struct A(T)
{
    B!T fun()
    {
        return B!T.init;
    }
}

struct B(T)
{
    private A!T _s;
    alias _s this;
}

void main() {
    A!(int) s;
}

./test.d(15): Error: alias this there can be only one alias this
./test.d(6): Error: template instance test.B!(int) error instantiating
./test.d(15): Error: alias this there can be only one alias this