Unexpected ClassnotFoundException on reflective Class#getMethod

[Sanne Grinovero]

Hello all,
looks like I've found an issue on invoking Class#getMethod.

This method is used by Maven when scanning the project's classpath to
identify JUnit tests - which it does by default on any Maven project -
so I'm afraid the impact could be quite large.

I've been able to narrow it down to this small test which doesn't need
neither Maven nor JUnit, however to reproduce the issue the project
must have a dependency to some third party jar.
In this reproducer I'm using javax.transaction.Synchronization, a copy
can be obtained from:
 - https://repository.jboss.org/nexus/service/local/repositories/central/content/org/jboss/spec/javax/transaction/jboss-transaction-api_1.2_spec/1.0.0.Final/jboss-transaction-api_1.2_spec-1.0.0.Final.jar


==== Main.java ====
public class Main {

public static void main(String[] args) {
Class clazz = SecondClass.class;
try {
clazz.getMethod("notexisting", new Class[0]);
} catch (NoSuchMethodException e) {
e.printStackTrace();
}
System.out.println("All good");
}

}
==== SecondClass.java ====
import javax.transaction.Synchronization;

public class SecondClass {

public void registerSynchronization(Synchronization synchronization) {
}

}
==== EOF ====


On Java8 or Java9 build 9-ea+110 the output is, as expected:

> java.lang.NoSuchMethodException: SecondClass.notexisting()
> at java.lang.Class.getMethod(Class.java:1786)
> at Main.main(Main.java:6)
> All good


On Java9 build 9-ea+111 though I'll have this:

> Exception in thread "main" java.lang.NoClassDefFoundError: javax/transaction/Synchronization
> at java.lang.Class.getDeclaredMethods0(java.base at 9-ea/Native Method)
> at java.lang.Class.privateGetDeclaredMethods(java.base at 9-ea/Class.java:2937)
> at java.lang.Class.privateGetMethodRecursive(java.base at 9-ea/Class.java:3282)
> at java.lang.Class.getMethod0(java.base at 9-ea/Class.java:3252)
> at java.lang.Class.getMethod(java.base at 9-ea/Class.java:1961)
> at Main.main(Main.java:6)
> Caused by: java.lang.ClassNotFoundException: javax.transaction.Synchronization
> at jdk.internal.loader.BuiltinClassLoader.loadClass(java.base at 9-ea/BuiltinClassLoader.java:368)
> at jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(java.base at 9-ea/ClassLoaders.java:185)
> at java.lang.ClassLoader.loadClass(java.base at 9-ea/ClassLoader.java:419)
> ... 6 more

I hope I have sent this to the right mailing list.
I've reported the same issue on bugreport.java.com, but the only ID I
have about that report is the "Review ID": JI-9033943
The reproducer in this email is much better than in the other report,
I can't check what I sent but I believe I might have sent an outdated
version; apologies for any confusion.

Thanks,
Sanne Grinovero