Invalid default method multi-inheritance.

Let the following Xtend code:

class TestMultiInheritance<T> extends AbstractCollection<T> implements Set<T> {
	
	override iterator() {
		spliterator
                null
	}
	
	override size() {
               0
	}
	
}

The Xtend compiler generates the error "The type TestMultiInheritance inherits multiple implementations of the method spliterator() from Iterable and Set."

However, the equivalent Java code is compiling:

public class TestMultiInheritance<T extends Object> extends AbstractCollection<T> implements Set<T> {
  public Iterator<T> iterator() {
    this.spliterator();
    return null;
  }
  
  public int size() {
    return 0;
  }
}

The spliteraor function is defined in the Iterable and Set interfaces with different code. The Java compiler takes the default implementation from Set because is it the closest definition from the call in the type hierarchy.

Is a feature of Xtend to fail in this case? Or should Xtend be fixed in order to have a similar behavior as the Java compiler?

Start with the Xtend compiler handling of default methods for the reported TestMultiInheritance example, then compare its resolution with the equivalent Java code. Reproduce the multiple-inheritance error and determine whether the generated behavior should select Set's closer spliterator implementation, with a regression test covering the case.