1 files changed, 52 insertions, 0 deletions
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/ambiguity.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/ambiguity.rs
new file mode 100644
index 000000000..752b53fbc
--- /dev/null
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/ambiguity.rs
@@ -0,0 +1,52 @@
+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
+}