xai-org/x-algorithm · error · SemanticCheckFailure

%s is not a derived feature function

Error message

%s is not a derived feature function

What it means

The expression calls a function that looks like a derived feature invocation, but no DerivedFeature with that name is registered in the compilation context (and it was not caught as a builtin or macro earlier).

Source

Thrown at botmaker/src/java/com/twitter/botmaker/compiler/Compiler.java:1155

    if (varExprASTNode.getReturnType() == Type.SYMBOL) {
      throw new SemanticCheckFailure("Cannot assign SYMBOL type to variable");
    }

    return Pair.of(variableName, varExprASTNode);
  }

  private ASTNode toDerivedFeatureFunction(
      CompilerContext context, String funcName, int lineNo, List<ASTNode> children
  ) throws ParseFailure, SemanticCheckFailure {
    if (context.containsMacro(funcName)) {
      throw new SemanticCheckFailure(String.format(
          "Recursive invocation of derived feature function %s is prohibited", funcName));
    }

    Optional<DerivedFeature> dfOpt = context.getDerivedFeature(funcName);
    if (!dfOpt.isPresent()) {
      throw new SemanticCheckFailure(String.format(
          "%s is not a derived feature function", funcName));
    }

    DerivedFeature derivedFeature = dfOpt.get();
    context.trackUsage(derivedFeature);

    List<Tuple3<Tree, String, Optional<Tree>>> params = derivedFeature.getParams();
    boolean isLogged = derivedFeature.isLogged();

    List<ASTNode> args = children;
    if (params.size() != children.size()) {

      if (params.size() < children.size()
          || !params.get(children.size()).getThird().isPresent()) {
        throw new SemanticCheckFailure(String.format(
            "Derived Feature %s has %d parameters, received %d",
            funcName, params.size(), children.size()));
      }

View on GitHub (pinned to 24c60942c5)

Solutions

1. Verify the derived feature name and casing matches its declaration
2. Ensure the defining rule/feature file is included in the same compilation
3. If the feature was removed, update all call sites

Example fix

// before
value = myFeautre(x)
// after
value = myFeature(x)

if (!context.getDerivedFeature(funcName).isPresent() && !builtins.contains(funcName)) throw new IllegalArgumentException("Undeclared derived feature: " + funcName);

catch (SemanticCheckFailure e) { if (e.getMessage().contains("is not a derived feature function")) reportMissingFeature(e); else throw e; }

When it happens

Trigger: Calling a derived feature that was never declared, was declared in a different rule set/unit, or after a rename; also stale references after deleting a feature.

Common situations: Multi-file rule sets where a feature is used before its defining file is compiled, feature removed during cleanup but references remain, or name casing mistakes.

Related errors

• Recursive invocation of derived feature function %s is prohi
• Derived Feature %s has %d parameters, received %d
• Parameter #%d of %s should be %s, received %s instead
• unrecognized function name:
• class to be imported has to be either a TBase or ThriftStruc

AI-assisted analysis of xai-org/x-algorithm@24c60942c5 (2026-08-28). Data as JSON: /api/errors/1fec59fd23c098d1. Report an issue: GitHub.