quarkusio/quarkus · error · IllegalStateException

No observer type found for: ${observerType}

Error message

No observer type found for: ${observerType}

What it means

During observer registration in ComponentsProvider generation, each observer must have a generated class name in observerToGeneratedName. A missing entry means no observer type was generated, so the generator cannot emit the addObserver call and throws IllegalStateException. (Note: the throw passes the local ClassDesc variable observerType, which is null, instead of the observer — a minor message quirk.)

Source

Thrown at independent-projects/arc/processor/src/main/java/io/quarkus/arc/processor/ComponentsProviderGenerator.java:396

    private void generateAddObservers(String generatedName, Gizmo gizmo, CodeGenInfo info,
            Map<ObserverInfo, String> observerToGeneratedName) {

        for (Container<ObserverGroup> container : info.observers()) {
            gizmo.class_(container.className(generatedName, ADD_OBSERVERS), cc -> {
                cc.final_();
                for (ObserverGroup group : container) {
                    cc.staticMethod(ADD_OBSERVERS + group.id(), mc -> {
                        mc.packagePrivate();
                        mc.returning(void.class);
                        ParamVar beanIdToBean = mc.parameter("beanIdToBean", Map.class);
                        ParamVar observers = mc.parameter("observers", List.class);
                        mc.body(bc -> {
                            for (ObserverInfo observer : group.observers()) {
                                ClassDesc observerType = observerToGeneratedName.containsKey(observer)
                                        ? ClassDesc.of(observerToGeneratedName.get(observer))
                                        : null;
                                if (observerType == null) {
                                    throw new IllegalStateException("No observer type found for: " + observerType);
                                }
                                List<ClassDesc> params = new ArrayList<>();
                                List<Expr> args = new ArrayList<>();

                                if (!observer.isSynthetic()) {
                                    List<InjectionPointInfo> injectionPoints = observer.getInjection().injectionPoints.stream()
                                            .filter(ip -> !BuiltinBean.resolvesTo(ip))
                                            .toList();
                                    // declaring bean
                                    params.add(ClassDesc.of(Supplier.class.getName()));
                                    args.add(bc.withMap(beanIdToBean)
                                            .get(Const.of(observer.getDeclaringBean().getIdentifier())));
                                    // injections
                                    for (InjectionPointInfo injectionPoint : injectionPoints) {
                                        params.add(ClassDesc.of(Supplier.class.getName()));
                                        args.add(bc.withMap(beanIdToBean).get(
                                                Const.of(injectionPoint.getResolvedBean().getIdentifier())));
                                    }

View on GitHub (pinned to e1c734241f)

Solutions

1. Clean rebuild (mvn clean install) to regenerate components
2. Verify the extension registering the observer uses supported registration APIs
3. If reproducible on a minimal project, report as an ArC bug or try another Quarkus version

Example fix

null

try {
    quarkusBuild.start();
} catch (IllegalStateException e) {
    if (e.getMessage() != null && e.getMessage().startsWith("No observer type found for:")) {
        logger.errorf("Clean rebuild or report ArC bug: %s", e.getMessage());
    }
    throw e;
}

When it happens

Trigger: generateAddObservers iterates group.observers(); an ObserverInfo is absent from observerToGeneratedName, so observerType is null and the IllegalStateException is thrown.

Common situations: Synthetic observers registered by extensions without generated backing classes; stale incremental-build artifacts; ArC generator bugs after Quarkus version changes.

Related errors

• No bean type found for: ${bean}
• AnnotationTransformation is not an AnnotationsTransformer: <
• Invalid configuration value set for 'quarkus.arc.remove-unus
• Different default scopes defined for additional bean class:
• Unexpected value: <arcConfig.optimizeContexts()>

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/2d5374d28e10b5d5. Report an issue: GitHub.