apple/pkl · error · VmException

objectCannotHaveProperty

objectCannotHaveProperty

Error message

Object of type `{0}` cannot have a property (other than `default`).

What it means

A `Listing` can only contain positional elements plus an optional `default` element; it cannot carry named properties. `checkIsValidListingAmendment` throws `objectCannotHaveProperty` (parameterized with the base `Listing` class) when a Listing amendment declares a named member other than `default`.

Source

Thrown at pkl-core/src/main/java/org/pkl/core/ast/expression/literal/SpecializedObjectLiteralNode.java:150

        if (!(key instanceof Long)) {
          CompilerDirectives.transferToInterpreter();
          throw exceptionBuilder()
              .evalError("wrongListingKeyType", new ProgramValue("", VmUtils.getClass(key)))
              .withSourceSection(member.getHeaderSection())
              .build();
        }

        long index = (long) key;
        if (index < 0) {
          // defer handling of negative index to checkMaxListingMemberIndex() (gives more uniform
          // error messages)
          maxIndex = Long.MAX_VALUE;
          break;
        } else if (index > maxIndex) {
          maxIndex = index;
        }
      } else if (memberName != Identifier.DEFAULT) {
        throw exceptionBuilder()
            .evalError("objectCannotHaveProperty", BaseModule.getListingClass())
            .withSourceSection(member.getHeaderSection())
            .build();
      }
    }

    if (parametersDescriptor != null) {
      throw exceptionBuilder()
          .evalError("listingAmendmentCannotHaveParameters")
          .withSourceSection(getParentNode().getSourceSection())
          .build();
    }

    maxListingMemberIndex = maxIndex;
    return true;
  }

  @SuppressWarnings("SameReturnValue")

View on GitHub (pinned to f3efcbfc9b)

Solutions

1. Remove the named property from the Listing amendment
2. Move the property to an element: `["name"]` won't work either — instead put the data into elements via `[0] = ...` or restructure the container as a `Mapping`
3. Use `default { ... }` if you intended to set the default element

Example fix

// before (items: Listing)
items { label = "x"; [0] = 1 }
// after
items { [0] = 1 }

// In a Listing amendment, allowed members are only [i] = v and default { ... } — review body before eval.

When it happens

Trigger: Adding a named property inside a Listing amendment, e.g. `items { name = "x" }` where `items` is a `Listing`; forgetting that within a Listing body only `[index] = ...` and `default { ... }` are legal.

Common situations: Mixing Mapping-style and Listing-style member syntax in one amendment; pasting property overrides into a Listing block; schema drift where a field was moved from a property to an element.

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

• object
• array
• expectedNonEmptyCollection
• defaultMember/cannotFindMember
• expectedNonEmptyListing

AI-assisted analysis of apple/pkl@f3efcbfc9b (2026-09-08). Data as JSON: /api/errors/e6b8e05d91d6d87e. Report an issue: GitHub.