{"ast_node_type":"other","tokens":[{"end":73,"kind":"keyword","start":0,"text":"type_op_ascribe_user_type_with_span(&ocx,"}]}
        type_op_ascribe_user_type_with_span(&ocx, key, cause.span).ok()?;
        let ocx = ObligationCtxt::new(&infcx);
        let diag = try_extract_error_from_fulfill_cx(