Using `__FILE__.ptr` will get const-folded, meaning it will always be the caller's site showing up:

```
// a.d
import b;

void main ()
{
    foo();
}
```

```
// b.d
import core.stdc.stdio;

void foo(const(char)* file = __FILE__.ptr)
{
    printf("Called from %s\n", file);
}
```

Using the latest DMD (v2.093.1):
```
$ dmd -i -run a.d
Called from b.d
```

But why would one ever use `__FILE__.ptr`, might you ask ? Just use `__FILE__` !
Well I would, but in my original code, `foo` is `extern(C++)`...