syntax_data: {"ast_node_type":"other","tokens":[{"end":70,"kind":"keyword","start":0,"text":"debug!(\"walk_chain_collapsed:"}]}
source_snippet:         debug!("walk_chain_collapsed: span ctxt = {:?}", span.ctxt());
context_before:         debug!("walk_chain_collapsed({:?}, {:?})", span, to);
context_after:         while let ctxt = span.ctxt()