syntax_data: {"ast_node_type":"variable","tokens":[{"end":46,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:         let sf = self.lookup_source_file(pos);
context_before:     pub fn lookup_char_pos(&self, pos: BytePos) -> Loc {
context_after:         let (line, col, col_display) = sf.lookup_file_pos_with_col_display(pos);