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use rustc_hir::def_id::DefId;
use rustc_infer::infer::InferCtxt;
use rustc_infer::traits::{Obligation, ObligationCause, TraitObligation};
use rustc_span::DUMMY_SP;
use crate::traits::ObligationCtxt;
pub fn recompute_applicable_impls<'tcx>(
infcx: &InferCtxt<'tcx>,
obligation: &TraitObligation<'tcx>,
) -> Vec<DefId> {
let tcx = infcx.tcx;
let param_env = obligation.param_env;
let dummy_cause = ObligationCause::dummy();
let impl_may_apply = |impl_def_id| {
let ocx = ObligationCtxt::new_in_snapshot(infcx);
let placeholder_obligation =
infcx.replace_bound_vars_with_placeholders(obligation.predicate);
let obligation_trait_ref =
ocx.normalize(&dummy_cause, param_env, placeholder_obligation.trait_ref);
let impl_substs = infcx.fresh_substs_for_item(DUMMY_SP, impl_def_id);
let impl_trait_ref = tcx.bound_impl_trait_ref(impl_def_id).unwrap().subst(tcx, impl_substs);
let impl_trait_ref = ocx.normalize(&ObligationCause::dummy(), param_env, impl_trait_ref);
if let Err(_) = ocx.eq(&dummy_cause, param_env, obligation_trait_ref, impl_trait_ref) {
return false;
}
let impl_predicates = tcx.predicates_of(impl_def_id).instantiate(tcx, impl_substs);
ocx.register_obligations(
impl_predicates
.predicates
.iter()
.map(|&predicate| Obligation::new(tcx, dummy_cause.clone(), param_env, predicate)),
);
ocx.select_where_possible().is_empty()
};
let mut impls = Vec::new();
tcx.for_each_relevant_impl(
obligation.predicate.def_id(),
obligation.predicate.skip_binder().trait_ref.self_ty(),
|impl_def_id| {
if infcx.probe(move |_snapshot| impl_may_apply(impl_def_id)) {
impls.push(impl_def_id)
}
},
);
impls
}
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