function realDone(error, file) {
        if (error || !file) {
          reject(error)
        } else if (resolve) {
          resolve(file)
        } else {
          assert(done, '`done` is defined if `resolve` is not')
          done(undefined, file)
        }
      }
@param {Error | undefined} error
@param {VFileWithOutput<CompileResult> | undefined} [file]
@returns {undefined}