xai-org/x-algorithm · error · SemanticCheckFailure

expect a FieldAccessibleType, but %s received

Error message

expect a FieldAccessibleType, but %s received

What it means

FieldAccessor.mkFieldAccessor throws SemanticCheckFailure when the root node's return type is not a FieldAccessibleType (i.e. not a thrift struct/union/map-like type with accessible fields). Field access paths like a.b.c require the base expression to be field-accessible.

Source

Thrown at botmaker/src/java/com/twitter/botmaker/function/thrift/FieldAccessor.java:47

  protected CacheLevel getCacheLevel() {
    return CacheLevel.Global;
  }

  private static ASTNode.Signature getSignature(ASTNode node, Type valueType) {
    return new ASTNode.Signature(ImmutableList.of(node.getReturnType()), valueType);
  }

  @SuppressWarnings("unchecked")
  public static ASTNode mkFieldAccessor(
      String exprText,
      ASTNode node,
      ImmutableList<String> fields
  ) throws SemanticCheckFailure {



    if (!(node.getReturnType() instanceof FieldAccessibleType)) {
      throw new SemanticCheckFailure(
          String.format("expect a FieldAccessibleType, but %s received",
              node.getReturnType().toString())
      );
    }

    List<Tuple3<FieldAccessibleType, Type, Function<Object, Object>>> fieldInfosBuilder =
        Lists.newArrayListWithCapacity(fields.size());
    FieldAccessibleType objType = (FieldAccessibleType) node.getReturnType();
    for (String field : fields.subList(0, fields.size() - 1)) {
      Tuple3<FieldAccessibleType, Type, Function<Object, Object>> fieldInfo =
          getFieldInfo(objType, field);
      fieldInfosBuilder.add(fieldInfo);
      if (!(fieldInfo.getSecond() instanceof FieldAccessibleType)) {
        throw new SemanticCheckFailure(
            String.format("expect a FieldAccessibleType, but %s received",
                fieldInfo.getSecond().toString())
        );
      }

View on GitHub (pinned to 24c60942c5)

Solutions

1. Check the base expression's return type and fix it to produce a thrift struct/FieldAccessibleType
2. If the type changed after a schema update, regenerate/refresh the type definitions
3. Verify you passed the intended node (not a child/constant) to toFieldAccessor

Example fix

// before
FieldAccessor.mkFieldAccessor(constantNode, fields); // returns String -> failure
// after
FieldAccessor.mkFieldAccessor(structNode, fields); // returns thrift struct type

if (!(node.getReturnType() instanceof FieldAccessibleType)) {
  throw new IllegalArgumentException("base expression is not field-accessible: " + node.getReturnType());
}

public static boolean isFieldAccessible(ASTNode n) {
  return n.getReturnType() instanceof FieldAccessibleType;
}

try {
  return FieldAccessor.mkFieldAccessor(node, fields);
} catch (SemanticCheckFailure e) {
  // log base type and field path, fail expression compilation with context
}

When it happens

Trigger: Applying toFieldAccessor to a node whose getReturnType() is a primitive, string, or collection, e.g. building a field accessor over a Constant or over a numeric expression.

Common situations: Typos in field paths, accessing fields on scalar intermediates, schema changes that made the base type non-struct, or wiring the wrong source node into the accessor.

Related errors

• field name %s has to be a String.
• field %s expects %s type but %s received.
• Failed to create serializer for ThriftStruct %s: %s
• unknown struct value
• Class %s is not assignable from %s for field %s

AI-assisted analysis of xai-org/x-algorithm@24c60942c5 (2026-08-28). Data as JSON: /api/errors/255eea275d1393e7. Report an issue: GitHub.