syntax_data: {"ast_node_type":"other","tokens":[{"end":83,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:             // FIXME: This does limit the usefulness of the error when the macro is
context_before:             // and the span isn't "imported" (i.e. from unavailable sources).
context_after:             // from a foreign crate; we could also take into account `-Zmacro-backtrace`,