FR: Off-by-default Clang warning when publicly inheriting from a class with public non-virtual dtor

[pkasting]

Publicly inheriting from a class with a (possibly autogenerated) public, non-virtual dtor risks incorrect behavior if an instance is deleted through the base class destructor.

#include <memory>

struct Base {};
struct Derived : Base {};

void f() {
  std::unique_ptr<Base> ptr = std::make_unique<Derived>();
  ptr.reset();  // ~Derived() not called; negative consequences depend on actual struct contents
}

We already have -Wnon-virtual-dtor and -Wdelete-non-virtual-dtor, but neither catch this, because they're focused on cases where there is a vtable. At least in Chromium, it's not unknown to "extend" existing classes that lack vtables by inheriting from them, hence the desire for this warning.

The author would be expected to fix by either making ~Base() protected or virtual (or by using composition instead of inheritance).

One way to reduce warning instances on "clearly harmless" cases would be to omit this warning when the derived class is scoped to something the compiler can see all of (e.g. inside an anonymous namespace) and is never heap-allocated in that scope. That might be too complex to implement, though.

[shafik]

Your case makes sense, I am just wondering why we don't already catch that either w/ a diagnostic or via clang-tidy.