oracle/graal · error · RuntimeException

Unimplemented: most specific mapping: {} vs. {}

Error message

Unimplemented: most specific mapping: {} vs. {}

What it means

Error "Unimplemented: most specific mapping: {} vs. {}" thrown in oracle/graal.

Source

Thrown at espresso-compiler-stub/src/com.oracle.truffle.espresso.vmaccess/src/com/oracle/truffle/espresso/vmaccess/EspressoExternalHostProxies.java:512

    }

    private Method findHostMethod(Class<?> hostClass, ResolvedJavaMethod method) {
        Method hostMethod = null;
        JavaType guestReturnType = method.getSignature().getReturnType(null);
        for (Method hostMethodCandidate : hostClass.getMethods()) {
            if (!hostMethodCandidate.getName().equals(method.getName())) {
                continue;
            }
            if (!argumentsCompatible(method, hostMethodCandidate.getParameterTypes())) {
                continue;
            }
            if (!typesCompatible(guestReturnType, method.getDeclaringClass(), hostMethodCandidate.getReturnType())) {
                continue;
            }
            if (hostMethod == null) {
                hostMethod = hostMethodCandidate;
            } else {
                throw new RuntimeException("Unimplemented: most specific mapping: " + hostMethod + " vs. " + hostMethodCandidate);
            }
        }
        if (hostMethod == null && !method.isDefault()) {
            throw new IllegalArgumentException("Method compatible with " + method.format("%r %h.%n(%p)") + " not found in class " + hostClass.getName());
        }
        return hostMethod;
    }

    private boolean argumentsCompatible(ResolvedJavaMethod method, Class<?>[] hostParameterTypes) {
        Signature guestSignature = method.getSignature();
        int parameterCount = guestSignature.getParameterCount(false);
        if (hostParameterTypes.length != parameterCount) {
            return false;
        }
        for (int i = 0; i < parameterCount; i++) {
            JavaType guestParameterType = guestSignature.getParameterType(i, null);
            Class<?> hostParameterType = hostParameterTypes[i];
            if (!typesCompatible(guestParameterType, method.getDeclaringClass(), hostParameterType)) {

View on GitHub (pinned to a66e9ccd1d)

Solutions

1. Fix the condition reported by the error: Unimplemented: most specific mapping: {} vs. {}
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: Unimplemented: most specific mapping: {} vs. {}

When it happens

Trigger: Thrown at espresso-compiler-stub/src/com.oracle.truffle.espresso.vmaccess/src/com/oracle/truffle/espresso/vmaccess/EspressoExternalHostProxies.java:512 when the library encounters an invalid state.

Common situations: Occurs when a caller violates the contract guarded by this check: Unimplemented: most specific mapping: {} vs. {}

AI-assisted analysis of oracle/graal@a66e9ccd1d (2026-08-14). Data as JSON: /api/errors/03f1d258c2dfe43c. Report an issue: GitHub.