[Xbase] Java Method body changes leed to rebuilds once a structural change occured

We observe the following behaviour of xbase based languages e.g. domain model example

• we create a java type Base
• we reference it inside a xbase file e.g entity Demo extends Base
• we create a new (public) method in Base. Demo is rebuilt as expected.
• we edit the body of the Method. Demo is rebuild. that is NOT expected.

I think this has to do with the implementation of JdtQueuedBuildData.needsRebuild
it basically never updates oldState. i think it should "update" it after needsRebuild was called.

  override needsRebuild(IProject it, Collection<Delta> deltas) {
        val oldState = javaBuildState.get(name)
        val newState = lastBuiltState
        try {
            return newState.doNeedRebuild(
                if (oldState === null || oldState.lastStructuralBuildTime != newState.lastStructuralBuildTime) {
                    [
                        val structurallyChangedTypes = newState.structurallyChangedTypes
                        if (getNew.namesIntersect(structurallyChangedTypes) || old.namesIntersect(structurallyChangedTypes)) {
                            deltas += it
                        }
                    ]
                } else {
                    null
                })
        } finally {
            if (newState !== null) {
                javaBuildState.put(name, newState)    
            } else {
                javaBuildState.remove(name);
            }
       

Am not sure how to properly test that. AbstractSingleEditorQueuedBuildTest is to whiteboxy and cirumvents jdt (JdtQueuedBuildData instance not shared)

Start with JdtQueuedBuildData.needsRebuild and inspect how javaBuildState and lastBuiltState are handled. Use the Base/Demo scenario from the issue to distinguish a structural method addition from a method-body edit, then investigate an integration test beyond AbstractSingleEditorQueuedBuildTest, which does not share the JdtQueuedBuildData instance. Done means structural changes rebuild Demo while body-only changes do not.