Function stacks 

pub fn stacks(
    out: impl Write,
    err: Option<impl Write>,
    walk_options: WalkOptions,
    paths: Vec<PathBuf>,
    max_depth: Option<usize>,
) -> Result<WalkResult>

Traverse paths and write the tree to out as folded stacks, one entry per line, ready to pipe into flame-graph tools like inferno.

Each line is an entry’s path from the traversal root, with its components separated by ;, followed by a single space and the entry’s own size in bytes. A directory contributes only the size of its own directory entry, as the sizes of everything it contains appear on the lines of the contained entries.

Without max_depth, each entry’s own size is known when it is traversed, so its line can be written immediately without retaining the complete tree. With max_depth, sizes below the limit must be folded into their nearest visible ancestor. Because an ancestor is visited before its descendants, its final size is unknown until traversal finishes; the requested levels are therefore retained and written afterward instead of streamed.