isRetracted, err := r.retractedVersions(ctx)
	if err != nil {
		isRetracted = func(string) bool { return false }
	}

	// tagToVersion returns the version obtained by trimming tagPrefix from tag.
	// If the tag is invalid, retracted, or a pseudo-version, tagToVersion returns
	// an empty version.
	tagToVersion := func(tag string) (v string, tagIsCanonical bool) {
		if !strings.HasPrefix(tag, tagPrefix) {
			return "", false
		}