code: function parsePlatformFilePath(
    filePath: string,
    platforms: Set<string>,
  ): PlatformFilePathParts {
    const dirPath = path.dirname(filePath);
    const fileName = path.basename(filePath);
    const match = fileName.match(PATH_RE);
    if (!match) {
      return {dirPath, baseName: fileName, platform: null, extension: null};
    }
    const extension = match[4] || null;
    const platform = match[3] || null;
    if (platform == null || platforms.has(platform)) {
      return {dirPath, baseName: match[1], platform, extension};
    }
    const baseName = `${match[1]}.${platform}`;
    return {dirPath, baseName, platform: null, extension};
  }
docs: Extract the components of a file path that can have a platform specifier: Ex.
  `index.ios.js` is specific to the `ios` platform and has the extension `js`.