syntax_data: {"ast_node_type":"function","tokens":[{"end":65,"kind":"keyword","start":0,"text":"fn"}]}
source_snippet:     fn bytepos_to_file_charpos(&self, bpos: BytePos) -> CharPos {
context_before:     /// Converts an absolute `BytePos` to a `CharPos` relative to the `SourceFile`.
context_after:         let idx = self.lookup_source_file_idx(bpos);