code: func SourceFileFor(path string) (*SourceFile, error) {
  	absPath, err := filepath.Abs(path)
  	if err != nil {
  		absPath = path
  	}
  	p, err := PackageFor(absPath)
  	if err != nil {
  		return nil, err
  	}
  	return p.OpenSourceFile(filepath.Base(absPath))
  }
docs: // SourceFileFor returns a SourceFile for the file at the given path.