Rest Client Reactive default methods fail with Kotlin

[kdubb]

Describe the bug

Using a default method in a Kotlin interface defining a REST client results in an AbstractMethodError being thrown.

Expected behavior

Default methods should be usable in REST client methods. This is expected behavior according to #19226 (comment)

Actual behavior

AbstractMethodError is thrown for any defined default methods.

How to Reproduce?

1. Run the Quarkus application
2. Use curl -v http://localhost:8080/todos/block to see failure in a blocking method.
3. Use curl -v http://localhost:8080/todos/co to see failure in a Kotlin coroutine.

code-with-quarkus.zip

Output of uname -a or ver

macOS 12.0.1

Output of java -version

17

GraalVM version (if different from Java)

No response

Quarkus version or git rev

2.6.0.CR1

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

gradle

Additional information

No response

[quarkus-bot]

/cc @evanchooly, @michalszynkiewicz

[geoand]

I don't think we should fix this on our side actually, because it's very easy to work around the problem by adding:

          <args>
            <arg>-Xjvm-default=all</arg>
          </args>

in the configuration section of the kotlin-maven-plugin. See this for more details.

@michalszynkiewicz, @evanchooly do you agree?

[kdubb]

The only issue I have with this is that it is infectious, you have to remember to add this to all projects. When it fails it's pretty easy to miss that it's the default methods that are causing it. It would be nice for it to "just work" or to have a warning/error generated.

That being said it seems like this is basically a Kotlin issue.

[kdubb]

@geoand FYI, I did not know about this option previously. Thank you for the fix workaround.

[evanchooly]

I agree. That flag seems to fix it so we should go with that until that proves insufficient. Anything we try to do would be susceptible to variations in kotlin compiler changes which has already bitten us with panache.