nit: what the heck is o

Author: compiler-errors

compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs

@@ -114,7 +114,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                         //
                         // We rely on a few heuristics to identify cases where this root
                         // obligation is more important than the leaf obligation:
-                        let (main_trait_predicate, o) = if let ty::PredicateKind::Clause(
+                        let (main_trait_predicate, main_obligation) = if let ty::PredicateKind::Clause(
                             ty::ClauseKind::Trait(root_pred)
                         ) = root_obligation.predicate.kind().skip_binder()
                             && !leaf_trait_predicate.self_ty().skip_binder().has_escaping_bound_vars()
@@ -199,7 +199,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                             notes,
                             parent_label,
                             append_const_msg,
-                        } = self.on_unimplemented_note(main_trait_predicate, o, &mut long_ty_file);
+                        } = self.on_unimplemented_note(main_trait_predicate, main_obligation, &mut long_ty_file);
 
                         let have_alt_message = message.is_some() || label.is_some();
                         let is_try_conversion = self.is_try_conversion(span, main_trait_ref.def_id());