rule/rule.go
func (f *File) Save(path string) error {
	f.Sync()
	data := bzl.Format(f.File)
	return ioutil.WriteFile(path, data, 0666)
}
func (f *File) Save(path string) error {
	f.Sync()
	data := bzl.Format(f.File)
	return ioutil.WriteFile(path, data, 0666)
}
// Save writes the build file to disk. This method calls Sync internally.