tcx>, |
| idx: usize, |
| ) -> Result<Vec<PredicateObligation<'tcx>>, SelectionError<'tcx>> { |
| self.infcx.commit_unconditionally(|_| { |
| let tcx = self.tcx(); |
| |
| let trait_predicate = self.infcx.shallow_resolve(obligation.predicate); |
| let placeholder_trait_predicate = |
| self.infcx().replace_bound_vars_with_placeholders(trait_predicate); |
| let placeholder_self_ty = placeholder_trait_predicate.self_ty(); |
| let (def_id, substs) = match *placeholder_self_ty.kind() { |
| ty::Projection(proj) => (proj.item_def_id, proj.substs), |
| ty::Opaque(def_id, substs) => (def_id, substs), |
| _ => bug!("projection candidate for unexpected type: {:?}", placeholder_self_ty), |
| }; |
| |
| let candidate_predicate = tcx.item_bounds(def_id)[idx].subst(tcx, substs); |
| let candidate = candidate_predicate |
| .to_opt_poly_trait_ref() |
| .expect("projection candidate is not a trait predicate"); |
| let mut obligations = Vec::new(); |
| let candidate = normalize_with_depth_to( |
| self, |
| obligation.param_env, |
| obligation.cause.clone(), |
| obligation.recursion_depth + 1, |
| candidate, |
| &mut obligations, |
| ); |
| |
| obligations.extend(self.infcx.commit_if_ok(|_| { |
| self.infcx |
| .at(&obligation.cause, obligation.param_env) |
| .sup(placeholder_trait_predicate.trait_ref.to_poly_trait_ref(), candidate.value) |
| .map(|InferOk { obligations, .. }| obligations) |
| .map_err(|_| Unimplemented) |
| })?); |
| |
| if let ty::Projection(..) = placeholder_self_ty.kind() { |
| for predicate in tcx.predicates_of(def_id).instantiate_own(tcx, substs).predicates { |
| let normalized = normalize_with_depth_to( |
| self, |
| obligation.param_env, |
| obligation.cause.clone(), |
| obligation.recursion_depth + 1, |
| predicate, |
| &mut obligations, |
| ); |
| obligations.push(Obligation::with_depth( |
| obligation.cause.clone(), |
| obligation.recursion_depth + 1, |
| obligation.param_env, |
| normalized, |
| )); |
| } |
| } |
| |
| Ok(obligations) |
| }) |
| } |
| |
| fn confirm_param_candidate( |
| &mut self, |
| obligation: &TraitObligation<'tcx>, |
| param: ty::PolyTraitRef<'tcx>, |
| ) -> Vec<PredicateObligation<'tcx>> { |
| debug!(?obligation, ?param, "confirm_param_candidate"); |
| |
| // During evaluation, we already checked that this |
| // where-clause trait-ref could be unified with the obligation |
| // trait-ref. Repeat that unification now without any |
| // transactional boundary; it should not fail. |
| match self.match_where_clause_trait_ref(obligation, param) { |
| Ok(obligations) => obligations, |
| Err(()) => { |
| bug!( |
| "Where clause `{:?}` was applicable to `{:?}` but now is not", |
| param, |
| obligation |
| ); |
| } |
| } |
| } |
| |
| fn confirm_builtin_candidate( |
| &mut self, |
| obligation: &TraitObligation<'tcx>, |
| has_nested: bool, |
| ) -> ImplSourceBuiltinData<PredicateObligation<'tcx>> { |
| debug!(?obligation, ?has_nested, "confirm_builtin_candidate"); |
| |
| let lang_items = self.tcx().lang_items(); |
| let obligations = if has_nested { |
| let trait_def = obligation.predicate.def_id(); |
| let conditions = if Some(trait_def) == lang_items.sized_trait() { |
| self.sized_conditions(obligation) |
| } else if Some(trait_def) == lang_items.copy_trait() { |
| self.copy_clone_conditions(obligation) |
| } else if Some(trait_def) == lang_items.clone_trait() { |
| self.copy_clone_conditions(obligation) |
| } else { |
| bug!("unexpected builtin trait {:?}", trait_def) |
| }; |
| let nested = match conditions { |
| BuiltinImplConditions::Where(nested) => nested, |
| _ => bug!("obligation {:?} had matched a builtin impl but now doesn't", obligation), |
| }; |
| |
| let cause = obligation.derived_cause(BuiltinDerivedObligation); |
| ensure_sufficient_stack(|| { |
| self.collect_predicates_for_types( |
| obligation.param_env, |
| cause, |
| obligation.recursion_depth + 1, |
| trait_def, |
| nested, |
| ) |
| }) |
| } else { |
| vec![] |
| }; |
| |
| debug!(?obligations); |
| |
| ImplSourceBuiltinData { nested: obligations } |
| } |
| |
| /// This handles the case where a `auto trait Foo` impl is being used. |
| /// The idea is that the impl applies to `X : Foo` if the following conditions are met: |
| /// |
| /// 1. For each constituent type `Y` in `X`, `Y : Foo` holds |
| /// 2. For each where-clause `C` declared on `Foo`, `[Self => X] C` holds. |
| fn confirm_auto_impl_candidate( |
| &mut self, |
| obligation: &TraitObligation<'tcx>, |
| trait_def_id: DefId, |
| ) -> ImplSourceAutoImplData<PredicateObligation<'tcx>> { |
| debug!(?obligation, ?trait_def_id, "confirm_auto_impl_candidate"); |
| |
| let self_ty = self.infcx.shallow_resolve(obligation.predicate.self_ty()); |
| let types = self.constituent_types_for_ty(self_ty); |
| self.vtable_auto_impl(obligation, trait_def_id, types) |
| } |
| |
| /// See `confirm_auto_impl_candidate`. |
| fn vtable_auto_impl( |
| &mut self, |
| obligation: &TraitObligation<'tcx>, |
| trait_def_id: DefId, |
| nested: ty::Binder<Vec<Ty<'tcx>>>, |
| ) -> ImplSourceAutoImplData<PredicateObligation<'tcx>> { |
| debug!(?nested, "vtable_auto_impl"); |
| ensure_sufficient_stack(|| { |
| let cause = obligation.derived_cause(BuiltinDerivedObligation); |
| let mut obligations = self.collect_predicates_for_types( |
| obligation.param_env, |
| cause, |
| obligation.recursion_depth + 1, |
| trait_def_id, |
| nested, |
| ); |
| |
| let trait_obligations: Vec<PredicateObligation<'_>> = |
| self.infcx.commit_unconditionally(|_| { |
| let poly_trait_ref = obligation.predicate.to_poly_trait_ref(); |
| let trait_ref = self.infcx.replace_bound_vars_with_placeholders(poly_trait_ref); |
| let cause = obligation.derived_cause(ImplDerivedObligation); |
| self.impl_or_trait_obligations( |
| cause, |
| obligation.recursion_depth + 1, |
| obligation.param_env, |
| trait_def_id, |
| &trait_ref.substs, |
| ) |
| }); |
| |
| // Adds the predicates from the trait. Note that this contains a `Self: Trait` |
| // predicate as usual. It won't have any effect since auto traits are coinductive. |
| obligations.extend(trait_obligations); |
| |
| debug!(?obligations, "vtable_auto_impl"); |
| |
| ImplSourceAutoImplData { trait_def_id, nested: obligations } |
| }) |
| } |
| |
| fn confirm_impl_candidate( |
| &mut self, |
| obligation: &TraitObligation<'tcx>, |
| impl_def_id: DefId, |
| ) -> ImplSourceUserDefinedData<'tcx, PredicateObligation<'tcx>> { |
| debug!(?obligation, ?impl_def_id, "confirm_impl_candidate"); |
| |
| // First, create the substitutions by matching the impl again, |
| // this time not in a probe. |
| self.infcx.commit_unconditionally(|_| { |
| let substs = self.rematch_impl(impl_def_id, obligation); |
| debug!(?substs, "impl substs"); |
| let cause = obligation.derived_cause(ImplDerivedObligation); |
| ensure_sufficient_stack(|| { |
| self.vtable_impl( |
| impl_def_id, |
| substs, |
| cause, |
| obligation.recursion_depth + 1, |
| obligation.param_env, |
| ) |
| }) |
| }) |
| } |
| |
| fn vtable_impl( |
| &mut self, |
| impl_def_id: DefId, |
| substs: Normalized<'tcx, SubstsRef<'tcx>>, |
| cause: ObligationCause<'tcx>, |
| recursion_depth: usize, |
| param_env: ty::ParamEnv<'tcx>, |
| ) -> ImplSourceUserDefinedData<'tcx, PredicateObligation<'tcx>> { |
| debug!(?impl_def_id, ?substs, ?recursion_depth, "vtable_impl"); |
| |
| let mut impl_obligations = self.impl_or_trait_obligations( |
| cause, |
| recursion_depth, |
| param_env, |
| impl_def_id, |
| &substs.value, |
| ); |
| |
| debug!(?impl_obligations, "vtable_impl"); |
| |
| // Because of RFC447, the impl-trait-ref and obligations |
| // are sufficient to determine the impl substs, without |
| // relying on projections in the impl-trait-ref. |
| // |
| // e.g., `impl<U: Tr, V: Iterator<Item=U>> Foo<<U as Tr>::T> for V` |
| impl_obligations.extend(substs.obligations); |
| |
| ImplSourceUserDefinedData { impl_def_id, substs: substs.value, nested: impl_obligations } |
| } |
| |
| fn confirm_object_candidate( |
| &mut self, |
| obligation: &TraitObligation<'tcx>, |
| index: usize, |
| ) -> Result<ImplSourceObjectData<'tcx, PredicateObligation<'tcx>>, SelectionError<'tcx>> { |
| let tcx = self.tcx(); |
| debug!(?obligation, ?index, "confirm_object_candidate"); |
| |
| let trait_predicate = self.infcx.replace_bound_vars_with_placeholders(obligation.predicate); |
| let self_ty = self.infcx.shallow_resolve(trait_predicate.self_ty()); |
| let obligation_trait_ref = ty::Binder::dummy(trait_predicate.trait_ref); |
| let data = match *self_ty.kind() { |
| ty::Dynamic(data, ..) => data, |
| _ => span_bug!(obligation.cause.span, "object candidate with non-object"), |
| }; |
| |
| let object_trait_ref = data.principal().unwrap_or_else(|| { |
| span_bug!(obligation.cause.span, "object candidate with no principal") |
| }); |
| let object_trait_ref = self |
| .infcx |
| .replace_bound_vars_with_fresh_vars( |
| obligation.cause.span, |
| HigherRankedType, |
| object_trait_ref, |
| ) |
| .0; |
| let object_trait_ref = object_trait_ref.with_self_ty(self.tcx(), self_ty); |
| |
| let mut nested = vec![]; |
| |
| let mut supertraits = util::supertraits(tcx, ty::Binder::dummy(object_trait_ref)); |
| |
| // For each of the non-matching predicates that |
| // we pass over, we sum up the set of number of vtable |
| // entries, so that we can compute the offset for the selected |
| // trait. |
| let vtable_base = supertraits |
| .by_ref() |
| .take(index) |
| .map(|t| super::util::count_own_vtable_entries(tcx, t)) |
| .sum(); |
| |
| let unnormalized_upcast_trait_ref = |
| supertraits.next().expect("supertraits iterator no longer has as many elements"); |
| |
| let upcast_trait_ref = normalize_with_depth_to( |
| self, |
| obligation.param_env, |
| obligation.cause.clone(), |
| obligation.recursion_depth + 1, |
| unnormalized_upcast_trait_ref, |
| &mut nested, |
| ); |
| |
| nested.extend(self.infcx.commit_if_ok(|_| { |
| self.infcx |
| .at(&obligation.cause, obligation.param_env) |
| .sup(obligation_trait_ref, upcast_trait_ref) |
| .map(|InferOk { obligations, .. }| obligations) |
| .map_err(|_| Unimplemented) |
| })?); |
| |
| // Check supertraits hold. This is so that their associated type bounds |
| // will be checked in the code below. |
| for super_trait in tcx |
| .super_predicates_of(trait_predicate.def_id()) |
| .instantiate(tcx, trait_predicate.trait_ref.substs) |
| .predicates |
| .into_iter() |
| { |
| if let ty::PredicateAtom::Trait(..) = super_trait.skip_binders() { |
| let normalized_super_trait = normalize_with_depth_to( |
| self, |
| obligation.param_env, |
| obligation.cause.clone(), |
| obligation.recursion_depth + 1, |
| super_trait, |
| &mut nested, |
| ); |
| nested.push(Obligation::new( |
| obligation.cause.clone(), |
| obligation.param_env, |
| normalized_super_trait, |
| )); |
| } |
| } |
| |
| let assoc_types: Vec<_> = tcx |
| .associated_items(trait_predicate.def_id()) |
| .in_definition_order() |
| .filter_map( |
| |item| if item.kind == ty::AssocKind::Type { Some(item.def_id) } else { None }, |
| ) |
| .collect(); |
| |
| for assoc_type in assoc_types { |
| if !tcx.generics_of(assoc_type).params.is_empty() { |
| // FIXME(generic_associated_types) generate placeholders to |
| // extend the trait substs. |
| tcx.sess.span_fatal( |
| obligation.cause.span, |
| "generic associated types in trait objects are not supported yet", |
| ); |
| } |
| // This maybe belongs in wf, but that can't (doesn't) handle |
| // higher-ranked things. |
| // Prevent, e.g., `dyn Iterator<Item = str>`. |
| for bound in self.tcx().item_bounds(assoc_type) { |
| let subst_bound = bound.subst(tcx, trait_predicate.trait_ref.substs); |
| let normalized_bound = normalize_with_depth_to( |
| self, |
| obligation.param_env, |
| obligation.cause.clone(), |
| obligation.recursion_depth + 1, |
| subst_bound, |
| &mut nested, |
| ); |
| nested.push(Obligation::new( |
| obligation.cause.clone(), |
| obligation.param_env, |
| normalized_bound, |
| )); |
| } |
| } |
| |
| debug!(?nested, "object nested obligations"); |
| Ok(ImplSourceObjectData { upcast_trait_ref, vtable_base, nested }) |
| } |
| |
| fn confirm_fn_pointer_candidate( |
| &mut self, |
| obligation: &TraitObligation<'tcx>, |
| ) -> Result<ImplSourceFnPointerData<'tcx, PredicateObligation<'tcx>>, SelectionError<'tcx>> |
| { |
| debug!(?obligation, "confirm_fn_pointer_candidate"); |
| |
| // Okay to skip binder; it is reintroduced below. |
| let self_ty = self.infcx.shallow_resolve(obligation.self_ty().skip_binder()); |
| let sig = self_ty.fn_sig(self.tcx()); |
| let trait_ref = closure_trait_ref_and_return_type( |
| self.tcx(), |
| obligation.predicate.def_id(), |
| self_ty, |
| sig, |
| util::TupleArgumentsFlag::Yes, |
| ) |
| .map_bound(|(trait_ref, _)| trait_ref); |
| |
| let Normalized { value: trait_ref, mut obligations } = ensure_sufficient_stack(|| { |
| normalize_with_depth( |
| self, |
| obligation.param_env, |
| obligation.cause.clone(), |
| obligation.recursion_depth + 1, |
| trait_ref, |
| ) |
| }); |
| |
| obligations.extend(self.confirm_poly_trait_refs( |
| obligation.cause.clone(), |
| obligation.param_env, |
| obligation.predicate.to_poly_trait_ref(), |
| trait_ref, |
| )?); |
| Ok(ImplSourceFnPointerData { fn_ty: self_ty, nested: obligations }) |
| } |
| |
| fn confirm_trait_alias_candidate( |
| &mut self, |
| obligation: &TraitObligation<'tcx>, |
| alias_def_id: DefId, |
| ) -> ImplSourceTraitAliasData<'tcx, PredicateObligation<'tcx>> { |
| debug!(?obligation, ?alias_def_id, "confirm_trait_alias_candidate"); |
| |
| self.infcx.commit_unconditionally(|_| { |
| let predicate = self.infcx().replace_bound_vars_with_placeholders(obligation.predicate); |
| let trait_ref = predicate.trait_ref; |
| let trait_def_id = trait_ref.def_id; |
| let substs = trait_ref.substs; |
| |
| let trait_obligations = self.impl_or_trait_obligations( |
| obligation.cause.clone(), |
| obligation.recursion_depth, |
| obligation.param_env, |
| trait_def_id, |
| &substs, |
| ); |
| |
| debug!(?trait_def_id, ?trait_obligations, "trait alias obligations"); |
| |
| ImplSourceTraitAliasData { alias_def_id, substs, nested: trait_obligations } |
| }) |
| } |
| |
| fn confirm_generator_candidate( |
| &mut self, |
| obligation: &TraitObligation<'tcx>, |
| ) -> Result<ImplSourceGeneratorData<'tcx, PredicateObligation<'tcx>>, SelectionError<'tcx>> |
| { |
| // Okay to skip binder because the substs on generator types never |
| // touch bound regions, they just capture the in-scope |
| // type/region parameters. |
| let self_ty = self.infcx.shallow_resolve(obligation.self_ty().skip_binder()); |
| let (generator_def_id, substs) = match *self_ty.kind() { |
| ty::Generator(id, substs, _) => (id, substs), |
| _ => bug!("closure candidate for non-closure {:?}", obligation), |
| }; |
| |
| debug!(?obligation, ?generator_def_id, ?substs, "confirm_generator_candidate"); |
| |
| let trait_ref = self.generator_trait_ref_unnormalized(obligation, substs); |
| let Normalized { value: trait_ref, mut obligations } = ensure_sufficient_stack(|| { |
| normalize_with_depth( |
| self, |
| obligation.param_env, |
| obligation.cause.clone(), |
| obligation.recursion_depth + 1, |
| trait_ref, |
| ) |
| }); |
| |
| debug!(?trait_ref, ?obligations, "generator candidate obligations"); |
| |
| obligations.extend(self.confirm_poly_trait_refs( |
| obligation.cause.clone(), |
| obligation.param_env, |
| obligation.predicate.to_poly_trait_ref(), |
| trait_ref, |
| )?); |
| |
| Ok(ImplSourceGeneratorData { generator_def_id, substs, nested: obligations }) |
| } |
| |
| fn confirm_closure_candidate( |
| &mut self, |
| obligation: &TraitObligation<'tcx>, |
| ) -> Result<ImplSourceClosureData<'tcx, PredicateObligation<'tcx>>, SelectionError<'tcx>> { |
| debug!(?obligation, "confirm_closure_candidate"); |
| |
| let kind = self |
| .tcx() |
| .fn_trait_kind_from_lang_item(obligation.predicate.def_id()) |
| .unwrap_or_else(|| bug!("closure candidate for non-fn trait {:?}", obligation)); |
| |
| // Okay to skip binder because the substs on closure types never |
| // touch bound regions, they just capture the in-scope |
| // type/region parameters. |
| let self_ty = self.infcx.shallow_resolve(obligation.self_ty().skip_binder()); |
| let (closure_def_id, substs) = match *self_ty.kind() { |
| ty::Closure(id, substs) => (id, substs), |
| _ => bug!("closure candidate for non-closure {:?}", obligation), |
| }; |
| |
| let trait_ref = self.closure_trait_ref_unnormalized(obligation, substs); |
| let Normalized { value: trait_ref, mut obligations } = ensure_sufficient_stack(|| { |
| normalize_with_depth( |
| self, |
| obligation.param_env, |
| obligation.cause.clone(), |
| obligation.recursion_depth + 1, |
| trait_ref, |
| ) |
| }); |
| |
| debug!(?closure_def_id, ?trait_ref, ?obligations, "confirm closure candidate obligations"); |
| |
| obligations.extend(self.confirm_poly_trait_refs( |
| obligation.cause.clone(), |
| obligation.param_env, |
| obligation.predicate.to_poly_trait_ref(), |
| trait_ref, |
| )?); |
| |
| // FIXME: Chalk |
| |
| if !self.tcx().sess.opts.debugging_opts.chalk { |
| obligations.push(Obligation::new( |
| obligation.cause.clone(), |
| obligation.param_env, |
| ty::PredicateAtom::ClosureKind(closure_def_id, substs, kind) |
| .to_predicate(self.tcx()), |
| )); |
| } |
| |
| Ok(ImplSourceClosureData { closure_def_id, substs, nested: obligations }) |
| } |
| |
| /// In the case of closure types and fn pointers, |
| /// we currently treat the input type parameters on the trait as |
| /// outputs. This means that when we have a match we have only |
| /// considered the self type, so we have to go back and make sure |
| /// to relate the argument types too. This is kind of wrong, but |
| /// since we control the full set of impls, also not that wrong, |
| /// and it DOES yield better error messages (since we don't report |
| /// errors as if there is no applicable impl, but rather report |
| /// errors are about mismatched argument types. |
| /// |
| /// Here is an example. Imagine we have a closure expression |
| /// and we desugared it so that the type of the expression is |
| /// `Closure`, and `Closure` expects `i32` as argument. Then it |
| /// is "as if" the compiler generated this impl: |
| /// |
| /// impl Fn(i32) for Closure { ... } |
| /// |
| /// Now imagine our obligation is `Closure: Fn(usize)`. So far |
| /// we have matched the self type `Closure`. At this point we'll |
| /// compare the `i32` to `usize` and generate an error. |
| /// |
| /// Note that this checking occurs *after* the impl has selected, |
| /// because these output type parameters should not affect the |
| /// selection of the impl. Therefore, if there is a mismatch, we |
| /// report an error to the user. |
| fn confirm_poly_trait_refs( |
| &mut self, |
| obligation_cause: ObligationCause<'tcx>, |
| obligation_param_env: ty::ParamEnv<'tcx>, |
| obligation_trait_ref: ty::PolyTraitRef<'tcx>, |
| expected_trait_ref: ty::PolyTraitRef<'tcx>, |
| ) -> Result<Vec<PredicateObligation<'tcx>>, SelectionError<'tcx>> { |
| self.infcx |
| .at(&obligation_cause, obligation_param_env) |
| .sup(obligation_trait_ref, expected_trait_ref) |
| .map(|InferOk { obligations, .. }| obligations) |
| .map_err(|e| OutputTypeParameterMismatch(expected_trait_ref, obligation_trait_ref, e)) |
| } |
| |
| fn confirm_builtin_unsize_candidate( |
| &mut self, |
| obligation: &TraitObligation<'tcx>, |
| ) -> Result<ImplSourceBuiltinData<PredicateObligation<'tcx>>, SelectionError<'tcx>> { |
| let tcx = self.tcx(); |
| |
| // `assemble_candidates_for_unsizing` should ensure there are no late-bound |
| // regions here. See the comment there for more details. |
| let source = self.infcx.shallow_resolve(obligation.self_ty().no_bound_vars().unwrap()); |
| let target = obligation.predicate.skip_binder().trait_ref.substs.type_at(1); |
| let target = self.infcx.shallow_resolve(target); |
| |
| debug!(?source, ?target, "confirm_builtin_unsize_candidate"); |
| |
| let mut nested = vec![]; |
| match (source.kind(), target.kind()) { |
| // Trait+Kx+'a -> Trait+Ky+'b (upcasts). |
| (&ty::Dynamic(ref data_a, r_a), &ty::Dynamic(ref data_b, r_b)) => { |
| // See `assemble_candidates_for_unsizing` for more info. |
| let iter = data_a |
| .principal() |
| .map(|b| b.map_bound(ty::ExistentialPredicate::Trait)) |
| .into_iter() |
| .chain( |
| data_a |
| .projection_bounds() |
| .map(|b| b.map_bound(ty::ExistentialPredicate::Projection)), |
| ) |
| .chain( |
| data_b |
| .auto_traits() |
| .map(ty::ExistentialPredicate::AutoTrait) |
| .map(ty::Binder::dummy), |
| ); |
| let existential_predicates = tcx.mk_poly_existential_predicates(iter); |
| let source_trait = tcx.mk_dynamic(existential_predicates, r_b); |
| |
| // Require that the traits involved in this upcast are **equal**; |
| // only the **lifetime bound** is changed. |
| let InferOk { obligations, .. } = self |
| .infcx |
| .at(&obligation.cause, obligation.param_env) |
| .sup(target, source_trait) |
| .map_err(|_| Unimplemented)?; |
| nested.extend(obligations); |
| |
| // Register one obligation for 'a: 'b. |
| let cause = ObligationCause::new( |
| obligation.cause.span, |
| obligation.cause.body_id, |
| ObjectCastObligation(target), |
| ); |
| let outlives = ty::OutlivesPredicate(r_a, r_b); |
| nested.push(Obligation::with_depth( |
| cause, |
| obligation.recursion_depth + 1, |
| obligation.param_env, |
| ty::Binder::bind(outlives).to_predicate(tcx), |
| )); |
| } |
| |
| // `T` -> `Trait` |
| (_, &ty::Dynamic(ref data, r)) => { |
| let mut object_dids = data.auto_traits().chain(data.principal_def_id()); |
| if let Some(did) = object_dids.find(|did| !tcx.is_object_safe(*did)) { |
| return Err(TraitNotObjectSafe(did)); |
| } |
| |
| let cause = ObligationCause::new( |
| obligation.cause.span, |
| obligation.cause.body_id, |
| ObjectCastObligation(target), |
| ); |
| |
| let predicate_to_obligation = |predicate| { |
| Obligation::with_depth( |
| cause.clone(), |
| obligation.recursion_depth + 1, |
| obligation.param_env, |
| predicate, |
| ) |
| }; |
| |
| // Create obligations: |
| // - Casting `T` to `Trait` |
| // - For all the various builtin bounds attached to the object cast. (In other |
| // words, if the object type is `Foo + Send`, this would create an obligation for |
| // the `Send` check.) |
| // - Projection predicates |
| nested.extend( |
| data.iter().map(|predicate| { |
| predicate_to_obligation(predicate.with_self_ty(tcx, source)) |
| }), |
| ); |
| |
| // We can only make objects from sized types. |
| let tr = ty::TraitRef::new( |
| tcx.require_lang_item(LangItem::Sized, None), |
| tcx.mk_substs_trait(source, &[]), |
| ); |
| nested.push(predicate_to_obligation(tr.without_const().to_predicate(tcx))); |
| |
| // If the type is `Foo + 'a`, ensure that the type |
| // being cast to `Foo + 'a` outlives `'a`: |
| let outlives = ty::OutlivesPredicate(source, r); |
| nested.push(predicate_to_obligation(ty::Binder::dummy(outlives).to_predicate(tcx))); |
| } |
| |
| // `[T; n]` -> `[T]` |
| (&ty::Array(a, _), &ty::Slice(b)) => { |
| let InferOk { obligations, .. } = self |
| .infcx |
| .at(&obligation.cause, obligation.param_env) |
| .eq(b, a) |
| .map_err(|_| Unimplemented)?; |
| nested.extend(obligations); |
| } |
| |
| // `Struct<T>` -> `Struct<U>` |
| (&ty::Adt(def, substs_a), &ty::Adt(_, substs_b)) => { |
| let maybe_unsizing_param_idx = |arg: GenericArg<'tcx>| match arg.unpack() { |
| GenericArgKind::Type(ty) => match ty.kind() { |
| ty::Param(p) => Some(p.index), |
| _ => None, |
| }, |
| |
| // Lifetimes aren't allowed to change during unsizing. |
| GenericArgKind::Lifetime(_) => None, |
| |
| GenericArgKind::Const(ct) => match ct.val { |
| ty::ConstKind::Param(p) => Some(p.index), |
| _ => None, |
| }, |
| }; |
| |
| // The last field of the structure has to exist and contain type/const parameters. |
| let (tail_field, prefix_fields) = |
| def.non_enum_variant().fields.split_last().ok_or(Unimplemented)?; |
| let tail_field_ty = tcx.type_of(tail_field.did); |
| |
| let mut unsizing_params = GrowableBitSet::new_empty(); |
| let mut found = false; |
| for arg in tail_field_ty.walk() { |
| if let Some(i) = maybe_unsizing_param_idx(arg) { |
| unsizing_params.insert(i); |
| found = true; |
| } |
| } |
| if !found { |
| return Err(Unimplemented); |
| } |
| |
| // Ensure none of the other fields mention the parameters used |
| // in unsizing. |
| // FIXME(eddyb) cache this (including computing `unsizing_params`) |
| // by putting it in a query; it would only need the `DefId` as it |
| // looks at declared field types, not anything substituted. |
| for field in prefix_fields { |
| let ty = tcx.normalize_consts(tcx.type_of(field.did)); |
| |
| for arg in ty.walk() { |
| if let Some(i) = maybe_unsizing_param_idx(arg) { |
| if unsizing_params.contains(i) { |
| return Err(Unimplemented); |
| } |
| } |
| } |
| } |
| |
| // Extract `TailField<T>` and `TailField<U>` from `Struct<T>` and `Struct<U>`. |
| let source_tail = tail_field_ty.subst(tcx, substs_a); |
| let target_tail = tail_field_ty.subst(tcx, substs_b); |
| |
| // Check that the source struct with the target's |
| // unsizing parameters is equal to the target. |
| let substs = tcx.mk_substs(substs_a.iter().enumerate().map(|(i, k)| { |
| if unsizing_params.contains(i as u32) { substs_b[i] } else { k } |
| })); |
| let new_struct = tcx.mk_adt(def, substs); |
| let InferOk { obligations, .. } = self |
| .infcx |
| .at(&obligation.cause, obligation.param_env) |
| .eq(target, new_struct) |
| .map_err(|_| Unimplemented)?; |
| nested.extend(obligations); |
| |
| // Construct the nested `TailField<T>: Unsize<TailField<U>>` predicate. |
| nested.push(predicate_for_trait_def( |
| tcx, |
| obligation.param_env, |
| obligation.cause.clone(), |
| obligation.predicate.def_id(), |
| obligation.recursion_depth + 1, |
| source_tail, |
| &[target_tail.into()], |
| )); |
| } |
| |
| // `(.., T)` -> `(.., U)` |
| (&ty::Tuple(tys_a), &ty::Tuple(tys_b)) => { |
| assert_eq!(tys_a.len(), tys_b.len()); |
| |
| // The last field of the tuple has to exist. |
| let (&a_last, a_mid) = tys_a.split_last().ok_or(Unimplemented)?; |
| let &b_last = tys_b.last().unwrap(); |
| |
| // Check that the source tuple with the target's |
| // last element is equal to the target. |
| let new_tuple = tcx.mk_tup( |
| a_mid.iter().map(|k| k.expect_ty()).chain(iter::once(b_last.expect_ty())), |
| ); |
| let InferOk { obligations, .. } = self |
| .infcx |
| .at(&obligation.cause, obligation.param_env) |
| .eq(target, new_tuple) |
| .map_err(|_| Unimplemented)?; |
| nested.extend(obligations); |
| |
| // Construct the nested `T: Unsize<U>` predicate. |
| nested.push(ensure_sufficient_stack(|| { |
| predicate_for_trait_def( |
| tcx, |
| obligation.param_env, |
| obligation.cause.clone(), |
| obligation.predicate.def_id(), |
| obligation.recursion_depth + 1, |
| a_last.expect_ty(), |
| &[b_last], |
| ) |
| })); |
| } |
| |
| _ => bug!(), |
| }; |
| |
| Ok(ImplSourceBuiltinData { nested }) |
| } |
| } |
