syntax_data: {"ast_node_type":"variable","tokens":[{"end":28,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:         let old = self.span;
context_before:     fn visit_spanned(&mut self, span: Span, value: impl TypeVisitable<TyCtxt<'tcx>>) {
context_after:         self.span = Some(span);