oracle/graal · error · IllegalArgumentException

Unexpected enum type: {}

Error message

Unexpected enum type: {}

What it means

Error "Unexpected enum type: {}" thrown in oracle/graal.

Source

Thrown at espresso-compiler-stub/src/com.oracle.truffle.espresso.vmaccess/src/com/oracle/truffle/espresso/vmaccess/EspressoExternalHostProxies.java:726

        };
    }

    /**
     * Boxes a scalar primitive annotation member while leaving primitive array elements unboxed for
     * guest array construction.
     */
    private JavaConstant primitiveAnnotationMemberValue(JavaConstant primitive, boolean arrayElement) {
        return arrayElement ? primitive : access.getProviders().getConstantReflection().boxPrimitive(primitive);
    }

    /**
     * Resolves an enum element in the guest context, preserving a missing constant as a deferred
     * guest exception proxy.
     */
    private JavaConstant guestEnumValue(EnumElement enumElement, JavaType expectedType) {
        ResolvedJavaType enumType = enumElement.enumType;
        if (!(expectedType instanceof ResolvedJavaType expectedEnumType) || !expectedEnumType.equals(enumType)) {
            throw new IllegalArgumentException("Unexpected enum type: " + enumType.toJavaName());
        }
        JavaConstant enumClass = access.getProviders().getConstantReflection().asJavaClass(enumType);
        JavaConstant enumName = access.getProviders().getConstantReflection().forString(enumElement.name);
        return access.invoke(access.com_oracle_truffle_espresso_vmaccess_guest_GuestAnnotationProxyBuilder_enumValue, null, enumClass, enumName);
    }

    /**
     * Converts a nested annotation value after verifying its concrete type against the enclosing
     * member declaration.
     */
    private JavaConstant guestAnnotationValue(AnnotationValue annotationValue, JavaType expectedType) {
        if (!(expectedType instanceof ResolvedJavaType expectedAnnotationType)) {
            throw new IllegalArgumentException("Expected resolved annotation member type, got " + expectedType);
        }
        validateAnnotationType(expectedAnnotationType, annotationValue.getAnnotationType(), "annotation member type");
        return createGuestAnnotation(annotationValue);
    }

View on GitHub (pinned to a66e9ccd1d)

Solutions

1. Fix the condition reported by the error: Unexpected enum type: {}
2. Check the throwing call site and ensure its documented preconditions (argument values, types, environment, or configuration) are satisfied before the call.

Example fix

Validate inputs and environment so that the failing condition does not occur: Unexpected enum type: {}

When it happens

Trigger: Thrown at espresso-compiler-stub/src/com.oracle.truffle.espresso.vmaccess/src/com/oracle/truffle/espresso/vmaccess/EspressoExternalHostProxies.java:726 when the library encounters an invalid state.

Common situations: Occurs when a caller violates the contract guarded by this check: Unexpected enum type: {}

AI-assisted analysis of oracle/graal@a66e9ccd1d (2026-08-14). Data as JSON: /api/errors/2bc02afe7222e232. Report an issue: GitHub.