Keep obligation chain when elaborating obligations

1 files changed, 15 insertions, 3 deletions

diff --git a/compiler/rustc_infer/src/traits/util.rs b/compiler/rustc_infer/src/traits/util.rs
index 8f0bd3a9abe..1817bbf9228 100644
--- a/compiler/rustc_infer/src/traits/util.rs
+++ b/compiler/rustc_infer/src/traits/util.rs
@@ -1,7 +1,7 @@
 use smallvec::smallvec;
 
 use crate::infer::outlives::components::{push_outlives_components, Component};
-use crate::traits::{Obligation, ObligationCause, PredicateObligation};
+use crate::traits::{self, Obligation, ObligationCause, PredicateObligation};
 use rustc_data_structures::fx::{FxHashSet, FxIndexSet};
 use rustc_middle::ty::{self, ToPredicate, TyCtxt};
 use rustc_span::symbol::Ident;
@@ -145,16 +145,28 @@ impl<'tcx> Elaborator<'tcx> {
                 // Get predicates declared on the trait.
                 let predicates = tcx.super_predicates_of(data.def_id());
 
-                let obligations = predicates.predicates.iter().map(|&(mut pred, _)| {
+                let obligations = predicates.predicates.iter().map(|&(mut pred, span)| {
                     // when parent predicate is non-const, elaborate it to non-const predicates.
                     if data.constness == ty::BoundConstness::NotConst {
                         pred = pred.without_const(tcx);
                     }
 
+                    let cause = obligation.cause.clone().derived_cause(
+                        bound_predicate.rebind(data),
+                        |derived| {
+                            traits::ImplDerivedObligation(Box::new(
+                                traits::ImplDerivedObligationCause {
+                                    derived,
+                                    impl_def_id: data.def_id(),
+                                    span,
+                                },
+                            ))
+                        },
+                    );
                     predicate_obligation(
                         pred.subst_supertrait(tcx, &bound_predicate.rebind(data.trait_ref)),
                         obligation.param_env,
-                        obligation.cause.clone(),
+                        cause,
                     )
                 });
                 debug!(?data, ?obligations, "super_predicates");