Function difft::diff::graph::allocate_if_new

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