2414 lines
94 KiB
Rust
2414 lines
94 KiB
Rust
//! Code for projecting associated types out of trait references.
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use super::specialization_graph;
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use super::translate_substs;
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use super::util;
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use super::MismatchedProjectionTypes;
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use super::Obligation;
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use super::ObligationCause;
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use super::PredicateObligation;
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use super::Selection;
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use super::SelectionContext;
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use super::SelectionError;
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use super::{
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ImplSourceClosureData, ImplSourceDiscriminantKindData, ImplSourceFnPointerData,
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ImplSourceGeneratorData, ImplSourcePointeeData, ImplSourceUserDefinedData,
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};
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use super::{Normalized, NormalizedTy, ProjectionCacheEntry, ProjectionCacheKey};
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use crate::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
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use crate::infer::{InferCtxt, InferOk, LateBoundRegionConversionTime};
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use crate::traits::error_reporting::InferCtxtExt as _;
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use crate::traits::query::evaluate_obligation::InferCtxtExt as _;
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use crate::traits::select::ProjectionMatchesProjection;
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use rustc_data_structures::sso::SsoHashSet;
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use rustc_data_structures::stack::ensure_sufficient_stack;
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use rustc_errors::ErrorGuaranteed;
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use rustc_hir::def::DefKind;
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use rustc_hir::def_id::DefId;
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use rustc_hir::lang_items::LangItem;
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use rustc_infer::infer::resolve::OpportunisticRegionResolver;
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use rustc_middle::traits::select::OverflowError;
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use rustc_middle::ty::fold::{TypeFoldable, TypeFolder, TypeSuperFoldable};
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use rustc_middle::ty::visit::{MaxUniverse, TypeVisitable};
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use rustc_middle::ty::DefIdTree;
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use rustc_middle::ty::{self, Term, ToPredicate, Ty, TyCtxt};
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use rustc_span::symbol::sym;
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use std::collections::BTreeMap;
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pub use rustc_middle::traits::Reveal;
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pub type PolyProjectionObligation<'tcx> = Obligation<'tcx, ty::PolyProjectionPredicate<'tcx>>;
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pub type ProjectionObligation<'tcx> = Obligation<'tcx, ty::ProjectionPredicate<'tcx>>;
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pub type ProjectionTyObligation<'tcx> = Obligation<'tcx, ty::ProjectionTy<'tcx>>;
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pub(super) struct InProgress;
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/// When attempting to resolve `<T as TraitRef>::Name` ...
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#[derive(Debug)]
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pub enum ProjectionError<'tcx> {
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/// ...we found multiple sources of information and couldn't resolve the ambiguity.
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TooManyCandidates,
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/// ...an error occurred matching `T : TraitRef`
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TraitSelectionError(SelectionError<'tcx>),
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}
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#[derive(PartialEq, Eq, Debug)]
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enum ProjectionCandidate<'tcx> {
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/// From a where-clause in the env or object type
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ParamEnv(ty::PolyProjectionPredicate<'tcx>),
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/// From the definition of `Trait` when you have something like <<A as Trait>::B as Trait2>::C
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TraitDef(ty::PolyProjectionPredicate<'tcx>),
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/// Bounds specified on an object type
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Object(ty::PolyProjectionPredicate<'tcx>),
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/// From an "impl" (or a "pseudo-impl" returned by select)
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Select(Selection<'tcx>),
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ImplTraitInTrait(ImplTraitInTraitCandidate<'tcx>),
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}
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#[derive(PartialEq, Eq, Debug)]
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enum ImplTraitInTraitCandidate<'tcx> {
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// The `impl Trait` from a trait function's default body
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Trait,
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// A concrete type provided from a trait's `impl Trait` from an impl
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Impl(ImplSourceUserDefinedData<'tcx, PredicateObligation<'tcx>>),
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}
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enum ProjectionCandidateSet<'tcx> {
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None,
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Single(ProjectionCandidate<'tcx>),
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Ambiguous,
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Error(SelectionError<'tcx>),
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}
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impl<'tcx> ProjectionCandidateSet<'tcx> {
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fn mark_ambiguous(&mut self) {
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*self = ProjectionCandidateSet::Ambiguous;
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}
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fn mark_error(&mut self, err: SelectionError<'tcx>) {
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*self = ProjectionCandidateSet::Error(err);
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}
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// Returns true if the push was successful, or false if the candidate
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// was discarded -- this could be because of ambiguity, or because
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// a higher-priority candidate is already there.
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fn push_candidate(&mut self, candidate: ProjectionCandidate<'tcx>) -> bool {
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use self::ProjectionCandidate::*;
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use self::ProjectionCandidateSet::*;
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// This wacky variable is just used to try and
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// make code readable and avoid confusing paths.
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// It is assigned a "value" of `()` only on those
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// paths in which we wish to convert `*self` to
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// ambiguous (and return false, because the candidate
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// was not used). On other paths, it is not assigned,
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// and hence if those paths *could* reach the code that
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// comes after the match, this fn would not compile.
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let convert_to_ambiguous;
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match self {
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None => {
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*self = Single(candidate);
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return true;
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}
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Single(current) => {
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// Duplicates can happen inside ParamEnv. In the case, we
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// perform a lazy deduplication.
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if current == &candidate {
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return false;
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}
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// Prefer where-clauses. As in select, if there are multiple
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// candidates, we prefer where-clause candidates over impls. This
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// may seem a bit surprising, since impls are the source of
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// "truth" in some sense, but in fact some of the impls that SEEM
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// applicable are not, because of nested obligations. Where
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// clauses are the safer choice. See the comment on
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// `select::SelectionCandidate` and #21974 for more details.
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match (current, candidate) {
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(ParamEnv(..), ParamEnv(..)) => convert_to_ambiguous = (),
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(ParamEnv(..), _) => return false,
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(_, ParamEnv(..)) => unreachable!(),
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(_, _) => convert_to_ambiguous = (),
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}
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}
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Ambiguous | Error(..) => {
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return false;
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}
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}
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// We only ever get here when we moved from a single candidate
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// to ambiguous.
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let () = convert_to_ambiguous;
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*self = Ambiguous;
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false
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}
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}
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/// States returned from `poly_project_and_unify_type`. Takes the place
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/// of the old return type, which was:
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/// ```ignore (not-rust)
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/// Result<
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/// Result<Option<Vec<PredicateObligation<'tcx>>>, InProgress>,
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/// MismatchedProjectionTypes<'tcx>,
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/// >
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/// ```
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pub(super) enum ProjectAndUnifyResult<'tcx> {
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/// The projection bound holds subject to the given obligations. If the
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/// projection cannot be normalized because the required trait bound does
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/// not hold, this is returned, with `obligations` being a predicate that
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/// cannot be proven.
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Holds(Vec<PredicateObligation<'tcx>>),
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/// The projection cannot be normalized due to ambiguity. Resolving some
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/// inference variables in the projection may fix this.
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FailedNormalization,
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/// The project cannot be normalized because `poly_project_and_unify_type`
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/// is called recursively while normalizing the same projection.
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Recursive,
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// the projection can be normalized, but is not equal to the expected type.
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// Returns the type error that arose from the mismatch.
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MismatchedProjectionTypes(MismatchedProjectionTypes<'tcx>),
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}
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/// Evaluates constraints of the form:
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/// ```ignore (not-rust)
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/// for<...> <T as Trait>::U == V
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/// ```
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/// If successful, this may result in additional obligations. Also returns
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/// the projection cache key used to track these additional obligations.
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#[instrument(level = "debug", skip(selcx))]
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pub(super) fn poly_project_and_unify_type<'cx, 'tcx>(
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selcx: &mut SelectionContext<'cx, 'tcx>,
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obligation: &PolyProjectionObligation<'tcx>,
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) -> ProjectAndUnifyResult<'tcx> {
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let infcx = selcx.infcx();
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let r = infcx.commit_if_ok(|_snapshot| {
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let old_universe = infcx.universe();
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let placeholder_predicate =
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infcx.replace_bound_vars_with_placeholders(obligation.predicate);
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let new_universe = infcx.universe();
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let placeholder_obligation = obligation.with(placeholder_predicate);
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match project_and_unify_type(selcx, &placeholder_obligation) {
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ProjectAndUnifyResult::MismatchedProjectionTypes(e) => Err(e),
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ProjectAndUnifyResult::Holds(obligations)
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if old_universe != new_universe
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&& selcx.tcx().features().generic_associated_types_extended =>
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{
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// If the `generic_associated_types_extended` feature is active, then we ignore any
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// obligations references lifetimes from any universe greater than or equal to the
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// universe just created. Otherwise, we can end up with something like `for<'a> I: 'a`,
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// which isn't quite what we want. Ideally, we want either an implied
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// `for<'a where I: 'a> I: 'a` or we want to "lazily" check these hold when we
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// substitute concrete regions. There is design work to be done here; until then,
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// however, this allows experimenting potential GAT features without running into
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// well-formedness issues.
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let new_obligations = obligations
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.into_iter()
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.filter(|obligation| {
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let mut visitor = MaxUniverse::new();
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obligation.predicate.visit_with(&mut visitor);
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visitor.max_universe() < new_universe
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})
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.collect();
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Ok(ProjectAndUnifyResult::Holds(new_obligations))
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}
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other => Ok(other),
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}
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});
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match r {
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Ok(inner) => inner,
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Err(err) => ProjectAndUnifyResult::MismatchedProjectionTypes(err),
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}
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}
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/// Evaluates constraints of the form:
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/// ```ignore (not-rust)
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/// <T as Trait>::U == V
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/// ```
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/// If successful, this may result in additional obligations.
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///
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/// See [poly_project_and_unify_type] for an explanation of the return value.
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#[instrument(level = "debug", skip(selcx))]
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fn project_and_unify_type<'cx, 'tcx>(
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selcx: &mut SelectionContext<'cx, 'tcx>,
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obligation: &ProjectionObligation<'tcx>,
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) -> ProjectAndUnifyResult<'tcx> {
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let mut obligations = vec![];
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let infcx = selcx.infcx();
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let normalized = match opt_normalize_projection_type(
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selcx,
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obligation.param_env,
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obligation.predicate.projection_ty,
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obligation.cause.clone(),
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obligation.recursion_depth,
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&mut obligations,
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) {
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Ok(Some(n)) => n,
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Ok(None) => return ProjectAndUnifyResult::FailedNormalization,
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Err(InProgress) => return ProjectAndUnifyResult::Recursive,
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};
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debug!(?normalized, ?obligations, "project_and_unify_type result");
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let actual = obligation.predicate.term;
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// For an example where this is neccessary see src/test/ui/impl-trait/nested-return-type2.rs
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// This allows users to omit re-mentioning all bounds on an associated type and just use an
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// `impl Trait` for the assoc type to add more bounds.
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let InferOk { value: actual, obligations: new } =
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selcx.infcx().replace_opaque_types_with_inference_vars(
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actual,
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obligation.cause.body_id,
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obligation.cause.span,
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obligation.param_env,
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);
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obligations.extend(new);
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match infcx.at(&obligation.cause, obligation.param_env).eq(normalized, actual) {
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Ok(InferOk { obligations: inferred_obligations, value: () }) => {
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obligations.extend(inferred_obligations);
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ProjectAndUnifyResult::Holds(obligations)
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}
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Err(err) => {
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debug!("equating types encountered error {:?}", err);
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ProjectAndUnifyResult::MismatchedProjectionTypes(MismatchedProjectionTypes { err })
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}
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}
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}
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/// Normalizes any associated type projections in `value`, replacing
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/// them with a fully resolved type where possible. The return value
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/// combines the normalized result and any additional obligations that
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/// were incurred as result.
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pub fn normalize<'a, 'b, 'tcx, T>(
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selcx: &'a mut SelectionContext<'b, 'tcx>,
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param_env: ty::ParamEnv<'tcx>,
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cause: ObligationCause<'tcx>,
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value: T,
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) -> Normalized<'tcx, T>
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where
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T: TypeFoldable<'tcx>,
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{
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let mut obligations = Vec::new();
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let value = normalize_to(selcx, param_env, cause, value, &mut obligations);
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Normalized { value, obligations }
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}
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pub fn normalize_to<'a, 'b, 'tcx, T>(
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selcx: &'a mut SelectionContext<'b, 'tcx>,
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param_env: ty::ParamEnv<'tcx>,
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cause: ObligationCause<'tcx>,
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value: T,
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obligations: &mut Vec<PredicateObligation<'tcx>>,
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) -> T
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where
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T: TypeFoldable<'tcx>,
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{
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normalize_with_depth_to(selcx, param_env, cause, 0, value, obligations)
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}
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/// As `normalize`, but with a custom depth.
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pub fn normalize_with_depth<'a, 'b, 'tcx, T>(
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selcx: &'a mut SelectionContext<'b, 'tcx>,
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param_env: ty::ParamEnv<'tcx>,
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cause: ObligationCause<'tcx>,
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depth: usize,
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value: T,
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) -> Normalized<'tcx, T>
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where
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T: TypeFoldable<'tcx>,
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{
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let mut obligations = Vec::new();
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let value = normalize_with_depth_to(selcx, param_env, cause, depth, value, &mut obligations);
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Normalized { value, obligations }
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}
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#[instrument(level = "info", skip(selcx, param_env, cause, obligations))]
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pub fn normalize_with_depth_to<'a, 'b, 'tcx, T>(
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selcx: &'a mut SelectionContext<'b, 'tcx>,
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param_env: ty::ParamEnv<'tcx>,
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cause: ObligationCause<'tcx>,
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depth: usize,
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value: T,
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obligations: &mut Vec<PredicateObligation<'tcx>>,
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) -> T
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where
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T: TypeFoldable<'tcx>,
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{
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debug!(obligations.len = obligations.len());
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let mut normalizer = AssocTypeNormalizer::new(selcx, param_env, cause, depth, obligations);
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let result = ensure_sufficient_stack(|| normalizer.fold(value));
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debug!(?result, obligations.len = normalizer.obligations.len());
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debug!(?normalizer.obligations,);
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result
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}
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#[instrument(level = "info", skip(selcx, param_env, cause, obligations))]
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pub fn try_normalize_with_depth_to<'a, 'b, 'tcx, T>(
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selcx: &'a mut SelectionContext<'b, 'tcx>,
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param_env: ty::ParamEnv<'tcx>,
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cause: ObligationCause<'tcx>,
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depth: usize,
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value: T,
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obligations: &mut Vec<PredicateObligation<'tcx>>,
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) -> T
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where
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T: TypeFoldable<'tcx>,
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{
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debug!(obligations.len = obligations.len());
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let mut normalizer = AssocTypeNormalizer::new_without_eager_inference_replacement(
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selcx,
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param_env,
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cause,
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depth,
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obligations,
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);
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let result = ensure_sufficient_stack(|| normalizer.fold(value));
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debug!(?result, obligations.len = normalizer.obligations.len());
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debug!(?normalizer.obligations,);
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result
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}
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pub(crate) fn needs_normalization<'tcx, T: TypeVisitable<'tcx>>(value: &T, reveal: Reveal) -> bool {
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match reveal {
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Reveal::UserFacing => value
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.has_type_flags(ty::TypeFlags::HAS_TY_PROJECTION | ty::TypeFlags::HAS_CT_PROJECTION),
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Reveal::All => value.has_type_flags(
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ty::TypeFlags::HAS_TY_PROJECTION
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| ty::TypeFlags::HAS_TY_OPAQUE
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| ty::TypeFlags::HAS_CT_PROJECTION,
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),
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}
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}
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struct AssocTypeNormalizer<'a, 'b, 'tcx> {
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selcx: &'a mut SelectionContext<'b, 'tcx>,
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param_env: ty::ParamEnv<'tcx>,
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cause: ObligationCause<'tcx>,
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obligations: &'a mut Vec<PredicateObligation<'tcx>>,
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depth: usize,
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universes: Vec<Option<ty::UniverseIndex>>,
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/// If true, when a projection is unable to be completed, an inference
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/// variable will be created and an obligation registered to project to that
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/// inference variable. Also, constants will be eagerly evaluated.
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eager_inference_replacement: bool,
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}
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impl<'a, 'b, 'tcx> AssocTypeNormalizer<'a, 'b, 'tcx> {
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fn new(
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selcx: &'a mut SelectionContext<'b, 'tcx>,
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param_env: ty::ParamEnv<'tcx>,
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cause: ObligationCause<'tcx>,
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depth: usize,
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obligations: &'a mut Vec<PredicateObligation<'tcx>>,
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) -> AssocTypeNormalizer<'a, 'b, 'tcx> {
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AssocTypeNormalizer {
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selcx,
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param_env,
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cause,
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obligations,
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depth,
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universes: vec![],
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eager_inference_replacement: true,
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}
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}
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fn new_without_eager_inference_replacement(
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selcx: &'a mut SelectionContext<'b, 'tcx>,
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param_env: ty::ParamEnv<'tcx>,
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cause: ObligationCause<'tcx>,
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depth: usize,
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obligations: &'a mut Vec<PredicateObligation<'tcx>>,
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) -> AssocTypeNormalizer<'a, 'b, 'tcx> {
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AssocTypeNormalizer {
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selcx,
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param_env,
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cause,
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obligations,
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depth,
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universes: vec![],
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eager_inference_replacement: false,
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}
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}
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fn fold<T: TypeFoldable<'tcx>>(&mut self, value: T) -> T {
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let value = self.selcx.infcx().resolve_vars_if_possible(value);
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debug!(?value);
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assert!(
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!value.has_escaping_bound_vars(),
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"Normalizing {:?} without wrapping in a `Binder`",
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value
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);
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if !needs_normalization(&value, self.param_env.reveal()) {
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value
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} else {
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value.fold_with(self)
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}
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}
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}
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impl<'a, 'b, 'tcx> TypeFolder<'tcx> for AssocTypeNormalizer<'a, 'b, 'tcx> {
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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) => {
|
|
// 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.super_fold_with(self).into())
|
|
};
|
|
// For cases like #95134 we would like to catch overflows early
|
|
// otherwise they slip away away and cause ICE.
|
|
let recursion_limit = self.tcx().recursion_limit();
|
|
if !recursion_limit.value_within_limit(self.depth)
|
|
// HACK: Don't overflow when running cargo doc see #100991
|
|
&& !self.tcx().sess.opts.actually_rustdoc
|
|
{
|
|
let obligation = Obligation::with_depth(
|
|
self.cause.clone(),
|
|
recursion_limit.0,
|
|
self.param_env,
|
|
ty,
|
|
);
|
|
self.selcx.infcx().report_overflow_error(&obligation, true);
|
|
}
|
|
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> {
|
|
let tcx = self.selcx.tcx();
|
|
if tcx.lazy_normalization() {
|
|
constant
|
|
} else {
|
|
let constant = constant.super_fold_with(self);
|
|
debug!(?constant, ?self.param_env);
|
|
with_replaced_escaping_bound_vars(
|
|
self.selcx.infcx(),
|
|
&mut self.universes,
|
|
constant,
|
|
|constant| constant.eval(tcx, self.param_env),
|
|
)
|
|
}
|
|
}
|
|
|
|
#[inline]
|
|
fn fold_predicate(&mut self, p: ty::Predicate<'tcx>) -> ty::Predicate<'tcx> {
|
|
if p.allow_normalization() && needs_normalization(&p, self.param_env.reveal()) {
|
|
p.super_fold_with(self)
|
|
} else {
|
|
p
|
|
}
|
|
}
|
|
}
|
|
|
|
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>>,
|
|
}
|
|
|
|
/// Executes `f` on `value` after replacing all escaping bound variables with placeholders
|
|
/// and then replaces these placeholders with the original bound variables in the result.
|
|
///
|
|
/// In most places, bound variables should be replaced right when entering a binder, making
|
|
/// this function unnecessary. However, normalization currently does not do that, so we have
|
|
/// to do this lazily.
|
|
///
|
|
/// You should not add any additional uses of this function, at least not without first
|
|
/// discussing it with t-types.
|
|
///
|
|
/// FIXME(@lcnr): We may even consider experimenting with eagerly replacing bound vars during
|
|
/// normalization as well, at which point this function will be unnecessary and can be removed.
|
|
pub fn with_replaced_escaping_bound_vars<'a, 'tcx, T: TypeFoldable<'tcx>, R: TypeFoldable<'tcx>>(
|
|
infcx: &'a InferCtxt<'a, 'tcx>,
|
|
universe_indices: &'a mut Vec<Option<ty::UniverseIndex>>,
|
|
value: T,
|
|
f: impl FnOnce(T) -> R,
|
|
) -> R {
|
|
if value.has_escaping_bound_vars() {
|
|
let (value, mapped_regions, mapped_types, mapped_consts) =
|
|
BoundVarReplacer::replace_bound_vars(infcx, universe_indices, value);
|
|
let result = f(value);
|
|
PlaceholderReplacer::replace_placeholders(
|
|
infcx,
|
|
mapped_regions,
|
|
mapped_types,
|
|
mapped_consts,
|
|
universe_indices,
|
|
result,
|
|
)
|
|
} else {
|
|
f(value)
|
|
}
|
|
}
|
|
|
|
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
|
|
#[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;
|
|
|
|
assemble_candidate_for_impl_trait_in_trait(selcx, obligation, &mut candidates);
|
|
|
|
// 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),
|
|
}
|
|
}
|
|
|
|
/// If the predicate's item is an `ImplTraitPlaceholder`, we do a select on the
|
|
/// corresponding trait ref. If this yields an `impl`, then we're able to project
|
|
/// to a concrete type, since we have an `impl`'s method to provide the RPITIT.
|
|
fn assemble_candidate_for_impl_trait_in_trait<'cx, 'tcx>(
|
|
selcx: &mut SelectionContext<'cx, 'tcx>,
|
|
obligation: &ProjectionTyObligation<'tcx>,
|
|
candidate_set: &mut ProjectionCandidateSet<'tcx>,
|
|
) {
|
|
let tcx = selcx.tcx();
|
|
if tcx.def_kind(obligation.predicate.item_def_id) == DefKind::ImplTraitPlaceholder {
|
|
let trait_fn_def_id = tcx.impl_trait_in_trait_parent(obligation.predicate.item_def_id);
|
|
// If we are trying to project an RPITIT with trait's default `Self` parameter,
|
|
// then we must be within a default trait body.
|
|
if obligation.predicate.self_ty()
|
|
== ty::InternalSubsts::identity_for_item(tcx, obligation.predicate.item_def_id)
|
|
.type_at(0)
|
|
&& tcx.associated_item(trait_fn_def_id).defaultness(tcx).has_value()
|
|
{
|
|
candidate_set.push_candidate(ProjectionCandidate::ImplTraitInTrait(
|
|
ImplTraitInTraitCandidate::Trait,
|
|
));
|
|
return;
|
|
}
|
|
|
|
let trait_def_id = tcx.parent(trait_fn_def_id);
|
|
let trait_substs =
|
|
obligation.predicate.substs.truncate_to(tcx, tcx.generics_of(trait_def_id));
|
|
// FIXME(named-returns): Binders
|
|
let trait_predicate =
|
|
ty::Binder::dummy(ty::TraitRef { def_id: trait_def_id, substs: trait_substs })
|
|
.to_poly_trait_predicate();
|
|
|
|
let _ =
|
|
selcx.infcx().commit_if_ok(|_| match selcx.select(&obligation.with(trait_predicate)) {
|
|
Ok(Some(super::ImplSource::UserDefined(data))) => {
|
|
candidate_set.push_candidate(ProjectionCandidate::ImplTraitInTrait(
|
|
ImplTraitInTraitCandidate::Impl(data),
|
|
));
|
|
Ok(())
|
|
}
|
|
Ok(None) => {
|
|
candidate_set.mark_ambiguous();
|
|
return Err(());
|
|
}
|
|
Ok(Some(_)) => {
|
|
// Don't know enough about the impl to provide a useful signature
|
|
return Err(());
|
|
}
|
|
Err(e) => {
|
|
debug!(error = ?e, "selection error");
|
|
candidate_set.mark_error(e);
|
|
return Err(());
|
|
}
|
|
});
|
|
}
|
|
}
|
|
|
|
/// 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,
|
|
);
|
|
}
|
|
|
|
#[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_non_region_infer()
|
|
{
|
|
// 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 => {}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
#[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>,
|
|
) {
|
|
// Can't assemble candidate from impl for RPITIT
|
|
if selcx.tcx().def_kind(obligation.predicate.item_def_id) == DefKind::ImplTraitPlaceholder {
|
|
return;
|
|
}
|
|
|
|
// 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(_)
|
|
| super::ImplSource::Tuple => {
|
|
// 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)
|
|
}
|
|
ProjectionCandidate::ImplTraitInTrait(ImplTraitInTraitCandidate::Impl(data)) => {
|
|
confirm_impl_trait_in_trait_candidate(selcx, obligation, data)
|
|
}
|
|
// If we're projecting an RPITIT for a default trait body, that's just
|
|
// the same def-id, but as an opaque type (with regular RPIT semantics).
|
|
ProjectionCandidate::ImplTraitInTrait(ImplTraitInTraitCandidate::Trait) => Progress {
|
|
term: selcx
|
|
.tcx()
|
|
.mk_opaque(obligation.predicate.item_def_id, obligation.predicate.substs)
|
|
.into(),
|
|
obligations: vec![],
|
|
},
|
|
};
|
|
|
|
// 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(_)
|
|
| super::ImplSource::Tuple => {
|
|
// 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::UnevaluatedConst::new(did, identity_substs));
|
|
ty.map_bound(|ty| tcx.mk_const(ty::ConstS { ty, kind }).into())
|
|
} else {
|
|
ty.map_bound(|ty| ty.into())
|
|
};
|
|
if !check_substs_compatible(tcx, &assoc_ty.item, substs) {
|
|
let err = tcx.ty_error_with_message(
|
|
obligation.cause.span,
|
|
"impl item and trait item have different parameters",
|
|
);
|
|
Progress { term: err.into(), obligations: nested }
|
|
} else {
|
|
assoc_ty_own_obligations(selcx, obligation, &mut nested);
|
|
Progress { term: term.subst(tcx, substs), obligations: nested }
|
|
}
|
|
}
|
|
|
|
// Verify that the trait item and its implementation have compatible substs lists
|
|
fn check_substs_compatible<'tcx>(
|
|
tcx: TyCtxt<'tcx>,
|
|
assoc_ty: &ty::AssocItem,
|
|
substs: ty::SubstsRef<'tcx>,
|
|
) -> bool {
|
|
fn check_substs_compatible_inner<'tcx>(
|
|
tcx: TyCtxt<'tcx>,
|
|
generics: &'tcx ty::Generics,
|
|
args: &'tcx [ty::GenericArg<'tcx>],
|
|
) -> bool {
|
|
if generics.count() != args.len() {
|
|
return false;
|
|
}
|
|
|
|
let (parent_args, own_args) = args.split_at(generics.parent_count);
|
|
|
|
if let Some(parent) = generics.parent
|
|
&& let parent_generics = tcx.generics_of(parent)
|
|
&& !check_substs_compatible_inner(tcx, parent_generics, parent_args) {
|
|
return false;
|
|
}
|
|
|
|
for (param, arg) in std::iter::zip(&generics.params, own_args) {
|
|
match (¶m.kind, arg.unpack()) {
|
|
(ty::GenericParamDefKind::Type { .. }, ty::GenericArgKind::Type(_))
|
|
| (ty::GenericParamDefKind::Lifetime, ty::GenericArgKind::Lifetime(_))
|
|
| (ty::GenericParamDefKind::Const { .. }, ty::GenericArgKind::Const(_)) => {}
|
|
_ => return false,
|
|
}
|
|
}
|
|
|
|
true
|
|
}
|
|
|
|
check_substs_compatible_inner(tcx, tcx.generics_of(assoc_ty.def_id), substs.as_slice())
|
|
}
|
|
|
|
fn confirm_impl_trait_in_trait_candidate<'tcx>(
|
|
selcx: &mut SelectionContext<'_, 'tcx>,
|
|
obligation: &ProjectionTyObligation<'tcx>,
|
|
data: ImplSourceUserDefinedData<'tcx, PredicateObligation<'tcx>>,
|
|
) -> Progress<'tcx> {
|
|
let tcx = selcx.tcx();
|
|
let mut obligations = data.nested;
|
|
|
|
let trait_fn_def_id = tcx.impl_trait_in_trait_parent(obligation.predicate.item_def_id);
|
|
let Ok(leaf_def) = assoc_def(selcx, data.impl_def_id, trait_fn_def_id) else {
|
|
return Progress { term: tcx.ty_error().into(), obligations };
|
|
};
|
|
if !leaf_def.item.defaultness(tcx).has_value() {
|
|
return Progress { term: tcx.ty_error().into(), obligations };
|
|
}
|
|
|
|
// Use the default `impl Trait` for the trait, e.g., for a default trait body
|
|
if leaf_def.item.container == ty::AssocItemContainer::TraitContainer {
|
|
return Progress {
|
|
term: tcx
|
|
.mk_opaque(obligation.predicate.item_def_id, obligation.predicate.substs)
|
|
.into(),
|
|
obligations,
|
|
};
|
|
}
|
|
|
|
let impl_fn_def_id = leaf_def.item.def_id;
|
|
let impl_fn_substs = obligation.predicate.substs.rebase_onto(tcx, trait_fn_def_id, data.substs);
|
|
|
|
let cause = ObligationCause::new(
|
|
obligation.cause.span,
|
|
obligation.cause.body_id,
|
|
super::ItemObligation(impl_fn_def_id),
|
|
);
|
|
let predicates = normalize_with_depth_to(
|
|
selcx,
|
|
obligation.param_env,
|
|
cause.clone(),
|
|
obligation.recursion_depth + 1,
|
|
tcx.predicates_of(impl_fn_def_id).instantiate(tcx, impl_fn_substs),
|
|
&mut obligations,
|
|
);
|
|
obligations.extend(std::iter::zip(predicates.predicates, predicates.spans).map(
|
|
|(pred, span)| {
|
|
Obligation::with_depth(
|
|
ObligationCause::new(
|
|
obligation.cause.span,
|
|
obligation.cause.body_id,
|
|
if span.is_dummy() {
|
|
super::ItemObligation(impl_fn_def_id)
|
|
} else {
|
|
super::BindingObligation(impl_fn_def_id, span)
|
|
},
|
|
),
|
|
obligation.recursion_depth + 1,
|
|
obligation.param_env,
|
|
pred,
|
|
)
|
|
},
|
|
));
|
|
|
|
let ty = super::normalize_to(
|
|
selcx,
|
|
obligation.param_env,
|
|
cause.clone(),
|
|
tcx.bound_trait_impl_trait_tys(impl_fn_def_id)
|
|
.map_bound(|tys| {
|
|
tys.map_or_else(|_| tcx.ty_error(), |tys| tys[&obligation.predicate.item_def_id])
|
|
})
|
|
.subst(tcx, impl_fn_substs),
|
|
&mut obligations,
|
|
);
|
|
|
|
Progress { term: ty.into(), obligations }
|
|
}
|
|
|
|
// Get obligations corresponding to the predicates from the where-clause of the
|
|
// associated type itself.
|
|
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),
|
|
)
|
|
})
|
|
}
|
|
}
|