Example program:

---
struct Inner
{
    @system ~this() {}
}

struct Outer
{
    Inner inner;
    @safe ~this() {}
}

@safe void main()
{	
    Outer outer;
}
---

Output when compiled with DMD v2.093.1:

---
onlineapp.d(14): Error: @safe function D main cannot call @system destructor onlineapp.Outer.~this
onlineapp.d(9):        onlineapp.Outer.~this is declared here
---

The error message incorrectly states that Outer.~this is @system, even though it is @safe. The actual problem is that Inner.~this is @system.