{"ast_node_type":"variable","tokens":[{"end":71,"kind":"keyword","start":0,"text":"let"}]}
                let ocx = ObligationCtxt::new_with_diagnostics(&infcx);
            } else if let &[(_, ty_a, ty_b, field_span)] = &coerced_fields[..] {
                ocx.register_obligation(Obligation::new(