Reported by Remi in Valhalla-dev:

The following program fails to compile:

public final __ByValue class GenBug<E> {
  private final boolean value;
  
  private GenBug() {
    value = false;
    throw new AssertionError();
  }

  public static <E> GenBug<E> create() {
    GenBug<E> bug = __MakeDefault GenBug<E>();
    bug = __WithField(bug.value, true);
    return bug;
  }
}

X.java:11: error: incompatible types: GenBug<E#1> cannot be converted to GenBug<E#2>
    bug = __WithField(bug.value, true);
          ^
  where E#1,E#2 are type-variables:
    E#1 extends Object declared in class GenBug
    E#2 extends Object declared in method <E#2>create()