This change-set should annotate final stage builder interfaces (BuildFinal) with CanIgnoreReturnValue, and allow downstream projects using Error Prone to use Staged Builders without method chaining or disabling the CheckReturnValue bug-checker. This aligns with the existing implementation and "normal" and strict builders.

Aside from this change, I have a broader question:

We encountered this while trying to propagate optional values to default primitive members in our immutable models. For example, the following model Foo will produce a single builder method for Foo#bar, BuildFinal bar(int bar), which cannot be called with an Optional<Integer> with method chaining, only conditionally with the optional unwrapped.

interface Foo {
  default int bar() {
    return 99;
  }
}

Have you considered generating "optional" builder methods for default non-optional members? In this example, BuildFinal bar(Optional<Integer> bar)?

I've managed to implement this for object types, but not for primitives. I didn't yet find a way to map primitives to their boxed optional types.

If this feature would be welcome, I may give it a go, and ask for you input, pointers on it.

Thanks all!