Quarkus and Java 21 Instance Main Methods is not working

[rsvoboda]

Describe the bug

I tried customized QuarkusMain method as shown in https://quarkus.io/guides/lifecycle#the-main-method with Java 21 Instance Main Methods (preview feature).

Code example in https://github.com/rsvoboda/code-with-quarkus/tree/21-main

@QuarkusMain
public class Main {
    void main() {
        System.out.println("==> Running main method");
        Quarkus.run();
    }
}

maven-compiler-plugin enabled to use preview features

    <maven.compiler.release>21</maven.compiler.release>
...
      <plugin>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>${compiler-plugin.version}</version>
        <configuration>
          <compilerArgs>
            <arg>--enable-preview</arg>
          </compilerArgs>
        </configuration>
      </plugin>

And I received:

Exception in thread "main" java.lang.NoSuchMethodException: org.acme.Main.main([Ljava.lang.String;)
	at java.base/java.lang.Class.getMethod(Class.java:2395)
	at io.quarkus.bootstrap.runner.QuarkusEntryPoint.doRun(QuarkusEntryPoint.java:61)
	at io.quarkus.bootstrap.runner.QuarkusEntryPoint.main(QuarkusEntryPoint.java:32)

I checked if I will see System.out.println("==> Running main method"); when calling the compiled jar just to ensure compilation went well. Message was printed

java --enable-preview -cp target/quarkus-app/app/code-with-quarkus-1.0.0-SNAPSHOT.jar org.acme.Main

==> Running main method
Exception in thread "main" java.lang.NoClassDefFoundError: io/quarkus/runtime/Quarkus
	at org.acme.Main.main(Main.java:10)
Caused by: java.lang.ClassNotFoundException: io.quarkus.runtime.Quarkus
	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)
	... 1 more

Expected behavior

Quarkus boots

Actual behavior

Quarkus fails to start

How to Reproduce?

• Get example code from 21-main branch - https://github.com/rsvoboda/code-with-quarkus/tree/21-main
• Run mvn clean package -DskipTests && java --enable-preview -jar target/quarkus-app/quarkus-run.jar

Output of uname -a or ver

macOS

Output of java -version

Java 21

GraalVM version (if different from Java)

No response

Quarkus version or git rev

3.4.1

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

No response

Additional information

No response

[quarkus-bot]

/cc @Sanne (core), @aloubyansky (core), @gsmet (core), @radcortez (core), @stuartwdouglas (core)

[geoand]

Interesting find!

Seems like we'll need to follow the rules in Selecting a main method of https://openjdk.org/jeps/445.