compiler/rustc_trait_selection/src/traits/relationships.rs

   1 use crate::infer::InferCtxt;
   2 use crate::traits::query::evaluate_obligation::InferCtxtExt;
   3 use crate::traits::{ObligationCause, PredicateObligation};
   4 use rustc_infer::traits::TraitEngine;
   5 use rustc_middle::ty::{self, ToPredicate};
   6
   7 pub(crate) fn update<'tcx, T>(
   8     engine: &mut T,
   9     infcx: &InferCtxt<'_, 'tcx>,
  10     obligation: &PredicateObligation<'tcx>,
  11 ) where
  12     T: TraitEngine<'tcx>,
  13 {
  14     // (*) binder skipped
  15     if let ty::PredicateKind::Trait(tpred) = obligation.predicate.kind().skip_binder()
  16         && let Some(ty) = infcx.shallow_resolve(tpred.self_ty()).ty_vid().map(|t| infcx.root_var(t))
  17         && infcx.tcx.lang_items().sized_trait().map_or(false, |st| st != tpred.trait_ref.def_id)
  18     {
  19         let new_self_ty = infcx.tcx.types.unit;
  20
  21         let trait_ref = ty::TraitRef {
  22             substs: infcx.tcx.mk_substs_trait(new_self_ty, &tpred.trait_ref.substs[1..]),
  23             ..tpred.trait_ref
  24         };
  25
  26         // Then construct a new obligation with Self = () added
  27         // to the ParamEnv, and see if it holds.
  28         let o = rustc_infer::traits::Obligation::new(
  29             ObligationCause::dummy(),
  30             obligation.param_env,
  31             obligation
  32                 .predicate
  33                 .kind()
  34                 .rebind(
  35                     // (*) binder moved here
  36                     ty::PredicateKind::Trait(ty::TraitPredicate {
  37                         trait_ref,
  38                         constness: tpred.constness,
  39                         polarity: tpred.polarity,
  40                     })
  41                 )
  42                 .to_predicate(infcx.tcx),
  43         );
  44         // Don't report overflow errors. Otherwise equivalent to may_hold.
  45         if let Ok(result) = infcx.probe(|_| infcx.evaluate_obligation(&o)) && result.may_apply() {
  46             engine.relationships().entry(ty).or_default().self_in_trait = true;
  47         }
  48     }
  49
  50     if let ty::PredicateKind::Projection(predicate) = obligation.predicate.kind().skip_binder() {
  51         // If the projection predicate (Foo::Bar == X) has X as a non-TyVid,
  52         // we need to make it into one.
  53         if let Some(vid) = predicate.term.ty().and_then(|ty| ty.ty_vid()) {
  54             debug!("relationship: {:?}.output = true", vid);
  55             engine.relationships().entry(vid).or_default().output = true;
  56         }
  57     }
  58 }