syntax_data: {"ast_node_type":"variable","tokens":[{"end":95,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:         let new_file_and_idx = if !file_contains(&self.line_cache[oldest].file, span_data.lo) {
context_before:         // Return early if the file containing beginning of span doesn't contain end of span.
context_after:             let new_file_and_idx = self.file_for_position(span_data.lo)?;