Function is_notable_trait_passthrough 

fn is_notable_trait_passthrough(did: DefId, cx: &Context<'_>) -> bool

Box has pass-through impls for Read, Write, Iterator, and Future when the boxed type implements one of those. We don’t want to treat every Box return as being notably an Iterator (etc), though, so we exempt it. Pin has the same issue, with a pass-through impl for Future.