syntax_data: {"ast_node_type":"other","tokens":[{"end":64,"kind":"keyword","start":0,"text":"///"}]}
source_snippet:     /// the expansion would point to the `bar!` invocation; that
context_before:     /// expression inside `bar!`; the call_site of the expression in
context_after:     /// call_site span would have its own ExpnData, with the call_site