presto-main/src/main/java/io/prestosql/metadata/ResolvedFunction.java/ResolvedFunction/encodeSimpleSignature
class ResolvedFunction:    private static String encodeSimpleSignature(Signature signature)
    {
        List<Object> parts = new ArrayList<>(2 + signature.getArgumentTypes().size());
        parts.add(signature.getName());
        parts.add(signature.getReturnType());
        parts.addAll(signature.getArgumentTypes());
        // TODO: this needs to be canonicalized elsewhere
        return Joiner.on('|').join(parts).toLowerCase(Locale.US);
    }