compiler/rustc_trait_selection/src/traits/error_reporting/ambiguity.rs

   1 use rustc_hir::def_id::DefId;
   2 use rustc_infer::infer::InferCtxt;
   3 use rustc_infer::traits::{Obligation, ObligationCause, TraitObligation};
   4 use rustc_span::DUMMY_SP;
   5
   6 use crate::traits::ObligationCtxt;
   7
   8 pub fn recompute_applicable_impls<'tcx>(
   9     infcx: &InferCtxt<'tcx>,
  10     obligation: &TraitObligation<'tcx>,
  11 ) -> Vec<DefId> {
  12     let tcx = infcx.tcx;
  13     let param_env = obligation.param_env;
  14     let dummy_cause = ObligationCause::dummy();
  15     let impl_may_apply = |impl_def_id| {
  16         let ocx = ObligationCtxt::new_in_snapshot(infcx);
  17         let placeholder_obligation =
  18             infcx.replace_bound_vars_with_placeholders(obligation.predicate);
  19         let obligation_trait_ref =
  20             ocx.normalize(&dummy_cause, param_env, placeholder_obligation.trait_ref);
  21
  22         let impl_substs = infcx.fresh_substs_for_item(DUMMY_SP, impl_def_id);
  23         let impl_trait_ref = tcx.bound_impl_trait_ref(impl_def_id).unwrap().subst(tcx, impl_substs);
  24         let impl_trait_ref = ocx.normalize(&ObligationCause::dummy(), param_env, impl_trait_ref);
  25
  26         if let Err(_) = ocx.eq(&dummy_cause, param_env, obligation_trait_ref, impl_trait_ref) {
  27             return false;
  28         }
  29
  30         let impl_predicates = tcx.predicates_of(impl_def_id).instantiate(tcx, impl_substs);
  31         ocx.register_obligations(
  32             impl_predicates
  33                 .predicates
  34                 .iter()
  35                 .map(|&predicate| Obligation::new(tcx, dummy_cause.clone(), param_env, predicate)),
  36         );
  37
  38         ocx.select_where_possible().is_empty()
  39     };
  40
  41     let mut impls = Vec::new();
  42     tcx.for_each_relevant_impl(
  43         obligation.predicate.def_id(),
  44         obligation.predicate.skip_binder().trait_ref.self_ty(),
  45         |impl_def_id| {
  46             if infcx.probe(move |_snapshot| impl_may_apply(impl_def_id)) {
  47                 impls.push(impl_def_id)
  48             }
  49         },
  50     );
  51     impls
  52 }