@Fallback strategy seems not to work with Kotlin coroutines and additional exception in method signature

[thjaeckle]

Hi.
I am trying to adjust my Kotlin code to use "coroutines" while still defining a @Fallback method:

    @Incoming("lorawan")
    @Acknowledgment(Acknowledgment.Strategy.MANUAL)
    @Asynchronous
    @Retry(delay = 25, maxRetries = 5)
    @ExponentialBackoff
    @Fallback(fallbackMethod = "fallbackProcessor")
    suspend fun processor(kafkaMessage: Message<LoRaWanMessage>) {
       ...
    }

The following fallback method signature works as expected:

    suspend fun fallbackProcessor(kafkaMessage: Message<LoRaWanMessage>) {
       ...
    }

However, if I add an Exception like documented in the Fallback Methods with Exception Parameter
:

    suspend fun fallbackProcessor(kafkaMessage: Message<LoRaWanMessage>, ex: Exception) {
       ...
    }

I get a java.lang.RuntimeException: java.lang.RuntimeException: Failed to start quarkus error:

Caused by: jakarta.enterprise.inject.spi.DeploymentException: org.eclipse.microprofile.faulttolerance.exceptions.FaultToleranceDefinitionException: Invalid @Fallback on LoRaUplinkKafkaGateway.processor(org.eclipse.microprofile.reactive.messaging.Message, kotlin.coroutines.Continuation): can't find fallback method 'fallbackProcessor' with matching parameter types and return type
	at io.quarkus.smallrye.faulttolerance.runtime.SmallRyeFaultToleranceRecorder.createFaultToleranceOperation(SmallRyeFaultToleranceRecorder.java:44)
	at io.quarkus.deployment.steps.SmallRyeFaultToleranceProcessor$processFaultToleranceAnnotations1906679055.deploy_0(Unknown Source)
	at io.quarkus.deployment.steps.SmallRyeFaultToleranceProcessor$processFaultToleranceAnnotations1906679055.deploy(Unknown Source)
	... 68 more
Caused by: org.eclipse.microprofile.faulttolerance.exceptions.FaultToleranceDefinitionException: Invalid @Fallback on LoRaUplinkKafkaGateway.processor(org.eclipse.microprofile.reactive.messaging.Message, kotlin.coroutines.Continuation): can't find fallback method 'fallbackProcessor' with matching parameter types and return type
	at io.smallrye.faulttolerance.config.FallbackConfig.validate(FallbackConfig.java:42)
	at io.smallrye.faulttolerance.config.FaultToleranceOperation.validate(FaultToleranceOperation.java:365)
	at io.quarkus.smallrye.faulttolerance.runtime.SmallRyeFaultToleranceRecorder.createFaultToleranceOperation(SmallRyeFaultToleranceRecorder.java:28)
	... 70 more

I am again overseeing something obvious in the documentation?
io.smallrye:smallrye-fault-tolerance-kotlin is on the classpath.
I am using Quarkus version 3.0.3 and smallrye-fault-tolerance 6.2.2.

Without Kotlin coroutines the fallback method with additional Exception in the signature work as expected.

[Ladicek]

You're not missing anything, this is a bug. The problem is that the search for the fallback method expects that the exception parameter is the last one, which it isn't in case of Kotlin suspend functions.

The processor method has the following parameters in the JVM bytecode: (Message, Continuation). We append an exception type to that list when looking for the fallback method, so we expect to find a method with the following parameters: (Message, Continuation, Exception). Obviously, that's not what happens; the fallbackProcessor method has parameters (Message, Exception, Continuation).

Need to think about proper fix.