Function collect_items_rec

fn collect_items_rec<'tcx>(
    tcx: TyCtxt<'tcx>,
    starting_item: Spanned<MonoItem<'tcx>>,
    state: LRef<'_, SharedState<'tcx>>,
    recursion_depths: &mut DefIdMap<usize>,
    recursion_limit: Limit,
    mode: CollectionMode,
)

Collect all monomorphized items reachable from starting_point, and emit a note diagnostic if a post-monomorphization error is encountered during a collection step.

mode determined whether we are scanning for used items or mentioned items.