What causes "Thrift enums are not supported in strato JSON" in xai-org/x-algorithm?

Convert the enum to its integer value or name string before strato JSON serialization and serialize with intOf()/stringOf().

xai-org/x-algorithm · error · IllegalArgumentException

Thrift enums are not supported in strato JSON

Error message

Thrift enums are not supported in strato JSON

What it means

The thrift enum serializer (thriftEnumOf for TEnum classes) renders enums as NULL in fingerprint scripts but throws IllegalArgumentException in toStratoJson: thrift enums have no strato JSON encoding here. Any feature/constant typed as a thrift enum fails as soon as it goes through the strato JSON path.

Source

Thrown at botmaker/src/java/com/twitter/botmaker/compiler/Serializer.java:1586

      @Override
      protected void serialize(TProtocol prot, T value) throws Exception {
        prot.writeI32(value.getValue());
      }

      @Override
      protected T deserialize(TProtocol prot) throws Exception {
        int v = prot.readI32();
        return enumMap.get(v);
      }

      @Override
      protected void toScript(GenScript script, T value) {
        script.builder.append("NULL");
      }

      @Override
      protected void toStratoJson(GenScript script, T value) {
        throw new IllegalArgumentException("Thrift enums are not supported in strato JSON");
      }
    };
  }

  public static <T extends ThriftStruct> Serializer<T> thriftStructOf(Class<T> clazz)
      throws SemanticCheckFailure {
    try {
      ThriftStructCodec codec = ThriftStructCodec.forStructClass(clazz);

      return new Serializer<T>() {

        @Override
        public void computeFingerprint(Hasher hasher, T value) throws TException {
          TFingerprintProtocol prot = new TFingerprintProtocol(hasher);
          codec.encode(value, prot);
        }

        @Override

View on GitHub (pinned to 24c60942c5)

Solutions

Convert the enum to its integer value or name string before strato JSON serialization and serialize with intOf()/stringOf().
Model the field as an I32/string in the serving schema and map the enum at the edges.
Extend toStratoJson in the enum serializer to emit the enum's name/value if the strato format can accept it.

Example fix

// before
Serializer.thriftEnumOf(MyEnum.class).genStratoJson(script, MyEnum.A);
// throws Thrift enums are not supported in strato JSON

// after
Serializer.intOf().genStratoJson(script, MyEnum.A.getValue());
// or
Serializer.stringOf().genStratoJson(script, MyEnum.A.name());

Defensive patterns

Strategy: fallback

Validate before calling

if (value instanceof TEnum) {
  value = ((TEnum) value).getValue(); // serialize as int
}

Type guard

static boolean isThriftEnum(Class<?> c) {
  return TEnum.class.isAssignableFrom(c);
}

Try / catch

catch (IllegalArgumentException e) {
  if (e.getMessage().contains("Thrift enums")) {
    return serializeAsIntOrName(enumValue);
  }
  throw e;
}

Prevention

Map thrift enums to int/string at the boundary before serialization.
Avoid enum-typed fields in strato-served feature schemas.
Test enum-typed constants through both fingerprint and strato JSON paths.

When it happens

Trigger: Creating a serializer via Serializer.thriftEnumOf(EnumClass.class) and invoking genStratoJson with any enum value (even a valid one).

Common situations: Rule predicates referencing thrift enum constants that are then exported/served via strato; assuming enums serialize like strings; adding an enum-typed field to a strato-served feature.

Related errors

AI-assisted analysis of xai-org/x-algorithm@24c60942c5 (2026-08-28). Data as JSON: /api/errors/cf535360c19da4ab. Report an issue: GitHub.