//# publish
module 0x42.N {
    foo() {
    label b0:
        return;
    }
}

//# publish
module 0x42.M {
    friend 0x42.N;
    public(friend) foo() {
    label b0:
        return;
    }
}

//# publish
module 0x42.N {
    import 0x42.M;
    foo() {
    label b0:
        M.foo();
        return;
    }
}

//# publish
module 0x42.M {
    friend 0x42.N;
    // cannot remove visible function
}
// check: BACKWARD_INCOMPATIBLE_MODULE_UPDATE