| //! 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_index::bit_set::GrowableBitSet; |
| use rustc_infer::infer::InferOk; |
| 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::{self, normalize_with_depth}; |
| 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> { |
| pub(super) fn confirm_candidate( |
| &mut self, |
| obligation: &TraitObligation<'tcx>, |
| candidate: SelectionCandidate<'tcx>, |
| ) -> Result<Selection<'tcx>, SelectionError<'tcx>> { |
| debug!("confirm_candidate({:?}, {:?})", obligation, candidate); |
| |
| 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); |
| Ok(ImplSource::Param(obligations)) |
| } |
| |
| 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 => { |
| self.confirm_projection_candidate(obligation); |
| Ok(ImplSource::Param(Vec::new())) |
| } |
| |
| 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)) |
| } |
| |
| ObjectCandidate => { |
| let data = self.confirm_object_candidate(obligation); |
| Ok(ImplSource::Object(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())) |
| } |
| |
| BuiltinUnsizeCandidate => { |
| let data = self.confirm_builtin_unsize_candidate(obligation)?; |
| Ok(ImplSource::Builtin(data)) |
| } |
| } |
| } |
| |
| fn confirm_projection_candidate(&mut self, obligation: &TraitObligation<'tcx>) { |
| self.infcx.commit_unconditionally(|_| { |
| let result = self.match_projection_obligation_against_definition_bounds(obligation); |
| assert!(result); |
| }) |
| } |
| |
| fn confirm_param_candidate( |
| &mut self, |
| obligation: &TraitObligation<'tcx>, |
| param: ty::PolyTraitRef<'tcx>, |
| ) -> Vec<PredicateObligation<'tcx>> { |
| debug!("confirm_param_candidate({:?},{:?})", obligation, param); |
| |
| // 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!("confirm_builtin_candidate({:?}, {:?})", obligation, has_nested); |
| |
| 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!("confirm_builtin_candidate: obligations={:?}", 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!("confirm_auto_impl_candidate({:?}, {:?})", obligation, trait_def_id); |
| |
| let types = obligation.predicate.map_bound(|inner| { |
| let self_ty = self.infcx.shallow_resolve(inner.self_ty()); |
| 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!("vtable_auto_impl: nested={:?}", nested); |
| 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!("vtable_auto_impl: obligations={:?}", obligations); |
| |
| ImplSourceAutoImplData { trait_def_id, nested: obligations } |
| }) |
| } |
| |
| fn confirm_impl_candidate( |
| &mut self, |
| obligation: &TraitObligation<'tcx>, |
| impl_def_id: DefId, |
| ) -> ImplSourceUserDefinedData<'tcx, PredicateObligation<'tcx>> { |
| debug!("confirm_impl_candidate({:?},{:?})", obligation, impl_def_id); |
| |
| // 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!("confirm_impl_candidate: substs={:?}", 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, |
| mut substs: Normalized<'tcx, SubstsRef<'tcx>>, |
| cause: ObligationCause<'tcx>, |
| recursion_depth: usize, |
| param_env: ty::ParamEnv<'tcx>, |
| ) -> ImplSourceUserDefinedData<'tcx, PredicateObligation<'tcx>> { |
| debug!( |
| "vtable_impl(impl_def_id={:?}, substs={:?}, recursion_depth={})", |
| impl_def_id, substs, recursion_depth, |
| ); |
| |
| let mut impl_obligations = self.impl_or_trait_obligations( |
| cause, |
| recursion_depth, |
| param_env, |
| impl_def_id, |
| &substs.value, |
| ); |
| |
| debug!( |
| "vtable_impl: impl_def_id={:?} impl_obligations={:?}", |
| impl_def_id, impl_obligations |
| ); |
| |
| // 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.append(&mut substs.obligations); |
| |
| ImplSourceUserDefinedData { impl_def_id, substs: substs.value, nested: impl_obligations } |
| } |
| |
| fn confirm_object_candidate( |
| &mut self, |
| obligation: &TraitObligation<'tcx>, |
| ) -> ImplSourceObjectData<'tcx, PredicateObligation<'tcx>> { |
| debug!("confirm_object_candidate({:?})", obligation); |
| |
| // FIXME(nmatsakis) skipping binder here seems wrong -- we should |
| // probably flatten the binder from the obligation and the binder |
| // from the object. Have to try to make a broken test case that |
| // results. |
| let self_ty = self.infcx.shallow_resolve(obligation.self_ty().skip_binder()); |
| let poly_trait_ref = match self_ty.kind() { |
| ty::Dynamic(data, ..) => data |
| .principal() |
| .unwrap_or_else(|| { |
| span_bug!(obligation.cause.span, "object candidate with no principal") |
| }) |
| .with_self_ty(self.tcx(), self_ty), |
| _ => span_bug!(obligation.cause.span, "object candidate with non-object"), |
| }; |
| |
| let mut upcast_trait_ref = None; |
| let mut nested = vec![]; |
| let vtable_base; |
| |
| { |
| let tcx = self.tcx(); |
| |
| // We want to find the first supertrait in the list of |
| // supertraits that we can unify with, and do that |
| // unification. We know that there is exactly one in the list |
| // where we can unify, because otherwise select would have |
| // reported an ambiguity. (When we do find a match, also |
| // record it for later.) |
| let nonmatching = util::supertraits(tcx, poly_trait_ref).take_while(|&t| { |
| match self.infcx.commit_if_ok(|_| self.match_poly_trait_ref(obligation, t)) { |
| Ok(obligations) => { |
| upcast_trait_ref = Some(t); |
| nested.extend(obligations); |
| false |
| } |
| Err(_) => true, |
| } |
| }); |
| |
| // Additionally, 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. |
| vtable_base = nonmatching.map(|t| super::util::count_own_vtable_entries(tcx, t)).sum(); |
| } |
| |
| ImplSourceObjectData { upcast_trait_ref: upcast_trait_ref.unwrap(), vtable_base, nested } |
| } |
| |
| fn confirm_fn_pointer_candidate( |
| &mut self, |
| obligation: &TraitObligation<'tcx>, |
| ) -> Result<ImplSourceFnPointerData<'tcx, PredicateObligation<'tcx>>, SelectionError<'tcx>> |
| { |
| debug!("confirm_fn_pointer_candidate({:?})", obligation); |
| |
| // 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, obligations } = ensure_sufficient_stack(|| { |
| project::normalize_with_depth( |
| self, |
| obligation.param_env, |
| obligation.cause.clone(), |
| obligation.recursion_depth + 1, |
| &trait_ref, |
| ) |
| }); |
| |
| 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!("confirm_trait_alias_candidate({:?}, {:?})", obligation, alias_def_id); |
| |
| 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!( |
| "confirm_trait_alias_candidate: trait_def_id={:?} trait_obligations={:?}", |
| trait_def_id, trait_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!("confirm_generator_candidate({:?},{:?},{:?})", obligation, generator_def_id, substs); |
| |
| 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!( |
| "confirm_generator_candidate(generator_def_id={:?}, \ |
| trait_ref={:?}, obligations={:?})", |
| generator_def_id, trait_ref, 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!("confirm_closure_candidate({:?})", obligation); |
| |
| 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!( |
| "confirm_closure_candidate(closure_def_id={:?}, trait_ref={:?}, obligations={:?})", |
| closure_def_id, trait_ref, 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!("confirm_builtin_unsize_candidate(source={:?}, target={:?})", source, target); |
| |
| 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 existential_predicates = data_a.map_bound(|data_a| { |
| let iter = data_a |
| .principal() |
| .map(ty::ExistentialPredicate::Trait) |
| .into_iter() |
| .chain(data_a.projection_bounds().map(ty::ExistentialPredicate::Projection)) |
| .chain(data_b.auto_traits().map(ty::ExistentialPredicate::AutoTrait)); |
| tcx.mk_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 { |
| for arg in tcx.type_of(field.did).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 }) |
| } |
| } |
