| //! Dealing with trait goals, i.e. `T: Trait<'a, U>`. |
| |
| use super::assembly::{self, structural_traits}; |
| use super::{EvalCtxt, SolverMode}; |
| use rustc_hir::def_id::DefId; |
| use rustc_hir::{LangItem, Movability}; |
| use rustc_infer::traits::query::NoSolution; |
| use rustc_middle::traits::solve::inspect::ProbeKind; |
| use rustc_middle::traits::solve::{CanonicalResponse, Certainty, Goal, QueryResult}; |
| use rustc_middle::traits::{BuiltinImplSource, Reveal}; |
| use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams, TreatProjections}; |
| use rustc_middle::ty::{self, ToPredicate, Ty, TyCtxt}; |
| use rustc_middle::ty::{TraitPredicate, TypeVisitableExt}; |
| use rustc_span::{ErrorGuaranteed, DUMMY_SP}; |
| |
| impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> { |
| fn self_ty(self) -> Ty<'tcx> { |
| self.self_ty() |
| } |
| |
| fn trait_ref(self, _: TyCtxt<'tcx>) -> ty::TraitRef<'tcx> { |
| self.trait_ref |
| } |
| |
| fn polarity(self) -> ty::ImplPolarity { |
| self.polarity |
| } |
| |
| fn with_self_ty(self, tcx: TyCtxt<'tcx>, self_ty: Ty<'tcx>) -> Self { |
| self.with_self_ty(tcx, self_ty) |
| } |
| |
| fn trait_def_id(self, _: TyCtxt<'tcx>) -> DefId { |
| self.def_id() |
| } |
| |
| fn consider_impl_candidate( |
| ecx: &mut EvalCtxt<'_, 'tcx>, |
| goal: Goal<'tcx, TraitPredicate<'tcx>>, |
| impl_def_id: DefId, |
| ) -> QueryResult<'tcx> { |
| let tcx = ecx.tcx(); |
| |
| let impl_trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap(); |
| let drcx = DeepRejectCtxt { treat_obligation_params: TreatParams::ForLookup }; |
| if !drcx |
| .args_refs_may_unify(goal.predicate.trait_ref.args, impl_trait_ref.skip_binder().args) |
| { |
| return Err(NoSolution); |
| } |
| |
| let impl_polarity = tcx.impl_polarity(impl_def_id); |
| // An upper bound of the certainty of this goal, used to lower the certainty |
| // of reservation impl to ambiguous during coherence. |
| let maximal_certainty = match impl_polarity { |
| ty::ImplPolarity::Positive | ty::ImplPolarity::Negative => { |
| match impl_polarity == goal.predicate.polarity { |
| true => Certainty::Yes, |
| false => return Err(NoSolution), |
| } |
| } |
| ty::ImplPolarity::Reservation => match ecx.solver_mode() { |
| SolverMode::Normal => return Err(NoSolution), |
| SolverMode::Coherence => Certainty::AMBIGUOUS, |
| }, |
| }; |
| |
| ecx.probe_misc_candidate("impl").enter(|ecx| { |
| let impl_args = ecx.fresh_args_for_item(impl_def_id); |
| let impl_trait_ref = impl_trait_ref.instantiate(tcx, impl_args); |
| |
| ecx.eq(goal.param_env, goal.predicate.trait_ref, impl_trait_ref)?; |
| let where_clause_bounds = tcx |
| .predicates_of(impl_def_id) |
| .instantiate(tcx, impl_args) |
| .predicates |
| .into_iter() |
| .map(|pred| goal.with(tcx, pred)); |
| ecx.add_goals(where_clause_bounds); |
| |
| ecx.evaluate_added_goals_and_make_canonical_response(maximal_certainty) |
| }) |
| } |
| |
| fn consider_error_guaranteed_candidate( |
| ecx: &mut EvalCtxt<'_, 'tcx>, |
| _guar: ErrorGuaranteed, |
| ) -> QueryResult<'tcx> { |
| ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes) |
| } |
| |
| fn probe_and_match_goal_against_assumption( |
| ecx: &mut EvalCtxt<'_, 'tcx>, |
| goal: Goal<'tcx, Self>, |
| assumption: ty::Clause<'tcx>, |
| then: impl FnOnce(&mut EvalCtxt<'_, 'tcx>) -> QueryResult<'tcx>, |
| ) -> QueryResult<'tcx> { |
| if let Some(trait_clause) = assumption.as_trait_clause() { |
| if trait_clause.def_id() == goal.predicate.def_id() |
| && trait_clause.polarity() == goal.predicate.polarity |
| { |
| // FIXME: Constness |
| ecx.probe_misc_candidate("assumption").enter(|ecx| { |
| let assumption_trait_pred = ecx.instantiate_binder_with_infer(trait_clause); |
| ecx.eq( |
| goal.param_env, |
| goal.predicate.trait_ref, |
| assumption_trait_pred.trait_ref, |
| )?; |
| then(ecx) |
| }) |
| } else { |
| Err(NoSolution) |
| } |
| } else { |
| Err(NoSolution) |
| } |
| } |
| |
| fn consider_auto_trait_candidate( |
| ecx: &mut EvalCtxt<'_, 'tcx>, |
| goal: Goal<'tcx, Self>, |
| ) -> QueryResult<'tcx> { |
| if goal.predicate.polarity != ty::ImplPolarity::Positive { |
| return Err(NoSolution); |
| } |
| |
| if let Some(result) = ecx.disqualify_auto_trait_candidate_due_to_possible_impl(goal) { |
| return result; |
| } |
| |
| // Don't call `type_of` on a local TAIT that's in the defining scope, |
| // since that may require calling `typeck` on the same item we're |
| // currently type checking, which will result in a fatal cycle that |
| // ideally we want to avoid, since we can make progress on this goal |
| // via an alias bound or a locally-inferred hidden type instead. |
| // |
| // Also, don't call `type_of` on a TAIT in `Reveal::All` mode, since |
| // we already normalize the self type in |
| // `assemble_candidates_after_normalizing_self_ty`, and we'd |
| // just be registering an identical candidate here. |
| // |
| // We always return `Err(NoSolution)` here in `SolverMode::Coherence` |
| // since we'll always register an ambiguous candidate in |
| // `assemble_candidates_after_normalizing_self_ty` due to normalizing |
| // the TAIT. |
| if let ty::Alias(ty::Opaque, opaque_ty) = goal.predicate.self_ty().kind() { |
| if matches!(goal.param_env.reveal(), Reveal::All) |
| || matches!(ecx.solver_mode(), SolverMode::Coherence) |
| || opaque_ty |
| .def_id |
| .as_local() |
| .is_some_and(|def_id| ecx.can_define_opaque_ty(def_id)) |
| { |
| return Err(NoSolution); |
| } |
| } |
| |
| ecx.probe_and_evaluate_goal_for_constituent_tys( |
| goal, |
| structural_traits::instantiate_constituent_tys_for_auto_trait, |
| ) |
| } |
| |
| fn consider_trait_alias_candidate( |
| ecx: &mut EvalCtxt<'_, 'tcx>, |
| goal: Goal<'tcx, Self>, |
| ) -> QueryResult<'tcx> { |
| if goal.predicate.polarity != ty::ImplPolarity::Positive { |
| return Err(NoSolution); |
| } |
| |
| let tcx = ecx.tcx(); |
| |
| ecx.probe_misc_candidate("trait alias").enter(|ecx| { |
| let nested_obligations = tcx |
| .predicates_of(goal.predicate.def_id()) |
| .instantiate(tcx, goal.predicate.trait_ref.args); |
| ecx.add_goals(nested_obligations.predicates.into_iter().map(|p| goal.with(tcx, p))); |
| ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes) |
| }) |
| } |
| |
| fn consider_builtin_sized_candidate( |
| ecx: &mut EvalCtxt<'_, 'tcx>, |
| goal: Goal<'tcx, Self>, |
| ) -> QueryResult<'tcx> { |
| if goal.predicate.polarity != ty::ImplPolarity::Positive { |
| return Err(NoSolution); |
| } |
| |
| ecx.probe_and_evaluate_goal_for_constituent_tys( |
| goal, |
| structural_traits::instantiate_constituent_tys_for_sized_trait, |
| ) |
| } |
| |
| fn consider_builtin_copy_clone_candidate( |
| ecx: &mut EvalCtxt<'_, 'tcx>, |
| goal: Goal<'tcx, Self>, |
| ) -> QueryResult<'tcx> { |
| if goal.predicate.polarity != ty::ImplPolarity::Positive { |
| return Err(NoSolution); |
| } |
| |
| ecx.probe_and_evaluate_goal_for_constituent_tys( |
| goal, |
| structural_traits::instantiate_constituent_tys_for_copy_clone_trait, |
| ) |
| } |
| |
| fn consider_builtin_pointer_like_candidate( |
| ecx: &mut EvalCtxt<'_, 'tcx>, |
| goal: Goal<'tcx, Self>, |
| ) -> QueryResult<'tcx> { |
| if goal.predicate.polarity != ty::ImplPolarity::Positive { |
| return Err(NoSolution); |
| } |
| |
| // The regions of a type don't affect the size of the type |
| let tcx = ecx.tcx(); |
| // We should erase regions from both the param-env and type, since both |
| // may have infer regions. Specifically, after canonicalizing and instantiating, |
| // early bound regions turn into region vars in both the new and old solver. |
| let key = tcx.erase_regions(goal.param_env.and(goal.predicate.self_ty())); |
| // But if there are inference variables, we have to wait until it's resolved. |
| if key.has_non_region_infer() { |
| return ecx.evaluate_added_goals_and_make_canonical_response(Certainty::AMBIGUOUS); |
| } |
| |
| if let Ok(layout) = tcx.layout_of(key) |
| && layout.layout.is_pointer_like(&tcx.data_layout) |
| { |
| // FIXME: We could make this faster by making a no-constraints response |
| ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes) |
| } else { |
| Err(NoSolution) |
| } |
| } |
| |
| fn consider_builtin_fn_ptr_trait_candidate( |
| ecx: &mut EvalCtxt<'_, 'tcx>, |
| goal: Goal<'tcx, Self>, |
| ) -> QueryResult<'tcx> { |
| let self_ty = goal.predicate.self_ty(); |
| match goal.predicate.polarity { |
| ty::ImplPolarity::Positive => { |
| if self_ty.is_fn_ptr() { |
| ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes) |
| } else { |
| Err(NoSolution) |
| } |
| } |
| ty::ImplPolarity::Negative => { |
| // If a type is rigid and not a fn ptr, then we know for certain |
| // that it does *not* implement `FnPtr`. |
| if !self_ty.is_fn_ptr() && self_ty.is_known_rigid() { |
| ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes) |
| } else { |
| Err(NoSolution) |
| } |
| } |
| ty::ImplPolarity::Reservation => bug!(), |
| } |
| } |
| |
| fn consider_builtin_fn_trait_candidates( |
| ecx: &mut EvalCtxt<'_, 'tcx>, |
| goal: Goal<'tcx, Self>, |
| goal_kind: ty::ClosureKind, |
| ) -> QueryResult<'tcx> { |
| if goal.predicate.polarity != ty::ImplPolarity::Positive { |
| return Err(NoSolution); |
| } |
| |
| let tcx = ecx.tcx(); |
| let tupled_inputs_and_output = |
| match structural_traits::extract_tupled_inputs_and_output_from_callable( |
| tcx, |
| goal.predicate.self_ty(), |
| goal_kind, |
| )? { |
| Some(a) => a, |
| None => { |
| return ecx |
| .evaluate_added_goals_and_make_canonical_response(Certainty::AMBIGUOUS); |
| } |
| }; |
| let output_is_sized_pred = tupled_inputs_and_output.map_bound(|(_, output)| { |
| ty::TraitRef::from_lang_item(tcx, LangItem::Sized, DUMMY_SP, [output]) |
| }); |
| |
| let pred = tupled_inputs_and_output |
| .map_bound(|(inputs, _)| { |
| ty::TraitRef::new(tcx, goal.predicate.def_id(), [goal.predicate.self_ty(), inputs]) |
| }) |
| .to_predicate(tcx); |
| // A built-in `Fn` impl only holds if the output is sized. |
| // (FIXME: technically we only need to check this if the type is a fn ptr...) |
| Self::consider_implied_clause(ecx, goal, pred, [goal.with(tcx, output_is_sized_pred)]) |
| } |
| |
| fn consider_builtin_tuple_candidate( |
| ecx: &mut EvalCtxt<'_, 'tcx>, |
| goal: Goal<'tcx, Self>, |
| ) -> QueryResult<'tcx> { |
| if goal.predicate.polarity != ty::ImplPolarity::Positive { |
| return Err(NoSolution); |
| } |
| |
| if let ty::Tuple(..) = goal.predicate.self_ty().kind() { |
| ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes) |
| } else { |
| Err(NoSolution) |
| } |
| } |
| |
| fn consider_builtin_pointee_candidate( |
| ecx: &mut EvalCtxt<'_, 'tcx>, |
| goal: Goal<'tcx, Self>, |
| ) -> QueryResult<'tcx> { |
| if goal.predicate.polarity != ty::ImplPolarity::Positive { |
| return Err(NoSolution); |
| } |
| |
| ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes) |
| } |
| |
| fn consider_builtin_future_candidate( |
| ecx: &mut EvalCtxt<'_, 'tcx>, |
| goal: Goal<'tcx, Self>, |
| ) -> QueryResult<'tcx> { |
| if goal.predicate.polarity != ty::ImplPolarity::Positive { |
| return Err(NoSolution); |
| } |
| |
| let ty::Coroutine(def_id, _, _) = *goal.predicate.self_ty().kind() else { |
| return Err(NoSolution); |
| }; |
| |
| // Coroutines are not futures unless they come from `async` desugaring |
| let tcx = ecx.tcx(); |
| if !tcx.coroutine_is_async(def_id) { |
| return Err(NoSolution); |
| } |
| |
| // Async coroutine unconditionally implement `Future` |
| // Technically, we need to check that the future output type is Sized, |
| // but that's already proven by the coroutine being WF. |
| ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes) |
| } |
| |
| fn consider_builtin_iterator_candidate( |
| ecx: &mut EvalCtxt<'_, 'tcx>, |
| goal: Goal<'tcx, Self>, |
| ) -> QueryResult<'tcx> { |
| if goal.predicate.polarity != ty::ImplPolarity::Positive { |
| return Err(NoSolution); |
| } |
| |
| let ty::Coroutine(def_id, _, _) = *goal.predicate.self_ty().kind() else { |
| return Err(NoSolution); |
| }; |
| |
| // Coroutines are not iterators unless they come from `gen` desugaring |
| let tcx = ecx.tcx(); |
| if !tcx.coroutine_is_gen(def_id) { |
| return Err(NoSolution); |
| } |
| |
| // Gen coroutines unconditionally implement `Iterator` |
| // Technically, we need to check that the iterator output type is Sized, |
| // but that's already proven by the coroutines being WF. |
| ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes) |
| } |
| |
| fn consider_builtin_coroutine_candidate( |
| ecx: &mut EvalCtxt<'_, 'tcx>, |
| goal: Goal<'tcx, Self>, |
| ) -> QueryResult<'tcx> { |
| if goal.predicate.polarity != ty::ImplPolarity::Positive { |
| return Err(NoSolution); |
| } |
| |
| let self_ty = goal.predicate.self_ty(); |
| let ty::Coroutine(def_id, args, _) = *self_ty.kind() else { |
| return Err(NoSolution); |
| }; |
| |
| // `async`-desugared coroutines do not implement the coroutine trait |
| let tcx = ecx.tcx(); |
| if !tcx.is_general_coroutine(def_id) { |
| return Err(NoSolution); |
| } |
| |
| let coroutine = args.as_coroutine(); |
| Self::consider_implied_clause( |
| ecx, |
| goal, |
| ty::TraitRef::new(tcx, goal.predicate.def_id(), [self_ty, coroutine.resume_ty()]) |
| .to_predicate(tcx), |
| // Technically, we need to check that the coroutine types are Sized, |
| // but that's already proven by the coroutine being WF. |
| [], |
| ) |
| } |
| |
| fn consider_builtin_discriminant_kind_candidate( |
| ecx: &mut EvalCtxt<'_, 'tcx>, |
| goal: Goal<'tcx, Self>, |
| ) -> QueryResult<'tcx> { |
| if goal.predicate.polarity != ty::ImplPolarity::Positive { |
| return Err(NoSolution); |
| } |
| |
| // `DiscriminantKind` is automatically implemented for every type. |
| ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes) |
| } |
| |
| fn consider_builtin_destruct_candidate( |
| ecx: &mut EvalCtxt<'_, 'tcx>, |
| goal: Goal<'tcx, Self>, |
| ) -> QueryResult<'tcx> { |
| if goal.predicate.polarity != ty::ImplPolarity::Positive { |
| return Err(NoSolution); |
| } |
| |
| // FIXME(-Ztrait-solver=next): Implement this when we get const working in the new solver |
| |
| // `Destruct` is automatically implemented for every type in |
| // non-const environments. |
| ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes) |
| } |
| |
| fn consider_builtin_transmute_candidate( |
| ecx: &mut EvalCtxt<'_, 'tcx>, |
| goal: Goal<'tcx, Self>, |
| ) -> QueryResult<'tcx> { |
| if goal.predicate.polarity != ty::ImplPolarity::Positive { |
| return Err(NoSolution); |
| } |
| |
| // `rustc_transmute` does not have support for type or const params |
| if goal.has_non_region_placeholders() { |
| return Err(NoSolution); |
| } |
| |
| // Erase regions because we compute layouts in `rustc_transmute`, |
| // which will ICE for region vars. |
| let args = ecx.tcx().erase_regions(goal.predicate.trait_ref.args); |
| |
| let Some(assume) = |
| rustc_transmute::Assume::from_const(ecx.tcx(), goal.param_env, args.const_at(3)) |
| else { |
| return Err(NoSolution); |
| }; |
| |
| let certainty = ecx.is_transmutable( |
| rustc_transmute::Types { dst: args.type_at(0), src: args.type_at(1) }, |
| args.type_at(2), |
| assume, |
| )?; |
| ecx.evaluate_added_goals_and_make_canonical_response(certainty) |
| } |
| |
| fn consider_unsize_to_dyn_candidate( |
| ecx: &mut EvalCtxt<'_, 'tcx>, |
| goal: Goal<'tcx, Self>, |
| ) -> QueryResult<'tcx> { |
| ecx.probe(|_| ProbeKind::UnsizeAssembly).enter(|ecx| { |
| let a_ty = goal.predicate.self_ty(); |
| // We need to normalize the b_ty since it's destructured as a `dyn Trait`. |
| let Some(b_ty) = |
| ecx.try_normalize_ty(goal.param_env, goal.predicate.trait_ref.args.type_at(1))? |
| else { |
| return ecx.evaluate_added_goals_and_make_canonical_response(Certainty::OVERFLOW); |
| }; |
| |
| let ty::Dynamic(b_data, b_region, ty::Dyn) = *b_ty.kind() else { |
| return Err(NoSolution); |
| }; |
| |
| let tcx = ecx.tcx(); |
| |
| // Can only unsize to an object-safe trait. |
| if b_data.principal_def_id().is_some_and(|def_id| !tcx.check_is_object_safe(def_id)) { |
| return Err(NoSolution); |
| } |
| |
| // Check that the type implements all of the predicates of the trait object. |
| // (i.e. the principal, all of the associated types match, and any auto traits) |
| ecx.add_goals(b_data.iter().map(|pred| goal.with(tcx, pred.with_self_ty(tcx, a_ty)))); |
| |
| // The type must be `Sized` to be unsized. |
| if let Some(sized_def_id) = tcx.lang_items().sized_trait() { |
| ecx.add_goal(goal.with(tcx, ty::TraitRef::new(tcx, sized_def_id, [a_ty]))); |
| } else { |
| return Err(NoSolution); |
| } |
| |
| // The type must outlive the lifetime of the `dyn` we're unsizing into. |
| ecx.add_goal(goal.with(tcx, ty::OutlivesPredicate(a_ty, b_region))); |
| ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes) |
| }) |
| } |
| |
| /// ```ignore (builtin impl example) |
| /// trait Trait { |
| /// fn foo(&self); |
| /// } |
| /// // results in the following builtin impl |
| /// impl<'a, T: Trait + 'a> Unsize<dyn Trait + 'a> for T {} |
| /// ``` |
| fn consider_structural_builtin_unsize_candidates( |
| ecx: &mut EvalCtxt<'_, 'tcx>, |
| goal: Goal<'tcx, Self>, |
| ) -> Vec<(CanonicalResponse<'tcx>, BuiltinImplSource)> { |
| if goal.predicate.polarity != ty::ImplPolarity::Positive { |
| return vec![]; |
| } |
| |
| let misc_candidate = |ecx: &mut EvalCtxt<'_, 'tcx>, certainty| { |
| ( |
| ecx.evaluate_added_goals_and_make_canonical_response(certainty).unwrap(), |
| BuiltinImplSource::Misc, |
| ) |
| }; |
| |
| let result_to_single = |result, source| match result { |
| Ok(resp) => vec![(resp, source)], |
| Err(NoSolution) => vec![], |
| }; |
| |
| ecx.probe(|_| ProbeKind::UnsizeAssembly).enter(|ecx| { |
| let a_ty = goal.predicate.self_ty(); |
| // We need to normalize the b_ty since it's matched structurally |
| // in the other functions below. |
| let b_ty = match ecx |
| .try_normalize_ty(goal.param_env, goal.predicate.trait_ref.args.type_at(1)) |
| { |
| Ok(Some(b_ty)) => b_ty, |
| Ok(None) => return vec![misc_candidate(ecx, Certainty::OVERFLOW)], |
| Err(_) => return vec![], |
| }; |
| |
| let goal = goal.with(ecx.tcx(), (a_ty, b_ty)); |
| match (a_ty.kind(), b_ty.kind()) { |
| (ty::Infer(ty::TyVar(..)), ..) => bug!("unexpected infer {a_ty:?} {b_ty:?}"), |
| (_, ty::Infer(ty::TyVar(..))) => vec![misc_candidate(ecx, Certainty::AMBIGUOUS)], |
| |
| // Trait upcasting, or `dyn Trait + Auto + 'a` -> `dyn Trait + 'b`. |
| ( |
| &ty::Dynamic(a_data, a_region, ty::Dyn), |
| &ty::Dynamic(b_data, b_region, ty::Dyn), |
| ) => ecx.consider_builtin_dyn_upcast_candidates( |
| goal, a_data, a_region, b_data, b_region, |
| ), |
| |
| // `T` -> `dyn Trait` unsizing is handled separately in `consider_unsize_to_dyn_candidate` |
| (_, &ty::Dynamic(..)) => vec![], |
| |
| // `[T; N]` -> `[T]` unsizing |
| (&ty::Array(a_elem_ty, ..), &ty::Slice(b_elem_ty)) => result_to_single( |
| ecx.consider_builtin_array_unsize(goal, a_elem_ty, b_elem_ty), |
| BuiltinImplSource::Misc, |
| ), |
| |
| // `Struct<T>` -> `Struct<U>` where `T: Unsize<U>` |
| (&ty::Adt(a_def, a_args), &ty::Adt(b_def, b_args)) |
| if a_def.is_struct() && a_def == b_def => |
| { |
| result_to_single( |
| ecx.consider_builtin_struct_unsize(goal, a_def, a_args, b_args), |
| BuiltinImplSource::Misc, |
| ) |
| } |
| |
| // `(A, B, T)` -> `(A, B, U)` where `T: Unsize<U>` |
| (&ty::Tuple(a_tys), &ty::Tuple(b_tys)) |
| if a_tys.len() == b_tys.len() && !a_tys.is_empty() => |
| { |
| result_to_single( |
| ecx.consider_builtin_tuple_unsize(goal, a_tys, b_tys), |
| BuiltinImplSource::TupleUnsizing, |
| ) |
| } |
| |
| _ => vec![], |
| } |
| }) |
| } |
| } |
| |
| impl<'tcx> EvalCtxt<'_, 'tcx> { |
| /// Trait upcasting allows for coercions between trait objects: |
| /// ```ignore (builtin impl example) |
| /// trait Super {} |
| /// trait Trait: Super {} |
| /// // results in builtin impls upcasting to a super trait |
| /// impl<'a, 'b: 'a> Unsize<dyn Super + 'a> for dyn Trait + 'b {} |
| /// // and impls removing auto trait bounds. |
| /// impl<'a, 'b: 'a> Unsize<dyn Trait + 'a> for dyn Trait + Send + 'b {} |
| /// ``` |
| fn consider_builtin_dyn_upcast_candidates( |
| &mut self, |
| goal: Goal<'tcx, (Ty<'tcx>, Ty<'tcx>)>, |
| a_data: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>, |
| a_region: ty::Region<'tcx>, |
| b_data: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>, |
| b_region: ty::Region<'tcx>, |
| ) -> Vec<(CanonicalResponse<'tcx>, BuiltinImplSource)> { |
| let tcx = self.tcx(); |
| let Goal { predicate: (a_ty, _b_ty), .. } = goal; |
| |
| // All of a's auto traits need to be in b's auto traits. |
| let auto_traits_compatible = |
| b_data.auto_traits().all(|b| a_data.auto_traits().any(|a| a == b)); |
| if !auto_traits_compatible { |
| return vec![]; |
| } |
| |
| let mut responses = vec![]; |
| // If the principal def ids match (or are both none), then we're not doing |
| // trait upcasting. We're just removing auto traits (or shortening the lifetime). |
| if a_data.principal_def_id() == b_data.principal_def_id() { |
| if let Ok(resp) = self.consider_builtin_upcast_to_principal( |
| goal, |
| a_data, |
| a_region, |
| b_data, |
| b_region, |
| a_data.principal(), |
| ) { |
| responses.push((resp, BuiltinImplSource::Misc)); |
| } |
| } else if let Some(a_principal) = a_data.principal() { |
| self.walk_vtable( |
| a_principal.with_self_ty(tcx, a_ty), |
| |ecx, new_a_principal, _, vtable_vptr_slot| { |
| if let Ok(resp) = ecx.probe_misc_candidate("dyn upcast").enter(|ecx| { |
| ecx.consider_builtin_upcast_to_principal( |
| goal, |
| a_data, |
| a_region, |
| b_data, |
| b_region, |
| Some(new_a_principal.map_bound(|trait_ref| { |
| ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref) |
| })), |
| ) |
| }) { |
| responses |
| .push((resp, BuiltinImplSource::TraitUpcasting { vtable_vptr_slot })); |
| } |
| }, |
| ); |
| } |
| |
| responses |
| } |
| |
| fn consider_builtin_upcast_to_principal( |
| &mut self, |
| goal: Goal<'tcx, (Ty<'tcx>, Ty<'tcx>)>, |
| a_data: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>, |
| a_region: ty::Region<'tcx>, |
| b_data: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>, |
| b_region: ty::Region<'tcx>, |
| upcast_principal: Option<ty::PolyExistentialTraitRef<'tcx>>, |
| ) -> QueryResult<'tcx> { |
| let param_env = goal.param_env; |
| |
| // More than one projection in a_ty's bounds may match the projection |
| // in b_ty's bound. Use this to first determine *which* apply without |
| // having any inference side-effects. We process obligations because |
| // unification may initially succeed due to deferred projection equality. |
| let projection_may_match = |
| |ecx: &mut Self, |
| source_projection: ty::PolyExistentialProjection<'tcx>, |
| target_projection: ty::PolyExistentialProjection<'tcx>| { |
| source_projection.item_def_id() == target_projection.item_def_id() |
| && ecx |
| .probe(|_| ProbeKind::UpcastProjectionCompatibility) |
| .enter(|ecx| -> Result<(), NoSolution> { |
| ecx.eq(param_env, source_projection, target_projection)?; |
| let _ = ecx.try_evaluate_added_goals()?; |
| Ok(()) |
| }) |
| .is_ok() |
| }; |
| |
| for bound in b_data { |
| match bound.skip_binder() { |
| // Check that a's supertrait (upcast_principal) is compatible |
| // with the target (b_ty). |
| ty::ExistentialPredicate::Trait(target_principal) => { |
| self.eq(param_env, upcast_principal.unwrap(), bound.rebind(target_principal))?; |
| } |
| // Check that b_ty's projection is satisfied by exactly one of |
| // a_ty's projections. First, we look through the list to see if |
| // any match. If not, error. Then, if *more* than one matches, we |
| // return ambiguity. Otherwise, if exactly one matches, equate |
| // it with b_ty's projection. |
| ty::ExistentialPredicate::Projection(target_projection) => { |
| let target_projection = bound.rebind(target_projection); |
| let mut matching_projections = |
| a_data.projection_bounds().filter(|source_projection| { |
| projection_may_match(self, *source_projection, target_projection) |
| }); |
| let Some(source_projection) = matching_projections.next() else { |
| return Err(NoSolution); |
| }; |
| if matching_projections.next().is_some() { |
| return self.evaluate_added_goals_and_make_canonical_response( |
| Certainty::AMBIGUOUS, |
| ); |
| } |
| self.eq(param_env, source_projection, target_projection)?; |
| } |
| // Check that b_ty's auto traits are present in a_ty's bounds. |
| ty::ExistentialPredicate::AutoTrait(def_id) => { |
| if !a_data.auto_traits().any(|source_def_id| source_def_id == def_id) { |
| return Err(NoSolution); |
| } |
| } |
| } |
| } |
| |
| // Also require that a_ty's lifetime outlives b_ty's lifetime. |
| self.add_goal(Goal::new( |
| self.tcx(), |
| param_env, |
| ty::Binder::dummy(ty::OutlivesPredicate(a_region, b_region)), |
| )); |
| |
| self.evaluate_added_goals_and_make_canonical_response(Certainty::Yes) |
| } |
| |
| /// We have the following builtin impls for arrays: |
| /// ```ignore (builtin impl example) |
| /// impl<T: ?Sized, const N: usize> Unsize<[T]> for [T; N] {} |
| /// ``` |
| /// While the impl itself could theoretically not be builtin, |
| /// the actual unsizing behavior is builtin. Its also easier to |
| /// make all impls of `Unsize` builtin as we're able to use |
| /// `#[rustc_deny_explicit_impl]` in this case. |
| fn consider_builtin_array_unsize( |
| &mut self, |
| goal: Goal<'tcx, (Ty<'tcx>, Ty<'tcx>)>, |
| a_elem_ty: Ty<'tcx>, |
| b_elem_ty: Ty<'tcx>, |
| ) -> QueryResult<'tcx> { |
| self.eq(goal.param_env, a_elem_ty, b_elem_ty)?; |
| self.evaluate_added_goals_and_make_canonical_response(Certainty::Yes) |
| } |
| |
| /// We generate a builtin `Unsize` impls for structs with generic parameters only |
| /// mentioned by the last field. |
| /// ```ignore (builtin impl example) |
| /// struct Foo<T, U: ?Sized> { |
| /// sized_field: Vec<T>, |
| /// unsizable: Box<U>, |
| /// } |
| /// // results in the following builtin impl |
| /// impl<T: ?Sized, U: ?Sized, V: ?Sized> Unsize<Foo<T, V>> for Foo<T, U> |
| /// where |
| /// Box<U>: Unsize<Box<V>>, |
| /// {} |
| /// ``` |
| fn consider_builtin_struct_unsize( |
| &mut self, |
| goal: Goal<'tcx, (Ty<'tcx>, Ty<'tcx>)>, |
| def: ty::AdtDef<'tcx>, |
| a_args: ty::GenericArgsRef<'tcx>, |
| b_args: ty::GenericArgsRef<'tcx>, |
| ) -> QueryResult<'tcx> { |
| let tcx = self.tcx(); |
| let Goal { predicate: (_a_ty, b_ty), .. } = goal; |
| |
| let unsizing_params = tcx.unsizing_params_for_adt(def.did()); |
| // We must be unsizing some type parameters. This also implies |
| // that the struct has a tail field. |
| if unsizing_params.is_empty() { |
| return Err(NoSolution); |
| } |
| |
| let tail_field = def.non_enum_variant().tail(); |
| let tail_field_ty = tcx.type_of(tail_field.did); |
| |
| let a_tail_ty = tail_field_ty.instantiate(tcx, a_args); |
| let b_tail_ty = tail_field_ty.instantiate(tcx, b_args); |
| |
| // Substitute just the unsizing params from B into A. The type after |
| // this substitution must be equal to B. This is so we don't unsize |
| // unrelated type parameters. |
| let new_a_args = tcx.mk_args_from_iter( |
| a_args |
| .iter() |
| .enumerate() |
| .map(|(i, a)| if unsizing_params.contains(i as u32) { b_args[i] } else { a }), |
| ); |
| let unsized_a_ty = Ty::new_adt(tcx, def, new_a_args); |
| |
| // Finally, we require that `TailA: Unsize<TailB>` for the tail field |
| // types. |
| self.eq(goal.param_env, unsized_a_ty, b_ty)?; |
| self.add_goal(goal.with( |
| tcx, |
| ty::TraitRef::new( |
| tcx, |
| tcx.lang_items().unsize_trait().unwrap(), |
| [a_tail_ty, b_tail_ty], |
| ), |
| )); |
| self.evaluate_added_goals_and_make_canonical_response(Certainty::Yes) |
| } |
| |
| /// We generate the following builtin impl for tuples of all sizes. |
| /// |
| /// This impl is still unstable and we emit a feature error when it |
| /// when it is used by a coercion. |
| /// ```ignore (builtin impl example) |
| /// impl<T: ?Sized, U: ?Sized, V: ?Sized> Unsize<(T, V)> for (T, U) |
| /// where |
| /// U: Unsize<V>, |
| /// {} |
| /// ``` |
| fn consider_builtin_tuple_unsize( |
| &mut self, |
| goal: Goal<'tcx, (Ty<'tcx>, Ty<'tcx>)>, |
| a_tys: &'tcx ty::List<Ty<'tcx>>, |
| b_tys: &'tcx ty::List<Ty<'tcx>>, |
| ) -> QueryResult<'tcx> { |
| let tcx = self.tcx(); |
| let Goal { predicate: (_a_ty, b_ty), .. } = goal; |
| |
| let (&a_last_ty, a_rest_tys) = a_tys.split_last().unwrap(); |
| let &b_last_ty = b_tys.last().unwrap(); |
| |
| // Substitute just the tail field of B., and require that they're equal. |
| let unsized_a_ty = |
| Ty::new_tup_from_iter(tcx, a_rest_tys.iter().copied().chain([b_last_ty])); |
| self.eq(goal.param_env, unsized_a_ty, b_ty)?; |
| |
| // Similar to ADTs, require that we can unsize the tail. |
| self.add_goal(goal.with( |
| tcx, |
| ty::TraitRef::new( |
| tcx, |
| tcx.lang_items().unsize_trait().unwrap(), |
| [a_last_ty, b_last_ty], |
| ), |
| )); |
| self.evaluate_added_goals_and_make_canonical_response(Certainty::Yes) |
| } |
| |
| // Return `Some` if there is an impl (built-in or user provided) that may |
| // hold for the self type of the goal, which for coherence and soundness |
| // purposes must disqualify the built-in auto impl assembled by considering |
| // the type's constituent types. |
| fn disqualify_auto_trait_candidate_due_to_possible_impl( |
| &mut self, |
| goal: Goal<'tcx, TraitPredicate<'tcx>>, |
| ) -> Option<QueryResult<'tcx>> { |
| let self_ty = goal.predicate.self_ty(); |
| match *self_ty.kind() { |
| // Stall int and float vars until they are resolved to a concrete |
| // numerical type. That's because the check for impls below treats |
| // int vars as matching any impl. Even if we filtered such impls, |
| // we probably don't want to treat an `impl !AutoTrait for i32` as |
| // disqualifying the built-in auto impl for `i64: AutoTrait` either. |
| ty::Infer(ty::IntVar(_) | ty::FloatVar(_)) => { |
| Some(self.evaluate_added_goals_and_make_canonical_response(Certainty::AMBIGUOUS)) |
| } |
| |
| // These types cannot be structurally decomposed into constituent |
| // types, and therefore have no built-in auto impl. |
| ty::Dynamic(..) |
| | ty::Param(..) |
| | ty::Foreign(..) |
| | ty::Alias(ty::Projection | ty::Weak | ty::Inherent, ..) |
| | ty::Placeholder(..) => Some(Err(NoSolution)), |
| |
| ty::Infer(_) | ty::Bound(_, _) => bug!("unexpected type `{self_ty}`"), |
| |
| // Coroutines have one special built-in candidate, `Unpin`, which |
| // takes precedence over the structural auto trait candidate being |
| // assembled. |
| ty::Coroutine(_, _, movability) |
| if Some(goal.predicate.def_id()) == self.tcx().lang_items().unpin_trait() => |
| { |
| match movability { |
| Movability::Static => Some(Err(NoSolution)), |
| Movability::Movable => { |
| Some(self.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)) |
| } |
| } |
| } |
| |
| // For rigid types, any possible implementation that could apply to |
| // the type (even if after unification and processing nested goals |
| // it does not hold) will disqualify the built-in auto impl. |
| // |
| // This differs from the current stable behavior and fixes #84857. |
| // Due to breakage found via crater, we currently instead lint |
| // patterns which can be used to exploit this unsoundness on stable, |
| // see #93367 for more details. |
| ty::Bool |
| | ty::Char |
| | ty::Int(_) |
| | ty::Uint(_) |
| | ty::Float(_) |
| | ty::Str |
| | ty::Array(_, _) |
| | ty::Slice(_) |
| | ty::RawPtr(_) |
| | ty::Ref(_, _, _) |
| | ty::FnDef(_, _) |
| | ty::FnPtr(_) |
| | ty::Closure(_, _) |
| | ty::Coroutine(_, _, _) |
| | ty::CoroutineWitness(..) |
| | ty::Never |
| | ty::Tuple(_) |
| | ty::Adt(_, _) |
| // FIXME: Handling opaques here is kinda sus. Especially because we |
| // simplify them to SimplifiedType::Placeholder. |
| | ty::Alias(ty::Opaque, _) => { |
| let mut disqualifying_impl = None; |
| self.tcx().for_each_relevant_impl_treating_projections( |
| goal.predicate.def_id(), |
| goal.predicate.self_ty(), |
| TreatProjections::NextSolverLookup, |
| |impl_def_id| { |
| disqualifying_impl = Some(impl_def_id); |
| }, |
| ); |
| if let Some(def_id) = disqualifying_impl { |
| debug!(?def_id, ?goal, "disqualified auto-trait implementation"); |
| // No need to actually consider the candidate here, |
| // since we do that in `consider_impl_candidate`. |
| return Some(Err(NoSolution)); |
| } else { |
| None |
| } |
| } |
| ty::Error(_) => None, |
| } |
| } |
| |
| /// Convenience function for traits that are structural, i.e. that only |
| /// have nested subgoals that only change the self type. Unlike other |
| /// evaluate-like helpers, this does a probe, so it doesn't need to be |
| /// wrapped in one. |
| fn probe_and_evaluate_goal_for_constituent_tys( |
| &mut self, |
| goal: Goal<'tcx, TraitPredicate<'tcx>>, |
| constituent_tys: impl Fn(&EvalCtxt<'_, 'tcx>, Ty<'tcx>) -> Result<Vec<Ty<'tcx>>, NoSolution>, |
| ) -> QueryResult<'tcx> { |
| self.probe_misc_candidate("constituent tys").enter(|ecx| { |
| ecx.add_goals( |
| constituent_tys(ecx, goal.predicate.self_ty())? |
| .into_iter() |
| .map(|ty| goal.with(ecx.tcx(), goal.predicate.with_self_ty(ecx.tcx(), ty))) |
| .collect::<Vec<_>>(), |
| ); |
| ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes) |
| }) |
| } |
| |
| #[instrument(level = "debug", skip(self))] |
| pub(super) fn compute_trait_goal( |
| &mut self, |
| goal: Goal<'tcx, TraitPredicate<'tcx>>, |
| ) -> QueryResult<'tcx> { |
| let candidates = self.assemble_and_evaluate_candidates(goal); |
| self.merge_candidates(candidates) |
| } |
| } |
