Prefer Java over Xtend

[JanWittler]

As long term support for Xtend cannot be guaranteed anymore, future contributions to Vitruv should prefer Java over Xtend. New classes are required to be written in Java, and instead of major refactorings of Xtend classes the functionality should be re-implemented in Java.

As of now, Xtend only supports running on Java 17 with Java 11 target. As such, we cannot update to Java 17 and thus cannot use the new language features. As soon as Java 17 as target is supported, we will migrate. See Xtend Release Notes.

[JanWittler]

Xtend 2.29 with Java 17 as source and target was released on Nov 25. Thus, we will migrate to it with the next Eclipse release (2022-12) which should be released on Dec 05.

[JanWittler]

Java 17 supports was just recently added. As such, besides of refactoring as much Xtend as possible to Java, Java source code should also be optimized to use modern Java 17 features.

[JanWittler]

If at some point we were able to replace Xtend entirely with Java, we can migrate the code to use Java 17 (or newer) features. This include sealed interfaces which might be useful for e.g. VitruviusChange, and also records.
Incomplete list of classes that should be refactored to record:

• HierarchicalId
• Uuid
• CompositeContainerChangeImpl
• TransactionalChangeImpl
• PropagatedChange

As of now, this is not possible because records are not visible for Xtend.