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, QueryResult};
7 use rustc_errors::ErrorGuaranteed;
8 use rustc_hir::def::DefKind;
9 use rustc_hir::def_id::DefId;
10 use rustc_hir::LangItem;
11 use rustc_infer::infer::InferCtxt;
12 use rustc_infer::traits::query::NoSolution;
13 use rustc_infer::traits::specialization_graph::LeafDef;
14 use rustc_infer::traits::Reveal;
15 use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams};
16 use rustc_middle::ty::{self, Ty, TyCtxt};
17 use rustc_middle::ty::{ProjectionPredicate, TypeSuperVisitable, TypeVisitor};
18 use rustc_middle::ty::{ToPredicate, TypeVisitable};
19 use rustc_span::{sym, DUMMY_SP};
21 use std::ops::ControlFlow;
23 impl<'tcx> EvalCtxt<'_, 'tcx> {
24 pub(super) fn compute_projection_goal(
26 goal: Goal<'tcx, ProjectionPredicate<'tcx>>,
27 ) -> QueryResult<'tcx> {
28 // To only compute normalization once for each projection we only
29 // normalize if the expected term is an unconstrained inference variable.
31 // E.g. for `<T as Trait>::Assoc == u32` we recursively compute the goal
32 // `exists<U> <T as Trait>::Assoc == U` and then take the resulting type for
33 // `U` and equate it with `u32`. This means that we don't need a separate
34 // projection cache in the solver.
35 if self.term_is_fully_unconstrained(goal) {
36 let candidates = self.assemble_and_evaluate_candidates(goal);
37 self.merge_project_candidates(candidates)
39 let predicate = goal.predicate;
40 let unconstrained_rhs = match predicate.term.unpack() {
41 ty::TermKind::Ty(_) => self.infcx.next_ty_infer().into(),
42 ty::TermKind::Const(ct) => self.infcx.next_const_infer(ct.ty()).into(),
44 let unconstrained_predicate = ty::Clause::Projection(ProjectionPredicate {
45 projection_ty: goal.predicate.projection_ty,
46 term: unconstrained_rhs,
48 let (_has_changed, normalize_certainty) =
49 self.evaluate_goal(goal.with(self.tcx(), unconstrained_predicate))?;
52 self.infcx.eq(goal.param_env, unconstrained_rhs, predicate.term)?;
53 let eval_certainty = self.evaluate_all(nested_eq_goals)?;
54 self.make_canonical_response(normalize_certainty.unify_and(eval_certainty))
58 /// Is the projection predicate is of the form `exists<T> <Ty as Trait>::Assoc = T`.
60 /// This is the case if the `term` is an inference variable in the innermost universe
61 /// and does not occur in any other part of the predicate.
62 fn term_is_fully_unconstrained(&self, goal: Goal<'tcx, ProjectionPredicate<'tcx>>) -> bool {
63 let infcx = self.infcx;
64 let term_is_infer = match goal.predicate.term.unpack() {
65 ty::TermKind::Ty(ty) => {
66 if let &ty::Infer(ty::TyVar(vid)) = ty.kind() {
67 match infcx.probe_ty_var(vid) {
68 Ok(value) => bug!("resolved var in query: {goal:?} {value:?}"),
69 Err(universe) => universe == infcx.universe(),
75 ty::TermKind::Const(ct) => {
76 if let ty::ConstKind::Infer(ty::InferConst::Var(vid)) = ct.kind() {
77 match self.infcx.probe_const_var(vid) {
78 Ok(value) => bug!("resolved var in query: {goal:?} {value:?}"),
79 Err(universe) => universe == infcx.universe(),
87 // Guard against `<T as Trait<?0>>::Assoc = ?0>`.
88 struct ContainsTerm<'tcx> {
91 impl<'tcx> TypeVisitor<'tcx> for ContainsTerm<'tcx> {
93 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
95 if ty::Term::from(t) == self.term {
98 t.super_visit_with(self)
101 ControlFlow::CONTINUE
105 fn visit_const(&mut self, c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
107 if ty::Term::from(c) == self.term {
110 c.super_visit_with(self)
113 ControlFlow::CONTINUE
118 let mut visitor = ContainsTerm { term: goal.predicate.term };
121 && goal.predicate.projection_ty.visit_with(&mut visitor).is_continue()
122 && goal.param_env.visit_with(&mut visitor).is_continue()
125 fn merge_project_candidates(
127 mut candidates: Vec<Candidate<'tcx>>,
128 ) -> QueryResult<'tcx> {
129 match candidates.len() {
130 0 => return Err(NoSolution),
131 1 => return Ok(candidates.pop().unwrap().result),
135 if candidates.len() > 1 {
137 'outer: while i < candidates.len() {
138 for j in (0..candidates.len()).filter(|&j| i != j) {
139 if self.project_candidate_should_be_dropped_in_favor_of(
143 debug!(candidate = ?candidates[i], "Dropping candidate #{}/{}", i, candidates.len());
144 candidates.swap_remove(i);
149 debug!(candidate = ?candidates[i], "Retaining candidate #{}/{}", i, candidates.len());
150 // If there are *STILL* multiple candidates, give up
151 // and report ambiguity.
154 debug!("multiple matches, ambig");
155 // FIXME: return overflow if all candidates overflow, otherwise return ambiguity.
161 Ok(candidates.pop().unwrap().result)
164 fn project_candidate_should_be_dropped_in_favor_of(
166 candidate: &Candidate<'tcx>,
167 other: &Candidate<'tcx>,
169 // FIXME: implement this
170 match (candidate.source, other.source) {
171 (CandidateSource::Impl(_), _)
172 | (CandidateSource::ParamEnv(_), _)
173 | (CandidateSource::BuiltinImpl, _)
174 | (CandidateSource::AliasBound(_), _) => unimplemented!(),
179 impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> {
180 fn self_ty(self) -> Ty<'tcx> {
184 fn with_self_ty(self, tcx: TyCtxt<'tcx>, self_ty: Ty<'tcx>) -> Self {
185 self.with_self_ty(tcx, self_ty)
188 fn trait_def_id(self, tcx: TyCtxt<'tcx>) -> DefId {
189 self.trait_def_id(tcx)
192 fn consider_impl_candidate(
193 ecx: &mut EvalCtxt<'_, 'tcx>,
194 goal: Goal<'tcx, ProjectionPredicate<'tcx>>,
196 ) -> QueryResult<'tcx> {
199 let goal_trait_ref = goal.predicate.projection_ty.trait_ref(tcx);
200 let impl_trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
201 let drcx = DeepRejectCtxt { treat_obligation_params: TreatParams::AsPlaceholder };
202 if iter::zip(goal_trait_ref.substs, impl_trait_ref.skip_binder().substs)
203 .any(|(goal, imp)| !drcx.generic_args_may_unify(goal, imp))
205 return Err(NoSolution);
208 ecx.infcx.probe(|_| {
209 let impl_substs = ecx.infcx.fresh_substs_for_item(DUMMY_SP, impl_def_id);
210 let impl_trait_ref = impl_trait_ref.subst(tcx, impl_substs);
212 let mut nested_goals = ecx.infcx.eq(goal.param_env, goal_trait_ref, impl_trait_ref)?;
213 let where_clause_bounds = tcx
214 .predicates_of(impl_def_id)
215 .instantiate(tcx, impl_substs)
218 .map(|pred| goal.with(tcx, pred));
220 nested_goals.extend(where_clause_bounds);
221 let trait_ref_certainty = ecx.evaluate_all(nested_goals)?;
223 // In case the associated item is hidden due to specialization, we have to
224 // return ambiguity this would otherwise be incomplete, resulting in
225 // unsoundness during coherence (#105782).
226 let Some(assoc_def) = fetch_eligible_assoc_item_def(
230 goal.predicate.def_id(),
233 return ecx.make_canonical_response(trait_ref_certainty.unify_and(Certainty::AMBIGUOUS));
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::AMBIGUOUS)
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);
396 fn consider_builtin_pointee_candidate(
397 ecx: &mut EvalCtxt<'_, 'tcx>,
398 goal: Goal<'tcx, Self>,
399 ) -> QueryResult<'tcx> {
401 ecx.infcx.probe(|_| {
402 let metadata_ty = match goal.predicate.self_ty().kind() {
414 | ty::Infer(ty::IntVar(..) | ty::FloatVar(..))
416 | ty::GeneratorWitness(..)
417 | ty::GeneratorWitnessMIR(..)
419 | ty::Foreign(..) => tcx.types.unit,
421 ty::Error(e) => tcx.ty_error_with_guaranteed(*e),
423 ty::Str | ty::Slice(_) => tcx.types.usize,
425 ty::Dynamic(_, _, _) => {
426 let dyn_metadata = tcx.require_lang_item(LangItem::DynMetadata, None);
427 tcx.bound_type_of(dyn_metadata)
428 .subst(tcx, &[ty::GenericArg::from(goal.predicate.self_ty())])
431 ty::Alias(_, _) | ty::Param(_) | ty::Placeholder(..) => {
432 // FIXME(ptr_metadata): It would also be possible to return a `Ok(Ambig)` with no constraints.
433 let sized_predicate = ty::Binder::dummy(tcx.at(DUMMY_SP).mk_trait_ref(
435 [ty::GenericArg::from(goal.predicate.self_ty())],
438 let mut nested_goals = ecx.infcx.eq(
440 goal.predicate.term.ty().unwrap(),
443 nested_goals.push(goal.with(tcx, sized_predicate));
445 return ecx.evaluate_all_and_make_canonical_response(nested_goals);
448 ty::Adt(def, substs) if def.is_struct() => {
449 match def.non_enum_variant().fields.last() {
450 None => tcx.types.unit,
452 let self_ty = field_def.ty(tcx, substs);
453 let new_goal = goal.with(
455 ty::Binder::dummy(goal.predicate.with_self_ty(tcx, self_ty)),
457 return ecx.evaluate_all_and_make_canonical_response(vec![new_goal]);
461 ty::Adt(_, _) => tcx.types.unit,
463 ty::Tuple(elements) => match elements.last() {
464 None => tcx.types.unit,
466 let new_goal = goal.with(
468 ty::Binder::dummy(goal.predicate.with_self_ty(tcx, self_ty)),
470 return ecx.evaluate_all_and_make_canonical_response(vec![new_goal]);
475 ty::TyVar(_) | ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_),
477 | ty::Bound(..) => bug!(
478 "unexpected self ty `{:?}` when normalizing `<T as Pointee>::Metadata`",
479 goal.predicate.self_ty()
484 ecx.infcx.eq(goal.param_env, goal.predicate.term.ty().unwrap(), metadata_ty)?;
485 ecx.evaluate_all_and_make_canonical_response(nested_goals)
489 fn consider_builtin_future_candidate(
490 ecx: &mut EvalCtxt<'_, 'tcx>,
491 goal: Goal<'tcx, Self>,
492 ) -> QueryResult<'tcx> {
493 let self_ty = goal.predicate.self_ty();
494 let ty::Generator(def_id, substs, _) = *self_ty.kind() else {
495 return Err(NoSolution);
498 // Generators are not futures unless they come from `async` desugaring
500 if !tcx.generator_is_async(def_id) {
501 return Err(NoSolution);
504 let term = substs.as_generator().return_ty().into();
506 Self::consider_assumption(
509 ty::Binder::dummy(ty::ProjectionPredicate {
510 projection_ty: ecx.tcx().mk_alias_ty(goal.predicate.def_id(), [self_ty]),
517 fn consider_builtin_generator_candidate(
518 ecx: &mut EvalCtxt<'_, 'tcx>,
519 goal: Goal<'tcx, Self>,
520 ) -> QueryResult<'tcx> {
521 let self_ty = goal.predicate.self_ty();
522 let ty::Generator(def_id, substs, _) = *self_ty.kind() else {
523 return Err(NoSolution);
526 // `async`-desugared generators do not implement the generator trait
528 if tcx.generator_is_async(def_id) {
529 return Err(NoSolution);
532 let generator = substs.as_generator();
534 let name = tcx.associated_item(goal.predicate.def_id()).name;
535 let term = if name == sym::Return {
536 generator.return_ty().into()
537 } else if name == sym::Yield {
538 generator.yield_ty().into()
540 bug!("unexpected associated item `<{self_ty} as Generator>::{name}`")
543 Self::consider_assumption(
546 ty::Binder::dummy(ty::ProjectionPredicate {
549 .mk_alias_ty(goal.predicate.def_id(), [self_ty, generator.resume_ty()]),
557 /// This behavior is also implemented in `rustc_ty_utils` and in the old `project` code.
559 /// FIXME: We should merge these 3 implementations as it's likely that they otherwise
561 #[instrument(level = "debug", skip(infcx, param_env), ret)]
562 fn fetch_eligible_assoc_item_def<'tcx>(
563 infcx: &InferCtxt<'tcx>,
564 param_env: ty::ParamEnv<'tcx>,
565 goal_trait_ref: ty::TraitRef<'tcx>,
566 trait_assoc_def_id: DefId,
568 ) -> Result<Option<LeafDef>, NoSolution> {
569 let node_item = specialization_graph::assoc_def(infcx.tcx, impl_def_id, trait_assoc_def_id)
570 .map_err(|ErrorGuaranteed { .. }| NoSolution)?;
572 let eligible = if node_item.is_final() {
573 // Non-specializable items are always projectable.
576 // Only reveal a specializable default if we're past type-checking
577 // and the obligation is monomorphic, otherwise passes such as
578 // transmute checking and polymorphic MIR optimizations could
579 // get a result which isn't correct for all monomorphizations.
580 if param_env.reveal() == Reveal::All {
581 let poly_trait_ref = infcx.resolve_vars_if_possible(goal_trait_ref);
582 !poly_trait_ref.still_further_specializable()
584 debug!(?node_item.item.def_id, "not eligible due to default");
589 if eligible { Ok(Some(node_item)) } else { Ok(None) }