code: function filterNeverIgnoredFiles(p) {
      const basedir = path.dirname(p.filePath)
      const mainFilePath =
          typeof p.main === "string" ? path.join(basedir, p.main) : null
  
      return filePath =>
          path.join(basedir, filePath) !== mainFilePath &&
          filePath !== "package.json" &&
          !NEVER_IGNORED.test(path.relative(basedir, filePath))
  }
docs: Creates a function which checks whether or not a given file is ignoreable.
  
  @param {object} p - An object of package.json.
  @returns {function} A function which checks whether or not a given file is ignoreable.