apple/pkl · error

${getValidationErrorKey()}

Error message

${getValidationErrorKey()}

What it means

Raised during type-alias validation in `ValidatingObjectSlotTypeNode.validate()`: when a type-checking node detects a constraint violation (a non-null "violating node"), it throws an evaluation error whose message key comes from `getValidationErrorKey()` (e.g. expected-constraint, expected-type). The stack frames are built from the violating node's location, so the error points at the member that failed validation.

Source

Thrown at pkl-core/src/main/java/org/pkl/core/ast/type/TypeNode.java:3334

    protected PType doExport() {
      return new PType.Class(BaseModule.getClassClass().export(), typeNode.doExport());
    }
  }

  public abstract static class ValidatingObjectSlotTypeNode extends ObjectSlotTypeNode {

    protected ValidatingObjectSlotTypeNode(SourceSection sourceSection) {
      super(sourceSection);
    }

    protected abstract String getValidationErrorKey();

    protected abstract @Nullable Node getViolatingNode();

    protected final void validate() {
      var violation = getViolatingNode();
      if (violation == null) return;
      throw exceptionBuilder()
          .evalError(getValidationErrorKey())
          .withLeadingStackFrames(buildLeadingFrames(violation, getSourceSection(), null))
          .build();
    }

    public final void validate(TypeAliasTypeNode outermostAliasNode) {
      var violation = getViolatingNode();
      if (violation == null) return;

      throw exceptionBuilder()
          .withLocation(outermostAliasNode)
          .evalError(getValidationErrorKey())
          .withLeadingStackFrames(
              buildLeadingFrames(
                  violation,
                  outermostAliasNode.getSourceSection(),
                  outermostAliasNode.getTypeAlias()))
          .build();

View on GitHub (pinned to f3efcbfc9b)

Solutions

1. Read the reported validation key and stack frames to find the exact member that violated the alias constraint.
2. Fix the value so it satisfies the alias's predicate (e.g. bring an Int within the constrained range).
3. Relax the type alias definition if the constraint is legitimately too strict for your use case.
4. If the alias is from a third-party package, check its documentation for the expected value shape.

Example fix

// before
port: Port = 70000  // fails Port = Int(isBetween(0, 65535))
// after
port: Port = 8080

function checkPort(p) {
  if (!Number.isInteger(p) || p < 0 || p > 65535) throw new Error(`not a valid Port: ${p}`);
}

function isPort(v) { return Number.isInteger(v) && v >= 0 && v <= 65535; }

try {
  validateAliasConstraints(cfg);
} catch (e) {
  // report member that violated the type alias
}

When it happens

Trigger: Validating a type-alias-constrained member whose violation node is non-null and which is not nested inside an outer type-alias validation (the plain `validate()` path). Occurs when a value fails an `amends`/`is` constraint or expected type declared by the type alias during object slot validation.

Common situations: Using a type alias like `port: Port` (where `Port = Int(isBetween(0, 65535))`) with an out-of-range value; aliases that constrain object shape (`amends`) receiving objects missing required members.

Understand the failure class

Background: Schema validation failed / invalid input schema: payload rejected because its shape doesn't match the expected schema — this error's family across 28 libraries.

Related errors

• Values of type `TypeAlias` cannot be rendered as Properties.
• expectedNonEmptyCollection
• expectedSingleElementCollection
• invalidRegexSyntax
• invalidSettingsFile

AI-assisted analysis of apple/pkl@f3efcbfc9b (2026-09-08). Data as JSON: /api/errors/6e91b60e96902f91. Report an issue: GitHub.