syntax_data: {"ast_node_type":"other","tokens":[{"end":47,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:             // a.k.a. unit type, which is Sized
context_before:             // If returned by `struct_tail_raw` this is the empty tuple,
context_after:             | ty::Tuple(..) => Ok(tcx.types.unit),