apple/pkl · error · VmReferenceAccessError

cannotFindMember

Error message

cannotFindMember

What it means

A reference-validation access error raised while resolving the property type for a `Reference` type-checking access: the accessed type is not a class type (e.g. an unknown/union/alias type), so its properties cannot be referenced at all. Pkl only allows property references on class types.

Source

Thrown at pkl-core/src/main/java/org/pkl/core/runtime/VmReference.java:216

  @TruffleBoundary
  private VmReference withAccess(
      BiConsumer<PType, Set<PType>> checkCandidate, Supplier<VmTyped> makeAccess) {
    Set<PType> candidates = new HashSet<>();
    for (var t : iterateTypes(referentType)) {
      checkCandidate.accept(t, candidates);
    }
    return new VmReference(domain, data, path.append(makeAccess.get()), minimizeTypes(candidates));
  }

  @SuppressWarnings("DuplicatedCode")
  private static void getCandidatePropertyType(PType type, String property, Set<PType> result) {
    if (type == PType.UNKNOWN) {
      result.add(type);
      return;
    }
    // restriction: only class types can have their properties referenced
    if (!(type instanceof PType.Class clazz)) {
      throw new VmReferenceAccessError(type, VmReferenceAccessErrorType.CANNOT_FIND_MEMBER);
    }
    if (clazz.getPClass().getInfo() == PClassInfo.Dynamic) {
      if (property.equals("default")) {
        // restriction: cannot reference Dynamic.default
        throw new VmReferenceAccessError(type, VmReferenceAccessErrorType.DEFAULT_MEMBER);
      }
      result.add(PType.UNKNOWN);
      return;
    }
    // restriction: cannot reference Listing/Mapping.default
    if (clazz.getPClass().getInfo() == PClassInfo.Listing
        || clazz.getPClass().getInfo() == PClassInfo.Mapping) {
      var errorType =
          property.equals("default")
              ? VmReferenceAccessErrorType.DEFAULT_MEMBER
              : VmReferenceAccessErrorType.CANNOT_FIND_MEMBER;
      throw new VmReferenceAccessError(type, errorType);
    }

View on GitHub (pinned to f3efcbfc9b)

Solutions

1. Narrow the expression to a concrete class type before referencing its properties.
2. Fix the type annotation so it names a class, not a union/alias.
3. Check for typos in the type reference; the resolved type may be falling back to non-class.
4. Use `is`/type tests or restructure so the referenced property lives on a class.

Example fix

// before (union type member reference)
x: Int | String
y = x.someProp
// after
x: SomeClass
y = x.someProp

// Pkl: only reference properties on concrete class types
if (x is SomeClass) { ... }
typealias ValidType = SomeClass // avoid aliasing to unions you later access by property

// Pkl
function isClassTyped(x: Any): Boolean = x is SomeClass

try {
  eval(modSrc);
} catch (EvalException e) {
  if (e.getMessage().contains("cannotFindMember")) {
    // check that the referenced expression resolves to a class type
  }
}

When it happens

Trigger: Using property access/type-reference machinery (`withPropertyAccess`) against a value whose static type is not a PType.Class, e.g. referencing a property on an aliased union or a non-class type.

Common situations: Type annotations referencing properties of union types or type aliases; referencing members of `unknown`-typed values in `amends`/typechecked contexts.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

• externalMember
• defaultMember
• defaultMember/cannotFindMember
• cannotFindMember
• cannotInstantiateAbstractClass

AI-assisted analysis of apple/pkl@f3efcbfc9b (2026-09-08). Data as JSON: /api/errors/bd06d8ec6841b21d. Report an issue: GitHub.