[Bug c++/104266] New: Temporaries with protected destructor are erroneously permitted

[Bug c++/104266] New: Temporaries with protected destructor are erroneously permitted

[fchelnokov at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104266

            Bug ID: 104266
           Summary: Temporaries with protected destructor are erroneously
                    permitted
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: fchelnokov at gmail dot com
  Target Milestone: ---

This is invalid code currently accepted by GCC:
```
struct A {
protected:
  ~A() { }
};

struct B : A {};

int main() {
    B b{};
}
```
but rejected in Clang and MSVC, because `B b{}` during aggregate initialization
implicitly creates a temporary `A{}`, which is not allowed in the context.

Demo: https://gcc.godbolt.org/z/Yehch5PzK

[Bug c++/104266] Temporaries with protected destructor are erroneously permitted

[de34 at live dot cn]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104266

Jiang An <de34 at live dot cn> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |de34 at live dot cn

--- Comment #1 from Jiang An <de34 at live dot cn> ---
I think this is CWG DR 2227 (https://wg21.link/cwg2227).

And IIUC although it is correct to reject this code, clang's error message is
wrong, because there's no temporary of type 'A' created due to guaranteed RVO
since C++17.

[Bug c++/104266] Temporaries with protected destructor are erroneously permitted

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104266

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2022-01-29

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
So clang, ICC and MSVC all reject it for at least in C++17 mode (clang and ICC
accepted it for C++14).

Confirmed.

[Bug c++/104266] Temporaries with protected destructor are erroneously permitted

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104266

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Here is another example:
   class X { protected: ~X(); friend struct Y; }; 
   struct Y { X x = {}; }; 

int main() {
   Y b {}; 
}

But unlike the previous example, this one is rejected by clang in C++14 but
accepted for C++11.
And even accepted by ICC for C++17 and C++14.
Note it is rejected by MSVC though.

[Bug c++/104266] Temporaries with protected destructor are erroneously permitted

[fchelnokov at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104266

--- Comment #4 from Fedor Chelnokov <fchelnokov at gmail dot com> ---
In your last example, I think Clang is right, because `Y` is not an aggregate
in C++11 due to the presence of default member initializer. And it becomes an
aggregate only in C++14.