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 | 430 |
1 files changed, 430 insertions, 0 deletions
diff --git a/compiler/rustc_trait_selection/src/solve/project_goals.rs b/compiler/rustc_trait_selection/src/solve/project_goals.rs new file mode 100644 index 000000000..e39fa0533 --- /dev/null +++ b/compiler/rustc_trait_selection/src/solve/project_goals.rs @@ -0,0 +1,430 @@ +use crate::traits::{specialization_graph, translate_substs}; + +use super::assembly::{self, Candidate, CandidateSource}; +use super::infcx_ext::InferCtxtExt; +use super::trait_goals::structural_traits; +use super::{Certainty, EvalCtxt, Goal, MaybeCause, QueryResult}; +use rustc_errors::ErrorGuaranteed; +use rustc_hir::def::DefKind; +use rustc_hir::def_id::DefId; +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::{self, Ty, TyCtxt}; +use rustc_middle::ty::{ProjectionPredicate, TypeSuperVisitable, TypeVisitor}; +use rustc_middle::ty::{ToPredicate, TypeVisitable}; +use rustc_span::DUMMY_SP; +use std::iter; +use std::ops::ControlFlow; + +impl<'tcx> EvalCtxt<'_, 'tcx> { + pub(super) fn compute_projection_goal( + &mut self, + goal: Goal<'tcx, ProjectionPredicate<'tcx>>, + ) -> QueryResult<'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 + // `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) + } 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(), + }; + 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 nested_eq_goals = + self.infcx.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() + } + + fn merge_project_candidates( + &mut self, + mut candidates: Vec<Candidate<'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; + } + } + + 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!(); + } + } + } + + 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!(), + } + } +} + +impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> { + fn self_ty(self) -> Ty<'tcx> { + self.self_ty() + } + + 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, tcx: TyCtxt<'tcx>) -> DefId { + self.trait_def_id(tcx) + } + + fn consider_impl_candidate( + ecx: &mut EvalCtxt<'_, 'tcx>, + goal: Goal<'tcx, ProjectionPredicate<'tcx>>, + impl_def_id: DefId, + ) -> QueryResult<'tcx> { + let tcx = ecx.tcx(); + + let goal_trait_ref = goal.predicate.projection_ty.trait_ref(tcx); + let impl_trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap(); + let drcx = DeepRejectCtxt { treat_obligation_params: TreatParams::AsPlaceholder }; + if iter::zip(goal_trait_ref.substs, impl_trait_ref.skip_binder().substs) + .any(|(goal, imp)| !drcx.generic_args_may_unify(goal, imp)) + { + return Err(NoSolution); + } + + ecx.infcx.probe(|_| { + let impl_substs = ecx.infcx.fresh_substs_for_item(DUMMY_SP, 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 where_clause_bounds = tcx + .predicates_of(impl_def_id) + .instantiate(tcx, impl_substs) + .predicates + .into_iter() + .map(|pred| goal.with(tcx, pred)); + + nested_goals.extend(where_clause_bounds); + let trait_ref_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 + // unsoundness during coherence (#105782). + let Some(assoc_def) = fetch_eligible_assoc_item_def( + ecx.infcx, + goal.param_env, + goal_trait_ref, + 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)); + }; + + if !assoc_def.item.defaultness(tcx).has_value() { + tcx.sess.delay_span_bug( + tcx.def_span(assoc_def.item.def_id), + "missing value for assoc item in impl", + ); + } + + // Getting the right substitutions here is complex, e.g. given: + // - a goal `<Vec<u32> as Trait<i32>>::Assoc<u64>` + // - the applicable impl `impl<T> Trait<i32> for Vec<T>` + // - and the impl which defines `Assoc` being `impl<T, U> Trait<U> for Vec<T>` + // + // We first rebase the goal substs onto the impl, going from `[Vec<u32>, i32, u64]` + // to `[u32, u64]`. + // + // And then map these substs to the substs of the defining impl of `Assoc`, going + // from `[u32, u64]` to `[u32, i32, u64]`. + let impl_substs_with_gat = goal.predicate.projection_ty.substs.rebase_onto( + tcx, + goal_trait_ref.def_id, + impl_substs, + ); + let substs = translate_substs( + ecx.infcx, + goal.param_env, + impl_def_id, + impl_substs_with_gat, + assoc_def.defining_node, + ); + + // 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 term: ty::EarlyBinder<ty::Term<'tcx>> = if is_const { + let identity_substs = + ty::InternalSubsts::identity_for_item(tcx, assoc_def.item.def_id); + let did = ty::WithOptConstParam::unknown(assoc_def.item.def_id); + let kind = + ty::ConstKind::Unevaluated(ty::UnevaluatedConst::new(did, identity_substs)); + ty.map_bound(|ty| tcx.mk_const(kind, ty).into()) + } else { + 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)) + }) + } + + 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>, + ) -> QueryResult<'tcx> { + bug!("auto traits do not have associated types: {:?}", goal); + } + + fn consider_trait_alias_candidate( + _ecx: &mut EvalCtxt<'_, 'tcx>, + goal: Goal<'tcx, Self>, + ) -> QueryResult<'tcx> { + bug!("trait aliases do not have associated types: {:?}", goal); + } + + fn consider_builtin_sized_candidate( + _ecx: &mut EvalCtxt<'_, 'tcx>, + goal: Goal<'tcx, Self>, + ) -> QueryResult<'tcx> { + bug!("`Sized` does not have an associated type: {:?}", goal); + } + + fn consider_builtin_copy_clone_candidate( + _ecx: &mut EvalCtxt<'_, 'tcx>, + goal: Goal<'tcx, Self>, + ) -> QueryResult<'tcx> { + bug!("`Copy`/`Clone` does not have an associated type: {:?}", goal); + } + + fn consider_builtin_pointer_sized_candidate( + _ecx: &mut EvalCtxt<'_, 'tcx>, + goal: Goal<'tcx, Self>, + ) -> QueryResult<'tcx> { + bug!("`PointerSized` does not have an associated type: {:?}", goal); + } + + fn consider_builtin_fn_trait_candidates( + ecx: &mut EvalCtxt<'_, '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)) + } + } + + fn consider_builtin_tuple_candidate( + _ecx: &mut EvalCtxt<'_, 'tcx>, + goal: Goal<'tcx, Self>, + ) -> QueryResult<'tcx> { + bug!("`Tuple` does not have an associated type: {:?}", goal); + } +} + +/// This behavior is also implemented in `rustc_ty_utils` and in the old `project` code. +/// +/// FIXME: We should merge these 3 implementations as it's likely that they otherwise +/// diverge. +#[instrument(level = "debug", skip(infcx, param_env), ret)] +fn fetch_eligible_assoc_item_def<'tcx>( + infcx: &InferCtxt<'tcx>, + param_env: ty::ParamEnv<'tcx>, + goal_trait_ref: ty::TraitRef<'tcx>, + trait_assoc_def_id: DefId, + impl_def_id: DefId, +) -> Result<Option<LeafDef>, NoSolution> { + let node_item = specialization_graph::assoc_def(infcx.tcx, impl_def_id, trait_assoc_def_id) + .map_err(|ErrorGuaranteed { .. }| NoSolution)?; + + let eligible = if node_item.is_final() { + // Non-specializable items are always projectable. + true + } else { + // Only reveal a specializable default if we're past type-checking + // and the obligation is monomorphic, otherwise passes such as + // transmute checking and polymorphic MIR optimizations could + // get a result which isn't correct for all monomorphizations. + if param_env.reveal() == Reveal::All { + let poly_trait_ref = infcx.resolve_vars_if_possible(goal_trait_ref); + !poly_trait_ref.still_further_specializable() + } else { + debug!(?node_item.item.def_id, "not eligible due to default"); + false + } + }; + + if eligible { Ok(Some(node_item)) } else { Ok(None) } +} |