syntax_data: {"ast_node_type":"function","tokens":[{"end":61,"kind":"keyword","start":0,"text":"fn"}]}
source_snippet:     fn next(&mut self) -> Option<NeedsDropResult<Ty<'tcx>>> {
context_before:     #[instrument(level = "debug", skip(self), ret)]
context_after:         let tcx = self.tcx;