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::PredicateObligation;
   4 use rustc_infer::traits::TraitEngine;
   5 use rustc_middle::ty;
   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::Clause(ty::Clause::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         // Then construct a new obligation with Self = () added
  22         // to the ParamEnv, and see if it holds.
  23         let o = obligation.with(infcx.tcx,
  24             obligation
  25                 .predicate
  26                 .kind()
  27                 .rebind(
  28                     // (*) binder moved here
  29                     ty::PredicateKind::Clause(ty::Clause::Trait(tpred.with_self_ty(infcx.tcx, new_self_ty)))
  30                 ),
  31         );
  32         // Don't report overflow errors. Otherwise equivalent to may_hold.
  33         if let Ok(result) = infcx.probe(|_| infcx.evaluate_obligation(&o)) && result.may_apply() {
  34             engine.relationships().entry(ty).or_default().self_in_trait = true;
  35         }
  36     }
  37
  38     if let ty::PredicateKind::Clause(ty::Clause::Projection(predicate)) =
  39         obligation.predicate.kind().skip_binder()
  40     {
  41         // If the projection predicate (Foo::Bar == X) has X as a non-TyVid,
  42         // we need to make it into one.
  43         if let Some(vid) = predicate.term.ty().and_then(|ty| ty.ty_vid()) {
  44             debug!("relationship: {:?}.output = true", vid);
  45             engine.relationships().entry(vid).or_default().output = true;
  46         }
  47     }
  48 }