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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-17 12:02:58 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-17 12:02:58 +0000 |
commit | 698f8c2f01ea549d77d7dc3338a12e04c11057b9 (patch) | |
tree | 173a775858bd501c378080a10dca74132f05bc50 /compiler/rustc_trait_selection/src/traits/select/confirmation.rs | |
parent | Initial commit. (diff) | |
download | rustc-698f8c2f01ea549d77d7dc3338a12e04c11057b9.tar.xz rustc-698f8c2f01ea549d77d7dc3338a12e04c11057b9.zip |
Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'compiler/rustc_trait_selection/src/traits/select/confirmation.rs')
-rw-r--r-- | compiler/rustc_trait_selection/src/traits/select/confirmation.rs | 1266 |
1 files changed, 1266 insertions, 0 deletions
diff --git a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs new file mode 100644 index 000000000..2a1099fc8 --- /dev/null +++ b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs @@ -0,0 +1,1266 @@ +//! 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_infer::infer::LateBoundRegionConversionTime::HigherRankedType; +use rustc_middle::ty::subst::{GenericArg, GenericArgKind, InternalSubsts, Subst, SubstsRef}; +use rustc_middle::ty::{self, GenericParamDefKind, Ty, TyCtxt}; +use rustc_middle::ty::{ToPolyTraitRef, ToPredicate}; +use rustc_span::def_id::DefId; + +use crate::traits::project::{normalize_with_depth, normalize_with_depth_to}; +use crate::traits::util::{self, closure_trait_ref_and_return_type, predicate_for_trait_def}; +use crate::traits::{ + BuiltinDerivedObligation, ImplDerivedObligation, ImplDerivedObligationCause, ImplSource, + ImplSourceAutoImplData, ImplSourceBuiltinData, ImplSourceClosureData, + ImplSourceConstDestructData, ImplSourceDiscriminantKindData, ImplSourceFnPointerData, + ImplSourceGeneratorData, ImplSourceObjectData, ImplSourcePointeeData, ImplSourceTraitAliasData, + ImplSourceTraitUpcastingData, ImplSourceUserDefinedData, Normalized, ObjectCastObligation, + Obligation, ObligationCause, OutputTypeParameterMismatch, PredicateObligation, Selection, + SelectionError, TraitNotObjectSafe, TraitObligation, Unimplemented, VtblSegment, +}; + +use super::BuiltinImplConditions; +use super::SelectionCandidate::{self, *}; +use super::SelectionContext; + +use std::iter; +use std::ops::ControlFlow; + +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>> { + let mut impl_src = match candidate { + BuiltinCandidate { has_nested } => { + let data = self.confirm_builtin_candidate(obligation, has_nested); + ImplSource::Builtin(data) + } + + TransmutabilityCandidate => { + let data = self.confirm_transmutability_candidate(obligation)?; + ImplSource::Builtin(data) + } + + ParamCandidate(param) => { + let obligations = + self.confirm_param_candidate(obligation, param.map_bound(|t| t.trait_ref)); + ImplSource::Param(obligations, param.skip_binder().constness) + } + + ImplCandidate(impl_def_id) => { + 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); + ImplSource::AutoImpl(data) + } + + ProjectionCandidate(idx) => { + let obligations = self.confirm_projection_candidate(obligation, idx)?; + // FIXME(jschievink): constness + ImplSource::Param(obligations, ty::BoundConstness::NotConst) + } + + ObjectCandidate(idx) => { + let data = self.confirm_object_candidate(obligation, idx)?; + ImplSource::Object(data) + } + + ClosureCandidate => { + let vtable_closure = self.confirm_closure_candidate(obligation)?; + ImplSource::Closure(vtable_closure) + } + + GeneratorCandidate => { + let vtable_generator = self.confirm_generator_candidate(obligation)?; + ImplSource::Generator(vtable_generator) + } + + FnPointerCandidate { .. } => { + let data = self.confirm_fn_pointer_candidate(obligation)?; + ImplSource::FnPointer(data) + } + + DiscriminantKindCandidate => { + ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData) + } + + PointeeCandidate => ImplSource::Pointee(ImplSourcePointeeData), + + TraitAliasCandidate(alias_def_id) => { + let data = self.confirm_trait_alias_candidate(obligation, alias_def_id); + 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. + ImplSource::Param(Vec::new(), ty::BoundConstness::NotConst) + } + + BuiltinUnsizeCandidate => { + let data = self.confirm_builtin_unsize_candidate(obligation)?; + ImplSource::Builtin(data) + } + + TraitUpcastingUnsizeCandidate(idx) => { + let data = self.confirm_trait_upcasting_unsize_candidate(obligation, idx)?; + ImplSource::TraitUpcasting(data) + } + + ConstDestructCandidate(def_id) => { + let data = self.confirm_const_destruct_candidate(obligation, def_id)?; + ImplSource::ConstDestruct(data) + } + }; + + if !obligation.predicate.is_const_if_const() { + // normalize nested predicates according to parent predicate's constness. + impl_src = impl_src.map(|mut o| { + o.predicate = o.predicate.without_const(self.tcx()); + o + }); + } + + Ok(impl_src) + } + + fn confirm_projection_candidate( + &mut self, + obligation: &TraitObligation<'tcx>, + idx: usize, + ) -> Result<Vec<PredicateObligation<'tcx>>, SelectionError<'tcx>> { + 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).trait_ref; + let placeholder_self_ty = placeholder_trait_predicate.self_ty(); + let placeholder_trait_predicate = ty::Binder::dummy(placeholder_trait_predicate); + 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.bound_item_bounds(def_id).map_bound(|i| i[idx]).subst(tcx, substs); + let candidate = candidate_predicate + .to_opt_poly_trait_pred() + .expect("projection candidate is not a trait predicate") + .map_bound(|t| t.trait_ref); + 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, candidate) + .map(|InferOk { obligations, .. }| obligations) + .map_err(|_| Unimplemented) + })?); + + if let ty::Projection(..) = placeholder_self_ty.kind() { + let predicates = tcx.predicates_of(def_id).instantiate_own(tcx, substs).predicates; + debug!(?predicates, "projection predicates"); + 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( + 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 BuiltinImplConditions::Where(nested) = conditions else { + 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 } + } + + fn confirm_transmutability_candidate( + &mut self, + obligation: &TraitObligation<'tcx>, + ) -> Result<ImplSourceBuiltinData<PredicateObligation<'tcx>>, SelectionError<'tcx>> { + debug!(?obligation, "confirm_transmutability_candidate"); + + let predicate = obligation.predicate; + + let type_at = |i| predicate.map_bound(|p| p.trait_ref.substs.type_at(i)); + let bool_at = |i| { + predicate + .skip_binder() + .trait_ref + .substs + .const_at(i) + .try_eval_bool(self.tcx(), obligation.param_env) + .unwrap_or(true) + }; + + let src_and_dst = predicate.map_bound(|p| rustc_transmute::Types { + src: p.trait_ref.substs.type_at(1), + dst: p.trait_ref.substs.type_at(0), + }); + + let scope = type_at(2).skip_binder(); + + let assume = rustc_transmute::Assume { + alignment: bool_at(3), + lifetimes: bool_at(4), + validity: bool_at(5), + visibility: bool_at(6), + }; + + let cause = obligation.cause.clone(); + + let mut transmute_env = rustc_transmute::TransmuteTypeEnv::new(self.infcx); + + let maybe_transmutable = transmute_env.is_transmutable(cause, src_and_dst, scope, assume); + + use rustc_transmute::Answer; + + match maybe_transmutable { + Answer::Yes => Ok(ImplSourceBuiltinData { nested: vec![] }), + _ => Err(Unimplemented), + } + } + + /// 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: &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<'tcx, Vec<Ty<'tcx>>>, + ) -> ImplSourceAutoImplData<PredicateObligation<'tcx>> { + debug!(?nested, "vtable_auto_impl"); + ensure_sufficient_stack(|| { + let cause = obligation.derived_cause(BuiltinDerivedObligation); + + let poly_trait_ref = obligation.predicate.to_poly_trait_ref(); + let trait_ref = self.infcx.replace_bound_vars_with_placeholders(poly_trait_ref); + let trait_obligations: Vec<PredicateObligation<'_>> = self.impl_or_trait_obligations( + &cause, + obligation.recursion_depth + 1, + obligation.param_env, + trait_def_id, + &trait_ref.substs, + obligation.predicate, + ); + + let mut obligations = self.collect_predicates_for_types( + obligation.param_env, + cause, + obligation.recursion_depth + 1, + trait_def_id, + nested, + ); + + // 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. + let substs = self.rematch_impl(impl_def_id, obligation); + debug!(?substs, "impl substs"); + ensure_sufficient_stack(|| { + self.vtable_impl( + impl_def_id, + substs, + &obligation.cause, + obligation.recursion_depth + 1, + obligation.param_env, + obligation.predicate, + ) + }) + } + + 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>, + parent_trait_pred: ty::Binder<'tcx, ty::TraitPredicate<'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, + parent_trait_pred, + ); + + 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 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.replace_bound_vars_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 = vec![]; + + 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 = 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() + { + 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 { + let defs: &ty::Generics = tcx.generics_of(assoc_type); + + if !defs.params.is_empty() && !tcx.features().generic_associated_types_extended { + tcx.sess.delay_span_bug( + obligation.cause.span, + "GATs in trait object shouldn't have been considered", + ); + return Err(SelectionError::Unimplemented); + } + + // 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().bound_item_bounds(assoc_type).transpose_iter() { + let subst_bound = + if defs.count() == 0 { + bound.subst(tcx, trait_predicate.trait_ref.substs) + } else { + let mut substs = smallvec::SmallVec::with_capacity(defs.count()); + substs.extend(trait_predicate.trait_ref.substs.iter()); + let mut bound_vars: smallvec::SmallVec<[ty::BoundVariableKind; 8]> = + smallvec::SmallVec::with_capacity( + bound.0.kind().bound_vars().len() + defs.count(), + ); + bound_vars.extend(bound.0.kind().bound_vars().into_iter()); + InternalSubsts::fill_single(&mut substs, defs, &mut |param, _| match param + .kind + { + GenericParamDefKind::Type { .. } => { + let kind = ty::BoundTyKind::Param(param.name); + let bound_var = ty::BoundVariableKind::Ty(kind); + bound_vars.push(bound_var); + tcx.mk_ty(ty::Bound( + ty::INNERMOST, + ty::BoundTy { + var: ty::BoundVar::from_usize(bound_vars.len() - 1), + kind, + }, + )) + .into() + } + GenericParamDefKind::Lifetime => { + let kind = ty::BoundRegionKind::BrNamed(param.def_id, param.name); + let bound_var = ty::BoundVariableKind::Region(kind); + bound_vars.push(bound_var); + tcx.mk_region(ty::ReLateBound( + ty::INNERMOST, + ty::BoundRegion { + var: ty::BoundVar::from_usize(bound_vars.len() - 1), + kind, + }, + )) + .into() + } + GenericParamDefKind::Const { .. } => { + let bound_var = ty::BoundVariableKind::Const; + bound_vars.push(bound_var); + tcx.mk_const(ty::ConstS { + ty: tcx.type_of(param.def_id), + kind: ty::ConstKind::Bound( + ty::INNERMOST, + ty::BoundVar::from_usize(bound_vars.len() - 1), + ), + }) + .into() + } + }); + let bound_vars = tcx.mk_bound_variable_kinds(bound_vars.into_iter()); + let assoc_ty_substs = tcx.intern_substs(&substs); + + let bound_vars = tcx.mk_bound_variable_kinds(bound_vars.into_iter()); + let bound = + bound.map_bound(|b| b.kind().skip_binder()).subst(tcx, assoc_ty_substs); + tcx.mk_predicate(ty::Binder::bind_with_vars(bound, bound_vars)) + }; + 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"); + + let vtable_base = super::super::vtable_trait_first_method_offset( + tcx, + (unnormalized_upcast_trait_ref, ty::Binder::dummy(object_trait_ref)), + ); + + 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 nested = self.confirm_poly_trait_refs(obligation, trait_ref)?; + Ok(ImplSourceFnPointerData { fn_ty: self_ty, nested }) + } + + 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"); + + 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, + obligation.recursion_depth, + obligation.param_env, + trait_def_id, + &substs, + obligation.predicate, + ); + + 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 ty::Generator(generator_def_id, substs, _) = *self_ty.kind() else { + 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 nested = self.confirm_poly_trait_refs(obligation, trait_ref)?; + debug!(?trait_ref, ?nested, "generator candidate obligations"); + + Ok(ImplSourceGeneratorData { generator_def_id, substs, nested }) + } + + #[instrument(skip(self), level = "debug")] + fn confirm_closure_candidate( + &mut self, + obligation: &TraitObligation<'tcx>, + ) -> Result<ImplSourceClosureData<'tcx, PredicateObligation<'tcx>>, SelectionError<'tcx>> { + 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 ty::Closure(closure_def_id, substs) = *self_ty.kind() else { + bug!("closure candidate for non-closure {:?}", obligation); + }; + + let trait_ref = self.closure_trait_ref_unnormalized(obligation, substs); + let mut nested = self.confirm_poly_trait_refs(obligation, trait_ref)?; + + debug!(?closure_def_id, ?trait_ref, ?nested, "confirm closure candidate obligations"); + + // FIXME: Chalk + + if !self.tcx().sess.opts.unstable_opts.chalk { + nested.push(Obligation::new( + obligation.cause.clone(), + obligation.param_env, + ty::Binder::dummy(ty::PredicateKind::ClosureKind(closure_def_id, substs, kind)) + .to_predicate(self.tcx()), + )); + } + + Ok(ImplSourceClosureData { closure_def_id, substs, 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 confirm_poly_trait_refs( + &mut self, + obligation: &TraitObligation<'tcx>, + expected_trait_ref: ty::PolyTraitRef<'tcx>, + ) -> Result<Vec<PredicateObligation<'tcx>>, SelectionError<'tcx>> { + let obligation_trait_ref = obligation.predicate.to_poly_trait_ref(); + // Normalize the obligation and expected trait refs together, because why not + let Normalized { obligations: nested, value: (obligation_trait_ref, expected_trait_ref) } = + ensure_sufficient_stack(|| { + normalize_with_depth( + self, + obligation.param_env, + obligation.cause.clone(), + obligation.recursion_depth + 1, + (obligation_trait_ref, expected_trait_ref), + ) + }); + + self.infcx + .at(&obligation.cause, obligation.param_env) + .sup(obligation_trait_ref, expected_trait_ref) + .map(|InferOk { mut obligations, .. }| { + obligations.extend(nested); + obligations + }) + .map_err(|e| OutputTypeParameterMismatch(expected_trait_ref, obligation_trait_ref, e)) + } + + fn confirm_trait_upcasting_unsize_candidate( + &mut self, + obligation: &TraitObligation<'tcx>, + idx: usize, + ) -> Result<ImplSourceTraitUpcastingData<'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.substs.type_at(1); + let target = self.infcx.shallow_resolve(target); + + debug!(?source, ?target, "confirm_trait_upcasting_unsize_candidate"); + + let mut nested = vec![]; + let source_trait_ref; + let upcast_trait_ref; + match (source.kind(), target.kind()) { + // TraitA+Kx+'a -> TraitB+Ky+'b (trait upcasting coercion). + (&ty::Dynamic(ref data_a, r_a), &ty::Dynamic(ref data_b, r_b)) => { + // See `assemble_candidates_for_unsizing` for more info. + // We already checked the compatibility of auto traits within `assemble_candidates_for_unsizing`. + let principal_a = data_a.principal().unwrap(); + source_trait_ref = principal_a.with_self_ty(tcx, source); + upcast_trait_ref = util::supertraits(tcx, source_trait_ref).nth(idx).unwrap(); + assert_eq!(data_b.principal_def_id(), Some(upcast_trait_ref.def_id())); + let existential_predicate = upcast_trait_ref.map_bound(|trait_ref| { + ty::ExistentialPredicate::Trait(ty::ExistentialTraitRef::erase_self_ty( + tcx, trait_ref, + )) + }); + let iter = Some(existential_predicate) + .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(source, target), + ); + let outlives = ty::OutlivesPredicate(r_a, r_b); + nested.push(Obligation::with_depth( + cause, + obligation.recursion_depth + 1, + obligation.param_env, + obligation.predicate.rebind(outlives).to_predicate(tcx), + )); + } + _ => bug!(), + }; + + let vtable_segment_callback = { + let mut vptr_offset = 0; + move |segment| { + match segment { + VtblSegment::MetadataDSA => { + vptr_offset += TyCtxt::COMMON_VTABLE_ENTRIES.len(); + } + VtblSegment::TraitOwnEntries { trait_ref, emit_vptr } => { + vptr_offset += util::count_own_vtable_entries(tcx, trait_ref); + if trait_ref == upcast_trait_ref { + if emit_vptr { + return ControlFlow::Break(Some(vptr_offset)); + } else { + return ControlFlow::Break(None); + } + } + + if emit_vptr { + vptr_offset += 1; + } + } + } + ControlFlow::Continue(()) + } + }; + + let vtable_vptr_slot = + super::super::prepare_vtable_segments(tcx, source_trait_ref, vtable_segment_callback) + .unwrap(); + + Ok(ImplSourceTraitUpcastingData { upcast_trait_ref, vtable_vptr_slot, nested }) + } + + 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 (auto traits and lifetime subtyping). + (&ty::Dynamic(ref data_a, r_a), &ty::Dynamic(ref data_b, r_b)) => { + // See `assemble_candidates_for_unsizing` for more info. + // We already checked the compatibility of auto traits within `assemble_candidates_for_unsizing`. + 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(source, target), + ); + let outlives = ty::OutlivesPredicate(r_a, r_b); + nested.push(Obligation::with_depth( + cause, + obligation.recursion_depth + 1, + obligation.param_env, + obligation.predicate.rebind(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(source, 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::Binder::dummy(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.kind() { + ty::ConstKind::Param(p) => Some(p.index), + _ => None, + }, + }; + + // 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. + + // 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.bound_type_of(tail_field.did); + + let mut unsizing_params = GrowableBitSet::new_empty(); + for arg in tail_field_ty.0.walk() { + if let Some(i) = maybe_unsizing_param_idx(arg) { + unsizing_params.insert(i); + } + } + + // Ensure none of the other fields mention the parameters used + // in unsizing. + for field in prefix_fields { + for arg in tcx.type_of(field.did).walk() { + if let Some(i) = maybe_unsizing_param_idx(arg) { + unsizing_params.remove(i); + } + } + } + + if unsizing_params.is_empty() { + 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().copied().chain(iter::once(b_last))); + 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, + &[b_last.into()], + ) + })); + } + + _ => bug!(), + }; + + Ok(ImplSourceBuiltinData { nested }) + } + + fn confirm_const_destruct_candidate( + &mut self, + obligation: &TraitObligation<'tcx>, + impl_def_id: Option<DefId>, + ) -> Result<ImplSourceConstDestructData<PredicateObligation<'tcx>>, SelectionError<'tcx>> { + // `~const Destruct` in a non-const environment is always trivially true, since our type is `Drop` + if !obligation.is_const() { + return Ok(ImplSourceConstDestructData { nested: vec![] }); + } + + let drop_trait = self.tcx().require_lang_item(LangItem::Drop, None); + + let tcx = self.tcx(); + let self_ty = self.infcx.shallow_resolve(obligation.self_ty()); + + let mut nested = vec![]; + let cause = obligation.derived_cause(BuiltinDerivedObligation); + + // If we have a custom `impl const Drop`, then + // first check it like a regular impl candidate. + // This is copied from confirm_impl_candidate but remaps the predicate to `~const Drop` beforehand. + if let Some(impl_def_id) = impl_def_id { + let mut new_obligation = obligation.clone(); + new_obligation.predicate = new_obligation.predicate.map_bound(|mut trait_pred| { + trait_pred.trait_ref.def_id = drop_trait; + trait_pred + }); + let substs = self.rematch_impl(impl_def_id, &new_obligation); + debug!(?substs, "impl substs"); + + let cause = obligation.derived_cause(|derived| { + ImplDerivedObligation(Box::new(ImplDerivedObligationCause { + derived, + impl_def_id, + span: obligation.cause.span, + })) + }); + let obligations = ensure_sufficient_stack(|| { + self.vtable_impl( + impl_def_id, + substs, + &cause, + new_obligation.recursion_depth + 1, + new_obligation.param_env, + obligation.predicate, + ) + }); + nested.extend(obligations.nested); + } + + // We want to confirm the ADT's fields if we have an ADT + let mut stack = match *self_ty.skip_binder().kind() { + ty::Adt(def, substs) => def.all_fields().map(|f| f.ty(tcx, substs)).collect(), + _ => vec![self_ty.skip_binder()], + }; + + while let Some(nested_ty) = stack.pop() { + match *nested_ty.kind() { + // We know these types are trivially drop + ty::Bool + | ty::Char + | ty::Int(_) + | ty::Uint(_) + | ty::Float(_) + | ty::Infer(ty::IntVar(_)) + | ty::Infer(ty::FloatVar(_)) + | ty::Str + | ty::RawPtr(_) + | ty::Ref(..) + | ty::FnDef(..) + | ty::FnPtr(_) + | ty::Never + | ty::Foreign(_) => {} + + // These types are built-in, so we can fast-track by registering + // nested predicates for their constituent type(s) + ty::Array(ty, _) | ty::Slice(ty) => { + stack.push(ty); + } + ty::Tuple(tys) => { + stack.extend(tys.iter()); + } + ty::Closure(_, substs) => { + stack.push(substs.as_closure().tupled_upvars_ty()); + } + ty::Generator(_, substs, _) => { + let generator = substs.as_generator(); + stack.extend([generator.tupled_upvars_ty(), generator.witness()]); + } + ty::GeneratorWitness(tys) => { + stack.extend(tcx.erase_late_bound_regions(tys).to_vec()); + } + + // If we have a projection type, make sure to normalize it so we replace it + // with a fresh infer variable + ty::Projection(..) => { + let predicate = normalize_with_depth_to( + self, + obligation.param_env, + cause.clone(), + obligation.recursion_depth + 1, + self_ty + .rebind(ty::TraitPredicate { + trait_ref: ty::TraitRef { + def_id: self.tcx().require_lang_item(LangItem::Destruct, None), + substs: self.tcx().mk_substs_trait(nested_ty, &[]), + }, + constness: ty::BoundConstness::ConstIfConst, + polarity: ty::ImplPolarity::Positive, + }) + .to_predicate(tcx), + &mut nested, + ); + + nested.push(Obligation::with_depth( + cause.clone(), + obligation.recursion_depth + 1, + obligation.param_env, + predicate, + )); + } + + // If we have any other type (e.g. an ADT), just register a nested obligation + // since it's either not `const Drop` (and we raise an error during selection), + // or it's an ADT (and we need to check for a custom impl during selection) + _ => { + let predicate = self_ty + .rebind(ty::TraitPredicate { + trait_ref: ty::TraitRef { + def_id: self.tcx().require_lang_item(LangItem::Destruct, None), + substs: self.tcx().mk_substs_trait(nested_ty, &[]), + }, + constness: ty::BoundConstness::ConstIfConst, + polarity: ty::ImplPolarity::Positive, + }) + .to_predicate(tcx); + + nested.push(Obligation::with_depth( + cause.clone(), + obligation.recursion_depth + 1, + obligation.param_env, + predicate, + )); + } + } + } + + Ok(ImplSourceConstDestructData { nested }) + } +} |