struct Container(T)
{
    // T.sizeof/alignof causes circular reference!
    enum AllocAlignment = T.sizeof;

    T* ptr;
}

struct Test
{
    Container!Test test;
}

error : struct `main.Test` no size because of forward reference
error : template instance `main.Container!(Test)` error instantiating


Checking T.sizeof causes a forward referencing error; but it doesn't need to evaluate that enum to determine the size of `Container!T` which has a know-able size with no T knowledge... evaluation should be deferred.