emit ConstEquate in TypeRelating<D>

compiler/rustc_infer/src/infer/nll_relate/mod.rs

@@ -817,12 +817,13 @@ impl<'tcx, D> ConstEquateRelation<'tcx> for TypeRelating<'_, 'tcx, D>
 where
     D: TypeRelatingDelegate<'tcx>,
 {
-    fn const_equate_obligation(&mut self, _a: ty::Const<'tcx>, _b: ty::Const<'tcx>) {
-        // We don't have to worry about the equality of consts during borrow checking
-        // as consts always have a static lifetime.
-        // FIXME(oli-obk): is this really true? We can at least have HKL and with
-        // inline consts we may have further lifetimes that may be unsound to treat as
-        // 'static.
+    fn const_equate_obligation(&mut self, a: ty::Const<'tcx>, b: ty::Const<'tcx>) {
+        self.delegate.register_obligations(vec![Obligation::new(
+            self.tcx(),
+            ObligationCause::dummy(),
+            self.param_env(),
+            ty::Binder::dummy(ty::PredicateKind::ConstEquate(a, b)),
+        )]);
     }
 }