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https://github.com/rust-lang/rust.git
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1534 lines
59 KiB
Rust
1534 lines
59 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, 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;
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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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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 a "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 = "debug", 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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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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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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}
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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 }
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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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if !value.has_projections() { value } else { value.fold_with(self) }
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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_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
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if !ty.has_projections() {
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return ty;
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}
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// We don't want to normalize associated types that occur inside of region
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// binders, because they may contain bound regions, and we can't cope with that.
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//
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// Example:
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//
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// for<'a> fn(<T as Foo<&'a>>::A)
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//
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// Instead of normalizing `<T as Foo<&'a>>::A` here, we'll
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// normalize it when we instantiate those bound regions (which
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// should occur eventually).
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let ty = ty.super_fold_with(self);
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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,
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Reveal::All => {
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let recursion_limit = self.tcx().sess.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 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(ref data) if !data.has_escaping_bound_vars() => {
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// This is kind of hacky -- we need to be able to
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// handle normalization within binders because
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// otherwise we wind up a need to normalize when doing
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// trait matching (since you can have a trait
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// obligation like `for<'a> T::B: Fn(&'a i32)`), but
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// we can't normalize with bound regions in scope. So
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// far now we just ignore binders but only normalize
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// if all bound regions are gone (and then we still
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// have to renormalize whenever we instantiate a
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// binder). It would be better to normalize in a
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// binding-aware fashion.
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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,
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}
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}
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fn fold_const(&mut self, constant: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
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if self.selcx.tcx().lazy_normalization() {
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constant
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} else {
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let constant = constant.super_fold_with(self);
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constant.eval(self.selcx.tcx(), self.param_env)
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}
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}
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}
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/// The guts of `normalize`: normalize a specific projection like `<T
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/// as Trait>::Item`. The result is always a type (and possibly
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/// additional obligations). If ambiguity arises, which implies that
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/// there are unresolved type variables in the projection, we will
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/// substitute a fresh type variable `$X` and generate a new
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/// obligation `<T as Trait>::Item == $X` for later.
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pub fn normalize_projection_type<'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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projection_ty: ty::ProjectionTy<'tcx>,
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cause: ObligationCause<'tcx>,
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depth: usize,
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obligations: &mut Vec<PredicateObligation<'tcx>>,
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) -> Ty<'tcx> {
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opt_normalize_projection_type(
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selcx,
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param_env,
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projection_ty,
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cause.clone(),
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depth,
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obligations,
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)
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.ok()
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.flatten()
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.unwrap_or_else(move || {
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// if we bottom out in ambiguity, create a type variable
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// and a deferred predicate to resolve this when more type
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// information is available.
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let tcx = selcx.infcx().tcx;
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let def_id = projection_ty.item_def_id;
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let ty_var = selcx.infcx().next_ty_var(TypeVariableOrigin {
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kind: TypeVariableOriginKind::NormalizeProjectionType,
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span: tcx.def_span(def_id),
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});
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let projection = ty::Binder::dummy(ty::ProjectionPredicate { projection_ty, ty: ty_var });
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let obligation =
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Obligation::with_depth(cause, depth + 1, param_env, projection.to_predicate(tcx));
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obligations.push(obligation);
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ty_var
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})
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}
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|
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/// The guts of `normalize`: normalize a specific projection like `<T
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/// as Trait>::Item`. The result is always a type (and possibly
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/// additional obligations). Returns `None` in the case of ambiguity,
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/// which indicates that there are unbound type variables.
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///
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/// This function used to return `Option<NormalizedTy<'tcx>>`, which contains a
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/// `Ty<'tcx>` and an obligations vector. But that obligation vector was very
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/// often immediately appended to another obligations vector. So now this
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/// function takes an obligations vector and appends to it directly, which is
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/// slightly uglier but avoids the need for an extra short-lived allocation.
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#[instrument(level = "debug", skip(selcx, param_env, cause, obligations))]
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fn opt_normalize_projection_type<'a, 'b, 'tcx>(
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selcx: &'a mut SelectionContext<'b, 'tcx>,
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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(()) => {}
|
|
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) => {
|
|
// If while normalized A::B, we are asked to normalize
|
|
// A::B, just return A::B itself. This is a conservative
|
|
// answer, in the sense that A::B *is* clearly equivalent
|
|
// to A::B, though there may be a better value we can
|
|
// find.
|
|
|
|
// 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");
|
|
|
|
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");
|
|
|
|
// Once we have inferred everything we need to know, we
|
|
// can ignore the `obligations` from that point on.
|
|
if infcx.unresolved_type_vars(&ty.value).is_none() {
|
|
infcx.inner.borrow_mut().projection_cache().complete_normalized(cache_key, &ty);
|
|
// No need to extend `obligations`.
|
|
} else {
|
|
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
|
|
|
|
debug!(?projected_ty, ?depth, ?projected_obligations);
|
|
|
|
let 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 cache_value = prune_cache_value_obligations(infcx, &result);
|
|
infcx.inner.borrow_mut().projection_cache().insert_ty(cache_key, cache_value);
|
|
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 there are unresolved type variables, then we need to include
|
|
/// any subobligations that bind them, at least until those type
|
|
/// variables are fully resolved.
|
|
fn prune_cache_value_obligations<'a, 'tcx>(
|
|
infcx: &'a InferCtxt<'a, 'tcx>,
|
|
result: &NormalizedTy<'tcx>,
|
|
) -> NormalizedTy<'tcx> {
|
|
if infcx.unresolved_type_vars(&result.value).is_none() {
|
|
return NormalizedTy { value: result.value, obligations: vec![] };
|
|
}
|
|
|
|
let mut obligations: Vec<_> = result
|
|
.obligations
|
|
.iter()
|
|
.filter(|obligation| {
|
|
let bound_predicate = obligation.predicate.bound_atom();
|
|
match bound_predicate.skip_binder() {
|
|
// We found a `T: Foo<X = U>` predicate, let's check
|
|
// if `U` references any unresolved type
|
|
// variables. In principle, we only care if this
|
|
// projection can help resolve any of the type
|
|
// variables found in `result.value` -- but we just
|
|
// check for any type variables here, for fear of
|
|
// indirect obligations (e.g., we project to `?0`,
|
|
// but we have `T: Foo<X = ?1>` and `?1: Bar<X =
|
|
// ?0>`).
|
|
ty::PredicateAtom::Projection(data) => {
|
|
infcx.unresolved_type_vars(&bound_predicate.rebind(data.ty)).is_some()
|
|
}
|
|
|
|
// We are only interested in `T: Foo<X = U>` predicates, whre
|
|
// `U` references one of `unresolved_type_vars`. =)
|
|
_ => false,
|
|
}
|
|
})
|
|
.cloned()
|
|
.collect();
|
|
|
|
obligations.shrink_to_fit();
|
|
|
|
NormalizedTy { value: result.value, obligations }
|
|
}
|
|
|
|
/// 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 a `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
|
|
fn project_type<'cx, 'tcx>(
|
|
selcx: &mut SelectionContext<'cx, 'tcx>,
|
|
obligation: &ProjectionTyObligation<'tcx>,
|
|
) -> Result<ProjectedTy<'tcx>, ProjectionTyError<'tcx>> {
|
|
debug!(?obligation, "project_type");
|
|
|
|
if !selcx.tcx().sess.recursion_limit().value_within_limit(obligation.recursion_depth) {
|
|
debug!("project: overflow!");
|
|
return Err(ProjectionTyError::TraitSelectionError(SelectionError::Overflow));
|
|
}
|
|
|
|
let obligation_trait_ref = &obligation.predicate.trait_ref(selcx.tcx());
|
|
|
|
debug!(?obligation_trait_ref);
|
|
|
|
if obligation_trait_ref.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, &obligation_trait_ref, &mut candidates);
|
|
|
|
assemble_candidates_from_trait_def(selcx, obligation, &obligation_trait_ref, &mut candidates);
|
|
|
|
assemble_candidates_from_object_ty(selcx, obligation, &obligation_trait_ref, &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 do special case this.
|
|
} else {
|
|
assemble_candidates_from_impls(selcx, obligation, &obligation_trait_ref, &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>,
|
|
obligation_trait_ref: &ty::TraitRef<'tcx>,
|
|
candidate_set: &mut ProjectionTyCandidateSet<'tcx>,
|
|
) {
|
|
debug!("assemble_candidates_from_param_env(..)");
|
|
assemble_candidates_from_predicates(
|
|
selcx,
|
|
obligation,
|
|
obligation_trait_ref,
|
|
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>,
|
|
obligation_trait_ref: &ty::TraitRef<'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_trait_ref.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,
|
|
obligation_trait_ref,
|
|
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>,
|
|
obligation_trait_ref: &ty::TraitRef<'tcx>,
|
|
candidate_set: &mut ProjectionTyCandidateSet<'tcx>,
|
|
) {
|
|
debug!("assemble_candidates_from_object_ty(..)");
|
|
|
|
let tcx = selcx.tcx();
|
|
|
|
let self_ty = obligation_trait_ref.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,
|
|
obligation_trait_ref,
|
|
candidate_set,
|
|
ProjectionTyCandidate::Object,
|
|
env_predicates,
|
|
false,
|
|
);
|
|
}
|
|
|
|
fn assemble_candidates_from_predicates<'cx, 'tcx>(
|
|
selcx: &mut SelectionContext<'cx, 'tcx>,
|
|
obligation: &ProjectionTyObligation<'tcx>,
|
|
obligation_trait_ref: &ty::TraitRef<'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.bound_atom();
|
|
if let ty::PredicateAtom::Projection(data) = predicate.skip_binders() {
|
|
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,
|
|
obligation_trait_ref,
|
|
&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>,
|
|
obligation_trait_ref: &ty::TraitRef<'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_trait_ref.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::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::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(..) => {
|
|
// 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::Object(_)
|
|
| super::ImplSource::AutoImpl(..)
|
|
| super::ImplSource::Param(..)
|
|
| super::ImplSource::Builtin(..)
|
|
| 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());
|
|
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),
|
|
};
|
|
|
|
confirm_param_env_candidate(selcx, obligation, ty::Binder::bind(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_trait_ref = cache_entry.projection_ty.trait_ref(infcx.tcx);
|
|
let obligation_trait_ref = obligation.predicate.trait_ref(infcx.tcx);
|
|
let mut nested_obligations = Vec::new();
|
|
let cache_trait_ref = if potentially_unnormalized_candidate {
|
|
ensure_sufficient_stack(|| {
|
|
normalize_with_depth_to(
|
|
selcx,
|
|
obligation.param_env,
|
|
obligation.cause.clone(),
|
|
obligation.recursion_depth + 1,
|
|
&cache_trait_ref,
|
|
&mut nested_obligations,
|
|
)
|
|
})
|
|
} else {
|
|
cache_trait_ref
|
|
};
|
|
|
|
match infcx.at(cause, param_env).eq(cache_trait_ref, obligation_trait_ref) {
|
|
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),
|
|
)
|
|
})
|
|
}
|
|
}
|