syntax_data: {"ast_node_type":"other","tokens":[{"end":61,"kind":"keyword","start":0,"text":"debug!(\"walk_chain_collapsed({:?},"}]}
source_snippet:         debug!("walk_chain_collapsed({:?}, {:?})", span, to);
context_before:         let mut ret_span = span;
context_after:         debug!("walk_chain_collapsed: span ctxt = {:?}", span.ctxt());