syntax_data: {"ast_node_type":"other","tokens":[{"end":59,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:             // Oldest cache entry is for span_data.lo line.
context_before:         let (lo_idx, hi_idx) = match (lo_cache_idx, hi_cache_idx) {
context_after:             (-1, -1) => {