syntax_data: {"ast_node_type":"variable","tokens":[{"end":100,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:             let n = s[end..].char_indices().find(|&(_, c)| !f(c)).map_or(s.len() - end, |(i, _)| i);
context_before:         self.span_to_source(span, |s, _start, end| {
context_after:             Ok(span.with_hi(span.hi() + BytePos(n as u32)))