| //! 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 std::ops::ControlFlow; |
| |
| use rustc_ast::Mutability; |
| use rustc_data_structures::stack::ensure_sufficient_stack; |
| use rustc_hir::lang_items::LangItem; |
| use rustc_infer::infer::{DefineOpaqueTypes, HigherRankedType, InferOk}; |
| use rustc_infer::traits::ObligationCauseCode; |
| use rustc_middle::traits::{BuiltinImplSource, SignatureMismatchData}; |
| use rustc_middle::ty::{self, GenericArgsRef, Ty, TyCtxt, Upcast}; |
| use rustc_middle::{bug, span_bug}; |
| use rustc_span::def_id::DefId; |
| use rustc_type_ir::elaborate; |
| use thin_vec::thin_vec; |
| use tracing::{debug, instrument}; |
| |
| use super::SelectionCandidate::{self, *}; |
| use super::{BuiltinImplConditions, PredicateObligations, SelectionContext}; |
| use crate::traits::normalize::{normalize_with_depth, normalize_with_depth_to}; |
| use crate::traits::util::{self, closure_trait_ref_and_return_type}; |
| use crate::traits::{ |
| ImplSource, ImplSourceUserDefinedData, Normalized, Obligation, ObligationCause, |
| PolyTraitObligation, PredicateObligation, Selection, SelectionError, SignatureMismatch, |
| TraitDynIncompatible, TraitObligation, Unimplemented, |
| }; |
| |
| impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> { |
| #[instrument(level = "debug", skip(self))] |
| pub(super) fn confirm_candidate( |
| &mut self, |
| obligation: &PolyTraitObligation<'tcx>, |
| candidate: SelectionCandidate<'tcx>, |
| ) -> Result<Selection<'tcx>, SelectionError<'tcx>> { |
| Ok(match candidate { |
| SizedCandidate { has_nested } => { |
| let data = self.confirm_builtin_candidate(obligation, has_nested); |
| ImplSource::Builtin(BuiltinImplSource::Misc, data) |
| } |
| |
| BuiltinCandidate { has_nested } => { |
| let data = self.confirm_builtin_candidate(obligation, has_nested); |
| ImplSource::Builtin(BuiltinImplSource::Misc, data) |
| } |
| |
| TransmutabilityCandidate => { |
| let data = self.confirm_transmutability_candidate(obligation)?; |
| ImplSource::Builtin(BuiltinImplSource::Misc, data) |
| } |
| |
| ParamCandidate(param) => { |
| let obligations = |
| self.confirm_param_candidate(obligation, param.map_bound(|t| t.trait_ref)); |
| ImplSource::Param(obligations) |
| } |
| |
| ImplCandidate(impl_def_id) => { |
| ImplSource::UserDefined(self.confirm_impl_candidate(obligation, impl_def_id)) |
| } |
| |
| AutoImplCandidate => { |
| let data = self.confirm_auto_impl_candidate(obligation)?; |
| ImplSource::Builtin(BuiltinImplSource::Misc, data) |
| } |
| |
| ProjectionCandidate(idx) => { |
| let obligations = self.confirm_projection_candidate(obligation, idx)?; |
| ImplSource::Param(obligations) |
| } |
| |
| ObjectCandidate(idx) => self.confirm_object_candidate(obligation, idx)?, |
| |
| ClosureCandidate { .. } => { |
| let vtable_closure = self.confirm_closure_candidate(obligation)?; |
| ImplSource::Builtin(BuiltinImplSource::Misc, vtable_closure) |
| } |
| |
| AsyncClosureCandidate => { |
| let vtable_closure = self.confirm_async_closure_candidate(obligation)?; |
| ImplSource::Builtin(BuiltinImplSource::Misc, vtable_closure) |
| } |
| |
| // No nested obligations or confirmation process. The checks that we do in |
| // candidate assembly are sufficient. |
| AsyncFnKindHelperCandidate => { |
| ImplSource::Builtin(BuiltinImplSource::Misc, PredicateObligations::new()) |
| } |
| |
| CoroutineCandidate => { |
| let vtable_coroutine = self.confirm_coroutine_candidate(obligation)?; |
| ImplSource::Builtin(BuiltinImplSource::Misc, vtable_coroutine) |
| } |
| |
| FutureCandidate => { |
| let vtable_future = self.confirm_future_candidate(obligation)?; |
| ImplSource::Builtin(BuiltinImplSource::Misc, vtable_future) |
| } |
| |
| IteratorCandidate => { |
| let vtable_iterator = self.confirm_iterator_candidate(obligation)?; |
| ImplSource::Builtin(BuiltinImplSource::Misc, vtable_iterator) |
| } |
| |
| AsyncIteratorCandidate => { |
| let vtable_iterator = self.confirm_async_iterator_candidate(obligation)?; |
| ImplSource::Builtin(BuiltinImplSource::Misc, vtable_iterator) |
| } |
| |
| FnPointerCandidate => { |
| let data = self.confirm_fn_pointer_candidate(obligation)?; |
| ImplSource::Builtin(BuiltinImplSource::Misc, data) |
| } |
| |
| TraitAliasCandidate => { |
| let data = self.confirm_trait_alias_candidate(obligation); |
| ImplSource::Builtin(BuiltinImplSource::Misc, 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. |
| ImplSource::Builtin(BuiltinImplSource::Misc, PredicateObligations::new()) |
| } |
| |
| BuiltinUnsizeCandidate => self.confirm_builtin_unsize_candidate(obligation)?, |
| |
| TraitUpcastingUnsizeCandidate(idx) => { |
| self.confirm_trait_upcasting_unsize_candidate(obligation, idx)? |
| } |
| |
| BikeshedGuaranteedNoDropCandidate => { |
| self.confirm_bikeshed_guaranteed_no_drop_candidate(obligation) |
| } |
| }) |
| } |
| |
| fn confirm_projection_candidate( |
| &mut self, |
| obligation: &PolyTraitObligation<'tcx>, |
| idx: usize, |
| ) -> Result<PredicateObligations<'tcx>, SelectionError<'tcx>> { |
| let tcx = self.tcx(); |
| |
| let placeholder_trait_predicate = |
| self.infcx.enter_forall_and_leak_universe(obligation.predicate).trait_ref; |
| let placeholder_self_ty = self.infcx.shallow_resolve(placeholder_trait_predicate.self_ty()); |
| let candidate_predicate = self |
| .for_each_item_bound( |
| placeholder_self_ty, |
| |_, clause, clause_idx| { |
| if clause_idx == idx { |
| ControlFlow::Break(clause) |
| } else { |
| ControlFlow::Continue(()) |
| } |
| }, |
| || unreachable!(), |
| ) |
| .break_value() |
| .expect("expected to index into clause that exists"); |
| let candidate = candidate_predicate |
| .as_trait_clause() |
| .expect("projection candidate is not a trait predicate") |
| .map_bound(|t| t.trait_ref); |
| |
| let candidate = self.infcx.instantiate_binder_with_fresh_vars( |
| obligation.cause.span, |
| HigherRankedType, |
| candidate, |
| ); |
| let mut obligations = PredicateObligations::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 |
| .at(&obligation.cause, obligation.param_env) |
| .eq(DefineOpaqueTypes::No, placeholder_trait_predicate, candidate) |
| .map(|InferOk { obligations, .. }| obligations) |
| .map_err(|_| Unimplemented)?, |
| ); |
| |
| // FIXME(compiler-errors): I don't think this is needed. |
| if let ty::Alias(ty::Projection, alias_ty) = placeholder_self_ty.kind() { |
| let predicates = tcx.predicates_of(alias_ty.def_id).instantiate_own(tcx, alias_ty.args); |
| for (predicate, _) in 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( |
| self.tcx(), |
| obligation.cause.clone(), |
| obligation.recursion_depth + 1, |
| obligation.param_env, |
| normalized, |
| )); |
| } |
| } |
| |
| Ok(obligations) |
| } |
| |
| fn confirm_param_candidate( |
| &mut self, |
| obligation: &PolyTraitObligation<'tcx>, |
| param: ty::PolyTraitRef<'tcx>, |
| ) -> PredicateObligations<'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: &PolyTraitObligation<'tcx>, |
| has_nested: bool, |
| ) -> PredicateObligations<'tcx> { |
| debug!(?obligation, ?has_nested, "confirm_builtin_candidate"); |
| |
| let tcx = self.tcx(); |
| let obligations = if has_nested { |
| let trait_def = obligation.predicate.def_id(); |
| let conditions = if tcx.is_lang_item(trait_def, LangItem::Sized) { |
| self.sized_conditions(obligation) |
| } else if tcx.is_lang_item(trait_def, LangItem::Copy) { |
| self.copy_clone_conditions(obligation) |
| } else if tcx.is_lang_item(trait_def, LangItem::Clone) { |
| self.copy_clone_conditions(obligation) |
| } else if tcx.is_lang_item(trait_def, LangItem::FusedIterator) { |
| self.fused_iterator_conditions(obligation) |
| } else { |
| bug!("unexpected builtin trait {:?}", trait_def) |
| }; |
| let BuiltinImplConditions::Where(types) = conditions else { |
| bug!("obligation {:?} had matched a builtin impl but now doesn't", obligation); |
| }; |
| let types = self.infcx.enter_forall_and_leak_universe(types); |
| |
| let cause = obligation.derived_cause(ObligationCauseCode::BuiltinDerived); |
| self.collect_predicates_for_types( |
| obligation.param_env, |
| cause, |
| obligation.recursion_depth + 1, |
| trait_def, |
| types, |
| ) |
| } else { |
| PredicateObligations::new() |
| }; |
| |
| debug!(?obligations); |
| |
| obligations |
| } |
| |
| #[instrument(level = "debug", skip(self))] |
| fn confirm_transmutability_candidate( |
| &mut self, |
| obligation: &PolyTraitObligation<'tcx>, |
| ) -> Result<PredicateObligations<'tcx>, SelectionError<'tcx>> { |
| use rustc_transmute::{Answer, Assume, Condition}; |
| |
| /// Generate sub-obligations for reference-to-reference transmutations. |
| fn reference_obligations<'tcx>( |
| tcx: TyCtxt<'tcx>, |
| obligation: &PolyTraitObligation<'tcx>, |
| (src_lifetime, src_ty, src_mut): (ty::Region<'tcx>, Ty<'tcx>, Mutability), |
| (dst_lifetime, dst_ty, dst_mut): (ty::Region<'tcx>, Ty<'tcx>, Mutability), |
| assume: Assume, |
| ) -> PredicateObligations<'tcx> { |
| let make_transmute_obl = |src, dst| { |
| let transmute_trait = obligation.predicate.def_id(); |
| let assume = obligation.predicate.skip_binder().trait_ref.args.const_at(2); |
| let trait_ref = ty::TraitRef::new( |
| tcx, |
| transmute_trait, |
| [ |
| ty::GenericArg::from(dst), |
| ty::GenericArg::from(src), |
| ty::GenericArg::from(assume), |
| ], |
| ); |
| Obligation::with_depth( |
| tcx, |
| obligation.cause.clone(), |
| obligation.recursion_depth + 1, |
| obligation.param_env, |
| trait_ref, |
| ) |
| }; |
| |
| let make_freeze_obl = |ty| { |
| let trait_ref = ty::TraitRef::new( |
| tcx, |
| tcx.require_lang_item(LangItem::Freeze, None), |
| [ty::GenericArg::from(ty)], |
| ); |
| Obligation::with_depth( |
| tcx, |
| obligation.cause.clone(), |
| obligation.recursion_depth + 1, |
| obligation.param_env, |
| trait_ref, |
| ) |
| }; |
| |
| let make_outlives_obl = |target, region| { |
| let outlives = ty::OutlivesPredicate(target, region); |
| Obligation::with_depth( |
| tcx, |
| obligation.cause.clone(), |
| obligation.recursion_depth + 1, |
| obligation.param_env, |
| outlives, |
| ) |
| }; |
| |
| // Given a transmutation from `&'a (mut) Src` and `&'dst (mut) Dst`, |
| // it is always the case that `Src` must be transmutable into `Dst`, |
| // and that that `'src` must outlive `'dst`. |
| let mut obls = PredicateObligations::with_capacity(1); |
| obls.push(make_transmute_obl(src_ty, dst_ty)); |
| if !assume.lifetimes { |
| obls.push(make_outlives_obl(src_lifetime, dst_lifetime)); |
| } |
| |
| // Given a transmutation from `&Src`, both `Src` and `Dst` must be |
| // `Freeze`, otherwise, using the transmuted value could lead to |
| // data races. |
| if src_mut == Mutability::Not { |
| obls.extend([make_freeze_obl(src_ty), make_freeze_obl(dst_ty)]) |
| } |
| |
| // Given a transmutation into `&'dst mut Dst`, it also must be the |
| // case that `Dst` is transmutable into `Src`. For example, |
| // transmuting bool -> u8 is OK as long as you can't update that u8 |
| // to be > 1, because you could later transmute the u8 back to a |
| // bool and get undefined behavior. It also must be the case that |
| // `'dst` lives exactly as long as `'src`. |
| if dst_mut == Mutability::Mut { |
| obls.push(make_transmute_obl(dst_ty, src_ty)); |
| if !assume.lifetimes { |
| obls.push(make_outlives_obl(dst_lifetime, src_lifetime)); |
| } |
| } |
| |
| obls |
| } |
| |
| /// Flatten the `Condition` tree into a conjunction of obligations. |
| #[instrument(level = "debug", skip(tcx, obligation))] |
| fn flatten_answer_tree<'tcx>( |
| tcx: TyCtxt<'tcx>, |
| obligation: &PolyTraitObligation<'tcx>, |
| cond: Condition<rustc_transmute::layout::rustc::Ref<'tcx>>, |
| assume: Assume, |
| ) -> PredicateObligations<'tcx> { |
| match cond { |
| // FIXME(bryangarza): Add separate `IfAny` case, instead of treating as `IfAll` |
| // Not possible until the trait solver supports disjunctions of obligations |
| Condition::IfAll(conds) | Condition::IfAny(conds) => conds |
| .into_iter() |
| .flat_map(|cond| flatten_answer_tree(tcx, obligation, cond, assume)) |
| .collect(), |
| Condition::IfTransmutable { src, dst } => reference_obligations( |
| tcx, |
| obligation, |
| (src.lifetime, src.ty, src.mutability), |
| (dst.lifetime, dst.ty, dst.mutability), |
| assume, |
| ), |
| } |
| } |
| |
| let predicate = self.infcx.enter_forall_and_leak_universe(obligation.predicate); |
| |
| let mut assume = predicate.trait_ref.args.const_at(2); |
| // FIXME(mgca): We should shallowly normalize this. |
| if self.tcx().features().generic_const_exprs() { |
| assume = crate::traits::evaluate_const(self.infcx, assume, obligation.param_env) |
| } |
| let Some(assume) = rustc_transmute::Assume::from_const(self.infcx.tcx, assume) else { |
| return Err(Unimplemented); |
| }; |
| |
| let dst = predicate.trait_ref.args.type_at(0); |
| let src = predicate.trait_ref.args.type_at(1); |
| |
| debug!(?src, ?dst); |
| let mut transmute_env = rustc_transmute::TransmuteTypeEnv::new(self.infcx.tcx); |
| let maybe_transmutable = |
| transmute_env.is_transmutable(rustc_transmute::Types { dst, src }, assume); |
| |
| let fully_flattened = match maybe_transmutable { |
| Answer::No(_) => Err(Unimplemented)?, |
| Answer::If(cond) => flatten_answer_tree(self.tcx(), obligation, cond, assume), |
| Answer::Yes => PredicateObligations::new(), |
| }; |
| |
| debug!(?fully_flattened); |
| Ok(fully_flattened) |
| } |
| |
| /// This handles the case where an `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: &PolyTraitObligation<'tcx>, |
| ) -> Result<PredicateObligations<'tcx>, SelectionError<'tcx>> { |
| ensure_sufficient_stack(|| { |
| assert_eq!(obligation.predicate.polarity(), ty::PredicatePolarity::Positive); |
| |
| let self_ty = |
| obligation.predicate.self_ty().map_bound(|ty| self.infcx.shallow_resolve(ty)); |
| |
| let types = self.constituent_types_for_ty(self_ty)?; |
| let types = self.infcx.enter_forall_and_leak_universe(types); |
| |
| let cause = obligation.derived_cause(ObligationCauseCode::BuiltinDerived); |
| let obligations = self.collect_predicates_for_types( |
| obligation.param_env, |
| cause, |
| obligation.recursion_depth + 1, |
| obligation.predicate.def_id(), |
| types, |
| ); |
| |
| Ok(obligations) |
| }) |
| } |
| |
| fn confirm_impl_candidate( |
| &mut self, |
| obligation: &PolyTraitObligation<'tcx>, |
| impl_def_id: DefId, |
| ) -> ImplSourceUserDefinedData<'tcx, PredicateObligation<'tcx>> { |
| debug!(?obligation, ?impl_def_id, "confirm_impl_candidate"); |
| |
| // First, create the generic parameters by matching the impl again, |
| // this time not in a probe. |
| let args = self.rematch_impl(impl_def_id, obligation); |
| debug!(?args, "impl args"); |
| ensure_sufficient_stack(|| { |
| self.vtable_impl( |
| impl_def_id, |
| args, |
| &obligation.cause, |
| obligation.recursion_depth + 1, |
| obligation.param_env, |
| obligation.predicate, |
| ) |
| }) |
| } |
| |
| fn vtable_impl( |
| &mut self, |
| impl_def_id: DefId, |
| args: Normalized<'tcx, GenericArgsRef<'tcx>>, |
| cause: &ObligationCause<'tcx>, |
| recursion_depth: usize, |
| param_env: ty::ParamEnv<'tcx>, |
| parent_trait_pred: ty::Binder<'tcx, ty::TraitPredicate<'tcx>>, |
| ) -> ImplSourceUserDefinedData<'tcx, PredicateObligation<'tcx>> { |
| debug!(?impl_def_id, ?args, ?recursion_depth, "vtable_impl"); |
| |
| let mut impl_obligations = self.impl_or_trait_obligations( |
| cause, |
| recursion_depth, |
| param_env, |
| impl_def_id, |
| args.value, |
| parent_trait_pred, |
| ); |
| |
| debug!(?impl_obligations, "vtable_impl"); |
| |
| // Because of RFC447, the impl-trait-ref and obligations |
| // are sufficient to determine the impl args, 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(args.obligations); |
| |
| ImplSourceUserDefinedData { impl_def_id, args: args.value, nested: impl_obligations } |
| } |
| |
| fn confirm_object_candidate( |
| &mut self, |
| obligation: &PolyTraitObligation<'tcx>, |
| index: usize, |
| ) -> Result<ImplSource<'tcx, PredicateObligation<'tcx>>, SelectionError<'tcx>> { |
| let tcx = self.tcx(); |
| debug!(?obligation, ?index, "confirm_object_candidate"); |
| |
| let trait_predicate = self.infcx.enter_forall_and_leak_universe(obligation.predicate); |
| let self_ty = self.infcx.shallow_resolve(trait_predicate.self_ty()); |
| let ty::Dynamic(data, ..) = *self_ty.kind() else { |
| 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.instantiate_binder_with_fresh_vars( |
| obligation.cause.span, |
| HigherRankedType, |
| object_trait_ref, |
| ); |
| let object_trait_ref = object_trait_ref.with_self_ty(self.tcx(), self_ty); |
| |
| let mut nested = PredicateObligations::new(); |
| |
| let mut supertraits = util::supertraits(tcx, ty::Binder::dummy(object_trait_ref)); |
| let unnormalized_upcast_trait_ref = |
| supertraits.nth(index).expect("supertraits iterator no longer has as many elements"); |
| |
| let upcast_trait_ref = self.infcx.instantiate_binder_with_fresh_vars( |
| obligation.cause.span, |
| HigherRankedType, |
| unnormalized_upcast_trait_ref, |
| ); |
| let upcast_trait_ref = normalize_with_depth_to( |
| self, |
| obligation.param_env, |
| obligation.cause.clone(), |
| obligation.recursion_depth + 1, |
| upcast_trait_ref, |
| &mut nested, |
| ); |
| |
| nested.extend( |
| self.infcx |
| .at(&obligation.cause, obligation.param_env) |
| .eq(DefineOpaqueTypes::No, trait_predicate.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 (supertrait, _) in tcx |
| .explicit_super_predicates_of(trait_predicate.def_id()) |
| .iter_instantiated_copied(tcx, trait_predicate.trait_ref.args) |
| { |
| let normalized_supertrait = normalize_with_depth_to( |
| self, |
| obligation.param_env, |
| obligation.cause.clone(), |
| obligation.recursion_depth + 1, |
| supertrait, |
| &mut nested, |
| ); |
| nested.push(obligation.with(tcx, normalized_supertrait)); |
| } |
| |
| let assoc_types: Vec<_> = tcx |
| .associated_items(trait_predicate.def_id()) |
| .in_definition_order() |
| // Associated types that require `Self: Sized` do not show up in the built-in |
| // implementation of `Trait for dyn Trait`, and can be dropped here. |
| .filter(|item| !tcx.generics_require_sized_self(item.def_id)) |
| .filter_map(|item| if item.is_type() { Some(item.def_id) } else { None }) |
| .collect(); |
| |
| for assoc_type in assoc_types { |
| let defs: &ty::Generics = tcx.generics_of(assoc_type); |
| |
| if !defs.own_params.is_empty() { |
| tcx.dcx().span_delayed_bug( |
| obligation.cause.span, |
| "GATs in trait object shouldn't have been considered", |
| ); |
| return Err(SelectionError::TraitDynIncompatible(trait_predicate.trait_ref.def_id)); |
| } |
| |
| // 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).transpose_iter() { |
| let normalized_bound = normalize_with_depth_to( |
| self, |
| obligation.param_env, |
| obligation.cause.clone(), |
| obligation.recursion_depth + 1, |
| bound.instantiate(tcx, trait_predicate.trait_ref.args), |
| &mut nested, |
| ); |
| nested.push(obligation.with(tcx, normalized_bound)); |
| } |
| } |
| |
| debug!(?nested, "object nested obligations"); |
| |
| Ok(ImplSource::Builtin(BuiltinImplSource::Object(index), nested)) |
| } |
| |
| fn confirm_fn_pointer_candidate( |
| &mut self, |
| obligation: &PolyTraitObligation<'tcx>, |
| ) -> Result<PredicateObligations<'tcx>, SelectionError<'tcx>> { |
| debug!(?obligation, "confirm_fn_pointer_candidate"); |
| let placeholder_predicate = self.infcx.enter_forall_and_leak_universe(obligation.predicate); |
| let self_ty = self.infcx.shallow_resolve(placeholder_predicate.self_ty()); |
| |
| let tcx = self.tcx(); |
| let sig = self_ty.fn_sig(tcx); |
| let trait_ref = closure_trait_ref_and_return_type( |
| tcx, |
| obligation.predicate.def_id(), |
| self_ty, |
| sig, |
| util::TupleArgumentsFlag::Yes, |
| ) |
| .map_bound(|(trait_ref, _)| trait_ref); |
| |
| let mut nested = |
| self.equate_trait_refs(obligation.with(tcx, placeholder_predicate), trait_ref)?; |
| let cause = obligation.derived_cause(ObligationCauseCode::BuiltinDerived); |
| |
| // Confirm the `type Output: Sized;` bound that is present on `FnOnce` |
| let output_ty = self.infcx.enter_forall_and_leak_universe(sig.output()); |
| let output_ty = normalize_with_depth_to( |
| self, |
| obligation.param_env, |
| cause.clone(), |
| obligation.recursion_depth, |
| output_ty, |
| &mut nested, |
| ); |
| let tr = ty::TraitRef::new( |
| self.tcx(), |
| self.tcx().require_lang_item(LangItem::Sized, Some(cause.span)), |
| [output_ty], |
| ); |
| nested.push(Obligation::new(self.infcx.tcx, cause, obligation.param_env, tr)); |
| |
| Ok(nested) |
| } |
| |
| fn confirm_trait_alias_candidate( |
| &mut self, |
| obligation: &PolyTraitObligation<'tcx>, |
| ) -> PredicateObligations<'tcx> { |
| debug!(?obligation, "confirm_trait_alias_candidate"); |
| |
| let predicate = self.infcx.enter_forall_and_leak_universe(obligation.predicate); |
| let trait_ref = predicate.trait_ref; |
| let trait_def_id = trait_ref.def_id; |
| let args = trait_ref.args; |
| |
| let trait_obligations = self.impl_or_trait_obligations( |
| &obligation.cause, |
| obligation.recursion_depth, |
| obligation.param_env, |
| trait_def_id, |
| args, |
| obligation.predicate, |
| ); |
| |
| debug!(?trait_def_id, ?trait_obligations, "trait alias obligations"); |
| |
| trait_obligations |
| } |
| |
| fn confirm_coroutine_candidate( |
| &mut self, |
| obligation: &PolyTraitObligation<'tcx>, |
| ) -> Result<PredicateObligations<'tcx>, SelectionError<'tcx>> { |
| let placeholder_predicate = self.infcx.enter_forall_and_leak_universe(obligation.predicate); |
| let self_ty = self.infcx.shallow_resolve(placeholder_predicate.self_ty()); |
| let ty::Coroutine(coroutine_def_id, args) = *self_ty.kind() else { |
| bug!("closure candidate for non-closure {:?}", obligation); |
| }; |
| |
| debug!(?obligation, ?coroutine_def_id, ?args, "confirm_coroutine_candidate"); |
| |
| let coroutine_sig = args.as_coroutine().sig(); |
| |
| let (trait_ref, _, _) = super::util::coroutine_trait_ref_and_outputs( |
| self.tcx(), |
| obligation.predicate.def_id(), |
| self_ty, |
| coroutine_sig, |
| ); |
| |
| let nested = self.equate_trait_refs( |
| obligation.with(self.tcx(), placeholder_predicate), |
| ty::Binder::dummy(trait_ref), |
| )?; |
| debug!(?trait_ref, ?nested, "coroutine candidate obligations"); |
| |
| Ok(nested) |
| } |
| |
| fn confirm_future_candidate( |
| &mut self, |
| obligation: &PolyTraitObligation<'tcx>, |
| ) -> Result<PredicateObligations<'tcx>, SelectionError<'tcx>> { |
| let placeholder_predicate = self.infcx.enter_forall_and_leak_universe(obligation.predicate); |
| let self_ty = self.infcx.shallow_resolve(placeholder_predicate.self_ty()); |
| let ty::Coroutine(coroutine_def_id, args) = *self_ty.kind() else { |
| bug!("closure candidate for non-closure {:?}", obligation); |
| }; |
| |
| debug!(?obligation, ?coroutine_def_id, ?args, "confirm_future_candidate"); |
| |
| let coroutine_sig = args.as_coroutine().sig(); |
| |
| let (trait_ref, _) = super::util::future_trait_ref_and_outputs( |
| self.tcx(), |
| obligation.predicate.def_id(), |
| self_ty, |
| coroutine_sig, |
| ); |
| |
| let nested = self.equate_trait_refs( |
| obligation.with(self.tcx(), placeholder_predicate), |
| ty::Binder::dummy(trait_ref), |
| )?; |
| debug!(?trait_ref, ?nested, "future candidate obligations"); |
| |
| Ok(nested) |
| } |
| |
| fn confirm_iterator_candidate( |
| &mut self, |
| obligation: &PolyTraitObligation<'tcx>, |
| ) -> Result<PredicateObligations<'tcx>, SelectionError<'tcx>> { |
| let placeholder_predicate = self.infcx.enter_forall_and_leak_universe(obligation.predicate); |
| let self_ty = self.infcx.shallow_resolve(placeholder_predicate.self_ty()); |
| let ty::Coroutine(coroutine_def_id, args) = *self_ty.kind() else { |
| bug!("closure candidate for non-closure {:?}", obligation); |
| }; |
| |
| debug!(?obligation, ?coroutine_def_id, ?args, "confirm_iterator_candidate"); |
| |
| let gen_sig = args.as_coroutine().sig(); |
| |
| let (trait_ref, _) = super::util::iterator_trait_ref_and_outputs( |
| self.tcx(), |
| obligation.predicate.def_id(), |
| self_ty, |
| gen_sig, |
| ); |
| |
| let nested = self.equate_trait_refs( |
| obligation.with(self.tcx(), placeholder_predicate), |
| ty::Binder::dummy(trait_ref), |
| )?; |
| debug!(?trait_ref, ?nested, "iterator candidate obligations"); |
| |
| Ok(nested) |
| } |
| |
| fn confirm_async_iterator_candidate( |
| &mut self, |
| obligation: &PolyTraitObligation<'tcx>, |
| ) -> Result<PredicateObligations<'tcx>, SelectionError<'tcx>> { |
| let placeholder_predicate = self.infcx.enter_forall_and_leak_universe(obligation.predicate); |
| let self_ty = self.infcx.shallow_resolve(placeholder_predicate.self_ty()); |
| let ty::Coroutine(coroutine_def_id, args) = *self_ty.kind() else { |
| bug!("closure candidate for non-closure {:?}", obligation); |
| }; |
| |
| debug!(?obligation, ?coroutine_def_id, ?args, "confirm_async_iterator_candidate"); |
| |
| let gen_sig = args.as_coroutine().sig(); |
| |
| let (trait_ref, _) = super::util::async_iterator_trait_ref_and_outputs( |
| self.tcx(), |
| obligation.predicate.def_id(), |
| self_ty, |
| gen_sig, |
| ); |
| |
| let nested = self.equate_trait_refs( |
| obligation.with(self.tcx(), placeholder_predicate), |
| ty::Binder::dummy(trait_ref), |
| )?; |
| debug!(?trait_ref, ?nested, "iterator candidate obligations"); |
| |
| Ok(nested) |
| } |
| |
| #[instrument(skip(self), level = "debug")] |
| fn confirm_closure_candidate( |
| &mut self, |
| obligation: &PolyTraitObligation<'tcx>, |
| ) -> Result<PredicateObligations<'tcx>, SelectionError<'tcx>> { |
| let placeholder_predicate = self.infcx.enter_forall_and_leak_universe(obligation.predicate); |
| let self_ty: Ty<'_> = self.infcx.shallow_resolve(placeholder_predicate.self_ty()); |
| |
| let trait_ref = match *self_ty.kind() { |
| ty::Closure(..) => { |
| self.closure_trait_ref_unnormalized(self_ty, obligation.predicate.def_id()) |
| } |
| ty::CoroutineClosure(_, args) => { |
| args.as_coroutine_closure().coroutine_closure_sig().map_bound(|sig| { |
| ty::TraitRef::new( |
| self.tcx(), |
| obligation.predicate.def_id(), |
| [self_ty, sig.tupled_inputs_ty], |
| ) |
| }) |
| } |
| _ => { |
| bug!("closure candidate for non-closure {:?}", obligation); |
| } |
| }; |
| |
| self.equate_trait_refs(obligation.with(self.tcx(), placeholder_predicate), trait_ref) |
| } |
| |
| #[instrument(skip(self), level = "debug")] |
| fn confirm_async_closure_candidate( |
| &mut self, |
| obligation: &PolyTraitObligation<'tcx>, |
| ) -> Result<PredicateObligations<'tcx>, SelectionError<'tcx>> { |
| let placeholder_predicate = self.infcx.enter_forall_and_leak_universe(obligation.predicate); |
| let self_ty = self.infcx.shallow_resolve(placeholder_predicate.self_ty()); |
| |
| let tcx = self.tcx(); |
| |
| let mut nested = PredicateObligations::new(); |
| let (trait_ref, kind_ty) = match *self_ty.kind() { |
| ty::CoroutineClosure(_, args) => { |
| let args = args.as_coroutine_closure(); |
| let trait_ref = args.coroutine_closure_sig().map_bound(|sig| { |
| ty::TraitRef::new( |
| self.tcx(), |
| obligation.predicate.def_id(), |
| [self_ty, sig.tupled_inputs_ty], |
| ) |
| }); |
| |
| // Note that unlike below, we don't need to check `Future + Sized` for |
| // the output coroutine because they are `Future + Sized` by construction. |
| |
| (trait_ref, args.kind_ty()) |
| } |
| ty::FnDef(..) | ty::FnPtr(..) => { |
| let sig = self_ty.fn_sig(tcx); |
| let trait_ref = sig.map_bound(|sig| { |
| ty::TraitRef::new( |
| self.tcx(), |
| obligation.predicate.def_id(), |
| [self_ty, Ty::new_tup(tcx, sig.inputs())], |
| ) |
| }); |
| |
| // We must additionally check that the return type impls `Future + Sized`. |
| let future_trait_def_id = tcx.require_lang_item(LangItem::Future, None); |
| nested.push(obligation.with( |
| tcx, |
| sig.output().map_bound(|output_ty| { |
| ty::TraitRef::new(tcx, future_trait_def_id, [output_ty]) |
| }), |
| )); |
| let sized_trait_def_id = tcx.require_lang_item(LangItem::Sized, None); |
| nested.push(obligation.with( |
| tcx, |
| sig.output().map_bound(|output_ty| { |
| ty::TraitRef::new(tcx, sized_trait_def_id, [output_ty]) |
| }), |
| )); |
| |
| (trait_ref, Ty::from_closure_kind(tcx, ty::ClosureKind::Fn)) |
| } |
| ty::Closure(_, args) => { |
| let args = args.as_closure(); |
| let sig = args.sig(); |
| let trait_ref = sig.map_bound(|sig| { |
| ty::TraitRef::new( |
| self.tcx(), |
| obligation.predicate.def_id(), |
| [self_ty, sig.inputs()[0]], |
| ) |
| }); |
| |
| // We must additionally check that the return type impls `Future + Sized`. |
| let future_trait_def_id = tcx.require_lang_item(LangItem::Future, None); |
| let placeholder_output_ty = self.infcx.enter_forall_and_leak_universe(sig.output()); |
| nested.push(obligation.with( |
| tcx, |
| ty::TraitRef::new(tcx, future_trait_def_id, [placeholder_output_ty]), |
| )); |
| let sized_trait_def_id = tcx.require_lang_item(LangItem::Sized, None); |
| nested.push(obligation.with( |
| tcx, |
| sig.output().map_bound(|output_ty| { |
| ty::TraitRef::new(tcx, sized_trait_def_id, [output_ty]) |
| }), |
| )); |
| |
| (trait_ref, args.kind_ty()) |
| } |
| _ => bug!("expected callable type for AsyncFn candidate"), |
| }; |
| |
| nested.extend( |
| self.equate_trait_refs(obligation.with(tcx, placeholder_predicate), trait_ref)?, |
| ); |
| |
| let goal_kind = |
| self.tcx().async_fn_trait_kind_from_def_id(obligation.predicate.def_id()).unwrap(); |
| |
| // If we have not yet determiend the `ClosureKind` of the closure or coroutine-closure, |
| // then additionally register an `AsyncFnKindHelper` goal which will fail if the kind |
| // is constrained to an insufficient type later on. |
| if let Some(closure_kind) = self.infcx.shallow_resolve(kind_ty).to_opt_closure_kind() { |
| if !closure_kind.extends(goal_kind) { |
| return Err(SelectionError::Unimplemented); |
| } |
| } else { |
| nested.push(Obligation::new( |
| self.tcx(), |
| obligation.derived_cause(ObligationCauseCode::BuiltinDerived), |
| obligation.param_env, |
| ty::TraitRef::new( |
| self.tcx(), |
| self.tcx().require_lang_item( |
| LangItem::AsyncFnKindHelper, |
| Some(obligation.cause.span), |
| ), |
| [kind_ty, Ty::from_closure_kind(self.tcx(), goal_kind)], |
| ), |
| )); |
| } |
| |
| Ok(nested) |
| } |
| |
| /// 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: |
| /// ```ignore (illustrative) |
| /// 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. |
| #[instrument(skip(self), level = "trace")] |
| fn equate_trait_refs( |
| &mut self, |
| obligation: TraitObligation<'tcx>, |
| found_trait_ref: ty::PolyTraitRef<'tcx>, |
| ) -> Result<PredicateObligations<'tcx>, SelectionError<'tcx>> { |
| let found_trait_ref = self.infcx.instantiate_binder_with_fresh_vars( |
| obligation.cause.span, |
| HigherRankedType, |
| found_trait_ref, |
| ); |
| // Normalize the obligation and expected trait refs together, because why not |
| let Normalized { obligations: nested, value: (obligation_trait_ref, found_trait_ref) } = |
| ensure_sufficient_stack(|| { |
| normalize_with_depth( |
| self, |
| obligation.param_env, |
| obligation.cause.clone(), |
| obligation.recursion_depth + 1, |
| (obligation.predicate.trait_ref, found_trait_ref), |
| ) |
| }); |
| |
| // needed to define opaque types for tests/ui/type-alias-impl-trait/assoc-projection-ice.rs |
| self.infcx |
| .at(&obligation.cause, obligation.param_env) |
| .eq(DefineOpaqueTypes::Yes, obligation_trait_ref, found_trait_ref) |
| .map(|InferOk { mut obligations, .. }| { |
| obligations.extend(nested); |
| obligations |
| }) |
| .map_err(|terr| { |
| SignatureMismatch(Box::new(SignatureMismatchData { |
| expected_trait_ref: obligation_trait_ref, |
| found_trait_ref, |
| terr, |
| })) |
| }) |
| } |
| |
| fn confirm_trait_upcasting_unsize_candidate( |
| &mut self, |
| obligation: &PolyTraitObligation<'tcx>, |
| idx: usize, |
| ) -> Result<ImplSource<'tcx, 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 predicate = obligation.predicate.no_bound_vars().unwrap(); |
| let a_ty = self.infcx.shallow_resolve(predicate.self_ty()); |
| let b_ty = self.infcx.shallow_resolve(predicate.trait_ref.args.type_at(1)); |
| |
| let ty::Dynamic(a_data, a_region, ty::Dyn) = *a_ty.kind() else { |
| bug!("expected `dyn` type in `confirm_trait_upcasting_unsize_candidate`") |
| }; |
| let ty::Dynamic(b_data, b_region, ty::Dyn) = *b_ty.kind() else { |
| bug!("expected `dyn` type in `confirm_trait_upcasting_unsize_candidate`") |
| }; |
| |
| let source_principal = a_data.principal().unwrap().with_self_ty(tcx, a_ty); |
| let unnormalized_upcast_principal = |
| util::supertraits(tcx, source_principal).nth(idx).unwrap(); |
| |
| let nested = self |
| .match_upcast_principal( |
| obligation, |
| unnormalized_upcast_principal, |
| a_data, |
| b_data, |
| a_region, |
| b_region, |
| )? |
| .expect("did not expect ambiguity during confirmation"); |
| |
| Ok(ImplSource::Builtin(BuiltinImplSource::TraitUpcasting(idx), nested)) |
| } |
| |
| fn confirm_builtin_unsize_candidate( |
| &mut self, |
| obligation: &PolyTraitObligation<'tcx>, |
| ) -> Result<ImplSource<'tcx, 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.args.type_at(1); |
| let target = self.infcx.shallow_resolve(target); |
| debug!(?source, ?target, "confirm_builtin_unsize_candidate"); |
| |
| Ok(match (source.kind(), target.kind()) { |
| // Trait+Kx+'a -> Trait+Ky+'b (auto traits and lifetime subtyping). |
| (&ty::Dynamic(data_a, r_a, dyn_a), &ty::Dynamic(data_b, r_b, dyn_b)) |
| if dyn_a == dyn_b => |
| { |
| // See `assemble_candidates_for_unsizing` for more info. |
| // We already checked the compatibility of auto traits within `assemble_candidates_for_unsizing`. |
| let existential_predicates = if data_b.principal().is_some() { |
| tcx.mk_poly_existential_predicates_from_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), |
| ), |
| ) |
| } else { |
| // If we're unsizing to a dyn type that has no principal, then drop |
| // the principal and projections from the type. We use the auto traits |
| // from the RHS type since as we noted that we've checked for auto |
| // trait compatibility during unsizing. |
| tcx.mk_poly_existential_predicates_from_iter( |
| data_b |
| .auto_traits() |
| .map(ty::ExistentialPredicate::AutoTrait) |
| .map(ty::Binder::dummy), |
| ) |
| }; |
| let source_trait = Ty::new_dynamic(tcx, existential_predicates, r_b, dyn_a); |
| |
| // Require that the traits involved in this upcast are **equal**; |
| // only the **lifetime bound** is changed. |
| let InferOk { mut obligations, .. } = self |
| .infcx |
| .at(&obligation.cause, obligation.param_env) |
| .sup(DefineOpaqueTypes::Yes, target, source_trait) |
| .map_err(|_| Unimplemented)?; |
| |
| // Register one obligation for 'a: 'b. |
| let outlives = ty::OutlivesPredicate(r_a, r_b); |
| obligations.push(Obligation::with_depth( |
| tcx, |
| obligation.cause.clone(), |
| obligation.recursion_depth + 1, |
| obligation.param_env, |
| obligation.predicate.rebind(outlives), |
| )); |
| |
| ImplSource::Builtin(BuiltinImplSource::Misc, obligations) |
| } |
| |
| // `T` -> `dyn Trait` |
| (_, &ty::Dynamic(data, r, ty::Dyn)) => { |
| let mut object_dids = data.auto_traits().chain(data.principal_def_id()); |
| if let Some(did) = object_dids.find(|did| !tcx.is_dyn_compatible(*did)) { |
| return Err(TraitDynIncompatible(did)); |
| } |
| |
| let predicate_to_obligation = |predicate| { |
| Obligation::with_depth( |
| tcx, |
| obligation.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 |
| let mut nested: PredicateObligations<'_> = data |
| .iter() |
| .map(|predicate| predicate_to_obligation(predicate.with_self_ty(tcx, source))) |
| .collect(); |
| |
| // We can only make objects from sized types. |
| let tr = ty::TraitRef::new( |
| tcx, |
| tcx.require_lang_item(LangItem::Sized, Some(obligation.cause.span)), |
| [source], |
| ); |
| nested.push(predicate_to_obligation(tr.upcast(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::ClauseKind::TypeOutlives(outlives).upcast(tcx), |
| )); |
| |
| // Require that all AFIT will return something that can be coerced into `dyn*` |
| // -- a shim will be responsible for doing the actual coercion to `dyn*`. |
| if let Some(principal) = data.principal() { |
| for supertrait in |
| elaborate::supertraits(tcx, principal.with_self_ty(tcx, source)) |
| { |
| if tcx.is_trait_alias(supertrait.def_id()) { |
| continue; |
| } |
| |
| for &assoc_item in tcx.associated_item_def_ids(supertrait.def_id()) { |
| if !tcx.is_impl_trait_in_trait(assoc_item) { |
| continue; |
| } |
| |
| // RPITITs with `Self: Sized` don't need to be checked. |
| if tcx.generics_require_sized_self(assoc_item) { |
| continue; |
| } |
| |
| let pointer_like_goal = pointer_like_goal_for_rpitit( |
| tcx, |
| supertrait, |
| assoc_item, |
| &obligation.cause, |
| ); |
| |
| nested.push(predicate_to_obligation(pointer_like_goal.upcast(tcx))); |
| } |
| } |
| } |
| |
| ImplSource::Builtin(BuiltinImplSource::Misc, nested) |
| } |
| |
| // `[T; n]` -> `[T]` |
| (&ty::Array(a, _), &ty::Slice(b)) => { |
| let InferOk { obligations, .. } = self |
| .infcx |
| .at(&obligation.cause, obligation.param_env) |
| .eq(DefineOpaqueTypes::Yes, b, a) |
| .map_err(|_| Unimplemented)?; |
| |
| ImplSource::Builtin(BuiltinImplSource::Misc, obligations) |
| } |
| |
| // `Struct<T>` -> `Struct<U>` |
| (&ty::Adt(def, args_a), &ty::Adt(_, args_b)) => { |
| let unsizing_params = tcx.unsizing_params_for_adt(def.did()); |
| if unsizing_params.is_empty() { |
| return Err(Unimplemented); |
| } |
| |
| let tail_field = def.non_enum_variant().tail(); |
| let tail_field_ty = tcx.type_of(tail_field.did); |
| |
| let mut nested = PredicateObligations::new(); |
| |
| // Extract `TailField<T>` and `TailField<U>` from `Struct<T>` and `Struct<U>`, |
| // normalizing in the process, since `type_of` returns something directly from |
| // HIR ty lowering (which means it's un-normalized). |
| let source_tail = normalize_with_depth_to( |
| self, |
| obligation.param_env, |
| obligation.cause.clone(), |
| obligation.recursion_depth + 1, |
| tail_field_ty.instantiate(tcx, args_a), |
| &mut nested, |
| ); |
| let target_tail = normalize_with_depth_to( |
| self, |
| obligation.param_env, |
| obligation.cause.clone(), |
| obligation.recursion_depth + 1, |
| tail_field_ty.instantiate(tcx, args_b), |
| &mut nested, |
| ); |
| |
| // Check that the source struct with the target's |
| // unsizing parameters is equal to the target. |
| let args = |
| tcx.mk_args_from_iter(args_a.iter().enumerate().map(|(i, k)| { |
| if unsizing_params.contains(i as u32) { args_b[i] } else { k } |
| })); |
| let new_struct = Ty::new_adt(tcx, def, args); |
| let InferOk { obligations, .. } = self |
| .infcx |
| .at(&obligation.cause, obligation.param_env) |
| .eq(DefineOpaqueTypes::Yes, target, new_struct) |
| .map_err(|_| Unimplemented)?; |
| nested.extend(obligations); |
| |
| // Construct the nested `TailField<T>: Unsize<TailField<U>>` predicate. |
| let tail_unsize_obligation = obligation.with( |
| tcx, |
| ty::TraitRef::new( |
| tcx, |
| obligation.predicate.def_id(), |
| [source_tail, target_tail], |
| ), |
| ); |
| nested.push(tail_unsize_obligation); |
| |
| ImplSource::Builtin(BuiltinImplSource::Misc, nested) |
| } |
| |
| _ => bug!("source: {source}, target: {target}"), |
| }) |
| } |
| |
| fn confirm_bikeshed_guaranteed_no_drop_candidate( |
| &mut self, |
| obligation: &PolyTraitObligation<'tcx>, |
| ) -> ImplSource<'tcx, PredicateObligation<'tcx>> { |
| let mut obligations = thin_vec![]; |
| |
| let tcx = self.tcx(); |
| let self_ty = obligation.predicate.self_ty(); |
| match *self_ty.skip_binder().kind() { |
| // `&mut T` and `&T` always implement `BikeshedGuaranteedNoDrop`. |
| ty::Ref(..) => {} |
| // `ManuallyDrop<T>` always implements `BikeshedGuaranteedNoDrop`. |
| ty::Adt(def, _) if def.is_manually_drop() => {} |
| // Arrays and tuples implement `BikeshedGuaranteedNoDrop` only if |
| // their constituent types implement `BikeshedGuaranteedNoDrop`. |
| ty::Tuple(tys) => { |
| obligations.extend(tys.iter().map(|elem_ty| { |
| obligation.with( |
| tcx, |
| self_ty.rebind(ty::TraitRef::new( |
| tcx, |
| obligation.predicate.def_id(), |
| [elem_ty], |
| )), |
| ) |
| })); |
| } |
| ty::Array(elem_ty, _) => { |
| obligations.push(obligation.with( |
| tcx, |
| self_ty.rebind(ty::TraitRef::new( |
| tcx, |
| obligation.predicate.def_id(), |
| [elem_ty], |
| )), |
| )); |
| } |
| |
| // All other types implement `BikeshedGuaranteedNoDrop` only if |
| // they implement `Copy`. We could be smart here and short-circuit |
| // some trivially `Copy`/`!Copy` types, but there's no benefit. |
| ty::FnDef(..) |
| | ty::FnPtr(..) |
| | ty::Error(_) |
| | ty::Uint(_) |
| | ty::Int(_) |
| | ty::Infer(ty::IntVar(_) | ty::FloatVar(_)) |
| | ty::Bool |
| | ty::Float(_) |
| | ty::Char |
| | ty::RawPtr(..) |
| | ty::Never |
| | ty::Pat(..) |
| | ty::Dynamic(..) |
| | ty::Str |
| | ty::Slice(_) |
| | ty::Foreign(..) |
| | ty::Adt(..) |
| | ty::Alias(..) |
| | ty::Param(_) |
| | ty::Placeholder(..) |
| | ty::Closure(..) |
| | ty::CoroutineClosure(..) |
| | ty::Coroutine(..) |
| | ty::UnsafeBinder(_) |
| | ty::CoroutineWitness(..) |
| | ty::Bound(..) => { |
| obligations.push(obligation.with( |
| tcx, |
| self_ty.map_bound(|ty| { |
| ty::TraitRef::new( |
| tcx, |
| tcx.require_lang_item(LangItem::Copy, Some(obligation.cause.span)), |
| [ty], |
| ) |
| }), |
| )); |
| } |
| |
| ty::Infer(ty::TyVar(_) | ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)) => { |
| panic!("unexpected type `{self_ty:?}`") |
| } |
| } |
| |
| ImplSource::Builtin(BuiltinImplSource::Misc, obligations) |
| } |
| } |
| |
| /// Compute a goal that some RPITIT (right now, only RPITITs corresponding to Futures) |
| /// implements the `PointerLike` trait, which is a requirement for the RPITIT to be |
| /// coercible to `dyn* Future`, which is itself a requirement for the RPITIT's parent |
| /// trait to be coercible to `dyn Trait`. |
| /// |
| /// We do this given a supertrait's substitutions, and then augment the substitutions |
| /// with bound variables to compute the goal universally. Given that `PointerLike` has |
| /// no region requirements (at least for the built-in pointer types), this shouldn't |
| /// *really* matter, but it is the best choice for soundness. |
| fn pointer_like_goal_for_rpitit<'tcx>( |
| tcx: TyCtxt<'tcx>, |
| supertrait: ty::PolyTraitRef<'tcx>, |
| rpitit_item: DefId, |
| cause: &ObligationCause<'tcx>, |
| ) -> ty::PolyTraitRef<'tcx> { |
| let mut bound_vars = supertrait.bound_vars().to_vec(); |
| |
| let args = supertrait.skip_binder().args.extend_to(tcx, rpitit_item, |arg, _| match arg.kind { |
| ty::GenericParamDefKind::Lifetime => { |
| let kind = ty::BoundRegionKind::Named(arg.def_id, tcx.item_name(arg.def_id)); |
| bound_vars.push(ty::BoundVariableKind::Region(kind)); |
| ty::Region::new_bound( |
| tcx, |
| ty::INNERMOST, |
| ty::BoundRegion { var: ty::BoundVar::from_usize(bound_vars.len() - 1), kind }, |
| ) |
| .into() |
| } |
| ty::GenericParamDefKind::Type { .. } | ty::GenericParamDefKind::Const { .. } => { |
| unreachable!() |
| } |
| }); |
| |
| ty::Binder::bind_with_vars( |
| ty::TraitRef::new( |
| tcx, |
| tcx.require_lang_item(LangItem::PointerLike, Some(cause.span)), |
| [Ty::new_projection_from_args(tcx, rpitit_item, args)], |
| ), |
| tcx.mk_bound_variable_kinds(&bound_vars), |
| ) |
| } |
