diff options
5 files changed, 274 insertions, 68 deletions
diff --git a/compiler/rustc_trait_selection/src/solve/assembly/mod.rs b/compiler/rustc_trait_selection/src/solve/assembly/mod.rs index 1e798998895..73cf15ff94b 100644 --- a/compiler/rustc_trait_selection/src/solve/assembly/mod.rs +++ b/compiler/rustc_trait_selection/src/solve/assembly/mod.rs @@ -10,9 +10,11 @@ use rustc_infer::traits::util::elaborate; use rustc_infer::traits::Reveal; use rustc_middle::traits::solve::inspect::CandidateKind; use rustc_middle::traits::solve::{CanonicalResponse, Certainty, Goal, MaybeCause, QueryResult}; -use rustc_middle::ty::fast_reject::TreatProjections; -use rustc_middle::ty::TypeFoldable; +use rustc_middle::ty::fast_reject::{SimplifiedType, TreatParams}; +use rustc_middle::ty::TypeVisitableExt; use rustc_middle::ty::{self, Ty, TyCtxt}; +use rustc_middle::ty::{fast_reject, TypeFoldable}; +use rustc_span::ErrorGuaranteed; use std::fmt::Debug; pub(super) mod structural_traits; @@ -109,10 +111,10 @@ pub(super) trait GoalKind<'tcx>: fn trait_def_id(self, tcx: TyCtxt<'tcx>) -> DefId; - // Try equating an assumption predicate against a goal's predicate. If it - // holds, then execute the `then` callback, which should do any additional - // work, then produce a response (typically by executing - // [`EvalCtxt::evaluate_added_goals_and_make_canonical_response`]). + /// Try equating an assumption predicate against a goal's predicate. If it + /// holds, then execute the `then` callback, which should do any additional + /// work, then produce a response (typically by executing + /// [`EvalCtxt::evaluate_added_goals_and_make_canonical_response`]). fn probe_and_match_goal_against_assumption( ecx: &mut EvalCtxt<'_, 'tcx>, goal: Goal<'tcx, Self>, @@ -120,9 +122,9 @@ pub(super) trait GoalKind<'tcx>: then: impl FnOnce(&mut EvalCtxt<'_, 'tcx>) -> QueryResult<'tcx>, ) -> QueryResult<'tcx>; - // Consider a clause, which consists of a "assumption" and some "requirements", - // to satisfy a goal. If the requirements hold, then attempt to satisfy our - // goal by equating it with the assumption. + /// Consider a clause, which consists of a "assumption" and some "requirements", + /// to satisfy a goal. If the requirements hold, then attempt to satisfy our + /// goal by equating it with the assumption. fn consider_implied_clause( ecx: &mut EvalCtxt<'_, 'tcx>, goal: Goal<'tcx, Self>, @@ -149,9 +151,9 @@ pub(super) trait GoalKind<'tcx>: }) } - // Consider a clause specifically for a `dyn Trait` self type. This requires - // additionally checking all of the supertraits and object bounds to hold, - // since they're not implied by the well-formedness of the object type. + /// Consider a clause specifically for a `dyn Trait` self type. This requires + /// additionally checking all of the supertraits and object bounds to hold, + /// since they're not implied by the well-formedness of the object type. fn consider_object_bound_candidate( ecx: &mut EvalCtxt<'_, 'tcx>, goal: Goal<'tcx, Self>, @@ -182,96 +184,106 @@ pub(super) trait GoalKind<'tcx>: impl_def_id: DefId, ) -> QueryResult<'tcx>; - // A type implements an `auto trait` if its components do as well. These components - // are given by built-in rules from [`instantiate_constituent_tys_for_auto_trait`]. + /// If the predicate contained an error, we want to avoid emitting unnecessary trait errors but + /// still want to emit errors for other trait goals. We have some special handling for this case. + /// + /// Trait goals always hold while projection goals never do. This is a bit arbitrary but prevents + /// incorrect normalization while hiding any trait errors. + fn consider_error_guaranteed_candidate( + ecx: &mut EvalCtxt<'_, 'tcx>, + guar: ErrorGuaranteed, + ) -> QueryResult<'tcx>; + + /// A type implements an `auto trait` if its components do as well. These components + /// are given by built-in rules from [`instantiate_constituent_tys_for_auto_trait`]. fn consider_auto_trait_candidate( ecx: &mut EvalCtxt<'_, 'tcx>, goal: Goal<'tcx, Self>, ) -> QueryResult<'tcx>; - // A trait alias holds if the RHS traits and `where` clauses hold. + /// A trait alias holds if the RHS traits and `where` clauses hold. fn consider_trait_alias_candidate( ecx: &mut EvalCtxt<'_, 'tcx>, goal: Goal<'tcx, Self>, ) -> QueryResult<'tcx>; - // A type is `Copy` or `Clone` if its components are `Sized`. These components - // are given by built-in rules from [`instantiate_constituent_tys_for_sized_trait`]. + /// A type is `Copy` or `Clone` if its components are `Sized`. These components + /// are given by built-in rules from [`instantiate_constituent_tys_for_sized_trait`]. fn consider_builtin_sized_candidate( ecx: &mut EvalCtxt<'_, 'tcx>, goal: Goal<'tcx, Self>, ) -> QueryResult<'tcx>; - // A type is `Copy` or `Clone` if its components are `Copy` or `Clone`. These - // components are given by built-in rules from [`instantiate_constituent_tys_for_copy_clone_trait`]. + /// A type is `Copy` or `Clone` if its components are `Copy` or `Clone`. These + /// components are given by built-in rules from [`instantiate_constituent_tys_for_copy_clone_trait`]. fn consider_builtin_copy_clone_candidate( ecx: &mut EvalCtxt<'_, 'tcx>, goal: Goal<'tcx, Self>, ) -> QueryResult<'tcx>; - // A type is `PointerLike` if we can compute its layout, and that layout - // matches the layout of `usize`. + /// A type is `PointerLike` if we can compute its layout, and that layout + /// matches the layout of `usize`. fn consider_builtin_pointer_like_candidate( ecx: &mut EvalCtxt<'_, 'tcx>, goal: Goal<'tcx, Self>, ) -> QueryResult<'tcx>; - // A type is a `FnPtr` if it is of `FnPtr` type. + /// A type is a `FnPtr` if it is of `FnPtr` type. fn consider_builtin_fn_ptr_trait_candidate( ecx: &mut EvalCtxt<'_, 'tcx>, goal: Goal<'tcx, Self>, ) -> QueryResult<'tcx>; - // A callable type (a closure, fn def, or fn ptr) is known to implement the `Fn<A>` - // family of traits where `A` is given by the signature of the type. + /// A callable type (a closure, fn def, or fn ptr) is known to implement the `Fn<A>` + /// family of traits where `A` is given by the signature of the type. fn consider_builtin_fn_trait_candidates( ecx: &mut EvalCtxt<'_, 'tcx>, goal: Goal<'tcx, Self>, kind: ty::ClosureKind, ) -> QueryResult<'tcx>; - // `Tuple` is implemented if the `Self` type is a tuple. + /// `Tuple` is implemented if the `Self` type is a tuple. fn consider_builtin_tuple_candidate( ecx: &mut EvalCtxt<'_, 'tcx>, goal: Goal<'tcx, Self>, ) -> QueryResult<'tcx>; - // `Pointee` is always implemented. - // - // See the projection implementation for the `Metadata` types for all of - // the built-in types. For structs, the metadata type is given by the struct - // tail. + /// `Pointee` is always implemented. + /// + /// See the projection implementation for the `Metadata` types for all of + /// the built-in types. For structs, the metadata type is given by the struct + /// tail. fn consider_builtin_pointee_candidate( ecx: &mut EvalCtxt<'_, 'tcx>, goal: Goal<'tcx, Self>, ) -> QueryResult<'tcx>; - // A generator (that comes from an `async` desugaring) is known to implement - // `Future<Output = O>`, where `O` is given by the generator's return type - // that was computed during type-checking. + /// A generator (that comes from an `async` desugaring) is known to implement + /// `Future<Output = O>`, where `O` is given by the generator's return type + /// that was computed during type-checking. fn consider_builtin_future_candidate( ecx: &mut EvalCtxt<'_, 'tcx>, goal: Goal<'tcx, Self>, ) -> QueryResult<'tcx>; - // A generator (that doesn't come from an `async` desugaring) is known to - // implement `Generator<R, Yield = Y, Return = O>`, given the resume, yield, - // and return types of the generator computed during type-checking. + /// A generator (that doesn't come from an `async` desugaring) is known to + /// implement `Generator<R, Yield = Y, Return = O>`, given the resume, yield, + /// and return types of the generator computed during type-checking. fn consider_builtin_generator_candidate( ecx: &mut EvalCtxt<'_, 'tcx>, goal: Goal<'tcx, Self>, ) -> QueryResult<'tcx>; - // The most common forms of unsizing are array to slice, and concrete (Sized) - // type into a `dyn Trait`. ADTs and Tuples can also have their final field - // unsized if it's generic. + /// The most common forms of unsizing are array to slice, and concrete (Sized) + /// type into a `dyn Trait`. ADTs and Tuples can also have their final field + /// unsized if it's generic. fn consider_builtin_unsize_candidate( ecx: &mut EvalCtxt<'_, 'tcx>, goal: Goal<'tcx, Self>, ) -> QueryResult<'tcx>; - // `dyn Trait1` can be unsized to `dyn Trait2` if they are the same trait, or - // if `Trait2` is a (transitive) supertrait of `Trait2`. + /// `dyn Trait1` can be unsized to `dyn Trait2` if they are the same trait, or + /// if `Trait2` is a (transitive) supertrait of `Trait2`. fn consider_builtin_dyn_upcast_candidates( ecx: &mut EvalCtxt<'_, 'tcx>, goal: Goal<'tcx, Self>, @@ -299,35 +311,60 @@ impl<'tcx> EvalCtxt<'_, 'tcx> { goal: Goal<'tcx, G>, ) -> Vec<Candidate<'tcx>> { debug_assert_eq!(goal, self.resolve_vars_if_possible(goal)); + if let Some(ambig) = self.self_ty_infer_ambiguity_hack(goal) { + return ambig; + } + + let mut candidates = self.assemble_candidates_via_self_ty(goal); + + self.assemble_blanket_impl_candidates(goal, &mut candidates); + + self.assemble_param_env_candidates(goal, &mut candidates); - // HACK: `_: Trait` is ambiguous, because it may be satisfied via a builtin rule, - // object bound, alias bound, etc. We are unable to determine this until we can at - // least structurally resolve the type one layer. - if goal.predicate.self_ty().is_ty_var() { - return vec![Candidate { + candidates + } + + fn self_ty_infer_ambiguity_hack<G: GoalKind<'tcx>>( + &mut self, + goal: Goal<'tcx, G>, + ) -> Option<Vec<Candidate<'tcx>>> { + goal.predicate.self_ty().is_ty_var().then(|| { + vec![Candidate { source: CandidateSource::BuiltinImpl(BuiltinImplSource::Ambiguity), result: self .evaluate_added_goals_and_make_canonical_response(Certainty::AMBIGUOUS) .unwrap(), - }]; + }] + }) + } + + /// Assemble candidates which apply to the self type. This only looks at candidate which + /// apply to the specific self type and ignores all others. + /// + /// Returns `None` if the self type is still ambiguous. + fn assemble_candidates_via_self_ty<G: GoalKind<'tcx>>( + &mut self, + goal: Goal<'tcx, G>, + ) -> Vec<Candidate<'tcx>> { + debug_assert_eq!(goal, self.resolve_vars_if_possible(goal)); + if let Some(ambig) = self.self_ty_infer_ambiguity_hack(goal) { + return ambig; } let mut candidates = Vec::new(); - self.assemble_candidates_after_normalizing_self_ty(goal, &mut candidates); - - self.assemble_impl_candidates(goal, &mut candidates); + self.assemble_non_blanket_impl_candidates(goal, &mut candidates); self.assemble_builtin_impl_candidates(goal, &mut candidates); - self.assemble_param_env_candidates(goal, &mut candidates); - self.assemble_alias_bound_candidates(goal, &mut candidates); self.assemble_object_bound_candidates(goal, &mut candidates); self.assemble_coherence_unknowable_candidates(goal, &mut candidates); + self.assemble_candidates_after_normalizing_self_ty(goal, &mut candidates); + candidates } @@ -385,7 +422,7 @@ impl<'tcx> EvalCtxt<'_, 'tcx> { // have a `Normalized` candidate. This doesn't work as long as we // use `CandidateSource` in winnowing. let goal = goal.with(tcx, goal.predicate.with_self_ty(tcx, normalized_ty)); - Ok(ecx.assemble_and_evaluate_candidates(goal)) + Ok(ecx.assemble_candidates_via_self_ty(goal)) }, ) }); @@ -396,22 +433,125 @@ impl<'tcx> EvalCtxt<'_, 'tcx> { } #[instrument(level = "debug", skip_all)] - fn assemble_impl_candidates<G: GoalKind<'tcx>>( + fn assemble_non_blanket_impl_candidates<G: GoalKind<'tcx>>( &mut self, goal: Goal<'tcx, G>, candidates: &mut Vec<Candidate<'tcx>>, ) { let tcx = self.tcx(); - tcx.for_each_relevant_impl_treating_projections( - goal.predicate.trait_def_id(tcx), - goal.predicate.self_ty(), - TreatProjections::NextSolverLookup, - |impl_def_id| match G::consider_impl_candidate(self, goal, impl_def_id) { + let self_ty = goal.predicate.self_ty(); + let trait_impls = tcx.trait_impls_of(goal.predicate.trait_def_id(tcx)); + let mut consider_impls_for_simplified_type = |simp| { + if let Some(impls_for_type) = trait_impls.non_blanket_impls().get(&simp) { + for &impl_def_id in impls_for_type { + match G::consider_impl_candidate(self, goal, impl_def_id) { + Ok(result) => candidates + .push(Candidate { source: CandidateSource::Impl(impl_def_id), result }), + Err(NoSolution) => (), + } + } + } + }; + + match self_ty.kind() { + ty::Bool + | ty::Char + | ty::Int(_) + | ty::Uint(_) + | ty::Float(_) + | ty::Adt(_, _) + | ty::Foreign(_) + | ty::Str + | ty::Array(_, _) + | ty::Slice(_) + | ty::RawPtr(_) + | ty::Ref(_, _, _) + | ty::FnDef(_, _) + | ty::FnPtr(_) + | ty::Dynamic(_, _, _) + | ty::Closure(_, _) + | ty::Generator(_, _, _) + | ty::Never + | ty::Tuple(_) => { + let simp = + fast_reject::simplify_type(tcx, self_ty, TreatParams::ForLookup).unwrap(); + consider_impls_for_simplified_type(simp); + } + + // HACK: For integer and float variables we have to manually look at all impls + // which have some integer or float as a self type. + ty::Infer(ty::IntVar(_)) => { + use ty::IntTy::*; + use ty::UintTy::*; + // This causes a compiler error if any new integer kinds are added. + let (I8 | I16 | I32 | I64 | I128 | Isize): ty::IntTy; + let (U8 | U16 | U32 | U64 | U128 | Usize): ty::UintTy; + let possible_integers = [ + // signed integers + SimplifiedType::Int(I8), + SimplifiedType::Int(I16), + SimplifiedType::Int(I32), + SimplifiedType::Int(I64), + SimplifiedType::Int(I128), + SimplifiedType::Int(Isize), + // unsigned integers + SimplifiedType::Uint(U8), + SimplifiedType::Uint(U16), + SimplifiedType::Uint(U32), + SimplifiedType::Uint(U64), + SimplifiedType::Uint(U128), + SimplifiedType::Uint(Usize), + ]; + for simp in possible_integers { + consider_impls_for_simplified_type(simp); + } + } + + ty::Infer(ty::FloatVar(_)) => { + // This causes a compiler error if any new float kinds are added. + let (ty::FloatTy::F32 | ty::FloatTy::F64); + let possible_floats = [ + SimplifiedType::Float(ty::FloatTy::F32), + SimplifiedType::Float(ty::FloatTy::F64), + ]; + + for simp in possible_floats { + consider_impls_for_simplified_type(simp); + } + } + + // The only traits applying to aliases and placeholders are blanket impls. + // + // Impls which apply to an alias after normalization are handled by + // `assemble_candidates_after_normalizing_self_ty`. + ty::Alias(_, _) | ty::Placeholder(..) | ty::Error(_) => (), + + // FIXME: These should ideally not exist as a self type. It would be nice for + // the builtin auto trait impls of generators should instead directly recurse + // into the witness. + ty::GeneratorWitness(_) | ty::GeneratorWitnessMIR(_, _) => (), + + // These variants should not exist as a self type. + ty::Infer(ty::TyVar(_) | ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)) + | ty::Param(_) + | ty::Bound(_, _) => bug!("unexpected self type: {self_ty}"), + } + } + + fn assemble_blanket_impl_candidates<G: GoalKind<'tcx>>( + &mut self, + goal: Goal<'tcx, G>, + candidates: &mut Vec<Candidate<'tcx>>, + ) { + let tcx = self.tcx(); + let trait_impls = tcx.trait_impls_of(goal.predicate.trait_def_id(tcx)); + for &impl_def_id in trait_impls.blanket_impls() { + match G::consider_impl_candidate(self, goal, impl_def_id) { Ok(result) => candidates .push(Candidate { source: CandidateSource::Impl(impl_def_id), result }), Err(NoSolution) => (), - }, - ); + } + } } #[instrument(level = "debug", skip_all)] @@ -420,8 +560,9 @@ impl<'tcx> EvalCtxt<'_, 'tcx> { goal: Goal<'tcx, G>, candidates: &mut Vec<Candidate<'tcx>>, ) { - let lang_items = self.tcx().lang_items(); - let trait_def_id = goal.predicate.trait_def_id(self.tcx()); + let tcx = self.tcx(); + let lang_items = tcx.lang_items(); + let trait_def_id = goal.predicate.trait_def_id(tcx); // N.B. When assembling built-in candidates for lang items that are also // `auto` traits, then the auto trait candidate that is assembled in @@ -430,9 +571,11 @@ impl<'tcx> EvalCtxt<'_, 'tcx> { // Instead of adding the logic here, it's a better idea to add it in // `EvalCtxt::disqualify_auto_trait_candidate_due_to_possible_impl` in // `solve::trait_goals` instead. - let result = if self.tcx().trait_is_auto(trait_def_id) { + let result = if let Err(guar) = goal.predicate.error_reported() { + G::consider_error_guaranteed_candidate(self, guar) + } else if tcx.trait_is_auto(trait_def_id) { G::consider_auto_trait_candidate(self, goal) - } else if self.tcx().trait_is_alias(trait_def_id) { + } else if tcx.trait_is_alias(trait_def_id) { G::consider_trait_alias_candidate(self, goal) } else if lang_items.sized_trait() == Some(trait_def_id) { G::consider_builtin_sized_candidate(self, goal) diff --git a/compiler/rustc_trait_selection/src/solve/project_goals.rs b/compiler/rustc_trait_selection/src/solve/project_goals.rs index d677fbdc7f4..222ed9939ba 100644 --- a/compiler/rustc_trait_selection/src/solve/project_goals.rs +++ b/compiler/rustc_trait_selection/src/solve/project_goals.rs @@ -2,7 +2,6 @@ use crate::traits::specialization_graph; use super::assembly::{self, structural_traits}; use super::EvalCtxt; -use rustc_errors::ErrorGuaranteed; use rustc_hir::def::DefKind; use rustc_hir::def_id::DefId; use rustc_hir::LangItem; @@ -15,7 +14,7 @@ use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams}; use rustc_middle::ty::ProjectionPredicate; use rustc_middle::ty::{self, Ty, TyCtxt}; use rustc_middle::ty::{ToPredicate, TypeVisitableExt}; -use rustc_span::{sym, DUMMY_SP}; +use rustc_span::{sym, ErrorGuaranteed, DUMMY_SP}; impl<'tcx> EvalCtxt<'_, 'tcx> { #[instrument(level = "debug", skip(self), ret)] @@ -246,6 +245,15 @@ impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> { }) } + /// Fail to normalize if the predicate contains an error, alternatively, we could normalize to `ty::Error` + /// and succeed. Can experiment with this to figure out what results in better error messages. + fn consider_error_guaranteed_candidate( + _ecx: &mut EvalCtxt<'_, 'tcx>, + _guar: ErrorGuaranteed, + ) -> QueryResult<'tcx> { + Err(NoSolution) + } + fn consider_auto_trait_candidate( ecx: &mut EvalCtxt<'_, 'tcx>, goal: Goal<'tcx, Self>, diff --git a/compiler/rustc_trait_selection/src/solve/trait_goals.rs b/compiler/rustc_trait_selection/src/solve/trait_goals.rs index 29889614620..930e62d6388 100644 --- a/compiler/rustc_trait_selection/src/solve/trait_goals.rs +++ b/compiler/rustc_trait_selection/src/solve/trait_goals.rs @@ -11,7 +11,7 @@ use rustc_middle::traits::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::DUMMY_SP; +use rustc_span::{ErrorGuaranteed, DUMMY_SP}; impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> { fn self_ty(self) -> Ty<'tcx> { @@ -78,6 +78,13 @@ impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> { }) } + 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>, diff --git a/tests/ui/traits/new-solver/assembly/assemble-normalizing-self-ty-impl-ambiguity.rs b/tests/ui/traits/new-solver/assembly/assemble-normalizing-self-ty-impl-ambiguity.rs new file mode 100644 index 00000000000..727ce84ba35 --- /dev/null +++ b/tests/ui/traits/new-solver/assembly/assemble-normalizing-self-ty-impl-ambiguity.rs @@ -0,0 +1,25 @@ +// compile-flags: -Ztrait-solver=next + +// Checks that we do not get ambiguity by considering an impl +// multiple times if we're able to normalize the self type. +trait Trait<'a> {} + +impl<'a, T: 'a> Trait<'a> for T {} + +fn impls_trait<'a, T: Trait<'a>>() {} + +trait Id { + type Assoc; +} +impl<T> Id for T { + type Assoc = T; +} + +fn call<T>() { + impls_trait::<<T as Id>::Assoc>(); +} + +fn main() { + call::<()>(); + impls_trait::<<<() as Id>::Assoc as Id>::Assoc>(); +} diff --git a/tests/ui/traits/new-solver/assembly/assemble-normalizing-self-ty-impl-ambiguity.stderr b/tests/ui/traits/new-solver/assembly/assemble-normalizing-self-ty-impl-ambiguity.stderr new file mode 100644 index 00000000000..91b635b35eb --- /dev/null +++ b/tests/ui/traits/new-solver/assembly/assemble-normalizing-self-ty-impl-ambiguity.stderr @@ -0,0 +1,23 @@ +error[E0283]: type annotations needed: cannot satisfy `<T as Id>::Assoc: Trait<'_>` + --> $DIR/assemble-normalizing-self-ty-impl-ambiguity.rs:19:5 + | +LL | impls_trait::<<T as Id>::Assoc>(); + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + | + = note: cannot satisfy `<T as Id>::Assoc: Trait<'_>` +note: required by a bound in `impls_trait` + --> $DIR/assemble-normalizing-self-ty-impl-ambiguity.rs:9:23 + | +LL | fn impls_trait<'a, T: Trait<'a>>() {} + | ^^^^^^^^^ required by this bound in `impls_trait` + +error[E0282]: type annotations needed + --> $DIR/assemble-normalizing-self-ty-impl-ambiguity.rs:24:5 + | +LL | impls_trait::<<<() as Id>::Assoc as Id>::Assoc>(); + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot infer type of the type parameter `T` declared on the function `impls_trait` + +error: aborting due to 2 previous errors + +Some errors have detailed explanations: E0282, E0283. +For more information about an error, try `rustc --explain E0282`. |