Opt-in diagnostics reporting to avoid doing extra work in the new solver

compiler/rustc_trait_selection/src/traits/coherence.rs

@@ -360,7 +360,7 @@ fn impl_intersection_has_impossible_obligation<'a, 'cx, 'tcx>(
     let infcx = selcx.infcx;
 
     if infcx.next_trait_solver() {
-        let ocx = ObligationCtxt::new(infcx);
+        let ocx = ObligationCtxt::new_with_diagnostics(infcx);
         ocx.register_obligations(obligations.iter().cloned());
         let errors_and_ambiguities = ocx.select_all_or_error();
         // We only care about the obligations that are *definitely* true errors.