Cannot Inherit from Generated Factory Builder

Given the following class:

import org.immutables.builder.Builder.Constructor;
import org.immutables.value.Value;

@Value.Style(visibility=Value.Style.ImplementationVisibility.PACKAGE)
public class Foo {
    private final String bar;
    private final String baz;

    @Constructor
    /*package-private*/ Foo(final String bar, final String baz) {
        this.bar = bar;
        this.baz = baz;
    }

    public static class Builder extends FooBuilder {
    }

    public static Builder builder() {
        return new Builder();
    }
}

The output of the generated factory builder is a final class:

@Generated(from = "Foo", generator = "Immutables")
@SuppressWarnings({"all"})
@SuppressFBWarnings
@ParametersAreNonnullByDefault
@javax.annotation.Generated("org.immutables.processor.ProxyProcessor")
@NotThreadSafe
public final class FooBuilder {
  private static final long INIT_BIT_BAR = 0x1L;
  private static final long INIT_BIT_BAZ = 0x2L;
  private long initBits = 0x3L;

  private @Nullable String bar;
  private @Nullable String baz;

Resulting in the following compilation failure:

Foo.java:15: error: cannot inherit from final FooBuilder
    public static class Builder extends FooBuilder {
                                        ^
1 error

When following this same pattern with Immutable builders, the builder is generated as a non-final class.

Would it be possible to achieve parity between normal immutable builders and factory builders in this respect?

Thanks.

[Sarev0k]

Actually I take it back, I don’t think what you describe will solve my issue, because I need some level of overshadowImplementation to work, otherwise I won’t be able to use the chained builders from the derived type.

Ideally I’d like to be able to define my class like so:

@Value.Style(builderVisibility=Value.Style.BuilderVisibility.PACKAGE, overshadowImplementation=true)
public class Foo {
    private final String bar;
    private final String baz;

    @Constructor
    /*package-private*/ Foo(final String bar, final String baz) {
        this.bar = bar;
        this.baz = baz;
    }

    public static class Builder extends FooBuilder {
    }

    public static Builder builder() {
        return new Builder();
    }
}

And initialize it like:

Foo foo = Foo.builder()
             .setBar("bar")
             .setBaz("baz")
             .build()

[ambition-consulting]

I was also surprised - especially that this is still open? I would also really like to customise the builder, which is currently final and has only private constructor - at least for staged/strict builders.