rule/rule.go
func ShouldKeep(e bzl.Expr) bool {
	for _, c := range append(e.Comment().Before, e.Comment().Suffix...) {
		text := strings.TrimSpace(strings.TrimPrefix(c.Token, "#"))
		if text == "keep" {
			return true
		}
	}
	return false
}
func ShouldKeep(e bzl.Expr) bool {
	for _, c := range append(e.Comment().Before, e.Comment().Suffix...) {
		text := strings.TrimSpace(strings.TrimPrefix(c.Token, "#"))
		if text == "keep" {
			return true
		}
	}
	return false
}
// ShouldKeep returns whether e is marked with a "# keep" comment. Kept
// expressions should not be removed or modified.