1937 lines
76 KiB
Rust
1937 lines
76 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::TraitQueryMode;
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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 rustc_data_structures::stack::ensure_sufficient_stack;
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use rustc_errors::ErrorReported;
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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::ty::fold::{TypeFoldable, TypeFolder};
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use rustc_middle::ty::subst::Subst;
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use rustc_middle::ty::{self, ToPolyTraitRef, ToPredicate, Ty, TyCtxt, WithConstness};
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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 ProjectionTyError<'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 ProjectionTyCandidate<'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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}
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enum ProjectionTyCandidateSet<'tcx> {
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None,
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Single(ProjectionTyCandidate<'tcx>),
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Ambiguous,
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Error(SelectionError<'tcx>),
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}
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impl<'tcx> ProjectionTyCandidateSet<'tcx> {
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fn mark_ambiguous(&mut self) {
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*self = ProjectionTyCandidateSet::Ambiguous;
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}
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fn mark_error(&mut self, err: SelectionError<'tcx>) {
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*self = ProjectionTyCandidateSet::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: ProjectionTyCandidate<'tcx>) -> bool {
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use self::ProjectionTyCandidate::*;
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use self::ProjectionTyCandidateSet::*;
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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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/// Evaluates constraints of the form:
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///
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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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///
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/// ## Returns
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///
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/// - `Err(_)`: the projection can be normalized, but is not equal to the
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/// expected type.
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/// - `Ok(Err(InProgress))`: this is called recursively while normalizing
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/// the same projection.
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/// - `Ok(Ok(None))`: The projection cannot be normalized due to ambiguity
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/// (resolving some inference variables in the projection may fix this).
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/// - `Ok(Ok(Some(obligations)))`: The projection bound holds subject to
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/// the given obligations. If the projection cannot be normalized because
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/// the required trait bound doesn't hold this returned with `obligations`
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/// being a predicate that cannot be proven.
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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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) -> 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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let infcx = selcx.infcx();
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infcx.commit_if_ok(|_snapshot| {
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let placeholder_predicate =
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infcx.replace_bound_vars_with_placeholders(obligation.predicate);
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let placeholder_obligation = obligation.with(placeholder_predicate);
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let result = project_and_unify_type(selcx, &placeholder_obligation)?;
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Ok(result)
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})
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}
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/// Evaluates constraints of the form:
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///
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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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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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) -> 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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debug!(?obligation, "project_and_unify_type");
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let mut obligations = vec![];
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let normalized_ty = 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 Ok(Ok(None)),
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Err(InProgress) => return Ok(Err(InProgress)),
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};
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debug!(?normalized_ty, ?obligations, "project_and_unify_type result");
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let infcx = selcx.infcx();
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match infcx
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.at(&obligation.cause, obligation.param_env)
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.eq(normalized_ty, obligation.predicate.ty)
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{
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Ok(InferOk { obligations: inferred_obligations, value: () }) => {
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obligations.extend(inferred_obligations);
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Ok(Ok(Some(obligations)))
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}
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Err(err) => {
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debug!("project_and_unify_type: equating types encountered error {:?}", err);
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Err(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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pub(crate) fn needs_normalization<'tcx, T: TypeFoldable<'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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}
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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 { selcx, param_env, cause, obligations, depth, universes: vec![] }
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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> {
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self.selcx.tcx()
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}
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fn fold_binder<T: TypeFoldable<'tcx>>(
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&mut self,
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t: ty::Binder<'tcx, T>,
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) -> ty::Binder<'tcx, T> {
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self.universes.push(None);
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let t = t.super_fold_with(self);
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self.universes.pop();
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t
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}
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fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
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if !needs_normalization(&ty, self.param_env.reveal()) {
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return ty;
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}
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// We try to be a little clever here as a performance optimization in
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// cases where there are nested projections under binders.
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// For example:
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// ```
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// for<'a> fn(<T as Foo>::One<'a, Box<dyn Bar<'a, Item=<T as Foo>::Two<'a>>>>)
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// ```
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// We normalize the substs on the projection before the projecting, but
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// if we're naive, we'll
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// replace bound vars on inner, project inner, replace placeholders on inner,
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// replace bound vars on outer, project outer, replace placeholders on outer
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//
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// However, if we're a bit more clever, we can replace the bound vars
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// on the entire type before normalizing nested projections, meaning we
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// replace bound vars on outer, project inner,
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// project outer, replace placeholders on outer
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//
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// This is possible because the inner `'a` will already be a placeholder
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// when we need to normalize the inner projection
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//
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// On the other hand, this does add a bit of complexity, since we only
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// replace bound vars if the current type is a `Projection` and we need
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// to make sure we don't forget to fold the substs regardless.
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match *ty.kind() {
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ty::Opaque(def_id, substs) => {
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// Only normalize `impl Trait` after type-checking, usually in codegen.
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match self.param_env.reveal() {
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Reveal::UserFacing => ty.super_fold_with(self),
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Reveal::All => {
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// N.b. there is an assumption here all this code can handle
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// escaping bound vars.
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let recursion_limit = self.tcx().recursion_limit();
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if !recursion_limit.value_within_limit(self.depth) {
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let obligation = Obligation::with_depth(
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self.cause.clone(),
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recursion_limit.0,
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self.param_env,
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ty,
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);
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self.selcx.infcx().report_overflow_error(&obligation, true);
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}
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let substs = substs.super_fold_with(self);
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let generic_ty = self.tcx().type_of(def_id);
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let concrete_ty = generic_ty.subst(self.tcx(), substs);
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self.depth += 1;
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let folded_ty = self.fold_ty(concrete_ty);
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self.depth -= 1;
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folded_ty
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}
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}
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}
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ty::Projection(data) if !data.has_escaping_bound_vars() => {
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// This branch is *mostly* just an optimization: when we don't
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// have escaping bound vars, we don't need to replace them with
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// placeholders (see branch below). *Also*, we know that we can
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// register an obligation to *later* project, since we know
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// there won't be bound vars there.
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let data = data.super_fold_with(self);
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let normalized_ty = normalize_projection_type(
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self.selcx,
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self.param_env,
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data,
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self.cause.clone(),
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self.depth,
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&mut self.obligations,
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);
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debug!(
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?self.depth,
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?ty,
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?normalized_ty,
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obligations.len = ?self.obligations.len(),
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"AssocTypeNormalizer: normalized type"
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);
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normalized_ty
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}
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ty::Projection(data) => {
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// If there are escaping bound vars, we temporarily replace the
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// bound vars with placeholders. Note though, that in the case
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// that we still can't project for whatever reason (e.g. self
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// type isn't known enough), we *can't* register an obligation
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// and return an inference variable (since then that obligation
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// would have bound vars and that's a can of worms). Instead,
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// we just give up and fall back to pretending like we never tried!
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//
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// Note: this isn't necessarily the final approach here; we may
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// want to figure out how to register obligations with escaping vars
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// or handle this some other way.
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let infcx = self.selcx.infcx();
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let (data, mapped_regions, mapped_types, mapped_consts) =
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BoundVarReplacer::replace_bound_vars(infcx, &mut self.universes, data);
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let data = data.super_fold_with(self);
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let normalized_ty = opt_normalize_projection_type(
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self.selcx,
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self.param_env,
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data,
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self.cause.clone(),
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self.depth,
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&mut self.obligations,
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)
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.ok()
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.flatten()
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.map(|normalized_ty| {
|
||
PlaceholderReplacer::replace_placeholders(
|
||
infcx,
|
||
mapped_regions,
|
||
mapped_types,
|
||
mapped_consts,
|
||
&self.universes,
|
||
normalized_ty,
|
||
)
|
||
})
|
||
.unwrap_or_else(|| ty.super_fold_with(self));
|
||
|
||
debug!(
|
||
?self.depth,
|
||
?ty,
|
||
?normalized_ty,
|
||
obligations.len = ?self.obligations.len(),
|
||
"AssocTypeNormalizer: normalized type"
|
||
);
|
||
normalized_ty
|
||
}
|
||
|
||
_ => ty.super_fold_with(self),
|
||
}
|
||
}
|
||
|
||
fn fold_const(&mut self, constant: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
|
||
if self.selcx.tcx().lazy_normalization() {
|
||
constant
|
||
} else {
|
||
let constant = constant.super_fold_with(self);
|
||
constant.eval(self.selcx.tcx(), self.param_env)
|
||
}
|
||
}
|
||
}
|
||
|
||
pub struct BoundVarReplacer<'me, 'tcx> {
|
||
infcx: &'me InferCtxt<'me, 'tcx>,
|
||
// These three maps track the bound variable that were replaced by placeholders. It might be
|
||
// nice to remove these since we already have the `kind` in the placeholder; we really just need
|
||
// the `var` (but we *could* bring that into scope if we were to track them as we pass them).
|
||
mapped_regions: BTreeMap<ty::PlaceholderRegion, ty::BoundRegion>,
|
||
mapped_types: BTreeMap<ty::PlaceholderType, ty::BoundTy>,
|
||
mapped_consts: BTreeMap<ty::PlaceholderConst<'tcx>, ty::BoundVar>,
|
||
// The current depth relative to *this* folding, *not* the entire normalization. In other words,
|
||
// the depth of binders we've passed here.
|
||
current_index: ty::DebruijnIndex,
|
||
// The `UniverseIndex` of the binding levels above us. These are optional, since we are lazy:
|
||
// we don't actually create a universe until we see a bound var we have to replace.
|
||
universe_indices: &'me mut Vec<Option<ty::UniverseIndex>>,
|
||
}
|
||
|
||
impl<'me, 'tcx> BoundVarReplacer<'me, 'tcx> {
|
||
/// Returns `Some` if we *were* able to replace bound vars. If there are any bound vars that
|
||
/// use a binding level above `universe_indices.len()`, we fail.
|
||
pub fn replace_bound_vars<T: TypeFoldable<'tcx>>(
|
||
infcx: &'me InferCtxt<'me, 'tcx>,
|
||
universe_indices: &'me mut Vec<Option<ty::UniverseIndex>>,
|
||
value: T,
|
||
) -> (
|
||
T,
|
||
BTreeMap<ty::PlaceholderRegion, ty::BoundRegion>,
|
||
BTreeMap<ty::PlaceholderType, ty::BoundTy>,
|
||
BTreeMap<ty::PlaceholderConst<'tcx>, ty::BoundVar>,
|
||
) {
|
||
let mapped_regions: BTreeMap<ty::PlaceholderRegion, ty::BoundRegion> = BTreeMap::new();
|
||
let mapped_types: BTreeMap<ty::PlaceholderType, ty::BoundTy> = BTreeMap::new();
|
||
let mapped_consts: BTreeMap<ty::PlaceholderConst<'tcx>, ty::BoundVar> = BTreeMap::new();
|
||
|
||
let mut replacer = BoundVarReplacer {
|
||
infcx,
|
||
mapped_regions,
|
||
mapped_types,
|
||
mapped_consts,
|
||
current_index: ty::INNERMOST,
|
||
universe_indices,
|
||
};
|
||
|
||
let value = value.super_fold_with(&mut replacer);
|
||
|
||
(value, replacer.mapped_regions, replacer.mapped_types, replacer.mapped_consts)
|
||
}
|
||
|
||
fn universe_for(&mut self, debruijn: ty::DebruijnIndex) -> ty::UniverseIndex {
|
||
let infcx = self.infcx;
|
||
let index =
|
||
self.universe_indices.len() - debruijn.as_usize() + self.current_index.as_usize() - 1;
|
||
let universe = self.universe_indices[index].unwrap_or_else(|| {
|
||
for i in self.universe_indices.iter_mut().take(index + 1) {
|
||
*i = i.or_else(|| Some(infcx.create_next_universe()))
|
||
}
|
||
self.universe_indices[index].unwrap()
|
||
});
|
||
universe
|
||
}
|
||
}
|
||
|
||
impl TypeFolder<'tcx> for BoundVarReplacer<'_, 'tcx> {
|
||
fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
|
||
self.infcx.tcx
|
||
}
|
||
|
||
fn fold_binder<T: TypeFoldable<'tcx>>(
|
||
&mut self,
|
||
t: ty::Binder<'tcx, T>,
|
||
) -> ty::Binder<'tcx, T> {
|
||
self.current_index.shift_in(1);
|
||
let t = t.super_fold_with(self);
|
||
self.current_index.shift_out(1);
|
||
t
|
||
}
|
||
|
||
fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
|
||
match *r {
|
||
ty::ReLateBound(debruijn, _)
|
||
if debruijn.as_usize() + 1
|
||
> self.current_index.as_usize() + self.universe_indices.len() =>
|
||
{
|
||
bug!("Bound vars outside of `self.universe_indices`");
|
||
}
|
||
ty::ReLateBound(debruijn, br) if debruijn >= self.current_index => {
|
||
let universe = self.universe_for(debruijn);
|
||
let p = ty::PlaceholderRegion { universe, name: br.kind };
|
||
self.mapped_regions.insert(p, br);
|
||
self.infcx.tcx.mk_region(ty::RePlaceholder(p))
|
||
}
|
||
_ => r,
|
||
}
|
||
}
|
||
|
||
fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
|
||
match *t.kind() {
|
||
ty::Bound(debruijn, _)
|
||
if debruijn.as_usize() + 1
|
||
> self.current_index.as_usize() + self.universe_indices.len() =>
|
||
{
|
||
bug!("Bound vars outside of `self.universe_indices`");
|
||
}
|
||
ty::Bound(debruijn, bound_ty) if debruijn >= self.current_index => {
|
||
let universe = self.universe_for(debruijn);
|
||
let p = ty::PlaceholderType { universe, name: bound_ty.var };
|
||
self.mapped_types.insert(p, bound_ty);
|
||
self.infcx.tcx.mk_ty(ty::Placeholder(p))
|
||
}
|
||
_ if t.has_vars_bound_at_or_above(self.current_index) => t.super_fold_with(self),
|
||
_ => t,
|
||
}
|
||
}
|
||
|
||
fn fold_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
|
||
match *ct {
|
||
ty::Const { val: ty::ConstKind::Bound(debruijn, _), ty: _ }
|
||
if debruijn.as_usize() + 1
|
||
> self.current_index.as_usize() + self.universe_indices.len() =>
|
||
{
|
||
bug!("Bound vars outside of `self.universe_indices`");
|
||
}
|
||
ty::Const { val: ty::ConstKind::Bound(debruijn, bound_const), ty }
|
||
if debruijn >= self.current_index =>
|
||
{
|
||
let universe = self.universe_for(debruijn);
|
||
let p = ty::PlaceholderConst {
|
||
universe,
|
||
name: ty::BoundConst { var: bound_const, ty },
|
||
};
|
||
self.mapped_consts.insert(p, bound_const);
|
||
self.infcx.tcx.mk_const(ty::Const { val: ty::ConstKind::Placeholder(p), ty })
|
||
}
|
||
_ if ct.has_vars_bound_at_or_above(self.current_index) => ct.super_fold_with(self),
|
||
_ => ct,
|
||
}
|
||
}
|
||
}
|
||
|
||
// The inverse of `BoundVarReplacer`: replaces placeholders with the bound vars from which they came.
|
||
pub struct PlaceholderReplacer<'me, 'tcx> {
|
||
infcx: &'me InferCtxt<'me, 'tcx>,
|
||
mapped_regions: BTreeMap<ty::PlaceholderRegion, ty::BoundRegion>,
|
||
mapped_types: BTreeMap<ty::PlaceholderType, ty::BoundTy>,
|
||
mapped_consts: BTreeMap<ty::PlaceholderConst<'tcx>, ty::BoundVar>,
|
||
universe_indices: &'me Vec<Option<ty::UniverseIndex>>,
|
||
current_index: ty::DebruijnIndex,
|
||
}
|
||
|
||
impl<'me, 'tcx> PlaceholderReplacer<'me, 'tcx> {
|
||
pub fn replace_placeholders<T: TypeFoldable<'tcx>>(
|
||
infcx: &'me InferCtxt<'me, 'tcx>,
|
||
mapped_regions: BTreeMap<ty::PlaceholderRegion, ty::BoundRegion>,
|
||
mapped_types: BTreeMap<ty::PlaceholderType, ty::BoundTy>,
|
||
mapped_consts: BTreeMap<ty::PlaceholderConst<'tcx>, ty::BoundVar>,
|
||
universe_indices: &'me Vec<Option<ty::UniverseIndex>>,
|
||
value: T,
|
||
) -> T {
|
||
let mut replacer = PlaceholderReplacer {
|
||
infcx,
|
||
mapped_regions,
|
||
mapped_types,
|
||
mapped_consts,
|
||
universe_indices,
|
||
current_index: ty::INNERMOST,
|
||
};
|
||
value.super_fold_with(&mut replacer)
|
||
}
|
||
}
|
||
|
||
impl TypeFolder<'tcx> for PlaceholderReplacer<'_, 'tcx> {
|
||
fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
|
||
self.infcx.tcx
|
||
}
|
||
|
||
fn fold_binder<T: TypeFoldable<'tcx>>(
|
||
&mut self,
|
||
t: ty::Binder<'tcx, T>,
|
||
) -> ty::Binder<'tcx, T> {
|
||
if !t.has_placeholders() && !t.has_infer_regions() {
|
||
return t;
|
||
}
|
||
self.current_index.shift_in(1);
|
||
let t = t.super_fold_with(self);
|
||
self.current_index.shift_out(1);
|
||
t
|
||
}
|
||
|
||
fn fold_region(&mut self, r0: ty::Region<'tcx>) -> ty::Region<'tcx> {
|
||
let r1 = match r0 {
|
||
ty::ReVar(_) => self
|
||
.infcx
|
||
.inner
|
||
.borrow_mut()
|
||
.unwrap_region_constraints()
|
||
.opportunistic_resolve_region(self.infcx.tcx, r0),
|
||
_ => r0,
|
||
};
|
||
|
||
let r2 = match *r1 {
|
||
ty::RePlaceholder(p) => {
|
||
let replace_var = self.mapped_regions.get(&p);
|
||
match replace_var {
|
||
Some(replace_var) => {
|
||
let index = self
|
||
.universe_indices
|
||
.iter()
|
||
.position(|u| matches!(u, Some(pu) if *pu == p.universe))
|
||
.unwrap_or_else(|| bug!("Unexpected placeholder universe."));
|
||
let db = ty::DebruijnIndex::from_usize(
|
||
self.universe_indices.len() - index + self.current_index.as_usize() - 1,
|
||
);
|
||
self.tcx().mk_region(ty::ReLateBound(db, *replace_var))
|
||
}
|
||
None => r1,
|
||
}
|
||
}
|
||
_ => r1,
|
||
};
|
||
|
||
debug!(?r0, ?r1, ?r2, "fold_region");
|
||
|
||
r2
|
||
}
|
||
|
||
fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
|
||
match *ty.kind() {
|
||
ty::Placeholder(p) => {
|
||
let replace_var = self.mapped_types.get(&p);
|
||
match replace_var {
|
||
Some(replace_var) => {
|
||
let index = self
|
||
.universe_indices
|
||
.iter()
|
||
.position(|u| matches!(u, Some(pu) if *pu == p.universe))
|
||
.unwrap_or_else(|| bug!("Unexpected placeholder universe."));
|
||
let db = ty::DebruijnIndex::from_usize(
|
||
self.universe_indices.len() - index + self.current_index.as_usize() - 1,
|
||
);
|
||
self.tcx().mk_ty(ty::Bound(db, *replace_var))
|
||
}
|
||
None => ty,
|
||
}
|
||
}
|
||
|
||
_ if ty.has_placeholders() || ty.has_infer_regions() => ty.super_fold_with(self),
|
||
_ => ty,
|
||
}
|
||
}
|
||
|
||
fn fold_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
|
||
if let ty::Const { val: ty::ConstKind::Placeholder(p), ty } = *ct {
|
||
let replace_var = self.mapped_consts.get(&p);
|
||
match replace_var {
|
||
Some(replace_var) => {
|
||
let index = self
|
||
.universe_indices
|
||
.iter()
|
||
.position(|u| matches!(u, Some(pu) if *pu == p.universe))
|
||
.unwrap_or_else(|| bug!("Unexpected placeholder universe."));
|
||
let db = ty::DebruijnIndex::from_usize(
|
||
self.universe_indices.len() - index + self.current_index.as_usize() - 1,
|
||
);
|
||
self.tcx()
|
||
.mk_const(ty::Const { val: ty::ConstKind::Bound(db, *replace_var), ty })
|
||
}
|
||
None => ct,
|
||
}
|
||
} else {
|
||
ct.super_fold_with(self)
|
||
}
|
||
}
|
||
}
|
||
|
||
/// The guts of `normalize`: normalize a specific projection like `<T
|
||
/// as Trait>::Item`. The result is always a type (and possibly
|
||
/// additional obligations). If ambiguity arises, which implies that
|
||
/// there are unresolved type variables in the projection, we will
|
||
/// substitute a fresh type variable `$X` and generate a new
|
||
/// obligation `<T as Trait>::Item == $X` for later.
|
||
pub fn normalize_projection_type<'a, 'b, 'tcx>(
|
||
selcx: &'a mut SelectionContext<'b, 'tcx>,
|
||
param_env: ty::ParamEnv<'tcx>,
|
||
projection_ty: ty::ProjectionTy<'tcx>,
|
||
cause: ObligationCause<'tcx>,
|
||
depth: usize,
|
||
obligations: &mut Vec<PredicateObligation<'tcx>>,
|
||
) -> Ty<'tcx> {
|
||
opt_normalize_projection_type(
|
||
selcx,
|
||
param_env,
|
||
projection_ty,
|
||
cause.clone(),
|
||
depth,
|
||
obligations,
|
||
)
|
||
.ok()
|
||
.flatten()
|
||
.unwrap_or_else(move || {
|
||
// if we bottom out in ambiguity, create a type variable
|
||
// and a deferred predicate to resolve this when more type
|
||
// information is available.
|
||
|
||
let tcx = selcx.infcx().tcx;
|
||
let def_id = projection_ty.item_def_id;
|
||
let ty_var = selcx.infcx().next_ty_var(TypeVariableOrigin {
|
||
kind: TypeVariableOriginKind::NormalizeProjectionType,
|
||
span: tcx.def_span(def_id),
|
||
});
|
||
let projection = ty::Binder::dummy(ty::ProjectionPredicate { projection_ty, ty: ty_var });
|
||
let obligation =
|
||
Obligation::with_depth(cause, depth + 1, param_env, projection.to_predicate(tcx));
|
||
obligations.push(obligation);
|
||
ty_var
|
||
})
|
||
}
|
||
|
||
/// The guts of `normalize`: normalize a specific projection like `<T
|
||
/// as Trait>::Item`. The result is always a type (and possibly
|
||
/// additional obligations). Returns `None` in the case of ambiguity,
|
||
/// which indicates that there are unbound type variables.
|
||
///
|
||
/// This function used to return `Option<NormalizedTy<'tcx>>`, which contains a
|
||
/// `Ty<'tcx>` and an obligations vector. But that obligation vector was very
|
||
/// often immediately appended to another obligations vector. So now this
|
||
/// function takes an obligations vector and appends to it directly, which is
|
||
/// slightly uglier but avoids the need for an extra short-lived allocation.
|
||
#[instrument(level = "debug", skip(selcx, param_env, cause, obligations))]
|
||
fn opt_normalize_projection_type<'a, 'b, 'tcx>(
|
||
selcx: &'a mut SelectionContext<'b, 'tcx>,
|
||
param_env: ty::ParamEnv<'tcx>,
|
||
projection_ty: ty::ProjectionTy<'tcx>,
|
||
cause: ObligationCause<'tcx>,
|
||
depth: usize,
|
||
obligations: &mut Vec<PredicateObligation<'tcx>>,
|
||
) -> Result<Option<Ty<'tcx>>, InProgress> {
|
||
let infcx = selcx.infcx();
|
||
|
||
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 = infcx.inner.borrow_mut().projection_cache().try_start(cache_key);
|
||
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.
|
||
|
||
infcx.inner.borrow_mut().projection_cache().recur(cache_key);
|
||
return Err(InProgress);
|
||
}
|
||
Err(ProjectionCacheEntry::Recur) => {
|
||
debug!("recur cache");
|
||
return Err(InProgress);
|
||
}
|
||
Err(ProjectionCacheEntry::NormalizedTy(ty)) => {
|
||
// This is the hottest path in this function.
|
||
//
|
||
// If we find the value in the cache, then return it along
|
||
// with the obligations that went along with it. Note
|
||
// that, when using a fulfillment context, these
|
||
// obligations could in principle be ignored: they have
|
||
// already been registered when the cache entry was
|
||
// created (and hence the new ones will quickly be
|
||
// discarded as duplicated). But when doing trait
|
||
// evaluation this is not the case, and dropping the trait
|
||
// evaluations can causes ICEs (e.g., #43132).
|
||
debug!(?ty, "found normalized ty");
|
||
obligations.extend(ty.obligations);
|
||
return Ok(Some(ty.value));
|
||
}
|
||
Err(ProjectionCacheEntry::Error) => {
|
||
debug!("opt_normalize_projection_type: found error");
|
||
let result = normalize_to_error(selcx, param_env, projection_ty, cause, depth);
|
||
obligations.extend(result.obligations);
|
||
return Ok(Some(result.value));
|
||
}
|
||
}
|
||
|
||
let obligation = Obligation::with_depth(cause.clone(), depth, param_env, projection_ty);
|
||
|
||
match project_type(selcx, &obligation) {
|
||
Ok(ProjectedTy::Progress(Progress {
|
||
ty: projected_ty,
|
||
obligations: mut projected_obligations,
|
||
})) => {
|
||
// if projection succeeded, then what we get out of this
|
||
// is also non-normalized (consider: it was derived from
|
||
// an impl, where-clause etc) and hence we must
|
||
// re-normalize it
|
||
|
||
let projected_ty = selcx.infcx().resolve_vars_if_possible(projected_ty);
|
||
debug!(?projected_ty, ?depth, ?projected_obligations);
|
||
|
||
let mut result = if projected_ty.has_projections() {
|
||
let mut normalizer = AssocTypeNormalizer::new(
|
||
selcx,
|
||
param_env,
|
||
cause,
|
||
depth + 1,
|
||
&mut projected_obligations,
|
||
);
|
||
let normalized_ty = normalizer.fold(projected_ty);
|
||
|
||
debug!(?normalized_ty, ?depth);
|
||
|
||
Normalized { value: normalized_ty, obligations: projected_obligations }
|
||
} else {
|
||
Normalized { value: projected_ty, obligations: projected_obligations }
|
||
};
|
||
|
||
let mut canonical =
|
||
SelectionContext::with_query_mode(selcx.infcx(), TraitQueryMode::Canonical);
|
||
result.obligations.drain_filter(|projected_obligation| {
|
||
// If any global obligations always apply, considering regions, then we don't
|
||
// need to include them. The `is_global` check rules out inference variables,
|
||
// so there's no need for the caller of `opt_normalize_projection_type`
|
||
// to evaluate them.
|
||
// Note that we do *not* discard obligations that evaluate to
|
||
// `EvaluatedtoOkModuloRegions`. Evaluating these obligations
|
||
// inside of a query (e.g. `evaluate_obligation`) can change
|
||
// the result to `EvaluatedToOkModuloRegions`, while an
|
||
// `EvaluatedToOk` obligation will never change the result.
|
||
// See #85360 for more details
|
||
projected_obligation.is_global(canonical.tcx())
|
||
&& canonical
|
||
.evaluate_root_obligation(projected_obligation)
|
||
.map_or(false, |res| res.must_apply_considering_regions())
|
||
});
|
||
|
||
infcx.inner.borrow_mut().projection_cache().insert_ty(cache_key, result.clone());
|
||
obligations.extend(result.obligations);
|
||
Ok(Some(result.value))
|
||
}
|
||
Ok(ProjectedTy::NoProgress(projected_ty)) => {
|
||
debug!(?projected_ty, "opt_normalize_projection_type: no progress");
|
||
let result = Normalized { value: projected_ty, obligations: vec![] };
|
||
infcx.inner.borrow_mut().projection_cache().insert_ty(cache_key, result.clone());
|
||
// No need to extend `obligations`.
|
||
Ok(Some(result.value))
|
||
}
|
||
Err(ProjectionTyError::TooManyCandidates) => {
|
||
debug!("opt_normalize_projection_type: too many candidates");
|
||
infcx.inner.borrow_mut().projection_cache().ambiguous(cache_key);
|
||
Ok(None)
|
||
}
|
||
Err(ProjectionTyError::TraitSelectionError(_)) => {
|
||
debug!("opt_normalize_projection_type: ERROR");
|
||
// if we got an error processing the `T as Trait` part,
|
||
// just return `ty::err` but add the obligation `T :
|
||
// Trait`, which when processed will cause the error to be
|
||
// reported later
|
||
|
||
infcx.inner.borrow_mut().projection_cache().error(cache_key);
|
||
let result = normalize_to_error(selcx, param_env, projection_ty, cause, depth);
|
||
obligations.extend(result.obligations);
|
||
Ok(Some(result.value))
|
||
}
|
||
}
|
||
}
|
||
|
||
/// If we are projecting `<T as Trait>::Item`, but `T: Trait` does not
|
||
/// hold. In various error cases, we cannot generate a valid
|
||
/// normalized projection. Therefore, we create an inference variable
|
||
/// return an associated obligation that, when fulfilled, will lead to
|
||
/// an error.
|
||
///
|
||
/// Note that we used to return `Error` here, but that was quite
|
||
/// dubious -- the premise was that an error would *eventually* be
|
||
/// reported, when the obligation was processed. But in general once
|
||
/// you see an `Error` you are supposed to be able to assume that an
|
||
/// error *has been* reported, so that you can take whatever heuristic
|
||
/// paths you want to take. To make things worse, it was possible for
|
||
/// cycles to arise, where you basically had a setup like `<MyType<$0>
|
||
/// as Trait>::Foo == $0`. Here, normalizing `<MyType<$0> as
|
||
/// Trait>::Foo> to `[type error]` would lead to an obligation of
|
||
/// `<MyType<[type error]> as Trait>::Foo`. We are supposed to report
|
||
/// an error for this obligation, but we legitimately should not,
|
||
/// because it contains `[type error]`. Yuck! (See issue #29857 for
|
||
/// one case where this arose.)
|
||
fn normalize_to_error<'a, 'tcx>(
|
||
selcx: &mut SelectionContext<'a, 'tcx>,
|
||
param_env: ty::ParamEnv<'tcx>,
|
||
projection_ty: ty::ProjectionTy<'tcx>,
|
||
cause: ObligationCause<'tcx>,
|
||
depth: usize,
|
||
) -> NormalizedTy<'tcx> {
|
||
let trait_ref = projection_ty.trait_ref(selcx.tcx()).to_poly_trait_ref();
|
||
let trait_obligation = Obligation {
|
||
cause,
|
||
recursion_depth: depth,
|
||
param_env,
|
||
predicate: trait_ref.without_const().to_predicate(selcx.tcx()),
|
||
};
|
||
let tcx = selcx.infcx().tcx;
|
||
let def_id = projection_ty.item_def_id;
|
||
let new_value = selcx.infcx().next_ty_var(TypeVariableOrigin {
|
||
kind: TypeVariableOriginKind::NormalizeProjectionType,
|
||
span: tcx.def_span(def_id),
|
||
});
|
||
Normalized { value: new_value, obligations: vec![trait_obligation] }
|
||
}
|
||
|
||
enum ProjectedTy<'tcx> {
|
||
Progress(Progress<'tcx>),
|
||
NoProgress(Ty<'tcx>),
|
||
}
|
||
|
||
struct Progress<'tcx> {
|
||
ty: Ty<'tcx>,
|
||
obligations: Vec<PredicateObligation<'tcx>>,
|
||
}
|
||
|
||
impl<'tcx> Progress<'tcx> {
|
||
fn error(tcx: TyCtxt<'tcx>) -> Self {
|
||
Progress { ty: tcx.ty_error(), obligations: vec![] }
|
||
}
|
||
|
||
fn with_addl_obligations(mut self, mut obligations: Vec<PredicateObligation<'tcx>>) -> Self {
|
||
debug!(
|
||
self.obligations.len = ?self.obligations.len(),
|
||
obligations.len = obligations.len(),
|
||
"with_addl_obligations"
|
||
);
|
||
|
||
debug!(?self.obligations, ?obligations, "with_addl_obligations");
|
||
|
||
self.obligations.append(&mut obligations);
|
||
self
|
||
}
|
||
}
|
||
|
||
/// Computes the result of a projection type (if we can).
|
||
///
|
||
/// IMPORTANT:
|
||
/// - `obligation` must be fully normalized
|
||
#[tracing::instrument(level = "info", skip(selcx))]
|
||
fn project_type<'cx, 'tcx>(
|
||
selcx: &mut SelectionContext<'cx, 'tcx>,
|
||
obligation: &ProjectionTyObligation<'tcx>,
|
||
) -> Result<ProjectedTy<'tcx>, ProjectionTyError<'tcx>> {
|
||
if !selcx.tcx().recursion_limit().value_within_limit(obligation.recursion_depth) {
|
||
debug!("project: overflow!");
|
||
// This should really be an immediate error, but some existing code
|
||
// relies on being able to recover from this.
|
||
return Err(ProjectionTyError::TraitSelectionError(SelectionError::Overflow));
|
||
}
|
||
|
||
if obligation.predicate.references_error() {
|
||
return Ok(ProjectedTy::Progress(Progress::error(selcx.tcx())));
|
||
}
|
||
|
||
let mut candidates = ProjectionTyCandidateSet::None;
|
||
|
||
// Make sure that the following procedures are kept in order. ParamEnv
|
||
// needs to be first because it has highest priority, and Select checks
|
||
// the return value of push_candidate which assumes it's ran at last.
|
||
assemble_candidates_from_param_env(selcx, obligation, &mut candidates);
|
||
|
||
assemble_candidates_from_trait_def(selcx, obligation, &mut candidates);
|
||
|
||
assemble_candidates_from_object_ty(selcx, obligation, &mut candidates);
|
||
|
||
if let ProjectionTyCandidateSet::Single(ProjectionTyCandidate::Object(_)) = candidates {
|
||
// Avoid normalization cycle from selection (see
|
||
// `assemble_candidates_from_object_ty`).
|
||
// FIXME(lazy_normalization): Lazy normalization should save us from
|
||
// having to special case this.
|
||
} else {
|
||
assemble_candidates_from_impls(selcx, obligation, &mut candidates);
|
||
};
|
||
|
||
match candidates {
|
||
ProjectionTyCandidateSet::Single(candidate) => {
|
||
Ok(ProjectedTy::Progress(confirm_candidate(selcx, obligation, candidate)))
|
||
}
|
||
ProjectionTyCandidateSet::None => Ok(ProjectedTy::NoProgress(
|
||
selcx
|
||
.tcx()
|
||
.mk_projection(obligation.predicate.item_def_id, obligation.predicate.substs),
|
||
)),
|
||
// Error occurred while trying to processing impls.
|
||
ProjectionTyCandidateSet::Error(e) => Err(ProjectionTyError::TraitSelectionError(e)),
|
||
// Inherent ambiguity that prevents us from even enumerating the
|
||
// candidates.
|
||
ProjectionTyCandidateSet::Ambiguous => Err(ProjectionTyError::TooManyCandidates),
|
||
}
|
||
}
|
||
|
||
/// The first thing we have to do is scan through the parameter
|
||
/// environment to see whether there are any projection predicates
|
||
/// there that can answer this question.
|
||
fn assemble_candidates_from_param_env<'cx, 'tcx>(
|
||
selcx: &mut SelectionContext<'cx, 'tcx>,
|
||
obligation: &ProjectionTyObligation<'tcx>,
|
||
candidate_set: &mut ProjectionTyCandidateSet<'tcx>,
|
||
) {
|
||
debug!("assemble_candidates_from_param_env(..)");
|
||
assemble_candidates_from_predicates(
|
||
selcx,
|
||
obligation,
|
||
candidate_set,
|
||
ProjectionTyCandidate::ParamEnv,
|
||
obligation.param_env.caller_bounds().iter(),
|
||
false,
|
||
);
|
||
}
|
||
|
||
/// In the case of a nested projection like <<A as Foo>::FooT as Bar>::BarT, we may find
|
||
/// that the definition of `Foo` has some clues:
|
||
///
|
||
/// ```
|
||
/// trait Foo {
|
||
/// type FooT : Bar<BarT=i32>
|
||
/// }
|
||
/// ```
|
||
///
|
||
/// Here, for example, we could conclude that the result is `i32`.
|
||
fn assemble_candidates_from_trait_def<'cx, 'tcx>(
|
||
selcx: &mut SelectionContext<'cx, 'tcx>,
|
||
obligation: &ProjectionTyObligation<'tcx>,
|
||
candidate_set: &mut ProjectionTyCandidateSet<'tcx>,
|
||
) {
|
||
debug!("assemble_candidates_from_trait_def(..)");
|
||
|
||
let tcx = selcx.tcx();
|
||
// Check whether the self-type is itself a projection.
|
||
// If so, extract what we know from the trait and try to come up with a good answer.
|
||
let bounds = match *obligation.predicate.self_ty().kind() {
|
||
ty::Projection(ref data) => tcx.item_bounds(data.item_def_id).subst(tcx, data.substs),
|
||
ty::Opaque(def_id, substs) => tcx.item_bounds(def_id).subst(tcx, substs),
|
||
ty::Infer(ty::TyVar(_)) => {
|
||
// If the self-type is an inference variable, then it MAY wind up
|
||
// being a projected type, so induce an ambiguity.
|
||
candidate_set.mark_ambiguous();
|
||
return;
|
||
}
|
||
_ => return,
|
||
};
|
||
|
||
assemble_candidates_from_predicates(
|
||
selcx,
|
||
obligation,
|
||
candidate_set,
|
||
ProjectionTyCandidate::TraitDef,
|
||
bounds.iter(),
|
||
true,
|
||
)
|
||
}
|
||
|
||
/// In the case of a trait object like
|
||
/// `<dyn Iterator<Item = ()> as Iterator>::Item` we can use the existential
|
||
/// predicate in the trait object.
|
||
///
|
||
/// We don't go through the select candidate for these bounds to avoid cycles:
|
||
/// In the above case, `dyn Iterator<Item = ()>: Iterator` would create a
|
||
/// nested obligation of `<dyn Iterator<Item = ()> as Iterator>::Item: Sized`,
|
||
/// this then has to be normalized without having to prove
|
||
/// `dyn Iterator<Item = ()>: Iterator` again.
|
||
fn assemble_candidates_from_object_ty<'cx, 'tcx>(
|
||
selcx: &mut SelectionContext<'cx, 'tcx>,
|
||
obligation: &ProjectionTyObligation<'tcx>,
|
||
candidate_set: &mut ProjectionTyCandidateSet<'tcx>,
|
||
) {
|
||
debug!("assemble_candidates_from_object_ty(..)");
|
||
|
||
let tcx = selcx.tcx();
|
||
|
||
let self_ty = obligation.predicate.self_ty();
|
||
let object_ty = selcx.infcx().shallow_resolve(self_ty);
|
||
let data = match object_ty.kind() {
|
||
ty::Dynamic(data, ..) => data,
|
||
ty::Infer(ty::TyVar(_)) => {
|
||
// If the self-type is an inference variable, then it MAY wind up
|
||
// being an object type, so induce an ambiguity.
|
||
candidate_set.mark_ambiguous();
|
||
return;
|
||
}
|
||
_ => return,
|
||
};
|
||
let env_predicates = data
|
||
.projection_bounds()
|
||
.filter(|bound| bound.item_def_id() == obligation.predicate.item_def_id)
|
||
.map(|p| p.with_self_ty(tcx, object_ty).to_predicate(tcx));
|
||
|
||
assemble_candidates_from_predicates(
|
||
selcx,
|
||
obligation,
|
||
candidate_set,
|
||
ProjectionTyCandidate::Object,
|
||
env_predicates,
|
||
false,
|
||
);
|
||
}
|
||
|
||
fn assemble_candidates_from_predicates<'cx, 'tcx>(
|
||
selcx: &mut SelectionContext<'cx, 'tcx>,
|
||
obligation: &ProjectionTyObligation<'tcx>,
|
||
candidate_set: &mut ProjectionTyCandidateSet<'tcx>,
|
||
ctor: fn(ty::PolyProjectionPredicate<'tcx>) -> ProjectionTyCandidate<'tcx>,
|
||
env_predicates: impl Iterator<Item = ty::Predicate<'tcx>>,
|
||
potentially_unnormalized_candidates: bool,
|
||
) {
|
||
debug!(?obligation, "assemble_candidates_from_predicates");
|
||
|
||
let infcx = selcx.infcx();
|
||
for predicate in env_predicates {
|
||
debug!(?predicate);
|
||
let bound_predicate = predicate.kind();
|
||
if let ty::PredicateKind::Projection(data) = predicate.kind().skip_binder() {
|
||
let data = bound_predicate.rebind(data);
|
||
let same_def_id = data.projection_def_id() == obligation.predicate.item_def_id;
|
||
|
||
let is_match = same_def_id
|
||
&& infcx.probe(|_| {
|
||
selcx.match_projection_projections(
|
||
obligation,
|
||
data,
|
||
potentially_unnormalized_candidates,
|
||
)
|
||
});
|
||
|
||
debug!(?data, ?is_match, ?same_def_id);
|
||
|
||
if is_match {
|
||
candidate_set.push_candidate(ctor(data));
|
||
|
||
if potentially_unnormalized_candidates
|
||
&& !obligation.predicate.has_infer_types_or_consts()
|
||
{
|
||
// HACK: Pick the first trait def candidate for a fully
|
||
// inferred predicate. This is to allow duplicates that
|
||
// differ only in normalization.
|
||
return;
|
||
}
|
||
}
|
||
}
|
||
}
|
||
}
|
||
|
||
fn assemble_candidates_from_impls<'cx, 'tcx>(
|
||
selcx: &mut SelectionContext<'cx, 'tcx>,
|
||
obligation: &ProjectionTyObligation<'tcx>,
|
||
candidate_set: &mut ProjectionTyCandidateSet<'tcx>,
|
||
) {
|
||
debug!("assemble_candidates_from_impls");
|
||
|
||
// If we are resolving `<T as TraitRef<...>>::Item == Type`,
|
||
// start out by selecting the predicate `T as TraitRef<...>`:
|
||
let poly_trait_ref = obligation.predicate.trait_ref(selcx.tcx()).to_poly_trait_ref();
|
||
let trait_obligation = obligation.with(poly_trait_ref.to_poly_trait_predicate());
|
||
let _ = selcx.infcx().commit_if_ok(|_| {
|
||
let impl_source = match selcx.select(&trait_obligation) {
|
||
Ok(Some(impl_source)) => impl_source,
|
||
Ok(None) => {
|
||
candidate_set.mark_ambiguous();
|
||
return Err(());
|
||
}
|
||
Err(e) => {
|
||
debug!(error = ?e, "selection error");
|
||
candidate_set.mark_error(e);
|
||
return Err(());
|
||
}
|
||
};
|
||
|
||
let eligible = match &impl_source {
|
||
super::ImplSource::Closure(_)
|
||
| super::ImplSource::Generator(_)
|
||
| super::ImplSource::FnPointer(_)
|
||
| super::ImplSource::TraitAlias(_) => {
|
||
debug!(?impl_source);
|
||
true
|
||
}
|
||
super::ImplSource::UserDefined(impl_data) => {
|
||
// We have to be careful when projecting out of an
|
||
// impl because of specialization. If we are not in
|
||
// codegen (i.e., projection mode is not "any"), and the
|
||
// impl's type is declared as default, then we disable
|
||
// projection (even if the trait ref is fully
|
||
// monomorphic). In the case where trait ref is not
|
||
// fully monomorphic (i.e., includes type parameters),
|
||
// this is because those type parameters may
|
||
// ultimately be bound to types from other crates that
|
||
// may have specialized impls we can't see. In the
|
||
// case where the trait ref IS fully monomorphic, this
|
||
// is a policy decision that we made in the RFC in
|
||
// order to preserve flexibility for the crate that
|
||
// defined the specializable impl to specialize later
|
||
// for existing types.
|
||
//
|
||
// In either case, we handle this by not adding a
|
||
// candidate for an impl if it contains a `default`
|
||
// type.
|
||
//
|
||
// NOTE: This should be kept in sync with the similar code in
|
||
// `rustc_ty_utils::instance::resolve_associated_item()`.
|
||
let node_item =
|
||
assoc_ty_def(selcx, impl_data.impl_def_id, obligation.predicate.item_def_id)
|
||
.map_err(|ErrorReported| ())?;
|
||
|
||
if node_item.is_final() {
|
||
// Non-specializable items are always projectable.
|
||
true
|
||
} else {
|
||
// Only reveal a specializable default if we're past type-checking
|
||
// and the obligation is monomorphic, otherwise passes such as
|
||
// transmute checking and polymorphic MIR optimizations could
|
||
// get a result which isn't correct for all monomorphizations.
|
||
if obligation.param_env.reveal() == Reveal::All {
|
||
// NOTE(eddyb) inference variables can resolve to parameters, so
|
||
// assume `poly_trait_ref` isn't monomorphic, if it contains any.
|
||
let poly_trait_ref = selcx.infcx().resolve_vars_if_possible(poly_trait_ref);
|
||
!poly_trait_ref.still_further_specializable()
|
||
} else {
|
||
debug!(
|
||
assoc_ty = ?selcx.tcx().def_path_str(node_item.item.def_id),
|
||
?obligation.predicate,
|
||
"assemble_candidates_from_impls: not eligible due to default",
|
||
);
|
||
false
|
||
}
|
||
}
|
||
}
|
||
super::ImplSource::DiscriminantKind(..) => {
|
||
// While `DiscriminantKind` is automatically implemented for every type,
|
||
// the concrete discriminant may not be known yet.
|
||
//
|
||
// Any type with multiple potential discriminant types is therefore not eligible.
|
||
let self_ty = selcx.infcx().shallow_resolve(obligation.predicate.self_ty());
|
||
|
||
match self_ty.kind() {
|
||
ty::Bool
|
||
| ty::Char
|
||
| ty::Int(_)
|
||
| ty::Uint(_)
|
||
| ty::Float(_)
|
||
| ty::Adt(..)
|
||
| ty::Foreign(_)
|
||
| ty::Str
|
||
| ty::Array(..)
|
||
| ty::Slice(_)
|
||
| ty::RawPtr(..)
|
||
| ty::Ref(..)
|
||
| ty::FnDef(..)
|
||
| ty::FnPtr(..)
|
||
| ty::Dynamic(..)
|
||
| ty::Closure(..)
|
||
| ty::Generator(..)
|
||
| ty::GeneratorWitness(..)
|
||
| ty::Never
|
||
| ty::Tuple(..)
|
||
// Integers and floats always have `u8` as their discriminant.
|
||
| ty::Infer(ty::InferTy::IntVar(_) | ty::InferTy::FloatVar(..)) => true,
|
||
|
||
ty::Projection(..)
|
||
| ty::Opaque(..)
|
||
| ty::Param(..)
|
||
| ty::Bound(..)
|
||
| ty::Placeholder(..)
|
||
| ty::Infer(..)
|
||
| ty::Error(_) => false,
|
||
}
|
||
}
|
||
super::ImplSource::Pointee(..) => {
|
||
// While `Pointee` is automatically implemented for every type,
|
||
// the concrete metadata type may not be known yet.
|
||
//
|
||
// Any type with multiple potential metadata types is therefore not eligible.
|
||
let self_ty = selcx.infcx().shallow_resolve(obligation.predicate.self_ty());
|
||
|
||
// FIXME: should this normalize?
|
||
let tail = selcx.tcx().struct_tail_without_normalization(self_ty);
|
||
match tail.kind() {
|
||
ty::Bool
|
||
| ty::Char
|
||
| ty::Int(_)
|
||
| ty::Uint(_)
|
||
| ty::Float(_)
|
||
| ty::Foreign(_)
|
||
| ty::Str
|
||
| ty::Array(..)
|
||
| ty::Slice(_)
|
||
| ty::RawPtr(..)
|
||
| ty::Ref(..)
|
||
| ty::FnDef(..)
|
||
| ty::FnPtr(..)
|
||
| ty::Dynamic(..)
|
||
| ty::Closure(..)
|
||
| ty::Generator(..)
|
||
| ty::GeneratorWitness(..)
|
||
| ty::Never
|
||
// If returned by `struct_tail_without_normalization` this is a unit struct
|
||
// without any fields, or not a struct, and therefore is Sized.
|
||
| ty::Adt(..)
|
||
// If returned by `struct_tail_without_normalization` this is the empty tuple.
|
||
| ty::Tuple(..)
|
||
// Integers and floats are always Sized, and so have unit type metadata.
|
||
| ty::Infer(ty::InferTy::IntVar(_) | ty::InferTy::FloatVar(..)) => true,
|
||
|
||
ty::Projection(..)
|
||
| ty::Opaque(..)
|
||
| ty::Param(..)
|
||
| ty::Bound(..)
|
||
| ty::Placeholder(..)
|
||
| ty::Infer(..)
|
||
| ty::Error(_) => false,
|
||
}
|
||
}
|
||
super::ImplSource::Param(..) => {
|
||
// This case tell us nothing about the value of an
|
||
// associated type. Consider:
|
||
//
|
||
// ```
|
||
// trait SomeTrait { type Foo; }
|
||
// fn foo<T:SomeTrait>(...) { }
|
||
// ```
|
||
//
|
||
// If the user writes `<T as SomeTrait>::Foo`, then the `T
|
||
// : SomeTrait` binding does not help us decide what the
|
||
// type `Foo` is (at least, not more specifically than
|
||
// what we already knew).
|
||
//
|
||
// But wait, you say! What about an example like this:
|
||
//
|
||
// ```
|
||
// fn bar<T:SomeTrait<Foo=usize>>(...) { ... }
|
||
// ```
|
||
//
|
||
// Doesn't the `T : Sometrait<Foo=usize>` predicate help
|
||
// resolve `T::Foo`? And of course it does, but in fact
|
||
// that single predicate is desugared into two predicates
|
||
// in the compiler: a trait predicate (`T : SomeTrait`) and a
|
||
// projection. And the projection where clause is handled
|
||
// in `assemble_candidates_from_param_env`.
|
||
false
|
||
}
|
||
super::ImplSource::Object(_) => {
|
||
// Handled by the `Object` projection candidate. See
|
||
// `assemble_candidates_from_object_ty` for an explanation of
|
||
// why we special case object types.
|
||
false
|
||
}
|
||
super::ImplSource::AutoImpl(..)
|
||
| super::ImplSource::Builtin(..)
|
||
| super::ImplSource::TraitUpcasting(_) => {
|
||
// These traits have no associated types.
|
||
selcx.tcx().sess.delay_span_bug(
|
||
obligation.cause.span,
|
||
&format!("Cannot project an associated type from `{:?}`", impl_source),
|
||
);
|
||
return Err(());
|
||
}
|
||
};
|
||
|
||
if eligible {
|
||
if candidate_set.push_candidate(ProjectionTyCandidate::Select(impl_source)) {
|
||
Ok(())
|
||
} else {
|
||
Err(())
|
||
}
|
||
} else {
|
||
Err(())
|
||
}
|
||
});
|
||
}
|
||
|
||
fn confirm_candidate<'cx, 'tcx>(
|
||
selcx: &mut SelectionContext<'cx, 'tcx>,
|
||
obligation: &ProjectionTyObligation<'tcx>,
|
||
candidate: ProjectionTyCandidate<'tcx>,
|
||
) -> Progress<'tcx> {
|
||
debug!(?obligation, ?candidate, "confirm_candidate");
|
||
let mut progress = match candidate {
|
||
ProjectionTyCandidate::ParamEnv(poly_projection)
|
||
| ProjectionTyCandidate::Object(poly_projection) => {
|
||
confirm_param_env_candidate(selcx, obligation, poly_projection, false)
|
||
}
|
||
|
||
ProjectionTyCandidate::TraitDef(poly_projection) => {
|
||
confirm_param_env_candidate(selcx, obligation, poly_projection, true)
|
||
}
|
||
|
||
ProjectionTyCandidate::Select(impl_source) => {
|
||
confirm_select_candidate(selcx, obligation, impl_source)
|
||
}
|
||
};
|
||
// When checking for cycle during evaluation, we compare predicates with
|
||
// "syntactic" equality. Since normalization generally introduces a type
|
||
// with new region variables, we need to resolve them to existing variables
|
||
// when possible for this to work. See `auto-trait-projection-recursion.rs`
|
||
// for a case where this matters.
|
||
if progress.ty.has_infer_regions() {
|
||
progress.ty = OpportunisticRegionResolver::new(selcx.infcx()).fold_ty(progress.ty);
|
||
}
|
||
progress
|
||
}
|
||
|
||
fn confirm_select_candidate<'cx, 'tcx>(
|
||
selcx: &mut SelectionContext<'cx, 'tcx>,
|
||
obligation: &ProjectionTyObligation<'tcx>,
|
||
impl_source: Selection<'tcx>,
|
||
) -> Progress<'tcx> {
|
||
match impl_source {
|
||
super::ImplSource::UserDefined(data) => confirm_impl_candidate(selcx, obligation, data),
|
||
super::ImplSource::Generator(data) => confirm_generator_candidate(selcx, obligation, data),
|
||
super::ImplSource::Closure(data) => confirm_closure_candidate(selcx, obligation, data),
|
||
super::ImplSource::FnPointer(data) => confirm_fn_pointer_candidate(selcx, obligation, data),
|
||
super::ImplSource::DiscriminantKind(data) => {
|
||
confirm_discriminant_kind_candidate(selcx, obligation, data)
|
||
}
|
||
super::ImplSource::Pointee(data) => confirm_pointee_candidate(selcx, obligation, data),
|
||
super::ImplSource::Object(_)
|
||
| super::ImplSource::AutoImpl(..)
|
||
| super::ImplSource::Param(..)
|
||
| super::ImplSource::Builtin(..)
|
||
| super::ImplSource::TraitUpcasting(_)
|
||
| super::ImplSource::TraitAlias(..) => {
|
||
// we don't create Select candidates with this kind of resolution
|
||
span_bug!(
|
||
obligation.cause.span,
|
||
"Cannot project an associated type from `{:?}`",
|
||
impl_source
|
||
)
|
||
}
|
||
}
|
||
}
|
||
|
||
fn confirm_generator_candidate<'cx, 'tcx>(
|
||
selcx: &mut SelectionContext<'cx, 'tcx>,
|
||
obligation: &ProjectionTyObligation<'tcx>,
|
||
impl_source: ImplSourceGeneratorData<'tcx, PredicateObligation<'tcx>>,
|
||
) -> Progress<'tcx> {
|
||
let gen_sig = impl_source.substs.as_generator().poly_sig();
|
||
let Normalized { value: gen_sig, obligations } = normalize_with_depth(
|
||
selcx,
|
||
obligation.param_env,
|
||
obligation.cause.clone(),
|
||
obligation.recursion_depth + 1,
|
||
gen_sig,
|
||
);
|
||
|
||
debug!(?obligation, ?gen_sig, ?obligations, "confirm_generator_candidate");
|
||
|
||
let tcx = selcx.tcx();
|
||
|
||
let gen_def_id = tcx.require_lang_item(LangItem::Generator, None);
|
||
|
||
let predicate = super::util::generator_trait_ref_and_outputs(
|
||
tcx,
|
||
gen_def_id,
|
||
obligation.predicate.self_ty(),
|
||
gen_sig,
|
||
)
|
||
.map_bound(|(trait_ref, yield_ty, return_ty)| {
|
||
let name = tcx.associated_item(obligation.predicate.item_def_id).ident.name;
|
||
let ty = if name == sym::Return {
|
||
return_ty
|
||
} else if name == sym::Yield {
|
||
yield_ty
|
||
} else {
|
||
bug!()
|
||
};
|
||
|
||
ty::ProjectionPredicate {
|
||
projection_ty: ty::ProjectionTy {
|
||
substs: trait_ref.substs,
|
||
item_def_id: obligation.predicate.item_def_id,
|
||
},
|
||
ty,
|
||
}
|
||
});
|
||
|
||
confirm_param_env_candidate(selcx, obligation, predicate, false)
|
||
.with_addl_obligations(impl_source.nested)
|
||
.with_addl_obligations(obligations)
|
||
}
|
||
|
||
fn confirm_discriminant_kind_candidate<'cx, 'tcx>(
|
||
selcx: &mut SelectionContext<'cx, 'tcx>,
|
||
obligation: &ProjectionTyObligation<'tcx>,
|
||
_: ImplSourceDiscriminantKindData,
|
||
) -> Progress<'tcx> {
|
||
let tcx = selcx.tcx();
|
||
|
||
let self_ty = selcx.infcx().shallow_resolve(obligation.predicate.self_ty());
|
||
// We get here from `poly_project_and_unify_type` which replaces bound vars
|
||
// with placeholders
|
||
debug_assert!(!self_ty.has_escaping_bound_vars());
|
||
let substs = tcx.mk_substs([self_ty.into()].iter());
|
||
|
||
let discriminant_def_id = tcx.require_lang_item(LangItem::Discriminant, None);
|
||
|
||
let predicate = ty::ProjectionPredicate {
|
||
projection_ty: ty::ProjectionTy { substs, item_def_id: discriminant_def_id },
|
||
ty: self_ty.discriminant_ty(tcx),
|
||
};
|
||
|
||
// We get here from `poly_project_and_unify_type` which replaces bound vars
|
||
// with placeholders, so dummy is okay here.
|
||
confirm_param_env_candidate(selcx, obligation, ty::Binder::dummy(predicate), false)
|
||
}
|
||
|
||
fn confirm_pointee_candidate<'cx, 'tcx>(
|
||
selcx: &mut SelectionContext<'cx, 'tcx>,
|
||
obligation: &ProjectionTyObligation<'tcx>,
|
||
_: ImplSourcePointeeData,
|
||
) -> Progress<'tcx> {
|
||
let tcx = selcx.tcx();
|
||
|
||
let self_ty = selcx.infcx().shallow_resolve(obligation.predicate.self_ty());
|
||
let substs = tcx.mk_substs([self_ty.into()].iter());
|
||
|
||
let metadata_def_id = tcx.require_lang_item(LangItem::Metadata, None);
|
||
|
||
let predicate = ty::ProjectionPredicate {
|
||
projection_ty: ty::ProjectionTy { substs, item_def_id: metadata_def_id },
|
||
ty: self_ty.ptr_metadata_ty(tcx),
|
||
};
|
||
|
||
confirm_param_env_candidate(selcx, obligation, ty::Binder::dummy(predicate), false)
|
||
}
|
||
|
||
fn confirm_fn_pointer_candidate<'cx, 'tcx>(
|
||
selcx: &mut SelectionContext<'cx, 'tcx>,
|
||
obligation: &ProjectionTyObligation<'tcx>,
|
||
fn_pointer_impl_source: ImplSourceFnPointerData<'tcx, PredicateObligation<'tcx>>,
|
||
) -> Progress<'tcx> {
|
||
let fn_type = selcx.infcx().shallow_resolve(fn_pointer_impl_source.fn_ty);
|
||
let sig = fn_type.fn_sig(selcx.tcx());
|
||
let Normalized { value: sig, obligations } = normalize_with_depth(
|
||
selcx,
|
||
obligation.param_env,
|
||
obligation.cause.clone(),
|
||
obligation.recursion_depth + 1,
|
||
sig,
|
||
);
|
||
|
||
confirm_callable_candidate(selcx, obligation, sig, util::TupleArgumentsFlag::Yes)
|
||
.with_addl_obligations(fn_pointer_impl_source.nested)
|
||
.with_addl_obligations(obligations)
|
||
}
|
||
|
||
fn confirm_closure_candidate<'cx, 'tcx>(
|
||
selcx: &mut SelectionContext<'cx, 'tcx>,
|
||
obligation: &ProjectionTyObligation<'tcx>,
|
||
impl_source: ImplSourceClosureData<'tcx, PredicateObligation<'tcx>>,
|
||
) -> Progress<'tcx> {
|
||
let closure_sig = impl_source.substs.as_closure().sig();
|
||
let Normalized { value: closure_sig, obligations } = normalize_with_depth(
|
||
selcx,
|
||
obligation.param_env,
|
||
obligation.cause.clone(),
|
||
obligation.recursion_depth + 1,
|
||
closure_sig,
|
||
);
|
||
|
||
debug!(?obligation, ?closure_sig, ?obligations, "confirm_closure_candidate");
|
||
|
||
confirm_callable_candidate(selcx, obligation, closure_sig, util::TupleArgumentsFlag::No)
|
||
.with_addl_obligations(impl_source.nested)
|
||
.with_addl_obligations(obligations)
|
||
}
|
||
|
||
fn confirm_callable_candidate<'cx, 'tcx>(
|
||
selcx: &mut SelectionContext<'cx, 'tcx>,
|
||
obligation: &ProjectionTyObligation<'tcx>,
|
||
fn_sig: ty::PolyFnSig<'tcx>,
|
||
flag: util::TupleArgumentsFlag,
|
||
) -> Progress<'tcx> {
|
||
let tcx = selcx.tcx();
|
||
|
||
debug!(?obligation, ?fn_sig, "confirm_callable_candidate");
|
||
|
||
let fn_once_def_id = tcx.require_lang_item(LangItem::FnOnce, None);
|
||
let fn_once_output_def_id = tcx.require_lang_item(LangItem::FnOnceOutput, None);
|
||
|
||
let predicate = super::util::closure_trait_ref_and_return_type(
|
||
tcx,
|
||
fn_once_def_id,
|
||
obligation.predicate.self_ty(),
|
||
fn_sig,
|
||
flag,
|
||
)
|
||
.map_bound(|(trait_ref, ret_type)| ty::ProjectionPredicate {
|
||
projection_ty: ty::ProjectionTy {
|
||
substs: trait_ref.substs,
|
||
item_def_id: fn_once_output_def_id,
|
||
},
|
||
ty: ret_type,
|
||
});
|
||
|
||
confirm_param_env_candidate(selcx, obligation, predicate, false)
|
||
}
|
||
|
||
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 obligation_projection = obligation.predicate;
|
||
let mut nested_obligations = Vec::new();
|
||
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
|
||
};
|
||
|
||
match infcx.at(cause, param_env).eq(cache_projection, obligation_projection) {
|
||
Ok(InferOk { value: _, obligations }) => {
|
||
nested_obligations.extend(obligations);
|
||
assoc_ty_own_obligations(selcx, obligation, &mut nested_obligations);
|
||
Progress { ty: cache_entry.ty, obligations: nested_obligations }
|
||
}
|
||
Err(e) => {
|
||
let msg = format!(
|
||
"Failed to unify obligation `{:?}` with poly_projection `{:?}`: {:?}",
|
||
obligation, poly_cache_entry, e,
|
||
);
|
||
debug!("confirm_param_env_candidate: {}", msg);
|
||
let err = infcx.tcx.ty_error_with_message(obligation.cause.span, &msg);
|
||
Progress { ty: err, obligations: vec![] }
|
||
}
|
||
}
|
||
}
|
||
|
||
fn confirm_impl_candidate<'cx, 'tcx>(
|
||
selcx: &mut SelectionContext<'cx, 'tcx>,
|
||
obligation: &ProjectionTyObligation<'tcx>,
|
||
impl_impl_source: ImplSourceUserDefinedData<'tcx, PredicateObligation<'tcx>>,
|
||
) -> Progress<'tcx> {
|
||
let tcx = selcx.tcx();
|
||
|
||
let ImplSourceUserDefinedData { impl_def_id, substs, mut nested } = impl_impl_source;
|
||
let assoc_item_id = obligation.predicate.item_def_id;
|
||
let trait_def_id = tcx.trait_id_of_impl(impl_def_id).unwrap();
|
||
|
||
let param_env = obligation.param_env;
|
||
let assoc_ty = match assoc_ty_def(selcx, impl_def_id, assoc_item_id) {
|
||
Ok(assoc_ty) => assoc_ty,
|
||
Err(ErrorReported) => return Progress { ty: tcx.ty_error(), obligations: nested },
|
||
};
|
||
|
||
if !assoc_ty.item.defaultness.has_value() {
|
||
// This means that the impl is missing a definition for the
|
||
// associated type. This error will be reported by the type
|
||
// checker method `check_impl_items_against_trait`, so here we
|
||
// just return Error.
|
||
debug!(
|
||
"confirm_impl_candidate: no associated type {:?} for {:?}",
|
||
assoc_ty.item.ident, obligation.predicate
|
||
);
|
||
return Progress { ty: tcx.ty_error(), obligations: nested };
|
||
}
|
||
// If we're trying to normalize `<Vec<u32> as X>::A<S>` using
|
||
//`impl<T> X for Vec<T> { type A<Y> = Box<Y>; }`, then:
|
||
//
|
||
// * `obligation.predicate.substs` is `[Vec<u32>, S]`
|
||
// * `substs` is `[u32]`
|
||
// * `substs` ends up as `[u32, S]`
|
||
let substs = obligation.predicate.substs.rebase_onto(tcx, trait_def_id, substs);
|
||
let substs =
|
||
translate_substs(selcx.infcx(), param_env, impl_def_id, substs, assoc_ty.defining_node);
|
||
let ty = tcx.type_of(assoc_ty.item.def_id);
|
||
if substs.len() != tcx.generics_of(assoc_ty.item.def_id).count() {
|
||
let err = tcx.ty_error_with_message(
|
||
obligation.cause.span,
|
||
"impl item and trait item have different parameter counts",
|
||
);
|
||
Progress { ty: err, obligations: nested }
|
||
} else {
|
||
assoc_ty_own_obligations(selcx, obligation, &mut nested);
|
||
Progress { ty: ty.subst(tcx, substs), obligations: nested }
|
||
}
|
||
}
|
||
|
||
// Get obligations corresponding to the predicates from the where-clause of the
|
||
// associated type itself.
|
||
// Note: `feature(generic_associated_types)` is required to write such
|
||
// predicates, even for non-generic associcated types.
|
||
fn assoc_ty_own_obligations<'cx, 'tcx>(
|
||
selcx: &mut SelectionContext<'cx, 'tcx>,
|
||
obligation: &ProjectionTyObligation<'tcx>,
|
||
nested: &mut Vec<PredicateObligation<'tcx>>,
|
||
) {
|
||
let tcx = selcx.tcx();
|
||
for predicate in tcx
|
||
.predicates_of(obligation.predicate.item_def_id)
|
||
.instantiate_own(tcx, obligation.predicate.substs)
|
||
.predicates
|
||
{
|
||
let normalized = normalize_with_depth_to(
|
||
selcx,
|
||
obligation.param_env,
|
||
obligation.cause.clone(),
|
||
obligation.recursion_depth + 1,
|
||
predicate,
|
||
nested,
|
||
);
|
||
nested.push(Obligation::with_depth(
|
||
obligation.cause.clone(),
|
||
obligation.recursion_depth + 1,
|
||
obligation.param_env,
|
||
normalized,
|
||
));
|
||
}
|
||
}
|
||
|
||
/// Locate the definition of an associated type in the specialization hierarchy,
|
||
/// starting from the given impl.
|
||
///
|
||
/// Based on the "projection mode", this lookup may in fact only examine the
|
||
/// topmost impl. See the comments for `Reveal` for more details.
|
||
fn assoc_ty_def(
|
||
selcx: &SelectionContext<'_, '_>,
|
||
impl_def_id: DefId,
|
||
assoc_ty_def_id: DefId,
|
||
) -> Result<specialization_graph::LeafDef, ErrorReported> {
|
||
let tcx = selcx.tcx();
|
||
let assoc_ty_name = tcx.associated_item(assoc_ty_def_id).ident;
|
||
let trait_def_id = tcx.impl_trait_ref(impl_def_id).unwrap().def_id;
|
||
let trait_def = tcx.trait_def(trait_def_id);
|
||
|
||
// This function may be called while we are still building the
|
||
// specialization graph that is queried below (via TraitDef::ancestors()),
|
||
// so, in order to avoid unnecessary infinite recursion, we manually look
|
||
// for the associated item at the given impl.
|
||
// If there is no such item in that impl, this function will fail with a
|
||
// cycle error if the specialization graph is currently being built.
|
||
let impl_node = specialization_graph::Node::Impl(impl_def_id);
|
||
for item in impl_node.items(tcx) {
|
||
if matches!(item.kind, ty::AssocKind::Type)
|
||
&& tcx.hygienic_eq(item.ident, assoc_ty_name, trait_def_id)
|
||
{
|
||
return Ok(specialization_graph::LeafDef {
|
||
item: *item,
|
||
defining_node: impl_node,
|
||
finalizing_node: if item.defaultness.is_default() { None } else { Some(impl_node) },
|
||
});
|
||
}
|
||
}
|
||
|
||
let ancestors = trait_def.ancestors(tcx, impl_def_id)?;
|
||
if let Some(assoc_item) = ancestors.leaf_def(tcx, assoc_ty_name, ty::AssocKind::Type) {
|
||
Ok(assoc_item)
|
||
} else {
|
||
// This is saying that neither the trait nor
|
||
// the impl contain a definition for this
|
||
// associated type. Normally this situation
|
||
// could only arise through a compiler bug --
|
||
// if the user wrote a bad item name, it
|
||
// should have failed in astconv.
|
||
bug!("No associated type `{}` for {}", assoc_ty_name, tcx.def_path_str(impl_def_id))
|
||
}
|
||
}
|
||
|
||
crate trait ProjectionCacheKeyExt<'tcx>: Sized {
|
||
fn from_poly_projection_predicate(
|
||
selcx: &mut SelectionContext<'cx, 'tcx>,
|
||
predicate: ty::PolyProjectionPredicate<'tcx>,
|
||
) -> Option<Self>;
|
||
}
|
||
|
||
impl<'tcx> ProjectionCacheKeyExt<'tcx> for ProjectionCacheKey<'tcx> {
|
||
fn from_poly_projection_predicate(
|
||
selcx: &mut SelectionContext<'cx, 'tcx>,
|
||
predicate: ty::PolyProjectionPredicate<'tcx>,
|
||
) -> Option<Self> {
|
||
let infcx = selcx.infcx();
|
||
// We don't do cross-snapshot caching of obligations with escaping regions,
|
||
// so there's no cache key to use
|
||
predicate.no_bound_vars().map(|predicate| {
|
||
ProjectionCacheKey::new(
|
||
// We don't attempt to match up with a specific type-variable state
|
||
// from a specific call to `opt_normalize_projection_type` - if
|
||
// there's no precise match, the original cache entry is "stranded"
|
||
// anyway.
|
||
infcx.resolve_vars_if_possible(predicate.projection_ty),
|
||
)
|
||
})
|
||
}
|
||
}
|