syntax_data: {"ast_node_type":"variable","tokens":[{"end":69,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:         let source_file_end = RelativeBytePos::from_usize(src.len());
context_before:     if let Some(&last_line_start) = lines.last() {
context_after:         assert!(source_file_end >= last_line_start);