quarkusio/quarkus · error · IllegalStateException

Either function or runtimeValue must be provided

Error message

Either function or runtimeValue must be provided

What it means

Thrown by the subscription builder of BuildTimeActionBuildItem at build() when a Dev UI subscription is registered without a backing implementation. Subscriptions differ from plain actions in that they stream updates, so only a deployment function or a runtimeValue is accepted; providing neither leaves the subscription with nothing to push, and the guard rejects it during the extension build.

Solutions

1. Add .function(...) or .runtime(...) before build()
2. Remove any assistantFunction(...) call — subscriptions do not support it

Example fix

// before
subscriptionBuilder.assistantFunction(af).build();
// after
subscriptionBuilder.function(map -> computeUpdate()).build();

if (subFunction == null && subRuntimeValue == null) {
    throw new IllegalArgumentException("Provide function or runtimeValue for the subscription");
}

try {
    subscriptionBuilder.build();
} catch (IllegalStateException e) {
    if (e.getMessage().contains("must be provided")) { /* attach function or runtime */ }
    else throw e;
}

When it happens

Trigger: Building a SubscriptionBuilder with a methodName but no implementation; or trying to supply an assistantFunction which the builder ignores.

Common situations: Copy-pasting an ActionBuilder chain into a SubscriptionBuilder, including assistantFunction(...) which does not count as an implementation here.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

• Either function, assistantFunction or runtimeValue must be…
• methodName must be provided
• Only one of runtimeValue, function or assistantFunction is…
• FileName is mandatory, for example 'index.html'
• Invalid build time data key, can not be empty

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/f93949e3c9f3c944. Report an issue: GitHub.

Appendix: source

Thrown at extensions/devui/deployment-spi/src/main/java/io/quarkus/devui/spi/buildtime/BuildTimeActionBuildItem.java:293

            this.runtimeValue = runtimeValue;
            return this;
        }

        public void build() {
            if (methodName == null || methodName.isBlank())
                throw new IllegalStateException("methodName must be provided");
            if (parameters.isEmpty())
                parameters = null;
            if (function != null) {
                addSubscription(new DeploymentJsonRpcMethod(methodName, description, parameters, autoUsage(usage, description),
                        mcpEnabledByDefault,
                        function));
            } else if (runtimeValue != null) {
                addSubscription(
                        new RecordedJsonRpcMethod(methodName, description, autoUsage(usage, description), mcpEnabledByDefault,
                                runtimeValue));
            } else {
                throw new IllegalStateException("Either function or runtimeValue must be provided");
            }
        }
    }

    private EnumSet<Usage> autoUsage(EnumSet<Usage> usage, String description) {
        if (usage == null && description == null) {
            usage = Usage.onlyDevUI();
        } else if (usage == null) {
            usage = Usage.devUIandDevMCP();
        }
        return usage;
    }
}

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