syntax_data: {"ast_node_type":"other","tokens":[{"end":73,"kind":"keyword","start":0,"text":"///"}]}
source_snippet:     /// A stack of types left to process, and the recursion depth when we
context_before:     seen_tys: FxHashSet<Ty<'tcx>>,
context_after:     /// pushed that type. Each round, we pop something from the stack and check