syntax_data: {"ast_node_type":"other","tokens":[{"end":48,"kind":"keyword","start":0,"text":"///"}]}
source_snippet:     /// since `source_files` is a `MonotonicVec`
context_before:     /// This index is guaranteed to be valid for the lifetime of this `SourceMap`,
context_after:     pub fn lookup_source_file_idx(&self, pos: BytePos) -> usize {