code: func WithFileContextForFile(e error, realFilename, filename string, fs afero.Fs, matcher LineMatcherFn) (error, bool) {
  	f, err := fs.Open(filename)
  	if err != nil {
  		return e, false
  	}
  	defer f.Close()
  	return WithFileContext(e, realFilename, f, matcher)
  }
docs: // WithFileContextForFile will try to add a file context with lines matching the given matcher.
  // If no match could be found, the original error is returned with false as the second return value.