syntax_data: {"ast_node_type":"function","tokens":[{"end":65,"kind":"keyword","start":0,"text":"pub"}]}
source_snippet:     pub fn lookup_source_file_idx(&self, pos: BytePos) -> usize {
context_before:     /// since `source_files` is a `MonotonicVec`
context_after:         self.files.borrow().source_files.partition_point(|x| x.start_pos <= pos) - 1