diff options
Diffstat (limited to 'compiler/rustc_trait_selection/src/solve/project_goals.rs')
| -rw-r--r-- | compiler/rustc_trait_selection/src/solve/project_goals.rs | 533 |
1 files changed, 332 insertions, 201 deletions
diff --git a/compiler/rustc_trait_selection/src/solve/project_goals.rs b/compiler/rustc_trait_selection/src/solve/project_goals.rs index e39fa0533..33c66d072 100644 --- a/compiler/rustc_trait_selection/src/solve/project_goals.rs +++ b/compiler/rustc_trait_selection/src/solve/project_goals.rs @@ -1,23 +1,22 @@ use crate::traits::{specialization_graph, translate_substs}; -use super::assembly::{self, Candidate, CandidateSource}; -use super::infcx_ext::InferCtxtExt; +use super::assembly; use super::trait_goals::structural_traits; -use super::{Certainty, EvalCtxt, Goal, MaybeCause, QueryResult}; +use super::{Certainty, EvalCtxt, Goal, QueryResult}; use rustc_errors::ErrorGuaranteed; use rustc_hir::def::DefKind; use rustc_hir::def_id::DefId; +use rustc_hir::LangItem; use rustc_infer::infer::InferCtxt; use rustc_infer::traits::query::NoSolution; use rustc_infer::traits::specialization_graph::LeafDef; use rustc_infer::traits::Reveal; use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams}; +use rustc_middle::ty::ProjectionPredicate; use rustc_middle::ty::{self, Ty, TyCtxt}; -use rustc_middle::ty::{ProjectionPredicate, TypeSuperVisitable, TypeVisitor}; -use rustc_middle::ty::{ToPredicate, TypeVisitable}; -use rustc_span::DUMMY_SP; +use rustc_middle::ty::{ToPredicate, TypeVisitableExt}; +use rustc_span::{sym, DUMMY_SP}; use std::iter; -use std::ops::ControlFlow; impl<'tcx> EvalCtxt<'_, 'tcx> { pub(super) fn compute_projection_goal( @@ -27,151 +26,62 @@ impl<'tcx> EvalCtxt<'_, 'tcx> { // To only compute normalization once for each projection we only // normalize if the expected term is an unconstrained inference variable. // - // E.g. for `<T as Trait>::Assoc = u32` we recursively compute the goal - // `exists<U> <T as Trait>::Assoc = U` and then take the resulting type for + // E.g. for `<T as Trait>::Assoc == u32` we recursively compute the goal + // `exists<U> <T as Trait>::Assoc == U` and then take the resulting type for // `U` and equate it with `u32`. This means that we don't need a separate // projection cache in the solver. if self.term_is_fully_unconstrained(goal) { let candidates = self.assemble_and_evaluate_candidates(goal); - self.merge_project_candidates(candidates) + self.merge_candidates_and_discard_reservation_impls(candidates) } else { let predicate = goal.predicate; let unconstrained_rhs = match predicate.term.unpack() { - ty::TermKind::Ty(_) => self.infcx.next_ty_infer().into(), - ty::TermKind::Const(ct) => self.infcx.next_const_infer(ct.ty()).into(), + ty::TermKind::Ty(_) => self.next_ty_infer().into(), + ty::TermKind::Const(ct) => self.next_const_infer(ct.ty()).into(), }; let unconstrained_predicate = ty::Clause::Projection(ProjectionPredicate { projection_ty: goal.predicate.projection_ty, term: unconstrained_rhs, }); - let (_has_changed, normalize_certainty) = - self.evaluate_goal(goal.with(self.tcx(), unconstrained_predicate))?; + let (_has_changed, normalize_certainty) = self.in_projection_eq_hack(|this| { + this.evaluate_goal(goal.with(this.tcx(), unconstrained_predicate)) + })?; - let nested_eq_goals = - self.infcx.eq(goal.param_env, unconstrained_rhs, predicate.term)?; + let nested_eq_goals = self.eq(goal.param_env, unconstrained_rhs, predicate.term)?; let eval_certainty = self.evaluate_all(nested_eq_goals)?; self.make_canonical_response(normalize_certainty.unify_and(eval_certainty)) } } - /// Is the projection predicate is of the form `exists<T> <Ty as Trait>::Assoc = T`. - /// - /// This is the case if the `term` is an inference variable in the innermost universe - /// and does not occur in any other part of the predicate. - fn term_is_fully_unconstrained(&self, goal: Goal<'tcx, ProjectionPredicate<'tcx>>) -> bool { - let infcx = self.infcx; - let term_is_infer = match goal.predicate.term.unpack() { - ty::TermKind::Ty(ty) => { - if let &ty::Infer(ty::TyVar(vid)) = ty.kind() { - match infcx.probe_ty_var(vid) { - Ok(value) => bug!("resolved var in query: {goal:?} {value:?}"), - Err(universe) => universe == infcx.universe(), - } - } else { - false - } - } - ty::TermKind::Const(ct) => { - if let ty::ConstKind::Infer(ty::InferConst::Var(vid)) = ct.kind() { - match self.infcx.probe_const_var(vid) { - Ok(value) => bug!("resolved var in query: {goal:?} {value:?}"), - Err(universe) => universe == infcx.universe(), - } - } else { - false - } - } - }; - - // Guard against `<T as Trait<?0>>::Assoc = ?0>`. - struct ContainsTerm<'tcx> { - term: ty::Term<'tcx>, - } - impl<'tcx> TypeVisitor<'tcx> for ContainsTerm<'tcx> { - type BreakTy = (); - fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> { - if t.needs_infer() { - if ty::Term::from(t) == self.term { - ControlFlow::BREAK - } else { - t.super_visit_with(self) - } - } else { - ControlFlow::CONTINUE - } - } - - fn visit_const(&mut self, c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> { - if c.needs_infer() { - if ty::Term::from(c) == self.term { - ControlFlow::BREAK - } else { - c.super_visit_with(self) - } - } else { - ControlFlow::CONTINUE - } - } - } - - let mut visitor = ContainsTerm { term: goal.predicate.term }; - - term_is_infer - && goal.predicate.projection_ty.visit_with(&mut visitor).is_continue() - && goal.param_env.visit_with(&mut visitor).is_continue() + /// This sets a flag used by a debug assert in [`EvalCtxt::evaluate_goal`], + /// see the comment in that method for more details. + fn in_projection_eq_hack<T>(&mut self, f: impl FnOnce(&mut Self) -> T) -> T { + self.in_projection_eq_hack = true; + let result = f(self); + self.in_projection_eq_hack = false; + result } - fn merge_project_candidates( + /// After normalizing the projection to `normalized_alias` with the given + /// `normalization_certainty`, constrain the inference variable `term` to it + /// and return a query response. + fn eq_term_and_make_canonical_response( &mut self, - mut candidates: Vec<Candidate<'tcx>>, + goal: Goal<'tcx, ProjectionPredicate<'tcx>>, + normalization_certainty: Certainty, + normalized_alias: impl Into<ty::Term<'tcx>>, ) -> QueryResult<'tcx> { - match candidates.len() { - 0 => return Err(NoSolution), - 1 => return Ok(candidates.pop().unwrap().result), - _ => {} - } - - if candidates.len() > 1 { - let mut i = 0; - 'outer: while i < candidates.len() { - for j in (0..candidates.len()).filter(|&j| i != j) { - if self.project_candidate_should_be_dropped_in_favor_of( - &candidates[i], - &candidates[j], - ) { - debug!(candidate = ?candidates[i], "Dropping candidate #{}/{}", i, candidates.len()); - candidates.swap_remove(i); - continue 'outer; - } - } + // The term of our goal should be fully unconstrained, so this should never fail. + // + // It can however be ambiguous when the `normalized_alias` contains a projection. + let nested_goals = self + .eq(goal.param_env, goal.predicate.term, normalized_alias.into()) + .expect("failed to unify with unconstrained term"); - debug!(candidate = ?candidates[i], "Retaining candidate #{}/{}", i, candidates.len()); - // If there are *STILL* multiple candidates, give up - // and report ambiguity. - i += 1; - if i > 1 { - debug!("multiple matches, ambig"); - // FIXME: return overflow if all candidates overflow, otherwise return ambiguity. - unimplemented!(); - } - } - } + let unify_certainty = + self.evaluate_all(nested_goals).expect("failed to unify with unconstrained term"); - Ok(candidates.pop().unwrap().result) - } - - fn project_candidate_should_be_dropped_in_favor_of( - &self, - candidate: &Candidate<'tcx>, - other: &Candidate<'tcx>, - ) -> bool { - // FIXME: implement this - match (candidate.source, other.source) { - (CandidateSource::Impl(_), _) - | (CandidateSource::ParamEnv(_), _) - | (CandidateSource::BuiltinImpl, _) - | (CandidateSource::AliasBound(_), _) => unimplemented!(), - } + self.make_canonical_response(normalization_certainty.unify_and(unify_certainty)) } } @@ -188,6 +98,82 @@ impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> { self.trait_def_id(tcx) } + fn consider_implied_clause( + ecx: &mut EvalCtxt<'_, 'tcx>, + goal: Goal<'tcx, Self>, + assumption: ty::Predicate<'tcx>, + requirements: impl IntoIterator<Item = Goal<'tcx, ty::Predicate<'tcx>>>, + ) -> QueryResult<'tcx> { + if let Some(poly_projection_pred) = assumption.to_opt_poly_projection_pred() + && poly_projection_pred.projection_def_id() == goal.predicate.def_id() + { + ecx.probe(|ecx| { + let assumption_projection_pred = + ecx.instantiate_binder_with_infer(poly_projection_pred); + let mut nested_goals = ecx.eq( + goal.param_env, + goal.predicate.projection_ty, + assumption_projection_pred.projection_ty, + )?; + nested_goals.extend(requirements); + let subst_certainty = ecx.evaluate_all(nested_goals)?; + + ecx.eq_term_and_make_canonical_response( + goal, + subst_certainty, + assumption_projection_pred.term, + ) + }) + } else { + Err(NoSolution) + } + } + + fn consider_object_bound_candidate( + ecx: &mut EvalCtxt<'_, 'tcx>, + goal: Goal<'tcx, Self>, + assumption: ty::Predicate<'tcx>, + ) -> QueryResult<'tcx> { + if let Some(poly_projection_pred) = assumption.to_opt_poly_projection_pred() + && poly_projection_pred.projection_def_id() == goal.predicate.def_id() + { + ecx.probe(|ecx| { + let assumption_projection_pred = + ecx.instantiate_binder_with_infer(poly_projection_pred); + let mut nested_goals = ecx.eq( + goal.param_env, + goal.predicate.projection_ty, + assumption_projection_pred.projection_ty, + )?; + + let tcx = ecx.tcx(); + let ty::Dynamic(bounds, _, _) = *goal.predicate.self_ty().kind() else { + bug!("expected object type in `consider_object_bound_candidate`"); + }; + nested_goals.extend( + structural_traits::predicates_for_object_candidate( + ecx, + goal.param_env, + goal.predicate.projection_ty.trait_ref(tcx), + bounds, + ) + .into_iter() + .map(|pred| goal.with(tcx, pred)), + ); + + let subst_certainty = ecx.evaluate_all(nested_goals)?; + + ecx.eq_term_and_make_canonical_response( + goal, + subst_certainty, + assumption_projection_pred.term, + ) + }) + } else { + Err(NoSolution) + } + } + fn consider_impl_candidate( ecx: &mut EvalCtxt<'_, 'tcx>, goal: Goal<'tcx, ProjectionPredicate<'tcx>>, @@ -204,11 +190,11 @@ impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> { return Err(NoSolution); } - ecx.infcx.probe(|_| { - let impl_substs = ecx.infcx.fresh_substs_for_item(DUMMY_SP, impl_def_id); + ecx.probe(|ecx| { + let impl_substs = ecx.fresh_substs_for_item(impl_def_id); let impl_trait_ref = impl_trait_ref.subst(tcx, impl_substs); - let mut nested_goals = ecx.infcx.eq(goal.param_env, goal_trait_ref, impl_trait_ref)?; + let mut nested_goals = ecx.eq(goal.param_env, goal_trait_ref, impl_trait_ref)?; let where_clause_bounds = tcx .predicates_of(impl_def_id) .instantiate(tcx, impl_substs) @@ -217,7 +203,7 @@ impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> { .map(|pred| goal.with(tcx, pred)); nested_goals.extend(where_clause_bounds); - let trait_ref_certainty = ecx.evaluate_all(nested_goals)?; + let match_impl_certainty = ecx.evaluate_all(nested_goals)?; // In case the associated item is hidden due to specialization, we have to // return ambiguity this would otherwise be incomplete, resulting in @@ -229,8 +215,7 @@ impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> { goal.predicate.def_id(), impl_def_id )? else { - let certainty = Certainty::Maybe(MaybeCause::Ambiguity); - return ecx.make_canonical_response(trait_ref_certainty.unify_and(certainty)); + return ecx.make_canonical_response(match_impl_certainty.unify_and(Certainty::AMBIGUOUS)); }; if !assoc_def.item.defaultness(tcx).has_value() { @@ -265,7 +250,7 @@ impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> { // Finally we construct the actual value of the associated type. let is_const = matches!(tcx.def_kind(assoc_def.item.def_id), DefKind::AssocConst); - let ty = tcx.bound_type_of(assoc_def.item.def_id); + let ty = tcx.type_of(assoc_def.item.def_id); let term: ty::EarlyBinder<ty::Term<'tcx>> = if is_const { let identity_substs = ty::InternalSubsts::identity_for_item(tcx, assoc_def.item.def_id); @@ -277,54 +262,10 @@ impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> { ty.map_bound(|ty| ty.into()) }; - // The term of our goal should be fully unconstrained, so this should never fail. - // - // It can however be ambiguous when the resolved type is a projection. - let nested_goals = ecx - .infcx - .eq(goal.param_env, goal.predicate.term, term.subst(tcx, substs)) - .expect("failed to unify with unconstrained term"); - let rhs_certainty = - ecx.evaluate_all(nested_goals).expect("failed to unify with unconstrained term"); - - ecx.make_canonical_response(trait_ref_certainty.unify_and(rhs_certainty)) + ecx.eq_term_and_make_canonical_response(goal, match_impl_certainty, term.subst(tcx, substs)) }) } - fn consider_assumption( - ecx: &mut EvalCtxt<'_, 'tcx>, - goal: Goal<'tcx, Self>, - assumption: ty::Predicate<'tcx>, - ) -> QueryResult<'tcx> { - if let Some(poly_projection_pred) = assumption.to_opt_poly_projection_pred() { - ecx.infcx.probe(|_| { - let assumption_projection_pred = - ecx.infcx.instantiate_bound_vars_with_infer(poly_projection_pred); - let nested_goals = ecx.infcx.eq( - goal.param_env, - goal.predicate.projection_ty, - assumption_projection_pred.projection_ty, - )?; - let subst_certainty = ecx.evaluate_all(nested_goals)?; - - // The term of our goal should be fully unconstrained, so this should never fail. - // - // It can however be ambiguous when the resolved type is a projection. - let nested_goals = ecx - .infcx - .eq(goal.param_env, goal.predicate.term, assumption_projection_pred.term) - .expect("failed to unify with unconstrained term"); - let rhs_certainty = ecx - .evaluate_all(nested_goals) - .expect("failed to unify with unconstrained term"); - - ecx.make_canonical_response(subst_certainty.unify_and(rhs_certainty)) - }) - } else { - Err(NoSolution) - } - } - fn consider_auto_trait_candidate( _ecx: &mut EvalCtxt<'_, 'tcx>, goal: Goal<'tcx, Self>, @@ -353,11 +294,11 @@ impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> { bug!("`Copy`/`Clone` does not have an associated type: {:?}", goal); } - fn consider_builtin_pointer_sized_candidate( + fn consider_builtin_pointer_like_candidate( _ecx: &mut EvalCtxt<'_, 'tcx>, goal: Goal<'tcx, Self>, ) -> QueryResult<'tcx> { - bug!("`PointerSized` does not have an associated type: {:?}", goal); + bug!("`PointerLike` does not have an associated type: {:?}", goal); } fn consider_builtin_fn_trait_candidates( @@ -365,25 +306,28 @@ impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> { goal: Goal<'tcx, Self>, goal_kind: ty::ClosureKind, ) -> QueryResult<'tcx> { - if let Some(tupled_inputs_and_output) = - structural_traits::extract_tupled_inputs_and_output_from_callable( - ecx.tcx(), - goal.predicate.self_ty(), - goal_kind, - )? - { - let pred = tupled_inputs_and_output - .map_bound(|(inputs, output)| ty::ProjectionPredicate { - projection_ty: ecx - .tcx() - .mk_alias_ty(goal.predicate.def_id(), [goal.predicate.self_ty(), inputs]), - term: output.into(), - }) - .to_predicate(ecx.tcx()); - Self::consider_assumption(ecx, goal, pred) - } else { - ecx.make_canonical_response(Certainty::Maybe(MaybeCause::Ambiguity)) - } + let tcx = ecx.tcx(); + let Some(tupled_inputs_and_output) = + structural_traits::extract_tupled_inputs_and_output_from_callable( + tcx, + goal.predicate.self_ty(), + goal_kind, + )? else { + return ecx.make_canonical_response(Certainty::AMBIGUOUS); + }; + let output_is_sized_pred = tupled_inputs_and_output + .map_bound(|(_, output)| tcx.at(DUMMY_SP).mk_trait_ref(LangItem::Sized, [output])); + + let pred = tupled_inputs_and_output + .map_bound(|(inputs, output)| ty::ProjectionPredicate { + projection_ty: tcx + .mk_alias_ty(goal.predicate.def_id(), [goal.predicate.self_ty(), inputs]), + term: output.into(), + }) + .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( @@ -392,6 +336,193 @@ impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> { ) -> QueryResult<'tcx> { bug!("`Tuple` does not have an associated type: {:?}", goal); } + + fn consider_builtin_pointee_candidate( + ecx: &mut EvalCtxt<'_, 'tcx>, + goal: Goal<'tcx, Self>, + ) -> QueryResult<'tcx> { + let tcx = ecx.tcx(); + ecx.probe(|ecx| { + let metadata_ty = match goal.predicate.self_ty().kind() { + ty::Bool + | ty::Char + | ty::Int(..) + | ty::Uint(..) + | ty::Float(..) + | ty::Array(..) + | ty::RawPtr(..) + | ty::Ref(..) + | ty::FnDef(..) + | ty::FnPtr(..) + | ty::Closure(..) + | ty::Infer(ty::IntVar(..) | ty::FloatVar(..)) + | ty::Generator(..) + | ty::GeneratorWitness(..) + | ty::GeneratorWitnessMIR(..) + | ty::Never + | ty::Foreign(..) => tcx.types.unit, + + ty::Error(e) => tcx.ty_error(*e), + + ty::Str | ty::Slice(_) => tcx.types.usize, + + ty::Dynamic(_, _, _) => { + let dyn_metadata = tcx.require_lang_item(LangItem::DynMetadata, None); + tcx.type_of(dyn_metadata) + .subst(tcx, &[ty::GenericArg::from(goal.predicate.self_ty())]) + } + + ty::Alias(_, _) | ty::Param(_) | ty::Placeholder(..) => { + // FIXME(ptr_metadata): It would also be possible to return a `Ok(Ambig)` with no constraints. + let sized_predicate = ty::Binder::dummy(tcx.at(DUMMY_SP).mk_trait_ref( + LangItem::Sized, + [ty::GenericArg::from(goal.predicate.self_ty())], + )); + + let (_, is_sized_certainty) = + ecx.evaluate_goal(goal.with(tcx, sized_predicate))?; + return ecx.eq_term_and_make_canonical_response( + goal, + is_sized_certainty, + tcx.types.unit, + ); + } + + ty::Adt(def, substs) if def.is_struct() => { + match def.non_enum_variant().fields.last() { + None => tcx.types.unit, + Some(field_def) => { + let self_ty = field_def.ty(tcx, substs); + let new_goal = goal.with( + tcx, + ty::Binder::dummy(goal.predicate.with_self_ty(tcx, self_ty)), + ); + let (_, certainty) = ecx.evaluate_goal(new_goal)?; + return ecx.make_canonical_response(certainty); + } + } + } + ty::Adt(_, _) => tcx.types.unit, + + ty::Tuple(elements) => match elements.last() { + None => tcx.types.unit, + Some(&self_ty) => { + let new_goal = goal.with( + tcx, + ty::Binder::dummy(goal.predicate.with_self_ty(tcx, self_ty)), + ); + let (_, certainty) = ecx.evaluate_goal(new_goal)?; + return ecx.make_canonical_response(certainty); + } + }, + + ty::Infer( + ty::TyVar(_) | ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_), + ) + | ty::Bound(..) => bug!( + "unexpected self ty `{:?}` when normalizing `<T as Pointee>::Metadata`", + goal.predicate.self_ty() + ), + }; + + ecx.eq_term_and_make_canonical_response(goal, Certainty::Yes, metadata_ty) + }) + } + + fn consider_builtin_future_candidate( + ecx: &mut EvalCtxt<'_, 'tcx>, + goal: Goal<'tcx, Self>, + ) -> QueryResult<'tcx> { + let self_ty = goal.predicate.self_ty(); + let ty::Generator(def_id, substs, _) = *self_ty.kind() else { + return Err(NoSolution); + }; + + // Generators are not futures unless they come from `async` desugaring + let tcx = ecx.tcx(); + if !tcx.generator_is_async(def_id) { + return Err(NoSolution); + } + + let term = substs.as_generator().return_ty().into(); + + Self::consider_implied_clause( + ecx, + goal, + ty::Binder::dummy(ty::ProjectionPredicate { + projection_ty: ecx.tcx().mk_alias_ty(goal.predicate.def_id(), [self_ty]), + term, + }) + .to_predicate(tcx), + // Technically, we need to check that the future type is Sized, + // but that's already proven by the generator being WF. + [], + ) + } + + fn consider_builtin_generator_candidate( + ecx: &mut EvalCtxt<'_, 'tcx>, + goal: Goal<'tcx, Self>, + ) -> QueryResult<'tcx> { + let self_ty = goal.predicate.self_ty(); + let ty::Generator(def_id, substs, _) = *self_ty.kind() else { + return Err(NoSolution); + }; + + // `async`-desugared generators do not implement the generator trait + let tcx = ecx.tcx(); + if tcx.generator_is_async(def_id) { + return Err(NoSolution); + } + + let generator = substs.as_generator(); + + let name = tcx.associated_item(goal.predicate.def_id()).name; + let term = if name == sym::Return { + generator.return_ty().into() + } else if name == sym::Yield { + generator.yield_ty().into() + } else { + bug!("unexpected associated item `<{self_ty} as Generator>::{name}`") + }; + + Self::consider_implied_clause( + ecx, + goal, + ty::Binder::dummy(ty::ProjectionPredicate { + projection_ty: ecx + .tcx() + .mk_alias_ty(goal.predicate.def_id(), [self_ty, generator.resume_ty()]), + term, + }) + .to_predicate(tcx), + // Technically, we need to check that the future type is Sized, + // but that's already proven by the generator being WF. + [], + ) + } + + fn consider_builtin_unsize_candidate( + _ecx: &mut EvalCtxt<'_, 'tcx>, + goal: Goal<'tcx, Self>, + ) -> QueryResult<'tcx> { + bug!("`Unsize` does not have an associated type: {:?}", goal); + } + + fn consider_builtin_dyn_upcast_candidates( + _ecx: &mut EvalCtxt<'_, 'tcx>, + goal: Goal<'tcx, Self>, + ) -> Vec<super::CanonicalResponse<'tcx>> { + bug!("`Unsize` does not have an associated type: {:?}", goal); + } + + fn consider_builtin_discriminant_kind_candidate( + ecx: &mut EvalCtxt<'_, 'tcx>, + goal: Goal<'tcx, Self>, + ) -> QueryResult<'tcx> { + let discriminant = goal.predicate.self_ty().discriminant_ty(ecx.tcx()); + ecx.probe(|ecx| ecx.eq_term_and_make_canonical_response(goal, Certainty::Yes, discriminant)) + } } /// This behavior is also implemented in `rustc_ty_utils` and in the old `project` code. |