On section: 9.8 Functional Interfaces of [1] we have this assertion:

 * A functional interface is an interface that is not declared with one of the modifiers sealed, identity, or value...

but this should apply too to functional interfaces which are not explicitly declared with the `identity` modifier. So this code should not be accepted:

    identity interface I {
        void m();
    }

    @FunctionalInterface
    interface J extends I {}

[1] http://cr.openjdk.java.net/~dlsmith/jep8277163/jep8277163-20220519/specs/value-objects-jls.html#jls-9.8