AutoValue Builder @This injection fails for certain Builder subtyping

[msridhar]

Here is a reduced version of a case I see in real code:

class BuilderInheritance {
  abstract static class Base {
    abstract String getProp();
    abstract static class Builder<B extends Builder<?>> {
      abstract B setProp(String value);
    }
  }
  @AutoValue
  abstract static class Sub extends Base {
    static Builder builder() {
      return new AutoValue_BuilderInheritance_Sub.Builder();
    }
    @AutoValue.Builder
    abstract static class Builder extends Base.Builder<Builder> {
      abstract Sub build();
    }
  }
}

The returns receiver checker reports an error for this code, as the generated setProp method for the AutoValue Builder has @This on the return, but the method in the abstract Base.Builder class does not (so it is an invalid override).

I don't know how to automatically fix this case other than looking for all overriding methods in the visitor to decide if @This should be injected. @kelloggm any thoughts?

[msridhar]

I'll note that for now this can be worked around by adding an @This annotation to Base.Builder.setProp()'s return type. But this weakens our automatic support of AutoValue.