syntax_data: {"ast_node_type":"other","tokens":[{"end":82,"kind":"keyword","start":0,"text":"debug!(\"walk_chain_collapsed({:?}):"}]}
source_snippet:             debug!("walk_chain_collapsed({:?}): expn_data={:?}", span, expn_data);
context_before:             let expn_data = self.expn_data(outer_expn);
context_after:             span = expn_data.call_site;