Issue with struct invariants

[Kirill Kryukov via Digitalmars-d-learn]

Hi all,

I was debugging an old project that started crashing after 
upgrading to a recent toolchain. I noticed that commenting out 
invariants helps. I reduced it to the following:

```
import std.conv: to;

struct A
{
    ulong n;
    string str()
    {
        if (n == 0) { return "0"; }
        return to!string(n);
    }
}

struct B
{
    ulong n;
    invariant() {}
    string str()
    {
        if (n == 0) { return "0"; }
        return to!string(n);
    }
}

void main()
{
    A a = { 1 };
    B b = { 2 };
    assert(a.str() == "1");  // OK
    assert(b.str() == "2");  // Fails
}
```

Is this a bug, or am I misunderstanding something?

Compiled with "gdc -Og -o repro repro.d", using gdc (GCC) 14.2.1 
20240912 (Red Hat 14.2.1-3), on Linux.

Thanks.