522 lines
21 KiB
Rust
522 lines
21 KiB
Rust
use crate::traits::{specialization_graph, translate_substs};
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use super::assembly::{self, Candidate, CandidateSource};
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use super::infcx_ext::InferCtxtExt;
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use super::trait_goals::structural_traits;
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use super::{Certainty, EvalCtxt, Goal, QueryResult};
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use rustc_errors::ErrorGuaranteed;
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use rustc_hir::def::DefKind;
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use rustc_hir::def_id::DefId;
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use rustc_hir::LangItem;
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use rustc_infer::infer::InferCtxt;
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use rustc_infer::traits::query::NoSolution;
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use rustc_infer::traits::specialization_graph::LeafDef;
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use rustc_infer::traits::Reveal;
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use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams};
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use rustc_middle::ty::{self, Ty, TyCtxt};
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use rustc_middle::ty::{ProjectionPredicate, TypeSuperVisitable, TypeVisitor};
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use rustc_middle::ty::{ToPredicate, TypeVisitable};
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use rustc_span::DUMMY_SP;
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use std::iter;
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use std::ops::ControlFlow;
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impl<'tcx> EvalCtxt<'_, 'tcx> {
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pub(super) fn compute_projection_goal(
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&mut self,
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goal: Goal<'tcx, ProjectionPredicate<'tcx>>,
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) -> QueryResult<'tcx> {
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// To only compute normalization once for each projection we only
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// normalize if the expected term is an unconstrained inference variable.
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//
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// E.g. for `<T as Trait>::Assoc = u32` we recursively compute the goal
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// `exists<U> <T as Trait>::Assoc = U` and then take the resulting type for
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// `U` and equate it with `u32`. This means that we don't need a separate
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// projection cache in the solver.
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if self.term_is_fully_unconstrained(goal) {
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let candidates = self.assemble_and_evaluate_candidates(goal);
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self.merge_project_candidates(candidates)
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} else {
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let predicate = goal.predicate;
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let unconstrained_rhs = match predicate.term.unpack() {
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ty::TermKind::Ty(_) => self.infcx.next_ty_infer().into(),
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ty::TermKind::Const(ct) => self.infcx.next_const_infer(ct.ty()).into(),
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};
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let unconstrained_predicate = ty::Clause::Projection(ProjectionPredicate {
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projection_ty: goal.predicate.projection_ty,
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term: unconstrained_rhs,
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});
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let (_has_changed, normalize_certainty) =
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self.evaluate_goal(goal.with(self.tcx(), unconstrained_predicate))?;
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let nested_eq_goals =
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self.infcx.eq(goal.param_env, unconstrained_rhs, predicate.term)?;
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let eval_certainty = self.evaluate_all(nested_eq_goals)?;
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self.make_canonical_response(normalize_certainty.unify_and(eval_certainty))
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}
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}
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/// Is the projection predicate is of the form `exists<T> <Ty as Trait>::Assoc = T`.
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///
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/// This is the case if the `term` is an inference variable in the innermost universe
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/// and does not occur in any other part of the predicate.
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fn term_is_fully_unconstrained(&self, goal: Goal<'tcx, ProjectionPredicate<'tcx>>) -> bool {
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let infcx = self.infcx;
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let term_is_infer = match goal.predicate.term.unpack() {
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ty::TermKind::Ty(ty) => {
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if let &ty::Infer(ty::TyVar(vid)) = ty.kind() {
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match infcx.probe_ty_var(vid) {
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Ok(value) => bug!("resolved var in query: {goal:?} {value:?}"),
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Err(universe) => universe == infcx.universe(),
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}
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} else {
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false
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}
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}
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ty::TermKind::Const(ct) => {
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if let ty::ConstKind::Infer(ty::InferConst::Var(vid)) = ct.kind() {
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match self.infcx.probe_const_var(vid) {
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Ok(value) => bug!("resolved var in query: {goal:?} {value:?}"),
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Err(universe) => universe == infcx.universe(),
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}
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} else {
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false
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}
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}
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};
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// Guard against `<T as Trait<?0>>::Assoc = ?0>`.
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struct ContainsTerm<'tcx> {
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term: ty::Term<'tcx>,
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}
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impl<'tcx> TypeVisitor<'tcx> for ContainsTerm<'tcx> {
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type BreakTy = ();
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fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
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if t.needs_infer() {
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if ty::Term::from(t) == self.term {
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ControlFlow::BREAK
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} else {
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t.super_visit_with(self)
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}
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} else {
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ControlFlow::CONTINUE
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}
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}
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fn visit_const(&mut self, c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
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if c.needs_infer() {
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if ty::Term::from(c) == self.term {
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ControlFlow::BREAK
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} else {
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c.super_visit_with(self)
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}
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} else {
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ControlFlow::CONTINUE
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}
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}
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}
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let mut visitor = ContainsTerm { term: goal.predicate.term };
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term_is_infer
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&& goal.predicate.projection_ty.visit_with(&mut visitor).is_continue()
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&& goal.param_env.visit_with(&mut visitor).is_continue()
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}
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fn merge_project_candidates(
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&mut self,
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mut candidates: Vec<Candidate<'tcx>>,
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) -> QueryResult<'tcx> {
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match candidates.len() {
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0 => return Err(NoSolution),
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1 => return Ok(candidates.pop().unwrap().result),
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_ => {}
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}
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if candidates.len() > 1 {
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let mut i = 0;
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'outer: while i < candidates.len() {
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for j in (0..candidates.len()).filter(|&j| i != j) {
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if self.project_candidate_should_be_dropped_in_favor_of(
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&candidates[i],
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&candidates[j],
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) {
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debug!(candidate = ?candidates[i], "Dropping candidate #{}/{}", i, candidates.len());
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candidates.swap_remove(i);
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continue 'outer;
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}
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}
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debug!(candidate = ?candidates[i], "Retaining candidate #{}/{}", i, candidates.len());
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// If there are *STILL* multiple candidates, give up
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// and report ambiguity.
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i += 1;
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if i > 1 {
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debug!("multiple matches, ambig");
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// FIXME: return overflow if all candidates overflow, otherwise return ambiguity.
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unimplemented!();
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}
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}
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}
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Ok(candidates.pop().unwrap().result)
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}
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fn project_candidate_should_be_dropped_in_favor_of(
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&self,
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candidate: &Candidate<'tcx>,
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other: &Candidate<'tcx>,
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) -> bool {
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// FIXME: implement this
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match (candidate.source, other.source) {
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(CandidateSource::Impl(_), _)
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| (CandidateSource::ParamEnv(_), _)
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| (CandidateSource::BuiltinImpl, _)
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| (CandidateSource::AliasBound(_), _) => unimplemented!(),
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}
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}
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}
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impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> {
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fn self_ty(self) -> Ty<'tcx> {
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self.self_ty()
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}
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fn with_self_ty(self, tcx: TyCtxt<'tcx>, self_ty: Ty<'tcx>) -> Self {
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self.with_self_ty(tcx, self_ty)
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}
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fn trait_def_id(self, tcx: TyCtxt<'tcx>) -> DefId {
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self.trait_def_id(tcx)
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}
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fn consider_impl_candidate(
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ecx: &mut EvalCtxt<'_, 'tcx>,
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goal: Goal<'tcx, ProjectionPredicate<'tcx>>,
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impl_def_id: DefId,
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) -> QueryResult<'tcx> {
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let tcx = ecx.tcx();
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let goal_trait_ref = goal.predicate.projection_ty.trait_ref(tcx);
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let impl_trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
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let drcx = DeepRejectCtxt { treat_obligation_params: TreatParams::AsPlaceholder };
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if iter::zip(goal_trait_ref.substs, impl_trait_ref.skip_binder().substs)
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.any(|(goal, imp)| !drcx.generic_args_may_unify(goal, imp))
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{
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return Err(NoSolution);
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}
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ecx.infcx.probe(|_| {
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let impl_substs = ecx.infcx.fresh_substs_for_item(DUMMY_SP, impl_def_id);
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let impl_trait_ref = impl_trait_ref.subst(tcx, impl_substs);
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let mut nested_goals = ecx.infcx.eq(goal.param_env, goal_trait_ref, impl_trait_ref)?;
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let where_clause_bounds = tcx
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.predicates_of(impl_def_id)
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.instantiate(tcx, impl_substs)
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.predicates
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.into_iter()
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.map(|pred| goal.with(tcx, pred));
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nested_goals.extend(where_clause_bounds);
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let trait_ref_certainty = ecx.evaluate_all(nested_goals)?;
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// In case the associated item is hidden due to specialization, we have to
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// return ambiguity this would otherwise be incomplete, resulting in
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// unsoundness during coherence (#105782).
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let Some(assoc_def) = fetch_eligible_assoc_item_def(
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ecx.infcx,
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goal.param_env,
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goal_trait_ref,
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goal.predicate.def_id(),
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impl_def_id
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)? else {
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return ecx.make_canonical_response(trait_ref_certainty.unify_and(Certainty::AMBIGUOUS));
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};
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if !assoc_def.item.defaultness(tcx).has_value() {
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tcx.sess.delay_span_bug(
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tcx.def_span(assoc_def.item.def_id),
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"missing value for assoc item in impl",
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);
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}
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// Getting the right substitutions here is complex, e.g. given:
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// - a goal `<Vec<u32> as Trait<i32>>::Assoc<u64>`
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// - the applicable impl `impl<T> Trait<i32> for Vec<T>`
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// - and the impl which defines `Assoc` being `impl<T, U> Trait<U> for Vec<T>`
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//
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// We first rebase the goal substs onto the impl, going from `[Vec<u32>, i32, u64]`
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// to `[u32, u64]`.
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//
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// And then map these substs to the substs of the defining impl of `Assoc`, going
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// from `[u32, u64]` to `[u32, i32, u64]`.
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let impl_substs_with_gat = goal.predicate.projection_ty.substs.rebase_onto(
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tcx,
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goal_trait_ref.def_id,
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impl_substs,
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);
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let substs = translate_substs(
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ecx.infcx,
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goal.param_env,
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impl_def_id,
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impl_substs_with_gat,
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assoc_def.defining_node,
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);
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// Finally we construct the actual value of the associated type.
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let is_const = matches!(tcx.def_kind(assoc_def.item.def_id), DefKind::AssocConst);
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let ty = tcx.bound_type_of(assoc_def.item.def_id);
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let term: ty::EarlyBinder<ty::Term<'tcx>> = if is_const {
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let identity_substs =
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ty::InternalSubsts::identity_for_item(tcx, assoc_def.item.def_id);
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let did = ty::WithOptConstParam::unknown(assoc_def.item.def_id);
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let kind =
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ty::ConstKind::Unevaluated(ty::UnevaluatedConst::new(did, identity_substs));
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ty.map_bound(|ty| tcx.mk_const(kind, ty).into())
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} else {
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ty.map_bound(|ty| ty.into())
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};
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// The term of our goal should be fully unconstrained, so this should never fail.
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//
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// It can however be ambiguous when the resolved type is a projection.
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let nested_goals = ecx
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.infcx
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.eq(goal.param_env, goal.predicate.term, term.subst(tcx, substs))
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.expect("failed to unify with unconstrained term");
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let rhs_certainty =
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ecx.evaluate_all(nested_goals).expect("failed to unify with unconstrained term");
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ecx.make_canonical_response(trait_ref_certainty.unify_and(rhs_certainty))
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})
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}
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fn consider_assumption(
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ecx: &mut EvalCtxt<'_, 'tcx>,
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goal: Goal<'tcx, Self>,
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assumption: ty::Predicate<'tcx>,
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) -> QueryResult<'tcx> {
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if let Some(poly_projection_pred) = assumption.to_opt_poly_projection_pred() {
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ecx.infcx.probe(|_| {
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let assumption_projection_pred =
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ecx.infcx.instantiate_bound_vars_with_infer(poly_projection_pred);
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let nested_goals = ecx.infcx.eq(
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goal.param_env,
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goal.predicate.projection_ty,
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assumption_projection_pred.projection_ty,
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)?;
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let subst_certainty = ecx.evaluate_all(nested_goals)?;
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// The term of our goal should be fully unconstrained, so this should never fail.
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//
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// It can however be ambiguous when the resolved type is a projection.
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let nested_goals = ecx
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.infcx
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.eq(goal.param_env, goal.predicate.term, assumption_projection_pred.term)
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.expect("failed to unify with unconstrained term");
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let rhs_certainty = ecx
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.evaluate_all(nested_goals)
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.expect("failed to unify with unconstrained term");
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ecx.make_canonical_response(subst_certainty.unify_and(rhs_certainty))
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})
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} else {
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Err(NoSolution)
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}
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}
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fn consider_auto_trait_candidate(
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_ecx: &mut EvalCtxt<'_, 'tcx>,
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goal: Goal<'tcx, Self>,
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) -> QueryResult<'tcx> {
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bug!("auto traits do not have associated types: {:?}", goal);
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}
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fn consider_trait_alias_candidate(
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_ecx: &mut EvalCtxt<'_, 'tcx>,
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goal: Goal<'tcx, Self>,
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) -> QueryResult<'tcx> {
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bug!("trait aliases do not have associated types: {:?}", goal);
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}
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fn consider_builtin_sized_candidate(
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_ecx: &mut EvalCtxt<'_, 'tcx>,
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goal: Goal<'tcx, Self>,
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) -> QueryResult<'tcx> {
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bug!("`Sized` does not have an associated type: {:?}", goal);
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}
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fn consider_builtin_copy_clone_candidate(
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_ecx: &mut EvalCtxt<'_, 'tcx>,
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goal: Goal<'tcx, Self>,
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) -> QueryResult<'tcx> {
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bug!("`Copy`/`Clone` does not have an associated type: {:?}", goal);
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}
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fn consider_builtin_pointer_sized_candidate(
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_ecx: &mut EvalCtxt<'_, 'tcx>,
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goal: Goal<'tcx, Self>,
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) -> QueryResult<'tcx> {
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bug!("`PointerSized` does not have an associated type: {:?}", goal);
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}
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fn consider_builtin_fn_trait_candidates(
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ecx: &mut EvalCtxt<'_, 'tcx>,
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goal: Goal<'tcx, Self>,
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goal_kind: ty::ClosureKind,
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) -> QueryResult<'tcx> {
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if let Some(tupled_inputs_and_output) =
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structural_traits::extract_tupled_inputs_and_output_from_callable(
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ecx.tcx(),
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goal.predicate.self_ty(),
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goal_kind,
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)?
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{
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let pred = tupled_inputs_and_output
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.map_bound(|(inputs, output)| ty::ProjectionPredicate {
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projection_ty: ecx
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.tcx()
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.mk_alias_ty(goal.predicate.def_id(), [goal.predicate.self_ty(), inputs]),
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term: output.into(),
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})
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.to_predicate(ecx.tcx());
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Self::consider_assumption(ecx, goal, pred)
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} else {
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ecx.make_canonical_response(Certainty::AMBIGUOUS)
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}
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}
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fn consider_builtin_tuple_candidate(
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_ecx: &mut EvalCtxt<'_, 'tcx>,
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goal: Goal<'tcx, Self>,
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) -> QueryResult<'tcx> {
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bug!("`Tuple` does not have an associated type: {:?}", goal);
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}
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fn consider_builtin_pointee_candidate(
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ecx: &mut EvalCtxt<'_, 'tcx>,
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goal: Goal<'tcx, Self>,
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) -> QueryResult<'tcx> {
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let tcx = ecx.tcx();
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ecx.infcx.probe(|_| {
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let metadata_ty = match goal.predicate.self_ty().kind() {
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ty::Bool
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| ty::Char
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| ty::Int(..)
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| ty::Uint(..)
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| ty::Float(..)
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| ty::Array(..)
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| ty::RawPtr(..)
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| ty::Ref(..)
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| ty::FnDef(..)
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| ty::FnPtr(..)
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| ty::Closure(..)
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| ty::Infer(ty::IntVar(..) | ty::FloatVar(..))
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| ty::Generator(..)
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| ty::GeneratorWitness(..)
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| ty::Never
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| ty::Foreign(..) => tcx.types.unit,
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ty::Error(e) => tcx.ty_error_with_guaranteed(*e),
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ty::Str | ty::Slice(_) => tcx.types.usize,
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ty::Dynamic(_, _, _) => {
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let dyn_metadata = tcx.require_lang_item(LangItem::DynMetadata, None);
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tcx.bound_type_of(dyn_metadata)
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.subst(tcx, &[ty::GenericArg::from(goal.predicate.self_ty())])
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}
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ty::Alias(_, _) | ty::Param(_) | ty::Placeholder(..) => {
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// FIXME(ptr_metadata): It would also be possible to return a `Ok(Ambig)` with no constraints.
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let sized_predicate = ty::Binder::dummy(tcx.at(DUMMY_SP).mk_trait_ref(
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LangItem::Sized,
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[ty::GenericArg::from(goal.predicate.self_ty())],
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));
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let mut nested_goals = ecx.infcx.eq(
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goal.param_env,
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goal.predicate.term.ty().unwrap(),
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tcx.types.unit,
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)?;
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nested_goals.push(goal.with(tcx, sized_predicate));
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return ecx.evaluate_all_and_make_canonical_response(nested_goals);
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}
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ty::Adt(def, substs) if def.is_struct() => {
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match def.non_enum_variant().fields.last() {
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None => tcx.types.unit,
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Some(field_def) => {
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let self_ty = field_def.ty(tcx, substs);
|
|
let new_goal = goal.with(
|
|
tcx,
|
|
ty::Binder::dummy(goal.predicate.with_self_ty(tcx, self_ty)),
|
|
);
|
|
return ecx.evaluate_all_and_make_canonical_response(vec![new_goal]);
|
|
}
|
|
}
|
|
}
|
|
ty::Adt(_, _) => tcx.types.unit,
|
|
|
|
ty::Tuple(elements) => match elements.last() {
|
|
None => tcx.types.unit,
|
|
Some(&self_ty) => {
|
|
let new_goal = goal.with(
|
|
tcx,
|
|
ty::Binder::dummy(goal.predicate.with_self_ty(tcx, self_ty)),
|
|
);
|
|
return ecx.evaluate_all_and_make_canonical_response(vec![new_goal]);
|
|
}
|
|
},
|
|
|
|
ty::Infer(
|
|
ty::TyVar(_) | ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_),
|
|
)
|
|
| ty::Bound(..) => bug!(
|
|
"unexpected self ty `{:?}` when normalizing `<T as Pointee>::Metadata`",
|
|
goal.predicate.self_ty()
|
|
),
|
|
};
|
|
|
|
let nested_goals =
|
|
ecx.infcx.eq(goal.param_env, goal.predicate.term.ty().unwrap(), metadata_ty)?;
|
|
ecx.evaluate_all_and_make_canonical_response(nested_goals)
|
|
})
|
|
}
|
|
}
|
|
|
|
/// This behavior is also implemented in `rustc_ty_utils` and in the old `project` code.
|
|
///
|
|
/// FIXME: We should merge these 3 implementations as it's likely that they otherwise
|
|
/// diverge.
|
|
#[instrument(level = "debug", skip(infcx, param_env), ret)]
|
|
fn fetch_eligible_assoc_item_def<'tcx>(
|
|
infcx: &InferCtxt<'tcx>,
|
|
param_env: ty::ParamEnv<'tcx>,
|
|
goal_trait_ref: ty::TraitRef<'tcx>,
|
|
trait_assoc_def_id: DefId,
|
|
impl_def_id: DefId,
|
|
) -> Result<Option<LeafDef>, NoSolution> {
|
|
let node_item = specialization_graph::assoc_def(infcx.tcx, impl_def_id, trait_assoc_def_id)
|
|
.map_err(|ErrorGuaranteed { .. }| NoSolution)?;
|
|
|
|
let eligible = 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 param_env.reveal() == Reveal::All {
|
|
let poly_trait_ref = infcx.resolve_vars_if_possible(goal_trait_ref);
|
|
!poly_trait_ref.still_further_specializable()
|
|
} else {
|
|
debug!(?node_item.item.def_id, "not eligible due to default");
|
|
false
|
|
}
|
|
};
|
|
|
|
if eligible { Ok(Some(node_item)) } else { Ok(None) }
|
|
}
|