diff options
Diffstat (limited to 'compiler/rustc_trait_selection/src/solve/trait_goals.rs')
| -rw-r--r-- | compiler/rustc_trait_selection/src/solve/trait_goals.rs | 289 |
1 files changed, 289 insertions, 0 deletions
diff --git a/compiler/rustc_trait_selection/src/solve/trait_goals.rs b/compiler/rustc_trait_selection/src/solve/trait_goals.rs new file mode 100644 index 000000000..9985d7181 --- /dev/null +++ b/compiler/rustc_trait_selection/src/solve/trait_goals.rs @@ -0,0 +1,289 @@ +//! Dealing with trait goals, i.e. `T: Trait<'a, U>`. + +use std::iter; + +use super::assembly::{self, Candidate, CandidateSource}; +use super::infcx_ext::InferCtxtExt; +use super::{Certainty, EvalCtxt, Goal, MaybeCause, QueryResult}; +use rustc_hir::def_id::DefId; +use rustc_infer::infer::InferCtxt; +use rustc_infer::traits::query::NoSolution; +use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams}; +use rustc_middle::ty::{self, ToPredicate, Ty, TyCtxt}; +use rustc_middle::ty::{TraitPredicate, TypeVisitable}; +use rustc_span::DUMMY_SP; + +pub mod structural_traits; + +impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'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, _: 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::AsPlaceholder }; + if iter::zip(goal.predicate.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.predicate.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); + ecx.evaluate_all_and_make_canonical_response(nested_goals) + }) + } + + fn consider_assumption( + ecx: &mut EvalCtxt<'_, 'tcx>, + goal: Goal<'tcx, Self>, + assumption: ty::Predicate<'tcx>, + ) -> QueryResult<'tcx> { + if let Some(poly_trait_pred) = assumption.to_opt_poly_trait_pred() { + // FIXME: Constness and polarity + ecx.infcx.probe(|_| { + let assumption_trait_pred = + ecx.infcx.instantiate_bound_vars_with_infer(poly_trait_pred); + let nested_goals = ecx.infcx.eq( + goal.param_env, + goal.predicate.trait_ref, + assumption_trait_pred.trait_ref, + )?; + ecx.evaluate_all_and_make_canonical_response(nested_goals) + }) + } else { + Err(NoSolution) + } + } + + fn consider_auto_trait_candidate( + ecx: &mut EvalCtxt<'_, 'tcx>, + goal: Goal<'tcx, Self>, + ) -> QueryResult<'tcx> { + 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> { + let tcx = ecx.tcx(); + + ecx.infcx.probe(|_| { + let nested_obligations = tcx + .predicates_of(goal.predicate.def_id()) + .instantiate(tcx, goal.predicate.trait_ref.substs); + ecx.evaluate_all_and_make_canonical_response( + nested_obligations.predicates.into_iter().map(|p| goal.with(tcx, p)).collect(), + ) + }) + } + + fn consider_builtin_sized_candidate( + ecx: &mut EvalCtxt<'_, 'tcx>, + goal: Goal<'tcx, Self>, + ) -> QueryResult<'tcx> { + 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> { + ecx.probe_and_evaluate_goal_for_constituent_tys( + goal, + structural_traits::instantiate_constituent_tys_for_copy_clone_trait, + ) + } + + fn consider_builtin_pointer_sized_candidate( + ecx: &mut EvalCtxt<'_, 'tcx>, + goal: Goal<'tcx, Self>, + ) -> QueryResult<'tcx> { + if goal.predicate.self_ty().has_non_region_infer() { + return ecx.make_canonical_response(Certainty::Maybe(MaybeCause::Ambiguity)); + } + + let tcx = ecx.tcx(); + let self_ty = tcx.erase_regions(goal.predicate.self_ty()); + + if let Ok(layout) = tcx.layout_of(goal.param_env.and(self_ty)) + && let usize_layout = tcx.layout_of(ty::ParamEnv::empty().and(tcx.types.usize)).unwrap().layout + && layout.layout.size() == usize_layout.size() + && layout.layout.align().abi == usize_layout.align().abi + { + // FIXME: We could make this faster by making a no-constraints response + ecx.make_canonical_response(Certainty::Yes) + } else { + Err(NoSolution) + } + } + + 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, _)| { + ecx.tcx() + .mk_trait_ref(goal.predicate.def_id(), [goal.predicate.self_ty(), inputs]) + }) + .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> { + if let ty::Tuple(..) = goal.predicate.self_ty().kind() { + ecx.make_canonical_response(Certainty::Yes) + } else { + Err(NoSolution) + } + } +} + +impl<'tcx> EvalCtxt<'_, 'tcx> { + /// 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(&InferCtxt<'tcx>, Ty<'tcx>) -> Result<Vec<Ty<'tcx>>, NoSolution>, + ) -> QueryResult<'tcx> { + self.infcx.probe(|_| { + self.evaluate_all_and_make_canonical_response( + constituent_tys(self.infcx, goal.predicate.self_ty())? + .into_iter() + .map(|ty| { + goal.with( + self.tcx(), + ty::Binder::dummy(goal.predicate.with_self_ty(self.tcx(), ty)), + ) + }) + .collect(), + ) + }) + } + + 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_trait_candidates_discard_reservation_impls(candidates) + } + + #[instrument(level = "debug", skip(self), ret)] + pub(super) fn merge_trait_candidates_discard_reservation_impls( + &mut self, + mut candidates: Vec<Candidate<'tcx>>, + ) -> QueryResult<'tcx> { + match candidates.len() { + 0 => return Err(NoSolution), + 1 => return Ok(self.discard_reservation_impl(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.trait_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(self.discard_reservation_impl(candidates.pop().unwrap()).result) + } + + fn trait_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::AliasBound(_), _) + | (CandidateSource::BuiltinImpl, _) => unimplemented!(), + } + } + + fn discard_reservation_impl(&self, candidate: Candidate<'tcx>) -> Candidate<'tcx> { + if let CandidateSource::Impl(def_id) = candidate.source { + if let ty::ImplPolarity::Reservation = self.tcx().impl_polarity(def_id) { + debug!("Selected reservation impl"); + // FIXME: reduce candidate to ambiguous + // FIXME: replace `var_values` with identity, yeet external constraints. + unimplemented!() + } + } + + candidate + } +} |