return {
  filetypes = { 'elixir', 'eelixir', 'heex', 'surface' },
  root_dir = function(bufnr, on_dir)
    local fname = vim.api.nvim_buf_get_name(bufnr)
    local matches = vim.fs.find({ 'mix.exs' }, { upward = true, limit = 2, path = fname })
    local child_or_root_path, maybe_umbrella_path = unpack(matches)
    local root_dir = vim.fs.dirname(maybe_umbrella_path or child_or_root_path)

    on_dir(root_dir)
  end,
}