Generated 'from' method has trouble with parameterized interfaces that declare properties

[stevenschlansker]

Hi, we use Immutables and love it, but recently ran into what feels like a bug.
We declare some properties on mixin interfaces so they can be shared among related types, and use from(otherImpl) liberally to copy all relevant properties between the different sub-types. In some cases, we parameterize the types Mixin<Self extends Mixin<Self>> in order to give proper return types to Self withProperty() methods.

However, this seems to break the from() method in some cases. Consider:

interface LastModified<Self extends LastModified<Self>> {
    Instant lastModified();
    Self withLastModified(Instant lastModified);
}

interface Property {
    @Nullable
    String property();
}

@Value.Immutable
interface ImplA extends Property, LastModified<ImplA> {}

@Value.Immutable
interface ImplB extends Property, LastModified<ImplB> {}

public class TestImmutableFrom {
    @Test
    public void testImmutableFrom() {
        final ImmutableImplA a = ImmutableImplA.builder()
                .lastModified(Instant.EPOCH)
                .build();
        ImmutableImplB.builder()
                .from(a)
                .build();
    }
}

Expected:
Since both ImplA and ImplB extend LastModified, and while the parameterization of the type is different, it does not affect the property in any way, I would expect the from method to copy the property.

Actual:
The generated ImmutableImplBBuilder.from method unfortunately seems to not be correct.

private void from(short _unused, Object object) {
  @Var long bits = 0;
  if (object instanceof Property) {
    Property instance = (Property) object;
    if ((bits & 0x1L) == 0) {
      @Nullable String propertyValue = instance.property();
      if (propertyValue != null) {
        property(propertyValue);
      }
      bits |= 0x1L;
    }
  }
  if (object instanceof ImplB) {
    ImplB instance = (ImplB) object;
    if ((bits & 0x1L) == 0) {
      @Nullable String propertyValue = instance.property();
      if (propertyValue != null) {
        property(propertyValue);
      }
      bits |= 0x1L;
    }
    lastModified(instance.lastModified());
  }
}

Since ImplB already implements Property, the two instanceof clauses are redundant. The second check should probably check for object instanceof LastModified.