--- /dev/null
+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) }
+}
projects / rustc.git / blobdiff