Configuration custom converters fail on primitive type arrays since Quarkus v3.18

[jdussouillez]

Describe the bug

Since Quarkus v3.18.0 and above, custom converters for primitive type arrays make Quarkus fail at startup with a ClassNotFoundException exception ([B class not found, so byte[] class).

Here's a simple converter to read a String value as a byte array:

public class ByteArrayConfigConverter implements Converter<byte[]> {

    @Override
    public byte[] convert(final String s) {
        return s.getBytes(StandardCharsets.UTF_8);
    }
}

In Quarkus v3.17.8, Quarkus is starting correctly and the converter works. Since Quarkus v3.18.0 (still in latest 3.18.2), Quarkus is failing when starting up.

Expected behavior

Quarkus should start correctly.

Actual behavior

Quarkus startup fails with ClassNotFoundException.

ERROR [io.qua.run.Quarkus] (Quarkus Main Thread) Error running Quarkus: java.lang.ExceptionInInitializerError
	at io.quarkus.runner.ApplicationImpl.<clinit>(Unknown Source)
	at java.base/jdk.internal.misc.Unsafe.allocateInstance(Native Method)
	at java.base/java.lang.invoke.DirectMethodHandle.allocateInstance(DirectMethodHandle.java:501)
	at io.quarkus.runtime.Quarkus.run(Quarkus.java:76)
	at io.quarkus.runtime.Quarkus.run(Quarkus.java:48)
	at io.quarkus.runtime.Quarkus.run(Quarkus.java:137)
	at io.quarkus.runner.GeneratedMain.main(Unknown Source)
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
	at java.base/java.lang.reflect.Method.invoke(Method.java:580)
	at io.quarkus.runner.bootstrap.StartupActionImpl$1.run(StartupActionImpl.java:116)
	at java.base/java.lang.Thread.run(Thread.java:1583)
Caused by: java.lang.RuntimeException: java.lang.ClassNotFoundException: [B
	at io.quarkus.runtime.configuration.AbstractConfigBuilder.withConverter(AbstractConfigBuilder.java:30)
	at io.quarkus.runtime.generated.StaticInitConfigCustomizer.configBuilder(Unknown Source)
	at io.smallrye.config.SmallRyeConfigBuilder.build(SmallRyeConfigBuilder.java:770)
	at io.quarkus.runtime.generated.Config.<clinit>(Unknown Source)
	... 11 more
Caused by: java.lang.ClassNotFoundException: [B
	at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:641)
	at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:188)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:526)
	at io.quarkus.bootstrap.classloading.QuarkusClassLoader.loadClass(QuarkusClassLoader.java:569)
	at io.quarkus.bootstrap.classloading.QuarkusClassLoader.loadClass(QuarkusClassLoader.java:517)
	at io.quarkus.bootstrap.classloading.QuarkusClassLoader.loadClass(QuarkusClassLoader.java:569)
	at io.quarkus.bootstrap.classloading.QuarkusClassLoader.loadClass(QuarkusClassLoader.java:517)
	at io.quarkus.runtime.configuration.AbstractConfigBuilder.withConverter(AbstractConfigBuilder.java:28)
	... 14 more

How to Reproduce?

Reproducer: https://github.com/jdussouillez/quarkus-custom-converter

1. Run ./mvnw quarkus:dev => Failure
2. Run ./mvnw quarkus:dev -Dquarkus.platform.version=3.17.8 => Works fine

Output of uname -a or ver

No response

Output of java -version

openjdk version "21.0.5" 2024-10-15 LTS

Quarkus version or git rev

v3.18.0 ... v3.18.2

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

Apache Maven 3.9.9

Additional information

I guess it's a regression because it's not mention in 3.18 migration guide. And it's not mentionned in Microprofile config documentation.

A workaround for v3.18 is to use a record to wrap the byte[] field.

public record KeyConfig(byte[] key) {
}

// ...

public class KeyConfigConverter implements Converter<KeyConfig> {

    @Override
    public KeyConfig convert(final String s) {
        return new KeyConfig(s.getBytes(StandardCharsets.UTF_8));
    }
}

// ...

@ConfigProperty(name = "myapp.key.value")
protected KeyConfig keyConfig;

[quarkus-bot]

/cc @radcortez (config)