syntax_data: {"ast_node_type":"variable","tokens":[{"end":52,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:         let idx = self.lookup_source_file_idx(bpos);
context_before:     fn bytepos_to_file_charpos(&self, bpos: BytePos) -> CharPos {
context_after:         let sf = &(*self.files.borrow().source_files)[idx];