Function difft::diff::graph::allocate_if_new

fn allocate_if_new<'s, 'v>(
    v: Vertex<'s, 'v>,
    alloc: &'v Bump,
    seen: &mut HashMap<&Vertex<'s, 'v>, SmallVec<[&'v Vertex<'s, 'v>; 2]>, BuildHasherDefault<FxHasher>>
) -> &'v Vertex<'s, 'v>