Don't autodetect Avro serde in case multiple Avro serdes are present on classpath

[Ladicek]

Describe the bug

The SmallRye Reactive Messaging Kafka support for autodetection behaves weirdly in case multiple Avro serdes are present on classpath. The autodetection algorithm will just pick one of those serdes in an opaque way. It really should either avoid autodetection entirely, so that the application fails with missing configuration during startup, or even fail the build entirely.

Expected behavior

Predictable serde autodetection outcome in case multiple serdes are present.

Actual behavior

Seemingly random serde autodetection outcome in case multiple serdes are present.

How to Reproduce?

No response

Output of uname -a or ver

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Output of java -version

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GraalVM version (if different from Java)

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Quarkus version or git rev

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Build tool (ie. output of mvnw --version or gradlew --version)

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Additional information

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[Ladicek]

Apparently there are elaborate use cases that involve having multiple Kafka serdes on the classpath, so failing the build is not an option. We simply should skip autodetection and let users configure Kafka serde manually.

[knutwannheden]

For the Avro use case, where most channels will be using the generic Avro serializer (specific to the schema registry implementation), I think that it would be useful with an explicit config property like quarkus.reactive-messaging.kafka.schema-registry.compatibility-mode (which can be set to auto (default), confluent, apicurio1, or apicurio2). This would allow the extension to correctly set the Avro-specific config for the channels.

With this approach the extension could fail the build when the property is set to auto and it detects multiple Avro serdes and instruct the user to set this config property to a value other than auto.

@Ladicek What do you think about this proposal?

[Ladicek]

I still don't want configuration for autodetection. It's a slippery slope and we'll eventually end up creating an alternative configuration system for SmallRye Reactive Messaging. Autodetection should work well for the most common 80% of cases, and if you need something advanced, you should just configure SmallRye Reactive Messaging directly.