add segfault example when using rc

libsafecxx/test/broken/rc_segfault.cxx

@@ -0,0 +1,65 @@
+#feature on safety
+
+template<class T+>
+class manually_drop
+{
+  T t_;
+
+public:
+  explicit manually_drop(T t) noexcept safe;
+  ~manually_drop() = trivial;
+
+  void destroy(self^) noexcept;
+  T const^ get(self const^) noexcept safe;
+};
+
+template<class T+>
+class [[unsafe::send(false)]] rc
+{
+  struct rc_inner;
+  rc_inner* unsafe p_;
+
+  struct rc_inner
+  {
+    manually_drop<T> data_;
+    std::size_t strong_;
+    std::size_t weak_;
+
+    explicit
+    rc_inner(T data) noexcept safe;
+  };
+
+public:
+
+  explicit rc(T t) safe;
+  rc(rc const^ rhs) safe;
+  [[unsafe::drop_only(T)]] ~rc() safe;
+
+  T const^ operator*(self const^) noexcept safe {
+    return *self->p_->data_.get();
+  }
+};
+
+template<class T, class U>
+void assert_eq(const T^ t, const U^ u) safe
+{
+  if (*t != *u) throw "unequal values";
+}
+
+void drop_only() safe
+{
+  {
+    rc<int^> p;
+
+    {
+      int x = 1234;
+      p = rc<int^>(^x);
+      assert_eq(**p, 1234);
+    }
+  }
+}
+
+int main() safe
+{
+  drop_only();
+}