code: function processFile() {
    return (file, callback) => {
      let parsed;
      if (file.meta !== undefined && file.meta.layout !== undefined) {
        const ext = path.extname(file.meta.layout);
        parsed = path.parse(`${trimExtension(file.path)}${ext}`);
      } else {
        parsed = path.parse(file.path);
      }
  
      const filePath = {
        dir: parsed.dir,
        name: parsed.name,
        ext: parsed.ext,
      };
      const meta = Object.assign({}, file.meta, { filePath });
      async.nextTick(callback, null, Object.assign({}, file, { meta }));
    };
  }
docs: Process a single file.