This segfaults at runtime (for all versions currently on run.dlang.io):
```
struct U { size_t[4] a; }
struct S
{
int x;
U u;
alias u this;
}
U foo()
{
S s = S(42, U([1, 2, 3, 4]));
return s;
}
void main()
{
assert(foo().a[0] == 1);
}
```
It's apparently caused by the frontend wrongly marking `s` in `foo()` as the NRVO variable (FuncDeclaration.nrvo_var), ignoring that it requires an implicit conversion via `alias this` - return type and variable type clearly differ.