PolyCollectorTypeVars.java

import java.util.Comparator;

class MyGen<K0> {}

abstract class Ordering<T> implements Comparator<T> {
    // Natural order

    public static <C extends Comparable> Ordering<C> natural() {
        return new Ordering<C>() {
            @Override
            public int compare(C o1, C o2) {
                return 0;
            }
        };
    }
}

class PolyCollectorTypeVars {
    // Both of these come from the extends Comparable on line 9
    @SuppressWarnings({"rawtypes", "type.argument.type.incompatible"})
    public static MyGen<Comparable> treeKeys2() {
        // See Limitation in DefaultTypeArgumentInference on interdependent methods
        return treeKeys(Ordering.natural());
    }

    public static <K0> MyGen<K0> treeKeys(final Comparator<K0> comparator) {
        return new MyGen<K0>();
    }
}