diff options
Diffstat (limited to 'compiler/rustc_trait_selection/src/traits/project.rs')
| -rw-r--r-- | compiler/rustc_trait_selection/src/traits/project.rs | 2150 |
1 files changed, 2150 insertions, 0 deletions
diff --git a/compiler/rustc_trait_selection/src/traits/project.rs b/compiler/rustc_trait_selection/src/traits/project.rs new file mode 100644 index 000000000..c4e80e1ba --- /dev/null +++ b/compiler/rustc_trait_selection/src/traits/project.rs @@ -0,0 +1,2150 @@ +//! Code for projecting associated types out of trait references. + +use super::specialization_graph; +use super::translate_substs; +use super::util; +use super::MismatchedProjectionTypes; +use super::Obligation; +use super::ObligationCause; +use super::PredicateObligation; +use super::Selection; +use super::SelectionContext; +use super::SelectionError; +use super::{ + ImplSourceClosureData, ImplSourceDiscriminantKindData, ImplSourceFnPointerData, + ImplSourceGeneratorData, ImplSourcePointeeData, ImplSourceUserDefinedData, +}; +use super::{Normalized, NormalizedTy, ProjectionCacheEntry, ProjectionCacheKey}; + +use crate::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind}; +use crate::infer::{InferCtxt, InferOk, LateBoundRegionConversionTime}; +use crate::traits::error_reporting::InferCtxtExt as _; +use crate::traits::query::evaluate_obligation::InferCtxtExt as _; +use crate::traits::select::ProjectionMatchesProjection; +use rustc_data_structures::sso::SsoHashSet; +use rustc_data_structures::stack::ensure_sufficient_stack; +use rustc_errors::ErrorGuaranteed; +use rustc_hir::def::DefKind; +use rustc_hir::def_id::DefId; +use rustc_hir::lang_items::LangItem; +use rustc_infer::infer::resolve::OpportunisticRegionResolver; +use rustc_middle::traits::select::OverflowError; +use rustc_middle::ty::fold::{TypeFoldable, TypeFolder, TypeSuperFoldable}; +use rustc_middle::ty::subst::Subst; +use rustc_middle::ty::visit::{MaxUniverse, TypeVisitable}; +use rustc_middle::ty::{self, Term, ToPredicate, Ty, TyCtxt}; +use rustc_span::symbol::sym; + +use std::collections::BTreeMap; + +pub use rustc_middle::traits::Reveal; + +pub type PolyProjectionObligation<'tcx> = Obligation<'tcx, ty::PolyProjectionPredicate<'tcx>>; + +pub type ProjectionObligation<'tcx> = Obligation<'tcx, ty::ProjectionPredicate<'tcx>>; + +pub type ProjectionTyObligation<'tcx> = Obligation<'tcx, ty::ProjectionTy<'tcx>>; + +pub(super) struct InProgress; + +/// When attempting to resolve `<T as TraitRef>::Name` ... +#[derive(Debug)] +pub enum ProjectionError<'tcx> { + /// ...we found multiple sources of information and couldn't resolve the ambiguity. + TooManyCandidates, + + /// ...an error occurred matching `T : TraitRef` + TraitSelectionError(SelectionError<'tcx>), +} + +#[derive(PartialEq, Eq, Debug)] +enum ProjectionCandidate<'tcx> { + /// From a where-clause in the env or object type + ParamEnv(ty::PolyProjectionPredicate<'tcx>), + + /// From the definition of `Trait` when you have something like <<A as Trait>::B as Trait2>::C + TraitDef(ty::PolyProjectionPredicate<'tcx>), + + /// Bounds specified on an object type + Object(ty::PolyProjectionPredicate<'tcx>), + + /// From an "impl" (or a "pseudo-impl" returned by select) + Select(Selection<'tcx>), +} + +enum ProjectionCandidateSet<'tcx> { + None, + Single(ProjectionCandidate<'tcx>), + Ambiguous, + Error(SelectionError<'tcx>), +} + +impl<'tcx> ProjectionCandidateSet<'tcx> { + fn mark_ambiguous(&mut self) { + *self = ProjectionCandidateSet::Ambiguous; + } + + fn mark_error(&mut self, err: SelectionError<'tcx>) { + *self = ProjectionCandidateSet::Error(err); + } + + // Returns true if the push was successful, or false if the candidate + // was discarded -- this could be because of ambiguity, or because + // a higher-priority candidate is already there. + fn push_candidate(&mut self, candidate: ProjectionCandidate<'tcx>) -> bool { + use self::ProjectionCandidate::*; + use self::ProjectionCandidateSet::*; + + // This wacky variable is just used to try and + // make code readable and avoid confusing paths. + // It is assigned a "value" of `()` only on those + // paths in which we wish to convert `*self` to + // ambiguous (and return false, because the candidate + // was not used). On other paths, it is not assigned, + // and hence if those paths *could* reach the code that + // comes after the match, this fn would not compile. + let convert_to_ambiguous; + + match self { + None => { + *self = Single(candidate); + return true; + } + + Single(current) => { + // Duplicates can happen inside ParamEnv. In the case, we + // perform a lazy deduplication. + if current == &candidate { + return false; + } + + // Prefer where-clauses. As in select, if there are multiple + // candidates, we prefer where-clause candidates over impls. This + // may seem a bit surprising, since impls are the source of + // "truth" in some sense, but in fact some of the impls that SEEM + // applicable are not, because of nested obligations. Where + // clauses are the safer choice. See the comment on + // `select::SelectionCandidate` and #21974 for more details. + match (current, candidate) { + (ParamEnv(..), ParamEnv(..)) => convert_to_ambiguous = (), + (ParamEnv(..), _) => return false, + (_, ParamEnv(..)) => unreachable!(), + (_, _) => convert_to_ambiguous = (), + } + } + + Ambiguous | Error(..) => { + return false; + } + } + + // We only ever get here when we moved from a single candidate + // to ambiguous. + let () = convert_to_ambiguous; + *self = Ambiguous; + false + } +} + +/// States returned from `poly_project_and_unify_type`. Takes the place +/// of the old return type, which was: +/// ```ignore (not-rust) +/// Result< +/// Result<Option<Vec<PredicateObligation<'tcx>>>, InProgress>, +/// MismatchedProjectionTypes<'tcx>, +/// > +/// ``` +pub(super) enum ProjectAndUnifyResult<'tcx> { + /// The projection bound holds subject to the given obligations. If the + /// projection cannot be normalized because the required trait bound does + /// not hold, this is returned, with `obligations` being a predicate that + /// cannot be proven. + Holds(Vec<PredicateObligation<'tcx>>), + /// The projection cannot be normalized due to ambiguity. Resolving some + /// inference variables in the projection may fix this. + FailedNormalization, + /// The project cannot be normalized because `poly_project_and_unify_type` + /// is called recursively while normalizing the same projection. + Recursive, + // the projection can be normalized, but is not equal to the expected type. + // Returns the type error that arose from the mismatch. + MismatchedProjectionTypes(MismatchedProjectionTypes<'tcx>), +} + +/// Evaluates constraints of the form: +/// ```ignore (not-rust) +/// for<...> <T as Trait>::U == V +/// ``` +/// If successful, this may result in additional obligations. Also returns +/// the projection cache key used to track these additional obligations. +#[instrument(level = "debug", skip(selcx))] +pub(super) fn poly_project_and_unify_type<'cx, 'tcx>( + selcx: &mut SelectionContext<'cx, 'tcx>, + obligation: &PolyProjectionObligation<'tcx>, +) -> ProjectAndUnifyResult<'tcx> { + let infcx = selcx.infcx(); + let r = infcx.commit_if_ok(|_snapshot| { + let old_universe = infcx.universe(); + let placeholder_predicate = + infcx.replace_bound_vars_with_placeholders(obligation.predicate); + let new_universe = infcx.universe(); + + let placeholder_obligation = obligation.with(placeholder_predicate); + match project_and_unify_type(selcx, &placeholder_obligation) { + ProjectAndUnifyResult::MismatchedProjectionTypes(e) => Err(e), + ProjectAndUnifyResult::Holds(obligations) + if old_universe != new_universe + && selcx.tcx().features().generic_associated_types_extended => + { + // If the `generic_associated_types_extended` feature is active, then we ignore any + // obligations references lifetimes from any universe greater than or equal to the + // universe just created. Otherwise, we can end up with something like `for<'a> I: 'a`, + // which isn't quite what we want. Ideally, we want either an implied + // `for<'a where I: 'a> I: 'a` or we want to "lazily" check these hold when we + // substitute concrete regions. There is design work to be done here; until then, + // however, this allows experimenting potential GAT features without running into + // well-formedness issues. + let new_obligations = obligations + .into_iter() + .filter(|obligation| { + let mut visitor = MaxUniverse::new(); + obligation.predicate.visit_with(&mut visitor); + visitor.max_universe() < new_universe + }) + .collect(); + Ok(ProjectAndUnifyResult::Holds(new_obligations)) + } + other => Ok(other), + } + }); + + match r { + Ok(inner) => inner, + Err(err) => ProjectAndUnifyResult::MismatchedProjectionTypes(err), + } +} + +/// Evaluates constraints of the form: +/// ```ignore (not-rust) +/// <T as Trait>::U == V +/// ``` +/// If successful, this may result in additional obligations. +/// +/// See [poly_project_and_unify_type] for an explanation of the return value. +#[tracing::instrument(level = "debug", skip(selcx))] +fn project_and_unify_type<'cx, 'tcx>( + selcx: &mut SelectionContext<'cx, 'tcx>, + obligation: &ProjectionObligation<'tcx>, +) -> ProjectAndUnifyResult<'tcx> { + let mut obligations = vec![]; + + let infcx = selcx.infcx(); + let normalized = match opt_normalize_projection_type( + selcx, + obligation.param_env, + obligation.predicate.projection_ty, + obligation.cause.clone(), + obligation.recursion_depth, + &mut obligations, + ) { + Ok(Some(n)) => n, + Ok(None) => return ProjectAndUnifyResult::FailedNormalization, + Err(InProgress) => return ProjectAndUnifyResult::Recursive, + }; + debug!(?normalized, ?obligations, "project_and_unify_type result"); + let actual = obligation.predicate.term; + // For an example where this is neccessary see src/test/ui/impl-trait/nested-return-type2.rs + // This allows users to omit re-mentioning all bounds on an associated type and just use an + // `impl Trait` for the assoc type to add more bounds. + let InferOk { value: actual, obligations: new } = + selcx.infcx().replace_opaque_types_with_inference_vars( + actual, + obligation.cause.body_id, + obligation.cause.span, + obligation.param_env, + ); + obligations.extend(new); + + match infcx.at(&obligation.cause, obligation.param_env).eq(normalized, actual) { + Ok(InferOk { obligations: inferred_obligations, value: () }) => { + obligations.extend(inferred_obligations); + ProjectAndUnifyResult::Holds(obligations) + } + Err(err) => { + debug!("equating types encountered error {:?}", err); + ProjectAndUnifyResult::MismatchedProjectionTypes(MismatchedProjectionTypes { err }) + } + } +} + +/// Normalizes any associated type projections in `value`, replacing +/// them with a fully resolved type where possible. The return value +/// combines the normalized result and any additional obligations that +/// were incurred as result. +pub fn normalize<'a, 'b, 'tcx, T>( + selcx: &'a mut SelectionContext<'b, 'tcx>, + param_env: ty::ParamEnv<'tcx>, + cause: ObligationCause<'tcx>, + value: T, +) -> Normalized<'tcx, T> +where + T: TypeFoldable<'tcx>, +{ + let mut obligations = Vec::new(); + let value = normalize_to(selcx, param_env, cause, value, &mut obligations); + Normalized { value, obligations } +} + +pub fn normalize_to<'a, 'b, 'tcx, T>( + selcx: &'a mut SelectionContext<'b, 'tcx>, + param_env: ty::ParamEnv<'tcx>, + cause: ObligationCause<'tcx>, + value: T, + obligations: &mut Vec<PredicateObligation<'tcx>>, +) -> T +where + T: TypeFoldable<'tcx>, +{ + normalize_with_depth_to(selcx, param_env, cause, 0, value, obligations) +} + +/// As `normalize`, but with a custom depth. +pub fn normalize_with_depth<'a, 'b, 'tcx, T>( + selcx: &'a mut SelectionContext<'b, 'tcx>, + param_env: ty::ParamEnv<'tcx>, + cause: ObligationCause<'tcx>, + depth: usize, + value: T, +) -> Normalized<'tcx, T> +where + T: TypeFoldable<'tcx>, +{ + let mut obligations = Vec::new(); + let value = normalize_with_depth_to(selcx, param_env, cause, depth, value, &mut obligations); + Normalized { value, obligations } +} + +#[instrument(level = "info", skip(selcx, param_env, cause, obligations))] +pub fn normalize_with_depth_to<'a, 'b, 'tcx, T>( + selcx: &'a mut SelectionContext<'b, 'tcx>, + param_env: ty::ParamEnv<'tcx>, + cause: ObligationCause<'tcx>, + depth: usize, + value: T, + obligations: &mut Vec<PredicateObligation<'tcx>>, +) -> T +where + T: TypeFoldable<'tcx>, +{ + debug!(obligations.len = obligations.len()); + let mut normalizer = AssocTypeNormalizer::new(selcx, param_env, cause, depth, obligations); + let result = ensure_sufficient_stack(|| normalizer.fold(value)); + debug!(?result, obligations.len = normalizer.obligations.len()); + debug!(?normalizer.obligations,); + result +} + +#[instrument(level = "info", skip(selcx, param_env, cause, obligations))] +pub fn try_normalize_with_depth_to<'a, 'b, 'tcx, T>( + selcx: &'a mut SelectionContext<'b, 'tcx>, + param_env: ty::ParamEnv<'tcx>, + cause: ObligationCause<'tcx>, + depth: usize, + value: T, + obligations: &mut Vec<PredicateObligation<'tcx>>, +) -> T +where + T: TypeFoldable<'tcx>, +{ + debug!(obligations.len = obligations.len()); + let mut normalizer = AssocTypeNormalizer::new_without_eager_inference_replacement( + selcx, + param_env, + cause, + depth, + obligations, + ); + let result = ensure_sufficient_stack(|| normalizer.fold(value)); + debug!(?result, obligations.len = normalizer.obligations.len()); + debug!(?normalizer.obligations,); + result +} + +pub(crate) fn needs_normalization<'tcx, T: TypeVisitable<'tcx>>(value: &T, reveal: Reveal) -> bool { + match reveal { + Reveal::UserFacing => value + .has_type_flags(ty::TypeFlags::HAS_TY_PROJECTION | ty::TypeFlags::HAS_CT_PROJECTION), + Reveal::All => value.has_type_flags( + ty::TypeFlags::HAS_TY_PROJECTION + | ty::TypeFlags::HAS_TY_OPAQUE + | ty::TypeFlags::HAS_CT_PROJECTION, + ), + } +} + +struct AssocTypeNormalizer<'a, 'b, 'tcx> { + selcx: &'a mut SelectionContext<'b, 'tcx>, + param_env: ty::ParamEnv<'tcx>, + cause: ObligationCause<'tcx>, + obligations: &'a mut Vec<PredicateObligation<'tcx>>, + depth: usize, + universes: Vec<Option<ty::UniverseIndex>>, + /// If true, when a projection is unable to be completed, an inference + /// variable will be created and an obligation registered to project to that + /// inference variable. Also, constants will be eagerly evaluated. + eager_inference_replacement: bool, +} + +impl<'a, 'b, 'tcx> AssocTypeNormalizer<'a, 'b, 'tcx> { + fn new( + selcx: &'a mut SelectionContext<'b, 'tcx>, + param_env: ty::ParamEnv<'tcx>, + cause: ObligationCause<'tcx>, + depth: usize, + obligations: &'a mut Vec<PredicateObligation<'tcx>>, + ) -> AssocTypeNormalizer<'a, 'b, 'tcx> { + AssocTypeNormalizer { + selcx, + param_env, + cause, + obligations, + depth, + universes: vec![], + eager_inference_replacement: true, + } + } + + fn new_without_eager_inference_replacement( + selcx: &'a mut SelectionContext<'b, 'tcx>, + param_env: ty::ParamEnv<'tcx>, + cause: ObligationCause<'tcx>, + depth: usize, + obligations: &'a mut Vec<PredicateObligation<'tcx>>, + ) -> AssocTypeNormalizer<'a, 'b, 'tcx> { + AssocTypeNormalizer { + selcx, + param_env, + cause, + obligations, + depth, + universes: vec![], + eager_inference_replacement: false, + } + } + + fn fold<T: TypeFoldable<'tcx>>(&mut self, value: T) -> T { + let value = self.selcx.infcx().resolve_vars_if_possible(value); + debug!(?value); + + assert!( + !value.has_escaping_bound_vars(), + "Normalizing {:?} without wrapping in a `Binder`", + value + ); + + if !needs_normalization(&value, self.param_env.reveal()) { + value + } else { + value.fold_with(self) + } + } +} + +impl<'a, 'b, 'tcx> TypeFolder<'tcx> for AssocTypeNormalizer<'a, 'b, 'tcx> { + fn tcx<'c>(&'c self) -> TyCtxt<'tcx> { + self.selcx.tcx() + } + + fn fold_binder<T: TypeFoldable<'tcx>>( + &mut self, + t: ty::Binder<'tcx, T>, + ) -> ty::Binder<'tcx, T> { + self.universes.push(None); + let t = t.super_fold_with(self); + self.universes.pop(); + t + } + + fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> { + if !needs_normalization(&ty, self.param_env.reveal()) { + return ty; + } + + // We try to be a little clever here as a performance optimization in + // cases where there are nested projections under binders. + // For example: + // ``` + // for<'a> fn(<T as Foo>::One<'a, Box<dyn Bar<'a, Item=<T as Foo>::Two<'a>>>>) + // ``` + // We normalize the substs on the projection before the projecting, but + // if we're naive, we'll + // replace bound vars on inner, project inner, replace placeholders on inner, + // replace bound vars on outer, project outer, replace placeholders on outer + // + // However, if we're a bit more clever, we can replace the bound vars + // on the entire type before normalizing nested projections, meaning we + // replace bound vars on outer, project inner, + // project outer, replace placeholders on outer + // + // This is possible because the inner `'a` will already be a placeholder + // when we need to normalize the inner projection + // + // On the other hand, this does add a bit of complexity, since we only + // replace bound vars if the current type is a `Projection` and we need + // to make sure we don't forget to fold the substs regardless. + + match *ty.kind() { + // This is really important. While we *can* handle this, this has + // severe performance implications for large opaque types with + // late-bound regions. See `issue-88862` benchmark. + ty::Opaque(def_id, substs) if !substs.has_escaping_bound_vars() => { + // Only normalize `impl Trait` outside of type inference, usually in codegen. + match self.param_env.reveal() { + Reveal::UserFacing => ty.super_fold_with(self), + + Reveal::All => { + let recursion_limit = self.tcx().recursion_limit(); + if !recursion_limit.value_within_limit(self.depth) { + let obligation = Obligation::with_depth( + self.cause.clone(), + recursion_limit.0, + self.param_env, + ty, + ); + self.selcx.infcx().report_overflow_error(&obligation, true); + } + + let substs = substs.fold_with(self); + let generic_ty = self.tcx().bound_type_of(def_id); + let concrete_ty = generic_ty.subst(self.tcx(), substs); + self.depth += 1; + let folded_ty = self.fold_ty(concrete_ty); + self.depth -= 1; + folded_ty + } + } + } + + ty::Projection(data) if !data.has_escaping_bound_vars() => { + // This branch is *mostly* just an optimization: when we don't + // have escaping bound vars, we don't need to replace them with + // placeholders (see branch below). *Also*, we know that we can + // register an obligation to *later* project, since we know + // there won't be bound vars there. + let data = data.fold_with(self); + let normalized_ty = if self.eager_inference_replacement { + normalize_projection_type( + self.selcx, + self.param_env, + data, + self.cause.clone(), + self.depth, + &mut self.obligations, + ) + } else { + opt_normalize_projection_type( + self.selcx, + self.param_env, + data, + self.cause.clone(), + self.depth, + &mut self.obligations, + ) + .ok() + .flatten() + .unwrap_or_else(|| ty::Term::Ty(ty.super_fold_with(self))) + }; + debug!( + ?self.depth, + ?ty, + ?normalized_ty, + obligations.len = ?self.obligations.len(), + "AssocTypeNormalizer: normalized type" + ); + normalized_ty.ty().unwrap() + } + + ty::Projection(data) => { + // If there are escaping bound vars, we temporarily replace the + // bound vars with placeholders. Note though, that in the case + // that we still can't project for whatever reason (e.g. self + // type isn't known enough), we *can't* register an obligation + // and return an inference variable (since then that obligation + // would have bound vars and that's a can of worms). Instead, + // we just give up and fall back to pretending like we never tried! + // + // Note: this isn't necessarily the final approach here; we may + // want to figure out how to register obligations with escaping vars + // or handle this some other way. + + let infcx = self.selcx.infcx(); + let (data, mapped_regions, mapped_types, mapped_consts) = + BoundVarReplacer::replace_bound_vars(infcx, &mut self.universes, data); + let data = data.fold_with(self); + let normalized_ty = opt_normalize_projection_type( + self.selcx, + self.param_env, + data, + self.cause.clone(), + self.depth, + &mut self.obligations, + ) + .ok() + .flatten() + .map(|term| term.ty().unwrap()) + .map(|normalized_ty| { + PlaceholderReplacer::replace_placeholders( + infcx, + mapped_regions, + mapped_types, + mapped_consts, + &self.universes, + normalized_ty, + ) + }) + .unwrap_or_else(|| ty.super_fold_with(self)); + + debug!( + ?self.depth, + ?ty, + ?normalized_ty, + obligations.len = ?self.obligations.len(), + "AssocTypeNormalizer: normalized type" + ); + normalized_ty + } + + _ => ty.super_fold_with(self), + } + } + + #[instrument(skip(self), level = "debug")] + fn fold_const(&mut self, constant: ty::Const<'tcx>) -> ty::Const<'tcx> { + if self.selcx.tcx().lazy_normalization() || !self.eager_inference_replacement { + constant + } else { + let constant = constant.super_fold_with(self); + debug!(?constant); + debug!("self.param_env: {:?}", self.param_env); + constant.eval(self.selcx.tcx(), self.param_env) + } + } +} + +pub struct BoundVarReplacer<'me, 'tcx> { + infcx: &'me InferCtxt<'me, 'tcx>, + // These three maps track the bound variable that were replaced by placeholders. It might be + // nice to remove these since we already have the `kind` in the placeholder; we really just need + // the `var` (but we *could* bring that into scope if we were to track them as we pass them). + mapped_regions: BTreeMap<ty::PlaceholderRegion, ty::BoundRegion>, + mapped_types: BTreeMap<ty::PlaceholderType, ty::BoundTy>, + mapped_consts: BTreeMap<ty::PlaceholderConst<'tcx>, ty::BoundVar>, + // The current depth relative to *this* folding, *not* the entire normalization. In other words, + // the depth of binders we've passed here. + current_index: ty::DebruijnIndex, + // The `UniverseIndex` of the binding levels above us. These are optional, since we are lazy: + // we don't actually create a universe until we see a bound var we have to replace. + universe_indices: &'me mut Vec<Option<ty::UniverseIndex>>, +} + +impl<'me, 'tcx> BoundVarReplacer<'me, 'tcx> { + /// Returns `Some` if we *were* able to replace bound vars. If there are any bound vars that + /// use a binding level above `universe_indices.len()`, we fail. + pub fn replace_bound_vars<T: TypeFoldable<'tcx>>( + infcx: &'me InferCtxt<'me, 'tcx>, + universe_indices: &'me mut Vec<Option<ty::UniverseIndex>>, + value: T, + ) -> ( + T, + BTreeMap<ty::PlaceholderRegion, ty::BoundRegion>, + BTreeMap<ty::PlaceholderType, ty::BoundTy>, + BTreeMap<ty::PlaceholderConst<'tcx>, ty::BoundVar>, + ) { + let mapped_regions: BTreeMap<ty::PlaceholderRegion, ty::BoundRegion> = BTreeMap::new(); + let mapped_types: BTreeMap<ty::PlaceholderType, ty::BoundTy> = BTreeMap::new(); + let mapped_consts: BTreeMap<ty::PlaceholderConst<'tcx>, ty::BoundVar> = BTreeMap::new(); + + let mut replacer = BoundVarReplacer { + infcx, + mapped_regions, + mapped_types, + mapped_consts, + current_index: ty::INNERMOST, + universe_indices, + }; + + let value = value.fold_with(&mut replacer); + + (value, replacer.mapped_regions, replacer.mapped_types, replacer.mapped_consts) + } + + fn universe_for(&mut self, debruijn: ty::DebruijnIndex) -> ty::UniverseIndex { + let infcx = self.infcx; + let index = + self.universe_indices.len() + self.current_index.as_usize() - debruijn.as_usize() - 1; + let universe = self.universe_indices[index].unwrap_or_else(|| { + for i in self.universe_indices.iter_mut().take(index + 1) { + *i = i.or_else(|| Some(infcx.create_next_universe())) + } + self.universe_indices[index].unwrap() + }); + universe + } +} + +impl<'tcx> TypeFolder<'tcx> for BoundVarReplacer<'_, 'tcx> { + fn tcx<'b>(&'b self) -> TyCtxt<'tcx> { + self.infcx.tcx + } + + fn fold_binder<T: TypeFoldable<'tcx>>( + &mut self, + t: ty::Binder<'tcx, T>, + ) -> ty::Binder<'tcx, T> { + self.current_index.shift_in(1); + let t = t.super_fold_with(self); + self.current_index.shift_out(1); + t + } + + fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> { + match *r { + ty::ReLateBound(debruijn, _) + if debruijn.as_usize() + 1 + > self.current_index.as_usize() + self.universe_indices.len() => + { + bug!("Bound vars outside of `self.universe_indices`"); + } + ty::ReLateBound(debruijn, br) if debruijn >= self.current_index => { + let universe = self.universe_for(debruijn); + let p = ty::PlaceholderRegion { universe, name: br.kind }; + self.mapped_regions.insert(p, br); + self.infcx.tcx.mk_region(ty::RePlaceholder(p)) + } + _ => r, + } + } + + fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> { + match *t.kind() { + ty::Bound(debruijn, _) + if debruijn.as_usize() + 1 + > self.current_index.as_usize() + self.universe_indices.len() => + { + bug!("Bound vars outside of `self.universe_indices`"); + } + ty::Bound(debruijn, bound_ty) if debruijn >= self.current_index => { + let universe = self.universe_for(debruijn); + let p = ty::PlaceholderType { universe, name: bound_ty.var }; + self.mapped_types.insert(p, bound_ty); + self.infcx.tcx.mk_ty(ty::Placeholder(p)) + } + _ if t.has_vars_bound_at_or_above(self.current_index) => t.super_fold_with(self), + _ => t, + } + } + + fn fold_const(&mut self, ct: ty::Const<'tcx>) -> ty::Const<'tcx> { + match ct.kind() { + ty::ConstKind::Bound(debruijn, _) + if debruijn.as_usize() + 1 + > self.current_index.as_usize() + self.universe_indices.len() => + { + bug!("Bound vars outside of `self.universe_indices`"); + } + ty::ConstKind::Bound(debruijn, bound_const) if debruijn >= self.current_index => { + let universe = self.universe_for(debruijn); + let p = ty::PlaceholderConst { universe, name: bound_const }; + self.mapped_consts.insert(p, bound_const); + self.infcx + .tcx + .mk_const(ty::ConstS { kind: ty::ConstKind::Placeholder(p), ty: ct.ty() }) + } + _ => ct.super_fold_with(self), + } + } + + fn fold_predicate(&mut self, p: ty::Predicate<'tcx>) -> ty::Predicate<'tcx> { + if p.has_vars_bound_at_or_above(self.current_index) { p.super_fold_with(self) } else { p } + } +} + +// The inverse of `BoundVarReplacer`: replaces placeholders with the bound vars from which they came. +pub struct PlaceholderReplacer<'me, 'tcx> { + infcx: &'me InferCtxt<'me, 'tcx>, + mapped_regions: BTreeMap<ty::PlaceholderRegion, ty::BoundRegion>, + mapped_types: BTreeMap<ty::PlaceholderType, ty::BoundTy>, + mapped_consts: BTreeMap<ty::PlaceholderConst<'tcx>, ty::BoundVar>, + universe_indices: &'me [Option<ty::UniverseIndex>], + current_index: ty::DebruijnIndex, +} + +impl<'me, 'tcx> PlaceholderReplacer<'me, 'tcx> { + pub fn replace_placeholders<T: TypeFoldable<'tcx>>( + infcx: &'me InferCtxt<'me, 'tcx>, + mapped_regions: BTreeMap<ty::PlaceholderRegion, ty::BoundRegion>, + mapped_types: BTreeMap<ty::PlaceholderType, ty::BoundTy>, + mapped_consts: BTreeMap<ty::PlaceholderConst<'tcx>, ty::BoundVar>, + universe_indices: &'me [Option<ty::UniverseIndex>], + value: T, + ) -> T { + let mut replacer = PlaceholderReplacer { + infcx, + mapped_regions, + mapped_types, + mapped_consts, + universe_indices, + current_index: ty::INNERMOST, + }; + value.fold_with(&mut replacer) + } +} + +impl<'tcx> TypeFolder<'tcx> for PlaceholderReplacer<'_, 'tcx> { + fn tcx<'b>(&'b self) -> TyCtxt<'tcx> { + self.infcx.tcx + } + + fn fold_binder<T: TypeFoldable<'tcx>>( + &mut self, + t: ty::Binder<'tcx, T>, + ) -> ty::Binder<'tcx, T> { + if !t.has_placeholders() && !t.has_infer_regions() { + return t; + } + self.current_index.shift_in(1); + let t = t.super_fold_with(self); + self.current_index.shift_out(1); + t + } + + fn fold_region(&mut self, r0: ty::Region<'tcx>) -> ty::Region<'tcx> { + let r1 = match *r0 { + ty::ReVar(_) => self + .infcx + .inner + .borrow_mut() + .unwrap_region_constraints() + .opportunistic_resolve_region(self.infcx.tcx, r0), + _ => r0, + }; + + let r2 = match *r1 { + ty::RePlaceholder(p) => { + let replace_var = self.mapped_regions.get(&p); + match replace_var { + Some(replace_var) => { + let index = self + .universe_indices + .iter() + .position(|u| matches!(u, Some(pu) if *pu == p.universe)) + .unwrap_or_else(|| bug!("Unexpected placeholder universe.")); + let db = ty::DebruijnIndex::from_usize( + self.universe_indices.len() - index + self.current_index.as_usize() - 1, + ); + self.tcx().mk_region(ty::ReLateBound(db, *replace_var)) + } + None => r1, + } + } + _ => r1, + }; + + debug!(?r0, ?r1, ?r2, "fold_region"); + + r2 + } + + fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> { + match *ty.kind() { + ty::Placeholder(p) => { + let replace_var = self.mapped_types.get(&p); + match replace_var { + Some(replace_var) => { + let index = self + .universe_indices + .iter() + .position(|u| matches!(u, Some(pu) if *pu == p.universe)) + .unwrap_or_else(|| bug!("Unexpected placeholder universe.")); + let db = ty::DebruijnIndex::from_usize( + self.universe_indices.len() - index + self.current_index.as_usize() - 1, + ); + self.tcx().mk_ty(ty::Bound(db, *replace_var)) + } + None => ty, + } + } + + _ if ty.has_placeholders() || ty.has_infer_regions() => ty.super_fold_with(self), + _ => ty, + } + } + + fn fold_const(&mut self, ct: ty::Const<'tcx>) -> ty::Const<'tcx> { + if let ty::ConstKind::Placeholder(p) = ct.kind() { + let replace_var = self.mapped_consts.get(&p); + match replace_var { + Some(replace_var) => { + let index = self + .universe_indices + .iter() + .position(|u| matches!(u, Some(pu) if *pu == p.universe)) + .unwrap_or_else(|| bug!("Unexpected placeholder universe.")); + let db = ty::DebruijnIndex::from_usize( + self.universe_indices.len() - index + self.current_index.as_usize() - 1, + ); + self.tcx().mk_const(ty::ConstS { + kind: ty::ConstKind::Bound(db, *replace_var), + ty: ct.ty(), + }) + } + None => ct, + } + } else { + ct.super_fold_with(self) + } + } +} + +/// The guts of `normalize`: normalize a specific projection like `<T +/// as Trait>::Item`. The result is always a type (and possibly +/// additional obligations). If ambiguity arises, which implies that +/// there are unresolved type variables in the projection, we will +/// substitute a fresh type variable `$X` and generate a new +/// obligation `<T as Trait>::Item == $X` for later. +pub fn normalize_projection_type<'a, 'b, 'tcx>( + selcx: &'a mut SelectionContext<'b, 'tcx>, + param_env: ty::ParamEnv<'tcx>, + projection_ty: ty::ProjectionTy<'tcx>, + cause: ObligationCause<'tcx>, + depth: usize, + obligations: &mut Vec<PredicateObligation<'tcx>>, +) -> Term<'tcx> { + opt_normalize_projection_type( + selcx, + param_env, + projection_ty, + cause.clone(), + depth, + obligations, + ) + .ok() + .flatten() + .unwrap_or_else(move || { + // if we bottom out in ambiguity, create a type variable + // and a deferred predicate to resolve this when more type + // information is available. + + selcx + .infcx() + .infer_projection(param_env, projection_ty, cause, depth + 1, obligations) + .into() + }) +} + +/// The guts of `normalize`: normalize a specific projection like `<T +/// as Trait>::Item`. The result is always a type (and possibly +/// additional obligations). Returns `None` in the case of ambiguity, +/// which indicates that there are unbound type variables. +/// +/// This function used to return `Option<NormalizedTy<'tcx>>`, which contains a +/// `Ty<'tcx>` and an obligations vector. But that obligation vector was very +/// often immediately appended to another obligations vector. So now this +/// function takes an obligations vector and appends to it directly, which is +/// slightly uglier but avoids the need for an extra short-lived allocation. +#[instrument(level = "debug", skip(selcx, param_env, cause, obligations))] +fn opt_normalize_projection_type<'a, 'b, 'tcx>( + selcx: &'a mut SelectionContext<'b, 'tcx>, + param_env: ty::ParamEnv<'tcx>, + projection_ty: ty::ProjectionTy<'tcx>, + cause: ObligationCause<'tcx>, + depth: usize, + obligations: &mut Vec<PredicateObligation<'tcx>>, +) -> Result<Option<Term<'tcx>>, InProgress> { + let infcx = selcx.infcx(); + // Don't use the projection cache in intercrate mode - + // the `infcx` may be re-used between intercrate in non-intercrate + // mode, which could lead to using incorrect cache results. + let use_cache = !selcx.is_intercrate(); + + let projection_ty = infcx.resolve_vars_if_possible(projection_ty); + let cache_key = ProjectionCacheKey::new(projection_ty); + + // FIXME(#20304) For now, I am caching here, which is good, but it + // means we don't capture the type variables that are created in + // the case of ambiguity. Which means we may create a large stream + // of such variables. OTOH, if we move the caching up a level, we + // would not benefit from caching when proving `T: Trait<U=Foo>` + // bounds. It might be the case that we want two distinct caches, + // or else another kind of cache entry. + + let cache_result = if use_cache { + infcx.inner.borrow_mut().projection_cache().try_start(cache_key) + } else { + Ok(()) + }; + match cache_result { + Ok(()) => debug!("no cache"), + Err(ProjectionCacheEntry::Ambiguous) => { + // If we found ambiguity the last time, that means we will continue + // to do so until some type in the key changes (and we know it + // hasn't, because we just fully resolved it). + debug!("found cache entry: ambiguous"); + return Ok(None); + } + Err(ProjectionCacheEntry::InProgress) => { + // Under lazy normalization, this can arise when + // bootstrapping. That is, imagine an environment with a + // where-clause like `A::B == u32`. Now, if we are asked + // to normalize `A::B`, we will want to check the + // where-clauses in scope. So we will try to unify `A::B` + // with `A::B`, which can trigger a recursive + // normalization. + + debug!("found cache entry: in-progress"); + + // Cache that normalizing this projection resulted in a cycle. This + // should ensure that, unless this happens within a snapshot that's + // rolled back, fulfillment or evaluation will notice the cycle. + + if use_cache { + infcx.inner.borrow_mut().projection_cache().recur(cache_key); + } + return Err(InProgress); + } + Err(ProjectionCacheEntry::Recur) => { + debug!("recur cache"); + return Err(InProgress); + } + Err(ProjectionCacheEntry::NormalizedTy { ty, complete: _ }) => { + // This is the hottest path in this function. + // + // If we find the value in the cache, then return it along + // with the obligations that went along with it. Note + // that, when using a fulfillment context, these + // obligations could in principle be ignored: they have + // already been registered when the cache entry was + // created (and hence the new ones will quickly be + // discarded as duplicated). But when doing trait + // evaluation this is not the case, and dropping the trait + // evaluations can causes ICEs (e.g., #43132). + debug!(?ty, "found normalized ty"); + obligations.extend(ty.obligations); + return Ok(Some(ty.value)); + } + Err(ProjectionCacheEntry::Error) => { + debug!("opt_normalize_projection_type: found error"); + let result = normalize_to_error(selcx, param_env, projection_ty, cause, depth); + obligations.extend(result.obligations); + return Ok(Some(result.value.into())); + } + } + + let obligation = Obligation::with_depth(cause.clone(), depth, param_env, projection_ty); + + match project(selcx, &obligation) { + Ok(Projected::Progress(Progress { + term: projected_term, + obligations: mut projected_obligations, + })) => { + // if projection succeeded, then what we get out of this + // is also non-normalized (consider: it was derived from + // an impl, where-clause etc) and hence we must + // re-normalize it + + let projected_term = selcx.infcx().resolve_vars_if_possible(projected_term); + + let mut result = if projected_term.has_projections() { + let mut normalizer = AssocTypeNormalizer::new( + selcx, + param_env, + cause, + depth + 1, + &mut projected_obligations, + ); + let normalized_ty = normalizer.fold(projected_term); + + Normalized { value: normalized_ty, obligations: projected_obligations } + } else { + Normalized { value: projected_term, obligations: projected_obligations } + }; + + let mut deduped: SsoHashSet<_> = Default::default(); + result.obligations.drain_filter(|projected_obligation| { + if !deduped.insert(projected_obligation.clone()) { + return true; + } + false + }); + + if use_cache { + infcx.inner.borrow_mut().projection_cache().insert_term(cache_key, result.clone()); + } + obligations.extend(result.obligations); + Ok(Some(result.value)) + } + Ok(Projected::NoProgress(projected_ty)) => { + let result = Normalized { value: projected_ty, obligations: vec![] }; + if use_cache { + infcx.inner.borrow_mut().projection_cache().insert_term(cache_key, result.clone()); + } + // No need to extend `obligations`. + Ok(Some(result.value)) + } + Err(ProjectionError::TooManyCandidates) => { + debug!("opt_normalize_projection_type: too many candidates"); + if use_cache { + infcx.inner.borrow_mut().projection_cache().ambiguous(cache_key); + } + Ok(None) + } + Err(ProjectionError::TraitSelectionError(_)) => { + debug!("opt_normalize_projection_type: ERROR"); + // if we got an error processing the `T as Trait` part, + // just return `ty::err` but add the obligation `T : + // Trait`, which when processed will cause the error to be + // reported later + + if use_cache { + infcx.inner.borrow_mut().projection_cache().error(cache_key); + } + let result = normalize_to_error(selcx, param_env, projection_ty, cause, depth); + obligations.extend(result.obligations); + Ok(Some(result.value.into())) + } + } +} + +/// If we are projecting `<T as Trait>::Item`, but `T: Trait` does not +/// hold. In various error cases, we cannot generate a valid +/// normalized projection. Therefore, we create an inference variable +/// return an associated obligation that, when fulfilled, will lead to +/// an error. +/// +/// Note that we used to return `Error` here, but that was quite +/// dubious -- the premise was that an error would *eventually* be +/// reported, when the obligation was processed. But in general once +/// you see an `Error` you are supposed to be able to assume that an +/// error *has been* reported, so that you can take whatever heuristic +/// paths you want to take. To make things worse, it was possible for +/// cycles to arise, where you basically had a setup like `<MyType<$0> +/// as Trait>::Foo == $0`. Here, normalizing `<MyType<$0> as +/// Trait>::Foo> to `[type error]` would lead to an obligation of +/// `<MyType<[type error]> as Trait>::Foo`. We are supposed to report +/// an error for this obligation, but we legitimately should not, +/// because it contains `[type error]`. Yuck! (See issue #29857 for +/// one case where this arose.) +fn normalize_to_error<'a, 'tcx>( + selcx: &mut SelectionContext<'a, 'tcx>, + param_env: ty::ParamEnv<'tcx>, + projection_ty: ty::ProjectionTy<'tcx>, + cause: ObligationCause<'tcx>, + depth: usize, +) -> NormalizedTy<'tcx> { + let trait_ref = ty::Binder::dummy(projection_ty.trait_ref(selcx.tcx())); + let trait_obligation = Obligation { + cause, + recursion_depth: depth, + param_env, + predicate: trait_ref.without_const().to_predicate(selcx.tcx()), + }; + let tcx = selcx.infcx().tcx; + let def_id = projection_ty.item_def_id; + let new_value = selcx.infcx().next_ty_var(TypeVariableOrigin { + kind: TypeVariableOriginKind::NormalizeProjectionType, + span: tcx.def_span(def_id), + }); + Normalized { value: new_value, obligations: vec![trait_obligation] } +} + +enum Projected<'tcx> { + Progress(Progress<'tcx>), + NoProgress(ty::Term<'tcx>), +} + +struct Progress<'tcx> { + term: ty::Term<'tcx>, + obligations: Vec<PredicateObligation<'tcx>>, +} + +impl<'tcx> Progress<'tcx> { + fn error(tcx: TyCtxt<'tcx>) -> Self { + Progress { term: tcx.ty_error().into(), obligations: vec![] } + } + + fn with_addl_obligations(mut self, mut obligations: Vec<PredicateObligation<'tcx>>) -> Self { + self.obligations.append(&mut obligations); + self + } +} + +/// Computes the result of a projection type (if we can). +/// +/// IMPORTANT: +/// - `obligation` must be fully normalized +#[tracing::instrument(level = "info", skip(selcx))] +fn project<'cx, 'tcx>( + selcx: &mut SelectionContext<'cx, 'tcx>, + obligation: &ProjectionTyObligation<'tcx>, +) -> Result<Projected<'tcx>, ProjectionError<'tcx>> { + if !selcx.tcx().recursion_limit().value_within_limit(obligation.recursion_depth) { + // This should really be an immediate error, but some existing code + // relies on being able to recover from this. + return Err(ProjectionError::TraitSelectionError(SelectionError::Overflow( + OverflowError::Canonical, + ))); + } + + if obligation.predicate.references_error() { + return Ok(Projected::Progress(Progress::error(selcx.tcx()))); + } + + let mut candidates = ProjectionCandidateSet::None; + + // Make sure that the following procedures are kept in order. ParamEnv + // needs to be first because it has highest priority, and Select checks + // the return value of push_candidate which assumes it's ran at last. + assemble_candidates_from_param_env(selcx, obligation, &mut candidates); + + assemble_candidates_from_trait_def(selcx, obligation, &mut candidates); + + assemble_candidates_from_object_ty(selcx, obligation, &mut candidates); + + if let ProjectionCandidateSet::Single(ProjectionCandidate::Object(_)) = candidates { + // Avoid normalization cycle from selection (see + // `assemble_candidates_from_object_ty`). + // FIXME(lazy_normalization): Lazy normalization should save us from + // having to special case this. + } else { + assemble_candidates_from_impls(selcx, obligation, &mut candidates); + }; + + match candidates { + ProjectionCandidateSet::Single(candidate) => { + Ok(Projected::Progress(confirm_candidate(selcx, obligation, candidate))) + } + ProjectionCandidateSet::None => Ok(Projected::NoProgress( + // FIXME(associated_const_generics): this may need to change in the future? + // need to investigate whether or not this is fine. + selcx + .tcx() + .mk_projection(obligation.predicate.item_def_id, obligation.predicate.substs) + .into(), + )), + // Error occurred while trying to processing impls. + ProjectionCandidateSet::Error(e) => Err(ProjectionError::TraitSelectionError(e)), + // Inherent ambiguity that prevents us from even enumerating the + // candidates. + ProjectionCandidateSet::Ambiguous => Err(ProjectionError::TooManyCandidates), + } +} + +/// The first thing we have to do is scan through the parameter +/// environment to see whether there are any projection predicates +/// there that can answer this question. +fn assemble_candidates_from_param_env<'cx, 'tcx>( + selcx: &mut SelectionContext<'cx, 'tcx>, + obligation: &ProjectionTyObligation<'tcx>, + candidate_set: &mut ProjectionCandidateSet<'tcx>, +) { + assemble_candidates_from_predicates( + selcx, + obligation, + candidate_set, + ProjectionCandidate::ParamEnv, + obligation.param_env.caller_bounds().iter(), + false, + ); +} + +/// In the case of a nested projection like <<A as Foo>::FooT as Bar>::BarT, we may find +/// that the definition of `Foo` has some clues: +/// +/// ```ignore (illustrative) +/// trait Foo { +/// type FooT : Bar<BarT=i32> +/// } +/// ``` +/// +/// Here, for example, we could conclude that the result is `i32`. +fn assemble_candidates_from_trait_def<'cx, 'tcx>( + selcx: &mut SelectionContext<'cx, 'tcx>, + obligation: &ProjectionTyObligation<'tcx>, + candidate_set: &mut ProjectionCandidateSet<'tcx>, +) { + debug!("assemble_candidates_from_trait_def(..)"); + + let tcx = selcx.tcx(); + // Check whether the self-type is itself a projection. + // If so, extract what we know from the trait and try to come up with a good answer. + let bounds = match *obligation.predicate.self_ty().kind() { + ty::Projection(ref data) => tcx.bound_item_bounds(data.item_def_id).subst(tcx, data.substs), + ty::Opaque(def_id, substs) => tcx.bound_item_bounds(def_id).subst(tcx, substs), + ty::Infer(ty::TyVar(_)) => { + // If the self-type is an inference variable, then it MAY wind up + // being a projected type, so induce an ambiguity. + candidate_set.mark_ambiguous(); + return; + } + _ => return, + }; + + assemble_candidates_from_predicates( + selcx, + obligation, + candidate_set, + ProjectionCandidate::TraitDef, + bounds.iter(), + true, + ); +} + +/// In the case of a trait object like +/// `<dyn Iterator<Item = ()> as Iterator>::Item` we can use the existential +/// predicate in the trait object. +/// +/// We don't go through the select candidate for these bounds to avoid cycles: +/// In the above case, `dyn Iterator<Item = ()>: Iterator` would create a +/// nested obligation of `<dyn Iterator<Item = ()> as Iterator>::Item: Sized`, +/// this then has to be normalized without having to prove +/// `dyn Iterator<Item = ()>: Iterator` again. +fn assemble_candidates_from_object_ty<'cx, 'tcx>( + selcx: &mut SelectionContext<'cx, 'tcx>, + obligation: &ProjectionTyObligation<'tcx>, + candidate_set: &mut ProjectionCandidateSet<'tcx>, +) { + debug!("assemble_candidates_from_object_ty(..)"); + + let tcx = selcx.tcx(); + + let self_ty = obligation.predicate.self_ty(); + let object_ty = selcx.infcx().shallow_resolve(self_ty); + let data = match object_ty.kind() { + ty::Dynamic(data, ..) => data, + ty::Infer(ty::TyVar(_)) => { + // If the self-type is an inference variable, then it MAY wind up + // being an object type, so induce an ambiguity. + candidate_set.mark_ambiguous(); + return; + } + _ => return, + }; + let env_predicates = data + .projection_bounds() + .filter(|bound| bound.item_def_id() == obligation.predicate.item_def_id) + .map(|p| p.with_self_ty(tcx, object_ty).to_predicate(tcx)); + + assemble_candidates_from_predicates( + selcx, + obligation, + candidate_set, + ProjectionCandidate::Object, + env_predicates, + false, + ); +} + +#[tracing::instrument( + level = "debug", + skip(selcx, candidate_set, ctor, env_predicates, potentially_unnormalized_candidates) +)] +fn assemble_candidates_from_predicates<'cx, 'tcx>( + selcx: &mut SelectionContext<'cx, 'tcx>, + obligation: &ProjectionTyObligation<'tcx>, + candidate_set: &mut ProjectionCandidateSet<'tcx>, + ctor: fn(ty::PolyProjectionPredicate<'tcx>) -> ProjectionCandidate<'tcx>, + env_predicates: impl Iterator<Item = ty::Predicate<'tcx>>, + potentially_unnormalized_candidates: bool, +) { + let infcx = selcx.infcx(); + for predicate in env_predicates { + let bound_predicate = predicate.kind(); + if let ty::PredicateKind::Projection(data) = predicate.kind().skip_binder() { + let data = bound_predicate.rebind(data); + if data.projection_def_id() != obligation.predicate.item_def_id { + continue; + } + + let is_match = infcx.probe(|_| { + selcx.match_projection_projections( + obligation, + data, + potentially_unnormalized_candidates, + ) + }); + + match is_match { + ProjectionMatchesProjection::Yes => { + candidate_set.push_candidate(ctor(data)); + + if potentially_unnormalized_candidates + && !obligation.predicate.has_infer_types_or_consts() + { + // HACK: Pick the first trait def candidate for a fully + // inferred predicate. This is to allow duplicates that + // differ only in normalization. + return; + } + } + ProjectionMatchesProjection::Ambiguous => { + candidate_set.mark_ambiguous(); + } + ProjectionMatchesProjection::No => {} + } + } + } +} + +#[tracing::instrument(level = "debug", skip(selcx, obligation, candidate_set))] +fn assemble_candidates_from_impls<'cx, 'tcx>( + selcx: &mut SelectionContext<'cx, 'tcx>, + obligation: &ProjectionTyObligation<'tcx>, + candidate_set: &mut ProjectionCandidateSet<'tcx>, +) { + // If we are resolving `<T as TraitRef<...>>::Item == Type`, + // start out by selecting the predicate `T as TraitRef<...>`: + let poly_trait_ref = ty::Binder::dummy(obligation.predicate.trait_ref(selcx.tcx())); + let trait_obligation = obligation.with(poly_trait_ref.to_poly_trait_predicate()); + let _ = selcx.infcx().commit_if_ok(|_| { + let impl_source = match selcx.select(&trait_obligation) { + Ok(Some(impl_source)) => impl_source, + Ok(None) => { + candidate_set.mark_ambiguous(); + return Err(()); + } + Err(e) => { + debug!(error = ?e, "selection error"); + candidate_set.mark_error(e); + return Err(()); + } + }; + + let eligible = match &impl_source { + super::ImplSource::Closure(_) + | super::ImplSource::Generator(_) + | super::ImplSource::FnPointer(_) + | super::ImplSource::TraitAlias(_) => true, + super::ImplSource::UserDefined(impl_data) => { + // We have to be careful when projecting out of an + // impl because of specialization. If we are not in + // codegen (i.e., projection mode is not "any"), and the + // impl's type is declared as default, then we disable + // projection (even if the trait ref is fully + // monomorphic). In the case where trait ref is not + // fully monomorphic (i.e., includes type parameters), + // this is because those type parameters may + // ultimately be bound to types from other crates that + // may have specialized impls we can't see. In the + // case where the trait ref IS fully monomorphic, this + // is a policy decision that we made in the RFC in + // order to preserve flexibility for the crate that + // defined the specializable impl to specialize later + // for existing types. + // + // In either case, we handle this by not adding a + // candidate for an impl if it contains a `default` + // type. + // + // NOTE: This should be kept in sync with the similar code in + // `rustc_ty_utils::instance::resolve_associated_item()`. + let node_item = + assoc_def(selcx, impl_data.impl_def_id, obligation.predicate.item_def_id) + .map_err(|ErrorGuaranteed { .. }| ())?; + + 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 obligation.param_env.reveal() == Reveal::All { + // NOTE(eddyb) inference variables can resolve to parameters, so + // assume `poly_trait_ref` isn't monomorphic, if it contains any. + let poly_trait_ref = selcx.infcx().resolve_vars_if_possible(poly_trait_ref); + !poly_trait_ref.still_further_specializable() + } else { + debug!( + assoc_ty = ?selcx.tcx().def_path_str(node_item.item.def_id), + ?obligation.predicate, + "assemble_candidates_from_impls: not eligible due to default", + ); + false + } + } + } + super::ImplSource::DiscriminantKind(..) => { + // While `DiscriminantKind` is automatically implemented for every type, + // the concrete discriminant may not be known yet. + // + // Any type with multiple potential discriminant types is therefore not eligible. + let self_ty = selcx.infcx().shallow_resolve(obligation.predicate.self_ty()); + + match self_ty.kind() { + ty::Bool + | ty::Char + | ty::Int(_) + | ty::Uint(_) + | ty::Float(_) + | ty::Adt(..) + | ty::Foreign(_) + | ty::Str + | ty::Array(..) + | ty::Slice(_) + | ty::RawPtr(..) + | ty::Ref(..) + | ty::FnDef(..) + | ty::FnPtr(..) + | ty::Dynamic(..) + | ty::Closure(..) + | ty::Generator(..) + | ty::GeneratorWitness(..) + | ty::Never + | ty::Tuple(..) + // Integers and floats always have `u8` as their discriminant. + | ty::Infer(ty::InferTy::IntVar(_) | ty::InferTy::FloatVar(..)) => true, + + ty::Projection(..) + | ty::Opaque(..) + | ty::Param(..) + | ty::Bound(..) + | ty::Placeholder(..) + | ty::Infer(..) + | ty::Error(_) => false, + } + } + super::ImplSource::Pointee(..) => { + // While `Pointee` is automatically implemented for every type, + // the concrete metadata type may not be known yet. + // + // Any type with multiple potential metadata types is therefore not eligible. + let self_ty = selcx.infcx().shallow_resolve(obligation.predicate.self_ty()); + + let tail = selcx.tcx().struct_tail_with_normalize( + self_ty, + |ty| { + // We throw away any obligations we get from this, since we normalize + // and confirm these obligations once again during confirmation + normalize_with_depth( + selcx, + obligation.param_env, + obligation.cause.clone(), + obligation.recursion_depth + 1, + ty, + ) + .value + }, + || {}, + ); + + match tail.kind() { + ty::Bool + | ty::Char + | ty::Int(_) + | ty::Uint(_) + | ty::Float(_) + | ty::Str + | ty::Array(..) + | ty::Slice(_) + | ty::RawPtr(..) + | ty::Ref(..) + | ty::FnDef(..) + | ty::FnPtr(..) + | ty::Dynamic(..) + | ty::Closure(..) + | ty::Generator(..) + | ty::GeneratorWitness(..) + | ty::Never + // Extern types have unit metadata, according to RFC 2850 + | ty::Foreign(_) + // If returned by `struct_tail_without_normalization` this is a unit struct + // without any fields, or not a struct, and therefore is Sized. + | ty::Adt(..) + // If returned by `struct_tail_without_normalization` this is the empty tuple. + | ty::Tuple(..) + // Integers and floats are always Sized, and so have unit type metadata. + | ty::Infer(ty::InferTy::IntVar(_) | ty::InferTy::FloatVar(..)) => true, + + // type parameters, opaques, and unnormalized projections have pointer + // metadata if they're known (e.g. by the param_env) to be sized + ty::Param(_) | ty::Projection(..) | ty::Opaque(..) + if selcx.infcx().predicate_must_hold_modulo_regions( + &obligation.with( + ty::Binder::dummy(ty::TraitRef::new( + selcx.tcx().require_lang_item(LangItem::Sized, None), + selcx.tcx().mk_substs_trait(self_ty, &[]), + )) + .without_const() + .to_predicate(selcx.tcx()), + ), + ) => + { + true + } + + // FIXME(compiler-errors): are Bound and Placeholder types ever known sized? + ty::Param(_) + | ty::Projection(..) + | ty::Opaque(..) + | ty::Bound(..) + | ty::Placeholder(..) + | ty::Infer(..) + | ty::Error(_) => { + if tail.has_infer_types() { + candidate_set.mark_ambiguous(); + } + false + } + } + } + super::ImplSource::Param(..) => { + // This case tell us nothing about the value of an + // associated type. Consider: + // + // ``` + // trait SomeTrait { type Foo; } + // fn foo<T:SomeTrait>(...) { } + // ``` + // + // If the user writes `<T as SomeTrait>::Foo`, then the `T + // : SomeTrait` binding does not help us decide what the + // type `Foo` is (at least, not more specifically than + // what we already knew). + // + // But wait, you say! What about an example like this: + // + // ``` + // fn bar<T:SomeTrait<Foo=usize>>(...) { ... } + // ``` + // + // Doesn't the `T : SomeTrait<Foo=usize>` predicate help + // resolve `T::Foo`? And of course it does, but in fact + // that single predicate is desugared into two predicates + // in the compiler: a trait predicate (`T : SomeTrait`) and a + // projection. And the projection where clause is handled + // in `assemble_candidates_from_param_env`. + false + } + super::ImplSource::Object(_) => { + // Handled by the `Object` projection candidate. See + // `assemble_candidates_from_object_ty` for an explanation of + // why we special case object types. + false + } + super::ImplSource::AutoImpl(..) + | super::ImplSource::Builtin(..) + | super::ImplSource::TraitUpcasting(_) + | super::ImplSource::ConstDestruct(_) => { + // These traits have no associated types. + selcx.tcx().sess.delay_span_bug( + obligation.cause.span, + &format!("Cannot project an associated type from `{:?}`", impl_source), + ); + return Err(()); + } + }; + + if eligible { + if candidate_set.push_candidate(ProjectionCandidate::Select(impl_source)) { + Ok(()) + } else { + Err(()) + } + } else { + Err(()) + } + }); +} + +fn confirm_candidate<'cx, 'tcx>( + selcx: &mut SelectionContext<'cx, 'tcx>, + obligation: &ProjectionTyObligation<'tcx>, + candidate: ProjectionCandidate<'tcx>, +) -> Progress<'tcx> { + debug!(?obligation, ?candidate, "confirm_candidate"); + let mut progress = match candidate { + ProjectionCandidate::ParamEnv(poly_projection) + | ProjectionCandidate::Object(poly_projection) => { + confirm_param_env_candidate(selcx, obligation, poly_projection, false) + } + + ProjectionCandidate::TraitDef(poly_projection) => { + confirm_param_env_candidate(selcx, obligation, poly_projection, true) + } + + ProjectionCandidate::Select(impl_source) => { + confirm_select_candidate(selcx, obligation, impl_source) + } + }; + + // When checking for cycle during evaluation, we compare predicates with + // "syntactic" equality. Since normalization generally introduces a type + // with new region variables, we need to resolve them to existing variables + // when possible for this to work. See `auto-trait-projection-recursion.rs` + // for a case where this matters. + if progress.term.has_infer_regions() { + progress.term = + progress.term.fold_with(&mut OpportunisticRegionResolver::new(selcx.infcx())); + } + progress +} + +fn confirm_select_candidate<'cx, 'tcx>( + selcx: &mut SelectionContext<'cx, 'tcx>, + obligation: &ProjectionTyObligation<'tcx>, + impl_source: Selection<'tcx>, +) -> Progress<'tcx> { + match impl_source { + super::ImplSource::UserDefined(data) => confirm_impl_candidate(selcx, obligation, data), + super::ImplSource::Generator(data) => confirm_generator_candidate(selcx, obligation, data), + super::ImplSource::Closure(data) => confirm_closure_candidate(selcx, obligation, data), + super::ImplSource::FnPointer(data) => confirm_fn_pointer_candidate(selcx, obligation, data), + super::ImplSource::DiscriminantKind(data) => { + confirm_discriminant_kind_candidate(selcx, obligation, data) + } + super::ImplSource::Pointee(data) => confirm_pointee_candidate(selcx, obligation, data), + super::ImplSource::Object(_) + | super::ImplSource::AutoImpl(..) + | super::ImplSource::Param(..) + | super::ImplSource::Builtin(..) + | super::ImplSource::TraitUpcasting(_) + | super::ImplSource::TraitAlias(..) + | super::ImplSource::ConstDestruct(_) => { + // we don't create Select candidates with this kind of resolution + span_bug!( + obligation.cause.span, + "Cannot project an associated type from `{:?}`", + impl_source + ) + } + } +} + +fn confirm_generator_candidate<'cx, 'tcx>( + selcx: &mut SelectionContext<'cx, 'tcx>, + obligation: &ProjectionTyObligation<'tcx>, + impl_source: ImplSourceGeneratorData<'tcx, PredicateObligation<'tcx>>, +) -> Progress<'tcx> { + let gen_sig = impl_source.substs.as_generator().poly_sig(); + let Normalized { value: gen_sig, obligations } = normalize_with_depth( + selcx, + obligation.param_env, + obligation.cause.clone(), + obligation.recursion_depth + 1, + gen_sig, + ); + + debug!(?obligation, ?gen_sig, ?obligations, "confirm_generator_candidate"); + + let tcx = selcx.tcx(); + + let gen_def_id = tcx.require_lang_item(LangItem::Generator, None); + + let predicate = super::util::generator_trait_ref_and_outputs( + tcx, + gen_def_id, + obligation.predicate.self_ty(), + gen_sig, + ) + .map_bound(|(trait_ref, yield_ty, return_ty)| { + let name = tcx.associated_item(obligation.predicate.item_def_id).name; + let ty = if name == sym::Return { + return_ty + } else if name == sym::Yield { + yield_ty + } else { + bug!() + }; + + ty::ProjectionPredicate { + projection_ty: ty::ProjectionTy { + substs: trait_ref.substs, + item_def_id: obligation.predicate.item_def_id, + }, + term: ty.into(), + } + }); + + confirm_param_env_candidate(selcx, obligation, predicate, false) + .with_addl_obligations(impl_source.nested) + .with_addl_obligations(obligations) +} + +fn confirm_discriminant_kind_candidate<'cx, 'tcx>( + selcx: &mut SelectionContext<'cx, 'tcx>, + obligation: &ProjectionTyObligation<'tcx>, + _: ImplSourceDiscriminantKindData, +) -> Progress<'tcx> { + let tcx = selcx.tcx(); + + let self_ty = selcx.infcx().shallow_resolve(obligation.predicate.self_ty()); + // We get here from `poly_project_and_unify_type` which replaces bound vars + // with placeholders + debug_assert!(!self_ty.has_escaping_bound_vars()); + let substs = tcx.mk_substs([self_ty.into()].iter()); + + let discriminant_def_id = tcx.require_lang_item(LangItem::Discriminant, None); + + let predicate = ty::ProjectionPredicate { + projection_ty: ty::ProjectionTy { substs, item_def_id: discriminant_def_id }, + term: self_ty.discriminant_ty(tcx).into(), + }; + + // We get here from `poly_project_and_unify_type` which replaces bound vars + // with placeholders, so dummy is okay here. + confirm_param_env_candidate(selcx, obligation, ty::Binder::dummy(predicate), false) +} + +fn confirm_pointee_candidate<'cx, 'tcx>( + selcx: &mut SelectionContext<'cx, 'tcx>, + obligation: &ProjectionTyObligation<'tcx>, + _: ImplSourcePointeeData, +) -> Progress<'tcx> { + let tcx = selcx.tcx(); + let self_ty = selcx.infcx().shallow_resolve(obligation.predicate.self_ty()); + + let mut obligations = vec![]; + let (metadata_ty, check_is_sized) = self_ty.ptr_metadata_ty(tcx, |ty| { + normalize_with_depth_to( + selcx, + obligation.param_env, + obligation.cause.clone(), + obligation.recursion_depth + 1, + ty, + &mut obligations, + ) + }); + if check_is_sized { + let sized_predicate = ty::Binder::dummy(ty::TraitRef::new( + tcx.require_lang_item(LangItem::Sized, None), + tcx.mk_substs_trait(self_ty, &[]), + )) + .without_const() + .to_predicate(tcx); + obligations.push(Obligation::new( + obligation.cause.clone(), + obligation.param_env, + sized_predicate, + )); + } + + let substs = tcx.mk_substs([self_ty.into()].iter()); + let metadata_def_id = tcx.require_lang_item(LangItem::Metadata, None); + + let predicate = ty::ProjectionPredicate { + projection_ty: ty::ProjectionTy { substs, item_def_id: metadata_def_id }, + term: metadata_ty.into(), + }; + + confirm_param_env_candidate(selcx, obligation, ty::Binder::dummy(predicate), false) + .with_addl_obligations(obligations) +} + +fn confirm_fn_pointer_candidate<'cx, 'tcx>( + selcx: &mut SelectionContext<'cx, 'tcx>, + obligation: &ProjectionTyObligation<'tcx>, + fn_pointer_impl_source: ImplSourceFnPointerData<'tcx, PredicateObligation<'tcx>>, +) -> Progress<'tcx> { + let fn_type = selcx.infcx().shallow_resolve(fn_pointer_impl_source.fn_ty); + let sig = fn_type.fn_sig(selcx.tcx()); + let Normalized { value: sig, obligations } = normalize_with_depth( + selcx, + obligation.param_env, + obligation.cause.clone(), + obligation.recursion_depth + 1, + sig, + ); + + confirm_callable_candidate(selcx, obligation, sig, util::TupleArgumentsFlag::Yes) + .with_addl_obligations(fn_pointer_impl_source.nested) + .with_addl_obligations(obligations) +} + +fn confirm_closure_candidate<'cx, 'tcx>( + selcx: &mut SelectionContext<'cx, 'tcx>, + obligation: &ProjectionTyObligation<'tcx>, + impl_source: ImplSourceClosureData<'tcx, PredicateObligation<'tcx>>, +) -> Progress<'tcx> { + let closure_sig = impl_source.substs.as_closure().sig(); + let Normalized { value: closure_sig, obligations } = normalize_with_depth( + selcx, + obligation.param_env, + obligation.cause.clone(), + obligation.recursion_depth + 1, + closure_sig, + ); + + debug!(?obligation, ?closure_sig, ?obligations, "confirm_closure_candidate"); + + confirm_callable_candidate(selcx, obligation, closure_sig, util::TupleArgumentsFlag::No) + .with_addl_obligations(impl_source.nested) + .with_addl_obligations(obligations) +} + +fn confirm_callable_candidate<'cx, 'tcx>( + selcx: &mut SelectionContext<'cx, 'tcx>, + obligation: &ProjectionTyObligation<'tcx>, + fn_sig: ty::PolyFnSig<'tcx>, + flag: util::TupleArgumentsFlag, +) -> Progress<'tcx> { + let tcx = selcx.tcx(); + + debug!(?obligation, ?fn_sig, "confirm_callable_candidate"); + + let fn_once_def_id = tcx.require_lang_item(LangItem::FnOnce, None); + let fn_once_output_def_id = tcx.require_lang_item(LangItem::FnOnceOutput, None); + + let predicate = super::util::closure_trait_ref_and_return_type( + tcx, + fn_once_def_id, + obligation.predicate.self_ty(), + fn_sig, + flag, + ) + .map_bound(|(trait_ref, ret_type)| ty::ProjectionPredicate { + projection_ty: ty::ProjectionTy { + substs: trait_ref.substs, + item_def_id: fn_once_output_def_id, + }, + term: ret_type.into(), + }); + + confirm_param_env_candidate(selcx, obligation, predicate, true) +} + +fn confirm_param_env_candidate<'cx, 'tcx>( + selcx: &mut SelectionContext<'cx, 'tcx>, + obligation: &ProjectionTyObligation<'tcx>, + poly_cache_entry: ty::PolyProjectionPredicate<'tcx>, + potentially_unnormalized_candidate: bool, +) -> Progress<'tcx> { + let infcx = selcx.infcx(); + let cause = &obligation.cause; + let param_env = obligation.param_env; + + let cache_entry = infcx.replace_bound_vars_with_fresh_vars( + cause.span, + LateBoundRegionConversionTime::HigherRankedType, + poly_cache_entry, + ); + + let cache_projection = cache_entry.projection_ty; + let mut nested_obligations = Vec::new(); + let obligation_projection = obligation.predicate; + let obligation_projection = ensure_sufficient_stack(|| { + normalize_with_depth_to( + selcx, + obligation.param_env, + obligation.cause.clone(), + obligation.recursion_depth + 1, + obligation_projection, + &mut nested_obligations, + ) + }); + let cache_projection = if potentially_unnormalized_candidate { + ensure_sufficient_stack(|| { + normalize_with_depth_to( + selcx, + obligation.param_env, + obligation.cause.clone(), + obligation.recursion_depth + 1, + cache_projection, + &mut nested_obligations, + ) + }) + } else { + cache_projection + }; + + debug!(?cache_projection, ?obligation_projection); + + match infcx.at(cause, param_env).eq(cache_projection, obligation_projection) { + Ok(InferOk { value: _, obligations }) => { + nested_obligations.extend(obligations); + assoc_ty_own_obligations(selcx, obligation, &mut nested_obligations); + // FIXME(associated_const_equality): Handle consts here as well? Maybe this progress type should just take + // a term instead. + Progress { term: cache_entry.term, obligations: nested_obligations } + } + Err(e) => { + let msg = format!( + "Failed to unify obligation `{:?}` with poly_projection `{:?}`: {:?}", + obligation, poly_cache_entry, e, + ); + debug!("confirm_param_env_candidate: {}", msg); + let err = infcx.tcx.ty_error_with_message(obligation.cause.span, &msg); + Progress { term: err.into(), obligations: vec![] } + } + } +} + +fn confirm_impl_candidate<'cx, 'tcx>( + selcx: &mut SelectionContext<'cx, 'tcx>, + obligation: &ProjectionTyObligation<'tcx>, + impl_impl_source: ImplSourceUserDefinedData<'tcx, PredicateObligation<'tcx>>, +) -> Progress<'tcx> { + let tcx = selcx.tcx(); + + let ImplSourceUserDefinedData { impl_def_id, substs, mut nested } = impl_impl_source; + let assoc_item_id = obligation.predicate.item_def_id; + let trait_def_id = tcx.trait_id_of_impl(impl_def_id).unwrap(); + + let param_env = obligation.param_env; + let Ok(assoc_ty) = assoc_def(selcx, impl_def_id, assoc_item_id) else { + return Progress { term: tcx.ty_error().into(), obligations: nested }; + }; + + if !assoc_ty.item.defaultness(tcx).has_value() { + // This means that the impl is missing a definition for the + // associated type. This error will be reported by the type + // checker method `check_impl_items_against_trait`, so here we + // just return Error. + debug!( + "confirm_impl_candidate: no associated type {:?} for {:?}", + assoc_ty.item.name, obligation.predicate + ); + return Progress { term: tcx.ty_error().into(), obligations: nested }; + } + // If we're trying to normalize `<Vec<u32> as X>::A<S>` using + //`impl<T> X for Vec<T> { type A<Y> = Box<Y>; }`, then: + // + // * `obligation.predicate.substs` is `[Vec<u32>, S]` + // * `substs` is `[u32]` + // * `substs` ends up as `[u32, S]` + let substs = obligation.predicate.substs.rebase_onto(tcx, trait_def_id, substs); + let substs = + translate_substs(selcx.infcx(), param_env, impl_def_id, substs, assoc_ty.defining_node); + let ty = tcx.bound_type_of(assoc_ty.item.def_id); + let is_const = matches!(tcx.def_kind(assoc_ty.item.def_id), DefKind::AssocConst); + let term: ty::EarlyBinder<ty::Term<'tcx>> = if is_const { + let identity_substs = + crate::traits::InternalSubsts::identity_for_item(tcx, assoc_ty.item.def_id); + let did = ty::WithOptConstParam::unknown(assoc_ty.item.def_id); + let kind = ty::ConstKind::Unevaluated(ty::Unevaluated::new(did, identity_substs)); + ty.map_bound(|ty| tcx.mk_const(ty::ConstS { ty, kind }).into()) + } else { + ty.map_bound(|ty| ty.into()) + }; + if substs.len() != tcx.generics_of(assoc_ty.item.def_id).count() { + let err = tcx.ty_error_with_message( + obligation.cause.span, + "impl item and trait item have different parameter counts", + ); + Progress { term: err.into(), obligations: nested } + } else { + assoc_ty_own_obligations(selcx, obligation, &mut nested); + Progress { term: term.subst(tcx, substs), obligations: nested } + } +} + +// Get obligations corresponding to the predicates from the where-clause of the +// associated type itself. +// Note: `feature(generic_associated_types)` is required to write such +// predicates, even for non-generic associated types. +fn assoc_ty_own_obligations<'cx, 'tcx>( + selcx: &mut SelectionContext<'cx, 'tcx>, + obligation: &ProjectionTyObligation<'tcx>, + nested: &mut Vec<PredicateObligation<'tcx>>, +) { + let tcx = selcx.tcx(); + for predicate in tcx + .predicates_of(obligation.predicate.item_def_id) + .instantiate_own(tcx, obligation.predicate.substs) + .predicates + { + let normalized = normalize_with_depth_to( + selcx, + obligation.param_env, + obligation.cause.clone(), + obligation.recursion_depth + 1, + predicate, + nested, + ); + nested.push(Obligation::with_depth( + obligation.cause.clone(), + obligation.recursion_depth + 1, + obligation.param_env, + normalized, + )); + } +} + +/// Locate the definition of an associated type in the specialization hierarchy, +/// starting from the given impl. +/// +/// Based on the "projection mode", this lookup may in fact only examine the +/// topmost impl. See the comments for `Reveal` for more details. +fn assoc_def( + selcx: &SelectionContext<'_, '_>, + impl_def_id: DefId, + assoc_def_id: DefId, +) -> Result<specialization_graph::LeafDef, ErrorGuaranteed> { + let tcx = selcx.tcx(); + let trait_def_id = tcx.impl_trait_ref(impl_def_id).unwrap().def_id; + let trait_def = tcx.trait_def(trait_def_id); + + // This function may be called while we are still building the + // specialization graph that is queried below (via TraitDef::ancestors()), + // so, in order to avoid unnecessary infinite recursion, we manually look + // for the associated item at the given impl. + // If there is no such item in that impl, this function will fail with a + // cycle error if the specialization graph is currently being built. + if let Some(&impl_item_id) = tcx.impl_item_implementor_ids(impl_def_id).get(&assoc_def_id) { + let item = tcx.associated_item(impl_item_id); + let impl_node = specialization_graph::Node::Impl(impl_def_id); + return Ok(specialization_graph::LeafDef { + item: *item, + defining_node: impl_node, + finalizing_node: if item.defaultness(tcx).is_default() { + None + } else { + Some(impl_node) + }, + }); + } + + let ancestors = trait_def.ancestors(tcx, impl_def_id)?; + if let Some(assoc_item) = ancestors.leaf_def(tcx, assoc_def_id) { + Ok(assoc_item) + } else { + // This is saying that neither the trait nor + // the impl contain a definition for this + // associated type. Normally this situation + // could only arise through a compiler bug -- + // if the user wrote a bad item name, it + // should have failed in astconv. + bug!( + "No associated type `{}` for {}", + tcx.item_name(assoc_def_id), + tcx.def_path_str(impl_def_id) + ) + } +} + +pub(crate) trait ProjectionCacheKeyExt<'cx, 'tcx>: Sized { + fn from_poly_projection_predicate( + selcx: &mut SelectionContext<'cx, 'tcx>, + predicate: ty::PolyProjectionPredicate<'tcx>, + ) -> Option<Self>; +} + +impl<'cx, 'tcx> ProjectionCacheKeyExt<'cx, 'tcx> for ProjectionCacheKey<'tcx> { + fn from_poly_projection_predicate( + selcx: &mut SelectionContext<'cx, 'tcx>, + predicate: ty::PolyProjectionPredicate<'tcx>, + ) -> Option<Self> { + let infcx = selcx.infcx(); + // We don't do cross-snapshot caching of obligations with escaping regions, + // so there's no cache key to use + predicate.no_bound_vars().map(|predicate| { + ProjectionCacheKey::new( + // We don't attempt to match up with a specific type-variable state + // from a specific call to `opt_normalize_projection_type` - if + // there's no precise match, the original cache entry is "stranded" + // anyway. + infcx.resolve_vars_if_possible(predicate.projection_ty), + ) + }) + } +} |