syntax_data: {"ast_node_type":"other","tokens":[{"end":60,"kind":"keyword","start":0,"text":"debug!(\"walk_chain:"}]}
source_snippet:         debug!("walk_chain: span ctxt = {:?}", span.ctxt());
context_before:         debug!("walk_chain({:?}, {:?})", span, to);
context_after:         while span.ctxt() != to && span.from_expansion() {