syntax_data: {"ast_node_type":"other","tokens":[{"end":39,"kind":"keyword","start":0,"text":"span"}]}
source_snippet:             span = expn_data.call_site;
context_before:             debug!("walk_chain_collapsed({:?}): expn_data={:?}", span, expn_data);
context_after:             if expn_data.collapse_debuginfo {