Avoid StackOverflowError in TypeUtils#resolveGenerics

[dodgex]

While the issue (#9855) is related to JDK21 and its new getFirst and getLast methods in the List/SequencedCollection interfaces, the current behaviour can in theory cause problems on JDK versions before 21 too.

With this fix the TypeUtils#resolveGenerics method falls back to TypeUtils#ensureBaseType (already used method-level type variables) when a type variable is used in the same class where it has been defined.

This class for example, currently causes a StackOverflowError. With this PR the error is avoided, and the T is resolved as java.lang.Object

class BrokenClass<T> {
    public T getT() {
        return null;
    }
}

Fixes #9855

[niloc132]

Thanks! Are you aware of any other issues preventing Java 21 from building and passing tests, or can we also add Java 21 to the nightly CI runs?

[dodgex]

Until now I did not build GWT on JDK21. But in a first build I just did, it fails due to errorprone beeing too old. Version v2.20.0 added support for JDK21 (ea builds), latest is v2.23.0

[dodgex]

Okay, updating errorprone might not be possible. At least not easy?

It requires JDK11 starting with v2.11.0. And in v2.22.0 they mention that they consider to require JDK 17 in a future release.

Either CI runs need to drop running on Java 8, or there has to be a way to use diffrent versions of errorprone per JDK version.

But I think this discussion deservers its own issue at this point. :)

[niloc132]

Thanks for the investigation. I'll see about manually running more tests on Java 21 to validate this fix, and after this release we'll be dropping support for building GWT or running the compiler on Java 8. We may keep Java 8 support for the server, it will depend on what kind of pushback we get on other changes.

[niloc132]

Running AutoBeanSuite on Java 21 reproduces this issue:

Testcase: testSplittable took 0.055 sec
	Caused an ERROR
java.lang.StackOverflowError
java.lang.RuntimeException: java.lang.StackOverflowError
	at com.google.web.bindery.autobean.vm.impl.ProxyAutoBean.traverseProperties(ProxyAutoBean.java:328)
	at com.google.web.bindery.autobean.shared.impl.AbstractAutoBean.traverse(AbstractAutoBean.java:166)
	at com.google.web.bindery.autobean.shared.impl.AbstractAutoBean.accept(AbstractAutoBean.java:101)
	at com.google.web.bindery.autobean.shared.impl.AutoBeanCodexImpl.doEncode(AutoBeanCodexImpl.java:560)
	at com.google.web.bindery.autobean.shared.AutoBeanCodex.encode(AutoBeanCodex.java:83)
	at com.google.web.bindery.autobean.shared.AutoBeanCodexTest.checkEncode(AutoBeanCodexTest.java:453)
	at com.google.web.bindery.autobean.shared.AutoBeanCodexTest.testSplittable(AutoBeanCodexTest.java:433)

While we can't build GWT with 21 yet, you can first do an ant clean dist-dev with Java 11/17, then cd into user/ and run something like

ant test '-Dgwt.junit.testcase.includes=**/AutoBeanSuite.class' '-Dgwt.nongwt.testcase.includes=**/AutoBeanSuite.class'

I confirmed that this patch fixed those tests, then ran ant test.web.htmlunit '-Dgwt.junit.testcase.includes=com/google/web/bindery/**/*Suite.class' in user/ with Java 21 to make sure we had no other surprises (from this patch or from Java 21 in general). That too passed - I'm now waiting locally for a full test.web.htmlunit run on all suites, but expect a pass from that too.

[niloc132]

All of test.web.htmlunit passed in Java 21, marking as approved, will merge in a day or so as usual to give time for any more discussion.