syntax_data: {"ast_node_type":"variable","tokens":[{"end":54,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:                 let lo = &mut self.line_cache[oldest];
context_before:             (-1, -1) => {
context_after:                 lo.update(new_file_and_idx, span_data.lo, self.time_stamp);