syntax_data: {"ast_node_type":"variable","tokens":[{"end":47,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:         let lo = self.lookup_char_pos(sp.lo());
context_before:     pub fn is_valid_span(&self, sp: Span) -> Result<(Loc, Loc), SpanLinesError> {
context_after:         trace!(?lo);