1726 lines
68 KiB
Rust
1726 lines
68 KiB
Rust
//! Code for projecting associated types out of trait references.
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use super::elaborate_predicates;
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use super::specialization_graph;
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use super::translate_substs;
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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::{VtableImplData, VtableClosureData, VtableGeneratorData, VtableFnPointerData};
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use super::util;
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use crate::hir::def_id::DefId;
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use crate::infer::{InferCtxt, InferOk, LateBoundRegionConversionTime};
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use crate::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
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use crate::mir::interpret::{GlobalId, ConstValue};
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use rustc_data_structures::snapshot_map::{Snapshot, SnapshotMap};
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use rustc_macros::HashStable;
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use syntax::ast::Ident;
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use syntax::symbol::sym;
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use crate::ty::subst::{Subst, InternalSubsts};
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use crate::ty::{self, ToPredicate, ToPolyTraitRef, Ty, TyCtxt};
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use crate::ty::fold::{TypeFoldable, TypeFolder};
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use crate::util::common::FN_OUTPUT_NAME;
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/// Depending on the stage of compilation, we want projection to be
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/// more or less conservative.
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#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash, HashStable)]
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pub enum Reveal {
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/// At type-checking time, we refuse to project any associated
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/// type that is marked `default`. Non-`default` ("final") types
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/// are always projected. This is necessary in general for
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/// soundness of specialization. However, we *could* allow
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/// projections in fully-monomorphic cases. We choose not to,
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/// because we prefer for `default type` to force the type
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/// definition to be treated abstractly by any consumers of the
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/// impl. Concretely, that means that the following example will
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/// fail to compile:
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///
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/// ```
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/// trait Assoc {
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/// type Output;
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/// }
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///
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/// impl<T> Assoc for T {
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/// default type Output = bool;
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/// }
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///
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/// fn main() {
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/// let <() as Assoc>::Output = true;
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/// }
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UserFacing,
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/// At codegen time, all monomorphic projections will succeed.
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/// Also, `impl Trait` is normalized to the concrete type,
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/// which has to be already collected by type-checking.
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///
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/// NOTE: as `impl Trait`'s concrete type should *never*
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/// be observable directly by the user, `Reveal::All`
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/// should not be used by checks which may expose
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/// type equality or type contents to the user.
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/// There are some exceptions, e.g., around OIBITS and
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/// transmute-checking, which expose some details, but
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/// not the whole concrete type of the `impl Trait`.
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All,
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}
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pub type PolyProjectionObligation<'tcx> =
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Obligation<'tcx, ty::PolyProjectionPredicate<'tcx>>;
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pub type ProjectionObligation<'tcx> =
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Obligation<'tcx, ty::ProjectionPredicate<'tcx>>;
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pub type ProjectionTyObligation<'tcx> =
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Obligation<'tcx, ty::ProjectionTy<'tcx>>;
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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(Clone)]
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pub struct MismatchedProjectionTypes<'tcx> {
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pub err: ty::error::TypeError<'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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// 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::ProjectionTyCandidateSet::*;
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use self::ProjectionTyCandidate::*;
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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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pub 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<Option<Vec<PredicateObligation<'tcx>>>, MismatchedProjectionTypes<'tcx>> {
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debug!("poly_project_and_unify_type(obligation={:?})",
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obligation);
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let infcx = selcx.infcx();
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infcx.commit_if_ok(|snapshot| {
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let (placeholder_predicate, placeholder_map) =
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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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infcx.leak_check(false, &placeholder_map, snapshot)
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.map_err(|err| MismatchedProjectionTypes { err })?;
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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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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<Option<Vec<PredicateObligation<'tcx>>>, MismatchedProjectionTypes<'tcx>> {
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debug!("project_and_unify_type(obligation={:?})",
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obligation);
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let mut obligations = vec![];
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let normalized_ty =
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match opt_normalize_projection_type(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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Some(n) => n,
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None => return Ok(None),
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};
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debug!("project_and_unify_type: normalized_ty={:?} obligations={:?}",
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normalized_ty,
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obligations);
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let infcx = selcx.infcx();
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match infcx.at(&obligation.cause, obligation.param_env)
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.eq(normalized_ty, obligation.predicate.ty) {
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Ok(InferOk { obligations: inferred_obligations, value: () }) => {
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obligations.extend(inferred_obligations);
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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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normalize_with_depth(selcx, param_env, cause, 0, value)
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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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debug!("normalize_with_depth(depth={}, value={:?})", depth, value);
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let mut normalizer = AssocTypeNormalizer::new(selcx, param_env, cause, depth);
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let result = normalizer.fold(value);
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debug!("normalize_with_depth: depth={} result={:?} with {} obligations",
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depth, result, normalizer.obligations.len());
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debug!("normalize_with_depth: depth={} obligations={:?}",
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depth, normalizer.obligations);
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Normalized {
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value: result,
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obligations: normalizer.obligations,
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}
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}
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struct AssocTypeNormalizer<'a, 'b: 'a, 'tcx: 'b> {
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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: 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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) -> AssocTypeNormalizer<'a, 'b, 'tcx> {
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AssocTypeNormalizer {
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selcx,
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param_env,
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cause,
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obligations: vec![],
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depth,
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}
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}
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fn fold<T:TypeFoldable<'tcx>>(&mut self, value: &T) -> T {
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let value = self.selcx.infcx().resolve_vars_if_possible(value);
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if !value.has_projections() {
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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_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
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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.sty {
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ty::Opaque(def_id, substs) if !substs.has_escaping_bound_vars() => { // (*)
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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.get();
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if self.depth >= recursion_limit {
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let obligation = Obligation::with_depth(
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self.cause.clone(),
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recursion_limit,
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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 int)`), 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(self.selcx,
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self.param_env,
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data.clone(),
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self.cause.clone(),
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self.depth,
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&mut self.obligations);
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debug!("AssocTypeNormalizer: depth={} normalized {:?} to {:?}, \
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now with {} obligations",
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self.depth, ty, normalized_ty, self.obligations.len());
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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 let ConstValue::Unevaluated(def_id, substs) = constant.val {
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let tcx = self.selcx.tcx().global_tcx();
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if let Some(param_env) = self.tcx().lift_to_global(&self.param_env) {
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if substs.needs_infer() || substs.has_placeholders() {
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let identity_substs = InternalSubsts::identity_for_item(tcx, def_id);
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let instance = ty::Instance::resolve(tcx, param_env, def_id, identity_substs);
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if let Some(instance) = instance {
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let cid = GlobalId {
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instance,
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promoted: None
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};
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if let Ok(evaluated) = tcx.const_eval(param_env.and(cid)) {
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let evaluated = evaluated.subst(tcx, substs);
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return evaluated;
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}
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}
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} else {
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if let Some(substs) = self.tcx().lift_to_global(&substs) {
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let instance = ty::Instance::resolve(tcx, param_env, def_id, substs);
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if let Some(instance) = instance {
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let cid = GlobalId {
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instance,
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promoted: None
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};
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if let Ok(evaluated) = tcx.const_eval(param_env.and(cid)) {
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return evaluated;
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}
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}
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}
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}
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}
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}
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constant
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}
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}
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#[derive(Clone)]
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pub struct Normalized<'tcx,T> {
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pub value: T,
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pub obligations: Vec<PredicateObligation<'tcx>>,
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}
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pub type NormalizedTy<'tcx> = Normalized<'tcx, Ty<'tcx>>;
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impl<'tcx,T> Normalized<'tcx,T> {
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pub fn with<U>(self, value: U) -> Normalized<'tcx,U> {
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Normalized { value: value, obligations: self.obligations }
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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(selcx, param_env, projection_ty.clone(), cause.clone(), depth,
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obligations)
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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(
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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
|
|
});
|
|
let obligation = Obligation::with_depth(
|
|
cause, depth + 1, param_env, projection.to_predicate());
|
|
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.
|
|
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>>,
|
|
) -> Option<Ty<'tcx>> {
|
|
let infcx = selcx.infcx();
|
|
|
|
let projection_ty = infcx.resolve_vars_if_possible(&projection_ty);
|
|
let cache_key = ProjectionCacheKey { ty: projection_ty };
|
|
|
|
debug!("opt_normalize_projection_type(\
|
|
projection_ty={:?}, \
|
|
depth={})",
|
|
projection_ty,
|
|
depth);
|
|
|
|
// 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.projection_cache.borrow_mut().try_start(cache_key);
|
|
match cache_result {
|
|
Ok(()) => { }
|
|
Err(ProjectionCacheEntry::Ambiguous) => {
|
|
// If we found ambiguity the last time, that generally
|
|
// 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). One exception though is closure
|
|
// types, which can transition from having a fixed kind to
|
|
// no kind with no visible change in the key.
|
|
//
|
|
// FIXME(#32286) refactor this so that closure type
|
|
// changes
|
|
debug!("opt_normalize_projection_type: \
|
|
found cache entry: ambiguous");
|
|
if !projection_ty.has_closure_types() {
|
|
return 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. In that case, I think we will want this code:
|
|
//
|
|
// ```
|
|
// let ty = selcx.tcx().mk_projection(projection_ty.item_def_id,
|
|
// projection_ty.substs;
|
|
// return Some(NormalizedTy { value: v, obligations: vec![] });
|
|
// ```
|
|
|
|
debug!("opt_normalize_projection_type: \
|
|
found cache entry: in-progress");
|
|
|
|
// But for now, let's classify this as an overflow:
|
|
let recursion_limit = *selcx.tcx().sess.recursion_limit.get();
|
|
let obligation = Obligation::with_depth(cause,
|
|
recursion_limit,
|
|
param_env,
|
|
projection_ty);
|
|
selcx.infcx().report_overflow_error(&obligation, false);
|
|
}
|
|
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!("opt_normalize_projection_type: \
|
|
found normalized ty `{:?}`",
|
|
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.projection_cache.borrow_mut().complete_normalized(cache_key, &ty);
|
|
// No need to extend `obligations`.
|
|
} else {
|
|
obligations.extend(ty.obligations);
|
|
}
|
|
|
|
obligations.push(get_paranoid_cache_value_obligation(infcx,
|
|
param_env,
|
|
projection_ty,
|
|
cause,
|
|
depth));
|
|
return 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 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!("opt_normalize_projection_type: \
|
|
projected_ty={:?} \
|
|
depth={} \
|
|
projected_obligations={:?}",
|
|
projected_ty,
|
|
depth,
|
|
projected_obligations);
|
|
|
|
let result = if projected_ty.has_projections() {
|
|
let mut normalizer = AssocTypeNormalizer::new(selcx,
|
|
param_env,
|
|
cause,
|
|
depth+1);
|
|
let normalized_ty = normalizer.fold(&projected_ty);
|
|
|
|
debug!("opt_normalize_projection_type: \
|
|
normalized_ty={:?} depth={}",
|
|
normalized_ty,
|
|
depth);
|
|
|
|
projected_obligations.extend(normalizer.obligations);
|
|
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.projection_cache.borrow_mut().insert_ty(cache_key, cache_value);
|
|
obligations.extend(result.obligations);
|
|
Some(result.value)
|
|
}
|
|
Ok(ProjectedTy::NoProgress(projected_ty)) => {
|
|
debug!("opt_normalize_projection_type: \
|
|
projected_ty={:?} no progress",
|
|
projected_ty);
|
|
let result = Normalized {
|
|
value: projected_ty,
|
|
obligations: vec![]
|
|
};
|
|
infcx.projection_cache.borrow_mut().insert_ty(cache_key, result.clone());
|
|
// No need to extend `obligations`.
|
|
Some(result.value)
|
|
}
|
|
Err(ProjectionTyError::TooManyCandidates) => {
|
|
debug!("opt_normalize_projection_type: \
|
|
too many candidates");
|
|
infcx.projection_cache.borrow_mut()
|
|
.ambiguous(cache_key);
|
|
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.projection_cache.borrow_mut()
|
|
.error(cache_key);
|
|
let result = normalize_to_error(selcx, param_env, projection_ty, cause, depth);
|
|
obligations.extend(result.obligations);
|
|
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| match obligation.predicate {
|
|
// 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::Predicate::Projection(ref data) =>
|
|
infcx.unresolved_type_vars(&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 }
|
|
}
|
|
|
|
/// Whenever we give back a cache result for a projection like `<T as
|
|
/// Trait>::Item ==> X`, we *always* include the obligation to prove
|
|
/// that `T: Trait` (we may also include some other obligations). This
|
|
/// may or may not be necessary -- in principle, all the obligations
|
|
/// that must be proven to show that `T: Trait` were also returned
|
|
/// when the cache was first populated. But there are some vague concerns,
|
|
/// and so we take the precautionary measure of including `T: Trait` in
|
|
/// the result:
|
|
///
|
|
/// Concern #1. The current setup is fragile. Perhaps someone could
|
|
/// have failed to prove the concerns from when the cache was
|
|
/// populated, but also not have used a snapshot, in which case the
|
|
/// cache could remain populated even though `T: Trait` has not been
|
|
/// shown. In this case, the "other code" is at fault -- when you
|
|
/// project something, you are supposed to either have a snapshot or
|
|
/// else prove all the resulting obligations -- but it's still easy to
|
|
/// get wrong.
|
|
///
|
|
/// Concern #2. Even within the snapshot, if those original
|
|
/// obligations are not yet proven, then we are able to do projections
|
|
/// that may yet turn out to be wrong. This *may* lead to some sort
|
|
/// of trouble, though we don't have a concrete example of how that
|
|
/// can occur yet. But it seems risky at best.
|
|
fn get_paranoid_cache_value_obligation<'a, 'tcx>(
|
|
infcx: &'a InferCtxt<'a, 'tcx>,
|
|
param_env: ty::ParamEnv<'tcx>,
|
|
projection_ty: ty::ProjectionTy<'tcx>,
|
|
cause: ObligationCause<'tcx>,
|
|
depth: usize,
|
|
) -> PredicateObligation<'tcx> {
|
|
let trait_ref = projection_ty.trait_ref(infcx.tcx).to_poly_trait_ref();
|
|
Obligation {
|
|
cause,
|
|
recursion_depth: depth,
|
|
param_env,
|
|
predicate: trait_ref.to_predicate(),
|
|
}
|
|
}
|
|
|
|
/// 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.to_predicate() };
|
|
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.types.err,
|
|
obligations: vec![],
|
|
}
|
|
}
|
|
|
|
fn with_addl_obligations(mut self,
|
|
mut obligations: Vec<PredicateObligation<'tcx>>)
|
|
-> Self {
|
|
debug!("with_addl_obligations: self.obligations.len={} obligations.len={}",
|
|
self.obligations.len(), obligations.len());
|
|
|
|
debug!("with_addl_obligations: self.obligations={:?} obligations={:?}",
|
|
self.obligations, 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!("project(obligation={:?})",
|
|
obligation);
|
|
|
|
let recursion_limit = *selcx.tcx().sess.recursion_limit.get();
|
|
if obligation.recursion_depth >= recursion_limit {
|
|
debug!("project: overflow!");
|
|
return Err(ProjectionTyError::TraitSelectionError(SelectionError::Overflow));
|
|
}
|
|
|
|
let obligation_trait_ref = &obligation.predicate.trait_ref(selcx.tcx());
|
|
|
|
debug!("project: obligation_trait_ref={:?}", 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_impls(selcx,
|
|
obligation,
|
|
&obligation_trait_ref,
|
|
&mut candidates);
|
|
|
|
match candidates {
|
|
ProjectionTyCandidateSet::Single(candidate) => Ok(ProjectedTy::Progress(
|
|
confirm_candidate(selcx,
|
|
obligation,
|
|
&obligation_trait_ref,
|
|
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().cloned());
|
|
}
|
|
|
|
/// 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.
|
|
let (def_id, substs) = match obligation_trait_ref.self_ty().sty {
|
|
ty::Projection(ref data) => {
|
|
(data.trait_ref(tcx).def_id, data.substs)
|
|
}
|
|
ty::Opaque(def_id, substs) => (def_id, 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
|
|
};
|
|
|
|
// If so, extract what we know from the trait and try to come up with a good answer.
|
|
let trait_predicates = tcx.predicates_of(def_id);
|
|
let bounds = trait_predicates.instantiate(tcx, substs);
|
|
let bounds = elaborate_predicates(tcx, bounds.predicates);
|
|
assemble_candidates_from_predicates(selcx,
|
|
obligation,
|
|
obligation_trait_ref,
|
|
candidate_set,
|
|
ProjectionTyCandidate::TraitDef,
|
|
bounds)
|
|
}
|
|
|
|
fn assemble_candidates_from_predicates<'cx, 'tcx, I>(
|
|
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: I,
|
|
) where
|
|
I: IntoIterator<Item = ty::Predicate<'tcx>>,
|
|
{
|
|
debug!("assemble_candidates_from_predicates(obligation={:?})",
|
|
obligation);
|
|
let infcx = selcx.infcx();
|
|
for predicate in env_predicates {
|
|
debug!("assemble_candidates_from_predicates: predicate={:?}",
|
|
predicate);
|
|
if let ty::Predicate::Projection(data) = predicate {
|
|
let same_def_id = data.projection_def_id() == obligation.predicate.item_def_id;
|
|
|
|
let is_match = same_def_id && infcx.probe(|_| {
|
|
let data_poly_trait_ref =
|
|
data.to_poly_trait_ref(infcx.tcx);
|
|
let obligation_poly_trait_ref =
|
|
obligation_trait_ref.to_poly_trait_ref();
|
|
infcx.at(&obligation.cause, obligation.param_env)
|
|
.sup(obligation_poly_trait_ref, data_poly_trait_ref)
|
|
.map(|InferOk { obligations: _, value: () }| {
|
|
// FIXME(#32730) -- do we need to take obligations
|
|
// into account in any way? At the moment, no.
|
|
})
|
|
.is_ok()
|
|
});
|
|
|
|
debug!("assemble_candidates_from_predicates: candidate={:?} \
|
|
is_match={} same_def_id={}",
|
|
data, is_match, same_def_id);
|
|
|
|
if is_match {
|
|
candidate_set.push_candidate(ctor(data));
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
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>,
|
|
) {
|
|
// 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 vtable = match selcx.select(&trait_obligation) {
|
|
Ok(Some(vtable)) => vtable,
|
|
Ok(None) => {
|
|
candidate_set.mark_ambiguous();
|
|
return Err(());
|
|
}
|
|
Err(e) => {
|
|
debug!("assemble_candidates_from_impls: selection error {:?}", e);
|
|
candidate_set.mark_error(e);
|
|
return Err(());
|
|
}
|
|
};
|
|
|
|
let eligible = match &vtable {
|
|
super::VtableClosure(_) |
|
|
super::VtableGenerator(_) |
|
|
super::VtableFnPointer(_) |
|
|
super::VtableObject(_) |
|
|
super::VtableTraitAlias(_) => {
|
|
debug!("assemble_candidates_from_impls: vtable={:?}",
|
|
vtable);
|
|
true
|
|
}
|
|
super::VtableImpl(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.
|
|
let node_item = assoc_ty_def(selcx,
|
|
impl_data.impl_def_id,
|
|
obligation.predicate.item_def_id);
|
|
|
|
let is_default = if node_item.node.is_from_trait() {
|
|
// If true, the impl inherited a `type Foo = Bar`
|
|
// given in the trait, which is implicitly default.
|
|
// Otherwise, the impl did not specify `type` and
|
|
// neither did the trait:
|
|
//
|
|
// ```rust
|
|
// trait Foo { type T; }
|
|
// impl Foo for Bar { }
|
|
// ```
|
|
//
|
|
// This is an error, but it will be
|
|
// reported in `check_impl_items_against_trait`.
|
|
// We accept it here but will flag it as
|
|
// an error when we confirm the candidate
|
|
// (which will ultimately lead to `normalize_to_error`
|
|
// being invoked).
|
|
node_item.item.defaultness.has_value()
|
|
} else {
|
|
node_item.item.defaultness.is_default() ||
|
|
selcx.tcx().impl_is_default(node_item.node.def_id())
|
|
};
|
|
|
|
// Only reveal a specializable default if we're past type-checking
|
|
// and the obligations is monomorphic, otherwise passes such as
|
|
// transmute checking and polymorphic MIR optimizations could
|
|
// get a result which isn't correct for all monomorphizations.
|
|
if !is_default {
|
|
true
|
|
} else if obligation.param_env.reveal == Reveal::All {
|
|
debug_assert!(!poly_trait_ref.needs_infer());
|
|
if !poly_trait_ref.needs_subst() {
|
|
true
|
|
} else {
|
|
false
|
|
}
|
|
} else {
|
|
false
|
|
}
|
|
}
|
|
super::VtableParam(..) => {
|
|
// 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::VtableAutoImpl(..) |
|
|
super::VtableBuiltin(..) => {
|
|
// These traits have no associated types.
|
|
span_bug!(
|
|
obligation.cause.span,
|
|
"Cannot project an associated type from `{:?}`",
|
|
vtable);
|
|
}
|
|
};
|
|
|
|
if eligible {
|
|
if candidate_set.push_candidate(ProjectionTyCandidate::Select(vtable)) {
|
|
Ok(())
|
|
} else {
|
|
Err(())
|
|
}
|
|
} else {
|
|
Err(())
|
|
}
|
|
});
|
|
}
|
|
|
|
fn confirm_candidate<'cx, 'tcx>(
|
|
selcx: &mut SelectionContext<'cx, 'tcx>,
|
|
obligation: &ProjectionTyObligation<'tcx>,
|
|
obligation_trait_ref: &ty::TraitRef<'tcx>,
|
|
candidate: ProjectionTyCandidate<'tcx>,
|
|
) -> Progress<'tcx> {
|
|
debug!("confirm_candidate(candidate={:?}, obligation={:?})",
|
|
candidate,
|
|
obligation);
|
|
|
|
match candidate {
|
|
ProjectionTyCandidate::ParamEnv(poly_projection) |
|
|
ProjectionTyCandidate::TraitDef(poly_projection) => {
|
|
confirm_param_env_candidate(selcx, obligation, poly_projection)
|
|
}
|
|
|
|
ProjectionTyCandidate::Select(vtable) => {
|
|
confirm_select_candidate(selcx, obligation, obligation_trait_ref, vtable)
|
|
}
|
|
}
|
|
}
|
|
|
|
fn confirm_select_candidate<'cx, 'tcx>(
|
|
selcx: &mut SelectionContext<'cx, 'tcx>,
|
|
obligation: &ProjectionTyObligation<'tcx>,
|
|
obligation_trait_ref: &ty::TraitRef<'tcx>,
|
|
vtable: Selection<'tcx>,
|
|
) -> Progress<'tcx> {
|
|
match vtable {
|
|
super::VtableImpl(data) =>
|
|
confirm_impl_candidate(selcx, obligation, data),
|
|
super::VtableGenerator(data) =>
|
|
confirm_generator_candidate(selcx, obligation, data),
|
|
super::VtableClosure(data) =>
|
|
confirm_closure_candidate(selcx, obligation, data),
|
|
super::VtableFnPointer(data) =>
|
|
confirm_fn_pointer_candidate(selcx, obligation, data),
|
|
super::VtableObject(_) =>
|
|
confirm_object_candidate(selcx, obligation, obligation_trait_ref),
|
|
super::VtableAutoImpl(..) |
|
|
super::VtableParam(..) |
|
|
super::VtableBuiltin(..) |
|
|
super::VtableTraitAlias(..) =>
|
|
// we don't create Select candidates with this kind of resolution
|
|
span_bug!(
|
|
obligation.cause.span,
|
|
"Cannot project an associated type from `{:?}`",
|
|
vtable),
|
|
}
|
|
}
|
|
|
|
fn confirm_object_candidate<'cx, 'tcx>(
|
|
selcx: &mut SelectionContext<'cx, 'tcx>,
|
|
obligation: &ProjectionTyObligation<'tcx>,
|
|
obligation_trait_ref: &ty::TraitRef<'tcx>,
|
|
) -> Progress<'tcx> {
|
|
let self_ty = obligation_trait_ref.self_ty();
|
|
let object_ty = selcx.infcx().shallow_resolve(self_ty);
|
|
debug!("confirm_object_candidate(object_ty={:?})",
|
|
object_ty);
|
|
let data = match object_ty.sty {
|
|
ty::Dynamic(ref data, ..) => data,
|
|
_ => {
|
|
span_bug!(
|
|
obligation.cause.span,
|
|
"confirm_object_candidate called with non-object: {:?}",
|
|
object_ty)
|
|
}
|
|
};
|
|
let env_predicates = data.projection_bounds().map(|p| {
|
|
p.with_self_ty(selcx.tcx(), object_ty).to_predicate()
|
|
}).collect();
|
|
let env_predicate = {
|
|
let env_predicates = elaborate_predicates(selcx.tcx(), env_predicates);
|
|
|
|
// select only those projections that are actually projecting an
|
|
// item with the correct name
|
|
let env_predicates = env_predicates.filter_map(|p| match p {
|
|
ty::Predicate::Projection(data) =>
|
|
if data.projection_def_id() == obligation.predicate.item_def_id {
|
|
Some(data)
|
|
} else {
|
|
None
|
|
},
|
|
_ => None
|
|
});
|
|
|
|
// select those with a relevant trait-ref
|
|
let mut env_predicates = env_predicates.filter(|data| {
|
|
let data_poly_trait_ref = data.to_poly_trait_ref(selcx.tcx());
|
|
let obligation_poly_trait_ref = obligation_trait_ref.to_poly_trait_ref();
|
|
selcx.infcx().probe(|_|
|
|
selcx.infcx().at(&obligation.cause, obligation.param_env)
|
|
.sup(obligation_poly_trait_ref, data_poly_trait_ref)
|
|
.is_ok()
|
|
)
|
|
});
|
|
|
|
// select the first matching one; there really ought to be one or
|
|
// else the object type is not WF, since an object type should
|
|
// include all of its projections explicitly
|
|
match env_predicates.next() {
|
|
Some(env_predicate) => env_predicate,
|
|
None => {
|
|
debug!("confirm_object_candidate: no env-predicate \
|
|
found in object type `{:?}`; ill-formed",
|
|
object_ty);
|
|
return Progress::error(selcx.tcx());
|
|
}
|
|
}
|
|
};
|
|
|
|
confirm_param_env_candidate(selcx, obligation, env_predicate)
|
|
}
|
|
|
|
fn confirm_generator_candidate<'cx, 'tcx>(
|
|
selcx: &mut SelectionContext<'cx, 'tcx>,
|
|
obligation: &ProjectionTyObligation<'tcx>,
|
|
vtable: VtableGeneratorData<'tcx, PredicateObligation<'tcx>>,
|
|
) -> Progress<'tcx> {
|
|
let gen_sig = vtable.substs.poly_sig(vtable.generator_def_id, selcx.tcx());
|
|
let Normalized {
|
|
value: gen_sig,
|
|
obligations
|
|
} = normalize_with_depth(selcx,
|
|
obligation.param_env,
|
|
obligation.cause.clone(),
|
|
obligation.recursion_depth+1,
|
|
&gen_sig);
|
|
|
|
debug!("confirm_generator_candidate: obligation={:?},gen_sig={:?},obligations={:?}",
|
|
obligation,
|
|
gen_sig,
|
|
obligations);
|
|
|
|
let tcx = selcx.tcx();
|
|
|
|
let gen_def_id = tcx.lang_items().gen_trait().unwrap();
|
|
|
|
let predicate =
|
|
tcx.generator_trait_ref_and_outputs(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: ty
|
|
}
|
|
});
|
|
|
|
confirm_param_env_candidate(selcx, obligation, predicate)
|
|
.with_addl_obligations(vtable.nested)
|
|
.with_addl_obligations(obligations)
|
|
}
|
|
|
|
fn confirm_fn_pointer_candidate<'cx, 'tcx>(
|
|
selcx: &mut SelectionContext<'cx, 'tcx>,
|
|
obligation: &ProjectionTyObligation<'tcx>,
|
|
fn_pointer_vtable: VtableFnPointerData<'tcx, PredicateObligation<'tcx>>,
|
|
) -> Progress<'tcx> {
|
|
let fn_type = selcx.infcx().shallow_resolve(fn_pointer_vtable.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_vtable.nested)
|
|
.with_addl_obligations(obligations)
|
|
}
|
|
|
|
fn confirm_closure_candidate<'cx, 'tcx>(
|
|
selcx: &mut SelectionContext<'cx, 'tcx>,
|
|
obligation: &ProjectionTyObligation<'tcx>,
|
|
vtable: VtableClosureData<'tcx, PredicateObligation<'tcx>>,
|
|
) -> Progress<'tcx> {
|
|
let tcx = selcx.tcx();
|
|
let infcx = selcx.infcx();
|
|
let closure_sig_ty = vtable.substs.closure_sig_ty(vtable.closure_def_id, tcx);
|
|
let closure_sig = infcx.shallow_resolve(closure_sig_ty).fn_sig(tcx);
|
|
let Normalized {
|
|
value: closure_sig,
|
|
obligations
|
|
} = normalize_with_depth(selcx,
|
|
obligation.param_env,
|
|
obligation.cause.clone(),
|
|
obligation.recursion_depth+1,
|
|
&closure_sig);
|
|
|
|
debug!("confirm_closure_candidate: obligation={:?},closure_sig={:?},obligations={:?}",
|
|
obligation,
|
|
closure_sig,
|
|
obligations);
|
|
|
|
confirm_callable_candidate(selcx,
|
|
obligation,
|
|
closure_sig,
|
|
util::TupleArgumentsFlag::No)
|
|
.with_addl_obligations(vtable.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!("confirm_callable_candidate({:?},{:?})",
|
|
obligation,
|
|
fn_sig);
|
|
|
|
// the `Output` associated type is declared on `FnOnce`
|
|
let fn_once_def_id = tcx.lang_items().fn_once_trait().unwrap();
|
|
|
|
let predicate =
|
|
tcx.closure_trait_ref_and_return_type(fn_once_def_id,
|
|
obligation.predicate.self_ty(),
|
|
fn_sig,
|
|
flag)
|
|
.map_bound(|(trait_ref, ret_type)|
|
|
ty::ProjectionPredicate {
|
|
projection_ty: ty::ProjectionTy::from_ref_and_name(
|
|
tcx,
|
|
trait_ref,
|
|
Ident::with_empty_ctxt(FN_OUTPUT_NAME),
|
|
),
|
|
ty: ret_type
|
|
}
|
|
);
|
|
|
|
confirm_param_env_candidate(selcx, obligation, predicate)
|
|
}
|
|
|
|
fn confirm_param_env_candidate<'cx, 'tcx>(
|
|
selcx: &mut SelectionContext<'cx, 'tcx>,
|
|
obligation: &ProjectionTyObligation<'tcx>,
|
|
poly_cache_entry: ty::PolyProjectionPredicate<'tcx>,
|
|
) -> 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);
|
|
match infcx.at(cause, param_env).eq(cache_trait_ref, obligation_trait_ref) {
|
|
Ok(InferOk { value: _, obligations }) => {
|
|
Progress {
|
|
ty: cache_entry.ty,
|
|
obligations,
|
|
}
|
|
}
|
|
Err(e) => {
|
|
let msg = format!(
|
|
"Failed to unify obligation `{:?}` with poly_projection `{:?}`: {:?}",
|
|
obligation,
|
|
poly_cache_entry,
|
|
e,
|
|
);
|
|
debug!("confirm_param_env_candidate: {}", msg);
|
|
infcx.tcx.sess.delay_span_bug(obligation.cause.span, &msg);
|
|
Progress {
|
|
ty: infcx.tcx.types.err,
|
|
obligations: vec![],
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
fn confirm_impl_candidate<'cx, 'tcx>(
|
|
selcx: &mut SelectionContext<'cx, 'tcx>,
|
|
obligation: &ProjectionTyObligation<'tcx>,
|
|
impl_vtable: VtableImplData<'tcx, PredicateObligation<'tcx>>,
|
|
) -> Progress<'tcx> {
|
|
let VtableImplData { impl_def_id, substs, nested } = impl_vtable;
|
|
|
|
let tcx = selcx.tcx();
|
|
let param_env = obligation.param_env;
|
|
let assoc_ty = assoc_ty_def(selcx, impl_def_id, obligation.predicate.item_def_id);
|
|
|
|
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.types.err,
|
|
obligations: nested,
|
|
};
|
|
}
|
|
let substs = translate_substs(selcx.infcx(), param_env, impl_def_id, substs, assoc_ty.node);
|
|
let ty = if let ty::AssocKind::Existential = assoc_ty.item.kind {
|
|
let item_substs = InternalSubsts::identity_for_item(tcx, assoc_ty.item.def_id);
|
|
tcx.mk_opaque(assoc_ty.item.def_id, item_substs)
|
|
} else {
|
|
tcx.type_of(assoc_ty.item.def_id)
|
|
};
|
|
Progress {
|
|
ty: ty.subst(tcx, substs),
|
|
obligations: nested,
|
|
}
|
|
}
|
|
|
|
/// 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<'cx, 'tcx>(
|
|
selcx: &SelectionContext<'cx, 'tcx>,
|
|
impl_def_id: DefId,
|
|
assoc_ty_def_id: DefId,
|
|
) -> specialization_graph::NodeItem<ty::AssocItem> {
|
|
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 TraidDef::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 item.kind == ty::AssocKind::Type &&
|
|
tcx.hygienic_eq(item.ident, assoc_ty_name, trait_def_id) {
|
|
return specialization_graph::NodeItem {
|
|
node: specialization_graph::Node::Impl(impl_def_id),
|
|
item,
|
|
};
|
|
}
|
|
}
|
|
|
|
if let Some(assoc_item) = trait_def
|
|
.ancestors(tcx, impl_def_id)
|
|
.defs(tcx, assoc_ty_name, ty::AssocKind::Type, trait_def_id)
|
|
.next() {
|
|
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))
|
|
}
|
|
}
|
|
|
|
// # Cache
|
|
|
|
/// The projection cache. Unlike the standard caches, this can include
|
|
/// infcx-dependent type variables, therefore we have to roll the
|
|
/// cache back each time we roll a snapshot back, to avoid assumptions
|
|
/// on yet-unresolved inference variables. Types with placeholder
|
|
/// regions also have to be removed when the respective snapshot ends.
|
|
///
|
|
/// Because of that, projection cache entries can be "stranded" and left
|
|
/// inaccessible when type variables inside the key are resolved. We make no
|
|
/// attempt to recover or remove "stranded" entries, but rather let them be
|
|
/// (for the lifetime of the infcx).
|
|
///
|
|
/// Entries in the projection cache might contain inference variables
|
|
/// that will be resolved by obligations on the projection cache entry (e.g.,
|
|
/// when a type parameter in the associated type is constrained through
|
|
/// an "RFC 447" projection on the impl).
|
|
///
|
|
/// When working with a fulfillment context, the derived obligations of each
|
|
/// projection cache entry will be registered on the fulfillcx, so any users
|
|
/// that can wait for a fulfillcx fixed point need not care about this. However,
|
|
/// users that don't wait for a fixed point (e.g., trait evaluation) have to
|
|
/// resolve the obligations themselves to make sure the projected result is
|
|
/// ok and avoid issues like #43132.
|
|
///
|
|
/// If that is done, after evaluation the obligations, it is a good idea to
|
|
/// call `ProjectionCache::complete` to make sure the obligations won't be
|
|
/// re-evaluated and avoid an exponential worst-case.
|
|
//
|
|
// FIXME: we probably also want some sort of cross-infcx cache here to
|
|
// reduce the amount of duplication. Let's see what we get with the Chalk reforms.
|
|
#[derive(Default)]
|
|
pub struct ProjectionCache<'tcx> {
|
|
map: SnapshotMap<ProjectionCacheKey<'tcx>, ProjectionCacheEntry<'tcx>>,
|
|
}
|
|
|
|
#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
|
|
pub struct ProjectionCacheKey<'tcx> {
|
|
ty: ty::ProjectionTy<'tcx>
|
|
}
|
|
|
|
impl<'cx, 'tcx> ProjectionCacheKey<'tcx> {
|
|
pub 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 {
|
|
// 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.
|
|
ty: infcx.resolve_vars_if_possible(&predicate.projection_ty)
|
|
})
|
|
}
|
|
}
|
|
|
|
#[derive(Clone, Debug)]
|
|
enum ProjectionCacheEntry<'tcx> {
|
|
InProgress,
|
|
Ambiguous,
|
|
Error,
|
|
NormalizedTy(NormalizedTy<'tcx>),
|
|
}
|
|
|
|
// N.B., intentionally not Clone
|
|
pub struct ProjectionCacheSnapshot {
|
|
snapshot: Snapshot,
|
|
}
|
|
|
|
impl<'tcx> ProjectionCache<'tcx> {
|
|
pub fn clear(&mut self) {
|
|
self.map.clear();
|
|
}
|
|
|
|
pub fn snapshot(&mut self) -> ProjectionCacheSnapshot {
|
|
ProjectionCacheSnapshot { snapshot: self.map.snapshot() }
|
|
}
|
|
|
|
pub fn rollback_to(&mut self, snapshot: ProjectionCacheSnapshot) {
|
|
self.map.rollback_to(snapshot.snapshot);
|
|
}
|
|
|
|
pub fn rollback_placeholder(&mut self, snapshot: &ProjectionCacheSnapshot) {
|
|
self.map.partial_rollback(&snapshot.snapshot, &|k| k.ty.has_re_placeholders());
|
|
}
|
|
|
|
pub fn commit(&mut self, snapshot: ProjectionCacheSnapshot) {
|
|
self.map.commit(snapshot.snapshot);
|
|
}
|
|
|
|
/// Try to start normalize `key`; returns an error if
|
|
/// normalization already occurred (this error corresponds to a
|
|
/// cache hit, so it's actually a good thing).
|
|
fn try_start(&mut self, key: ProjectionCacheKey<'tcx>)
|
|
-> Result<(), ProjectionCacheEntry<'tcx>> {
|
|
if let Some(entry) = self.map.get(&key) {
|
|
return Err(entry.clone());
|
|
}
|
|
|
|
self.map.insert(key, ProjectionCacheEntry::InProgress);
|
|
Ok(())
|
|
}
|
|
|
|
/// Indicates that `key` was normalized to `value`.
|
|
fn insert_ty(&mut self, key: ProjectionCacheKey<'tcx>, value: NormalizedTy<'tcx>) {
|
|
debug!("ProjectionCacheEntry::insert_ty: adding cache entry: key={:?}, value={:?}",
|
|
key, value);
|
|
let fresh_key = self.map.insert(key, ProjectionCacheEntry::NormalizedTy(value));
|
|
assert!(!fresh_key, "never started projecting `{:?}`", key);
|
|
}
|
|
|
|
/// Mark the relevant projection cache key as having its derived obligations
|
|
/// complete, so they won't have to be re-computed (this is OK to do in a
|
|
/// snapshot - if the snapshot is rolled back, the obligations will be
|
|
/// marked as incomplete again).
|
|
pub fn complete(&mut self, key: ProjectionCacheKey<'tcx>) {
|
|
let ty = match self.map.get(&key) {
|
|
Some(&ProjectionCacheEntry::NormalizedTy(ref ty)) => {
|
|
debug!("ProjectionCacheEntry::complete({:?}) - completing {:?}",
|
|
key, ty);
|
|
ty.value
|
|
}
|
|
ref value => {
|
|
// Type inference could "strand behind" old cache entries. Leave
|
|
// them alone for now.
|
|
debug!("ProjectionCacheEntry::complete({:?}) - ignoring {:?}",
|
|
key, value);
|
|
return
|
|
}
|
|
};
|
|
|
|
self.map.insert(key, ProjectionCacheEntry::NormalizedTy(Normalized {
|
|
value: ty,
|
|
obligations: vec![]
|
|
}));
|
|
}
|
|
|
|
/// A specialized version of `complete` for when the key's value is known
|
|
/// to be a NormalizedTy.
|
|
pub fn complete_normalized(&mut self, key: ProjectionCacheKey<'tcx>, ty: &NormalizedTy<'tcx>) {
|
|
// We want to insert `ty` with no obligations. If the existing value
|
|
// already has no obligations (as is common) we don't insert anything.
|
|
if !ty.obligations.is_empty() {
|
|
self.map.insert(key, ProjectionCacheEntry::NormalizedTy(Normalized {
|
|
value: ty.value,
|
|
obligations: vec![]
|
|
}));
|
|
}
|
|
}
|
|
|
|
/// Indicates that trying to normalize `key` resulted in
|
|
/// ambiguity. No point in trying it again then until we gain more
|
|
/// type information (in which case, the "fully resolved" key will
|
|
/// be different).
|
|
fn ambiguous(&mut self, key: ProjectionCacheKey<'tcx>) {
|
|
let fresh = self.map.insert(key, ProjectionCacheEntry::Ambiguous);
|
|
assert!(!fresh, "never started projecting `{:?}`", key);
|
|
}
|
|
|
|
/// Indicates that trying to normalize `key` resulted in
|
|
/// error.
|
|
fn error(&mut self, key: ProjectionCacheKey<'tcx>) {
|
|
let fresh = self.map.insert(key, ProjectionCacheEntry::Error);
|
|
assert!(!fresh, "never started projecting `{:?}`", key);
|
|
}
|
|
}
|