| //! 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::TraitQueryMode; |
| 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 rustc_data_structures::sso::SsoHashSet; |
| use rustc_data_structures::stack::ensure_sufficient_stack; |
| use rustc_errors::ErrorReported; |
| use rustc_hir::def_id::DefId; |
| use rustc_hir::lang_items::LangItem; |
| use rustc_infer::infer::resolve::OpportunisticRegionResolver; |
| use rustc_middle::ty::fold::{TypeFoldable, TypeFolder}; |
| use rustc_middle::ty::subst::Subst; |
| use rustc_middle::ty::{self, ToPredicate, Ty, TyCtxt, WithConstness}; |
| 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 ProjectionTyError<'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 ProjectionTyCandidate<'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 ProjectionTyCandidateSet<'tcx> { |
| None, |
| Single(ProjectionTyCandidate<'tcx>), |
| Ambiguous, |
| Error(SelectionError<'tcx>), |
| } |
| |
| impl<'tcx> ProjectionTyCandidateSet<'tcx> { |
| fn mark_ambiguous(&mut self) { |
| *self = ProjectionTyCandidateSet::Ambiguous; |
| } |
| |
| fn mark_error(&mut self, err: SelectionError<'tcx>) { |
| *self = ProjectionTyCandidateSet::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: ProjectionTyCandidate<'tcx>) -> bool { |
| use self::ProjectionTyCandidate::*; |
| use self::ProjectionTyCandidateSet::*; |
| |
| // 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 |
| } |
| } |
| |
| /// Evaluates constraints of the form: |
| /// |
| /// 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. |
| /// |
| /// ## Returns |
| /// |
| /// - `Err(_)`: the projection can be normalized, but is not equal to the |
| /// expected type. |
| /// - `Ok(Err(InProgress))`: this is called recursively while normalizing |
| /// the same projection. |
| /// - `Ok(Ok(None))`: The projection cannot be normalized due to ambiguity |
| /// (resolving some inference variables in the projection may fix this). |
| /// - `Ok(Ok(Some(obligations)))`: The projection bound holds subject to |
| /// the given obligations. If the projection cannot be normalized because |
| /// the required trait bound doesn't hold this returned with `obligations` |
| /// being a predicate that cannot be proven. |
| #[instrument(level = "debug", skip(selcx))] |
| pub(super) fn poly_project_and_unify_type<'cx, 'tcx>( |
| selcx: &mut SelectionContext<'cx, 'tcx>, |
| obligation: &PolyProjectionObligation<'tcx>, |
| ) -> Result< |
| Result<Option<Vec<PredicateObligation<'tcx>>>, InProgress>, |
| MismatchedProjectionTypes<'tcx>, |
| > { |
| let infcx = selcx.infcx(); |
| infcx.commit_if_ok(|_snapshot| { |
| let placeholder_predicate = |
| infcx.replace_bound_vars_with_placeholders(obligation.predicate); |
| |
| let placeholder_obligation = obligation.with(placeholder_predicate); |
| let result = project_and_unify_type(selcx, &placeholder_obligation)?; |
| Ok(result) |
| }) |
| } |
| |
| /// Evaluates constraints of the form: |
| /// |
| /// <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. |
| fn project_and_unify_type<'cx, 'tcx>( |
| selcx: &mut SelectionContext<'cx, 'tcx>, |
| obligation: &ProjectionObligation<'tcx>, |
| ) -> Result< |
| Result<Option<Vec<PredicateObligation<'tcx>>>, InProgress>, |
| MismatchedProjectionTypes<'tcx>, |
| > { |
| debug!(?obligation, "project_and_unify_type"); |
| |
| let mut obligations = vec![]; |
| let normalized_ty = 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 Ok(Ok(None)), |
| Err(InProgress) => return Ok(Err(InProgress)), |
| }; |
| |
| debug!(?normalized_ty, ?obligations, "project_and_unify_type result"); |
| |
| let infcx = selcx.infcx(); |
| match infcx |
| .at(&obligation.cause, obligation.param_env) |
| .eq(normalized_ty, obligation.predicate.ty) |
| { |
| Ok(InferOk { obligations: inferred_obligations, value: () }) => { |
| obligations.extend(inferred_obligations); |
| Ok(Ok(Some(obligations))) |
| } |
| Err(err) => { |
| debug!("project_and_unify_type: equating types encountered error {:?}", err); |
| Err(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 |
| } |
| |
| pub(crate) fn needs_normalization<'tcx, T: TypeFoldable<'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>>, |
| } |
| |
| 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![] } |
| } |
| |
| 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` after type-checking, 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.super_fold_with(self); |
| let generic_ty = self.tcx().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.super_fold_with(self); |
| let normalized_ty = normalize_projection_type( |
| self.selcx, |
| self.param_env, |
| data, |
| self.cause.clone(), |
| self.depth, |
| &mut self.obligations, |
| ); |
| debug!( |
| ?self.depth, |
| ?ty, |
| ?normalized_ty, |
| obligations.len = ?self.obligations.len(), |
| "AssocTypeNormalizer: normalized type" |
| ); |
| normalized_ty |
| } |
| |
| 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.super_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(|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), |
| } |
| } |
| |
| fn fold_const(&mut self, constant: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> { |
| if self.selcx.tcx().lazy_normalization() { |
| constant |
| } else { |
| let constant = constant.super_fold_with(self); |
| 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.super_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 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: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> { |
| match *ct { |
| ty::Const { val: ty::ConstKind::Bound(debruijn, _), ty: _ } |
| if debruijn.as_usize() + 1 |
| > self.current_index.as_usize() + self.universe_indices.len() => |
| { |
| bug!("Bound vars outside of `self.universe_indices`"); |
| } |
| ty::Const { val: ty::ConstKind::Bound(debruijn, bound_const), ty } |
| if debruijn >= self.current_index => |
| { |
| let universe = self.universe_for(debruijn); |
| let p = ty::PlaceholderConst { |
| universe, |
| name: ty::BoundConst { var: bound_const, ty }, |
| }; |
| self.mapped_consts.insert(p, bound_const); |
| self.infcx.tcx.mk_const(ty::Const { val: ty::ConstKind::Placeholder(p), ty }) |
| } |
| _ if ct.has_vars_bound_at_or_above(self.current_index) => ct.super_fold_with(self), |
| _ => ct, |
| } |
| } |
| } |
| |
| // 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 Vec<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 Vec<Option<ty::UniverseIndex>>, |
| value: T, |
| ) -> T { |
| let mut replacer = PlaceholderReplacer { |
| infcx, |
| mapped_regions, |
| mapped_types, |
| mapped_consts, |
| universe_indices, |
| current_index: ty::INNERMOST, |
| }; |
| value.super_fold_with(&mut replacer) |
| } |
| } |
| |
| impl 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: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> { |
| if let ty::Const { val: ty::ConstKind::Placeholder(p), ty } = *ct { |
| 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::Const { val: ty::ConstKind::Bound(db, *replace_var), 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>>, |
| ) -> Ty<'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) |
| }) |
| } |
| |
| /// 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<Ty<'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)) => { |
| // 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)); |
| } |
| } |
| |
| let obligation = Obligation::with_depth(cause.clone(), depth, param_env, projection_ty); |
| |
| match project_type(selcx, &obligation) { |
| Ok(ProjectedTy::Progress(Progress { |
| ty: projected_ty, |
| 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_ty = selcx.infcx().resolve_vars_if_possible(projected_ty); |
| debug!(?projected_ty, ?depth, ?projected_obligations); |
| |
| let mut result = if projected_ty.has_projections() { |
| let mut normalizer = AssocTypeNormalizer::new( |
| selcx, |
| param_env, |
| cause, |
| depth + 1, |
| &mut projected_obligations, |
| ); |
| let normalized_ty = normalizer.fold(projected_ty); |
| |
| debug!(?normalized_ty, ?depth); |
| |
| Normalized { value: normalized_ty, obligations: projected_obligations } |
| } else { |
| Normalized { value: projected_ty, obligations: projected_obligations } |
| }; |
| |
| let mut deduped: SsoHashSet<_> = Default::default(); |
| let mut canonical = |
| SelectionContext::with_query_mode(selcx.infcx(), TraitQueryMode::Canonical); |
| |
| result.obligations.drain_filter(|projected_obligation| { |
| if !deduped.insert(projected_obligation.clone()) { |
| return true; |
| } |
| // If any global obligations always apply, considering regions, then we don't |
| // need to include them. The `is_global` check rules out inference variables, |
| // so there's no need for the caller of `opt_normalize_projection_type` |
| // to evaluate them. |
| // Note that we do *not* discard obligations that evaluate to |
| // `EvaluatedtoOkModuloRegions`. Evaluating these obligations |
| // inside of a query (e.g. `evaluate_obligation`) can change |
| // the result to `EvaluatedToOkModuloRegions`, while an |
| // `EvaluatedToOk` obligation will never change the result. |
| // See #85360 for more details |
| projected_obligation.is_global(canonical.tcx()) |
| && canonical |
| .evaluate_root_obligation(projected_obligation) |
| .map_or(false, |res| res.must_apply_considering_regions()) |
| }); |
| |
| if use_cache { |
| infcx.inner.borrow_mut().projection_cache().insert_ty(cache_key, result.clone()); |
| } |
| obligations.extend(result.obligations); |
| Ok(Some(result.value)) |
| } |
| Ok(ProjectedTy::NoProgress(projected_ty)) => { |
| debug!(?projected_ty, "opt_normalize_projection_type: no progress"); |
| let result = Normalized { value: projected_ty, obligations: vec![] }; |
| if use_cache { |
| infcx.inner.borrow_mut().projection_cache().insert_ty(cache_key, result.clone()); |
| } |
| // No need to extend `obligations`. |
| Ok(Some(result.value)) |
| } |
| Err(ProjectionTyError::TooManyCandidates) => { |
| debug!("opt_normalize_projection_type: too many candidates"); |
| if use_cache { |
| infcx.inner.borrow_mut().projection_cache().ambiguous(cache_key); |
| } |
| Ok(None) |
| } |
| Err(ProjectionTyError::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)) |
| } |
| } |
| } |
| |
| /// 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 ProjectedTy<'tcx> { |
| Progress(Progress<'tcx>), |
| NoProgress(Ty<'tcx>), |
| } |
| |
| struct Progress<'tcx> { |
| ty: Ty<'tcx>, |
| obligations: Vec<PredicateObligation<'tcx>>, |
| } |
| |
| impl<'tcx> Progress<'tcx> { |
| fn error(tcx: TyCtxt<'tcx>) -> Self { |
| Progress { ty: tcx.ty_error(), obligations: vec![] } |
| } |
| |
| fn with_addl_obligations(mut self, mut obligations: Vec<PredicateObligation<'tcx>>) -> Self { |
| debug!( |
| self.obligations.len = ?self.obligations.len(), |
| obligations.len = obligations.len(), |
| "with_addl_obligations" |
| ); |
| |
| debug!(?self.obligations, ?obligations, "with_addl_obligations"); |
| |
| 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_type<'cx, 'tcx>( |
| selcx: &mut SelectionContext<'cx, 'tcx>, |
| obligation: &ProjectionTyObligation<'tcx>, |
| ) -> Result<ProjectedTy<'tcx>, ProjectionTyError<'tcx>> { |
| if !selcx.tcx().recursion_limit().value_within_limit(obligation.recursion_depth) { |
| debug!("project: overflow!"); |
| // This should really be an immediate error, but some existing code |
| // relies on being able to recover from this. |
| return Err(ProjectionTyError::TraitSelectionError(SelectionError::Overflow)); |
| } |
| |
| if obligation.predicate.references_error() { |
| return Ok(ProjectedTy::Progress(Progress::error(selcx.tcx()))); |
| } |
| |
| let mut candidates = ProjectionTyCandidateSet::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 ProjectionTyCandidateSet::Single(ProjectionTyCandidate::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 { |
| ProjectionTyCandidateSet::Single(candidate) => { |
| Ok(ProjectedTy::Progress(confirm_candidate(selcx, obligation, candidate))) |
| } |
| ProjectionTyCandidateSet::None => Ok(ProjectedTy::NoProgress( |
| selcx |
| .tcx() |
| .mk_projection(obligation.predicate.item_def_id, obligation.predicate.substs), |
| )), |
| // Error occurred while trying to processing impls. |
| ProjectionTyCandidateSet::Error(e) => Err(ProjectionTyError::TraitSelectionError(e)), |
| // Inherent ambiguity that prevents us from even enumerating the |
| // candidates. |
| ProjectionTyCandidateSet::Ambiguous => Err(ProjectionTyError::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 ProjectionTyCandidateSet<'tcx>, |
| ) { |
| debug!("assemble_candidates_from_param_env(..)"); |
| assemble_candidates_from_predicates( |
| selcx, |
| obligation, |
| candidate_set, |
| ProjectionTyCandidate::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: |
| /// |
| /// ``` |
| /// 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 ProjectionTyCandidateSet<'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.item_bounds(data.item_def_id).subst(tcx, data.substs), |
| ty::Opaque(def_id, substs) => tcx.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, |
| ProjectionTyCandidate::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 ProjectionTyCandidateSet<'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, |
| ProjectionTyCandidate::Object, |
| env_predicates, |
| false, |
| ); |
| } |
| |
| fn assemble_candidates_from_predicates<'cx, 'tcx>( |
| selcx: &mut SelectionContext<'cx, 'tcx>, |
| obligation: &ProjectionTyObligation<'tcx>, |
| candidate_set: &mut ProjectionTyCandidateSet<'tcx>, |
| ctor: fn(ty::PolyProjectionPredicate<'tcx>) -> ProjectionTyCandidate<'tcx>, |
| env_predicates: impl Iterator<Item = ty::Predicate<'tcx>>, |
| potentially_unnormalized_candidates: bool, |
| ) { |
| debug!(?obligation, "assemble_candidates_from_predicates"); |
| |
| let infcx = selcx.infcx(); |
| for predicate in env_predicates { |
| debug!(?predicate); |
| let bound_predicate = predicate.kind(); |
| if let ty::PredicateKind::Projection(data) = predicate.kind().skip_binder() { |
| let data = bound_predicate.rebind(data); |
| let same_def_id = data.projection_def_id() == obligation.predicate.item_def_id; |
| |
| let is_match = same_def_id |
| && infcx.probe(|_| { |
| selcx.match_projection_projections( |
| obligation, |
| data, |
| potentially_unnormalized_candidates, |
| ) |
| }); |
| |
| debug!(?data, ?is_match, ?same_def_id); |
| |
| if is_match { |
| 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; |
| } |
| } |
| } |
| } |
| } |
| |
| fn assemble_candidates_from_impls<'cx, 'tcx>( |
| selcx: &mut SelectionContext<'cx, 'tcx>, |
| obligation: &ProjectionTyObligation<'tcx>, |
| candidate_set: &mut ProjectionTyCandidateSet<'tcx>, |
| ) { |
| debug!("assemble_candidates_from_impls"); |
| |
| // 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(_) => { |
| debug!(?impl_source); |
| 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_ty_def(selcx, impl_data.impl_def_id, obligation.predicate.item_def_id) |
| .map_err(|ErrorReported| ())?; |
| |
| 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()); |
| |
| // FIXME:Â should this normalize? |
| let tail = selcx.tcx().struct_tail_without_normalization(self_ty); |
| match tail.kind() { |
| ty::Bool |
| | ty::Char |
| | ty::Int(_) |
| | ty::Uint(_) |
| | ty::Float(_) |
| | 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 |
| // 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, |
| |
| ty::Projection(..) |
| | ty::Opaque(..) |
| | ty::Param(..) |
| | ty::Bound(..) |
| | ty::Placeholder(..) |
| | ty::Infer(..) |
| | ty::Error(_) => 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::ConstDrop(_) => { |
| // 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(ProjectionTyCandidate::Select(impl_source)) { |
| Ok(()) |
| } else { |
| Err(()) |
| } |
| } else { |
| Err(()) |
| } |
| }); |
| } |
| |
| fn confirm_candidate<'cx, 'tcx>( |
| selcx: &mut SelectionContext<'cx, 'tcx>, |
| obligation: &ProjectionTyObligation<'tcx>, |
| candidate: ProjectionTyCandidate<'tcx>, |
| ) -> Progress<'tcx> { |
| debug!(?obligation, ?candidate, "confirm_candidate"); |
| let mut progress = match candidate { |
| ProjectionTyCandidate::ParamEnv(poly_projection) |
| | ProjectionTyCandidate::Object(poly_projection) => { |
| confirm_param_env_candidate(selcx, obligation, poly_projection, false) |
| } |
| |
| ProjectionTyCandidate::TraitDef(poly_projection) => { |
| confirm_param_env_candidate(selcx, obligation, poly_projection, true) |
| } |
| |
| ProjectionTyCandidate::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.ty.has_infer_regions() { |
| progress.ty = OpportunisticRegionResolver::new(selcx.infcx()).fold_ty(progress.ty); |
| } |
| 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::ConstDrop(_) => { |
| // 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).ident.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, |
| }, |
| ty, |
| } |
| }); |
| |
| 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 }, |
| ty: self_ty.discriminant_ty(tcx), |
| }; |
| |
| // 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 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 }, |
| ty: self_ty.ptr_metadata_ty(tcx), |
| }; |
| |
| confirm_param_env_candidate(selcx, obligation, ty::Binder::dummy(predicate), false) |
| } |
| |
| 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, |
| }, |
| ty: ret_type, |
| }); |
| |
| 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); |
| Progress { ty: cache_entry.ty, 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 { ty: err, 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 assoc_ty = match assoc_ty_def(selcx, impl_def_id, assoc_item_id) { |
| Ok(assoc_ty) => assoc_ty, |
| Err(ErrorReported) => return Progress { ty: tcx.ty_error(), obligations: nested }, |
| }; |
| |
| if !assoc_ty.item.defaultness.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.ident, obligation.predicate |
| ); |
| return Progress { ty: tcx.ty_error(), 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.type_of(assoc_ty.item.def_id); |
| 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 { ty: err, obligations: nested } |
| } else { |
| assoc_ty_own_obligations(selcx, obligation, &mut nested); |
| Progress { ty: ty.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 associcated 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_ty_def( |
| selcx: &SelectionContext<'_, '_>, |
| impl_def_id: DefId, |
| assoc_ty_def_id: DefId, |
| ) -> Result<specialization_graph::LeafDef, ErrorReported> { |
| let tcx = selcx.tcx(); |
| let assoc_ty_name = tcx.associated_item(assoc_ty_def_id).ident; |
| 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. |
| let impl_node = specialization_graph::Node::Impl(impl_def_id); |
| for item in impl_node.items(tcx) { |
| if matches!(item.kind, ty::AssocKind::Type) |
| && tcx.hygienic_eq(item.ident, assoc_ty_name, trait_def_id) |
| { |
| return Ok(specialization_graph::LeafDef { |
| item: *item, |
| defining_node: impl_node, |
| finalizing_node: if item.defaultness.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_ty_name, ty::AssocKind::Type) { |
| 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 {}", assoc_ty_name, tcx.def_path_str(impl_def_id)) |
| } |
| } |
| |
| crate trait ProjectionCacheKeyExt<'tcx>: Sized { |
| fn from_poly_projection_predicate( |
| selcx: &mut SelectionContext<'cx, 'tcx>, |
| predicate: ty::PolyProjectionPredicate<'tcx>, |
| ) -> Option<Self>; |
| } |
| |
| impl<'tcx> ProjectionCacheKeyExt<'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), |
| ) |
| }) |
| } |
| } |
