lib/collect-file-info.js
function filesUnder (rootDir) {
  return directoryContents(
    rootDir,
    stats => (stats.isFile() && stats.size !== 0),
    (path, stats) => [path, stats.size]
  )
}
function filesUnder (rootDir) {
  return directoryContents(
    rootDir,
    stats => (stats.isFile() && stats.size !== 0),
    (path, stats) => [path, stats.size]
  )
}
directoriesUnder