We probably don't handle recent Java features

[cpovirk]

Given that cb6486c only recently added support for try-with-resources, I'd assume that we aren't yet handling instanceof String s or switch expressions + yield, much less any preview features. (I pulled this list from the Java 17 TreeVisitor API.)

[eamonnmcmanus]

I think TreeDiffer.DiffVisitor is quite problematic as constructed. It extends SimpleTreeVisitor and does not override defaultAction, which means that the default behaviour for a visitor method it doesn't override is to do nothing. That includes methods that are already present in the JDK 8 API, specifically visitAnnotatedType, meaning that differences between annotated types are not currently noticed, even if both the annotations and the type are different.

Since the treatment of most node types is quite formulaic, I think we might be able to replace this with a Proxy implementing TreeVisitor in a way that doesn't need the code to know about specific node types. That way we should be able to make it work with both old and new JDKs.