1 use crate::traits::{specialization_graph, translate_substs};
3 use super::assembly::{self, Candidate, CandidateSource};
4 use super::infcx_ext::InferCtxtExt;
5 use super::trait_goals::structural_traits;
6 use super::{Certainty, EvalCtxt, Goal, MaybeCause, QueryResult};
7 use rustc_errors::ErrorGuaranteed;
8 use rustc_hir::def::DefKind;
9 use rustc_hir::def_id::DefId;
10 use rustc_infer::infer::InferCtxt;
11 use rustc_infer::traits::query::NoSolution;
12 use rustc_infer::traits::specialization_graph::LeafDef;
13 use rustc_infer::traits::Reveal;
14 use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams};
15 use rustc_middle::ty::{self, Ty, TyCtxt};
16 use rustc_middle::ty::{ProjectionPredicate, TypeSuperVisitable, TypeVisitor};
17 use rustc_middle::ty::{ToPredicate, TypeVisitable};
18 use rustc_span::DUMMY_SP;
20 use std::ops::ControlFlow;
22 impl<'tcx> EvalCtxt<'_, 'tcx> {
23 pub(super) fn compute_projection_goal(
25 goal: Goal<'tcx, ProjectionPredicate<'tcx>>,
26 ) -> QueryResult<'tcx> {
27 // To only compute normalization once for each projection we only
28 // normalize if the expected term is an unconstrained inference variable.
30 // E.g. for `<T as Trait>::Assoc = u32` we recursively compute the goal
31 // `exists<U> <T as Trait>::Assoc = U` and then take the resulting type for
32 // `U` and equate it with `u32`. This means that we don't need a separate
33 // projection cache in the solver.
34 if self.term_is_fully_unconstrained(goal) {
35 let candidates = self.assemble_and_evaluate_candidates(goal);
36 self.merge_project_candidates(candidates)
38 let predicate = goal.predicate;
39 let unconstrained_rhs = match predicate.term.unpack() {
40 ty::TermKind::Ty(_) => self.infcx.next_ty_infer().into(),
41 ty::TermKind::Const(ct) => self.infcx.next_const_infer(ct.ty()).into(),
43 let unconstrained_predicate = ty::Clause::Projection(ProjectionPredicate {
44 projection_ty: goal.predicate.projection_ty,
45 term: unconstrained_rhs,
47 let (_has_changed, normalize_certainty) =
48 self.evaluate_goal(goal.with(self.tcx(), unconstrained_predicate))?;
51 self.infcx.eq(goal.param_env, unconstrained_rhs, predicate.term)?;
52 let eval_certainty = self.evaluate_all(nested_eq_goals)?;
53 self.make_canonical_response(normalize_certainty.unify_and(eval_certainty))
57 /// Is the projection predicate is of the form `exists<T> <Ty as Trait>::Assoc = T`.
59 /// This is the case if the `term` is an inference variable in the innermost universe
60 /// and does not occur in any other part of the predicate.
61 fn term_is_fully_unconstrained(&self, goal: Goal<'tcx, ProjectionPredicate<'tcx>>) -> bool {
62 let infcx = self.infcx;
63 let term_is_infer = match goal.predicate.term.unpack() {
64 ty::TermKind::Ty(ty) => {
65 if let &ty::Infer(ty::TyVar(vid)) = ty.kind() {
66 match infcx.probe_ty_var(vid) {
67 Ok(value) => bug!("resolved var in query: {goal:?} {value:?}"),
68 Err(universe) => universe == infcx.universe(),
74 ty::TermKind::Const(ct) => {
75 if let ty::ConstKind::Infer(ty::InferConst::Var(vid)) = ct.kind() {
76 match self.infcx.probe_const_var(vid) {
77 Ok(value) => bug!("resolved var in query: {goal:?} {value:?}"),
78 Err(universe) => universe == infcx.universe(),
86 // Guard against `<T as Trait<?0>>::Assoc = ?0>`.
87 struct ContainsTerm<'tcx> {
90 impl<'tcx> TypeVisitor<'tcx> for ContainsTerm<'tcx> {
92 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
94 if ty::Term::from(t) == self.term {
97 t.super_visit_with(self)
100 ControlFlow::CONTINUE
104 fn visit_const(&mut self, c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
106 if ty::Term::from(c) == self.term {
109 c.super_visit_with(self)
112 ControlFlow::CONTINUE
117 let mut visitor = ContainsTerm { term: goal.predicate.term };
120 && goal.predicate.projection_ty.visit_with(&mut visitor).is_continue()
121 && goal.param_env.visit_with(&mut visitor).is_continue()
124 fn merge_project_candidates(
126 mut candidates: Vec<Candidate<'tcx>>,
127 ) -> QueryResult<'tcx> {
128 match candidates.len() {
129 0 => return Err(NoSolution),
130 1 => return Ok(candidates.pop().unwrap().result),
134 if candidates.len() > 1 {
136 'outer: while i < candidates.len() {
137 for j in (0..candidates.len()).filter(|&j| i != j) {
138 if self.project_candidate_should_be_dropped_in_favor_of(
142 debug!(candidate = ?candidates[i], "Dropping candidate #{}/{}", i, candidates.len());
143 candidates.swap_remove(i);
148 debug!(candidate = ?candidates[i], "Retaining candidate #{}/{}", i, candidates.len());
149 // If there are *STILL* multiple candidates, give up
150 // and report ambiguity.
153 debug!("multiple matches, ambig");
154 // FIXME: return overflow if all candidates overflow, otherwise return ambiguity.
160 Ok(candidates.pop().unwrap().result)
163 fn project_candidate_should_be_dropped_in_favor_of(
165 candidate: &Candidate<'tcx>,
166 other: &Candidate<'tcx>,
168 // FIXME: implement this
169 match (candidate.source, other.source) {
170 (CandidateSource::Impl(_), _)
171 | (CandidateSource::ParamEnv(_), _)
172 | (CandidateSource::BuiltinImpl, _)
173 | (CandidateSource::AliasBound(_), _) => unimplemented!(),
178 impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> {
179 fn self_ty(self) -> Ty<'tcx> {
183 fn with_self_ty(self, tcx: TyCtxt<'tcx>, self_ty: Ty<'tcx>) -> Self {
184 self.with_self_ty(tcx, self_ty)
187 fn trait_def_id(self, tcx: TyCtxt<'tcx>) -> DefId {
188 self.trait_def_id(tcx)
191 fn consider_impl_candidate(
192 ecx: &mut EvalCtxt<'_, 'tcx>,
193 goal: Goal<'tcx, ProjectionPredicate<'tcx>>,
195 ) -> QueryResult<'tcx> {
198 let goal_trait_ref = goal.predicate.projection_ty.trait_ref(tcx);
199 let impl_trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
200 let drcx = DeepRejectCtxt { treat_obligation_params: TreatParams::AsPlaceholder };
201 if iter::zip(goal_trait_ref.substs, impl_trait_ref.skip_binder().substs)
202 .any(|(goal, imp)| !drcx.generic_args_may_unify(goal, imp))
204 return Err(NoSolution);
207 ecx.infcx.probe(|_| {
208 let impl_substs = ecx.infcx.fresh_substs_for_item(DUMMY_SP, impl_def_id);
209 let impl_trait_ref = impl_trait_ref.subst(tcx, impl_substs);
211 let mut nested_goals = ecx.infcx.eq(goal.param_env, goal_trait_ref, impl_trait_ref)?;
212 let where_clause_bounds = tcx
213 .predicates_of(impl_def_id)
214 .instantiate(tcx, impl_substs)
217 .map(|pred| goal.with(tcx, pred));
219 nested_goals.extend(where_clause_bounds);
220 let trait_ref_certainty = ecx.evaluate_all(nested_goals)?;
222 // In case the associated item is hidden due to specialization, we have to
223 // return ambiguity this would otherwise be incomplete, resulting in
224 // unsoundness during coherence (#105782).
225 let Some(assoc_def) = fetch_eligible_assoc_item_def(
229 goal.predicate.def_id(),
232 let certainty = Certainty::Maybe(MaybeCause::Ambiguity);
233 return ecx.make_canonical_response(trait_ref_certainty.unify_and(certainty));
236 if !assoc_def.item.defaultness(tcx).has_value() {
237 tcx.sess.delay_span_bug(
238 tcx.def_span(assoc_def.item.def_id),
239 "missing value for assoc item in impl",
243 // Getting the right substitutions here is complex, e.g. given:
244 // - a goal `<Vec<u32> as Trait<i32>>::Assoc<u64>`
245 // - the applicable impl `impl<T> Trait<i32> for Vec<T>`
246 // - and the impl which defines `Assoc` being `impl<T, U> Trait<U> for Vec<T>`
248 // We first rebase the goal substs onto the impl, going from `[Vec<u32>, i32, u64]`
251 // And then map these substs to the substs of the defining impl of `Assoc`, going
252 // from `[u32, u64]` to `[u32, i32, u64]`.
253 let impl_substs_with_gat = goal.predicate.projection_ty.substs.rebase_onto(
255 goal_trait_ref.def_id,
258 let substs = translate_substs(
262 impl_substs_with_gat,
263 assoc_def.defining_node,
266 // Finally we construct the actual value of the associated type.
267 let is_const = matches!(tcx.def_kind(assoc_def.item.def_id), DefKind::AssocConst);
268 let ty = tcx.bound_type_of(assoc_def.item.def_id);
269 let term: ty::EarlyBinder<ty::Term<'tcx>> = if is_const {
270 let identity_substs =
271 ty::InternalSubsts::identity_for_item(tcx, assoc_def.item.def_id);
272 let did = ty::WithOptConstParam::unknown(assoc_def.item.def_id);
274 ty::ConstKind::Unevaluated(ty::UnevaluatedConst::new(did, identity_substs));
275 ty.map_bound(|ty| tcx.mk_const(kind, ty).into())
277 ty.map_bound(|ty| ty.into())
280 // The term of our goal should be fully unconstrained, so this should never fail.
282 // It can however be ambiguous when the resolved type is a projection.
283 let nested_goals = ecx
285 .eq(goal.param_env, goal.predicate.term, term.subst(tcx, substs))
286 .expect("failed to unify with unconstrained term");
288 ecx.evaluate_all(nested_goals).expect("failed to unify with unconstrained term");
290 ecx.make_canonical_response(trait_ref_certainty.unify_and(rhs_certainty))
294 fn consider_assumption(
295 ecx: &mut EvalCtxt<'_, 'tcx>,
296 goal: Goal<'tcx, Self>,
297 assumption: ty::Predicate<'tcx>,
298 ) -> QueryResult<'tcx> {
299 if let Some(poly_projection_pred) = assumption.to_opt_poly_projection_pred() {
300 ecx.infcx.probe(|_| {
301 let assumption_projection_pred =
302 ecx.infcx.instantiate_bound_vars_with_infer(poly_projection_pred);
303 let nested_goals = ecx.infcx.eq(
305 goal.predicate.projection_ty,
306 assumption_projection_pred.projection_ty,
308 let subst_certainty = ecx.evaluate_all(nested_goals)?;
310 // The term of our goal should be fully unconstrained, so this should never fail.
312 // It can however be ambiguous when the resolved type is a projection.
313 let nested_goals = ecx
315 .eq(goal.param_env, goal.predicate.term, assumption_projection_pred.term)
316 .expect("failed to unify with unconstrained term");
317 let rhs_certainty = ecx
318 .evaluate_all(nested_goals)
319 .expect("failed to unify with unconstrained term");
321 ecx.make_canonical_response(subst_certainty.unify_and(rhs_certainty))
328 fn consider_auto_trait_candidate(
329 _ecx: &mut EvalCtxt<'_, 'tcx>,
330 goal: Goal<'tcx, Self>,
331 ) -> QueryResult<'tcx> {
332 bug!("auto traits do not have associated types: {:?}", goal);
335 fn consider_trait_alias_candidate(
336 _ecx: &mut EvalCtxt<'_, 'tcx>,
337 goal: Goal<'tcx, Self>,
338 ) -> QueryResult<'tcx> {
339 bug!("trait aliases do not have associated types: {:?}", goal);
342 fn consider_builtin_sized_candidate(
343 _ecx: &mut EvalCtxt<'_, 'tcx>,
344 goal: Goal<'tcx, Self>,
345 ) -> QueryResult<'tcx> {
346 bug!("`Sized` does not have an associated type: {:?}", goal);
349 fn consider_builtin_copy_clone_candidate(
350 _ecx: &mut EvalCtxt<'_, 'tcx>,
351 goal: Goal<'tcx, Self>,
352 ) -> QueryResult<'tcx> {
353 bug!("`Copy`/`Clone` does not have an associated type: {:?}", goal);
356 fn consider_builtin_pointer_sized_candidate(
357 _ecx: &mut EvalCtxt<'_, 'tcx>,
358 goal: Goal<'tcx, Self>,
359 ) -> QueryResult<'tcx> {
360 bug!("`PointerSized` does not have an associated type: {:?}", goal);
363 fn consider_builtin_fn_trait_candidates(
364 ecx: &mut EvalCtxt<'_, 'tcx>,
365 goal: Goal<'tcx, Self>,
366 goal_kind: ty::ClosureKind,
367 ) -> QueryResult<'tcx> {
368 if let Some(tupled_inputs_and_output) =
369 structural_traits::extract_tupled_inputs_and_output_from_callable(
371 goal.predicate.self_ty(),
375 let pred = tupled_inputs_and_output
376 .map_bound(|(inputs, output)| ty::ProjectionPredicate {
379 .mk_alias_ty(goal.predicate.def_id(), [goal.predicate.self_ty(), inputs]),
382 .to_predicate(ecx.tcx());
383 Self::consider_assumption(ecx, goal, pred)
385 ecx.make_canonical_response(Certainty::Maybe(MaybeCause::Ambiguity))
389 fn consider_builtin_tuple_candidate(
390 _ecx: &mut EvalCtxt<'_, 'tcx>,
391 goal: Goal<'tcx, Self>,
392 ) -> QueryResult<'tcx> {
393 bug!("`Tuple` does not have an associated type: {:?}", goal);
397 /// This behavior is also implemented in `rustc_ty_utils` and in the old `project` code.
399 /// FIXME: We should merge these 3 implementations as it's likely that they otherwise
401 #[instrument(level = "debug", skip(infcx, param_env), ret)]
402 fn fetch_eligible_assoc_item_def<'tcx>(
403 infcx: &InferCtxt<'tcx>,
404 param_env: ty::ParamEnv<'tcx>,
405 goal_trait_ref: ty::TraitRef<'tcx>,
406 trait_assoc_def_id: DefId,
408 ) -> Result<Option<LeafDef>, NoSolution> {
409 let node_item = specialization_graph::assoc_def(infcx.tcx, impl_def_id, trait_assoc_def_id)
410 .map_err(|ErrorGuaranteed { .. }| NoSolution)?;
412 let eligible = if node_item.is_final() {
413 // Non-specializable items are always projectable.
416 // Only reveal a specializable default if we're past type-checking
417 // and the obligation is monomorphic, otherwise passes such as
418 // transmute checking and polymorphic MIR optimizations could
419 // get a result which isn't correct for all monomorphizations.
420 if param_env.reveal() == Reveal::All {
421 let poly_trait_ref = infcx.resolve_vars_if_possible(goal_trait_ref);
422 !poly_trait_ref.still_further_specializable()
424 debug!(?node_item.item.def_id, "not eligible due to default");
429 if eligible { Ok(Some(node_item)) } else { Ok(None) }