syntax_data: {"ast_node_type":"other","tokens":[{"end":55,"kind":"keyword","start":0,"text":"self.span_to_source(sp,"}]}
source_snippet:         self.span_to_source(sp, |src, start_index, _| {
context_before:     pub fn span_to_prev_source(&self, sp: Span) -> Result<String, SpanSnippetError> {
context_after:             src.get(..start_index).map(|s| s.to_string()).ok_or(SpanSnippetError::IllFormedSpan(sp))