syntax_data: {"ast_node_type":"other","tokens":[{"end":39,"kind":"keyword","start":0,"text":"///"}]}
source_snippet:     /// (which doesn't show up in MIR).
context_before:     /// for figuring out hidden types, even if they are only set in dead code
context_after:     pub concrete_opaque_types: FxIndexMap<LocalDefId, ty::OpaqueHiddenType<'tcx>>,